Rare Earth Elements: A Review of Production, Processing ...

Rare Earth Elements Review Section 2 – Introduction to Rare Earth Elements
2. Introduction to Rare Earth Elements
For the purposes of this report, the series of 15 lanthanide metals, plus scandium and yttrium, have been
designated as REEs; however, it should be noted that other elements also are sometimes referred to as REEs.
Rare earth oxides (REOs), and rare earth metals (REMs). While these elements are widely dispersed and
generally common in nature, minable concentrations of REEs are less common than for most other metal ores.
Rare earths have become important in modern commercial and industrial processing and products. Metallurgical
processing, alloying, and electronics applications (e.g., cell phones, computer components, electric motors,
specialty glass and lenses) represent the most significant uses of REEs. In addition, due to the dependence on
several of these elements for military applications, REEs are considered a national strategic resource. Analysis of
the future supply and demand for each of the REEs indicates that, by 2014, global demand could exceed 200,000
tons per year, which would exceed current production by over 75,000 tons per year. It is reported that if the new
mines under development are able to meet their projected production levels, world-wide demand for REEs will be
met from these new sources.
The International Union of Pure and Applied Chemistry, an organization devoted to maintaining
international consistency for chemical nomenclature, has identified the15 transition metals from the
periodic table of the elements with atomic numbers 57 (lanthanum) through 71 (lutetium) as lanthanides
or lanthanoids. These 15 elements share common physiochemical properties and are listed below:
� Lanthanum (57La) � Samarium (62Sm) � Holmium (67Ho)
� Cerium (58Ce) � Europium (63Eu) � Erbium (68Er)
� Praseodymium (59Pr) � Gadolinium (64Gd) � Thulium (69Tm)
� Neodymium (60Nd) � Terbium (65Tb) � Ytterbium (70Yb)
� Promethium (61Pm) � Dysprosium (66Dy) � Lutetium (71Lu).
Due to their similar physiochemistry, these lanthanides often occur together as elemental constituents of
their host minerals. Two other metals commonly found in association with lanthanides in the same
mineral assemblages are the following:
� Scandium (21Sc)
� Yttrium (39Y).
These two metals also have physiochemical characteristics that are very similar to the lanthanides.
2.1 Abundance of REEs in Earth’s Crust
Together, the lanthanides, yttrium, and scandium are commonly referred to as REEs or REMs, although
this is a misnomer since most of the REEs are common mineral constituents as compared with other metal
elements. The term “rare” is a carryover from metallurgical chemists from around the 1940s (Gupta and
Krishnamurthy, 2004). The metallurgical processes needed to isolate the individual metal species are
complex, and early technology prevented commodity-level production. As a result, lanthanide metals or
metal oxides (i.e., REOs) were difficult to obtain and thus are considered rare. The abundance of REEs in
the earth’s crust relative to other common metals is presented in Table 2-1; these abundances from
Wedephol (1995) are only one of several interpretations, but those presented here are generally
representative. As shown in the comparison, the content of lanthanides relative to other REEs in rockforming
minerals is not rare at all.
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