A comparative study of the attachment of air bubbles onto sphalerite and pyrite surfaces activated by copper sulphate

Abstract

Pyrite is a gangue mineral in the flotation of sphalerite activated by copper sulphate (CS). In this study, the attachment of air bubbles onto sphalerite and pyrite surfaces activated by CS was comparatively studied using a novel approach with High-Speed Video Microscopy (HSVM) and X-ray photoelectron spectroscopic (XPS). HSVM allowed for the in-situ determination of the liquid film Drainage Rate (DR) and Contact Angle (CA) of the bubble attachment. The results showed that after the activation sphalerite became hydrophobic by the formation of polysulphide as confirmed by XPS while pyrite remained hydrophilic. With increasing activation time and CS concentration, both DR and CA on the sphalerite surface rapidly increased at the beginning and reached constant values, while those on pyrite remained unchanged. The changes in the CA values of the sphalerite was successfully modelled by considering a second-order rate process for the CS activation which was proportional to initial copper concentration and available Zn active sites on the sphalerite surface. If both sphalerite and pyrite were simultaneously exposed to CS solutions (but not in the physical contact), the rate of CS activation of sphalerite remained unchanged when the ratio of sphalerite to pyrite surface areas exposed to CS solutions was equal to 1:1. However, the activation rate of sphalerite significantly dropped with increasing the sphalerite:pyrite surface area ratio from 1:3 to 1:6. The effect of the surface area ratio on the CS activation rate was prominent at activation times higher than 3min. The XPS results for the mixed minerals showed the reduction in sphalerite Cu/Zn exchange and polysulphide/Cu ratios with increasing available pyrite surface area in CS solutions, indicating the significant drop in the CS activation of sphalerite in the presence of pyrite. The outcomes of this study provided further insights into the selective flotation of sphalerite from pyrite.