The purpose of this research is to provide an investigation into identification of rare earth elements in some selected coal and ash samples. The scope of the work will include samples collected from commercial coal deposits and a few samples (dependent upon availability) from areas not yet engaged in commercial mining. In addition, some ash samples from different sources in Alaska will also be examined. Moreover, for one or two to samples from the above-mentioned sources (samples that may have near-term commercial potential), size and density effects on thepartition of REE elements will be examined by conducting screen analysis and floatsink
tests on selected size fractions.
Global concerns surrounding stable access to mineral supplies have led many countries to re-assess indigenous resources, particularly of the ‘critical’ metals (so labeled because of their growing economic importance and the higher risk of supply shortage). In addition to improving knowledge of primary mineral deposits, the potential for resource recovery from waste materials is attracting considerable attention.
Uses of Rare-Earth Elements (REEs)
Rare-earth elements, metals, and alloys that contain them are used in common consumer goods such as computer memory, DVDs, rechargeable batteries, cell phones, vehicle catalytic converters, magnets, fluorescent lighting, and much more.in these goods has surged over the past two decades. Many rechargeable batteries are made with rare-earth compounds. Rechargeable lanthanum–nickel–hydride (La–Ni–H) batteries are gradually replacing nickel– cadmium (Ni–Cd) batteries in computer and communications applications and could eventually replace lead–acid batteries in automobiles (1). Several pounds of rare-earth compounds are required for batteries that power electric vehicles and hybrid-electric vehicles. Rare-earth compounds are also used for powerful magnets in a wide range of products, from computer hard drives to wind turbines. As concerns for energy independence, climate change, and other issues impact the sale of electric vehicles and “green” energy systems like wind turbines and solar power panels, the demand for batteries made with rare-earth compounds is expected to increase dramatically. Rare earths are used as catalysts, phosphors, and polishing compounds. These are used in areas such as for air pollution control, illuminated screens on electronic devices, and optical-quality glass. Demand for all of these products is expected to rise. Rare-earth elements play an essential role in modern national defense. Night-vision goggles, precision-guided weapons, and other defense technology rely on various rare-earth metals. Rare-earth metals are key ingredients for radar systems, avionics, and satellites. (2-5)
Rare Earth Elements
REE’s are divided into two major groups as follows, and coal can be a source for both groups. LREE, light rare earth elements: Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, and Gd; also known as the cerium group. HREE, heavy rare earth elements: Y, Tb, Dy, Ho, Er, Tm, Yb, and Lu; also known as the yttrium group) (6,7) However, the densities of the LREEs (as pure elements) range from 2.989 (scandium) to 7.9 g/cc (gadolinium), while those of the HREEs are from 8.2 to 9.8, except for yttrium (4.47) and ytterbium (6.9-7). The distinction between the groups is more to do with atomic volume and geological behavior.
REE in Coal
Recent research indicates that some coals are significantly enriched with certain critical metals (8). Moreover, coals with high REE concentrations were recently discovered in Far Eastern areas, such as Kuznetsky, and some other Russian coal basins. These coals are now being actively studied as a new source of REE (9,10). A recent study from China looked at how different trace elements (including numerous REEs) partition in various size fractions of Antaibao coal from China. It is clear that the REEs, phosphorous, and thorium all have their high concentrations in the particle sizes 0.5 to 3 mm, and 6 to 25 mm. This suggests that REEs are often present as a phosphate such as monazite (11,12). In the US, Ekmann (12) in a REE prospectivity analysis, identified four regions as the Central Appalachian Basin (CentAPP), the Southern Appalachian Basin (SoAPP), the San Juan Basin (RckyMtn4Crnrs), and the Powder River Basin (PRB) by using the USGS COALQUAL database. He reported that REE contents were 930 ppm for RckyMtn4Crnrs, 950 ppm for CentAPP, 953 ppm for PRB, and 966 ppm for SoAPP. In general it was found that monazite was the most likely mineral form in which to find rare earths in coal formations. Cerium correlates well with the total amount of ash and with non-REE elements such as chromium (Cr), scandium (Sc), hafnium (Hf), lithium (Li), tantalum (Ta), vanadium (V) and lead (Pb). The rare earth element, Dysprosium, also correlated well to the presence of other rare earth elements, to the total ash, and to ash related elements such as lithium (Li), thorium (Th), vanadium (V), zirconium (Zr), chromium (Cr) and lead (Pb) (12,13).
