See discussions, stats, and author profiles for this publication at: https://www.researchgate.

net/publication/346882728

Hydrometallurgical Processes for the Recovery of Metals from Steel Industry

By-Products: A Critical Review

Article in Journal of Sustainable Metallurgy · November 2020

DOI: 10.1007/s40831-020-00306-2

CITATIONS READS

66 1,737

4 authors, including:

Koen Binnemans Peter Tom Jones

KU Leuven KU Leuven
731 PUBLICATIONS 42,578 CITATIONS 110 PUBLICATIONS 7,097 CITATIONS

SEE PROFILE SEE PROFILE

All content following this page was uploaded by Koen Binnemans on 19 December 2020.

The user has requested enhancement of the downloaded file.

Journal of Sustainable Metallurgy (2020) 6:505–540
https://doi.org/10.1007/s40831-020-00306-2

REVIEW ARTICLE

Hydrometallurgical Processes for the Recovery of Metals from Steel

Industry By‑Products: A Critical Review
Koen Binnemans1 · Peter Tom Jones2 · Álvaro Manjón Fernández3 · Victoria Masaguer Torres3

Received: 20 April 2020 / Accepted: 14 October 2020 / Published online: 13 November 2020
© The Author(s) 2020

Abstract
The state of the art for the recovery of metals from steel industry by-products using hydrometallurgical processes is reviewed.
The steel by-products are different slags, dusts, and sludges from a blast furnace (BF), basic oxygen furnace (BOF), electric
arc furnace (EAF), and sinter plant, as well as oily mill scale and pickling sludge. The review highlights that dusts and sludges
are harder to valorize than slags, while the internal recycling of dusts and sludges in steelmaking is inhibited by their high
zinc content. Although the objectives of treating BF sludges, BOF sludges, and EAF dust are similar, i.e., the removal of
zinc and the generation of an Fe-rich residue to be returned to the steel plant, these three classes of by-products have specific
mineralogical compositions and zinc contents. Because wide variations in the mineralogical composition and zinc content
occur, it is impossible to develop a one-size-fits-all flow sheet with a fixed set of process conditions. The reason for the interest
in EAF dust is its high zinc content, by far the highest of all steel by-products. However, EAF dust is usually studied from the
perspective of the zinc industry. There are not only different concentrations of zinc, but also variations in the all-important
ZnO/ZnFe2O4 (zincite-to-franklinite) ratio. In many chemical processes, only the ZnO dissolves, while the ­ZnFe2O4 is too
refractory and reports to the residue. It only dissolves in concentrated acids, or if the dust is pre-treated, e.g., with a reductive
roasting step. The dissolution of ­ZnFe2O4 in acidic solutions also brings significant amounts of iron in solution. Finally, due
to its high potassium chloride content, sinter-plant dust could be a source of potassium for the fertilizer industry.
Graphical Abstract

Keywords Hydrometallurgy · Iron · Industrial process residues · Steel · Recycling · Zinc

The contributing editor for this article was Markus Reuter.

Extended author information available on the last page of the article

13
Vol.:(0123456789)
506 Journal of Sustainable Metallurgy (2020) 6:505–540

Introduction this review complements others on the valorization of steel-

industry by-products [2–10].
Producing one ton of steel in an integrated steel plant gen-
erates about half a ton of by-products, i.e., slags (90% by
mass), dusts, and sludges. A blast furnace (BF) produces the Slags
most slag, with smaller amounts generated in a basic oxygen
furnace (BOF) and an electric arc furnace (EAF). Dusts and Blast Furnace Slag (BF Slag)
sludges originate from the off-gas produced in BF, BOF, and
EAF installations. Minor by-products include sinter-plant Almost 100% of BF slag is recovered, either internally or
dust, oily mill scale, and pickling sludge. Although most externally [11]. Its main use is in the cement industry (75%),
steel slags have applications, dusts and sludges are often as a hydraulic binder, or as a raw material for clinker kilns.
seen as waste. Research is turning to the valorization of About 18% of BF slags are used as aggregates in construc-
those steel by-products that have no applications yet. tion: for concrete, asphalt pavements, roads, and waterways.
The motivation can be the valorization of the metal con- The slag is crushed and screened (air-cooled slags) or granu-
tent. However, in most cases the removal of metals inhibits lated. The remainder is reused internally by steel plants for
the recycling of by-products. For instance, the zinc content roadmaking and landfills. There are currently no technical
of BF and BOF sludges is too low for zinc recovery, but limitations on the use of BF slags. Granulation is becoming
too high to recycle the by-products to the BF via the sinter the standard route, with cement being the high-value appli-
plant. Stewart and Barron suggested the reason for the sen- cation. In other words, BF slag has been promoted from a
sitivity to zinc is that, once charged into a blast furnace, any by-product to a co-product.
zinc component is reduced to elemental zinc [1]. Due to its Because there are no toxic or valuable metals, there is no
low boiling point (907 °C) compared to the blast furnace need to hydrometallurgically treat BF slag to remove and
(1600–1650 °C), the vapor re-condenses, leading to the con- recover metals. An exception are the slags produced from Ti-
densation of zinc scaffolds (accretions) on the blast-furnace rich iron ores. These also contain vanadium and chromium,
walls. These deposits affect the solid and gas flows through which are reduced by the coke in the BF and report to the
the furnace, so damaging the lining through burden slips. hot metal. In contrast, vanadium and chromium are oxidized
Zinc is also known to attack refractories in the upper stack in a BOF, where they are enriched in the BOF slag, usually
of the furnace, thus shortening its operating life. Therefore, called vanadium slag [12]. Titanium is not reduced in a BF
landfilling (or internal stockpiling) is often the only option. and is enriched in the form of ­TiO2 in a BF slag. The grade
Despite this, with partial removal (“bleeding”) of the zinc, of Ti-bearing slags is too low to recover the titanium and
these sludges can be recycled and their iron content recov- produce ­TiCl4 or ­TiO2, but too rich for use in the cement
ered in the BF. industry. As such, hydrometallurgical routes recover the tita-
Most studies were performed on dusts and sludges (with nium from these slags with concentrated H ­ 2SO4 [13]. How-
only a few references to slags), primarily on EAF dust, ever, these methods co-dissolve the CaO, MgO, and A ­ l 2O 3,
because it is sufficiently Zn-rich to be a secondary resource, and thus consume more acid. But with mild conditions, less
making extraction economically attractive. co-dissolution occurs.
With respect to pyrometallurgical processes, hydromet- Much more titanium was recovered from water-quenched
allurgical routes have several advantages. First, the capital and naturally cooled slag. Valighazvini et al. leached tita-
expenditure (CAPEX) required is lower, making them more nium from BF slags with ­H2SO4 [14]. They noted that the
suitable for small-scale operations. As a result, the by-prod- ­TiO2, ­Al2O3, and MgO became soluble, whereas the CaO
ucts do not require transport over long distances to large remained in the residue as C ­ aSO4. Nearly all the titanium
processing plants, such as Waelz kilns. Second, the operat- could be leached with 2-M H ­ 2SO4 in 2 h at 65 °C and a
ing expenses (OPEX) can be lower, because less energy is liquid-to-solid ratio of 30. He et al. described recovering
used. Third, hydrometallurgical processes are often more titanium by alkali roasting with NaOH, followed by leach-
selective, so they can be more efficient. ing with ­H2SO4 at 160 °C [15]. Under ideal conditions,
This paper reviews the state of the art for the recovery 93% of the titanium was recovered. It is also possible to
of metals from steel-industry by-products using hydromet- dissolve part of the matrix, which results in a residue with
allurgical processes. The steel by-products are different enough ­TiO2 for use as a secondary raw material. Mang et al.
types of slags, dusts, and sludges from a blast furnace (BF), leached titanium-bearing BF slag with hydrochloric acid to
basic oxygen furnace (BOF), electric acid furnace (EAF), dissolve the Ca, Mg, Al, and Fe, leaving behind a ­TiO2-rich
and sinter plant, as well as the oily mill scale and pickling residue. They increased the ­TiO2 content after solid/liquid
sludge. The literature covers the period to March 2020, and

13
Journal of Sustainable Metallurgy (2020) 6:505–540 507

separation to 40%, which is sufficient for titanium recovery ­Al2O3 content and a low iron content, which is an advan-
in the titanium industry [16]. tage in some applications. However, a high A ­ l2O3 content
Others have investigated BF slag as a source of rare-earth is undesirable for recycling in a sinter plant. This type of
elements (REEs) [17] by leaching with H ­ 2SO4 (1 M, 5% slag is used in construction, particularly for roads; however,
pulp density, 1 h, room temperature, and 95 °C), followed by about one-third is landfilled.
solvent extraction with Cyanex 923. The REEs were stripped The main problem with desulfurization slag is the high
from the loaded organic phase by oxalic acid. However, this content of sulfur, alkali, free lime, and sometimes fluorine.
is uneconomic at present, because of the low concentration This makes it more difficult to valorize than converter slag.
of REEs, e.g., 17 ppm La, 16 ppm Ce, and 44 ppm Nd. The It also contains metal droplets, so that metal recovery is
final product contained only 4–5% REEs. required. Some of these slags are recycled via the sinter
BF slag can be used for C
­ O2 sequestration with the leach- plant or the EAF and some to road construction. More than
ing-carbonation process [18–20]. Here, the calcium in the 40% was landfilled in 2006 [11].
slags is solubilized, using acetic acid or ammonium salts, The vanadium content of vanadium-titanium-contain-
and the dissolved calcium is precipitated as pure C­ aCO3 by ing magnetite iron ores—called “vanadium slags” (vide
carbonation. This ­CaCO3 is known as precipitated calcium supra)—reports to BOF slags in the primary steelmaking
carbonate (PCC) and can be used as filler for rubber, plas- process. Vanadium co-occurs with iron, titanium, man-
tics, and paper. ganese, aluminum, and silicon. The main mineral phases
in vanadium slag are fayalite ­(Fe2SiO4), titanomagnet-
ite ­(Fe2.5Ti0.5O4), and spinel (­ FeV2O4 or more generally
Basic Oxygen Furnace (BOF) Slag (Mn,Fe)(V,Cr)2O4). Chromium spinel phases can also be
present. Vanadium slag is an important resource of vana-
It is important to differentiate (1) BOF or converter slag in dium. For instance, it accounts for 40% of production in
primary steelmaking, (2) BOF secondary-metallurgy slag China [21].
(BOF SM slag), and (3) desulfurization slag (de-S slag) [11]. The molten NaOH roasting method can extract vanadium
Compared to BF slag, converter slag is difficult to from vanadium slag. But this process uses a lot of energy
recover. The problems are the presence of steel droplets and NaOH, making it costly. The conventional approach to
(making metal recovery necessary) and the free (unhydrated) recovering vanadium is roasting with NaCl, followed by
lime (CaO) and periclase (MgO) content, which varies from water leaching, purification of the vanadium solution, and
2 to 12%, with the former being more abundant. Both can precipitation of the vanadium as ammonium polyvanadate
hinder applications through expansion, a high fines con- ­(NH4V3O8). Finally, calcination yields vanadium pentoxide
tent and a high pH in water. The high free-lime content is a ­(V2O5). Figure 1 shows a flow sheet of this process [22].
problem in applications like aggregates, but can be used for The purpose of roasting with NaCl (or other sodium salts)
fertilizers and cement. is to convert the spinel phase into soluble sodium vanadate
BOF slags can be internally recycled to the sinter plant, ­(NaVO3). However, roasting with NaCl is being abandoned
the BF or the converter. External applications include ferti- due to the emissions of HCl and C ­ l2 and the loss of vana-
lizers, soil conditioners, cement components, raw material dium from volatile V ­ OCl3 during chlorination roasting
for clinker or rock wool, filler for concrete, and absorbent above 600 °C. The low vanadium recovery (< 60%) and high
for wastewater pollutants. As with BF slag, converter slag is energy use make this process uneconomic. Chromium spi-
used for ­CO2 sequestration, with the high lime content being nel, which is commonly found in vanadium slag, can be par-
an advantage. The phosphorus content of BOF slag limits its tially oxidized to hexavalent chromium when roasting with
internal recycling to the sinter plant or the BF. Phosphorus sodium salts [23]. Chromium can be leached with vanadium
reports to the hot metal and comes back in a loop to the in the water-leach process, resulting in toxic C ­ rO42− in the
converter, where it must be removed by consuming more water and the leaching residue. The removal of ­CrO42− from
lime and generating more slag, which is a costly process. wastewater involves reducing with sulfur or S ­ O2. This gener-
In general, the heavy-metal content of converter slags is ates a lot of chromium sludge, and so new vanadium-extrac-
not problematic, but there is concern about the chromium tion technologies have been developed.
content of slags used for clinker production. The average is By roasting with CaO, the problem of sodium salts can
460 ppm, with a maximum of 2000 ppm. The chromium in be avoided [23, 24]. After calcification roasting, the fayalite
slag is trivalent, but it can be oxidized in the clinker kiln and phase ­Fe2SiO4 is decomposed and transformed to ­CaSiO3
become the hazardous hexavalent chromium. and ­Fe2O3, and, subsequently, the spinel phase ­(FeV2O4) is
BOF secondary-metallurgy (SM) slag has a chemical oxidized and transformed to ­Ca2V2O7 and Ca(VO3)2 [25].
composition different to that of converter slag and so these The leaching involves dilute H ­ 2SO4 [23]. However, there
slags should be kept separate. BOF SM slags have a high are operational difficulties and a low vanadium recovery.

13
508 Journal of Sustainable Metallurgy (2020) 6:505–540

Fig. 2  Flow sheet for vanadium extraction from vanadium slag via
Fig. 1  Conventional flow sheet for vanadium extraction from vana- non-salt roasting and ammonium salt leaching. Adapted from [23]
dium slag. Adapted from [22]

Direct vanadium leaching with acids, without prior roast-

Furthermore, during acid leaching, calcium sulfate accumu- ing, is efficient and has no emission problems. Unfortunately,
lates in the residues, inhibiting further use as a raw material. it consumes a lot of acid and has poor selectivity. Zhang
Leaching is easier with ammonium carbonate, since it allows et al. recovered the vanadium from slag using high-pressure
the selective leaching of the vanadium into the liquor from oxidative acid leaching [21] where the fayalite and spinel
calcification-roasted vanadium slag, but maintains the phos- phases are decomposed by H ­ 2SO4, releasing vanadium and
phorus in the solid phase because of the differences in the iron in solution, while the unreacted silicon and titanium
reactivity of calcium vanadate and calcium phosphate with are enriched in the residues. With an initial 250 g L−1 con-
ammonium carbonate [25]. Vanadium was recovered from centration of ­H2SO4, leaching at 140 °C, a time of 50 min, a
Ca-rich slags by direct oxidative roasting, without added liquid-to-solid ratio of 10:1 mL g−1, and an oxygen pressure
salt, followed by leaching with a sodium carbonate solu- at 0.2 MPa, vanadium recovery reached 97.7%. To mitigate
tion [26]. During the oxidation roasting, the olivine phases the acid consumption, waste acids have been proposed [31].
and spinel phases decomposed at 500 and 800 °C, respec- To mitigate the low selectivity, the leachate can be purified
tively. Vanadium-rich phases were formed above 850 °C. To by solvent extraction. For instance, Zhang et al. purified a
recover the vanadium and titanium, the vanadium slag was leachate with bis(2-ethylhexyl)phosphoric acid (D2EHPA)
roasted with ammonium sulfate at moderately high tempera- as the extractant, tri-n-butyl phosphate (TBP) as the modi-
tures, followed by dilute ­H2SO4 leaching [27]. To enhance fier, and sulfonated kerosene as the diluent [32]. It is clear
the extraction, an activation pre-treatment of the vanadium that the recovery of vanadium from vanadium slags is an
slag via high-temperature water quenching was employed. active research field.
The activation accelerated the extraction, with the yields The US Bureau of Mines has developed a process to
increasing by 16% and 12%, respectively, compared with the recover manganese from BOF slag by leaching with ammo-
untreated slag. Li et al. developed non-salt roasting, followed nium carbamate [33]. Figure 3 shows the flow sheet. The
by leaching with ammonium carbonate [23, 28]. This can ammonium carbamate hydrates irreversibly to ammonium
be recycled in the process and the leaching residue can be carbonate: ­NH2CO2NH4 + H2O → (NH4)2CO3. Therefore,
returned to the blast furnace (Fig. 2). The vanadium is recov- leaching with mixtures of ­NH3 solution and ammonium
ered as ammonium vanadate ­(NH4VO3). Instead of ammo- carbamate is essentially ammonia–ammonium carbonate
nium carbonate, ammonium oxalate was found to be an effi- (AAC) leaching. The BOF slag was pre-treated at high tem-
cient lixiviant [29]. After roasting with CaO, the vanadium peratures in a reducing ­(H2 or CO) or oxidizing atmosphere
could be extracted from Cr-rich vanadium slag by leaching (air), for 2 h at 700 °C, prior to leaching. Only a treatment
with a ­(NH4)2SO4–H2SO4 mixture at 20 °C [30] and recov- with ­H2 improved the leaching compared to the as-received
ered from the leachate as a (­ NH4)2V6O16 precipitate after slag: 71% Mn recovery versus 34% recovery for the as-
heating to 60 °C and adjusting the pH to 8.0. Roasting the received slag. There was also a large co-dissolution of iron,
­(NH4)2V6O16 precipitate yielded ­V2O5.

13
Journal of Sustainable Metallurgy (2020) 6:505–540 509

Fig. 4  Flow sheet for recovery of chromium from stainless-steel slag

by alkali roasting, followed by water leaching. Adapted from [39]

an average of 1.03%, because in clinker production it can

be oxidized to the soluble and toxic hexavalent chromium.
Standard tests on EAF slag have investigated the leachability
Fig. 3  Flow sheet for ammonium carbamate leaching of manganese of chromium and other metals [35], where it is related to
and iron from BOF slag. Adapted from [33] the slag’s basicity and particle size [36]. The cooling condi-
tions also influence the leachability of chromium from EAF
indicating that it is present as Fe(II). After leaching, ­MnCO3 slags, e.g., a neutral or reducing atmosphere can prevent the
and ­FeCO3 were recovered from the solution by heating, formation of hexavalent chromium [37]. EAF slags are bet-
with the ­NH3 and ­CO2 driven off. Under optimum condi- ter for metal recovery than other slags due to their high iron
tions, 80% of the manganese and 50% of the iron could be and chromium contents [38]. Chromium is present in spinel
recovered. Manganese is a valuable, strategic metal, but the phases and FeCr metallic droplets. Few studies have looked
process was uneconomic because of the cost of roasting, the at metal recovery from EAF slags, and most of these concern
low manganese content, and ammonium carbamate cannot manganese recovery from ferromanganese slags.
leach manganese from all types of BOF slags. Researchers at the Flemish Institute for Technological
Krasheninin et al. recovered manganese from a residue Research (VITO) in Belgium studied the recovery of chro-
after leaching vanadium with N ­ a2CO3 from oxidatively mium from landfilled Cr-rich stainless-steel slags. They
roasted manganese-vanadium slag [34]. The manganese was used alkali roasting with a low concentration of alkaline
present as ­MnCO3 and could be recovered from the leachates salt (NaOH or NaOH + NaNO3), followed by water leaching
by adding ­(NH4)2CO3 and then calcining to ­Mn2O3. [39]. Figure 4 shows the flow sheet. The effects of the pro-
cessing parameters and a pre-treatment on leaching behav-
Electric Arc Furnace (EAF) Slag ior were checked. ­NaNO3 acts as an oxidizing agent and
increases the chromium recovery, while the residue could
There is a difference between EAF primary slag and EAF be used in construction. In a follow-up, alkaline pressure
secondary-metallurgy slag [11]. The main use of EAF slags leaching with a NaOH solution was investigated [40]. The
is in roads, waterways, railways, etc. The chemical compo- design-of-experiment method was used to optimize the pro-
sition of EAF slags varies, based on the type of feed. The cess parameters. The maximum chromium leaching was 46%
main components are calcium, iron, magnesium, aluminum, with 1-M NaOH, 240 °C, 6 h, mechanical activation 30 min,
and silicon oxides. Less than 1% of the calcium is present while the matrix material was only partially dissolved (Al
as free lime. EAF slags have high chromium and iron con- 2.88%, Si 0.12%, Ca 0.05%). After chromium leaching,
tents and low basicity (= CaO/SiO2 mass ratio). The metal- followed by alkali washing, a carbonation treatment stabi-
lic iron content is 0.8–11.4%, with an average of 4%. The lized the remaining chromium and the matrix was recycled
chromium content can be problematic, i.e., 0.01–2.52%, with for construction. Chromium can also be recovered under
milder reactions conditions, with a temperature-controlled

