Collectorless flotation of pyroxene in Merensky ore: Residual layer identification using statistical ToF-SIMS analysis

In Merensky (Bushveld Complex, South Africa) ore flotation, normally more than 2% of the gangue minerals, principally pyroxene with minor chromite, reports to the concentrate diluting the PGM recovery and contributing to subsequent processing costs. Understanding and controlling the mechanisms that cause this misreporting remains a primary target in PGM flotation. The orthopyroxene in Merensky ore can develop floatable properties through chemical interactions in the flotation system, principally through inadvertent copper-collector complexation, but this paper shows that this mechanism does not fully account for the true flotation of large pyroxene (20–150 µm) particles. Statistical comparison of ToF-SIMS analysis of particles from concentrate and tails reveals no significant difference in Cu and collector (IBX, DTP) signals between these streams but surface exposure of Mg and Si is favoured in the concentrate. Flotation of pyroxene without collector has confirmed this statistical discrimination. Hydrophobic talc-like residual layers, probably from partial serpentinisation of the pyroxene, seen in XRD differences between the concentrate and tails, explain this flotation mechanism.