Towards bioleaching of PGMS
Liberty Chipise, Sehliselo Ndlovu, Alan Shemi, S.S. Moodley, Anil Kumar, Geoffrey S. Simate, Clarence S. Yah
Abstract
This paper explores bioleaching as a viable method for extracting precious group metals (PGMs) with potential advantages over the traditional energy-intensive extraction processes that cannot cope with the depletion of high-grade ores. The proposed bioleaching process consists of three main steps: base metal removal, bio-decomposition of silicates and PGM extraction using biogenic cyanide. Base metals form stable complexes with cyanide under similar oxidative conditions required for PGM leaching. Such that efficient removal of base metals minimizes biogenic cyanide consumption, while the subsequent decomposition of silicates prevents PGM loss. The use of mixed thermophilic microorganisms enhances kinetics during base metal removal, resulting in a base metal-free residue for PGM bioleaching. For PGM bioleaching, a decoupled approach was proposed, involving biogenic cyanide production, followed by its utilization for PGM leaching. This accommodates the different conditions required by cyanide-producing microorganisms and those for PGM leaching. A conceptual flowsheet was drawn to illustrate the bioleaching of PGMs. The challenges related to the influence of PGM mineralogy on the flowsheet were brought to attention, along with their respective solutions.