HardAssetsInvestor

Written by Tom Vulcan  |

November 04, 2008

Rare Earth Metals: Not So Rare, But Still Valuable

Details

Delving in to the economic viability of the world's REM opportunities ...

• What exactly are they?
• Specific applications
• Mining the demand

 

The rare earth metals are, in fact, not that rare!

The most commonly occurring rare earth metals - cerium, lanthanum, neodymium and yttrium - are actually more common in the Earth's crust than lead. And even silver.

While cerium, the most abundant rare earth metal, is more prevalent (60 parts per million (ppm)) than copper, even lutetium (0.5 ppm) and thulium (0.5 ppm), the least abundant, are to be found in the Earth's crust in greater quantities than antimony, bismuth, cadmium and thallium. (The outlier is promethium, which, it appears, is not to be found in the Earth's crust, and which is only used in compound form, of which, to date, some 30 have been prepared.)

 

Abundance of Elements In The Earth's Crust

 

Note: Abundance (atom fraction) of the chemical elements in Earth's upper continental crust as a function of atomic number.

Many of the elements are classified into (partially overlapping) categories: (1) rock-forming elements (major elements in green field and minor elements in light green field); (2) rare earth elements (lanthanides, La-Lu, and Y; labeled in blue); (3) major industrial metals (global production > ~3x107 kg/year; labeled in bold); (4) precious metals (italic); and (5) the nine rarest "metals" - the six platinum group elements plus Au, Re, and Te (a metalloid).

Source: USGS

 

So, why are they called the "rare earth" metals? Probably from the uncommon oxide-type minerals, or earths, from which they were originally extracted. The corollary to their abundance is, however, the fact that, to date, their "discovered minable concentrations are less common than for most other ores."

 

What Are The Rare Earth Metals?

The rare earth metals (aka, REM, rare earth elements (REE) or, sometimes, just rare earths) are a group of 15 chemically similar elements (grouped separately in the periodic table) known as lanthanides. Commercially, the rare earth grouping usually also includes scandium and yttrium, both of which are actually elements above lanthanum in the periodic table.

 

 

In more physical terms, these metals range in color from shiny silver to iron gray. As the USGS describes them, they "are typically soft, malleable, ductile and usually reactive, especially at elevated temperatures or when finely divided." At the lower end, cerium has a melting point of 798° C and, at the upper, lutetium has a melting point of 1,663° C.

It will come as no surprise that the unique properties (catalytic, chemical, electrical, metallurgical, nuclear, magnetic and optical) of the REM, and, in particular, both their specificity and versatility, have led to their being used for a wide variety of purposes.

From relative obscurity, they are now important economically, environmentally and technologically.

 

What Are They Used for?

The range of applications in which they are used is extraordinarily wide, from the everyday (automotive catalysts and petroleum cracking catalysts, flints for lighters, pigments for glass and ceramics and compounds for polishing glass) to the highly specialized (miniature nuclear batteries, lasers repeaters, superconductors and miniature magnets).

 

The Rare Earths And Some Of Their End Uses

Name	Symbol	Some End Uses
Cerium	Ce	Catalysts, Ceramics, Glasses, Misch Metal*, Phosphors and Polishing Powders
Dysprosium‡	Dy	Ceramics, Phosphors and Nuclear Applications
Erbium‡	Er	Ceramics, Glass Dyes, Optical Fibers, Lasers and Nuclear Applications
Europium‡	Eu	Phosphors
Gadolinium‡	Gd	Ceramics, Glasses, Optical and Magnetic Detection and Medical Image Visualization
Holmium‡	Ho	Ceramics, Lasers and Nuclear Applications
Lanthanum	La	Automotive Catalysts, Ceramics, Glasses, Phosphors and Pigments
Lutetium‡	Lu	Single Crystal Scintillators
Neodymium	Nd	Catalysts, IR Filters, Lasers, Permanent Magnets and Pigments
Praseodymium	Pr	Ceramics, Glasses and Pigments
Promethium	Pm	Phosphors and Miniature Nuclear Batteries and Measuring Devices
Samarium	Sm	Microwave Filters, Nuclear Applications and Permanent Magnets
Scandium	Sc	Aerospace, Baseball Bats, Nuclear Applications, Lighting and Semiconductors
Terbium‡	Tb	Phosphors
Thulium‡	Tm	Electron Beam Tubes and Medical Image Visualization
Ytterbium‡	Yb	Chemical Industry and Metallurgy
Yttrium‡	Y	Capacitors, Phosphors (CRT and Lamp), Radars and Superconductors

Groups: yttrium and lanthanide (Scandium falls into neither category)

^‡ Heavy REM

* Misch Metal is an alloy of rare earth metals used not only for lighter flints, but also, probably more importantly, in purifying steel by removing oxygen and sulfur.

Separately, or as compounds, various rare earth metals are used also in the production of superalloys.