New insights into the sphalerite activated by copper sulfate in lime systems

The mechanism of how copper sulfate (CuSO4) activates sphalerite under lime-inhibiting sphalerite conditions has not been fully specified. In the paper, the activation mechanism of CuSO4 for sphalerite surfaces depressed with lime (pH=12) was investigated through micro-flotation experiments, solution chemical analysis, zeta potential measurement, and X-ray photoelectron spectroscopy. The solution chemical analysis and micro-flotation experiments indicated that the Cu2+ ions have produced copper hydroxide (Cu(OH)2) precipitation under alkaline conditions (pH=12); however, the activation effect of sphalerite by Cu(OH)2 is weak. Zeta potential measurement and X-ray photoelectron spectroscopy showed that the inhibition effect on sphalerite in the lime system was attributed to the adsorption of zinc hydroxide and calcium hydroxide on the sphalerite surface. After the treatment with CuSO4, not all of the Cu2+ ions in the lime system (pH=12) will immediately combine with hydroxide and convert to Cu(OH)2. A certain concentration of Cu2+ ions is still present in the lime system (pH=12). This part of the Cu2+ ions will eliminate zinc hydroxide (all) and calcium hydroxide (part) from the sphalerite surface in the lime system, and activate sphalerite by forming a cuprous sulfide film. Therefore, the activation of sphalerite by CuSO4 in the lime system can be explained as the activation process of sphalerite by Cu2+ ions, not copper hydroxide. These results provide a theoretical basis for improving the flotation separation of sphalerite and pyrite in the lime system. [Display omitted] •Sphalerite has poor floatability in the lime system (pH=12).•Sphalerite is inhibited by the adsorption of Zn(OH)2 and Ca(OH)2.•Activation of sphalerite by Ca(OH)2 is very weak in the lime system.•Cu2+ is responsible for the activation of sphalerite in the lime system.•Cu2+ removes Zn(OH)2 and Ca(OH)2, and forms a Cu2S film on sphalerite surface.