Investigation into the mineralogy and flotation performance of oxidised PGM ore

•Abundant naturally floating gangue, Fe-oxide and negligible BMS in oxidised PGM ore.•Best 4E recovery at high depressant dosages (750 g/t CMC).•Small improvements in PGE recovery with CPS and AM 28 due to high froth stability.

The 2.05 Ga Bushveld Complex in South Africa, host to many lucrative ore deposits, is surprisingly pristine and unaltered given its geological age. In some areas, however, there is evidence of low temperature weathering, alteration and oxidation, most commonly observed when the ore is near surface. The Pilanesburg Platinum Mines (PPM) operation in South Africa treats ore from an open pit and routinely suffers from low and erratic platinum group element (PGE) flotation recoveries. This study investigates the effect of oxidation on the mineralogy and flotation performance of PPM “silicate reef” ore and evaluates the effect of alkyl hydroxamate (AM 28) and controlled potential sulfidisation (CPS with NaHS) as a means to improve the poor flotation performance of the oxidised ore. Oxidised PPM ore is characterised by high contents of alteration minerals resulting in abundant naturally floating gangue (NFG), high contents of Fe-oxides/hydroxides and negligible base metal sulfides. Small improvements in PGE recovery with the addition of the hydroxamate co-collector with CPS or without it are more due to the high froth stability and increased water recovery rather than any selective action of the collector. The distinctly higher Pt recovery relative to Pd recovery is linked to the mobilisation and redistribution of Pd during the oxidation of the ore.