Sulfidization mechanism in malachite flotation: A heterogeneous solid-liquid reaction that yields CuxSy phases grown on malachite

Abstract

Sulfidizationfollowed byxanthateflotation is an effective technique to recover copper oxide minerals. However, the sulfidization mechanism of malachite has not been determined. In this work, the sulfidization mechanism was investigated by microflotation, field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), electron probe X-ray microanalysis (EPMA), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The flotation results showed that sulfide ions at an appropriate concentration could activate malachite flotation while excess sulfide ions could depress this. The depression of malachite flotation by excess sulfide ions was attributed to the residual sulfide species in the liquid. FESEM–EDS showed that sulfidization product grown on the malachite surface was heterogeneously distributed, which was consistent with the EPMA results. The XRD results for the sulfidized malachite samples showed that the amount of sulfidization product was insufficient for detection under flotation-related conditions. By the selective solvent action of sulfuric acid, the sulfidization product was extracted from the sulfidized malachite. The XRD results for the extracts indicated that the sulfidization product comprised djurleite (Cu31S16) and anilite (Cu7S4), which both were compounds of the chalcocite group (Cu2−xS), suggesting transformation of solid Cu2(OH)2CO3 to Cu2−xS on the malachite surfaces during sulfidization. Moreover, the XPS results were consistent with the XRD results. These results demonstrated that sulfidization of malachite is a phase-transition process driven by the solubility difference between Cu2(OH)2CO3 and Cu2−xS. In this case, Cu2−xS phases formation on malachite involves heterogeneous nucleation and growth, and sulfide ions act as a reductant and sulfidizing agent in malachite sulfidization. The copper sulfide grown on malachite radically changed the surface properties of malachite particles, rendering malachite amenable to xanthate flotation. Based on these findings, we present a new formula for malachite sulfidization and a schematic diagram of the sulfidized malachite particle.