Synergistic Recovery of Platinum Group Metals and Valuable Base Metals from Supergene Oxidized Ores via an Integrated Beneficiation–Hydrometallurgy Process

Abstract

Supergene oxidized ore bodies, which contain high-grade sulfide Platinum Group Metal (PGM) ore, are being increasingly explored for viable alternatives, as a result of depletion in the former reserves. There are more than 500 million metric tonnes of such oxidized reserves in the Great Dyke of Zimbabwe, but their exploitation has been hindered by the poor metallurgical performance of conventional flotation and pyrometallurgical processes. Weathering converts primary sulfide minerals into iron oxyhydroxides and silica passivating coatings and clay phases that inhibit mineral surface recovery of PGMs by less than 55%. In this study, an integrated five-stage beneficiation-hydrometallurgical flowsheet was developed and optimised experimentally using a bulk sample of 100 kg of an oxidized PGM ore, obtained from Karo Platinum Mine, Zimbabwe with certified grade of 2.667 g/t 3E; 1.695 g/t Pt, 0.476 g/t Pd, 0.496 g/t Au. The processing flowsheet included comminution to P₀ = 75 µm, Low-Intensity Magnetic Separation (LIMS) to reject the chromite, dilute H₂SO₄ acid scrubbing to remove the oxide coating, NaHS sulfidization to activate the surface, rougher froth flotation to concentrate the mineral (3E recovery 80.3%, 3E concentrate 28.64 g/t), cyanide gold leaching (Au recovery 88%), and oxidative chloride leaching (6 M HCl–H₂O₂, 120 min). This integrated flowsheet yielded an overall compound 3E recovery of 65.6%, a significant improvement over the recovery rate of less than 55% which was possible by conventional methods. A steady state process design was carried out at 100 t/h throughput which confirmed the technical viability of the proposed circuit.