13
510 Journal of Sustainable Metallurgy (2020) 6:505–540

extraction using NaOH in the presence of NaOCl, followed furnace feed. Therefore, the product was washed with dis-
by water leaching [41]. The dissolved chromium can be tilled water to produce a viable furnace feed. Pure ­MnCO3
precipitated as barium chromate ­(BaCrO4). The dissolution (> 92%) was produced; however, although technically viable,
of chromium was optimized by studying parameters like the large amounts of base reagent required to enhance the pH
NaOCl concentration, NaOH-to-slag ratio, leaching time and made the process uneconomic. An optimization to determine
temperature, and particle size. The reuse of the residue via the ideal amount of acid for the water-starved digestion stage
accelerated carbonation was also studied. Lab-scale batch was conducted, which reduced acid and base consumption
and column leaching showed that the process can be used while optimizing the quality of the pregnant leach solution,
in the heap leaching of chromium from landfilled stainless- and producing a leach residue that contained less than 1%
steel slags, allowing in-situ chromium recovery [42]. Mn. The outcome was an economically viable process.
Ferromanganese slag comprises waste from the produc- Hocheng et al. bioleached metals from EAF slag that was
tion of ferromanganese metal in BFs and EAFs [43]. The washed with water before bioleaching [48]. This reduced the
manganese content of the slag (> 30%) makes it attractive slag’s pH from 11.2 to 8.3. Culture supernatants of Acidith-
for manganese recovery with hydrometallurgical methods iobacillus thiooxidans (At.thiooxidans), Acidithiobacillus
and using the residue for cement. Mohanty et al. used dilute ferrooxidans (At. ferrooxidans), and Aspergillus niger (A.
­H2SO4 to leach ferromanganese slag at temperatures up to niger) were used for metal solubilization. The At. thioox-
80 °C at a liquid-to-solid ratio of 10:1 with almost 100% idans culture supernatant containing 0.016-M ­H2SO4 was
recovery of the manganese [44]. Step-wise leaching with the most effective for bioleaching metals from EAF slag.
dilute acid was proposed to reduce the dissolution of impuri- The maximum metal extraction was obtained for Mg (28%),
ties, which can be precipitated from the leachate by increas- while the lowest was obtained for Mo (0.1%) in 6 days.
ing the pH from 2.5 to 5.65. The purified ­MnSO4 can be Repeated bioleaching increased the metal recovery from 28
used as an electrolyte for the recovery of manganese metal, to 75%, from 14 to 60% and from 11 to 27%, for Mg, Zn,
with the residue containing only aluminum and calcium. and Cu, respectively.
Naganoor et al. used ­FeCl3 to leach ferromanganese slag
[45]. Roasting with CaO or ­CaCO3 prior to leaching ensured
the manganese was in soluble form. A manganese recovery Dusts and Sludges
of 82% was achieved with a 0.154-M ­FeCl3 solution in 2 h at
80 °C and a pulp density of 5–10%. The sucrose in the F ­ eCl3 BF Dust and Sludge
solution meant 86% of the manganese was recovered from
the slag in 1 h. The pregnant leach solution was then treated Chemistry and Mineralogy
to produce electrolytic ­MnO2 and manganese metal. Ferro-
manganese slags contain silicate phases, so leaching silicate Dust leaves a BF via the top gas, which carries the particles
minerals with dilute acids can be difficult due to silica-gel through the gas cleaner, creating a coarse fraction called
formation, which hinders solid–liquid separation. Silica-gel BF dust (or primary dust) and a wet-scrubbed, fine fraction,
formation can be avoided by dry digestion with concentrated called BF sludge (or secondary dust) [49]. Less BF dust and
acid. This creates water-starved conditions where the con- sludge are produced now, due to improvements in the coke
densation of orthosilicic acid to silica gel is impossible [46]. and sinter properties and better control of blast furnaces.
Kazadi et al. digested ferromanganese slags with concen- The average production in 2006 was 11.4 kg/ton of hot metal
trated ­H2SO4 and the residue was leached with water [47]. for primary dusts and 8.9 kg/ton of hot metal for secondary
Up to 90% manganese recovery was achieved, depending sludges [11]. It is not clear if the value for secondary sludge
on the number of leachings. The leachate could then be pro- is for wet or dry material.
cessed to manganese metal by electrolysis, as well as M ­ nO2 The difference between primary and secondary materials
or other salts. The residue obtained after solid–liquid separa- is the zinc and lead contents, with more of these elements
tion, containing amorphous silica and calcium sulfate, was in the finer BF sludge. On average, there is 0.2 wt% of Zn
tested as an additive for Portland cement. In a follow-up, in BF dusts and 1.5 wt% in BF sludges [11]. Maximum val-
Baumgartner and Groot purified a M ­ nSO4 leach solution ues are 1.2 wt% for the BF dusts and 2.7 wt% for the BF
[43], with the pregnant leach solution having 25–35 g/L of sludges. Zinc, with its boiling point of 907 °C, travels with
Mn. Impurities were removed by hydroxide precipitation the ascending gas in the BF, condensing in its upper parts.
using ­NH3 or NaOH. The N ­ H3 was the most effective, reduc- The dust-forming mechanism for zinc is therefore chemi-
ing Fe, Si, and Al to less than 1 ppm. ­MnCO3 precipitated at cal, not mechanical [49]. Consequently, the zinc, unable to
pH > 8 by adding N ­ a2CO3 or ­(NH4)2CO3. However, phases form larger particles, will be found in the finest particles.
such as ­(NH4)2 Mg(SO4)2·6H2O and ­Na2SO4 co-precipitated Furthermore, zinc will condense more on finer particles due
and contaminated the product, rendering it unsuitable as a to their large surface area. The Pb content in BF sludges is

13
Journal of Sustainable Metallurgy (2020) 6:505–540 511

0.1–0.9 wt%. The zinc (and lead) in BF off-gas, BF dusts and Zn-containing residues are fed to the sinter plant, some of
sludges, originates from the reuse of BOF dust in the sinter the zinc is evaporated. Therefore, when operating the BF on
plant. The zinc (and lead) in the BOF dust comes mainly pellets, recycling the BF dust via cold-bonded agglomer-
from the scrap (vide infra). These elements negatively affect ates and injection, the requirements for zinc removal from
the BF because they can destroy the refractory lining. The BF sludges are tougher than when operating on the sinter.
total iron content is 20–70%, while the carbon content is Hence, the aim of de-zincing is to introduce a bleed of zinc
10–50%. from the BF, regardless of the zinc starting content, rather
The main mineral phase in BF sludge is hematite (­ Fe2O3), than having a general zinc content of the de-zinced fraction
together with calcite, periclase, graphite, and amorphous to be recycled. Most research has focused on the removal of
coke. Magnetite and quartz have also been reported [50]. zinc from BF sludges, rather than the removal of lead.
Kretschmar stated that identifying zinc phases in BF sludges
is demanding, because of the low zinc content, the large Sulfuric Acid Leaching
amounts of amorphous phase, and the isomorphism of zinc-
containing phases with non-zinc phases [51]. For instance, Sulfuric acid ­(H2SO4) leaching is the most popular way
franklinite is isostructural with magnetite, and smithsonite is to recover zinc from BF sludges, because of its availabil-
isostructural with calcite. In general, zinc is associated with ity and price. A process was developed to leach BF sludge
all the phases in BF sludge [49, 52]. Since the zinc reactions with this acid at room temperature [60]. For 1.0-M H ­ 2SO4,
are in the gas phase, ZnO condenses on solid particles and liquid-to-solid ratio = 10, leaching time = 10 min, 82% of
can react with the particles’ matrix. For instance, if ZnO the zinc was recovered, with a 5% co-dissolution of iron.
condenses on a F ­ e3O4 particle, it can react with it to form Shorter times reduced the co-dissolution of iron, but only
­ZnFe2O4. This means solid particles with an F ­ e3O4 core, a at room temperature. The dissolved iron was precipitated
layer of ­ZnFe2O4, and an outer layer of ZnO can be found. from the leachate as jarosite, and the solution was purified
There are also reports that the zinc in BF sludge is in by solvent extraction using LIX622 and LIX984. Finally,
the form of zinc sulfide (ZnS, sphalerite) [53]. The sulfur zinc metal was obtained by electrowinning from the sulfate
is introduced in the BF via coke or coal. The highest sulfur solution. Havlik et al. leached BF sludges with 1-M and 2-M
contents occur when pulverized coal injection (PCI) is used ­H2SO4, at 20, 50, and 80 °C [61]. The zinc was dissolved in
[54], with the coal containing more sulfur than the coke. ­H2SO4 concentrations of 1 M or higher within a few min-
Although most of the sulfur reports to the slag, about 2–3% utes. Although the amount of iron leached at 20 °C was
is found in the dusts and off-gases, where it can react with relatively low, it increased with temperature. For 2-M ­H2SO4
zinc or ZnO to form ZnS [55, 56]. Furthermore, the weath- and 80 °C, a lot of iron went into solution. Banerjee leached
ering of BF sludges in landfills changes the zinc speciation. BF flue dust and sludge with a low zinc content (0.007%
For instance, zinc phyllosilicates and hydrozincite are found for the dust and 0.45% for the sludge) in H ­ 2SO4 solutions
in weathered samples, but not in fresh ones [51]. between 0.1 and 1.0 M and reported less selectivity with
Some sludges contain high levels of mercury. The levels higher concentrations: for 1.0-M H ­ 2SO4 a significant amount
in 14 samples of landfilled BF sludge were 3.91–20.8 mg/kg of iron was dissolved [62]. Steer and Griffiths reported very
[57]. Another study of 65 BF sludges gave values of 0.006 efficient zinc leaching: > 98% dissolved, but 47% of the iron
to 20.8 mg/kg (mean 3.08 mg/kg) [58]. However, these went into solution [52]. This is probably due to the longer
amounts do not pose an environmental risk. leaching time (24 h) and high acid concentration (1 mol/L).
Close to 100% of the primary dust is recovered in steel Andersson et al. found that leaching with H ­ 2SO4 is bet-
plants, with the favored internal route being the sinter plant. ter than with HCl or H ­ NO3 [49]. Hot leaching (80 °C)
This suggests that there are no significant barriers to recov- with ­H2SO4 at pH 1 dissolved 95% of the zinc, leaving
ery [11]. Although more than 80% of the secondary dust just 0.025% in the residue, which also had 91% of the iron.
and sludges are being recouped, some BF sludges are not The leaching took 10 min. Longer times increased the heat
recycled because of their high water content, fineness, and losses, acid consumption, and iron leaching. Therefore,
zinc/lead content. Using hydrocyclones and dry cyclones is shorter times mean more iron in the residue, which con-
an effective way to separate high-Zn BF dust into Zn-rich tained 86% of the original solid, 91% of the iron, and 100%
smaller particles and Zn-lean larger particles [59]. of the carbon. When using pH 3, iron recovery increased to
The recycling of all the dusts and sludges back to the 96%, with 93% of the original solid remaining. Although
BF means the zinc would accumulate, i.e., a formidable the leachate was not purified, cementation was suggested as
challenge recognized by the steel industry [49]. To recy- a way to remove the lead and recover the zinc as ­ZnCO3 by
cle the BF sludges to the BF, a “zinc bleed” must be intro- adding ­Na2CO3. ­ZnCO3 can then be calcined to ZnO. This
duced. By de-zincing the BF sludge, a Zn-depleted fraction suggests it is easy to de-zinc BF sludge, making it suitable
can be recycled, so reducing the amount of landfill. When for in-plant recycling. Nevertheless, although the process

13
512 Journal of Sustainable Metallurgy (2020) 6:505–540

works, the liquid-to-solid ratio is high (L/S = 10). By leach-

ing BF sludge with 0.1-M H ­ 2SO4 in a strongly oxidizing
ozone gas, the co-dissolution of iron could be suppressed,
while 85% of the zinc could be leached [63].
The microwave-assisted leaching of BF sludge with
­H2SO4 solutions recovered only slightly more zinc (4%),
although the authors claim that the process was faster [64].
Mikhailov et al. reported the ultrasound-assisted leaching
of BF sludge with H ­ 2SO4–H2O2 solutions [65]. For 0.4-M
­H2SO4 + 0.1-M ­H2O2 and a liquid-to-solid ratio of 10, 84%
of the zinc and 1.3% of the iron were removed, with hydro-
gen peroxide oxidizing the sulfides of sphalerite to sulfate
ions. A conceptual flow sheet for an industrial process is
shown in Fig. 5. The mechanism is not entirely clear and
probably has errors (for instance, that F ­ e2O3 would dissolve Fig. 6  Flow sheet of the SIDMAR process for the treatment of BF
by bringing ­Fe2+ into solution). sludge. Adapted from [53]
Pure ­ZnSO4·7H2O was leached from zinc-containing BF
sludge with ­H2SO4 [50]. Fe(II) was oxidized to iron(III) easily, and at higher pH values because the sulfide ions are
by ­H2O2 and precipitated as Fe(OH)3 with the addition of oxidized. In a BF dust sample, 17% of the zinc was present
­CaCO3. Calcium was removed from the filtrate by adding as ZnS, and only 3–4% as Z ­ nFe2O4. Leaching involved HCl
­ZnF2 to form insoluble C ­ aF2. High-purity (99.57%) hydrated and NaOCl, and/or ­FeCl3 as an oxidizing agent. The HCl
zinc sulfate, Z
­ nSO4·7H2O, was crystallized from the filtrate and NaOCl were added directly to the reactor to keep the pH
by evaporating the water. below 1.5 and the redox potential above 650 mV. The slurry
could leach zinc and lead, while iron and calcium dissolved.
Hydrochloric Acid Leaching The sludge was added to the bottom of the reactor, with the
reagents and the recirculate. The turbulent reaction mixed
SIDMAR (now ArcelorMittal Gent, Belgium) and the the sludge and the chemicals. A flocculant was added to the
Department of Chemical Engineering of KU Leuven (Bel- overflow of the reactor, with the solid/liquid separation car-
gium) have developed a hydrometallurgical process based on ried out by a filter band.
oxidative leaching in HCl to treat BF sludges in SIDMAR’s The leaching efficiencies were 95% for zinc and 92% for
tailings pond [53]. A flow sheet is shown in Fig. 6. Oxida- lead, while that for iron was 32–49%. Zinc and lead chloro-
tive leaching was chosen because part of the zinc was in the complexes were removed using two anion exchangers, which
form of ZnS (sphalerite), which only dissolves in very acidic did not retain the iron, calcium, and aluminum. That part of
conditions (pH < 0.25) because of the low solubility product. the iron was extracted was not a problem, as it is not retained
When oxidizing conditions are used, ZnS dissolves more on the anion exchanger. It is returned to the reactor to pre-
cipitate once more as goethite and remain with the residue
as the concentration increases. Recirculating the solution
limits the consumption of water and chemicals. The aver-
age consumption of reagent was 0.5 L of 12-M HCl per kg
of incoming dry solids and 0.4 L of NaOCl (min. 120 g of
active chlorine per L) per kg of incoming dry solids. The
overall costs for the process (including investment, person-
nel, reagents, energy, and maintenance) were estimated
in 2000 to be $125 per ton of dry solids. Belgian patent
BE1011619A3, assigned to SIDMAR, is the same process,
but with ­Cl2 replacing NaOCl [66]. The same claim is cov-
ered by patent WO 99/31285 [67].
Belgian patent BE1001781A6 discloses the use of an oxi-
dized, spent pickling liquor used for steel plate. The liquor
is oxidized with ­Cl2 solution to obtain one rich in ­FeCl3.
This ­FeCl3-enriched HCl solution is then used to leach BF
sludge, which is washed and sent to a sintering plant [68].
Fig. 5  Conceptual flow sheet for the ultrasound-assisted leaching of
BF sludge with a ­H2SO4–H2O2 solution. Adapted from [65] Canadian patent CA2985027A1, assigned to ArcelorMittal,

13
Journal of Sustainable Metallurgy (2020) 6:505–540 513

discloses the leaching of BF sludge with a mixture of HCl

and sodium chlorate (­ NaClO3) oxidizing agent [69]. To keep
the lead soluble, the leaching is at pH 0.8–1.2 and 50–60 °C.
If the pH is too low, too much iron dissolves. The iron is
precipitated as goethite by increasing the pH to > 1.5 with
lime. The method was used for BF sludges with 4.5–12%
zinc, i.e., well above normal levels.
In patent WO 2018/219464, ThyssenKrupp discloses how
to treat BF sludge with a HCl solution and dissolve most
of the iron, leaving behind a C-rich residue [70]. The HCl
solution has a concentration of 5–20%, a time of 5–15 min,
at temperature of 60–80 °C. Ultrasound can help to homog-
enize the solution and shorten reaction times. The C-rich
phase is filter-pressed and washed with water to remove any
chloride impurities. After drying, this C-rich phase can be
returned to the BF. After solid/liquid separation, the Fe- Fig. 7  Zinc and iron extractions from BF sludge for a range of acids
rich solution is treated to recover the iron as F ­ e2O3. The at 1 mol/L. Adapted from [52]
Fe-rich solution can be reduced by hydroxylammonium
chloride to ­Fe2+, and the lead and zinc are removed with an
ion exchanger. Next, the ­Fe2+ is oxidized to ­Fe3+ by ­H2O2
and the ­Fe3+ is trapped on a second ion exchanger. After
eluting the ­Fe3+ with HCl, the ­FeCl3 solution is treated by
pyrohydrolysis. The HCl is recovered and the residue is 99%
­Fe2O3. Alternatively, after solid/liquid separation the Fe-rich
solution can be treated with H ­ 2O2 to oxidize the F­ e2+ to
3+ 3+
­Fe , and the F ­ e is precipitated as Fe(OH)3 by adding lime.
Fe(OH)3 is separated by a filter press and Fe(OH)3 is trans-
formed into F ­ e2O3 in a roast furnace. The HCl is regenerated
for reuse in the process by treating the solution in a spray
roast furnace (pyrohydrolysis). The residue contains 90%
CaO as well as other alkali, alkaline earth, and transition-
metal oxides. It can be reused for making lime suspension.

Leaching with Organic Acids

Fig. 8  Extraction of zinc and iron from BF sludge using 1 mol/L
prop-2-enoic acid in different non-aqueous solvents. Adapted from
Steer and Griffith tested some carboxylic acids for zinc [52]
and iron extraction with a concentration of 1 mol/L: acetic,
citric, oxalic, benzoic, malonic, and acrylic acid (prop-2-
enoic acid) [52]. The BF sludge was from a tailing pond and iron with acrylic acid (Fig. 8). Mixtures of water and
with 2.25% zinc content. The results are shown in Fig. 7. methylbenzene (toluene) extracted around 85% of the zinc.
Although ­H2SO4 gave the highest zinc yield, large amounts More importantly, the co-dissolution of iron was just 0.1%
of iron were also co-dissolved. The authors then selected for 2:1 water:toluene mixtures. This is probably because
acrylic acid (prop-2-enoic acid). This gave a better extrac- the iron was re-precipitated after dissolution due to a high
tion efficiency for zinc (83.1%), with the co-dissolution of pH. There have been no follow-up studies.
small amounts of iron (8.5%). However, the use of acrylic Citric acid is often used to remove zinc from contami-
acid is not appropriate from the safety and environmental nated soils [71–74]. Therefore, we could anticipate that
points of view. It is very hazardous for skin (permeator) citric acid, and related chelating organic acids, have the
and eye contact (irritant, corrosive). Although the authors potential to remove zinc from landfilled BF sludges. Some-
considered acetic and benzoic acid to be inferior to acrylic thing that has not been investigated yet. Furthermore, there
acid, because of the lower zinc extraction, the acetic and is little on recycling the lixiviant in soil-remediation stud-
especially the benzoic acid (with just 0.1%) led to less co- ies with citric acid. All the lead (but not zinc) could be
dissolution of iron. An interesting feature of this paper is removed from BF sludges with an EDTA solution [75].
the effect of non-aqueous solvents on the extraction of zinc

13
514 Journal of Sustainable Metallurgy (2020) 6:505–540

Leaching with Ammonia + Ammonium Salts sludge by ArcelorMittal Monlevade, Brazil, showed that the
fine fraction is much richer in zinc and lead than the coarse
Tata Steel discloses in EP 3 333 272 A1 a process for leach- fraction. Whereas the coarse fraction contained 0.51% Zn
ing BF (and BOF) residues with a leaching solution of ­NH3 and < 0.010% Pb, the fine fraction contained 4.37% Zn and
and an ammonium salt, (­ NH4)2SO4, ­NH4Cl, or (­ NH4)2CO3, 0.068% Pb [77]. A study of the distribution of zinc in BOF
at pH 8–12 [76]. When leaching with an N ­ H3 + ammonium off-gases in two ArcelorMittal steelmaking plants showed
sulfate solution, dried and untreated BF sludge yielded 40% that the dusts collected close to the BOF vessels contain
zinc with only 1% of co-dissolved iron. With roasting in much less zinc than the dust collected downstream in the
air, the zinc recovery was 60%. Roasting with N­ a2CO3, fol- off-gas cleaning system. The primary dust contains such a
lowed by leaching with ­NH3 + (NH4)2SO4, gave 70%. These low zinc content and is so Fe-rich that it can be considered
increases are due to the decomposition of ­ZnFe2O4. as a secondary iron resource, comparable to high-quality
iron ores [78]. BOF sludge contains much less sulfur than
Bioleaching BF sludge [79].
A mineralogical study of BOF sludge from ArcelorMit-
Cheikh et al. suggested a clean-up for BF sludges that com- tal Monlevade found the following mineralogical phases
bined an initial leaching with Na-EDTA (pH 6) to remove were present in both the coarse and fine fractions: wüstite
the lead, followed by a second bioleaching with A. ferroox- (FeO), magnetite (­ Fe3O4), metallic iron (α-Fe), lepidocroc-
idans to remove the zinc [75]. For the bioleaching, 1 g of ite (γ-FeOOH), calcite ­(CaCO3), and portlandite (Ca(OH)2)
sludge was used in 50 mL of solution. [77]. Zincite (ZnO) was not identified, and franklinite
­(ZnFe2O4) could not be identified due to an overlap with
BOF Dust and Sludge the peaks of magnetite in the X-ray diffractogram. Graphite
(C) was only found in the fine fraction and fluorite (­ CaF2)
Chemistry and Mineralogy only in the coarse fraction. Sammut et al. made a zinc spe-
ciation in BOF dust and found 43% Z ­ nFe2O4, 23% ­ZnCO3,
According to a 2006 survey, the average amount of BOF and 16% ZnO [80]. The ­ZnCO3 was attributed to the pres-
dust and sludge is about 22 kg/ton of crude steel (range ence of limestone in the process. Veres et al. reported the
10–40 kg/ton) [11]. Most BOF dusts and sludges are col- following mineralogical phases in a 9.37%-Zn BF dust: mag-
lected in the secondary/fine systems. Improvements in gas netite, hematite, wüstite, franklinite, zincite, and amorphous
cleaning systems mean more material is being collected, phases [81]. Wang et al. investigated the zinc distribution
rather than emitted into the atmosphere. This has led to and zinc speciation in Zn-rich (3.4% ZnO) BOF sludge by
slightly increased amounts of BOF dusts and sludges over micro-XRD and micro-XANES. The main zinc phases were
the years. There are also increases in BOF dusts and sludges franklinite ­(ZnFe2O4) and smithsonite ­(ZnCO3) [82, 83].
due to altered process conditions, e.g., blowing rates, slag Since BOF dusts and sludges have a lot of iron, their recy-
practices, bath additions, and bath agitations. cling should be a high priority. Internal recycling via the
Tables 1 and 2 show the chemical composition of primary sinter plant/BF route is limited by the concentrations of zinc
(coarse) and secondary (fine) BOF dusts and sludges. These and lead. In such cases, steel plants can blend materials and
are mainly iron particles ejected from the BOF, which par- produce briquettes/pellets that are then charged back to the
tially oxidize within the gas cleaning system [11]. The extent BOF [11]. Another option is stockpiling, and a significant
of the oxidation depends on the extraction system. Due to the fraction is used by the cement industry. Environmental con-
high temperatures involved and the mechanism of formation, cerns are reducing the amount of landfilling, while the high
the carbon levels associated with BOF dusts and sludges moisture content of BOF sludge is an obstacle to recycling
are low compared to BF dusts and sludges. A study of BOF [84].

