Hydrometallurgy 188 (2019) 169–173

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Hydrometallurgy
journal homepage: www.elsevier.com/locate/hydromet

Efficient removal of iron(II) from manganese sulfate solution by using T

mechanically activated CaCO3
⁎
Kui Wang, Qiwu Zhang , Huimin Hu, Yanchu Liu
School of Resources and Environmental Engineering, Wuhan University of Technology, Wuhan 430070, China

A R T I C LE I N FO A B S T R A C T

Keywords: Trace amounts of iron impurity in manganese sulfate solution will seriously affect the quality of manganese
Iron(II) removal products if it is not purified. In this study, we utilized mechanically activated CaCO3 to remove iron from
Manganese sulfate solution manganese sulfate solution by co-grinding CaCO3 with manganese sulfate solution in a wet stirred ball mill.
Mechanical activation Effects of rotation speed, milling time, ball/liquid volume ratio, and CaCO3/Fe2+ molar ratio on the iron re-
CaCO3
moval were investigated. The results showed that the iron in the manganese sulfate solutions was efficiently
removed with an iron removal rate of approximately 100% under the optimum conditions. Mechanical acti-
vation clearly increased the reactivity of CaCO3. This study would provide an alternative method for removing
iron from manganese solution.

1. Introduction Fe2+ to Fe3+ with MnO2 at pH 2–3; (b) hydrolysis of Fe3+ into Fe(OH)3
colloid by the solution pH adjustment (Lin et al., 2016) and (c) se-
Manganese sulfate as a basic manganese salt is an important in- paration of Fe(OH)3 colloid from the solution. However, in order to
dustrial intermediate to produce electrolytic manganese products in- increase oxidation rate and achieve the complete oxidation of Fe2+, the
cluding electrolytic manganese and electrolytic manganese dioxide, oxidation process usually needs to be carried out at about 90 °C with
chemical manganese dioxide and manganese salts such as manganese more than the theoretical dosage of MnO2. Consequently, excess man-
carbonate (Fu et al., 2010; Nayl et al., 2011; Zhang and Cheng, 2007). ganese dioxide enters the solid residues and is not effectively utilized.
As a result, the purity of manganese sulfate will directly determine the Iron and manganese coexist in the residue and it is difficult to separate
quality of subsequent manganese products. For example, the maximum manganese from iron. This results in an increase in energy consumption
admissible iron impurities content in the manganese sulfate solution for and a waste of available resources which will add to the production
the production of electrolytic manganese is 10 mg/L (Zhang and Cheng, costs.
2007). Manganese sulfate is mainly prepared by the hydrometallurgical In our previous work, we found that Mn2+ was hard to precipitate
leaching of manganese ores with H2SO4 and subsequent solution pur- with CaCO3 (Hu et al., 2017; Hu et al., 2019), conversely, Fe2+ was
ification (Lin et al., 2016; Liu et al., 2014; Nayl et al., 2011). In the easy (Li et al., 2018). Based on this difference, CaCO3 may be used for
leaching process of manganese ores, iron impurity enters the manga- the removal of Fe2+ from manganese sulfate solution in order to avoid
nese sulfate solution along with manganese (Lin et al., 2016; Liu et al., the above problems caused by the utilization of MnO2 as the oxidant.
2014; Liu et al., 2019; Pakarinen and Paatero, 2011; Sahoo et al., Moreover, CaCO3 is an important environmental mineral material
1979), therefore the effective purification is required to remove iron which is low-cost, widely available and regard as eco-friendly in many
impurity from manganese sulfate solution. countries (Li et al., 2017a). CaCO3 is stable and slightly soluble in water
There are two forms of iron in the manganese sulfate solution: Fe2+ in the natural state (Li et al., 2016). An activation operation is needed
and Fe3+. Fe3+ can be directly removed by the neutralization and to raise its solubility and reactivity. Mechanical activation has proven
hydrolysis method at pH 3–4 (Zhang and Cheng, 2007), whereas the to be a simple and effective way to activate CaCO3 (Hu et al., 2017; Hu
removal of Fe2+ requires an oxidization operation to avoid the for- et al., 2019; Li et al., 2017b, 2017c; Zhang et al., 2018). Therefore, in
mation of manganese hydroxide precipitation due to the similar pH for the study, wet stirred ball milling was used to activate CaCO3 to remove
the hydrolysis of Fe2+ and Mn2+ (Lin et al., 2016; Yan and Qiu, 2014). Fe2+ from manganese sulfate solution. The effects of rotation speed,
The Fe2+ removal process includes the following steps: (a) oxidation of milling time, CaCO3/Fe2+ molar ratio, and ball/liquid volume ratio on

