Geochemistry and mineralogy of fly ash from the high-alumina coal, Datong Coalfield, Shanxi, China

Abstract

The abundance and distribution of minerals and elements in high-alumina coal fly ash (HACFA) is the basis for evaluating the resource utilization potential of HACFA and the key to developing a rare element extraction process. The geochemistry and mineralogy of HACFA were investigated by using alkali desilication and particle size screening, combined with multiple analytical techniques. As fly ash particles become finer, the content of mullite decreases, the content of quartz, corundum, and glass increases, and the content of hematite decreases first and then increases. The molecular structure of the glass phase is silicon-oxygen tetrahedron Q4(0Al). Minerals containing REE appear in the shape of fish eggs or oolitic particles, mainly composed of Ai, Si, REE, O. The maximum contents of Al, Li, Ga, and REE in HACFA are 67.65%, 240.57 μg/g, 77.97 μg/g, and 672.95 μg/g, showing a high utilization potential. However, the high contents of harmful elements Cd and Cr need special attention. Most of the trace elements in HACFA mainly reside in the glass phase. The iron-rich minerals are the main carriers of the ferrophilic elements Fe, Zn, Cr, Co, Mn, and Mg. The oxyphilic elements Al, Sc, Ta, Nb, and Ga mainly occur in corundum or mullite.