Table 1  Chemical composition of primary BOF dust and sludge Table 2  Chemical composition of secondary/fine BOF dust and
(wt%) [11] sludge (wt%) [11]
Element Minimum Maximum Average Element Minimum Maximum Average

Iron (total) 47.6 92 73.7 Iron (total) 39.9 82 60.5

Iron (metallic) 1.9 79.4 44.1 Iron (metallic) 2.1 25 12.9
Carbon 0.1 2.2 0.9 Carbon 0.1 5.9 1.9
Zinc 0.01 1.7 0.3 Zinc 0.05 8 1.6
Lead 0.0016 0.1 0.06 Lead 0.01 0.3 0.1

13
Journal of Sustainable Metallurgy (2020) 6:505–540 515

Leaching with Mineral Acids aimed to maximize zinc recovery and minimize iron dissolu-
tion. The filter cake was dried overnight at 105 °C, screened,
There are very few studies on leaching BOF dust and sludge and the 300–500-μm fraction was used. The sample had
with mineral acids. Kelebek et al. studied the leaching of 6.5% Zn. The main mineralogical phases were wüstite,
BOF sludge with H ­ 2SO4 [85]. Leaching with a solution at metallic iron, and magnetite. About half of the zinc in the fil-
pH 2 for 20 min reduced the zinc in the coarse fraction from ter cake was ZnO and franklinite, whereas the other half was
1.6 to 0.4% and in the fine fraction from 1.9 to 1.6%. In the present in solid solutions of ZnO and FeO (zincite–wüstite)
coarse fraction, the zinc removal rate was 80–85%, with an and ­ZnFe2O4 and ­Fe3O4 (franklinite–magnetite). For the
18% iron loss. However, in the fine fraction the zinc removal leaching, 150 mL of a 1-M acid solution was used with a
was only 29%, with a 1.85% iron loss. The differences were filter cake corresponding to 70% of the ratio of the actual
due to mineralogy (with more Z ­ nFe2O4 in the fine fraction). amount of acid to that theoretically consumed if all the iron
The flow sheet (Fig. 9) has an upfront size separator to split and zinc were present as FeO and ZnO. The leaching was at
the sludge stream into fine and coarse fractions (with a room temperature for 10 h. Figure 10 shows the efficiency
hydrocyclone). The fine stream is directed to a dewatering for zinc and iron with different acids as a function of time.
circuit (e.g., thickener) and then to a disposal site (with no Butyric acid was the most efficient lixiviant, with 49.7%
treatment). The coarse fraction is sent to a leaching system, Zn removal and 2.5% Fe leached. After 20 min, 23.2% of
preferably arranged as a counter-current circuit. The solid the zinc was extracted, with 41.0% after 3 h and 49.7%
particles leaving this system are relatively coarse and low in after 10 h. Although acetic and propionic acids extracted
zinc, and can be recycled to the sinter plant. more zinc, they also led to more iron dissolving. Oxalic
Trung et al. studied the leaching of BOF sludge with acid was not efficient for leaching. Citric acid dissolved
­H2SO4 [86, 87]. The BOF sludge was a very heterogeneous the most zinc, but also the most iron, i.e., poor selectiv-
material, so that it was hard to select a H
­ 2SO4 solution with ity. The efficiency of the zinc leaching was acetic > propi-
the right concentration for leaching. After 15 min at 80 °C, onic > butyric > valeric acid. The order for iron leaching was
70% of the zinc was removed with a 1-M solution. Veres acetic > propionic > butyric < valeric acid, i.e., a minimum
et al. used the microwave-assisted leaching of BOF sludge for butyric acid.
with a 1-M H ­ 2SO4 solution at a liquid-to-solid ratio of 20 Based on the most promising results for butyric acid,
[88]. The microwaves increased the zinc leaching, but also the authors then investigated the leaching behavior of BOF
the iron leaching, resulting in poor selectivity. US patent sludge with butyric acid in a follow-up study. The optimum
3,375,069 discloses how to remove zinc from BOF sludge leaching conditions were determined. In the best case, 51%
by leaching with spent pickling liquor (HCl) [89]. BOF dust of zinc was leached, with less than 1% of iron co-dissolu-
samples with 0.80% and 0.78% zinc were investigated. With tion [91]. The results showed that zinc extraction increased
the pH at 4–5, iron dissolution could be avoided. with a higher acid-to-filter-cake ratio. Acid concentration
had no effect on zinc, but iron dissolution decreased with
Leaching with Organic Acids a stronger acid. The authors suggested leaching in coun-
ter-current mode (Fig. 11). A key finding was butyric acid
Wang et al. recovered zinc from BOF sludge with different cannot dissolve ­ZnFe2O4 (franklinite). To assess the butyric
organic acids [90]: oxalic, citric, acetic, propionic, butyric, route, three BOF filter cakes with 2.42%, 6.52%, and 13.8%
and valeric acid. These organic acids are biodegradable, Zn, as well as weathered samples, were tested [92]. After
so that secondary waste can be avoided. The leaching tests optimum leaching, 2–3% Zn remained. The effects of adding
other organic or mineral acids to butyric acid on leaching
zinc and iron from BOF filter cake were investigated to find
the maximum-allowed impurity levels in butyric acid [93].
While the presence of acetic and propionic acids in butyric
acid has little effect on zinc leaching, the addition of ­H2SO4
or HCl reduced the selectivity, unless the acids were added
such that the pH did not fall below that of pure butyric acid.

Alkali Leaching

Leaching BOF sludge with 5-M sodium hydroxide (NaOH)

solution was very selective for zinc over iron [77]. How-
Fig. 9  Flow sheet for the mild treatment of BOF sludge at pH 2 with ever, as no ­ZnFe2O4 was dissolved, the total zinc recovery
a ­H2SO4 solution. Adapted from [85] rate was only 40–60%. The ­ZnFe2O4 could be decomposed

13
516 Journal of Sustainable Metallurgy (2020) 6:505–540

Fig. 10  Leaching efficiency for a zinc and b iron for different acids as a function of time. Adapted from [90]

Fig. 11  Conceptual flow sheet

of a counter-current process
for leaching BOF sludge with
butyric acid. Adapted from [91]

by heating with NaOH (T = 450 °C, t = 1–5 h, NaOH/ molybdenum and tungsten from steelmaking dust, with no
sludge ratio = 0.75). Leaching this BOF sludge sample significant co-dissolution of zinc [95].
with 5-M NaOH resulted in 94% of zinc recovered. The
main disadvantage of leaching with NaOH is that concen- Leaching with Ammonium Salts
trated solutions are required and a lot of reagent is con-
sumed (see section on “EAF Dust”). Gargul et al. reduced Gargul and Boryczko compared the leaching of a BOF
the zinc content of a BOF sludge from 2.82% Zn to 1% Zn sludge containing 2.82% Zn with an N ­ H3 solution and the
after leaching for 100 h with 5-M NaOH [94]. Leaching ammonium salts N ­ H4Cl and (­NH4)2CO3 [96]. The best
with a 1-M (or less) NaOH solution selectively recovered results came with N ­ H4Cl, where the zinc was reduced
to < 1%. Although the authors claimed minimal loss of iron,

13
Journal of Sustainable Metallurgy (2020) 6:505–540 517

there were no data for its co-dissolution. In European patent processed for zinc recovery. However, the content is low
EP 3 333 272 A1, Tata Steel discloses the leaching of BF and compared to conventional zinc-industry raw materials, and
BOF residues with a solution of ­NH3 and an ammonium salt, a proportion is present as Z ­ nFe2O4, a refractory phase. The
­(NH4)2SO4, ­NH4Cl or ­(NH4)2CO3), at pH 8–12 [76]. In an levels of toxic heavy metals, particularly lead, are far too
example, BOF and BF flue dusts were roasted at 750–900 °C high to permit disposal in sanitary landfills. Hence, there has
for 1 h with ­Na2CO3 to decompose the ­ZnFe2O4. After leach- been a trend to send less EAF dust to landfills and recover
ing with N­ H3 + ammonium sulfate solution, > 80% of the more using external methods. The most common of these is
zinc was recovered. the (pyrometallurgical) Waelz-kiln process [5, 99], account-
ing for around 80%. A Waelz kiln is expensive, but it is
EAF Dust and Sludge attractive for EAF dusts with 15–20% zinc and plant capaci-
ties of at least 50,000 tons/year [100]. In contrast, hydromet-
Chemistry and Mineralogy allurgical treatment methods are better suited to a smaller
scale. Their advantages are low energy consumption, high
EAF dust and sludge amount to 14.2 kg/ton of crude steel zinc solubility in different lixiviants, and the possibility to
(range 3.4–25 kg/ton) [11]. The first stage of the gas clean- recycle residues to the EAF or BF. Although these hydro-
ing (typically a baghouse) is the main generator of dust: metallurgical methods have lower CAPEX and OPEX, the
12.7 kg/ton of crude steel on average. The other dusts and purification process is more complex. The EAF dust recy-
sludges collected from the process represent a small fraction, cling produces a residue with a huge moisture content, which
and most studies focus on the primary dust. The chemical must be dried before it can enter the steelmaking process.
composition of EAF dust is shown in Table 3 [11]. Iron and Hydrometallurgical processes can recover metals other than
zinc are the dominant components, while there is a relatively zinc, such as lead, cadmium, and copper, generating iron
low carbon content (1.8% on average), similar to the carbon oxide with less metal contamination. As well as pyromet-
content of BOF dusts and sludges, suggesting it is driven allurgical and hydrometallurgical methods, EAF dust can
off during steelmaking. The zinc content of EAF dust varies be used in construction or as a filler in acoustic or thermal
with the steel plant because of the different zinc contents of insulators [97].
the input scrap and the grades being produced. EAF dust can It is difficult to compare studies on zinc leaching from
also contain various amounts of lead and cadmium. EAF dust, because the compositions can vary widely, not
The physical properties of EAF dust depend on the steel only from steel plant to steel plant, but also over time,
type and the melting process. The particle size is 0.1 μm because of feed fluctuations. Therefore, we have different
to > 200 μm. Therefore, EAF can be airborne, which makes concentrations of zinc, but also variations in ZnO/ZnFe2O4
it difficult to handle or separate using physical methods ratio, with ZnO (zincite) easy to dissolve, whereas ­ZnFe2O4
[97]. Due to the presence of salts (NaCl and KCl), the solu- (franklinite) is not. Because of the fluctuating chemical and
ble fraction can be up to 10 wt%. Zinc accumulates in the mineralogical compositions of EAF dust, the optimum pro-
fine fraction of the dust, whereas iron tends to report to the cess parameters also vary.
larger particles, being present as ZnO (zincite) or ­ZnFe2O4
(franklinite). The zincite in EAF dust is due to the high zinc Removal of Chlorides
content [98]. However, there is usually less zincite than
franklinite. EAF dust contains chloride salts. This is a problem when
leaching EAF dust with ­H2SO4, because the chloride will
Pyrometallurgical Versus Hydrometallurgical Processes end up in the leachate and, hence, in the electrolyte for the
electrowinning of zinc. Chloride impurities in Z ­ nSO4 elec-
The high zinc content of EAF dusts means they cannot trolytes are problematic because they corrode the electrodes,
be used in steelmaking. They must either be landfilled or incorporate lead dissolved from the anode in the zinc, and
make it hard to remove the electrodeposited zinc from the
aluminum cathode. Therefore, the chloride salts must be
Table 3  Chemical composition of EAF dust (wt%) [11] removed from the EAF dust prior to leaching or from the
Element Minimum Maximum Average pregnant leachate.
A convenient way to remove the chloride salts from EAF
Iron (total) 16 60.8 35.1
dust is washing with water, because the chlorides are mostly
Iron (metallic) 0.19 9.2 3.5
water soluble (NaCl and KCl). Bruckard et al. removed 99%
Carbon 0.94 4.1 1.8
by washing with tap water at room temperature for 60 min
Zinc 0.03 37 14.6
at the natural pH of EAF dust (pH 12). The residue had only
Lead 0.05 21.5 3.1
200 ppm chloride [101]; the liquid-to-solid ratio was 3:1; no

13
518 Journal of Sustainable Metallurgy (2020) 6:505–540

adjustment of the pH was necessary; and water at ambient of zinc over iron, it is better to use 0.5-M (or lower) ­H2SO4
temperature was as effective as hot water. The kinetic experi- solutions and to stop leaching after about 15 min. The co-
ments showed that about 1 h was sufficient to eliminate the dissolution of iron is suppressed by working at lower con-
water-soluble salts from the EAF dust. The washing step centrations [107, 108]. The reason why only a little iron is
removed all the potassium and sulfate in the sample, about dissolved at lower ­H2SO4 concentrations is that the other
50% of the sodium and less than about 10% of the calcium. elements are dissolved first and there is not enough free
Only trace amounts of zinc and manganese were leached. acid to dissolve all of the iron. The final pH after leaching
Environmentally significant amounts of lead, chromium, and with a dilute ­H2SO4 solution will be so elevated that co-
cadmium reported to the wash solution, so this solution must dissolved Fe(III) will precipitate on the residue. Lead is not
be treated for heavy-metal removal. This involved ­Na2S solu- solubilized by leaching with ­H2SO4, because poorly soluble
tion to precipitate the heavy metals and then adding a little ­PbSO4 (anglesite) is formed. A problem often encountered
Fe(II) sulfate to remove the excess of sulfide ions. H ­ 2SO4 when leaching with H ­ 2SO4 is the poor settling and filtration
was used to lower the pH from 12 to 8–10. behavior of the residues.
However, some of the chloride in EAF dust is in the form Leaching for longer times with higher H ­ 2SO4 concentra-
of water-insoluble lead hydroxyl chloride (PbOHCl) and tions at high temperatures will always bring significant iron
lead chloride carbonate (­ Pb2Cl2CO3) [102]. Washing with into solution [61, 109]. For instance, 100% of zinc and 90%
water cannot remove the chloride from these compounds. of iron were dissolved in 3-M H ­ 2SO4 at 80 °C and a liquid-
They require roasting of the EAF dust at < 600 °C before to-solid ratio of 5:1 for 6 h [109]. A small residual fraction
washing with water. Sulfation roasting is more efficient rich in lead was obtained. The iron could be precipitated
than carbonation or air roasting. The metal chlorides in the after sufficient dilution as goethite (α-FeOOH), which has
roasted EAF dust are NaCl and KCl, which can be easily the advantage that it can precipitate iron from an Fe(III)
removed with water. The roasting must be below 600 °C to sulfate solution without the need for high temperatures and
avoid the evaporation of zinc and lead. Carbonation roast- pressure. The main disadvantage is that a lot of alkali is
ing requires a ­CO2 gas stream, whereas sulfation roasting required for neutralization, although it is more efficient if the
requires ­SO2, and air roasting requires air. The washing step solution is neutralized by fresh EAF dust. A study of auto-
should be applied to freshly collected EAF dust, because it clave leaching of EAF dust with ­H2SO4 confirmed that cal-
absorbs ­CO2 from the atmosphere and this can lock up part cium dissolves up to 150 °C, but later precipitates as calcium
of the chloride in water-insoluble zinc hydroxyl-chloride, sulfate [110]. Above 150 °C, calcium remains permanently
­ZnCl2·4Zn(OH)2·H2O. in solution, even after cooling to room temperature after
After leaching with H ­ 2SO 4, chloride impurities can the leaching process. High concentrations of calcium in the
be removed by electrodialysis with a mono/bipolar ion- EAF dust have a negative influence on the cost of leaching,
exchange membrane [103]. Monopolar membranes are because the dissolution of CaO consumes H ­ 2SO4 and leads
either cation-exchange or anion-exchange membranes. A to the precipitation of ­CaSO4 [111].
bipolar membrane contains an anion-exchange and a cat- When leaching EAF dust with H ­ 2SO4, iron co-dissolution
ion-exchange layer. These membranes split water into ­H+ can be avoided by using moderate concentrations so that the
and ­OH− ions in an electric field. A one-step electrodialysis final pH is 4–5 [112] and the dissolved iron will precipitate
process produces a ­ZnSO4 solution with a low-enough chlo- as Fe(III) hydroxide.
ride concentration for an electrolytic zinc production process AMAX Inc. developed a two-stage leaching process to
from leaching solutions of Zn-bearing raw materials with up recover zinc from steel-plant dusts, with the complete rejec-
to 1% chloride. tion of iron as hematite [113]. The conceptual flow sheet is
shown in Fig. 12. The first stage is leaching at atmospheric
Sulfuric Acid Leaching pressure and a temperature below the boiling point. In the
second stage, leaching is at high pressures in an autoclave,
Solutions of sulfuric acid (­ H2SO4) are the most popular at 225–300 °C. The two stages are connected in counter-
lixiviants for a hydrometallurgical treatment of EAF dust. current fashion, with two liquid/solid separation steps. Under
­H2SO4 is cheap and it is possible to use the Z
­ nSO4 leachate autoclave conditions, most of the iron in the feed slurry was
for the electrowinning of zinc metal [104]. Zinc oxide (zin- converted to hematite ­(Fe2O3), which is more dense and sep-
cite) dissolves very rapidly in ­H2SO4 solutions, irrespec- arates more easily from the solution than goethite, jarosite,
tive of the concentration and the temperature [105]. The or Fe(III) hydroxide. Due to its high iron content and virtu-
diffusion-controlled reaction can take as little as 1 min. The ally zero sulfur content, hematite is the preferred form of
dissolution of ­ZnFe2O4 (franklinite) is much slower and iron precipitate for recycling in steelmaking furnaces. The
depends on the temperature [106]. The rate-limiting step is solids were washed to recover Z ­ nSO4. If lead is still present
the rate of the chemical reaction. For the highest selectivity in the residue, it can be leached with brine.

13
Journal of Sustainable Metallurgy (2020) 6:505–540 519

to ­H2SO4 by rehydration. Alternatively, the F ­ e2(SO4)3 can

be reacted with an ­NH3 solution. The resulting ammonium
sulfate can be thermally decomposed into ­NH3 and ­H2SO4,
both of which can be recycled.
The Modified Zincex Process involves the following steps
to recover the zinc from zincite in EAF dust: (1) atmos-
pheric leaching with 0.5 N ­H2SO4 at 40 °C, 1 h, pH 2 to
dissolve ZnO; (2) purifying the leachate by precipitating the
iron with lime; (3) extracting the zinc with bis(2-ethylhexyl)
phosphoric acid (D2EHPA), (4) stripping the zinc from the
loaded organic phase, and (5) electrowinning of the zinc
metal [115].
A design of experiment for leaching EAF dust with dilute
­H2SO4 indicated that the optimum leaching conditions were
3 N ­H2SO4, 60 °C and a liquid-to-solid ratio of 10:1 [116],
where 80% of the zinc was extracted, while 45% of iron was
co-dissolved. The main phases in the residue were basanite
­(CaSO4·1/2H2O), anhydrite ­(CaSO4), and anglesite ­(PbSO4).
The leachate was further purified [117]. The proposed
Fig. 12  Conceptual flow sheet for two-stage leaching of EAF dust flow sheet had four unit operations: (1) removal of iron as
with ­H2SO4, developed by AMAX Inc. Adapted from [113] jarosite, by precipitation at 95 °C and pH 3.5; (2) solvent
extraction of zinc by the extractant Cyanex 272 at pH 3.5,
40 °C, 25 vol% extractant, diluted in kerosene + 5 vol. TBP,
organic-to-aqueous phase volume ratio (O/A) = 2 (3) strip-
ping of the loaded organic phase by spent zinc electrolyte
(62.5 g/L ­Zn2+) at 40 °C, diluted with H ­ 2SO4 (3 M); (4)
zinc electrowinning from Z ­ nSO4 solutions at 38 °C, using
an aluminum cathode and a lead anode. The acidity of the
electrolyte was 180 g/L H ­ 2SO4, with a zinc concentration of
80.4 g/L, and a current density of 500 A/m2. Gotfryd et al.
leached EAF dust with H ­ 2SO4 and purified the leachate by
solvent extraction with D2EHPA [118, 119]. The tests were
performed on a pilot scale.
Montenegro et al. described an efficient process to
recover zinc from EAF dust [100]. The process has three
leaching stages: (1) 60% of zinc and 80% of cadmium can
be leached at ambient temperature with 2 N ­H2SO4 and 20%
Fig. 13  Flow sheet of a process based on leaching of EAF dust with
hot concentrated H­ 2SO4 and washing the residue with methanol.
pulp density, for 20 min. (2) A second leaching stage on the
Adapted from [114] first-stage leach residue with dilute H
­ 2SO4 (0.5 N) and 20%
pulp density at ambient temperature for 20 min led to total
dissolution of the zinc content contained in the EAF dust.
US patent 5,286,465 discloses the leaching EAF dust Zinc recovery in this stage is 75% and cadmium recovery is
with hot concentrated ­H2SO4 at 100–200 °C for 5–10 min 90%. (3) A third step of autoclave leaching using 2 N H ­ 2SO4
(Fig. 13) [114]. Under these conditions, zinc is dissolved as and 20% pulp density, at 200 °C for 60 min, led to total
­ZnSO4 and iron precipitates as ferric sulfate, ­Fe2(SO4)3. The zinc recovery from the second-stage leach residue, mainly
precipitate can be separated by filtration and washing with as ­ZnFe2O4. After three stages, the metal content in the final
methanol, which can be recovered by distillation. The zinc residue was 0.16% Zn, 5.67% Pb, 11.96% Fe, and 0.003%
can be recovered from the H ­ 2SO4 solution by adding water Cd. The total zinc recovery was 99% and the total cadmium
to precipitate hydrated ­ZnSO4 at 10 °C, separating it by fil- recovery was 94%. The process reduced the initial residue
tration and evaporating the water to regenerate the ­H2SO4. mass by 30%. EAF dust has a high calcium content, due
Iron can be recovered by roasting the F ­ e2(SO4)3, yielding to lime being added during the steelmaking process. The
ferric oxide and sulfur trioxide, which can be reconverted dissolution of ZnO in the first stage takes 20 min. Lead is
dissolved in the first stage, but precipitates as P
­ bSO4 in the

