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| Global production of rare earth oxides. Credit: ACS, Du and Graedel. Click to enlarge. |
A team at Yale has used published and unpublished information from China, Japan, the United
States, and elsewhere to estimate global flows into use and in-use stocks for 15 rare earth elements (REE): La (Lanthanum); Ce (Cerium); Pr (Praseodymium); Nd (Neodymium); Sm (Samarium); Eu (Europium); Gd (Gadolinium); Tb (Terbium); Dy (Dysprosium); Ho (Holmium); Er (Erbium); Tm (Thulium); Yb (Ytterbium); Lu (Lutetium); and Y (Yttrium).
In a paper published in the ACS journal Environmental Science & Technology, they show that the combined flows into use constituted about 90 Gg (90,000 tonnes) in
2007; the highest for individual metals were ~28 Gg Ce and ~22 Gg La, the
lowest were ~0.16 Gg Tm and ~0.15 Gg Lu. In-use stocks ranged from
144 Gg Ce to 0.2 Gg Tm and summed to 448 Gg total.
The authors, Xiaoyue Du and T. E. Graedel, found that Nd is the second largest in-use stock at 137 Gg. Together, Ce and ND stocks constituted nearly 63% of the total. They also found that 86 Gg La and 50 Gg Pr reside in stocks, as do 8.6 Gg Dy, 6.9 Gg Y, 3.6 Gg Gd, 3.3 Gg Sm, 0.7 Gg
Tb, and 0.4 Gg Eu. These stocks, if efficiently recycled, could provide a
valuable supplement to geological stocks, suggested the authors.
Because of their unique physical and
chemical properties, [rare earth elements] are used in a growing number of
applications and have become indispensible for a number of
critical technologies. For example, scandium is a currently
unmatched ingredient in solid oxide fuel cells and aluminum
alloys, neodymium is vital to high-performance permanent
magnets, and yttrium is a promising raw material for superconductors
and laser technology.
When these intermediate
products are incorporated in final products such as wind
turbines, hybrid electric vehicles, or defense applications, the
rare earths provide performance that is currently irreplaceable
by alternative materials. These and other technical innovations
will strongly influence future demand for rare earths.—Du and Graedel
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| Rare earth in-use stocks in principle applications, by element. Credit: ACS, Du and Graedel. Click to enlarge. |
Automobile catalytic converters and metallurgical uses constituted 50 Gg and
45 Gg of Ce in-use stocks, about 30% each of the total. 26 Gg Ce is stored in
glass additives. Both the nickel hydride battery and polishing
powder stocks of Ce were 9 Gg.
Among the findings of their study:
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The overall amount of REE use has increased from about 80 Gg
of in 1995 to about 120 Gg in 2007 (expressed as rare earth
oxides). For some of the less abundant REE, however (Sm, Gd,
Dy, Er, Yb) the use has at least tripled during that interval, a result
that emphasizes that, whereas REE can often be treated as a
group so far as geology is concerned, their employment in modern technology very much depends on the chemical and physical properties of the individual elements. -
In-use stocks of the REE totaled around 440 Gg in 2007, with
most of the stock in four elements: La, Ce, Nd, and Pr. That stock
is some four times the 2007 annual extraction rate, which suggests
that REE recycling may have the potential to offset a
significant part of REE virgin extraction in the future, they said. -
Recycling REE, although challenging, appears possible for metallurgical applications, automobile catalysts, and magnets in wind turbines and automobiles,
where REE are used in fairly large quantities. These applications mostly utilize the “big four” REE: La, Ce, Nd, and Pr. The recycling potential for other REE, which are
used in small but carefully selected amounts in imaging, displays,
defense, and similar applications, appears to be quite low. -
With China currently dominating the mining and processing of virgin REE ores, corporations and governments seeking to minimize supply risk in the next few
years do not have many promising options. One is to
encourage reuse and recycling of REE as the products containing
them are discarded. -
Over the longer term, the likely opening of REE mining in Mountain Pass in the US
and Mount Weld in Australia in the next few years will eventually
provide a more geographically dispersed extraction picture. -
As long as rates of use continue to increase, REE
availability, especially for the less abundant REE, will continue to
be a challenge.
Resources
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Xiaoyue Du, T. E. Graedel (2011) Global In-Use Stocks of the Rare Earth Elements: A First Estimate. Environmental Science & Technology. doi: 10.1021/es102836s