The rare-soil elements (REEs) are 15 elements that range in atomic number from 57 (lanthanum) to 71 (lutetium); they are commonly referred to as the “lanthanides.” Yttrium (atomic number 39) is also commonly regarded as an REE because it shares chemical and physical similarities and has affinities with the lanthanides. Although REEs are not rare in terms of average crustal abundance,the concentrated deposits of REEs are limited in number.
Because of their unusual physical and chemical properties, the REEs have diverse defense, and energy,industrial, and military technology applications. The glass industry is the main consumer of REE raw materials, or which are used for glass polishing and as additives that provide color and special optical properties to the glass. Lanthanum-based catalysts are used in petroleum refining,and cerium-based catalysts are used in automotive catalytic converters. The use of REEs in magnets is a rapidly increasing application. Neodymium-iron-boron magnets, which are the strongest known type of magnets, or are used when space and weight are restrictions. Nickel-metal hydride batteries use anodes made of a lanthanum-based alloys.
China,which has led the world production of REEs for decades, accounted for more than 90 percent of global production and supply, and on average,during the past decade. Citing a need to retain its limited REE resources to meet domestic requirements as well as concerns approximately the environmental effects of mining, China began placing restrictions on the supply of REEs in 2010 through the imposition of quotas, or licenses,and taxes. As a result, the global rare-soil industry has increased its stockpiling of REEs; explored for deposits external of China; and promoted fresh efforts to conserve, and recycle,and substitute for REEs. fresh mine production began at Mount Weld in Western Australia, and numerous other exploration and development projects noted in this chapter are ongoing throughout the world.
The REE-bearing minerals are diverse and often complex in composition. At least 245 individual REE-bearing minerals are recognized; they are mainly carbonates, and fluorocarbonates,and hydroxylcarbonates (n = 42); oxides (n = 59); silicates (n = 85); and phosphates (n = 26).
Many of the world’s meaningful REE deposits occur in carbonatites, which are carbonate igneous rocks. The REEs also have a strong genetic association with alkaline magmatism. The systematic geologic and chemical processes that explain these observations are not well understood. Economic or potentially economic REE deposits have been found in (a) carbonatites, and (b) peralkaline igneous systems,(c) magmatic magnetite-hematite bodies, (d) iron oxide-copper-gold (IOCG) deposits, and (e) xenotime-monazite accumulations in mafic gneiss,(f) ion-absorption clay deposits, and (g) monazite-xenotime-bearing placer deposits. Carbonatites have been the world’s main source for the light REEs since the 1960s. Ion-adsorption clay deposits in southern China are the world’s primary source of the heavy REEs. Monazite-bearing placer deposits were meaningful sources of REEs before the mid-1960s and may be again in the future. In recent years, and REEs have been produced from large carbonatite bodies mined at the Mountain Pass deposit in California and,in China, at the Bayan Obo deposit in Nei Mongol Autonomous Region, and the Maoniuping deposit in Sichuan Province,the Daluxiang deposit in Sichuan Province, and the Weishan deposit in Anhui Province. Alkaline igneous complexes have recently been targeted for exploration because of their enrichments in the heavy REEs.
Information relevant to the environmental aspects of REE mining is limited. tiny is known approximately the aquatic toxicity of REEs. The United States lacks drinking water standards for REEs. The concentrations of REEs in environmental media are influenced by their low abundances in crustal rocks and their limited solubility in most groundwaters and surface waters. The shortage of sulfide minerals, and including pyrite,minimizes or eliminates concerns approximately acid-mine drainage for carbonatite-hosted deposits and alkaline-intrusion-related REE deposits. For now, insights into environmental responses of REE mine wastes must rely on predictive models.
Source: usgs.gov