⁎
Corresponding author.
E-mail address: zhangqw@whut.edu.com (Q. Zhang).

https://doi.org/10.1016/j.hydromet.2019.07.003
Received 25 March 2019; Received in revised form 8 June 2019; Accepted 5 July 2019
Available online 08 July 2019
0304-386X/ © 2019 Published by Elsevier B.V.
K. Wang, et al. Hydrometallurgy 188 (2019) 169–173

5
100 (a) (b)
4

Manganese loss rate (%)

Iron removal rate (%)
80
3 CaCO3/Fe2+ molar ratio =1:1
2:1 3:1
4:1 5:1
60 2

CaCO3/Fe2+ molar ratio =1:1

1
40 2:1 3:1
4:1 5:1
0
200 250 300 350 200 250 300 350
Rotation speed (rpm) Rotation speed (rpm)

Fig. 1. Effect of the rotation speed on iron removal.

7 7
CaCO3/Fe2+ molar ratio =1:1
2:1 3:1
4:1 5:1
6 6

5 5
pH

pH
4 4
CaCO3/Fe2+ molar ratio =1:1
3 2:1 3:1 4:1 5:1
200 250 300 350 3
90 120 150 180 210 240
Rotation speed (rpm)
Milling time (min)
Fig. 2. Effect of the rotation speed on solution pH.
Fig. 4. Effect of the milling time on solution pH.

the processes were investigated and the mechanism of the Fe2+ re-
1000 mL and the balls used were yttrium-stabilized zirconia milling
moval process was also analyzed.
balls of 3 mm in diameter. 250 mL of manganese sulfate solution, a
known volume of milling balls and a defined amount of CaCO3 were
2. Experimental added into the grinding chamber for milling. The parameters of rotation
speed, milling time, ball/liquid volume ratio, and CaCO3/Fe2+ molar
2.1. Materials ratio were varied systematically changed. After each run, the suspen-
sion solution was allowed to settle before being filtered through a
All reagents (MnSO4·H2O, FeSO4·7H2O, CaCO3) used in this in- 0.22 μm pore size filter membrane to remove suspended solids to obtain
vestigation were of analytical grade and purchased from Sinopharm the supernatant for the pH and remaining metal concentrations mea-
Chemical Reagent Co., Ltd., China. De-ionized water was used to pre- surement. The precipitates obtained were dried at 80 °C for 24 h for
pare solutions with a Mn2+ concentration of 38 g/L and Fe2+ con- further analyses. All the experiments were conducted at room tem-
centration of 1 g/L. The initial pH of the solution is about 3.3. perature.

2.2. Methods 2.3. Characterizations

Milling operations were performed in a lab-scale stirred ball milling X-ray diffraction (RU-200B/D/MAX-RB, Rigaku, Japan) analysis
equipment (Changsha Tianchuang Powder Technology Corporation, was performed to identify the phases of the precipitated samples. The
YS7124-JM-1 L, China). The volume of the cylindrical stirred tank is morphology of the precipitated samples were observed by SEM (Ultra

5
100 (a) (b)
4
CaCO3/Fe2+ molar ratio =1:1
Manganese loss rate (%)
Iron removal rate (%)

80 2:1 3:1
3 4:1 5:1

60 2
2+
CaCO3/Fe molar ratio = 1:1
1
40 2:1 3:1
4:1 5:1
0
90 120 150 180 210 240 90 120 150 180 210 240
Milling time (min) Milling time (min)

Fig. 3. Effect of the milling time on iron removal.

