Hindawi Publishing Corporation

ISRN Metallurgy
Volume 2014, Article ID 907536, 10 pages
http://dx.doi.org/10.1155/2014/907536

Research Article
Life Cycle Impact of Rare Earth Elements

P. Koltun1 and A. Tharumarajah2

1
CSIRO Process Science and Engineering, Gate 5, Normanby Road, Clayton, VIC 3168, Australia
2
EnviSolutions, 20 Galahad Crescent, Glen Waverley, Melbourne, VIC 3150, Australia

Correspondence should be addressed to P. Koltun; paul.koltun@csiro.au

Received 19 December 2013; Accepted 14 January 2014; Published 4 May 2014

Academic Editors: M. Carboneras and P. Lukac

Copyright © 2014 P. Koltun and A. Tharumarajah. This is an open access article distributed under the Creative Commons
Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is
properly cited.

The diverse properties of rare earth elements have seen broad and growing applications in clean energy technologies, hybrid vehicles,
pollution control, optics, refrigeration, and so on. This study presents a “cradle-to-gate” life cycle assessment of the energy use,
resource depletion, and global warming potential resulting from the production of rare earth elements (REEs) using the Bayan
Obo rare earth operation in Inner Mongolia, China, as a representative system. The study aggregates data from the literature, LCI
databases, and reasonable estimations. A novel economic value-based allocation method for the multiple coproducts of the process
is proposed. It is found that four of the high priced REEs scandium, europium, terbium, and dysprosium have very high GWPs from
production relative to the rest. A mass-based allocation is also provided for comparison. Impacts on immediate local environment
from waste streams that can be toxic are not included in this study.

1. Introduction much less tendency to become concentrated in exploitable

ore deposits [2], in particular HREEs. This being so, only a
Rare earth elements (REEs) or RE metals are technically few mineral species, such as bastnasite, monazite, and RE-
defined as the 15 elements in the lanthanide (La) series, bearing clay, have been recovered for commercial production.
yttrium (Y), and scandium (Sc). Y and Sc are considered Bastnasite deposits in China and the United States constitute
REEs since they mostly occur in the same ore deposits and the largest percentage of the world’s rare-earth economic
have similar chemical properties. A precise classification resources [3].
often used in extraction is as follows [1]. REEs possess diverse nuclear, metallurgical, chemical,
catalytic, electrical, magnetic, and optical properties. This has
(i) Light rare earth elements (LREEs): lanthanum (La),
led to ever-increasing applications, some mundane (lighter
cerium (Ce), praseodymium (Pr), neodymium (Nd),
flints, glass polishing) to others that are highly specific.
and promethium (Pm).
Examples of the latter include catalysts in petroleum refining
(ii) Medium rare earth elements (MREEs): samarium industry, as alloying agents (used to enhance the oxidation
(Sm), europium (Eu), and gadolinium (Gd). resistance of alloys) in metallurgical processes, in glass, phos-
(iii) Heavy rare earth elements (HREEs): terbium (Tb), phors, optics, permanent magnets, and electronics. Emerging
dysprosium (Dy), holmium (Ho), erbium (Er), thuli- and potential applications include using rare earths to absorb
um (Tm), ytterbium (Yb), lutetium (Lu), scandium ultraviolet light in automotive glass, corrosion protection,
(Sc), and yttrium (Y). and metal coatings in corrosive and salty environments.
Futuristic applications of REE are in high-temperature super-
There are about 200 known rare-earth containing mineral conductivity, safe storage, and transport of hydrogen for a
deposits, mostly as carbonatites spread around the world. posthydrocarbon economy [2]. For applications of individual
Contrary to a lay persons’ understanding, REs are not rare REEs, see [4].
in natural occurrence (cerium is more abundant than tin Only small quantities of REEs are used in most applica-
and yttrium is more abundant than lead), though REEs have tions, for instance, 2 to 3 grams in a 20-watt phosphor lamp.
2 ISRN Metallurgy

