Surface characteristics and flotation behaviour of platinum and palladium arsenides

Abstract

Research on the flotation behaviour of platinum group minerals (PGM) has mainly focused on the flotation of base metal sulphides because of their association with the PGMs and due to the assumption that the PGMs would respond similarly to such sulphides in their flotation behaviour. It has been reported, however, that significant losses of PGMs may occur due to the poor floatability of arsenides of the platinum group elements which contribute around 21% of the PGMs present in the Platreef ore. Investigating the reasons for their poor floatability is the focus of this paper. The surface characteristics and flotation behaviour of synthetic sperrylite (PtAs 2) and palladoarsenide (Pd 2As) has been investigated. The results revealed that, of the two synthetic sperrylite samples described, the one synthesised at a short initial thermal treatment, floated well in the presence of xanthate whereas the other, synthesised for a longer period, floated poorly irrespective of the reagent suite used. The XRD spectra and bulk compositions of both samples were identical. The former sample however exhibited many Pt blebs within the material whereas the latter was a more homogeneous sample of PtAs 2. The latter sample when crushed to < 38 μm showed increased recoveries possibly due to the exposure of such Pt blebs. Zeta potential, ToF-SIMS and XPS results showed that, in the presence of copper sulphate, the surface was covered with colloidal Cu(OH) 2 precipitate. When a xanthate collector (SIBX) was subsequently added to the copper activated sample, the copper was reduced to the Cu + 1 form presumably due to the formation of Cu(I)X. Surprisingly activation with copper sulphate resulted in a slight decrease in flotation recovery compared to the case of only xanthate present. Proposals are made to explain these observations.