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K. Wang, et al. Hydrometallurgy 188 (2019) 169–173

5
100 (a) (b)
4

Manganese loss rate (%)

90

Iron removal rate (%)

3
80
2 CaCO3/Fe2+ molar ratio = 3:1
70
CaCO3/Fe2+ molar ratio = 3:1 CaCO3/Fe2+ molar ratio = 4:1
2+
60 CaCO3/Fe molar ratio = 4:1 1

50 0
6 9 12 15 6 9 12 15
Ball/liquid volume ratio (%) Ball/liquid volume ratio (%)

Fig. 5. Effect of the ball/liquid volume ratio on iron removal.

7 C 0 − Ce
R= × 100%
Co

6 where C0 and Ce are the initial concentration and the concentration

after the iron removal operation, respectively (mg/L).

5 3. Results and discussion

pH

3.1. Effect of rotation speed on iron removal

4 CaCO3/Fe2+ molar ratio = 3:1
2+
CaCO3/Fe molar ratio = 4:1
Rotation speed is an important parameter as an increase in the ro-
tation speed can increase the relative collision speed between the mil-
3
6 9 12 15 ling balls as well as between the milling balls and the material so that
Ball/liquid volume ratio (%) more energy is transferred between them.
Fig. 1(a) shows the iron removal rate at different rotation speeds for
Fig. 6. Effect of the ball/liquid volume ratio on solution pH. a series of CaCO3/Fe2+ molar ratios. Experiments were carried out with
milling time fixed at 180 min and ball/liquid volume ratio fixed at 15%.
Table 1 From this figure, it is observed that the iron removal rate increased for
The results of the comparative experiments. various CaCO3/Fe2+ molar ratios as the rotation speed increased. When
Iron removal rate Manganese loss rate pH
the rotation speed was greater than 300 rpm and the CaCO3/Fe2+
molar ratio was higher than 3:1, the iron removal rate was approxi-
Unactivated 10.6% 0 5.2 mately 100% demonstrating the efficiency of this process. Considering
Activated 100% 0.6% 6.6 that there was a need to reduce the amount of slag generated during the
iron removal process and to make full use of the added CaCO3 by ac-
tivation, the rotation speed of 350 rpm and CaCO3/Fe2+ molar ratio of
Plus-43-13, Zeiss, Germany). The pH of all the solutions was measured
3:1 were suitable for the iron removal operation. Fig. 1(b) shows the
by a pH meter (METTLER TOLEDO FE20-FiveEasy™, Switzerland).
manganese loss rate at a different rotation speed with a series of
Manganese concentration in the aqueous phase was determined by the
CaCO3/Fe2+ molar ratios. From this figure, it is observed that the
perchloric acid oxidation ammonium iron(II) sulphate titrimetric
manganese loss rate was maintaining at a very low level of less than
method (GB/T 1506-2016, 2016). Total iron concentration in the so-
2%, which is beneficial to the subsequent utilization of manganese
lution was determined by titanium(III) chloride reduction potassium
sulfate solution for the production of various manganese products after
dichromate titration methods (GB/T 6730.65-2009, 2009), whereas the
the iron removal operation.
trace iron concentration in the solution was determined by atomic ab-
Fig. 2 shows the changes in solution pH after the iron removal op-
sorption spectrophotometer (AAS: SHIMADZU AA-6880, Japan). The
eration. From this figure, it is observed that the solution pH increased as
iron removal rate and manganese loss rate were calculated by the fol-
the rotation speed increased when the CaCO3/Fe2+ molar ratio was
lowing equation:
over 1:1. The solution pH was between 6 and 7 when the CaCO3/Fe2+

3500
20000 (a) (b)
CaCO3 3000
CaSO4· 2H2O
15000 2500 CaCO3
Intensity (CPS)

Intensity (CPS)

2000
10000
1500

5000 1000
500
0 0
10 20 30 40 50 60 70 10 20 30 40 50 60 70
2 Theta (degree) 2 Theta (degree)

Fig. 7. XRD pattern of the precipitate samples. (a) the CaCO3 unactivated. (b) the CaCO3 activated.

