Enrichment of rare earth elements from coal and coal by-products by physical separations

Abstract

Rare earth elements (REE) are of strategic importance because they find numerous applications in various sectors of the global economy.The concern about the REE supply challenge has led to increasing interest and research in the recovery of REE from end-of-life products and secondary sources such as coal and coal by-products. The work reported here was focused on examining the technical feasibility of physical separation techniques for the enrichment of REE from coal and coal by-products. Particle size, magnetic and density separations were performed on coal, coal ash, clay and shale samples. It was found that the samples responded to particle size separation differently. For all ash samples, higher REE concentrations were found in the finer fractions. For the clay and shalesamples, however, the REE concentrations decrease as the particle size reduces possibly because RE minerals were not effectively released by grinding. Magnetic separation showed that REE are enriched in non-magnetic fractions for all ash samples. All samples responded similarly to density separation. Among the three methods, density separation showed the highest enrichment of REE. A combination of these methods is recommended. Finally, correlations between elements were demonstrated, which leads to the classification of three groups containing mainly Al/Si, Fe and Ca, respectively. REE are strongly associated with the Al/Si group.

Differences in bulk and microscale yttrium speciation in coal combustion fly ash

“…2 and 3), consistent with previous studies. 21,23,28 Quartz was easily identied in all three ash samples. Mullite was also found in all three ashes, but at low concentration in the Powder River Basin ash sample.…”

“…Previous research has determined that extractions should target the abundant glass phase where REE are hosted. 7,9,28,29 While the use of oxalic acid instead…”

“…9,24 Previous studies have shown several modes of occurrence for the REE that include forms evenly distributed throughout the glassy matrix of the y ash as well as discreet mineral phases within the ash matrix. 23,[25][26][27][28] For example, one study utilized electron microprobe wavelength dispersive elemental mapping to show that cerium (measured as a proxy for all REE) was dispersed throughout the glassy matrix of the y ash particles. 26 More recent microscopy studies indicated that some REE trace phases from the coal such as monazite crystals may persist in the ash but are fragmented due to thermal shock.…”

Mesoporous SiO2 Nanoparticles: A Unique Platform Enabling Sensitive Detection of Rare Earth Ions with Smartphone Camera

“…However, the market supply is not sufficient because of the limited conservation, poorly developed extraction techniques, and export restrictions [7]. Therefore, exploring new resources of the valuable rare earth elements represents an urgent research direction [8–16]. The recent efforts include the search and extraction of rare earth metals from waste streams, coals, and industrial residues [8, 10, 16–19].…”

“…Therefore, exploring new resources of the valuable rare earth elements represents an urgent research direction [8–16]. The recent efforts include the search and extraction of rare earth metals from waste streams, coals, and industrial residues [8, 10, 16–19]. Sensitive detection of the low-concentration rare earth elements in these resources is crucial for precisely evaluating the economic value of various resources.…”