13
520 Journal of Sustainable Metallurgy (2020) 6:505–540

solid residue. CaO reacts with ­H2SO4 forming ­CaSO4·2H2O By adding N ­ a2CO3 in 110% of the stoichiometric quantity,
(gypsum) and crystallizes in the residue. The reaction of 95% of the zinc could be recovered at pH 6.5–7.5, after the
CaO with ­H2SO4 consumes more acid. In the first stage, addition of Z ­ nCO3 seed crystals. The main mineralogical
the acid concentration was kept at 2 N ­H2SO4 to minimize phases were hydrozincite (­ Zn5(OH)6(CO3)2) and a hydrated
iron dissolution, but this led to lower ZnO dissolution. The basic zinc carbonate ­(Zn4(CO3)(OH)6·H2O).
leach residue after the first stage still contained zinc because Ultrasound was found to enhance the dissolution of
of the high concentration of zinc ions in solution, and the ­ZnFe2O4 at low H ­ 2SO4 concentrations, and resulted in
consumption of acid, due to the reaction with CaO, reduced more zinc recovery under all conditions [122]. For instance,
the dissolution of free ZnO. Therefore, a second stage at after 30 min of leaching in 0.5-M ­H2SO4 at 80 °C, the zinc
room temperature was used to dissolve any zinc from the recovery was 38% for conventional leaching and 59% for
ZnO and increase the metal recovery. No iron was dissolved ultrasound-assisted leaching, i.e., an increase of 55%. As
during the second stage. Iron was, however, dissolved during ultrasound brings more calcium into solution, it is assumed
the first stage, and re-precipitated as α-FeOOH during the that it destroys the ­CaSO4 layer that forms on top of the CaO
leaching when more acid was consumed and the pH rose to in the EAF dust. The CaO reacts with ­H2SO4 to C ­ aSO4,
4–5. The leachate from both stages could be combined and which enhances the pH.
directed to zinc and cadmium recovery by cementation or
solvent extraction, followed by zinc electrowinning. Pressure Hydrochloric Acid Leaching
leaching was applied to dissolve the remaining zinc, which is
present in the form of ­ZnFe2O4. The leachate after pressure Hydrochloric acid (HCl) has an extraordinary dissolving
leaching was contaminated by iron, which was removed by power for many oxides, hydroxides, and carbonates [123].
precipitation as jarosite at atmospheric pressure at pH 3.5 In contrast to H ­ 2SO4, HCl solutions are volatile and cor-
and 95 °C. rosive, but problems can be mitigated by selecting suitable
Montenegro et al. further improved their flow sheet for materials. Steel manufacturers have experience with chloride
­H2SO4 leaching of EAF dust with water washing, at ambi- hydrometallurgy because of steel pickling [124].
ent temperature and equilibrium pH 10, before the leaching Compared to H ­ 2SO4, which dissolves metallic iron, and
[120]. More than 50% of the calcium, present as free CaO, thus “blows” the iron oxide layer with ­H2 gas, HCl dissolves
dissolved without the co-dissolution of any other metals. the oxides and forms Fe(III) ions, which prevent the hydro-
Removing the CaO prior to leaching reduced the consump- gen forming. Since steel makers want to remove iron oxides
tion of ­H2SO4. The washing also removed the water-soluble and not iron metal, HCl pickling is preferred. Furthermore,
chloride salts. Next, the washed EAF dust was leached with HCl pickling offers better surface quality and higher pickling
dilute ­H2SO4 (2 N) at ambient temperature and pH 4. Almost rates. But the technology has to wait for a process by which
complete dissolution of the free ZnO took 10 min. The the HCl is regenerated through the thermal decomposition
recovery of zinc was 70% and that of cadmium was 90%. of Fe(II) chloride in a spray roaster or fluid bed. Solid/liq-
This leaching was very selective regarding iron and lead. uid separation of iron precipitated from chloride solutions
The pregnant leach solution could be directly treated for zinc is easier to filter than iron precipitated in sulfate solutions.
and cadmium recovery by solvent extraction and electrolysis. The chlorides present in the EAF dust must not be removed
The leaching residue from the previous step was treated with before HCl leaching [125], because the chlorides aid the
­H2SO4 (3 N) at 95 °C, in two stages. Under these condi- leaching process. Lead and cadmium can be removed from
tions, almost all the Z ­ nFe2O4 was dissolved in 120 min. The the dust as soluble chlorides if a high concentration of chlo-
total zinc recovery was 97%, with cadmium removal also rides is present in the lixiviant.
97%. The final leach residue consisted of ­CaSO4, ­PbSO4, AMAX Inc. developed a HCl leaching process for EAF
and ­Fe3O4. Its dry mass was about 27% of the initial dry dust [126]. The flow sheet is shown in Fig. 14. In the first
mass of the dust. It was proposed to remove the iron from step, EAF dust is leached with HCl. After liquid/solid sepa-
the pregnant leachate of the hot leaching step as jarosite or ration, the solution is oxidized by chlorine gas and simulta-
goethite, with subsequent recovery of zinc and cadmium by neously neutralized by adding lime to precipitate the iron.
solvent extraction and electrolysis. Lead could be extracted The Fe-rich residue is free of sulfur and can be recycled
by leaching with a NaCl solution at 95 °C and precipitation to the steel furnace. Alternatively, the leach residue can be
of the lead from PbS by adding ­Na2S at ambient temperature. treated to recover the lead prior to being fed back to the
The residue after NaCl leaching contained 1.3% Zn, 6.6% steel plant. The Fe-free solution, following solid/liquid sepa-
Fe, 0.5% Pb, and 19.5% Ca. Its dry mass was about 20% of ration from the residue, can be further purified by solvent
the dry mass of the original dust. The final residue could extraction with D2EHPA or Cyanex 272. The purified Z ­ nCl2
be used in the cement industry. Instead of electrowinning, electrolyte is electrolyzed and zinc metal is produced at the
the zinc in the pregnant leachates can be precipitated [121]. cathode. The chlorine gas released during electrowinning is

13
Journal of Sustainable Metallurgy (2020) 6:505–540 521

Fig. 15  Simplified flow sheet of the leaching part of the Terra Gaia
process. Adapted from [129]

solubilizing zinc and aluminum. Partial dissolution of alu-

minum is advantageous, because it provides aluminum ions
for the precipitation of fluoride ions. The mixed lixiviant
allows the use of chlorine as the oxidant in the iron oxida-
tion/precipitation stage. It is remarkable that in this patent
the formation of insoluble Pb(II) sulfate (anglesite) is seen
as an advantage, whereas it is seen as a disadvantage when
leaching EAF dust with ­H2SO4.
Terra Gaia Environmental Group Inc. developed a pro-
cess for leaching EAF dust with F ­ eCl3 solution [128, 129].
Fig. 14  Flow sheet of the AMAX HCl leaching process. Adapted Figure 15 shows a flow sheet of the leaching process. The
from [126]
first step is leaching the EAF dust with a F ­ eCl3 solution at
atmospheric pressure. The EAF dust is delivered to a tank,
recycled to the system, partly as chlorine gas to oxidize the where it is mixed with a ­FeCl3 solution. Hydrolyzing the
iron, and partly as HCl to dissolve more zinc. The process ­FeCl3 solution produces HCl, which dissolves ZnO and
can treat many Zn-containing feed materials, not only EAF PbO. The concentration of ­FeCl3 in the solution should
dust, and a wide range of concentrations. When a HCl con- be sufficient to provide the stoichiometric amount of ­Fe3+
centration of 75 g/L was used for leaching, 88% of the zinc required to dissolve all the ZnO and PbO, as well as to
and 48% of the iron were dissolved. Higher HCl concentra- leave a surplus of F ­ e3+ (5 g/L iron as F­ eCl3) to maintain
tions dissolved significantly more iron; at a HCl concentra- acidity. The leach solution should also contain at least
tion of 200 g/L, 100% of the zinc dissolved, but also 93% 140 g/L of chloride for the zinc solvent-extraction step. In
of the iron. The leaching was at 90 °C, because higher tem- the second step, the hydrous iron oxide slurry produced
peratures increased zinc recovery and the slurry was easier by the atmospheric leach settles sluggishly and is difficult
to filter. Leaching can also be in counter-current mode. The to filter. In the conditioning step, the slurry is treated in
first stage will receive all the HCl and discharge the leach an autoclave to convert the hydrous iron oxide slurry into
residue. This stage can be maintained at pH 0.5 or lower. a crystalline residue that can settle and be filtered. The
The last stage will receive the EAF dust and discharge the slurry is heated in an autoclave to more than 140 °C and
leach liquor. This stage can be operated at pH 2.5 to 3. A is held for at least 30 min. For higher temperatures, the
pulp density of 5–40% is recommended. Although counter- times are shorter. The conditioning involves the conver-
current leaching makes best use of reagents, it is more costly sion of the goethite (α-FeOOH) that is stable at low tem-
(inter-stage thickeners and pumps). peratures, or hydrous iron oxide, to crystalline hematite
Another AMAX Inc. patent describes the leaching of ­(Fe2O3) at temperatures above 110 °C in an acidic chlo-
EAF dust with a mixture of HCl and ­H2SO4 [127]. The ride solution: 2 α-FeOOH → Fe2O3 + H2O. The next step
inventors claim that H­ 2SO4 leaching is undesirable because in the process is a liquid/solid separation, which involves
the residue is hard to separate from the liquid. Likewise, hot filtration of the conditioned slurry, with brine wash-
direct HCl leaching must be avoided as it solubilizes nearly ing, to produce the hematite residue for recycling. The
all of the iron and most of the lead, leading to a separation hot brine washing removes the lead from the residue. The
problem. A mixed lixiviant, on the other hand, will pro- filtration and the washing require more than 80 °C to keep
vide sulfate ions for the formation of Pb(II) sulfate, while the Pb(II) chloride in solution, but which can be recovered

13
522 Journal of Sustainable Metallurgy (2020) 6:505–540

by precipitation upon cooling. Lead can be reclaimed penetration, boundary, and product layer breakdown. Iron
by reacting the solid Pb(II) chloride with iron scrap in recovery was inhibited by the ultrasound, attributed to the
a cementation reaction: ­Fe0 + PbCl2 → Pb0 + FeCl2. Zinc precipitation of any dissolved iron. The material investigated
is recovered from the filtrate by solvent extraction, fol- consisted largely of zincite, with a very small amount of
lowed by stripping and electrowinning. The chlorine gas refractory ­ZnFe2O4 phase.
evolved at the anode is used to oxidize the F ­ eCl2 of the
lead cementation step: 2­ FeCl2 + Cl2 → 2FeCl3. The excess Nitric Acid Leaching
chlorine gas is reacted with scrap iron to form ­F eCl 3:
­3Cl2 + 2Fe0 → 2FeCl3. Cadmium can be removed from the Nitric acid ­(HNO3) is less common for leaching EAF dust
circulation circuit via a bleed stream and precipitated as than ­H2SO4 or HCl. However, ­HNO3 can give a near-zero-
CdS by adding ­Na2S. Except for the washing of the leach waste valorization of EAF dust, with iron recovered as
residue, the system is closed for chloride. Any shortfall hematite. There are no insoluble metal nitrates, so H ­ NO3
can be overcome by adding NaCl or spent HCl picking can be regenerated by precipitating gypsum in a mixed
liquor. nitrate/sulfate system. Lead is solubilized by ­HNO3. ­HNO3
US patent 5,709,730 discloses the leaching of EAF dust processes were considered to be expensive, environmen-
with a mixed solution of C ­ aCl2 and HCl, with subsequent tally unfriendly, and unsafe, but this is changing. H ­ NO3
regeneration of the HCl with H ­ 2SO4 to produce gypsum as can be recycled [133–136], and ­HNO3 leaching is becom-
a building material [130]. The process makes use of the low ing more popular in hydrometallurgy, for instance, for
solubility of iron oxides in moderately acidic chloride solu- nickel laterites [137], where the advantage of H ­ NO 3 is
tions. Leaching is executed at pH 2.6 at 15–30% pulp den- not in digesting the ore, but in the way the acid can be
sity. Fe(II) is oxidized to Fe(III) and hematite is formed by recycled, eliminating a major cost of H ­ 2SO 4 high-pres-
heating the slurry in an oxygen atmosphere at 90–120 °C. sure leaching plants, i.e., neutralization after leaching. A
The combination C ­ aCl2/HCl puts more lead in solution com- hydrometallurgical ­HNO3 process plant can be built with
pared to leaching with only HCl. C ­ aCl2 alone will not dis- modular stainless-steel equipment, i.e., no titanium-lined
solve metal oxides, whereas HCl by itself will dissolve only autoclaves are required.
a minor fraction of the lead present in the EAF dust. Lead, Hematite produced from sulfate solutions often contains
cadmium, and copper can be recovered by cementation zinc and sulfate impurities, while that formed by the thermal
with zinc powder. Adding lime to the Zn-rich solution will decomposition of Fe(III) nitrate is purer [138]. The hydroly-
precipitate the zinc as zinc hydroxide and generate a ­CaCl2 sis of Fe(NO3)3 requires more than 100 °C in an autoclave.
solution. The lixiviant can be recovered by adding ­H2SO4 However, the advantage over conventional neutralization is
to the ­CaCl2 solution, and clean gypsum will precipitate. that the hydrolyzed product contains fewer impurities and
A two-stage leaching process with HCl was developed to the lixiviant can be regenerated without introducing foreign
extract the zinc from EAF dust [125, 131]. The first low-acid ions. Another advantage is that the precipitate has a larger
leaching dissolves the ZnO from the dust, while the second particle size and is easier to filter. Fe(III) hydroxides pro-
step reacts HCl at 90 °C with the Z ­ nFe2O4 residue from duced at room temperature can be gelatinous and it is hard
the first leach. ­H2O2 was found to be efficient for oxidizing to remove any entrained mother liquor. Below 140 °C, a
Fe(II) to Fe(III). This oxidation could also be with aeration. mixture of hematite and goethite is formed, whereas above
The iron residue from the hot-acid leach was hematite and 160 °C, only hematite [138]. The high-temperature pre-
goethite. Fresh EAF dust was added to the filtrate after the cipitate was free of nitrate ions. The precipitate formed at
hot-acid leach to raise the pH and precipitate iron. The ­ZnCl2 180 °C was dense (ρ ≈ 2450 kg/m3), while those obtained
solution was purified by activated carbon to eliminate the from more concentrated Fe(III) solutions were easier to filter
organics and by cementation with metallic zinc powder to than in the case of more dilute Fe(III) solutions.
remove the lead, cadmium, and copper. The purified ­ZnCl2 US patent 5,912,402 discloses a ­HNO3-based process for
solution was electrolyzed in electrowinning cells with a the zero-waste valorization of EAF dust [139]. The dust is
cation-exchange membrane to high-purity zinc metal and washed with water to remove soluble chlorides. Next, it is
regenerated the HCl. The spent electrolyte contained 1–2-M reacted with H­ NO3 (53%) to dissolve zinc, cadmium, copper,
HCl and was used for the residue in the hot-acid leach. The magnesium, calcium, manganese, and lead. The residue can
zinc recovery exceeded 90%. A drawback of the process is be recycled to the EAF. Dissolution in ­HNO3 results in ­NOx
the need for the costly membrane in the cell. gases that must be recovered for reconversion to ­HNO3. Iron
Barrera-Godinez et al. investigated ultrasound leaching is precipitated from the filtrate by increasing the pH of the
for the selectivity of zinc from double-kiln-treated EAF cal- solution with basic Z ­ nCO3. The dissolved lead, copper, and
cined with ­CaCl2 and HCl [132]. Recovery was enhanced cadmium can be recovered by electrolysis or sulfide precipi-
in this way, possibly due to a combination of lixiviant pore tation. The filtrate is evaporated and decomposed to obtain

13
Journal of Sustainable Metallurgy (2020) 6:505–540 523

a solid residue of metal oxides and Ca(NO3)2. The solid for 180 min at 15–20% pulp density with varying concen-
residue is leached with water to solubilize the Ca(NO3)2, trations of H
­ NO3. Recovering zinc from the leachate is not
which can be crystallized from the leachate. The zinc can described here.
be separated from the manganese and magnesium by leach-
ing with an AAC solution. After solid–liquid separation, the Acetic Acid Leaching
residue is treated with H
­ 2SO4 to solubilize the magnesium as
­MgSO4. The residue consists largely of M ­ nO2. The filtrate Acetic acid (­ CH3COOH, sometimes AcOH) is weak com-
of the AAC leaching step is heated to drive off the ­CO2 and pared with H ­ 2SO4, HCl, or H­ NO3. Since C­ H3COOH is an
to precipitate Z
­ nCO3. The advantages include the recycling organic acid consisting only of carbon, hydrogen, and oxy-
of the iron to the EAF and selling the other by-products. In gen, it does not contaminate the leaching residue with ele-
addition, the process can be carried out at atmospheric pres- ments that are incompatible with BF, BOF, or EAF instal-
sure, without an autoclave, and the ­HNO3 can be recycled. lations. ­CH3COOH will dissolve oxides and carbonates of
US patent 7,399,454 describes a process for leaching EAF calcium, zinc, and lead, but not of iron, and so can be used
dust with H­ NO3 at elevated temperatures and pressures, with for selective leaching. Unfortunately, C
­ H3COOH cannot dis-
the iron recovered as hematite [140]. The process is built on solve ­ZnFe2O4.
the principle that, at a certain pressure and temperature, the The UBC-Chaparral Process treats EAF dust so as
iron forms hematite in a ­HNO3/nitrate solution. Since many (1) to recover zinc, cadmium, and lead; (2) to render the
of the other metal contaminants are solubilized in ­HNO3 EAF dust non-toxic (1990s legislation), and (3) to process
when the ­Fe2O3 precipitates, the ­Fe2O3 can be separated. it at minimum cost [141]. The process decontaminates
Before the pressure leach, an atmospheric leach in condi- EAF dust for sanitary landfill, rather than recovering an
tions at which ZnO dissolves, but the ­ZnFe2O4 and other iron iron product for the steel industry. This complex process
compounds do not. Pressure leaching involves 180–220 °C combines ­CH3COOH leaching for calcium removal with

Fig. 16  Generalized flow sheet

for the UBC-Chaparral process.
Adapted from [141]

13
524 Journal of Sustainable Metallurgy (2020) 6:505–540

Fig. 18  Flow sheet of the Versatic acid leaching process. Adapted

from [148]

the recycling process. The zinc, cadmium, lead, and copper

Fig. 17  Generalized flow sheet of the Hatch Acetic Acid Leach Pro-
cess. Adapted from [143] are precipitated as a sulfide product using a stream of H ­ 2S
gas. The sulfide precipitation simplifies the process, because
the metals are recovered as useful sulfides, while regenerat-
AAC leaching for zinc removal (Fig. 16). The free CaO is ing the C­ H3COOH. The filtrate is then treated with H ­ 2SO4
removed before the zinc leach with AAC, so that the CaO to precipitate the calcium as a clean gypsum, which can be
does not react with ­CO2 to form ­CaCO3 (i.e., high ­CO2 con- sold, and reform the C­ H3COOH. Adding the correct amount
sumption). The CaO and C ­ aCO3 in the EAF dust will react of ­H2SO4 avoids any excess of sulfate ions. The remaining
with ­CH3COOH to form calcium acetate. The zinc acetate solution is treated with a strong acetic cation exchanger to
formed by the reaction between ZnO and ­CH3COOH will remove the ­Mg2+ and other cations, and a weakly basic anion
further react with the CaO as follows: CaO + Zn(OAc)2 exchanger in ­OH− form to remove the chloride and sulfate
+ H2O → Ca(OAc)2 + Zn(OH)2. Leaching involves add- anions. The cation exchanger can be regenerated by H ­ 2SO4,
ing EAF dust to a 3-M ­CH3COOH solution close to the the anion exchanger by NaOH. The C ­ H3COOH after the ion-
boiling point. Lead and calcium can be removed from the exchange step is too dilute to recycle to the leach step, and so
leachate by cementation with zinc powder. Calcium can be must be concentrated. The process minimizes the quantity of
removed by the addition of H ­ 2SO4, precipitating gypsum liquid effluents that require treatment before discharge. All
and regenerating the ­CH3COOH. The Zn-rich residue is the products are solid and either commercially valuable or
then leached with AAC, after which the zinc is precipitated recyclable in a steel-plant furnace. The Hatch Acetic Acid
as basic ­ZnCO2 by steam stripping. The final residue is Leaching Process is attractive if no Z­ nFe2O4 has to be recov-
resin-in-pulp treated with a very acidic cation exchanger ered. That it has not been developed further is probably due
in ­H+ form to dissolve the lead. A preliminary economic to the price of ­CH3COOH.
analysis was conducted. Siebenhofer et al. investigated leaching EAF dust with
The Hatch Acetic Acid Leach Process is a simplified ­CH3COOH in concentrations of 25% to 100% [144]. For
form of the UBC-Chaparral Process, developed to recover 80% ­CH3COOH, 90–93% of zinc and 5–7% of iron were
an Fe-rich residue for recycling to the steel plant rather extracted. For 100% glacial acetic acid, the zinc (35%) and
than landfilling [142, 143]. Figure 17 shows a flow sheet. iron (0.6%) extractions were much lower with water present.
First water removes the soluble chloride salts. Next, a 3-M This leaching process can be considered as a pure “solvo-
­CH3COOH leach at room temperature separates the easily metallurgical” process. Lead was recovered as P ­ bSO4 by
removable elements. The pulp density is 150 g/L. The leach adding ­H2SO4, while zinc required electrowinning. The solu-
residue is separated by filtration, washed, pelletized, and bility of the zinc from EAF dust in aqueous C ­ H3COOH was
­ H3COOH leaching
recycled to the EAF to recover the iron. C nearly twice that of analytical-grade zinc acetate [145]. The
removes zinc and lead from EAF dust to bleed them from solubility of zinc acetate is also highly temperature depend-
ent. The ­CH3COOH leaching of EAF dust is negatively

13
Journal of Sustainable Metallurgy (2020) 6:505–540 525

affected by an acid excess, while zinc can be electrowon solution through the contact between two immiscible phases.
from a zinc acetate solution [146]. This involves one or more stages, depending on the technical
procedure. Iron can be stripped from the organic phase by
Versatic Acid Leaching bringing it into contact with ­H2SO4 or another mineral acid
in one or more stages. In this way, the Versatic acid can be
A solvometallurgical process has been developed to recover regenerated and is ready to be loaded with zinc when reacted
zinc from chloride-containing solid residues, e.g., EAF dust with solid ZnO. Instead of Versatic acid, extractants such as
and the crude ZnO of the Waelz process [147–149]. It is D2EHPA can be used. With this approach, it is also possible
based on reacting fine-grained ZnO with acidic extractants, to separate zinc from copper.
particularly carboxylic acids, like naphthenic and Versatic (a
mixture of branched carboxylic acids with 10 carbon atoms). Ammonium Chloride Leaching
A flow sheet is shown in Fig. 18.
The carboxylic acids are used as a 30% solution in an ali- The advantage of ammonium chloride ­(NH4Cl) leaching is
phatic diluent. The co-dissolved chlorides can be scrubbed that the solution pH remains almost neutral (pH 6–7) [150],
from the organic phase with water. After this, the organic contains few dissolved impurities, and is totally iron-free.
phase is chloride-free and contains only the dissolved zinc The INDUTEC/EZINEX process is the only hydromet-
carboxylate salt. Zinc can be stripped from the loaded allurgical treatment that operates on an industrial scale
organic phase by ­H2SO4, resulting in a ­ZnSO4 solution, from [151–154]. In the 1990s, the Italian company Engitec devel-
which the zinc metal can be electrolyzed. Alternatively, the oped the EZINEX (“Engitec zinc extraction”) process and
­ZnSO4 can be crystallized (­ ZnSO4·7H2O) by stripping the a pilot plant to treat Zn-bearing EAF dust. In the following
organic phase with an excess of H ­ 2SO4. After stripping the year, a plant producing 2000 tons/year of cathode zinc was
zinc with ­H2SO4, the carboxylic acid is regenerated to leach introduced. A thermal pilot plant for converting Zn-bearing
a new batch. After leaching, the solid residue is decontami- materials to crude ZnO (C.Z.O.) was also built. This thermal
nated with hot water and ­Na2CO3 solution. The residue from fuming process, called INDUTEC, is based on an induction
the zinc ash was mainly metallic zinc particles, while the furnace. The first industrial scale EZINEX plant produced
residue from the flue dust was Pb-rich. zinc directly from EAF dust. Several tests using a C.Z.O.
To separate the zinc from the iron, the Versatic acid leach- feed were run in this plant, and the results were promising.
ing step can be combined with solvent extraction. ZnO is C.Z.O. simplified the problem of the EZINEX process: the
leached with a 30% solution of Versatic acid in an aliphatic recovery of zinc from Z ­ nFe2O4. EZINEX leaching involves a
diluent. After subsequent contact between the zinc-contain- hot concentrated ­NH4Cl + NaCl solution. The ZnO is almost
ing organic phase and an iron-containing Z ­ nSO4 solution, 100% leached, but the Z ­ nFe2O4 is unleached. When there are
an exchange between the zinc and iron takes place. The iron solubility problems, the leaching is at 70 to 80 °C, making
is transferred to the organic phase, where it is present as an it a very quick operation. The leaching residue with all the
Fe(III) versatate complex. In this exchange, an equivalent iron and ­ZnFe2O4 is then recycled to the thermal system
amount of zinc passes from the organic phase to the ­ZnSO4 that generated the C.Z.O. The lead, cadmium, and copper
solution. This completely removes the iron from the Z ­ nSO4 are removed by cementation with zinc powder. The chlo-
ride solution is electrowon with titanium cathode blanks and
graphite anodes at 65 °C to avoid solubility problems. The
electro-active complex should be [Zn(NH3)2]Cl2 (5 g/L).
Chlorine gas reacts with N ­ H3 at the anode to form N
­ 2 and
HCl without any hydrogen gas, which means a high current
efficiency. However, a major drawback of zinc electrowin-
ning from chloride solutions is the evolution of chlorine gas
at the anode, instead of oxygen. This problem can be over-
come by a cationic perm-selective membrane using ­H2SO4
in the anodic compartment to evolve oxygen at the anode.
However, this is not devoid of technical issues. Calcium and
magnesium are removed from the spent electrolyte by adding
­Na2CO3 or N ­ aHCO3 to precipitate C ­ aCO3 and M­ gCO3. The
presence of ­Ca2+ ions keeps the number of fluoride ions very
low due to ­CaF2 precipitation. HCl and NaCl are removed
Fig. 19  Conceptual flow sheet of the combined INDUTEC/EZINEX from the filtrate of the carbonation step by evaporation and
Process. Adapted from [154]

13
526 Journal of Sustainable Metallurgy (2020) 6:505–540

crystallization. Figure 19 shows a flow sheet of the com-

bined INDUTEC/EZINEX process.
Pedrosa et al. compared the leaching of EAF dust with
­H2SO4, HCl, and ­NH4Cl [155]. ­NH4Cl was more selective,
but less effective for zinc recovery, whereas the acids were
more effective, but less selective. N ­ H4Cl is very good for
iron rejection. Rao et al. reported leaching in an N
­ H3/NH4Cl
solution containing nitrilotriacetic acid (NTA) as a complex-
ing agent for leaching of low-grade ZnO [156]. The complex
formation between NTA and zinc ions enhanced the zinc
dissolution.