However, clean energy applications such as high capacity

nickel-metal hydride batteries in hybrid cars (in a third- Lovozerskoye
generation Toyota Prius) contain on average ∼0.6 kg/battery
of La [5] and RE magnets for electric motors as light weight Bayan Obo
alternative to iron magnets require around 1 kg of Nd [6, 7]. A Mount. Pass Strange
utility scale wind turbine, another green power source, uses Lake
more than a ton of heavy-duty and lightweight magnets, 700 Longnan Pocos de
Caldas
pounds of which is neodymium [8]. As the worldwide imple-
mentation of clean energy and other applications increase,
many studies have identified the supply of particular REEs
(dysprosium, neodymium, terbium, yttrium, and europium) Mount. Weld
to be at risk in the short and medium term [9, 10].
China currently accounts for 95% of global production of Carbonatite Conglomerate
rare earths (about 90% of REs used in the US) and domestic Alkaline complex Weathered carbonatite
industry consumes about 60% [18]. Bayan Obo mine (used Hydrothermal-skarn Weathered granite
as the reference site in this study) situated in Inner Mongolia Placer
is said to supply half of the total production [19]. However,
this situation may change due to China’s introduction of Figure 1: World distribution of rare earths [26].
progressively reducing export quotas since 2004/2005 [5]
for reasons of environmental concerns and conservation of
resources [20]. This potential risk to supply may be somewhat
believed that such data will be valuable and provide a basis
absorbed by recycling of in-use stocks of REEs in products
for constructing and comparing GHG impact profiles of rare
(an estimated 440,000 metric tons in 2007, [21]). In fact, this
earth based products for comparison purposes.
source can also help to reduce the impact on the environment
from the production of virgin REEs.
Many environmental issues surround the production and 2. Extraction and Production of Rare Earths
use of REEs. REEs having similar chemical structures are
difficult to separate [22] compounded by extremely low 2.1. Sources and Distribution of Rare Earth Minerals. Only
yield (net recovery from the ore at Bayan Obo is around a few mineral species, such as bastnasite (a rare earth
0.6% [23, 24]). Thus, apart from the electricity, acids, water, fluorocarbonate (Ce, La)(CO3 )F), monazite (a rare earth
and resources expended in production, there can be huge phosphate (Ce, La, Y Th) PO4 )), xenotime (YPO4 ), and RE-
amounts of waste that can be toxic with potential damage to bearing clay have been recovered for commercial production.
the ecosystem. Of these, bastnasites constitute the largest percentage (in US
One of the most important environmental issues for and China). Monazite deposits in Australia, Brazil, China,
producers of rare earths is the problem posed by the radioac- India, Malaysia, South Africa, Sri Lanka, Thailand, and the
tivity of thorium-containing monazite and xenotime ores. United States constitute the second largest segment. World
Australian monazite exports declined precipitously between distribution is shown in Figure 1. Undiscovered resources are
1989 and 1992 in part because of the radioactivity concern and thought to be very large relative to expected demand [3].
since 1992, Rhodia, at that time the world’s largest rare earth Around 95% of the world’s rare earth metals are produced
company, has used Chinese instead of Australian rare earth in China, and as mentioned before Bayan Obo mine supplies
concentrates for production of individual rare earth oxides about half of the total production. This mine is estimated
[25]. to contain at least 1.5 billion metric tons of iron (average
Other concerns of RE pollution relate contamination of grade 33% of iron oxide), 89 million tons of RE oxides
the local environment. These include potential bioaccumula- (REOs) (average grade 6%), and 1 million tons of niobium
tion in the food chain from waste or dust contamination of (average grade 0.13%) [23]. The principal RE minerals in
water ways and soil from mines when used in downstream Bayan Obo are bastnasite and monazite accompanied by RE-
industrial processes and in agricultural fertilisers [27, 28]. Nb minerals; further details of the geological distribution
This study, with the exception of impact on the local are given in [23]. This study uses Bayan Obo operations
environment, investigates the global warming impact and as a representative system for rare earth extraction and
intensity of use of energy and resources in the production of production. Rare earth production at Mount Pass in USA
RE oxides (REOs) and REEs. Each of the distinct stages from ceased operation in 2002 due to environmental concerns
mining, separation of REOs, and reduction to REEs is mod- (production has recommenced since 2008). The projected
elled and the input of resources (energy, water, chemicals) production in 2012 is expected to be between 8,000 and 10,000
and wastes is examined. GHG impacts and resource depletion metric tons [29]. Mining at the Mount Weld deposit in West-
potential are computed from the derived data. ern Australia began in 2007, and an estimated 98,000 cubic
It is the objective of this study to disseminate knowledge meters of ore has been stockpiled awaiting the completion
of the GHG and other impacts of producing REEs, in of a concentration plant at the mine site. The concentrates
particular at this time when their application is growing will be exported to an advanced materials plant being built
and such knowledge is not readily available. Further, it is in Malaysia [30].
ISRN Metallurgy 3