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K. Wang, et al. Hydrometallurgy 188 (2019) 169–173

Fig. 8. SEM images of the precipitate sample. (a) the CaCO3 unactivated. (b) the CaCO3 activated.

molar ratio was over 3:1 and the rotation speed was 350 rpm as ball shows the changes in solution pH after the iron removal operation. The
milling promotes the dissolution of CaCO3. The dissolution of CaCO3 solution pH increased as the ball/liquid volume ratio increased and was
resulted in the increase of the solution pH. According to Zhu et al. finally between 6 and 7.
(2017), the rate of Fe(II) oxidation is slow under acidic conditions,
while increases with the increase in pH and becomes rapid at pH greater 3.4. Mechanism discussion
than 4. Therefore, the increase in the solution pH is beneficial to the
oxidation and precipitation of Fe2+. In order to better understand the activation of CaCO3 by wet stirred
ball milling in manganese sulfate solution, a set of comparative ex-
3.2. Effect of milling time on iron removal periments were carried out under the optimum conditions (rotation
speed = 350 rpm, milling time = 240 min, CaCO3/Fe2+ molar
Milling time is also an important parameter as an increase in the ratio = 3:1). One was added with milling balls to achieve the activation
milling time can increase the reaction time to ensure the CaCO3 is fully of CaCO3 and the other was through a single agitation without ball
reacted. addition.
Fig. 3(a) shows the iron removal rate at the different milling time The results of the comparative experiments are presented in Table 1,
with a series of CaCO3/Fe2+ molar ratios. Experiments were carried out which shows the iron removal rate was only 10.6% under the un-
with the rotation speed fixed at 350 rpm and ball/liquid volume ratio of activated condition, while the iron removal rate was approximately
15%. The iron removal rate increased for various CaCO3/Fe2+ molar 100% under the activation condition. The result clearly demonstrates
ratios as the milling time increased. When the milling time was more that the operation of ball milling increased the reactivity of CaCO3
than 180 min and the CaCO3/Fe2+ molar ratio was over 3:1, the iron through ball milling and the reaction proceeded more fully which in-
removal rate was approximately 100%. Considering that there was a creased the utilization rate of CaCO3.The precipitated samples obtained
need to reduce the amount of slag generated during the iron removal under both conditions were analyzed by XRD and the results are shown
process and make full use of the added CaCO3 by activation, milling in Fig. 7.
time of 240 min and CaCO3/Fe2+ molar ratio of 3:1 was suitable for the As Fig. 7(a) shows, the main phase of the precipitate sample was
iron removal operation. Fig. 3(b) shows the manganese loss rate at the still CaCO3. As Fig. 7(b) shows, the main phases of the precipitate
different milling time with a series of CaCO3/Fe2+ molar ratios. The sample were CaSO4·2H2O and CaCO3. This clearly indicated that the
manganese loss rate could be still maintained at a very low level of less ball milling promoted the reaction between CaCO3 and the manganese
than 2%. sulfate solution. However, there was no clear information about the
Fig. 4 shows the changes in solution pH after the iron removal op- iron phase in Fig. 7(b) as the iron may have precipitated in amorphous
eration. When the CaCO3/Fe2+ molar ratio was 1:1, the solution pH phase. The chemical analysis shows that the iron in the precipitate
remains almost remained unchanged as the addition of CaCO3 was not sample was mainly Fe3+ which accounts for 99% of the total iron.
enough to neutralize the weak acidity in the solution. When the CaCO3/ Based on the above analysis, the reaction mechanism of for the iron
Fe2+ molar ratio was over 1:1, the solution pH increased as the milling removal from manganese sulfate solution may be described by the
time increased until a pH between 6 and 7 was achieved. The increase following Eqs. (1–6) (Li et al., 2018; Zhu et al., 2017):
in the milling time promoted the dissolution of CaCO3. CaCO3 → Ca2 + + CO32– (1)

