Rare Earth Elements Extraction from Coal Waste Using a Biooxidation Approach

Rare earth elements (REE) are moderately abundant and are presently extracted from limited resources of monazite, bastnaesite, and loparite minerals and ionic clays. Other potential sources include large coal resources in active coal mines and existing coal waste dumps. A technology has been proposed and demonstrated that can be used to deliver clean coal for the market as well as REE-bearing non-coal material that is concentrated in REE content and suitably sized for heap leaching. Additionally, a separate stream of concentrated sulfide minerals can be produced from mid to high sulfur coals suitable for the bio-oxidation production of a lixiviant suitable for leaching REE from the non-coal rock in a heap leach setting. The removal of the sulfide minerals cleans the coal, accelerates subsequent REE extraction, and eliminates the future potential for acid-rock drainage. For cost-effective enhanced leaching, bio-oxidation has been used that has been applied to coal-based materials. During bioleaching, Fe3+ ions generated from bioleaching oxidize sulfide minerals such as pyrite, and subsequent production of acid. These two species (acid and Fe3+ ions) are key drivers for REEs dissolution, as well as residual sulfides removal, thereby controlling future acid mine drainage and related liabilities. This paper discusses some associated results acquired for the proposed process.