Rare earth elements in select Main Karoo Basin (South Africa) coal and coal ash samples

Internationally, the demand for a variety of rare earth elements (REY/REY + Sc) (i.e. Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) for use in modern electronic and related components is increasing. This demand has led to a need to expand extraction from alternative sources, such as coal and combustion ash. South Africa has extensive coal resources and generates a significant amount of coal ash. The aim of the study is to determine the levels of REY + Sc in three South African power station feed coals and their associated ash products (eight samples), with a consideration of the viability of commercial extraction of REY + Sc from these materials. The coal and ash samples were analysed using a variety of routine and advanced techniques, including petrography, Malvern particle size analysis, X-ray diffraction (XRD), inductively coupled plasma-mass spectrometry (ICP-MS), and instrumental neutron activation analysis (INAA). Total REY concentrations ranged from 95 to 149 ppm in the coal samples, and H- and M-type REY enrichment types were determined. Total REY concentrations ranged from 402 to 599 ppm in the ash samples, far higher than the average upper crustal values, and higher than global average hard coal ash values, but lower than REY-rich coal ashes recorded for various deposits globally. The INAA data are comparable to the ICP-MS data for most elements considered, and Sc was determined. Further investigations are required to confirm the potential of the Main Karoo Basin coal ash for economically viable REY extraction.