Hematite (Fe)
Niobium ore (columbite)
Other

Stage 1
Iron ore mining and benefciation

- Energy
- Water
- Other services Bastnasite REO separation Monazite REO separation Stage 2a REO
- Natural Mineral “cracking” Mineral “cracking” separation
resources Impurity removal Impurity removal
REO separation REO separation

Emissions
LREOs MREOs HREOs Ce extraction

REO extraction REO extraction REO extraction Stage 2b REO

from LREOs from MREOs from HREOs separation

Separated REOs
Chemical Stage 3
production (acids,
solvents, etc.) REO reduction

REEs

Figure 2: System boundary: mining and production of RE metals in China.

REEs usually have very small differences in solubility 2.3. Stage 2: Purification and Separation of REO. The con-
and complex formation and hence their separation can be centrates of bastnasite and monazite (approximately 85%
difficult [22]. Thus, separation processes are often chemically concentration by weight within the slurry [24]) from min-
intensive using ion exchange methods, solvent extraction, ing and beneficiation separately undergo further process-
or fractional crystallization. The average recovery rate from ing (shown as Stage 2a in Figure 2). This stage purifies and
RE containing ores is extremely low at 10% [24]. This is separates the light, medium, and heavy oxide groups using
compounded by the low grade of REO in mined minerals at mineral cracking, acid leaching, impurity removal, and pre-
Bayan Obo (around 6% [23]). Thus, the net recovery is about cipitation. While Stage 2a processes are similar for both con-
0.6% and results in high resource inputs (electricity, acids, centrates, due to the substantial amount of radioactive ele-
water and resources expended in production) as well as huge ments in monazite (together thorium and uranium account
amounts of waste that can be toxic with potential damage to about 6.5% of monazite) and phosphorus (phosphorus oxide
the ecosystem. accounts about 28% of monazite), the monazite processing is
A representative system of extraction and production in more energy and chemical intensive than bastnasite.
Bayan Obo is shown in Figure 2. This representation is used The extraction of RE oxide groups from both bastnasite
as the system boundary for this LCA study and is explained and monazite produces cerium and separate streams of light,
briefly. medium, and heavy RE oxides. The separated streams are fur-
ther processed to produce the individual REOs. To extract the
individual REOs, the oxide groups are subject to multistage
2.2. Stage 1: Mining and Beneficiation. Bayan Obo mineral extraction process using extractants in acidic medium. LREO
Fe-REO-Nb deposit in China is the source of both iron- separation involves 22 stages: 8 for extraction, 8 for scrubbing,
ore and RE containing minerals bastnasite and monazite. and 6 for stripping [33]. MREOs have 29 extraction stages
In separating the concentrates of bastnasite and monazite, and 44 scrubbing stages [34]. Currently heavy RE oxides
a combination of separation processes (after grinding) are are separated by using ion exchange process with reagent
used including wet-magnetic separation and froth floatation. impregnated resins [35].
Since mining and beneficiation are established technologies,
data is mostly based on our previous studies in mining and 2.4. Stage 3: Reduction of REEs. The industrial reduction
beneficiation [31, 32]. to REEs from light REOs (La, Nd) including mischmetal
4 ISRN Metallurgy

Table 1: Bayan Obo iron ore composition and relative economic value of coproducts.

Commodity Fraction in Bayan 𝑃𝑐 —Price per tone∗ , 𝐶𝑐 —Normalised 𝑋𝑐 —Share in

Obo deposit, % US$ fraction, % economic value, %
Iron ore (hematite) 33 120.35 84.33 2.87
RE oxides (RE𝑥 O𝑦 ) 6 215400.00 15.33 93.31
Niobium ore (columbite) 0.13 41000.00 0.33 3.82
Fluorite (CaF2 ) 2 — — 0
Thorium oxide (ThO2 ) 0.16 — — 0
Phosporus oxide (PO4 ) 0.86 — — 0
Rest 57.85 — — 0
∗
Prices are shown for the year 2009-2010. Prices estimated for iron ore [11], REO [12], and niobium ore [13].