Ammonia–Ammonium Carbonate (AAC) Leaching

Leaching with ammonium–ammonium carbonate (AAC)

solutions has advantages [157]. The lixiviant can be pre-
pared by reacting ­NH3 and ­CO2, which are among the cheap-
est chemicals. Furthermore, they can be recycled in a pro-
cess with minimal environmental impact. ­NH3–(NH4)2CO3
can dissolve ZnO, but not Z ­ nFe2O4. The processes are as
follows: (1) leaching with ­NH3–(NH4)2CO3; (2) purifica-
tion by cementation with zinc powder; (3) air oxidation to Fig. 20  Flow sheet of the Cebedeau Process for EAF dust. Adapted
precipitate iron as Fe(OH)3; (4) process to recover N ­ H3; and from [165]
(5) precipitation of zinc as basic Z­ nCO2 by steam heating.
During the steam heating, ­(NH4)2CO3 is decomposed into
­NH3 and ­CO2; (6) recovery of ­NH3 and ­CO2, and recycling
of the leachant to the depleted solution; and (7) calcination
of the basic ­ZnCO2 to ZnO.
US patents 4,071,357 [158] and 5,538,532 [159] disclose
the AAC leaching process for EAF dust, Waelz oxide, and
C.Z.O [160]. Leaching must be below 60 °C or under pres-
sure. While heating is preferred, excessive heating results
in the undesirable evolution of N ­ H3 and C ­ O2, limiting the
capacity to dissolve zinc and risking the premature precipi-
tation of zinc. A stoichiometric excess of ­NH3 is required
to keep the zinc in solution as the ammine complex. In
general, the excess ­NH3 is such that the ratio ­NH3 to ­CO2
is 3:1. Steam stripping can remove the N ­ H3 in the steam
vapor. The N ­ H3 and C­ O2 stripped during the precipitation
of basic Z
­ nCO2 can be recovered in a condenser-absorber
to regenerate the lixiviant, so only steam is required as a
process input. When cool, the residual solution can be recy-
cled to the condenser-absorber to reconstitute the lixiviant Fig. 21  Flow sheet of the Cardiff Process for EAF dust. Adapted from
or discarded to get rid of the chloride salts. The calcination [165]
requires a suitable calcining vessel to decompose the basic
­ZnCO2 at 250–600 °C. Aeration after leaching can oxidize
the iron present as Fe(II) and precipitate Fe(III) hydroxides. increased tendency to form soluble carbonates. The addi-
The leaching capacity is affected by the ­NH3 and car- tion of ­NH3 should be enough for the sum of ­NH3 and
bonate in solution [158]. These substances are regulated by ammonium to be 3–7 mol/L. The addition of C ­ O2 should be
adding ­NH3 and C ­ O2, respectively. More free N
­ H3 increases enough for the sum of the carbonate and hydrogen carbonate
the total leaching capacity with respect to zinc, by a ten- ions to be 1–3 mol/L.
dency to form metal ammine complexes. On the other hand, After the AAC leaching of ZnO, iron can be removed
an increase in C­ O2 acts in the opposite direction, with an by oxidation [161]. Varga and Torok describe the AAC

13
Journal of Sustainable Metallurgy (2020) 6:505–540 527

leaching of EAF dust [162], where ­ZnCO2 is precipitated difference was the Cardiff Process had reduction roasting
by bubbling of C­ O2 gas, followed by steam distillation. Ruiz to break down the Z ­ nFe2O4, present in the leach residue.
et al. reported that the ammonium carbonate concentration The Cardiff process was able to recover 85–90% of the
(60–200 g/L) had hardly any influence on the leaching of zinc.
zinc [163]. The average zinc recovery was 45%. The solu- Mordogan et al. investigated leaching in solutions with a
tion needs 80–90 °C to drive out the ­NH3 and ­CO2, with the low concentration of NaOH (3.75 M), but the zinc yield was
gases used to reform the lixiviant. Wylock et al. developed only about 21% [166]. Dutra et al. achieved 76% at a NaOH
a model to predict the time evolution of pH during the injec- concentration of 6 M and 90 °C [167]. Orhan used even
tion of C­ O2 in aqueous solutions of N ­ H3 and ammonium more drastic conditions (10-M NaOH, 95 °C) and achieved
carbonate during the leaching of Waelz oxides [164]. 95% recovery [168]. Palimaka et al. investigated zinc extrac-
tion from EAF dust and found 88% for 8-M NaOH at 80 °C
and a liquid-to-solid ratio of 40 [169]. However, these yields
Alkaline Leaching are hard to compare because the different types of EAF dust.
It is important to note that ­ZnFe2O4 is, once more, not dis-
The motivation for the leaching of EAF dust with NaOH solved under these conditions.
solutions is the high rejection rate for iron and the compati- Although ­Z nFe 2O 4 cannot be dissolved in a NaOH
bility with the alkaline electrowinning of zinc. The approach solution, it can be decomposed by roasting with NaOH at
is based on the amphoteric character of ZnO, cadmium 350–450 °C [170]. Although the authors called it “caustic
oxide, and Pb(II) oxide, which dissolve in an alkaline solu- roasting,” “caustic fusion,” or “alkali fusion,” there are more
tion, unlike Fe(III) oxide. This is similar to the dissolution appropriate terms because the NaOH is above its melting
of aluminum oxide from bauxite in the Bayer process, where point of 318 °C. This treatment transfers the ­ZnFe2O4 in
Fe(III) oxide is not dissolved. However, the conditions used soluble sodium zincate ­(Na2ZnO2) and insoluble hematite
for alkaline leaching of EAF dust are milder than those of ­(Fe2O3). After the caustic roasting process, the EAF dust can
the Bayer process. The concentration of the NaOH solution be leached with a dilute NaOH solution, with zinc recover-
is 5 M or higher, which means high reagent consumption. ies in excess of 95%. The zinc can be reclaimed as zinc
Moreover, it is difficult to remove the sodium after leaching, metal with alkaline electrolysis. The main disadvantage
which is a problem for reuse of the iron residue in the BF. of this process is the large quantities of NaOH: depending
Also, alkaline leaching (also called caustic leaching) is much on the zinc content of the EAF dust, 100–500 kg of NaOH
slower than with acids, ­ZnFe2O4 cannot be dissolved, and per ton of EAF dust is required. It was reported that zinc
NaOH is more expensive than ­H2SO4. recovery from synthetic ­ZnFe2O4 by alkali fusion could be
In the Cebedeau Process, EAF dust is leached in hot increased by hydrolyzing with water or dilute NaOH prior
(95 °C) concentrated NaOH (6–12 M) for 1–2 h to dissolve to the fusion step [171, 172], although the mechanism for
the zinc, lead, and cadmium [165]. The flow sheet is shown this pre-treatment is not clear. Lenz and Martins applied this
in Fig. 20. It was developed commercially in France in 1986. method to EAF dust and recovered the dissolved lead as PbS
However, the plant closed due to problems with filtration. by adding ­Na2S, with the zinc recovered as ZnS by adding
The recovery of zinc is dependent on the amount of zinc that ­Na2S to the solution [173].
is present in Z­ nFe2O4, since this phase is not solubilized. ZnFe2O4 has been decomposed by roasting with lime
For the tested EAF dust, 65–85% of the zinc and 70–85% of (CaO). Xie et al. heated ­ZnFe2O4 with lime at 1000 °C
the lead were recovered. Centrifuging separated the leachate for 4 h (“calcified roasting”) [174]. This treatment trans-
from the solid residue, which is precipitated in a thickener forms the Z ­ nFe2O4 into ZnO and C ­ a2Fe2O5 in the reaction:
with starch (1 kg/ton) as a flocculant. After washing with ­ZnFe2O4 + 2 CaO → ZnO + Ca2Fe2O5. After roasting the
water, the residue was ready for disposal. The filtrate was solid was leached with ­NH3 and ­NH4Cl to dissolve the ZnO.
clarified by adding a calcium hydroxide solution. Lead and Zinc recoveries were close to 90%. Yakornov et al. roasted
cadmium were removed by cementation with zinc powder. EAF dust with lime at 1400 °C to decompose the ­ZnFe2O4.
The Pb-free purified solution was electrolyzed to produce The ZnO formed could be dissolved in 4-M NaOH [175].
high-quality zinc metal. Chairaksa-Fujimoto et al. used ZnO dissolution in 2-M
In the early 1980s, there was a pilot facility for treat- NaOH for a liquid-to-solid ratio of 300 [176].
ing EAF dust at Cardiff University (Wales, UK) (Fig. 21) Zhang et al. ball-milled Z ­ nFe2O4 with metallic iron
[165]. The Cardiff Process is similar to the Cebedeau (2:1 molar ratio Fe:ZnFe2O4), prior to leaching with 6 M
process, but used centrifugal filtration for solid–liquid NaOH at 90 °C [177]. The metallic iron reduced Fe(III) in
separation and a magnetic separator. The solids settling the ­ZnFe2O4 lattice to Fe(II), making it more susceptible
was very slow, the centrifugal separation disappointing, to leaching. Some 70% of zinc could be extracted from the
and the flocculants and filters were unsuccessful. Another mechanochemically reduced ­ZnFe2O4, compared to less than

13
528 Journal of Sustainable Metallurgy (2020) 6:505–540

2% from untreated Z ­ nFe2O4. However, the process would be glycol, malonic acid, lactic acid, citric acid) or mixtures
difficult to upscale. of choline chloride with a hydrated metal salt. DESs have
Microwave-assisted alkali leaching of EAF dust resulted much lower melting points than their individual compo-
in the rapid dissolution of ZnO [178]. Leaching took min- nents. Popular DESs are obtained by mixing chloride and
utes, whereas several hours were required for conventional urea in a 1:2 molar ratio, or choline chloride and ethylene
leaching to achieve the same recovery. With microwave glycol in a 1:2 molar ratio. These solvents are liquid at room
heating, the zinc recoveries were 10–15% higher than with temperature. DESs are relatively cheap, but more expensive
conventional heating, which indicates that some ­ZnFe2O4 than conventional lixiviants. They often have a significant
dissolved. The optimum NaOH concentration was 8 M. water content, but their properties are different from those
of aqueous solutions. It is claimed that DESs can be eas-
Leaching with Deep‑Eutectic Solvents ily recycled, but their long-term stability is questionable.
Moreover, DESs can be very corrosive due to their high
Deep-eutectic solvents (DESs) are an alternative to vola- chloride content. Another disadvantage is their high viscos-
tile organic solvents [179–181]. Most DESs are mixtures of ity, especially with a low water content, making solid/liquid
choline chloride and a hydrogen-bond donor (urea, ethylene separations difficult.

Fig. 22  Yield of zinc leaching from EAF dust in 27 different leaching media, in order of descending metal dissolution. Adapted from [186]

Fig. 23  Yield of iron leaching from EAF dust in 27 different leaching media, in order of descending metal dissolution. Adapted from [186]

13
Journal of Sustainable Metallurgy (2020) 6:505–540 529

Abbott et al. developed a DES process to extract the lead was leached, more than 80% of the lead, and with less than
and zinc from EAF dust. The DES choline chloride:urea 10% co-dissolution of iron. A study of leaching EAF dust in
(1:2) selectively dissolves ZnO and lead oxide, but has neg- organic acids (formic, acetic, and citric acid) confirmed that
ligible solubility for iron oxides [182]. DESs based on urea citric acid had the highest zinc yield (> 75%), with less than
can dissolve large amounts of ZnO and have high selectivity 20% iron co-dissolution [188]. The co-dissolution of lead
of zinc over iron, in contrast to DESs based on carboxylic by citric acid is seen as an advantage. Acetic acid (1.75 M)
acids. After the dissolution, lead and zinc can be recovered was the second best. All the organic acids dissolved ZnO,
by electrodeposition. However, the high viscosity of the DES but not ­ZnFe2O4. The citric acid needs to be 0.8–0.9 M for
(about 800 cP at 25 °C) resulted in impeded pumping and a good zinc recovery, which means dilute citric acid waste
more difficult separation of the DES from the undissolved streams (e.g., from fermentation) cannot be used. High con-
solids by filtration. A leaching time of 48 h at 60 °C was centrations of citric acid (3.0 M) removed 99% of the lead
used. The viscosity could be reduced by adding ethylene from EAF dust [189], while removing 54% of the zinc and
glycol to the choline chloride:urea DES [183]. A DES with 6% of the iron. In a follow-up study, Halli et al. recovered
the composition choline chloride:ethylene glycol:urea in lead and zinc from a citric acid leach solution [190]. The
the molar ratios 1:1.5:0.5 had a viscosity of 56 cP at room lead precipitated as ­PbSO4 by adding ­H2SO4 to a pH of 2.
temperature. A pulp density of up to 7 wt% was used, with a The zinc was extracted with D2EHPA and Cyanex 572. The
digestion time of at least 24 h. The fine-particulate EAF dust best results were for D2EHPA.
powder decreased the viscosity of the DES. Hardly any iron Wang et al. leached EAF dust with (­ NH4)Fe(SO4)2·12H2O
was co-dissolved (< 1 ppm). The DES can dissolve part of [191]. The reagent dissolved upon heating in its own crystal
the ­ZnFe2O4, but only very slowly, i.e., the extraction of zinc water and ionized to F ­ e3+, ­NH4+, and S­ O42−. ­Fe3+ hydro-
+
was incomplete after 72 h. Lead was recovered by cemen- lyses and released H ­ , and a solution with a high proton
tation with zinc dust, and zinc chloride could be precipi- concentration was formed. These protons reacted with EAF
tated by adding aqueous N ­ H3. The electrowinning of zinc dust and brought Z ­ n2+ in solution. In the meantime, N ­ H 4+,
2− 3+
showed that the process was very slow and that the current ­SO4 , and F ­ e ions in solution formed a jarosite precipi-
efficiency was poor. A pilot plant was built to process 5 kg tate, ­(NH4)Fe(SO4)2(OH)6. The reaction was for 6 to 12 h in
EAF dust batches. It consisted of a 125 L extraction tank, an autoclave at 180–220 °C. After leaching and cooling to
two 25 L cementation tanks, and a 12 L electrolysis cell. room temperature, the solid and liquid were separated. All
Difficulties were experienced with solid/liquid separation. the zinc was in solution (93% recovery). A disadvantage is
The cementation of lead was efficient, with levels below the high reagent consumption; the mass ratio for the reagent
12 ppm. ­NH3 could be boiled off the precipitate, leaving pure and EAF dust was 1:1 to 7:1.
zinc chloride. Bakkar repeated the work of Abbott et al. for
choline chloride:urea (1:2) [184] and the 1-M chloride:1.5- Bioleaching
M urea:0.5-M ethylene glycol systems [185], but provided
no additional information. The bioleaching of EAF dust is rare. Bayat et al. bioleached
zinc and iron with Acidithiobacillus ferrooxidans [192].
Miscellaneous Lixiviants Under optimum conditions, 35% of the zinc and 37% of
the iron were dissolved, i.e., poor selectivity. The pulp den-
Halli et al. leached EAF dust with 16 different lixiviants in sity was 1% and the process is slow. Carranza et al. treated
27 conditions, focusing on five elements: zinc, iron, lead, EAF dust and acid mine drainage (AMD) [193]. First, the
chromium, and manganese [186]. The objective was to EAF dust is leached with AMD water. Next, Fe(II) ions are
selectively leach zinc and lead to leave a recyclable Fe-rich bioxidized, and iron and aluminum are precipitated. Then,
material for the steel plant. The four lixiviants with the high- copper, nickel, cobalt, and cadmium are cemented by zinc
est zinc extraction (> 75%) and the lowest iron extraction metal, and finally the zinc is precipitated as zinc hydroxide.
(< 10%) were 10% aqua regia, 1.2-M HCl, 0.94-M citric Lime is used to neutralize the acidic water, with gypsum
acid, and 1.5-M H ­ NO3. There was also partial dissolution of precipitating.
lead, chromium, and manganese. The best for lead removal
was 1.75-M acetic acid. The results for zinc and iron are in Thermal Pre‑treatment
Figs. 22 and 23, respectively. In a follow-up study, leaching
with citric acid, which can dissolve ZnO but not ­ZnFe2O4, Stopic and Friedrich describe the thermal treatment of
was investigated in more detail [187]. Halli et al. alkali ­ZnFe2O4 to decompose it into ZnO and magnetite in nitro-
roasted with NaOH at 450 °C as a pre-treatment for Z ­ nFe2O4 gen at 1150 °C [194]. This avoids the energy intensive ZnO
decomposition, followed by leaching with 0.8-M citric acid reduction and Zn evaporation. The residue was leached
at 40 °C with oxygen purging for 2 h [187]. All of the zinc with ­H2SO4 at pH 4.3 at 60 °C to dissolve the ZnO, leaving

13
530 Journal of Sustainable Metallurgy (2020) 6:505–540

Fig. 24  Flow sheet for process-

ing of sinter-plant dust. Adapted
from [204]

­Fe3O4. ­ZnFe2O4 can be decomposed to ZnO and wüstite industry [202]. Peng et al. recovered 90% of the potassium in
(FeO) by a reductive thermal treatment in a CO/CO2 gas sinter-plant dust by leaching with water in a liquid-to-solid
mixture [195]. When iron is present as wüstite, it dissolves ratio of 2 for 5 min [203]. With a counter-current process,
with zinc during mild acid leaching. To avoid the unwanted close to 100% of the KCl could be leached, but 40% of the
formation of wüstite, it can be reoxidized to magnetite by other components dissolved. The washed residues could be
magnetization roasting in a ­CO2 atmosphere, after which the reused. The other compounds in solution were NaCl and
zinc can be extracted from ZnO at a low acid concentration ­CaCl2. Heavy metals (Pb, Cd, Zn, Cu) were precipitated by
[196]. ­ZnFe2O4 is decomposed to metallic iron and ZnO by adding ­Na2S. KCl could be obtained by evaporation, fol-
hydrogen gas at 600 °C [197]. The main advantages of this lowed by fractional crystallization. ­K2SO4 was selected as
are high reaction rates, low energy requirements, and no a precipitating agent for ­Ca2+ ions, and 95% pure KCl was
­CO2 emissions. Antrekowitsch and Antrekowitsch decom- obtained.
posed ­ZnFe2O4 in a N ­ 2/H2 mixture [198]. The reduction took A potassium chloride plant with a capacity of 10,000
30 min at 350 °C. A 100% zinc yield was possible by leach- tons/year was built in Tangshan (China) for potassium fer-
ing with ­H2SO4 or NaOH, when the ­ZnFe2O4 was decom- tilizer [204]. The flow sheet is shown in Fig. 24. The sinter-
posed in a N ­ 2/H2 mix with > 50% H ­ 2. Li et al. decomposed plant dust is leached with water and filtered, with the resi-
­ZnFe2O4 by roasting with ammonium sulfate [199]. due recycled to the plant. Heavy metals are removed from
In the section on alkali leaching of EAF dust (vide supra), the filtrate by sulfide precipitation, which is evaporated to
the decomposition of Z ­ nFe2O4 by alkali roasting or alkali obtain high-purity products. In a modified flow sheet, ­Ca2+
fusion with NaOH was discussed. Another approach is to is removed as spherical C ­ aCO3 particles by adding N ­ a2CO3
roast EAF dust with N ­ a2CO3 to form ZnO and N ­ aFeO2 before the ­CaSO 4 starts to crystallize [205]. Spherical
[200]. After roasting, the residue can be leached with ­CaCO3 is used in paint, ink, and other industries. The sulfate
­H2SO4 or NaOH. ­H2SO4 brings more iron into solution. The will crystallize as ­K2SO4.
advantage of N ­ a2CO3 roasting over NaOH roasting is that a Sinter-plant dust can also be a source of rubidium (Rb); it
smaller amount of ­Na2CO3 is required, compared to NaOH, contains about 0.30 wt% Rb in the form of RbCl [206], mak-
although ­Na2CO3 roasting needs higher temperatures. Typi- ing it richer than any other rubidium resource. Some 95%
cal ­Na2CO3 roasting of EAF dust requires 80% N ­ a2CO3 at of the rubidium could be leached at a liquid-to-solid ratio
950 °C. of 5, at 25 °C for 10 min. Also, 93% of the potassium and
EAF dust can also be reacted with CaO at high tempera- 95% of the sodium in the dust dissolved. In fact, 50% of the
tures. Miki et al. treated EAF dust with CaO (Ca/Fe molar dust dissolved. ­Ca2+ and ­Mg2+ impurities could be removed
ratio = 1.3) at 1100 °C for 5 h [201]. The ­ZnFe2O4 is decom- by adding N ­ a 2CO 3, precipitating C­ aCO 3 and ­M gCO 3.
posed into ZnO and ­Ca2Fe2O5. Leaching with N ­ H4Cl solu- The concentrations of metal ions in the leachate were
tion dissolves the ZnO, but not the ­Ca2Fe2O5. The optimum [Na] = 7.76 g/L, [K] = 33.85 g/L, [Rb] = 0.74 g/L. Potassium/
leaching conditions were 70 °C, 2-M N ­ H4Cl, liquid-to-solid rubidium were separated by solvent extraction with 4-tert-
ratio = 300, 2 h. butyl-2(α-methylbenzyl)phenol (t-BAMBP) in the N ­ a+ form.
The extraction used counter-current mode, with two mixer-
Sinter‑Plant Dust settler batteries, each consisting of 4 extraction, 6 washing,
and 3 stripping stages. The composition of the eluate was
About 0.2–3.6 kg of sinter-plant dust are produced per ton [Rb] = 11.36 g/L, [K] = 0.027 g/L, [Na] = 0.013 g/L. The
of sinter. The sinter dust has a high concentration of chloride recovery rate of rubidium was 58% and the purity of RbCl
salts, particularly KCl. The dust contains up to 28.7 wt% of after crystallization was 99.5%.
­K2O, with the potassium mainly in the fine particles. Sinter-
plant dust could be a source of potassium for the fertilizer

