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X-ray photoelectron spectroscopy and time of flight secondary ion mass spectrometry have been used to determine the specific effect of sulphite ions on the surface chemistry of copper-activated pyrite pre-treated with isobutyl xanthate in flotation experiments with nitrogen and air purging at pH 7. The results from these spectroscopic techniques illustrate that sulphite ions affect the surface chemistry of pyrite similarly whether nitrogen or air purged. It was found that sulphite ions interact with adsorbed collector species, as well as with the pyrite surface itself. A reduction in the adsorbed collector concentration and a commensurate increase in surface hydrophilicity explain the low flotation recovery of pyrite in the presence of sulphite. As expected, this effect was more pronounced in the flotation experiments with air purging.

The effect of sodium bisulphite on the xanthate-induced flotation of copper-activated sphalerite has been studied using batch flotation testing, surface analysis techniques (XPS and ToF-SIMS), and FTIR. The various techniques have been used to identify the mechanisms of interaction of sulphite ions with both collector and the sphalerite surface. The results indicate that sodium bisulphite depressed the flotation of sphalerite particles pre-treated with copper and xanthate at pH 9 with nitrogen and air purging. It was found that sodium bisulphite interacts with the sphalerite surface, as well as with xanthate in its adsorbed state. Based on the evidence obtained in the present study, and in conjunction with previous work, the mechanisms involved in the depression of the xanthate-induced flotation of copper-activated sphalerite by sulphite are proposed. It is suggested that copper xanthate decomposition on the surface of the activated sphalerite and the decomposition of the hydrophobic copper-sulphide-like species on the sphalerite surface are the active mechanisms for sphalerite depression by sodium bisulphite.

We present data from the surface analysis of a mineral mixture of chalcopyrite, pyrite, and sphalerite, elucidating surface reactions occurring during grinding and flotation. Flotation tests are also performed on the mixture, carried out in the presence of collector (SIBX) and also in the absence and presence of sodium bisulphite (NaHSO 3 ), a gangue sulphide mineral depressant. X-ray photoelectron spectroscopy (XPS) studies on the ground mineral sample prior to flotation indicate that the mineral feed is heavily oxidised, especially the sphalerite in the mixture. Flotation recovery data clearly shows the effect of this oxidation, with the mineral recoveries of all three phases being lower than those observed in single mineral studies. In addition, the flotation recoveries show the effect of the inadvertent copper activation of pyrite and sphalerite, and the effect of bisulphite in reducing the flotation of sphalerite and pyrite in the mixture. Time of flight secondary ion mass spectrometry(ToF-SIMS) data indicates that the depressing effect of bisulphite is due to the removal of copper and sulphur-like species from the surface of pyrite and sphalerite and a consequent increase in the oxidation of these minerals. ToF-SIMS data also indicates that the low recovery of pyrite and chalcopyrite in the absence of collector is most likely due to precipitation of zinc hydroxide on the surfaces of these minerals, formed in solution due to copper activation of sphalerite.

The effect of sodium bisulphite on the collectorless flotation of copper-activated sphalerite has been studied at pH 9 with nitrogen purging. X-ray photoelectron spectroscopy (XPS), time of flight secondary ion mass spectroscopy (ToF-SIMS) and ion chromatography (IC) have been used to identify a mechanism of interaction of sulphite ions with sphalerite particles. The results indicate that sodium bisulphite acts as an effective depressant for the collectorless flotation of copper-activated sphalerite and has a specific effect on the surface chemistry of sphalerite particles under the experimental conditions studied. It is suggested that sulphite ions react with the surface of copper-activated sphalerite and subsequently decompose the hydrophobic sulphur-like species responsible for flotation. Most likely, sulphite ions specifically interact with the reduced coordination sulphur atoms associated with copper activation and report into solution as a thiosulphate, which is then oxidised to sulphate. At the same time, zinc hydroxide is formed at the sphalerite surface. The consequent reduction in surface hydrophobicity explains the depression of copper-activated sphalerite in the presence of sulphite.