CO32– + H2 O → HCO3– + OH– (2)

3.3. Effect of ball/liquid volume ratio on iron removal
Ca2 + + SO4 2− + 2H2 O → CaSO4 ·2H2 O↓ (3)
The ball/liquid volume ratio refers to the volume of the used balls to
the volume of manganese sulfate solution. It is also an important Fe2 + + 2OH− → Fe(OH)2 ↓ (4)
parameter as an increase in the ball/liquid volume ratio can increase Fe(OH)2 + 1/4O2 + 1/2H2 O → Fe(OH)3 ↓ (5)
the collision between the milling balls and the material.
Fig. 5(a) shows the effect of the ball/liquid volume ratio on iron 2CaCO3 + Fe2 + + 2SO4 2 − + 1/4O2 + 13/2H2 O → 2CaSO4
removal rate with the rotation speed fixed at 350 rpm, milling time
·2H2 O ↓ + Fe(OH)3 ↓ + 2HCO3− (6)
240 min and a series of CaCO3/Fe2+ molar ratios. As can be seen in the
figure, the iron removal rate increased as the ball/liquid volume ratio Fig. 8 shows the SEM images of the precipitate sample. From
increased. A larger ball/liquid volume ratio was beneficial to the col- Fig. 8(a), we can see the typical rhombohedron morphology of CaCO3
lisions between the milling balls and the CaCO3. For these experiments, (Hu et al., 2019). From Fig. 8(b), we can only see irregular particles.
ball/liquid volume ratio of 15% was selected as suitable for the iron This indicates the increase of CaCO3 activity is related to the frag-
removal operation. Fig. 5(b) shows the effect of the ball/liquid volume mentation of calcium carbonate particles during the ball milling pro-
ratio on manganese loss rate at a very low level of less than 2%. Fig. 6 cess.

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4. Conclusions Technol. 172, 107–112.

