The use of heap bioleaching as a pre-treatment for platinum group metal leaching

Two samples, a Platreef flotation concentrate and coarse ore (<6 mm), were column bioleached at 65°C using a culture dominated by Metallosphaera hakonensis. Based on solution assays, extractions in excess of 90% Cu and Ni were achieved from the flotation concentrate, while from the coarse ore 96% Cu and 67% Ni extractions were achieved. The difference in extraction levels and leaching patterns despite identical conditions used for both samples is discussed, as is the performance of the samples during a follow-up leach step using cyanide to extract the PGMs in a separate column leach experiment. While the recovery of Pd and Au was excellent during these steps, recovery of Pt was limited to 35% after 45 days for the concentrate and 56% after 60 days for the whole ore material, primarily due to the presence of a refractory Pt mineral. Recovery from a concentrate without pre-treatment was substantially lower.