Review of recovery of valuable metals and rare earth elements from coal fly ash as a secondary resource

Abstract

The “black gold” coal, which humanity has known since the Neolithic age, has been the popular fuel after the 18th century industrial revolution. Recently, residues such as fly ash after combustion pose a problem both in terms of storage and environmental aspects. Such residues will continue to appear until coal consumption ceases completely. Coal fly ash is a secondary source in precious metals and rare earth elements, and it is important to recycle it to the industry. Although the final concentrate production by physical enrichment processes is limited, the ore preparation studies together for chemical enrichment and hydrometallurgy (leaching, solvent extraction, etc.) recovery are of great importance. It is important to examine the ratio of rare earth elements in fly ash, the effect of size on enrichment processes and especially the integrated physical-chemical enrichment methods in the choice of the methods to be selected. In this article, the general properties of coal ashes, and rare earths contents and especially physical enrichment processes of fly ash are discussed and recent studies on this subject are examined.