In this study, the effects of sodium thiosulphate on chalcopyrite and tennantite at various pH values were investigated. Contact angle, flotation (Hallimond tube), zeta potential and X-ray photoelectron spectroscopy were used to observe these effects and to investigate the mechanisms involved. The addition of sodium thiosulphate depressed both chalcopyrite and tennantite at all pH values. Further addition of diethyl dithiophosphate significantly increased the flotability of chalcopyrite at all pH values as well as tennanite in acidic conditions, but not tennantite in alkaline conditions. In light of the zeta potential measurements and due to the stability of thiosulphate over the pH range, the coverage of sulphate resulting from the oxidation of thiosulphate was responsible for the depression of both chalcopyrite and tennantite in acidic conditions. Adsorption of diethyl dithiophosphate species on the mineral surface resulted in flotability of tennantite which was almost as high as that of chalcopyrite. In alkaline conditions, coverage of the copper thiosulphate complex was responsible for the depression. The copper thiosulphate complex inhibited adsorption of diethyl dithiophosphate species on the mineral surface. Higher coverage of the copper thiosulphate complex on tennantite caused an insignificant increase in its flotability in comparison to that of chalcopyrite which allowed the separation of tennantite from chalcopyrite. The XPS spectra supported the proposed mechanism of thiosulphate depression on these minerals.
!!!All Science Journal Classification (ASJC) codes