(which are a mixture of light lanthanide metals) uses fused- (i.e., REEs from iron ore extraction) and their environmental
salt electrolysis (fused salt process is used when the reactivity impact as noted by [38]. It has also been suggested that
of the metal does not allow electrowinning from aqueous economic allocations may be suited for coproducts that vary
solutions). in prices [39] as is the case for REOs.
For MREEs and HREEs, metallothermic process using At Stage 1 iron ore mining (see Figure 2), three eco-
electrolysis from an aqueous solution or simple carbon based nomically significant commodities (coproducts) are mined:
pyrometallurgy is employed due to the high electropositive hematite (FeO), columbite (niobium ore), and REO bearing
nature of RE elements in these groups [36]. ore (i.e., bastnasite and monazite minerals). Mass-based allo-
Processes for disposing toxic and other waste from the cation uses the mass fractions of each product (see Table 1).
mining and processing are not considered in this study. Economic allocation among these ores is performed on
the basis of share of contribution of each product according to
(1), where 𝐶𝑐 , 𝑃𝑐 , and 𝑋𝑐 are, respectively, the mass fraction,
3. LCA Study Methodology and Assumptions price, and computed environmental share of commodity 𝑐.
The principal goal of this study is to investigate the cradle-to- Mass allocation uses 𝐶𝑐 as the basis. Share of allocation
gate energy use (assessed as electricity use, heating fuel use, for each of the mined coproducts is shown in Table 1. The
and total nonrenewable energy use), water use, and global mass fractions (𝐶𝑐 ) are adjusted (normalized) across the
warming impact of REEs produced in Bayan Obo, China. It is economically valuable ores (iron ore, REO, and niobium):
envisaged that the impact data of REEs created in this study 𝑃𝑐 ∗ 𝐶𝑐
could provide a basis for constructing and comparing impact 𝑋𝑐 = . (1)
profiles of rare earth based products. ∑𝑐 (𝑃𝑐 ∗ 𝐶𝑐 )
On defining the scope of this study, the system boundary
In Stages 2a and 2b, the plant produces a mixture of REOs
definition for ascertaining the impact is shown in Figure 2
as coproducts. This would require calculation of impact that
and is explained in Section 2.2. Other topics of scope such
can be assigned to each of the individual REOs. A combined
as allocation, data sources, and uncertainty treatment are
mass and economic allocation model similar to Stage 1 is
discussed below. Results of impact assessment are given in
developed and applied for this as described by the following
Section 4.
equations:
One aspect of scope that is given careful attention is
the allocation of impacts. Normally, extraction of REEs is 𝐶𝑖 = 𝑐𝑏 𝑏𝑖 + 𝑐𝑚 𝑚𝑖 , (2)
a multifunctional product system, meaning a number of
outputs as saleable products are produced at the different 𝑃𝑖 ∗ 𝐶𝑖
𝑋𝑖 = . (3)
stages of production. For instance, in Bayan Obo mining ∑𝑖 (𝑃𝑖 ∗ 𝐶𝑖 )
operation, hematite, niobium, and RE containing ores are
produced as saleable coproducts of mining. The separated RE In (2), the average mass composition (𝐶𝑖 , used for
containing ore is then processed into saleable REOs or can be mass-based allocation) of REO𝑖 is determined using itsmass
further reduced to produce individual REEs. Thus, properly composition in bastnasite (𝑏𝑖 ) and monazite (𝑚𝑖 ) weighted
allocating from “cradle to gate” (i.e., from mining to when according to the ratio of bastnasite (𝑐𝑏 ) and monazite (𝑐𝑚 )
REOs or reduced REEs are sold) is important. processed. The proportion of bastnasite and monazite in
Allocation among the coproducts uses both mass frac- Bayan Obo mineral deposit is taken as 3 : 1, respectively, with
tions (i.e., physical relationship) as well as an economic each containing 60% of RE oxides [40].
model. In fact, while mass-based allocation is sufficient as Equation (3) computes the share of the environmental
recommended by ISO 14044 [37], an additional economic burden (𝑋𝑖 ) using price per kg (𝑃𝑖 ) of REO𝑖 as the weighting
model that combines mass and price basis (market value) factor normalised over all REOs. This way, both mass and
is proposed here. This model reflects the underlying causal- economic proportions are combined to derive the final
ity between economic reasons for producing coproducts allocation given to each REO.
ISRN Metallurgy 5

Table 2: Share of environmental impact allocated for REOs.

