RARE EARTHS METALS
Classification of Rare Earths
The classification of the rare earth elements is as hotly disputed as the list of included metals. One common method of classification is by atomic weight. Low atomic weight elements are the light rare earth elements (LREEs). Elements with high atomic weight are the heavy rare earth elements (HREEs). Elements that fall between the two extremes are the middle rare earth elements (MREEs). One popular system categorizes atomic numbers up to 61 as LREEs and those higher than 62 as HREEs (with the middle range absent or up to interpretation).
Critical Rare Earths
What are “Critical Rare Earths”?
According to Dr. Alex King, U.S. Department of Energy, Ames Lab Director, critical refers to “the stuff you need the most but can’t get enough of.” In 2011, the US Department of Energy completed a study entitled, Critical Material Strategy. The study reviewed rare earths based on their role in clean energy as well as supply risk. They identified Neodymium (Nd), Europium (Eu), Terbium (Tb), Dysprosium (Dy) and Yttrium (Y) as critical rare earths (CREE) for both the short and long term. Rare Element includes Praseodymium (Pr) in this list because of its ability to be substituted for Neodymium in high-intensity permanent magnets.
The collapse of American rare earth mining — and lessons learned
Out in the Mojave Desert in California lies the Mountain Pass mine, once the world’s foremost supplier of valuable rare earth minerals — 17 elements deemed critical to modern society. In an age where China controls 80 percent of the global output of these minerals, it is strange to believe that a once-dominant source sits within the United States. Stranger still is the tale of how this mine came to supply the Chinese rare earths industry.
In 1952, Mountain Pass opened. First explored as a uranium deposit, it soon supplied rare earths for the electronic needs of the Cold War economy. Until the 1990s, it stood alone as the only major source of rare earths worldwide.
How Rare-Earth Mining Has Devastated China’s Environment
In general, the rare earths are used in alloys, for their special optical properties, and in electronics. Some specific uses of elements include:
Scandium: Use to make light alloys for the aerospace industry, as a radioactive tracer, and in lamps
Yttrium: Used in yttrium aluminum garnet (YAG) lasers, as a red phosphor, in superconductors, in fluorescent tubes, in LEDs, and as a cancer treatment
Lanthanum: Use to make high refractive index glass, camera lenses, and catalysts
Cerium: Use to impart a yellow color to glass, as a catalyst, as a polishing powder, and to make flints
Praseodymium: Used in lasers, arc lighting, magnets, flint steel, and as a glass colorant
Neodymium: Used to impart violet color to glass and ceramics, in lasers, magnets, capacitors, and electric motors
Promethium: Used in luminous paint and nuclear batteries
Samarium: Used in lasers, rare earth magnets, masers, nuclear reactor control rods
Europium: Used to prepare red and blue phosphors, in lasers, in fluorescent lamps, and as an NMR relaxant
Gadolinium: Used in lasers, x-ray tubes, computer memory, high refractive index glass, NMR relaxation, neutron capture, MRI contrast
Terbium: Use in green phosphors, magnets, lasers, fluorescent lamps, magnetostrictive alloys, and sonar systems
Dysprosium: Used in hard drive disks, magnetostrictive alloys, lasers, and magnets
Holmium: Use in lasers, magnets, and calibration of spectrophotometers
Erbium: Used in vanadium steel, infrared lasers, and fiber optics
Thulium: Used in lasers, metal halide lamps, and portable x-ray machines
Ytterbium: Used in infrared lasers, stainless steel, and nuclear medicine
Lutetium: Used in positron emission tomography (PET) scans, high refractive index glass, catalysts, and LEDs
The demand for rare earth elements has grown rapidly, but their occurrence in minable deposits is limited.
Article by: Hobart M. King, PhD, RPG
Rare Earth Element Production
Rare Earth Element Production: This chart shows a history of rare earth element production, in metric tons of rare earth oxide equivalent, between 1950 and 2018. It clearly shows the United States’ entry into the market in the mid-1960s when color television exploded demand. When China began selling rare earths at very low prices in the late 1980s and early 1990s, mines in the United States were forced to close because they could no longer make a profit.  When China cut exports in 2010, rare earth prices skyrocketed. That motivated new production in the United States, Australia, Russia, Thailand, Malaysia, and other countries.
Uses of rare earth elements: This chart shows the use of rare earth elements in the United States during 2017. Many vehicles use rare earth catalysts in their exhaust systems for air pollution control. A large number of alloys are made more durable by the addition of rare earth metals. Glass, granite, marble, and gemstones are often polished with cerium oxide powder. Many motors and generators contain magnets made with rare earth elements. Phosphors used in digital displays, monitors, and televisions are created with rare earth oxides. Most computer, cell phone, and electric vehicle batteries are made with rare earth metals.