13
Journal of Sustainable Metallurgy (2020) 6:505–540 531

Oily Mill Sludge De-oiling of mill scale and oily mill sludge was studied,
but no technology proved to be economic and eco-friendly,
In hot roll mill (HRM), due to oxidation, mill scale forms and there are presently no de-oiling plants in operation
on the surface of the steel in reheat furnaces, and on roll- [207]. Biological treatment for oil removal was investigated,
ing trains and stands [207]. It is removed by a water jet. but was reported to be difficult and impractical, due to the
Oil, used to lubricate rolling equipment, is also removed long treatment time and the low oil-removal efficiency [210].
[208]. The discarded sludge is treated in a series of horizon- Microwave heating was used to remove the water and to
tal settling tanks, and the clarified water is reused. Coarse reduce the oil content in oily mill sludge [209]. Microwave
sediments from the primary tanks (primary mill scale) with heating speeds up the drying of sludge, saving both energy
particles > 2 mm and an oil content of < 1% can be recycled, and time. After the microwave treatment, the material has
e.g., as an additive to the iron ore sinter mixture. Fine scale better rheological properties. The microwaved samples are
from the secondary tanks (secondary mill scale) has parti- less oxidized than conventionally heat treated, which is
cles > 2 mm, and contains up to 20 wt% of oil and 10 wt% of an advantage for recycling sludge because less carbon is
water. Mill scale consists mainly of iron oxides, with small required to reduce it to metallic iron. However, the costs of
amounts of sulfur, phosphorus, and alkali metals. Depend- microwave equipment versus gas heating or residual heat
ing on the steel grade, it also contains chromium, nickel, can be prohibitive.
vanadium, etc. At the wastewater treatment plant, oil, water, To the best of our knowledge, no studies were published
and oily mill sludge are generated. The oily mill sludge is a on the recovery of metals from oily HRM sludge by hydro-
mixture of mill scale, oil, water, and residual chemicals. It metallurgical methods. However, some studies looked at the
cannot be further separated and so is sent to landfills. The recovery of oily mill sludge generated by CRM process. Liu
oily mill sludge is a sticky solid that is difficult to handle et al. investigated the combined recovery of iron and organic
[209]. Also, during the cold roll mill (CRM), an oily mill materials from oily CRM sludge, and how to prepare mica-
sludge is generated. ceous iron oxide (MIO) pigment from the material [211].
The recycling of secondary scale is difficult due to the This pigment is used in construction materials, paints, and
negative effects of oil on the environment and equipment. coatings. The oily CRM sludge was leached in ­H2SO4, until
For instance, if the oiled scale is an additive to the iron ore complete dissolution (6-M H ­ 2SO4, 85 °C, 4 h, solid-to-liquid
sinter mixture, it is a problem for gas cleaning and can dam- ratio = 1:5). After leaching, the mixture was centrifuged into
age these installations with fires. One option to improve an organic part (used as fuel) and a solution. The solution
combustion of the scale’s oil in the sintering process is to consisted of ­FeSO4 and ­Fe2(SO4)3. The iron was precipitated
prepare a mixture with peat [208]. The oily mill sludge can as Fe(OH)2 and Fe(OH)3 by an ­NH3 solution. Fe(OH)2 was
be recycled with direct reduction iron (DRI), where the oil oxidized by air to Fe(OH)3. The MIO pigment was prepared
participates directly in the reactions for the reduction and by hydrothermal synthesis in alkaline media, starting from
conversion of hematite (­ Fe2O3) and magnetite (­ Fe3O4) to the hydroxide precursor. The pigment was metallic gray with
wüstite (FeO) [210]. uniform flake shape. A flow sheet is shown in Fig. 25. Later,
the authors reported an alternative for the preparation of the
MIO pigment, using H ­ 2O2 to oxidize F­ eSO4 to F
­ e2(SO4)3
[212]. Liu et al. removed the oil from oily CRM sludge by
vacuum distillation [213]. The oil can be used as fuel or
chemical feedstock. The distillation gases can be collected
and also reused as fuel. When the distillation residue is oxi-
dized by roasting, high-purity F ­ e2O3 is obtained, whereas
reduction with ­H2 leads to the formation of iron powder.

Pickling Sludge

Pickling is used in steel plants to remove oxide scales from

steel. These hydrometallurgical processes utilize mineral
acids for leaching. Carbon-steel pickling in hot-dip galvaniz-
ing works with HCl or H ­ 2SO4, whereas stainless-steel pick-
ling in rolling mills is based on mixtures of HF and ­HNO3
[214]. ­HNO3 dissolves and oxidizes the Fe(II) oxide scale,
Fig. 25  Flow sheet for the preparation of micaceous iron oxide (MIO) while HF is used for its reactivity and stabilizing capacity
pigment from oily CRM sludge. Adapted from [211] of metals in solution.

13
532 Journal of Sustainable Metallurgy (2020) 6:505–540

Conclusions and Outlook

The studies on the recovery of metals by hydrometallurgical

methods from steel by-products are very unequally divided
among the different by-products. Studies of metal recovery
from slags are outnumbered by those on dusts and sludges.
There are several reasons for this. Firstly, slags are much
easier to valorize. Secondly, the heavy-metal content of slags
does not hamper their valorization. There is an exception
with EAF slags that are intended for clinker production: in
this case the chromium content can be a major problem,
because Cr(III) can oxidize to Cr(VI) that is soluble in water
and toxic. Thirdly, the treatment of slags by hydrometal-
Fig. 26  Comparison of the number of studies devoted to the recovery lurgical methods not only generates a residue that is of less
of metals from different types of dusts and sludges commercial value than the original slag, it also yields aque-
ous waste streams that need further treatment. In contrast,
dusts and sludges are much more difficult to valorize than
Most methods for the treatment of spent pickling liquor
slags and internal recycling in steelmaking is often inhibited
involve acid recovery [215, 216]. The methods based on acid
by their high zinc content. The number of studies follows
retardation or diffusion dialysis only recover the free acid,
this order: EAF dust >  BF sludge > BOF sludge > sinter dust
producing a residual effluent with a high metal content that
(Fig. 26).
is treated by solvent extraction or precipitation. The precipi-
In the past 5 years, there has been a sharp increase in
tation involves adding lime (CaO) or alkali (NaOH or KOH).
research on the recovery of vanadium from vanadium slags,
The precipitation generates picking sludge, which is sent to
especially in China. This is an important trend, because of
landfills [217]. The metals in the sludge of stainless-steel
the increasing demand for vanadium for use in redox flow
pickling are iron, chromium, and nickel [218]. If lime is
batteries. In contrast, the economics of manganese recovery
used for neutralization, the sludge will also contain ­CaF2. A
from ferromanganese slags or chromium recovery from Cr-
chemical analysis of a pickling sludge yielded the following:
rich stainless-steel slags are much less favorable.
21.68 wt% Fe, 2.42 wt% Cr, and 2.78 wt% Ni [218].
Although the main objectives of the treatment of BF
There are few studies on the recovery of metals from
sludges, BOF sludges, and EAF dust are similar, i.e., the
pickling sludges, because if the objective is to recover the
removal of zinc and generating an Fe-rich residue that can be
metals, solvent extraction is used. For a good overview of
returned to the steel plant, these three classes of by-products
the treatment of spent pickling liquor by solvent extraction,
exhibit different mineralogical compositions and zinc con-
the reader is referred to a review by Regel-Rosocka [219].
tents. Moreover, within the same class of materials (e.g.,
One of the few studies on metal recovery from pickling
EAF dust), wide variations in composition and zinc content
sludge is by Ji et al. who recovered nickel by controlled
are possible, so that it is not simple to develop a “silver bul-
leaching with ­H2SO4, followed by solvent extraction [218].
let” process with the same set of process conditions.
Dufour et al. recovered metals from spent picking liquor
The majority of the studies described in the review relate
by sequential selective precipitation [215]. In the first stage,
to EAF dust. This interest in EAF dust is because of its
iron and chromium are precipitated as ­K3MF6 (M = Fe,
enhanced zinc content, which is by far the highest of all
Cr) by adding fluoride ions (as HF or KF) at pH 4. Also,
steel by-products. However, EAF dust is typically of inter-
molybdenum will precipitate at this pH. The effluent con-
est to the zinc industry rather than that of steel. This means
tains nickel(II) and nitrate ions, and nickel is precipitated
that the objective is to maximize zinc recovery from EAF
in a second precipitation step as Ni(OH)2 at pH 7 to 9. The
dust, using the processes of the zinc industry. Several of the
­K3MF6 compounds can be re-dissolved and iron and chro-
processes proposed for EAF dust treatment are similar to the
mium re-precipitated at pH 5. The same authors described
roast–leach–electrowinning (RLE) process that is state of the
the recovery of iron from a spent ­H2SO4 pickling liquor as
art in the zinc industry. In fact, EAF dust is similar to the
magnetite by oxidation-precipitation [220]. The crystalline
calcine that is obtained by dead-roasting ZnS concentrate,
magnetite could be used as a pigment in the paint indus-
with the difference that EAF dust is much richer in lime
try. Hermoso et al. described the selective precipitation of
(CaO). As a consequence, EAF dust will consume more acid
­K2FeF5, ­CrF3, and Ni(OH)2 [221].
during leaching than zinc calcine. Much less emphasis has
been paid to the destination of the iron in the process. As

13
Journal of Sustainable Metallurgy (2020) 6:505–540 533

a result, iron will often be precipitated as jarosite or goe- This is unnecessary for the dissolution of ZnO and leads
thite, which are of little interest to the steel industry. This is to unacceptable levels of iron co-dissolution. On the other
because these iron-containing compounds are too contami- hand, if the dissolution of the more refractory ­ZnFe2O4
nated with unwanted metals or their iron content is too low (franklinite) phase is targeted, much harsher conditions are
for economic use in the BF. required and a lot of iron will co-dissolve. Therefore, it is
Many processes for the treatment of EAF dust integrate, better to “bleed” the zinc from the system by dissolving
as a final step in the targeted flow sheet, the electrowin- the ZnO, and to return the ­ZnFe2O4 back to the BF or BOF.
ning of zinc from the leachate (to produce high-quality zinc In the BF or BOF, the Z ­ nFe2O4 is partly decomposed to
metal). They do this independently of the lixiviant ­(H2SO4, ZnO. The removal of zinc via ZnO, therefore, constitutes
HCl, or NaOH). However, this is less interesting for steel the “low-hanging fruit.” A compromise has to be found
plants that want to clean up EAF dust and do not have an between the zinc removal yield and the requirements in
electrolysis plant on site. On the other hand, zinc electrolyte terms of OPEX and CAPEX. The maximum permissible
is less convenient to transport than solid zinc compounds. value of the zinc concentration in the leaching residues of
For this reason, the treatments of EAF dust that are of inter- the dusts and sludges depends on the operational condi-
est to the zinc industry have a flow sheet that produces a tions of the BF or BOF, and in particular on the average
solid zinc compound, e.g., ZnO, Z ­ nCO2, basic Z ­ nCO2, or zinc content of the regular iron-containing feeds to the
ZnS. The latter is usually preferred. furnace. However, as a rule of thumb, the zinc content
It is very difficult to compare the leaching results and in the residue that is sent back to the BF or BOF must be
the zinc yields published for EAF dust in different studies, below 1 wt%.
because the composition of the EAF dusts varies widely. Dif- Since it is difficult to remove iron from leachates, it
ferent types of EAF dust not only have different concentra- is better to avoid bringing iron into solution in the first
tions of zinc, but also show variations in the ZnO/ZnFe2O4 place. When/if iron has to be precipitated from the solu-
ratio (zincite-to-franklinite ratio). In many processes, only tion, the preferred iron phase is hematite ­(Fe2O3), because
the ZnO is dissolved, while the refractory Z ­ nFe2O4 phase hematite is Fe-rich and has a very low level of impurities,
remains in the residue. ­ZnFe2O4 is only dissolved in con- in contrast to jarosite or goethite. Unfortunately, hematite
centrated acids, or if the EAF dust is pre-treated (e.g., by a can only be formed at elevated temperatures, i.e., above
reductive roasting step). Furthermore, dissolving Z ­ nFe2O4 100 °C, which requires an expensive autoclave. However,
in acidic solutions also brings iron into solution. there are ways to obtain hematite at lower temperatures,
Compared to EAF dust, there is much less research on for instance by seeding the iron-containing solution with
BF sludges, with most of it performed by the steel industry. a high concentration of hematite crystals. There is defini-
There has been limited interest in BF sludges from academ- tively room for research on the formation of hematite
ics, probably due to the low content of non-ferrous metals precipitates under milder conditions. Hematite is easier
such as zinc. This limits the value of BF sludge as a poten- to form from chloride than from sulfate solutions. Also,
tial secondary source of zinc. Very few studies focus on BF nitrate media can lead to hematite formation. The precipi-
sludges with a low zinc content. Some investigations have tation of jarosite or goethite is not sustainable, because it
considered BF sludges with exceptionally high zinc con- creates a solid-waste problem. It simply transfers the zinc
tents, which begs the question about how representative such industry’s solid-waste problem to the steel industry.
studies are. In some studies, it is evident that zinc is present Although this review focused on hydrometallurgical pro-
in BF sludges in the form of ZnS (sphalerite). This requires cesses, several process flow sheets contain a high-temper-
oxidative leaching, e.g., with F ­ eCl3. It is not clear how gen- ature pre-processing step. Examples include alkali roasting
eral the presence of ZnS in BF sludges actually is, because with NaOH or N ­ a2CO3 to decompose the Z ­ nFe2O4 phases
many studies did not report the sulfur content in BF sludges in EAF dust, the roasting of vanadium slags with NaCl to
or in the minor mineralogical phases. Concurrently, the high decompose the vanadium spinel phases, and the dry diges-
carbon content in BF sludges leads to operational problems tion with concentrated H ­ 2SO4 of silicate-rich slags. In all
with hydrometallurgical processes, because of foaming. these cases, the thermal pre-processing temperature should
The recovery of zinc from BOF dusts and sludges has be as low as possible, in order to curb the energy consump-
received little attention so far, and very little information tion. In any case, the reaction temperatures are much lower
has been published in the literature and as patents. than those of pyrometallurgical processes. A concern with
When treating dusts and sludges, it is recommended thermal pre-processing is that often large amounts of chemi-
to focus on the easily soluble zinc (in the form of ZnO), cals are used for the roasting step. Therefore, it is better to
because this needs relatively mild conditions and the dis- pay more attention to reducing the consumption of chemi-
solution takes just a couple of minutes. However, in gen- cals or developing reagent-free roasting processes.
eral, the selected leaching times are often much too long.

13
534 Journal of Sustainable Metallurgy (2020) 6:505–540

Acknowledgements The authors acknowledge funding from the 11. Worldsteel (2010) Steel industry by-products: project group
European Institute of Innovation and Technology (EIT), a body of the report 2007–2009. World Steel Association, Brussels
European Union, under Horizon 2020, part of the ‘KAVA Call 6,’ in 12. Ji Y, Shen S, Liu J, Xue Y (2017) Cleaner and effective process
the framework of the ’Innovation Theme’ No.3 of EIT Raw Materials for extracting vanadium from vanadium slag by using an innova-
Project Number 19205 (SAMEX). Alma Capa and Jose Luis García are tive three-phase roasting reaction. J Clean Prod 149:1068–1078.
acknowledged for their contributions during discussions and for editing https​://doi.org/10.1016/j.jclep​ro.2017.02.177
this paper. Paul McGuiness is acknowledged for his text editing work. 13. Jiang T, Dong H, Guo Y et al (2010) Study on leaching Ti from
Ti bearing blast furnace slag by sulphuric acid. Trans Inst Min
Metall Sect C 119:33–38. https​://doi.org/10.1179/03719​5509X​
Compliance with Ethical Standards 12585​44603​8807
14. Valighazvini F, Rashchi F, Nekouei RK (2013) Recovery of tita-
Conflict of interest On behalf of all authors, the corresponding author nium from blast furnace slag. Ind Eng Chem Res 52:1723–1730.
states that there is no conflict of interest. https​://doi.org/10.1021/ie301​837m
15. He S, Sun H, Tan D, Peng T (2016) Recovery of titanium com-
Open Access This article is licensed under a Creative Commons Attri- pounds from Ti-enriched product of alkali melting Ti-bearing
bution 4.0 International License, which permits use, sharing, adapta- blast furnace slag by dilute sulfuric acid leaching. Proce-
tion, distribution and reproduction in any medium or format, as long dia Environ Sci 31:977–984. https​://doi.org/10.1016/j.proen​
as you give appropriate credit to the original author(s) and the source, v.2016.03.003
provide a link to the Creative Commons licence, and indicate if changes 16. Mang G, Cheng M (2014) Research of Al and Fe leaching rate
were made. The images or other third party material in this article are in the process of slag leaching by hydrochloric acid. Appl Mech
included in the article’s Creative Commons licence, unless indicated Mater 675–677:1417–1420. https​://doi.org/10.4028/www.scien​
otherwise in a credit line to the material. If material is not included in tific​.net/AMM.675-677.1417
the article’s Creative Commons licence and your intended use is not 17. Meshram P, Sarkar S, Venugopalan T (2017) Exploring blast
permitted by statutory regulation or exceeds the permitted use, you will furnace slag as a secondary resource for extraction of rare earth
need to obtain permission directly from the copyright holder. To view a elements. Miner Metall Process 34:178–182
copy of this licence, visit http://creat​iveco​mmons​.org/licen​ses/by/4.0/. 18. Huijgen W, Witkamp G, Comans R (2005) Mineral ­CO2 seques-
tration by steel slag carbonation. Environ Sci Technol 39:9676–
9682. https​://doi.org/10.1021/es050​795f
19. Bilen M, Altiner M, Yildirim M (2018) Evaluation of steel-
making slag for C ­ O2 fixation by leaching-carbonation process.
References Part Sci Technol 36:368–377. https​://doi.org/10.1080/02726​
351.2016.12672​85
1. Stewart D, Barron A (2020) Pyrometallurgical removal of zinc 20. Hall C, Large DJ, Adderley B, West HM (2014) Calcium leaching
from basic oxygen steelmaking dust—a review of best available from waste steelmaking slag: significance of leachate chemistry
technology. Resour Conserv Recycl 157:104746. https​://doi. and effects on slag grain mineralogy. Miner Eng 65:156–162.
org/10.1016/j.resco​nrec.2020.10474​6 https​://doi.org/10.1016/j.minen​g.2014.06.002
2. Zhang H, Hong X (2011) An overview for the utilization of 21. Zhang G, Zhang T, Lu G et al (2015) Extraction of vanadium
wastes from stainless steel industries. Resour Conserv Recycl from vanadium slag by high pressure oxidative acid leaching. Int
55:745–754. https​://doi.org/10.1016/j.resco​nrec.2011.03.005 J Miner Metall Mater 22:21–26. https​://doi.org/10.1007/s1261​
3. Candian Lobato NC, Villegas EA, Mansur MB (2015) Manage- 3-015-1038-6
ment of solid wastes from steelmaking and galvanizing pro- 22. Zhang J, Zhang W, Zhang L, Gu S (2014) A critical review of
cesses: a brief review. Resour Conserv Recycl 102:49–57. https​ technology for selective recovery of vanadium from leaching
://doi.org/10.1016/j.resco​nrec.2015.05.025 solution in ­V2O5 production. Solvent Extr Ion Exch 32:221–248.
4. Fisher LV, Barron AR (2019) The recycling and reuse of steel- https​://doi.org/10.1080/07366​299.2013.87775​3
making slags - a review. Resour Conserv Recycl 146:244–255. 23. Li M, Zheng S, Liu B et al (2017) A clean and efficient method
https​://doi.org/10.1016/j.resco​nrec.2019.03.010 for recovery of vanadium from vanadium slag: nonsalt roasting
5. Lin X, Peng Z, Yan J et al (2017) Pyrometallurgical recycling of and ammonium carbonate leaching processes. Miner Process
electric arc furnace dust. J Clean Prod 149:1079–1100. https​:// Extr Metall Rev 38:228–237. https​://doi.org/10.1080/08827​
doi.org/10.1016/j.jclep​ro.2017.02.128 508.2017.12881​17
6. Yang C, Pan J, Zhu D et al (2019) Pyrometallurgical recycling 24. Zhang J, Zhang W, Xue Z (2019) An environment-friendly pro-
of stainless steel pickling sludge: a review. J Iron Steel Res Int cess featuring calcified roasting and precipitation purification to
26:547–557. https​://doi.org/10.1007/s4224​3-019-00278​-y prepare vanadium pentoxide from the converter vanadium slag.
7. Antunano N, Cambra JF, Arias PL (2019) Hydrometallurgi- Metals. https​://doi.org/10.3390/met90​10021​
cal processes for Waelz oxide valorisation - an overview. Pro- 25. Li H-Y, Wang K, Hua W-H et al (2016) Selective leaching of
cess Saf Environ Prot 129:308–320. https​://doi.org/10.1016/j. vanadium in calcification-roasted vanadium slag by ammo-
psep.2019.06.028 nium carbonate. Hydrometallurgy 160:18–25. https ​ : //doi.
8. Das B, Prakash S, Reddy PSR, Misra VN (2007) An overview org/10.1016/j.hydro​met.2015.11.014
of utilization of slag and sludge from steel industries. Resour 26. Li X, Xie B (2012) Extraction of vanadium from high calcium
Conserv Recycl 50:40–57. https ​ : //doi.org/10.1016/j.resco​ vanadium slag using direct roasting and soda leaching. Int J
nrec.2006.05.008 Miner Metall Mater 19:595–601. https​://doi.org/10.1007/s1261​
9. Du C, Gao X, Kitamura S (2019) Measures to decrease and uti- 3-012-0600-8
lize steelmaking slag. J Sustain Metall 5:141–153. https​://doi. 27. Zhang G, Luo D, Deng C et al (2018) Simultaneous extraction
org/10.1007/s4083​1-018-0202-4 of vanadium and titanium from vanadium slag using ammonium
10. Rieger J, Schenk J (2019) Residual processing in the european sulfate roasting-leaching process. J Alloys Compd 742:504–511.
steel industry: a technological overview. J Sustain Metall 5:295– https​://doi.org/10.1016/j.jallc​om.2018.01.300
309. https​://doi.org/10.1007/s4083​1-019-00220​-2