REE REO 𝑖 𝑏𝑖 , % 𝑚𝑖 , % 𝐶𝑖 , % 𝑃𝑖 , US$/kg 𝑋𝑖 , %

Lanthanum La2 O3 La 23.00 23.00 23.00 13.00 7.75
Cerium CeO2 Ce 50.00 46.00 49.00 12.00 15.24
Praseodymium (+3) Pr6 O11 Pr 6.20 5.00 5.90 95.00 14.53
Neodymium Nd2 O3 Nd 18.50 19.00 18.63 77.00 37.18
Promethium Pm2 O3 Pm — — 0.00 0.00 0.00
Samarium Sm2 O3 Sm 0.80 3.00 1.35 23.50 0.82
Europium Eu2 O3 Eu 0.20 0.10 0.18 2150.00 9.75
Gadolinium Gd2 O3 Gd 0.70 1.70 0.95 75.00 1.85
Terbium Tb4 O7 Tb 0.10 0.16 0.12 1750.00 5.22
Dysprosium Dy2 O3 Dy 0.10 0.50 0.20 975.00 5.05
Holmium Ho2 O3 Ho 0.00 0.00 0.00 — 0.00
Erbium Er2 O3 Er 0.00 0.13 0.03 77.00 0.06
Thulium Tm2 O3 Tm 0.00 0.00 0.00 — 0.00
Ytterbium Yb2 O3 Yb 0.00 0.06 0.02 69.12 0.03
Lutetium Lu2 O3 Lu — — 0.00 — 0.00
Scandium Sc2 O3 Sc — 0.04 0.01 7200.00 1.87
Yttrium Y2 O3 Y 0.00 2.00 0.50 50.00 0.65
References used: 𝑏𝑖 —[14]; 𝑚𝑖 —[1], Sc2 O3 —[15]; 𝑃𝑖 —[16], Sm2 O3 , Yb2 O3 —[17].

The values of pertinent parameters in (2) and (3) used in In deriving the allocation for each REE, the impact
calculating the share of the environmental burden assigned of REO-REE reduction stage is first assigned on a mass
to the REOs are given in Table 2. References used appear as basis, that is, the mass fraction of individual REE present
notes in the table. The following REOs are not considered. in the corresponding RE oxide. “Cradle to gate” impact per
Tm and Ho are least abundant and are found with other kilogram of individual REE is determined by adding the
rare earths such as gadolinite and other minerals containing impact of corresponding REO and this stage.
rare earths, and Lu is the rarest of the rare earths [41]. Due to Inventory data for the processes is obtained from publicly
data availability, these are not considered here. available information sources (cited appropriately under each
Pm is the only radioactive rare-earth metal of transition section) and by estimation. These include review of techno-
Group IIIb of the periodic table and not detected in nature logical processes for RE production and analogous processes,
[42]. It has a low period of half decay and its main route of environmental data pertaining to materials and chemicals
production is artificial synthesis. mainly from EcoInvent life cycle inventory (LCI) database
In Stage 3 REO-REE reduction, the mass fraction of [43], and other LCI databases combined with modeling and
individual REE present in the corresponding RE oxide is used estimation. Table 3 provides the basic data for energy and
for allocation. water use at each stage from mining to REO extraction. The
The manner in which the above methods are used to diverse sources of data require uncertainty analysis, such as
calculate the impact allocated to REO or REE products, Pedigree Matrix [44] combined with Monte Carlo simulation
covering mining to production life cycle stages, is described available in SimaPro software [45]. However, such analysis
below. will be performed as a future extension of this study.
First, for the production of REO products, a reference The major assumptions of this study include the follow-
flow for producing 1 kg mixture of REO products is consid- ing.
ered at Stage 2. To obtain this, 166.7 kg of iron ore has to
be mined (using average REE grade of 6% in the ore and (a) Distance between mining pit and beneficiation plant
REO recovery rate of 10%). Impact of mining this (Stage 1) and beneficiation and REO separation plant are
is allocated among Fe, Nb, and RE containing concentrates assumed as 15 km and 30 km, respectively. REO
(i.e., bastnasite and monazite) as described. reduction and subsequent reduction to REE occur at
For Stage 2a (separation of REO groups), share of allo- the same place, that is, Bayan Obo Township.
cation derived for each REO is used (Table 2). In the case of
Stage 2b (separation of REOs from REO groups), the same (b) In separating REOs from monazite concentrates
model as used for Stage 2a is used, though it is normalized for radioactive wastes can occur. Treatment of such waste
the REOs for the oxides occurring within each group. Impact can pose additional environmental effects including
from mining to REO production is the sum of the Stages 1-2 toxicity and soil and ground water contamination.
for the fraction of REOs in the reference flow. Finally, the The treatment processes of such waste are considered
impact per kg of individual REO is calculated. out of scope.
6 ISRN Metallurgy

Table 3: Life cycle inventory and impact of production stages for the production of 1 kg of RE oxide.

