October AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | O C T O B E R 2 0 1 8 2 6 EXTRACTING RARE EARTH ELEMENTS FROM COAL-BASED MATERIALS Rising concern among industrialized nations has driven a resurgence of global interest in rare earth element mineral exploration and extraction as well as related research on supply, demand, utilization, recycling, reuse, and substitution. Mary Anne Alvin, National Energy Technology Laboratory, Pittsburgh R are earth elements (REEs) are es- sential materials (Fig. 1) in a broad range of technologies significant to national security, energy, medical, and consumer products (Fig. 2). REEs occur throughout the earth’s crust, common- ly at low concentrations. They are not found in an isolated form readily avail- able for extraction, but are distribut- ed throughout a variety of minerals and are also found in coal and coal by-prod- ucts. REE-bearing mineral deposits are relatively rich in either light rare earth elements (LREEs) or heavy rare earth el- ements (HREEs), with LREEs being more abundant. The environmental footprint created by conventional REE processing techniques has long been a key consider- ation in determining where REEs can be mined and where the product elements are to be extracted. China has been the dominant supplier of REEs since 1988, providing 95% of the global REE market in 2011 (Fig. 3). As recently as 2011, decisions by China to restrict exports and favor its own domestic industries resulted in REE price volatility. Consequent- ly, rising concern among industrial- ized nations has driven a resurgence of global interest in REE mineral ex- ploration and extraction and related research on supply, demand, utiliza- tion, recycling, reuse, and substitution. Several new commercial REE proj- ects in various stages of planning and development are focused on diver- sifying supply, although new efforts to purify and refine REEs remain limited. Fig. 1 — Lanthanide series of rare earth elements including scandium and yttrium.