Characterisation of sphalerite and pyrite surfaces activated by copper sulphate

Adsorption of copper sulphate onto the sphalerite and pyrite surfaces during the selective flotation is not fully understood. In this paper, this phenomenon is investigated by Cryogenic X-ray Photoelectron Spectroscopy (Cryo-XPS) and zeta potential measurements. The Cryo-XPS results have showed that the copper activation occurs in two steps. For sphalerite, surface Zn2+ is substituted by Cu2+ by ion exchange reaction, and then CuS-type layer is formed by reduction of the exchanged Cu2+ to Cu+ and oxidation of surface S2− to S−. Cu2+ can also activate pyrite, first, through reduction of Cu2+ to Cu+ and oxidation of surface S2− species to S−, then surface Fe2+ is oxidised to Fe3+ by reduction of S− to S2−, leading to the formation of CuFeS2-type layer. In the reducing potential of the activation, enhancement of copper adsorption on the pyrite surface is confirmed by XPS. Depth profiling after 10 min activation revealed copper diffusion into the sphalerite lattice up to 10 nm, while the thickness of the activation product on pyrite surface was less than 3 nm. The zeta potential studies confirmed CuS-type layer formation on copper activated sphalerite, whereas the surface product of the activated pyrite was CuFeS2-type. This study leads to a better understanding of sphalerite-pyrite Cu2+ activation during flotation for an effective separation.