Energy consumption, MJ Environmental impact

Stage Process Water consumption, kL
Resource
Electricity Heat energy GHG emissions,
depletion, MJ
kg CO2 eq.
surplus
Stage 1 Mining and 4.64 10.11 3.24 3.95 5.46
beneficiation
REO extraction 5.60 90.00 19.09
Stage 2a 10.5 13.9
from bastnasite
REO extraction 55.60 11.90 18.15 18.3 19.6
from monazite
Light REO 12.60 0 0.58 3.3 2.80
separation
Stage 2b
Medium REO 5.20 0 0.16 1.3 1.29
separation
Heavy REO 15.50 0 8.52 5.5 5.57
separation

(c) Average grid-mix of electricity in China is 75% from the absence of more objective indicators resource depletion
coal power stations and the rest is from hydro [31]. is used here.
Examining Table 3, one can see that energy consumption
(d) Purity range of REOs produced (to derive the life and GHG emissions for the REO extraction (Stage 2a) are
cycle inventory data) is 98.0%–99.9% associated with much more for monazite than bastnasite, due to the required
current production technology in China. additional separation of uranium, thorium, and phosphorous
(e) A steady-state process with a constant rate of materi- for the former. In Stage 2b, the impact is the highest for
als and energy flows is assumed. separation of HREOs due to ion exchange process used.
While solvent extraction process is used for both LREOs
(f) Chemical and other materials used in the processes and MREOs with the latter being more difficult, impact
are assumed to be imported from Europe and hence, from LREO extraction is higher due to the higher mass
the energy consumption for their production is contribution (1 kg mixed REOs contains about 96% LREOs).
mostly based on data taken from the European LCI Out of all the stages, Stage 2a (REO extraction, see Table 3)
databases ([43, 45]). has the most resource deletion of around 33.5 MJ surplus
Impact for each of the separated REOs from Stages
4. Environmental Impact 1 and 2 is computed using both mass- and price-based
allocation methods described in the previous section. Price-
The life cycle inventory (LCI) of energy (both electric- based allocation of impact per kilogram of each REO is shown
ity and heat) and water consumption and corresponding in Table 4.
global warming impact for mining and separating REOs Comparison of environmental impacts among the REOs
(i.e. stages 1 and 2 in Figure 2) to produce 1 kg of mixed REOs shows that LREOs (La-Nd) have lower impact than the rest
are shown in Table 3. Assignment of impacts among products of the REOs with La and Ce being minimal within the LREO
uses the allocation methods described already. The widely group. The impact for other REOs varies substantially and
used Eco-indicator 99 impact assessment methodology [46] cannot be attributed to their classification as MREOs and
is used in selecting and computing the appropriate environ- HREOs.
mental damage indicators. SimaPro software [45] is used in The impacts assigned to REOs are influenced by the
deriving the indicator scores. concentration and price; the lower the percentage concen-
Two indicators selected for this study are GHG for tration and the higher the price, the higher the share of
global warming potential and resource depletion. Resource impact per kg. Among the REOs, scandium oxide (Sc2 O3 )
depletion is defined in the Eco-indicator 99 methodology has the highest GHG impact at ∼6,332 kg of CO2 eq./kg
report [46]. It is measured in terms of surplus energy due to its very high price (USD 7,200 per kg) and very low
(MJ) required to obtain the same quality of resource as occurrence (0.01%). The next highest impact is for europium
they become depleted. The calculation of this indicator uses oxide (Eu2 O3 ) at ∼1,884 kg of CO2 eq./kg. Its concentration
geostatistical models to analyse the concentration of a mining is comparatively higher and price is lower than Sc2 O3 . Other
resource at a reference year followed by assumptions on notable high-impact REOs are terbium oxide (Tb4 O7 , ∼
future depletion rates. The somewhat arbitrary and limiting 1,539 kg of CO2 eq./kg) and dysprosium oxide (Dy2 O3 , ∼
nature of assumptions and calculation makes this indicator 857 kg of CO2 eq/kg).
useful only as a comparative measure (the methodology When mass-based allocation is used, a separated REO
report in [46] provides more information). Nevertheless, in carries the same impact assigned to an RE group. This is due
ISRN Metallurgy 7

Table 4: Life cycle inventory and impact for the production of 1 kg RE oxides using price-based allocation.