Li, X.W., Lei, Z.W., Qu, J., Li, Z., Zhou, X.W., Zhang, Q.W., 2017b. Synthesizing slow-
release fertilizers via mechanochemical processing for potentially recycling the waste
In this study, CaCO3 mechanically activated in a stirred ball mill was ferrous sulfate from titanium dioxide production. J. Environ. Manag. 186, 120–126.
used to remove iron from manganese sulfate solution. Under optimised Li, X.W., Lei, Z.W., Qu, J., Zhou, X.W., Li, Z., Zhang, Q.W., 2017c. Separation of Cu (II)
conditions of rotation speed of 350 rpm, milling time of 240 min, ball/ from Cd (II) in sulfate solution using CaCO3 and FeSO4 based on mechanochemical
activation. RSC Adv. 7, 2002–2008.
liquid volume ratio of 15%, CaCO3/Fe2+ molar ratio of 3:1, the iron Li, Y.J., He, X.M., Hu, H.M., Zhang, T.T., Qu, J., Zhang, Q.W., 2018. Enhanced phosphate
removal rate was approximately 100% with an associated manganese removal from wastewater by using in situ generated fresh trivalent Fe composition
loss rate was less than 2%. The solution pH was 6–7 after the iron re- through the interaction of Fe(II) on CaCO3. J. Environ. Manag. 221, 38–44.
Lin, Q.Q., Gu, G.H., Wang, H., Zhu, R.F., Liu, Y.C., Fu, J.G., 2016. Preparation of man-
moval operation and it was found that increase in the solution pH is ganese sulfate from low-grade manganese carbonate ores by sulfuric acid leaching.
beneficial to the oxidation and precipitation of Fe2+. The operation of Int. J. Miner. Metall. Mater. 23 (5), 491–500.
ball milling increased the reactivity of CaCO3 when compared with the Liu, Y.C., Lin, Q.Q., Li, L.F., Fu, J.G., Zhu, Z.S., Wang, C.Q., Q, D., 2014. Study on hy-
drometallurgical process and kinetics of manganese extraction from low-grade
unactivated CaCO3 such that it can better remove Fe2+ from manga-
manganese carbonate ores. Int. J. Min. Sci. Technol. 24, 567–571.
nese sulfate solution. Liu, B.B., Zhang, Y.B., Lu, M.M., Su, Z.J., Li, G.H., Jiang, T., 2019. Extraction and se-
paration of manganese and iron from ferruginous manganese ores: A review. Miner.
References Eng. 131, 286–303.
Nayl, A.A., Ismail, I.M., Aly, H.F., 2011. Recovery of pure MnSO4·H2O by reductive
leaching of manganese from pyrolusite ore by sulfuric acid and hydrogen peroxide.
Fu, J.G., He, Z.X., Wang, H., Liang, W., Guo, C., 2010. Preparation of chemical manganese Int. J. Miner. Process. 100, 116–123.
dioxide from manganese sulfate. Min. Sci. Technol. 20, 0877–0881. Pakarinen, J., Paatero, E., 2011. Recovery of manganese from iron containing sulfate
GB/T 1506-2016, 2016. Manganese Ores—Determination of Manganese solutions by precipitation. Miner. Eng. 24, 1421–1429.
Content—Potentiometric Method and Ammonium Iron (II) Sulphate Titrimetric Sahoo, P.K., Das, S.C., Bose, S.K., Sircar, S.C., 1979. Separation of iron from manganese
Method. (China. in Chinese). ore roast-leach liquor. J. Chem. Technol. Biotechnol. 29, 307–310.
GB/T 6730.65-2009, 2009. Iron Ores—Determination of Total Iron Content—Titanium Yan, S., Qiu, Y.R., 2014. Preparation of electronic grade manganese sulfate from leaching
(III) Chloride Reduction Potassium Dichromate Titration Methods (Routine solution of ferromanganese slag. Trans. Nonferrous Metals Soc. China 24, 3716–3721.
Methods). (China. in Chinese). Zhang, W.S., Cheng, C.Y., 2007. Manganese metallurgy review. Part I: Leaching of ores/
Hu, H.M., Li, X.W., Huang, P.W., Zhang, Q.W., Yuan, W.Y., 2017. Efficient removal of secondary materials and recovery of electrolytic/chemical manganese dioxide.
copper from wastewater by using mechanically activated calcium carbonate. J. Hydrometallurgy 89, 137–159.
Environ. Manag. 203, 1–7. Zhang, T.T., Wen, T., Zhao, Y.L., Hu, H.M., Xiong, B.W., Zhang, Q.W., 2018. Antibacterial
Hu, H.M., Zhang, Q.W., Yuan, W.Y., Li, Z., Zhao, Y., Gu, W.J., 2019. Efficient Pb removal activity of the sediment of copper removal from wastewater by using mechanically
through the formations of (basic) carbonate precipitates from different sources during activated calcium carbonate. J. Clean. Prod. 203, 1019–1027.
wet stirred ball milling with CaCO3. Sci. Total Environ. 664, 53–59. Zhu, J., Zhang, P., Yuan, S.H., Liao, P., Qian, A., Liu, X.X., Tong, M., Li, L., 2017.
Li, X.W., Lei, Z.W., Qu, J., Li, Z., Zhang, Q.W., 2016. Separation of copper from cobalt in Production of Hydroxyl radicals from oxygenation of simulated AMD due to CaCO3-
sulphate solutions by using CaCO3. Sep. Sci. Technol. 51 (17), 2772–2779. induced pH increase. Water Res. 111, 118–126.
Li, X.W., Lei, Z.W., Qu, J., Hu, H.M., Zhang, Q.W., 2017a. Separation of copper from
nickel in sulfate solutions by mechanochemical activation with CaCO3. Sep. Purif.

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