13
Journal of Sustainable Metallurgy (2020) 6:505–540 535

28. Li M, Liu B, Zheng S et al (2017) A cleaner vanadium extraction Fines Jamshedpur India 2–3 Novemb 2000 Natl Metall Lab Jam-
method featuring non-salt roasting and ammonium bicarbonate shedpur 300–306
leaching. J Clean Prod 149:206–217. https​://doi.org/10.1016/j. 46. Kazadi DM, Groot DR, Steenkamp JD, Poellmann H (2016)
jclep​ro.2017.02.093 Control of silica polymerisation during ferromanganese slag
29. Li M, Du H, Zheng S et al (2017) Extraction of vanadium from sulphuric acid digestion and water leaching. Hydrometallurgy
vanadium slag via non-salt roasting and ammonium oxalate 166:214–221. https​://doi.org/10.1016/j.hydro​met.2016.06.024
leaching. JOM 69:1970–1975. https​://doi.org/10.1007/s1183​ 47. Kazadi D, Groot D, Pöllmann H et al (2013) Utilization of Fer-
7-017-2494-4 romanganese slags for manganese extraction and as a cement
30. Wen J, Jiang T, Zhou W et al (2019) A cleaner and efficient additive. Proceedings of the Advances in Cement and Concrete
process for extraction of vanadium from high chromium vana- Technology in Africa conference, Emperor’s Palace, Johannes-
dium slag: leaching in (­ NH4)2SO4-H2SO4 synergistic system burg (South Africa), 28– 30 January 2013, 983–995
and ­NH4+ recycle. Sep Purif Technol 216:126–135. https​://doi. 48. Hocheng H, Su C, Jadhav UU (2014) Bioleaching of metals from
org/10.1016/j.seppu​r.2019.01.078 steel slag by Acidithiobacillus thiooxidans culture supernatant.
31. Zhang G-Q, Zhang T-A, Zhang Y et al (2016) Pressure leaching Chemophere 117:652–657. https:​ //doi.org/10.1016/j.chemos​ pher​
of converter vanadium slag with waste titanium dioxide. Rare e.2014.09.089
Met 35:576–580. https​://doi.org/10.1007/s1259​8-014-0225-3 49. Andersson A, Ahmed H, Rosenkranz J et al (2017) Characteriza-
32. Zhang Y, Zhang T-A, Dreisinger D et al (2017) Extraction of tion and upgrading of a low zinc-containing and fine blast fur-
vanadium from direct acid leach solution of converter vanadium nace sludge - a multi-objective analysis. ISIJ Int 57:262–271.
slag. Can Metall Q 56:281–293. https​://doi.org/10.1080/00084​ https​://doi.org/10.2355/isiji​ntern​ation​al.ISIJI​NT-2016-512
433.2017.13275​01 50. Li B, Wei Y, Wang H et al (2019) Preparation of Z ­ nSO4.7H2O
33. McIntosh S, Baglin E (1992) Recovery of manganese from steel and separation of zinc from blast furnace sludge by leaching-
plant slag by carbamate leaching. US Bur Mines Rep Investig purification-crystallization method. ISIJ Int 59:201–207. https​
9400:1–16 ://doi.org/10.2355/isiji​ntern​ation​al.ISIJI​NT-2018-401
34. Krasheninin AG, Khalezov BD, Bornovolokov AS, Ordinartsev 51. Kretzschmar R, Mansfeldt T, Mandaliev PN et al (2012) Spe-
DP (2019) Technology for extracting manganese from vanadium ciation of Zn in blast furnace sludge from former sedimenta-
converter slag after leaching vanadium. Metallurgist 63:534–542. tion ponds using synchrotron X-ray diffraction, fluorescence,
https​://doi.org/10.1007/s1101​5-019-00854​-3 and absorption spectroscopy. Environ Sci Technol 46:12381–
35. Mombelli D, Mapelli C, Barella S et al (2016) The effect of 12390. https​://doi.org/10.1021/es302​981v
chemical composition on the leaching behaviour of electric arc 52. Steer JM, Griffiths AJ (2013) Investigation of carboxylic acids
furnace (EAF) carbon steel slag during a standard leaching test. and non-aqueous solvents for the selective leaching of zinc
J Environ Chem Eng 4:1050–1060. https​://doi.org/10.1016/j. from blast furnace dust slurry. Hydrometallurgy 140:34–41.
jece.2015.09.018 https​://doi.org/10.1016/j.hydro​met.2013.08.011
36. Mombelli D, Barella S, Gruttadauria A et al (2019) Effects of 53. Van Herck P, Vandecasteele C, Swennen R, Mortier R (2000)
basicity and mesh on Cr leaching of EAF carbon steel slag. Appl Zinc and lead removal from blast furnace sludge with a hydro-
Sci 9:1–12. https​://doi.org/10.3390/app90​10121​ metallurgical process. Environ Sci Technol 34:3802–3808.
37. Yu Y, Wang D, Li J et al (2018) Effect of cooling conditions on https​://doi.org/10.1021/es991​0331
the leachability of chromium in C ­ r2O3-containing steelmaking 54. Schrama F, Beunder E, Van den Berg B et al (2017) Sul-
slag. J South Afr Inst Min Metall 118:539–543 phur removal in ironmaking and oxygen steelmaking. Iron-
38. Wang X, Geysen D, Van Gerven T et al (2017) Characteriza- mak Steelmak 44:333–343. https​: //doi.org/10.1080/03019​
tion of landfilled stainless steel slags in view of metal recovery. 233.2017.13039​14
Front Chem Sci Eng 11:353–362. https​://doi.org/10.1007/s1170​ 55. Trinkel V, Mallow O, Thaler C et al (2015) Behavior of chro-
5-017-1656-9 mium, nickel, lead, zinc, cadmium, and mercury in the blast
39. Kim E, Spooren J, Broos K et al (2015) Selective recovery of furnace-a critical review of literature data and plant inves-
Cr from stainless steel slag by alkaline roasting followed by tigations. Ind Eng Chem Res 54:11759–11771. https​: //doi.
water leaching. Hydrometallurgy 158:139–148. https​://doi. org/10.1021/acs.iecr.5b034​42
org/10.1016/j.hydro​met.2015.10.024 56. Trinkel V, Mallow O, Aschenbrenner P et al (2016) Charac-
40. Kim E, Spooren J, Broos K et al (2016a) Valorization of stain- terization of blast furnace sludge with respect to heavy metal
less steel slag by selective chromium recovery and subsequent distribution. Ind Eng Chem Res 55:5590–5597. https​: //doi.
carbonation of the matrix material. J Clean Prod 117:221–228. org/10.1021/acs.iecr.6b006​17
https​://doi.org/10.1016/j.jclep​ro.2016.01.032 57. Foeldi C, Dohrmann R, Mansfeldt T (2015) Volatilization
41. Kim E, Spooren J, Broos K et al (2016b) New method for selec- of elemental mercury from fresh blast furnace sludge mixed
tive Cr recovery from stainless steel slag by NaOCl assisted alka- with basic oxygen furnace sludge under different tempera-
line leaching and consecutive ­BaCrO4 precipitation. Chem Eng tures. Environ Sci Process Impacts 17:1915–1922. https​://doi.
J 295:542–551. https​://doi.org/10.1016/j.cej.2016.03.073 org/10.1039/c5em0​0403a​
42. Spooren J, Kim E, Horckmans L et al (2016) In-situ chromium 58. Foeldi C, Dohrmann R, Mansfeldt T (2014) Mercury in
and vanadium recovery of landfilled ferrochromium and stainless dumped blast furnace sludge. Chemophere 99:248–253. https​
steel slags. Chem Eng J 303:359–368. https​://doi.org/10.1016/j. ://doi.org/10.1016/j.chemo​spher​e.2013.11.007
cej.2016.05.128 59. Ma N (2014) In-Process Separation of Zinc From Blast Fur-
43. Baumgartner S, Groot D (2014) The recovery of manganese nace Offgas Solid Wastes. In: AISTech 2014 Proceedings.
products from ferromanganese slag using a hydrometallurgical Association for Iron & Steel Technology, pp 623–634
route. J South Afr Inst Min Metall 114:331–340 60. Zeydabadi B, Mowla D, Shariat M, Kalajahi J (1997) Zinc
44. Mohanty J, Sahoo P, Nathsarma K et al (1998) Characteriza- recovery from blast furnace flue dust. Hydrometallurgy
tion and leaching of ferromanganese slag. Miner Metall Process 47:113–125. https​://doi.org/10.1016/S0304​-386X(97)00039​-X
15:30–33. https​://doi.org/10.1007/BF034​03221​ 61. Havlik T, Kukurugya F, Orac D, Parilak L (2012) Acidic leach-
45. Naganoor P, Prasanna A, Shivaprasad K, Bhat K (2000) Extrac- ing of EAF steelmaking dust. World Metall - ERZMETALL
tion of manganese from Ferro-manganese slag. Int Symp Process 65:48–56

13
536 Journal of Sustainable Metallurgy (2020) 6:505–540

62. Banerjee D (2007) Metal recovery from blast furnace sludge furnace dust. Trans Inst Min Metall Sect C 124:1–8. https​://doi.
and flue dust using leaching technologies. Res J Chem Environ org/10.1179/17432​85514​Y.00000​00069​
11:18–21 82. Wang L, Lu X, Huang Y (2013) Determination of Zn distribution
63. Soria-Aguilar MJ, Davila-Pulido GI, Carrillo-Pedroza FR et al and speciation in basic oxygen furnace sludge by synchrotron
(2019) Oxidative leaching of zinc and alkalis from iron blast radiation induced μ-XRF and μ-XANES microspectroscopy.
furnace sludge. METALS. https​://doi.org/10.3390/met90​91015​ X-Ray Spectrom 42:423–428. https​://doi.org/10.1002/xrs.2494
64. Veres J, Lovas M, Jakabsky S et al (2012) Characterization 83. Wang L, Huang Y, Lu X (2013) Zn distribution and speciation
of blast furnace sludge and removal of zinc by microwave in zinc-containing steelmaking wastes by synchrotron radiation
assisted extraction. Hydrometallurgy 129:67–73. https​://doi. induced μ-XRF and μ-XANES spectroscopy. J Phys Conf Ser
org/10.1016/j.hydro​met.2012.09.008 430:012097. https​://doi.org/10.1088/1742-6596/430/1/01209​7
65. Mikhailov I, Komarov S, Levina V et al (2017) Nanosized 84. Singh AKP, Raju MT (2011) Recycling of basic oxygen fur-
zero-valent iron as Fenton-like reagent for ultrasonic-assisted nace (BOF) sludge in iron and steel works. Int J Environ Technol
leaching of zinc from blast furnace sludge. J Hazard Mater Manag 14:19–32. https​://doi.org/10.1504/IJETM​.2011.03925​5
321:557–565. https​://doi.org/10.1016/j.jhazm​at.2016.09.046 85. Kelebek S, Yoruk S, Davis B (2004) Characterization of basic
66. SIDMAR (1999) Werkwijze voor het behandelen van gecon- oxygen furnace dust and zinc removal by acid leaching. Miner
tamineerd ijzerhoudend slib. Belgian Patent 1011619A3 Eng 17:285–291. https​://doi.org/10.1016/j.minen​g.2003.10.030
67. Mortier R (1999) Oxidising elutriation of contaminated sludge 86. Trung Z, Kukurugya H, Takáčová Z et al (2010) Leaching of
containing iron with separation of zinc and lead. Patent WO basic oxygen furnace sludge with sulphuric acid. Acta Montan
9931285 Slovaca 15:200–203
68. Josis C, Hissel J (1988) Procédé de traitement des matières 87. Trung ZH, Kukurugya F, Takacova Z et al (2011) Acidic leach-
contenant des metaux lourds par lixiviation acide. Belgian Pat- ing both of zinc and iron from basic oxygen furnace sludge. J
ent 1001781A6 Hazard Mater 192:1100–1107. https​://doi.org/10.1016/j.jhazm​
69. Giordana S (2016) Method for the treatment of iron-containing at.2011.06.016
sludge, and associated equipment. Canadian Patent CA 2985027 88. Veres J, Jakabsky S, Lovas M, Hredzak S (2010) Non-isothermal
A1 microwave leaching kinetics of zinc removal from basic oxygen
70. Flock J, Mittelstädt H, Pappert E, Tebeck A (2018) Integrated furnace dust. Acta Montan Slovaca 15:204–211
process for recycling washing tower sludge for recovery of iron 89. Duval L (1968) Process for removing zinc oxid from iron oxide
oxide and carbon. Patent WO 2018219464 flue dist by the use of spent pickle liquor. US Patent 3375069
71. Peters R (1999) Chelant extraction of heavy metals from contam- 90. Wang J, Wang Z, Zhang Z, Zhang G (2019a) Zinc removal from
inated soils. J Hazard Mater 66:151–210. https:​ //doi.org/10.1016/ basic oxygen steelmaking filter cake by leaching with organic
S0304​-3894(99)00010​-2 acids. Metall Mater Trans B 50:480–490. https:​ //doi.org/10.1007/
72. Wasay S, Barrington S, Tokunaga S (1998) Remediation of s1166​3-018-1440-3
soils polluted by heavy metals using salts of organic acids and 91. Wang J, Wang Z, Zhang Z, Zhang G (2019b) Removal of
chelating agents. Environ Technol 19:369–379. https​://doi. zinc from basic oxygen steelmaking filter cake by selective
org/10.1080/09593​33190​86166​92 leaching with butyric acid. J Clean Prod 209:1–9. https​://doi.
73. Voglar D, Lestan D (2014) Chelant soil-washing technology for org/10.1016/j.jclep​ro.2018.10.253
metal-contaminated soil. Environ Technol 35:1389–1400. https​ 92. Wang J, Wang Z, Zhang Z, Zhang G (2019c) Comparison of
://doi.org/10.1080/09593​330.2013.86926​5 butyric acid leaching behaviors of zinc from three basic oxy-
74. Chen Y, Zhang S, Xu X et al (2016) Effects of surfactants on gen steelmaking filter cakes. Metals 9:417–428. https​://doi.
low-molecular-weight organic acids to wash soil zinc. Environ org/10.3390/met90​40417​
Sci Pollut Res 23:4629–4638. https​://doi.org/10.1007/s1135​ 93. Wang J, Wang Z, Zhang Z, Zhang G (2019d) Effect of addi-
6-015-5700-3 tion of other acids into butyric acid on selective leaching of zinc
75. Cheikh M, Magnin J, Gondrexon N et al (2010) Zinc and lead from basic oxygen steelmaking filter cake. Metall Mater Trans
leaching from contaminated industrial waste sludges using cou- B 50:1378–1386. https​://doi.org/10.1007/s1166​3-019-01563​-7
pled processes. Environ Technol 31:1577–1585. https​://doi. 94. Gargul K, Jarosz P, Malecki S (2016) Alkaline leaching of low
org/10.1080/09593​33100​38015​48 zinc content iron-bearing sludges. Arch Metall Mater 61:43–49.
76. Peeters T, Xiao Y, Yang Y (2018) Process for selective removal https​://doi.org/10.1515/amm-2016-0013
of zinc from metallurgical plant waste. European Patent EP 3 333 95. Petranikova M, Ssenteza V, Lousada CM et al (2020) Novel
272 A1 process for decontamination and additional valorization of steel
77. Cantarino M, de Carvalho FC, Mansur M (2012) Selective making dust processing using two-step correlative leaching. J
removal of zinc from basic oxygen furnace sludges. Hydro- Hazard Mater. https​://doi.org/10.1016/j.jhazm​at.2019.12144​2
metallurgy 111:124–128. https ​ : //doi.org/10.1016/j.hydro​ 96. Gargul K, Boryczko B (2015) Removal of zinc from dusts and
met.2011.11.004 sludges from basic oxygen furnaces in the process of ammo-
78. Ma N (2016) Recycling of basic oxygen furnace steelmaking niacal leaching. Arch Civ Mech Eng 15:179–187. https​://doi.
dust by in-process separation of zinc from the dust. J Clean Prod org/10.1016/j.acme.2014.08.004
112:4497–4504. https​://doi.org/10.1016/j.jclep​ro.2015.07.009 97. Al-Harahsheh M, Al-Nuairat J, Al-Otoom A et al (2019) Treat-
79. Jalkanen H, Oghbasilasie H, Raipala K (2005) Recycling of steel- ments of electric arc furnace dust and halogenated plastic
making dusts - the Radust concept. J Min Metall 41B:1–16. https​ wastes: a review. J Environ Chem Eng. https​://doi.org/10.1016/j.
://doi.org/10.2298/JMMB0​50100​1J jece.2018.10285​6
80. Sammut ML, Rose J, Masion A et al (2008) Determination of 98. Keglevich W, de Buzin PJ, Heck NC, Faria Vilela AC (2017)
zinc speciation in basic oxygen furnace flying dust by chemical EAF dust: an overview on the influences of physical, chemi-
extractions and X-ray spectroscopy. Chemophere 70:1945–1951. cal and mineral features in its recycling and waste incorporation
https​://doi.org/10.1016/j.chemo​spher​e.2007.09.063 routes. J Mater Res Technol 6:194–202. https:​ //doi.org/10.1016/j.
81. Veres J, Sepelak V, Hredzak S (2015) Chemical, mineral- jrnxt​.2016.10.002
ogical and morphological characterisation of basic oxygen

13
Journal of Sustainable Metallurgy (2020) 6:505–540 537

99. Antrekowitsch J, Roesler G, Steinacker S (2015) State of the art by diluted sulphuric acid. J Hazard Mater 179:1–7. https​://doi.
in steel mill dust recycling. Chem Ing Tech 87:1498–1503. https​ org/10.1016/j.jhazm​at.2010.01.059
://doi.org/10.1002/cite.20150​0073 117. Tsakiridis PE, Oustadakis P, Katsiapi A, Agatzini-Leonardou S
100. Montenegro V, Oustadakis P, Tsakiridis PE, Agatzini-Leonardou (2010) Hydrometallurgical process for zinc recovery from elec-
S (2013) Hydrometallurgical treatment of steelmaking electric tric arc furnace dust (EAFD). Part II: downstream processing and
arc furnace dusts (EAFD). Metall Mater Trans B 44:1058–1069. zinc recovery by electrowinning. J Hazard Mater 179:8–14. https​
https​://doi.org/10.1007/s1166​3-013-9874-0 ://doi.org/10.1016/j.jhazm​at.2010.04.004
101. Bruckard W, Davey K, Rodopoulos T et al (2005) Water leaching 118. Gotfryd L, Chmielarz A, Szolomicki Z (2011a) Recovery of zinc
and magnetic separation for decreasing the chloride level and from arduous wastes using solvent extraction technique part I.
upgrading the zinc content of EAF steelmaking baghouse dusts. Preliminary laboratory studies. Physicochem Probl Miner Pro-
Int J Miner Process 75:1–20. https​://doi.org/10.1016/j.minpr​ cess 47:149–158
o.2004.04.007 119. Gotfryd L, Chmielarz A, Szolomicki Z (2011b) Recovery of zinc
102. Chen W-S, Shen Y-H, Tsai M-S, Chang F-C (2011) Removal of from arduous wastes using solvent extraction technique part II.
chloride from electric arc furnace dust. J Hazard Mater 190:639– Pilot plant tests. Physicochem Probl Miner Process 47:249–258
644. https​://doi.org/10.1016/j.jhazm​at.2011.03.096 120. Montenegro V, Agatzini-Leonardou S, Oustadakis P, Tsa-
103. Chmielarz A, Gnot W (2001) Conversion of zinc chloride to kiridis P (2016) Hydrometallurgical treatment of EAF dust by
zinc sulphate by electrodialysis - a new concept for solving the direct sulphuric acid leaching at atmospheric pressure. Waste
chloride ion problem in zinc hydrometallurgy. Hydrometallurgy Biomass Valoriz 7:1531–1548. https​://doi.org/10.1007/s1264​
61:21–43. https​://doi.org/10.1016/S0304​-386X(01)00153​-0 9-016-9543-z
104. Langova S, Matysek D (2010) Zinc recovery from steel-making 121. Xanthopoulos P, Agatzini-Leonardou S, Oustadakis P, Tsakiridis
wastes by acid pressure leaching and hematite precipitation. PE (2017) Zinc recovery from purified electric arc furnace dust
Hydrometallurgy 101:171–173. https​://doi.org/10.1016/j.hydro​ leach liquors by chemical precipitation. J Environ Chem Eng
met.2010.01.003 5:3550–3559. https​://doi.org/10.1016/j.jece.2017.07.023
105. Cruells M, Roca A, Nunez C (1992) Electric arc furnace 122. Brunelli K, Dabala M (2015) Ultrasound effects on zinc recov-
flue dusts: characterization and leaching with sulphuric acid. ery from EAF dust by sulfuric acid leaching. Int J Miner Metall
Hydrometallurgy 31:213–231. https​://doi.org/10.1016/0304- Mater 22:353–362. https​://doi.org/10.1007/s1261​3-015-1080-4
386X(92)90119​-K 123. Winand R (1991) Chloride hydrometallurgy. Hydrometallurgy
106. Kukurugya F, Vindt T, Havlik T (2015) Behavior of zinc, iron 27:285–316. https​://doi.org/10.1016/0304-386X(91)90055​-Q
and calcium from electric arc furnace (EAF) dust in hydromet- 124. Van Weert G, Peek E (1992) Reagent recovery in chloride
allurgical processing in sulfuric acid solutions: thermodynamic hydrometallurgy - some missing links. Hydrometallurgy
and kinetic aspects. Hydrometallurgy 154:20–32. https​://doi. 29:513–526. https​://doi.org/10.1016/0304-386X(92)90030​-4
org/10.1016/j.hydro​met.2015.03.008 125. Baik D, Fray D (2000) Recovery of zinc from electric-are
107. Havlik T, Turzakova M, Stopic S, Friedrich B (2005) Atmos- furnace dust by leaching with aqueous hydrochloric acid,
pheric leaching of EAF dust with diluted sulphuric acid. plating of zinc and regeneration of electrolyte. Trans Inst
Hydrometallurgy 77:41–50. https​: //doi.org/10.1016/j.hydro​ Min Metall Sect C 109:C121–C128. https​://doi.org/10.1179/
met.2004.10.008 mpm.2000.109.3.121
108. Havlik T, Vidor e Souza B, Bernandes AM et al (2006) 126. Duyvesteyn W, Jha M (1986) Zinc recovery from steel plant
Hydrometallurgical processing of carbon steel EAF dust. J dusts and other zinciferous materials. US Patent 4572771
Hazard Mater 135:311–318. https​://doi.org/10.1016/j.jhazm​ 127. Duyvesteyn W, Hogsett R (1986) Process for metal recovery
at.2005.11.067 from steel plant dust. US Patent 4610722
109. Langova S, Riplova J, Vallova S (2007) Atmospheric leaching 128. McElroy R (1994) Process for the treatment of electric arc
of steel-making wastes and the recipitation of goethite from the furnace dust. US Patent 5336297
ferric sulphate solution. Hydrometallurgy 87:157–162. https​:// 129. McElroy R (1994) Processing of electric arc furnace dust via
doi.org/10.1016/j.hydro​met.2007.03.002 chloride hydrometallurgy. Hydrometallurgy 94:993–1010.
110. Havlik T, Friedrich B, Stopic S (2004) Pressure leaching https​://doi.org/10.1007/978-94-011-1214-7_68
of EAF dust with sulphuric acid. World Metall-Erzmetall 130. Cashman J (1998) Hydrometallurgical processing of flue dust.
57:83–90 US Patent 5709730
111. Havlik T, Miskufova A, Turek P, Kobialkova IU (2019) Consider- 131. Lee H, Baik D, Jo H (2002) Hydrometallurgical method for
ing the influence of calcium on EAF dust acid leaching. Physico- recovery of zinc from electric arc furnace dust. US Patent
chem Probl Miner Process 55:528–536. https​://doi.org/10.5277/ 6338748
ppmp1​8164 132. Barrera-Godinez J, O’Keefe T, Watson J (1992) Effect of ultra-
112. Pazdej R (1982) Hydrometallurgical treatment of metallurgical sound on acidified brine leaching of double-kiln treated EAF
dust. US Patent 4332777 dust. Miner Eng 5:1365–1373. https​://doi.org/10.1016/0892-
113. Duyvesteyn W, Jha M (1986) Two-stage leaching process for 6875(92)90172​-6
steel plant dusts. US Patent 4610721 133. Prater J, Queneau P, Hudson T (1973) Nitric acid route to pro-
114. Zaromb S, Lawson D (1994) Hydrometallurgical process for cessing copper concentrates. AIME Trans 254:117–122
recovering iron sulfate and zinc sulfate from baghouse dust. US 134. Drinkard Jr. W (2001) Nitric acid production and recycle. US
Patent 5286465 Patent 6264909
115. Diaz G, Martin D (1994) Modified zincex process - the clean, 135. Matsuoka S, Kodama T, Kumagai M et al (2003) Develop-
safe and profitable solution to the zinc secondaries treatment. ment of adsorption process for NOx recycling in a repro-
Resour Conserv Recycl 10:43–57. https​://doi.org/10.1016/0921- cessing plant. J Nucl Sci Technol 40:410–416. https​: //doi.
3449(94)90037​-X org/10.1080/18811​248.2003.97153​73
116. Oustadakis P, Tsakiridis PE, Katsiapi A, Agatzini-Leonardou S 136. Matsuoka S, Kodama T, Izumi J et al (2004) Development of
(2010) Hydrometallurgical process for zinc recovery from elec- ­NOx recycle process for practical use at reprocessing plant. J
tric arc furnace dust (EAFD) part i: characterization and leaching Nucl Sci Technol 41:466–472. https​://doi.org/10.1080/18811​
248.2004.97155​09

