Evidence for surface cleaning of sulphide minerals by attritioning in stirred mills

Recent developments in large scale stirred milling technology using ceramic media have allowed its application to relatively coarse particle streams. Apart from benefits in grinding finer more efficiently, benefits may also be derived from the surface cleaning action of stirred mills. This paper discusses evidence for the cleaning action of a stirred mill on the surfaces of chalcocite and effects on its subsequent flotation. Single mineral samples of chalcocite were ground with either stainless or mild steel grinding media. The effects of surface contamination by iron hydroxide on chalcocite floatability were studied using ethylene diamine-tetra acetic acid (EDTA) extraction, X-ray photoelectron spectroscopy (XPS) surface analysis and contact angle measurements. Depression of both coarse (+75 μm) and fine (−10 μm) size fractions was attributed to the surface precipitation of iron hydroxide species. Transfer of iron hydroxides from coarse particles to fine particles was observed with XPS analysis. Recovery of coarse particles (+75 μm) was improved by attritioning, while additional collector was needed to fully restore chalcocite recovery in both fine and coarse size fractions.