PGM extraction from oxidized ores using flotation and leaching

Abstract

Synopsis Flotation and leaching were investigated as possible processing routes for improving PGM recovery from a Southern African oxidized PGM ore. Different flotation reagent schemes and lixiviants were evaluated and their PGMs extraction response measured. Characterization of the PGM ore used in this study indicated that it was enriched in oxide minerals as a result of weathering and therefore oxidic. The maximum PGM flotation recovery achieved using sulphide co-collector schemes was 55.1% 3E (Pt, Pd, and Au). Application of the hydroxamate oxide collector improved the flotation recovery to 74.7% 3E. The superior PGM recoveries achieved with hydroxamates probably lies in their ability to form complexes with base metals such as iron. Direct leaching of oxidic PGM ore using different acids yielded relatively low PGM extractions. Leaching in hydrochloric acid achieved extractions of 36.6% Pt and 8.8% Pd, nitric acid achieved extractions of 34.5% Pt and 7.1% Pd. The best leaching results were obtained using aqua regia, with extractions of 48% Pt and 24.5% Pd. In view of the low PGM extractions obtained by leaching ROM ore, it was considered more promising to leach the concentrate as a way of further upgrading it. The flotation concentrate with the highest PGM recovery was leached using sulphuric acid in order to remove the base metals and further enrich it in PGMs. Extractions of 73.3% Cu, 82.9% Ni, and 8.1% Fe were achieved.