Energy consumption Environmental impact

RE oxide Classification Water consumption, kL
Resources
Electricity, MJ Heat, MJ GHG emissions,
depletion, MJ
kg CO2 eq.
surplus
La2 O3 Light 26.13 34.39 12.82 11.16 12.52
CeO2 Light 24.12 31.74 11.83 10.30 11.56
Pr6 O11 Light 190.97 251.28 93.69 81.53 91.52
Nd2 O3 Light 154.78 203.67 75.94 66.09 74.18
Pm2 O3 Medium 0.00 0.00 0.00 0.00 0.00
Sm2 O3 Medium 37.95 62.16 22.74 17.73 20.59
Eu2 O3 Medium 3472.18 5686.98 2080.32 1622.04 1883.96
Gd2 O3 Heavy 121.12 198.38 72.57 56.58 65.72
Tb4 O7 Heavy 2826.83 4628.93 1718.02 1325.42 1538.92
Dy2 O3 Heavy 1574.95 2578.98 957.18 738.45 857.40
Ho2 O3 Heavy 0.00 0.00 0.00 0.00 0.00
Er2 O3 Heavy 124.38 203.67 75.59 58.32 67.71
Tm2 O3 Heavy 0.00 0.00 0.00 0.00 0.00
Yb2 O3 Heavy 111.65 182.83 67.86 52.35 60.78
Lu2 O3 Heavy 0.00 0.00 0.00 0.00 0.00
Sc2 O3 Heavy 11630.4 19044.8 7068.42 5453.15 6331.55
Y2 O3 Heavy 80.77 132.26 49.09 37.87 43.97

Table 5: Life cycle inventory and impact for the production of 1 kg RE oxides using mass-based allocation.

Energy consumption Environmental impact

Classification Water consumption, kL
Resources
Electricity, MJ Heat, MJ GHG emissions, kg
depletion, MJ
CO2 eq.
surplus
Light REOs 74.08 102.51 38.06 32.29 36.50
Medium REOs 66.68 102.51 37.64 30.29 34.99
Heavy REOs 76.98 102.51 37.64 34.49 39.27

to the allocation being normalized by group and derived on GHG of separated REOs
2000.00
a per kg basis. Table 5 shows the mass-based impact by RE
group. Here, the values in the table are affected by Stage 2b,
Kg CO2− e/kg of REO

which is particular to the groups. Hence, MREOs, being lower 1500.00

than others, have lower inventory and impact values.
A comparative GHG profile of REOs with allocations 1000.00
based on price and mass is shown in Figure 3. As noted, GHG
allocation using mass-based allocation is the same for REOs
500.00
in the same group.
Separated REOs are further processed in a reduction stage
to extract the individual REEs. This study assumes that the 0.00
CeO2
Pr6 O11
Nd2 O3
Pm2 O3
Sm2 O3
Eu2 O3
Gd2 O3
Tb4 O7
Dy2 O3
Ho2 O3
Er2 O3
Tm2 O3
Yb2 O3
Lu2 O3
Sc2 O3
Y2 O3
La2 O3

reduction plants are located in Bayan Obo and no or minimal

transport takes place. An average impact is calculated for
electrolytic process (for LREEs) and metallothermic process REOs
(HREEs and MREEs) based on [47] and [48], respectively. Price-based allocation
Thus, the impact calculated for this stage alone is affected by Mass-based allocation
the process yield of 80% for LREEs and 95% for other REEs;
Figure 3: Comparative GHG of rare earth oxides for mass- and
the impacts for reduction are, respectively, 5.64 and 5.04 kg
price-based allocations.
of CO2 eq./kg of REE.
8 ISRN Metallurgy

GHG impact of rare earth elements GHG impact of rare earth elements
Mass-based allocation Price-based allocation
70 3000

Kg CO2-e/kg of REE
Kg CO2-e/kg of REE

60 2500
50 2000
40
1500
30
20 1000
10 500
0 0
La
Ce
Pr
Nd
Pm
Sm
Eu
Gd
Tb

Ho
Er
Tm
Yb
Lu
Sc
Y
Dy

La
Ce
Pr
Nd
Pm
Sm
Eu
Gd
Tb

Ho
Er
Tm
Yb
Lu
Sc
Y
Dy
Mining and beneficiation:MB Mining and benefciation:PB
REO separation:MB REO separation:PB
RE reduction:MB RE reduction:PB
(a) (b)

Figure 4: Cradle-to-gate GHG emissions of rare earth elements.

