The depression of molybdenite flotation by sodium metabisulphite in fresh water and seawater

Sodium metabisulfite (MBS) has been widely applied to depress pyrite in copper-molybdenum flotation plants in particular when seawater is used as the main water resource. However, whether MBS depresses molybdenite flotation is unknown. In this study, the flotation of molybdenite at 106 and 53 mu m was carried out in the absence and presence of MBS in DI water and seawater to determine the depression role of MBS. Then the products formed on molybdenite faces and edges were detected by cryogenic X-ray photoelectron spectroscopy to understand the reactions involving MBS. This study confirmed the depression of MBS on molybdenite flotation especially for fine particles in DI water. The depression was caused by the adsorption and oxidation of sulphite ions on molybdenite edges, forming sulphate complexes which provided a steric barrier to collector adsorption on molybdenite faces. This study also confirmed little effect of MBS on the flotation of molybdenite at 106 and 53 mu m in seawater. This is because sulphite ions preferentially combined with calcium and magnesium ions in water rather adsorbed on molybdenite edges.