13
538 Journal of Sustainable Metallurgy (2020) 6:505–540

137. Ma B, Yang W, Yang B et al (2015) Pilot-scale plant study several aqueous media. Mater Sci Forum 730–732:636–641.
on the innovative nitric acid pressure leaching technology https​://doi.org/10.4028/www.scien​tific​.net/MSF.730-732.636
for laterite ores. Hydrometallurgy 155:88–94. https​: //doi. 156. Rao S, Yang T, Zhang D et al (2015) Leaching of low grade zinc
org/10.1016/j.hydro​met.2015.04.016 oxide ores in ­NH4Cl-NH3 solutions with nitrilotriacetic acid as
138. Shang Y, Van Weert G (1993) Iron control in nitrate hydro- complexing agents. Hydrometallurgy 158:101–106. https​://doi.
metallurgy by autoclave hydrolysis of iron(III) nitrate. org/10.1016/j.hydro​met.2015.10.013
Hydrometallurgy 33:273–290. https​://doi.org/10.1016/0304- 157. Harvey TG (2006) The hydrometallurgical extraction of
386X(93)90067​-N zinc by ammonium carbonate: a review of the Schnabel pro-
139. Drinkard Jr. W, Woerner H (1999) Metallurgical dust recycling cess. Miner Process Extr Metall Rev 27:231–279. https​://doi.
process. US Patent 5912402 org/10.1080/08827​50060​08152​71
140. Koningen D, Freund W (2008) Metallurgical dust reclamation 158. Peters M (1978) Process for recovering of zinc from steel-making
process. US Patent 7399454 flue dust. US Patent 4075357
141. Dreisinger D, Peters E, Morgan G (1990) The hydrometallurgi- 159. Keegel Jr. J (1996) Methods for recycling electric arc furnace
cal treatment of carbon-steel electric-arc furnace dusts by the dust. US Patent 5538532
UBC-Chaparral process. Hydrometallurgy 25:137–152. https​ 160. Bucket G, Fountain C, Sinclair R (1998) Refining of zinc sul-
://doi.org/10.1016/0304-386X(90)90035​-Z phides. World Patent WO1998036102A1
142. Barrett E, Nenniger E, Dziewinski J (1992) A hydrometal- 161. Antunano N, Cambra JF, Arias PL (2017) Development of a
lurgical process to treat carbon-steel electric-arc furnace dust. combined solid and liquid wastes treatment integrated into a high
Hydrometallurgy 30:59–68. https​: //doi.org/10.1016/0304- purity ZnO hydrometallurgical production process from Waelz
386X(92)90077​-D oxide. Hydrometallurgy 173:250–257. https​://doi.org/10.1016/j.
143. Barrett E, Nenniger E (1992) Processing of carbon steel fur- hydro​met.2017.09.002
nace dusts. US Patent 5082493 162. Varga T, Torok T (2013) Experimental investigation of zinc
144. Siebenhofer M, Zapfel W, Luttenberger H (1999) Method for precipitation from EAF dust leaching solutions. Mater Sci Eng
processing residues containing at least one non-ferrous metal 38:61–71
and/or compounds thereof. Patent WO 9960176 163. Ruiz O, Clemente C, Alonso M, Alguacil FJ (2007) Recycling
145. Hilber T, Marr R, Siebenhofer M, Zapfel W (2001) Solid/liquid of an electric arc furnace flue dust to obtain high grade ZnO.
extraction of zinc from EAF-dust. Sep Sci Technol 36:1323– J Hazard Mater 141:33–36. https​://doi.org/10.1016/j.jhazm​
1333. https​://doi.org/10.1081/SS-10010​3652 at.2006.06.079
146. Hilber T, Marr R, Siebenhofer M, Simon V (2003) Extractive 164. Wylock C, Antuñano N, Arias P, Haut B (2014) Analysis of the
separation of zinc from oxidic solid bulk feed. Sep Sci Technol simultaneous gas-liquid ­CO2 absorption and liquid-gas ­NH3 des-
38:2867–2880. https​://doi.org/10.1081/SS-12002​2576 orption in a hydrometallurgical waelz oxides purification process.
147. Thorsen G (1977) Extraction and separation of metals from solids Int J Chem React Eng 12:1–14
using liquid cation exchangers. US Patent 4008134 165. Xia D (1997) Recovery of zinc from zinc ferrite and electric
148. Thorsen G, Grislingas A, Steintveit G (1981) Recovery of zinc arc furnace dust. PhD Thesis Queens University of Kingston,
from zinc ash and flue dusts by hydrometallurgical processing. Ontario, Canada
JOM 33:24–29. https​://doi.org/10.1007/BF033​54397​ 166. Mordogan H, Cicek T, Isik A (1999) Caustic soda leach of elec-
149. Thorsen G, Svendsen H, Grislingas A (1984) The integrated tric arc furnace dust. Turk J Eng Environ Sci 23:199–207
organic leaching - solvent extraction operation in hydrometal- 167. Dutra A, Paiva P, Tavares L (2006) Alkaline leaching of zinc
lurgy. In: Hydrometallurgical Process Fundamentals, Proceed- from electric arc furnace steel dust. Miner Eng 19:478–485. https​
ings of a NATO Advanced Research Institute on Hydrometal- ://doi.org/10.1016/j.minen​g.2005.08.013
lurgical Process Fundamentals, held July 2 5 - 3 1 , 1982, in 168. Orhan G (2005) Leaching and cementation of heavy metals from
Churchill College, Cambridge University, Cambridge, United electric arc furnace dust in alkaline medium. Hydrometallurgy
Kingdom, Editor: R.G. Bautista. Springer, New York, pp 78:236–245. https​://doi.org/10.1016/j.hydro​met.2005.03.002
269–292 169. Palimaka P, Pietrzyk S, Stepien M et al (2018) Zinc recovery
150. Filippou D (2004) Innovative hydrometallurgical processes for from steelmaking dust by hydrometallurgical methods. Metals.
the primary processing of zinc. Miner Process Extr Metall Rev https​://doi.org/10.3390/met80​70547​
25:205–252. https​://doi.org/10.1080/08827​50049​04413​41 170. Xia D, Pickles C (1999) Caustic roasting and leaching of elec-
151. Olper M, Maccagni M (1993) Process for recovering zinc and tric arc furnace dust. Can Metall Q 38:175–186. https​://doi.
lead from flue dusts from electrical steel works and for recycling org/10.1016/S0008​-4433(99)00014​-2
said purified metals to the furnace, and installation for imple- 171. Youcai Z, Stanforth R (2000) Extraction of zinc from zinc ferrites
menting said process. European Patent EP 0 551 1 55 A1 by fusion with caustic soda. Miner Eng 13:1417–1421. https​://
152. Olper M, Maccagni M (2000) Electrolytic zinc production from doi.org/10.1016/S0892​-6875(00)00123​-0
crude zinc oxides with the EZINEX process. In: Recycling of 172. Zhao Y, Stanforth R (2000) Integrated hydrometallurgical
Metals and Engineered Materials, Edited by D.L. Stewart, Jr., process for production of zinc from electric arc furnace dust
J.C. Daley and R.L. Stephens. TMS (The Minerals, Metals & in alkaline medium. J Hazard Mater 80:223–240. https​://doi.
Materials Society), pp 379–396 org/10.1016/S0304​-3894(00)00305​-8
153. Olper M, Maccagni M (2008) From C.Z.O. to zinc cathode with- 173. Lenz D, Martins F (2007) Lead and zinc selective precipita-
out any pretreatment. The EZINEX process. In: Lead and Zinc tion from leach electric arc furnace dust solutions. Rev Matér
2008. The Southern African Institute of Mining and Metallurgy, 12:503–509
pp 85–98 174. Xie Z, Guo Y, Jiang T et al (2017) The Extraction of Zinc from
154. Maccagni MG (2016) INDUTEC/EZINEX integrate process on Zinc Ferrite by Calcified-Roasting and Ammonia-Leaching Pro-
secondary zinc-bearing materials. J Sustain Metall 2:133–140. cess. In: Hwang, JY and Jiang, T and Kennedy, MW and Yucel,
https​://doi.org/10.1007/s4083​1-016-0041-0 O and Pistorius, PC and Seshadri, V and Zhao, B and Gregurek,
155. Pedrosa F, Cabral M, Margarido F, Nogueira CA (2013) Recy- D and Keskinkilic, E (ed) 8th International Symposium on High-
cling of exhausted batteries and EAF dusts by leaching with temperature Metallurgical Processing. pp 485–493

13
Journal of Sustainable Metallurgy (2020) 6:505–540 539

175. Yakornov SA, Panshin AM, Grudinsky PI et al (2018) Method of Appl Biochem Biotechnol 152:117–126. https:​ //doi.org/10.1007/
electric arc furnace dust processing by calcination with lime with s1201​0-008-8257-5
following alkaline leaching. Russ Metall. https:​ //doi.org/10.1134/ 193. Carranza F, Romero R, Mazuelos A, Iglesias N (2016) Recovery
S0036​02951​81302​68 of Zn from acid mine water and electric arc furnace dust in an
176. Chairaksa-Fujimoto R, Maruyama K, Miki T, Nagasaka T (2016) integrated process. J Environ Manage 165:175–183. https​://doi.
The selective alkaline leaching of zinc oxide from Electric Arc org/10.1016/j.jenvm​an.2015.09.025
Furnace dust pre-treated with calcium oxide. Hydrometallurgy 194. Stopic S, Friedrich B (2009) Kinetics and mechanism of thermal
159:120–125. https​://doi.org/10.1016/j.hydro​met.2015.11.009 zinc-ferrite phase decomposition. Proceedings of the EMC 2009
177. Zhang C, Zhuang L, Wang J et al (2016) Extraction of zinc from conference, June 28-July 1, 2009, Innsbruck, Austria, 1–14
zinc ferrites by alkaline leaching: enhancing recovery by mecha- 195. Offenthaler D, Ludewig F, Antrekowitsch J (2009) Avoiding the
nochemical reduction with metallic iron. J South Afr Inst Min hot acid leaching process in zinc metallurgy by reduction of cal-
Metall 116:1111–1114 cine. World Metall - ERZMETALL 62:376–384
178. Xia D, Pickles C (2000) Microwave caustic leaching of electric 196. Han J, Liu W, Qin W et al (2016) Thermodynamic and kinetic
arc furnace dust. Miner Eng 13:79–94. https​://doi.org/10.1016/ studies for intensifying selective decomposition of zinc ferrite.
S0892​-6875(99)00151​-X JOM 68:2543–2550. https:​ //doi.org/10.1007/s11837​ -015-1807-8
179. Abbott A, Capper G, Davies D et al (2003) Novel solvent proper- 197. Kazemi M, Sichen D (2016) Investigation of selective reduction
ties of choline chloride/urea mixtures. Chem Commun. https​:// of iron oxide in zinc ferrite by carbon and hydrogen. J Sustain
doi.org/10.1039/b2107​14g Metall 2:73–78. https​://doi.org/10.1007/s4083​1-015-0037-1
180. Smith EL, Abbott AP, Ryder KS (2014) Deep eutectic solvents 198. Antrekowitsch J, Antrekowitsch H (2001) Hydrometallurgically
(DESs) and their applications. Chem Rev 114:11060–11082. recovering zinc from electric arc furnace dusts. JOM 53:26–28.
https​://doi.org/10.1021/cr300​162p https​://doi.org/10.1007/s1183​7-001-0008-9
181. Abbott AP, Frisch G, Hartley J, Ryder KS (2011) Processing 199. Li Y, Liu H, Peng B et al (2015) Study on separating of zinc and
of metals and metal oxides using ionic liquids. Green Chem iron from zinc leaching residues by roasting with ammonium
13:471–481. https​://doi.org/10.1039/c0gc0​0716a​ sulphate. Hydrometallurgy 158:42–48. https​://doi.org/10.1016/j.
182. Abbott A, Capper G, Davies D, Shikotra P (2006) Processing hydro​met.2015.10.004
metal oxides using ionic liquids. Miner Process Extr Metall 200. Holloway PC, Etsell TH, Murland AL (2007) Roasting of La
115:15–18. https​://doi.org/10.1179/17432​8506X​91293​ Oroya zinc ferrite with ­Na2CO3. Metall Mater Trans B 38:781–
183. Abbott A, Collins J, Dalrymple I et al (2009) Processing of elec- 791. https​://doi.org/10.1007/s1166​3-007-9082-x
tric arc furnace dust using deep eutectic solvents. Aust J Chem 201. Miki T, Chairaksa-Fujimoto R, Maruyama K, Nagasaka T (2016)
62:341–347. https​://doi.org/10.1071/CH084​76 Hydrometallurgical extraction of zinc from CaO treated EAF
184. Bakkar A (2014) Recycling of electric arc furnace dust through dust in ammonium chloride solution. J Hazard Mater 302:90–96.
dissolution in deep eutectic ionic liquids and electrowinning. https​://doi.org/10.1016/j.jhazm​at.2015.09.020
J Hazard Mater 280:191–199. https​://doi.org/10.1016/j.jhazm​ 202. Lanzerstorfer C (2019) Potential of industrial de-dusting residues
at.2014.07.066 as a source of potassium for fertilizer production - a mini review.
185. Bakkar A, Neubert V (2019) Recycling of cupola furnace dust: Resour Conserv Recycl 143:68–76. https​://doi.org/10.1016/j.
extraction and electrodeposition of zinc in deep eutectic solvents. resco​nrec.2018.12.013
J Alloys Compd 771:424–432. https​://doi.org/10.1016/j.jallc​ 203. Peng C, Zhang F, Guo Z (2009) Separation and recovery of
om.2018.08.246 potassium chloride from sintering dust of ironmaking works. ISIJ
186. Halli P, Hamuyuni J, Revitzer H, Lundstrom M (2017) Selection Int 49:735–742. https​://doi.org/10.2355/isiji​ntern​ation​al.49.735
of leaching media for metal dissolution from electric arc furnace 204. Zhan G, Guo Z (2013) Basic properties of sintering dust from
dust. J Clean Prod 164:265–276. https​://doi.org/10.1016/j.jclep​ iron and steel plant and potassium recovery. J Environ Sci
ro.2017.06.212 25:1226–1234. https​://doi.org/10.1016/S1001​-0742(12)60168​-5
187. Halli P, Hamuyuni J, Leikola M, Lundstrom M (2018) Devel- 205. Zhan G, Guo Z (2015) Preparation of potassium salt with joint
oping a sustainable solution for recycling electric arc furnace production of spherical calcium carbonate from sintering dust.
dust via organic acid leaching. Miner Eng 124:1–9. https​://doi. Trans Nonferrous Met Soc China 25:628–639. https​: //doi.
org/10.1016/j.minen​g.2018.05.011 org/10.1016/S1003​-6326(15)63646​-9
188. Hamuyuni J, Halli P, Tesfaye F et al (2018) A sustainable meth- 206. Tang H, Zhao L, Sun W et al (2018) Extraction of rubidium from
odology for recycling electric arc furnace dust. In: Sun Z, Wang respirable sintering dust. Hydrometallurgy 175:144–149. https:​ //
C, Guillen DP, Neelameggham NR, Zhang L, Howarter JA, doi.org/10.1016/j.hydro​met.2017.11.003
Wang T, Olivetti E, Zhang M, Verhulst D, Guan X, Anderson 207. Ma N, McDowell BJ, Houser JB et al (2019) Separation of mill
A, Ikhmayies S, Smith YR, Pandey A, Pisupati S, Lu H (eds) scale from flume wastewater using a dynamic separator toward
Energy technology 2018: carbon dioxide management and other zero wastes in the steel hot-rolling process. J Sustain Metall
technologies. Springer, Cham, pp 233–240 5:97–106. https​://doi.org/10.1007/s4083​1-018-0203-3
189. Forrester K, Francis A (1998) Extraction of metals from heavy 208. Shatokha VI, Gogenko OO, Kripak SM (2011) Utilising of the
metal-bearing wastes. Patent WO 9824938 oiled rolling mills scale in iron ore sintering process. Resour
190. Halli P, Agarwal V, Partinen J, Lundstrom M (2020) Recovery of Conserv Recycl 55:435–440. https​://doi.org/10.1016/j.resco​
Pb and Zn from a citrate leach liquor of a roasted EAF dust using nrec.2010.11.006
precipitation and solvent extraction. Sep Purif Technol. https​:// 209. Gomez V, Wright K, Esquenazi GL, Barron AR (2019) Micro-
doi.org/10.1016/j.seppu​r.2019.11626​4 wave treatment of a hot mill sludge from the steel industry: en
191. Wang H, Jia N, Liu W et al (2016) Efficient and selective hydro- route to recycling an industrial waste. J Clean Prod 207:182–189.
thermal extraction of zinc from zinc-containing electric arc https​://doi.org/10.1016/j.jclep​ro.2018.08.294
furnace dust using a novel bifunctional agent. Hydrometallurgy 210. Park J, Ahn J, Song H et al (2002) Reduction characteristics
166:107–112. https​://doi.org/10.1016/j.hydro​met.2016.10.013 of oily hot rolling mill sludge by direct reduced iron method.
192. Bayat O, Sever E, Bayat B et al (2009) Bioleaching of zinc and Resour Conserv Recycl 34:129–140. https​://doi.org/10.1016/
iron from steel plant waste using Acidithiobacillus ferrooxidans. S0921​-3449(01)00098​-2

13
540 Journal of Sustainable Metallurgy (2020) 6:505–540

211. Liu B, Zhang S, Tian J et al (2013a) New technology for recy- 217. Galvez JL, Dufour J, Negro C, Lopez-Mateos F (2009) Routine
cling materials from oily cold rolling mill sludge. Int J Miner to estimate composition of concentrated metal-nitric-hydrofluo-
Metall Mater 20:1141–1147. https​://doi.org/10.1007/s1261​ ric acid pickle liquors. Hydrometallurgy 96:88–94. https​://doi.
3-013-0847-8 org/10.1016/j.hydro​met.2008.08.007
212. Liu B, Zhang S, Pan D, Chang C (2016) Synthesis and charac- 218. Ji Z, Lou X, Wang W et al (2017) Recovery of nickel from stain-
terization of micaceous iron oxide pigment from oily cold roll- less steelmaking sludge by circular leaching and extraction. AIP
ing mill sludge. Procedia Environ Sci 31:653–661. https​://doi. Conf Proc 1794:030011. https​://doi.org/10.1063/1.49719​33
org/10.1016/j.proen​v.2016.02.121 219. Regel-Rosocka M (2010) A review on methods of regeneration
213. Liu B, Zhang S, Tian J et al (2013b) Recycle of valuable prod- of spent pickling solutions from steel processing. J Hazard Mater
ucts from oily cold rolling mill sludge. Int J Miner Metall Mater 177:57–69. https​://doi.org/10.1016/j.jhazm​at.2009.12.043
20:941–946. https​://doi.org/10.1007/s1261​3-013-0818-0 220. Dufour J, Lopez L, Negro C et al (2002) Mathematical model
214. Devi A, Singhal A, Gupta R, Panzade P (2014) A study on treat- of magnetite synthesis by oxidation of sulfuric pickling liquors
ment methods of spent pickling liquor generated by pickling pro- from steelmaking. Chem Eng Commun 189:285–297. https:​ //doi.
cess of steel. Clean Technol Environ Policy 16:1515–1527. https​ org/10.1080/00986​44021​2080
://doi.org/10.1007/s1009​8-014-0726-7 221. Hermoso J, Dufour J, Galvez J et al (2005) Nickel hydrox-
215. Dufour J, Negro C, Heras F, Lopez-Mateos F (2001) Recovery of ide recovery from stainless steel pickling liquors by selective
the metals from pickling liquors of stainless steel by precipitation precipitation. Ind Eng Chem Res 44:5750–5756. https​://doi.
methods. ISIJ Int 41:801–806. https​://doi.org/10.2355/isiji​ntern​ org/10.1021/ie050​422n
ation​al.41.801
216. Heras F, Dufour J, Lopez-Delgado A et al (2004) Feasibility Publisher’s Note Springer Nature remains neutral with regard to
study of metals recycling from nitric-hydrofluoric waste pickle jurisdictional claims in published maps and institutional affiliations.
baths. Environ Eng Sci 21:583–590. https​://doi.org/10.1089/
ees.2004.21.583

Affiliations

Koen Binnemans1 · Peter Tom Jones2 · Álvaro Manjón Fernández3 · Victoria Masaguer Torres3

2
* Koen Binnemans Department of Materials Engineering, KU Leuven,
Koen.Binnemans@kuleuven.be Kasteelpark Arenberg 44 ‑ box 2450, 3001 Leuven, Belgium
3
1 Global R&D Asturias, ArcelorMittal, P.O. Box 90,
Department of Chemistry, KU Leuven, Celestijnenlaan 200F
33400 Avilés, Spain
‑ box 2404, 3001 Leuven, Belgium

13

View publication stats