The role of sodium metabisulphite in depressing pyrite in chalcopyrite flotation using saline water

Abstract

In response to the high pyrite recovery in copper flotation using seawater, this study investigated the role of sodium metabisulphite (MBS), a widely used pyrite depressant, in depressing the flotation of copper-activated pyrite to identify a solution to maximising pyrite rejection. It started with chalcopyrite flotation against pyrite with MBS added in the mill before grinding and in the conditioning cell before flotation. The surface properties of pyrite exposed to different reagent schemes were investigated by X-ray photoelectron spectroscopy (XPS) analysis. The reactions on pyrite surface responsible for different flotation results were then investigated by cyclic voltammogram (CV) measurements and discussed in terms of a radical chain mechanism involving the redox cycling of Cu(I/II) induced by sulphite species. It was found that the addition of MBS during the conditioning stage was more efficient in depressing the flotation of copper-activated pyrite. This is because the combination of sulphite ions and oxygen may form a strongly oxidising radical SO5·- which can oxidise Cu(I)S, the copper activation product on pyrite surface, to form hydrophilic Cu(OH)2/CuSO4. The addition of MBS at low dosages in the mill depressed pyrite flotation to a less extent due to the less oxygen available, while its depression effect was even weakened at high dosages due to the consumption of dissolved oxygen and a strongly reducing environment which favoured copper activation on pyrite surface.