Decoupling the effect of hydraulic oil contamination on the flotation performance of UG2 PGE ore and its interaction with alteration minerals

Oil contamination inadvertently arising from underground mechanised South African platinum mines is known to compromise the subsequent flotation performance. Anecdotal observations suggest that this is further exacerbated in the presence of phyllosilicate alteration minerals. Two ores of varying degrees of alteration from the Bushveld Igneous Complex were utilized in this study to investigate the effects of oil on UG2 platinum group element (PGE) ore flotation and investigate the interaction mechanisms between the oil and phyllosilicate alteration minerals. Mineralogical characterization of the ores indicated a higher percentage of the alteration phyllosilicate minerals in the altered ore (9.2 wt%) in comparison to the normal ore (5.6 wt%); with talc predominating in both ores. Baseline batch flotation test work indicated a reduction of grade with hydraulic oil addition in the normal ore (Pt by 4.5 g/t and Pd by 3.6 g/t), whereas valuable metal grades in the altered ore showed no change. In contrast to the grades, the Pt and Pd recovery dropped by 6 % and 12 %, respectively, in the altered ore floats whereas nearly constant recoveries were obtained for the normal ore as oil concentration increased. The dynamic froth stability and slurry viscosity both increased in the presence of oil and were greater in the altered ore compared to the normal ore. The observed flotation performance of the normal ore was attributed to the increasing froth stability which promoted the recovery of gangue minerals and consequent grade decrease. For the altered ore, the greater increase in the slurry pulp viscosity with oil addition was proposed to lead to poor gas dispersion and reduced interaction between bubbles and particles resulting in the reduction of recovery. The addition of sodium metasilicate successfully mitigated these effects causing a decrease in the viscosity, improvement in particle dispersion and better froth drainage. This study highlighted the potentially harmful effects of oil spillages from mechanised mining and its complex interaction with alteration minerals contained within the ore.