5. Discussion In any case, the impact of individual REEs can vary with price
fluctuations.
GHG emissions from “cradle-to-gate” life cycle stages of pro- Comparison of the two allocation methods shows that
duction (i.e., mining, REO separation, and REE reduction) mass-based allocation is not sensitive to the scarcity of the
based on mass- and price-based allocation for extracting rare earth in the mineral (per kilogram basis). The suggested
1kg of individual REE are displayed in Figure 4. Mass- allocation based on combination mass, concentration, and
based approach allocates more emissions to more abundant price shows such sensitivity; for example, allocated GHG
elements, though when computed per kilogram of REE, emissions for low concentration REEs and those that are
the mass proportion becomes insensitive. Thus, the factor highly priced tend to be high.
that influences the comparative allocation is the energy and Further, Bayan Obo is unique as an iron ore mine that
materials expended (differs between RE groups) and the also produces rare earths, and though similar, Mountain Pass
extractable mass of REE from its oxide. This is apparent in does not produce iron ore or niobium. This means that in this
Figure 4(a) where Sc has the highest impact followed by Y. case only part of the total energy and environmental impacts
The extractable mass of REE from the 25 oxide for these two associated with mining stage is assigned to rare earths. While
is, respectively, 65% and 78% compared to others that are in the impact of this stage may be smaller than other stages, this
the range of 81%–85%. peculiarity of the model has to be recognised.
Unlike mass-based allocation, price-based allocation
model proposed here uses both mass concentrations in
mineral and price. The comparative impacts allocated are
hence influenced by: (1) energy and materials consumed at 6. Conclusion
each stage; (2) extractable mass of REE in the minerals,
that is concentrations in bastnasite and monazite and mass This study has in some detail investigated the cradle-to-gate
proportion in the respective oxides; and (3) price used in GHG impact of a rather complex route of producing REEs
calculating the share of environmental burden to be allocated. starting from extraction of rare earth minerals, separation of
In this model, scandium, europium, terbium, and dys- oxides, and final reduction of REEs.
prosium have relatively very high impact (Figure 4(b)). Both mass- and price-based allocation models have been
The corresponding REOs of these are high too for reasons employed in estimating the impact. The former is only sen-
cited in the last section. In reducing them to REEs, a sitive to the extractable mass concentrations, whereas price
further increase in the case of scandium occurs due to its based allocation model proposed in this study is additionally
lower extractable mass from its oxide of ∼65% compared sensitive to price. Thus, where the price of coproducts of
to ∼86% for europium, ∼85% for terbium, and ∼87% for product systems varies widely as in the case of rare earths, it
dysprosium. Thus, to produce 1 kg of Sc would require 30% tends to amplify the impact of highly priced rare earths that
more Sc2 O3 than other oxides. Additionally, Sc2 O3 , Tb4 O7, have lower concentrations. This information can be useful in
and Dy2 O3 are HREOs, the separation of which requires focussing efforts to improve process efficiency and recycling
more energy. Economic allocation is influenced by price to increase supply.
fluctuations. While the prices of REOs have been volatile Recycling is an attractive pathway given the increasing
dropping as much as 40%–60% in 2011-12 [16], neverthe- prices of rare earths (while 2011-12 prices were down, they are
less, the comparative prices of the above four high impact generally higher than 2010 prices) combined with the recent
REOs have been consistently higher than other REOs. Thus, clamp down on exports by China. The route to recycling
they remain the high impact rare earths relative to others. can be closed-loop, meaning the recovery of the original
ISRN Metallurgy 9

RE alloys with minimum loss of property for similar appli- Curtin Graduate School of Business; Curtin University &
cations. Such direct recycling, however, has its challenges Industrial Minerals Company of Australia Pty Ltd, Western,
in collecting, sorting, separating components, and finding Australia, June 2013.
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