Impact of gypsum supersaturated solution on the flotation of sphalerite

Gypsum supersaturation in process water is known to have detrimental effects on flotation performance of sulphide minerals. The motivation of this research is to develop a better understanding of the impact of gypsum supersaturation in process water on sphalerite flotation. For this purpose, this thesis focused on the impacts of gypsum supersaturation in process water on the surface properties of silica and sphalerite minerals, the interactions between flotation reagents and sphalerite, and the interactions between silica and sphalerite minerals in various types of process water.;Removing calcium ions by sodium carbonate addition can significantly offset the detrimental effect of gypsum supersaturated process water on the flotation performance of sphalerite. Micro-flotation of silica and sphalerite mixture minerals shows that the flotation recovery and selectivity of sphalerite are clearly improved after treating the gypsum supersaturated solutions with sodium carbonate.;Results from this study indicate that the adverse impact of gypsum supersaturation in process water on sphalerite flotation is mainly due to high calcium concentration in the gypsum supersaturated process water. This study shows that gypsum precipitates do not form or coat on silica and sphalerite mineral surfaces in the gypsum supersaturated solutions under the conditions studied. However, both silica and sphalerite mineral surfaces are coated by calcium after being conditioned in a gypsum supersaturated solution, resulting in identical surface charge between silica and sphalerite. The high calcium concentration in the gypsum supersaturated process water is found to retard the activation of sphalerite by copper and hence the subsequent xanthate adsorption. The adsorption of calcium ions is identified to compete with copper species for the reactive surface sites of sphalerite, resulting in the reduction in copper and xanthate uptake and hence flotation recovery of sphalerite. Hetero-aggregation between gangue minerals (quartz or silica for example) and sphalerite minerals is induced in the gypsum supersaturated process water. Direct colloidal force measurement using an atomic force microscopy (AFM) shows attractive force profile between silica and sphalerite minerals in both gypsum supersaturated solution and calcium chloride solution containing a similar calcium concentration to that of the gypsum supersaturated solution. The extent of slime coating of silica nanoparticles on sphalerite surfaces is found to increase with the increase in calcium concentration. The retardation of sphalerite activation and subsequent xanthate adsorption, in combination with slime coating of gangue mineral particles results in poor recovery and selectivity in sphalerite flotation process.