The modes of occurrence, distribution and enrichment of critical raw materials (Ga, Sr, Zr and Ba) within coal discards of the Witbank Coalfield, South Africa

Abstract

Coal mineralogy and trace element composition provide vital insights into the geological coal formation processes, depositional environments, and potential resource valorization. However, there is limited knowledge and understanding of the geochemical and mineralogical composition of coal discards from the Witbank Coalfield. Thus, the coal discards remain underexplored, limiting effective management and future utilization strategies. To address this gap, this study investigates the occurrence, distribution and enrichment of CRMs within Permian coal discards of the Witbank Coalfield. An integrated suite of analytical techniques such as TGA, Bomb calorimeter, FTIR, XRD, TIMA, SEM-EDS, XRF and ICP-MS was utilized to determine the dominant mineral assemblages and trace elemental enrichments. Results revealed quartz and kaolinite as the principal minerals, with subordinate carbonate and sulfide phases introduced through diagenetic and hydrothermal processes. The coal discards were enriched in trace elements such as Ga, Sr, Zr and Ba. Ga was associated with kaolinite and organic matter, Sr and Ba predominantly occurred in barite, and Zr was hosted primarily in detrital zircon grains. Their spatial variability reflects depositional and diagenetic controls. Geochemical proxies, such as Sr/Ba and TiO₂/Al₂O₃ ratios, indicate freshwater depositional conditions influenced by volcanic ash input and post-depositional alteration. These findings enhanced the understanding of the geochemical cycling within coal discards, their mineralogical stability, and potential environmental implications. Furthermore, the presence of acid-neutralizing minerals supports the potential use of these coal discards in mitigating acid mine drainage, while the enriched CRMs highlight opportunities for sustainable resource recovery.