The influence of grinding media and water chemistry on the closed-water flotation of single-mineral sulfide ores

The milling stage prior to flotation plays a significant role in determining the chemical characteristics of the pulp phase in mineral processing, in which the grinding media and nature of the process water play a key role. This study analysed the effects of using low or high-ionic-strength water and either forged steel or inert ceramic media. Pure sulfide minerals, viz., pyrite (FeS₂) and galena (PbS), were used, in which the former may also contribute, together with the forged steel media, to the presence of Fe ions in the mill pulp. Electrochemical effects were determined at controlled pHs 4 and 10 by measuring the mixed potential, Eh. Moreover, the dissolved Fe and Pb concentrations at the end of the milling process were measured. When pyrite was used, xanthate consumption during flotation showed some correlation with Eh and flotation results. In the case of galena, the xanthate collector rapidly complexes with Pb ions dissolved into the pulp phase. The findings showed that the optimal conditions for the effectiveness of the xanthate collector occurred when using inert ceramic media at low pH. However, using forged steel media at alkaline pHs proved advantageous in separating galena from pyrite in a mixed/complex ore. Using high ionic strength process water with forged steel media at high pH yielded the highest grades of pyrite and the lowest of galena. This correlated with the solids recovery results. In the case of galena, an alkaline pH improved Pb recovery but also resulted in significant froth overstabilisation − as indicated by the water recoveries −, hence the reduced grades. X-ray photoelectron spectroscopy (XPS) was used in order to attempt to elucidate the experimental findings. This research indicates that using recycled water under specific conditions did not negatively affect the flotation performance of either mineral. Different grinding media played a more significant role in that regard.