Abstract

During the last few years, the complexity and recurrence of operational problems in Chilean mineral processing plants associated with the presence of clays and other ultrafine minerals has increased. This trend is likely to persist in time, considering that the mineralogical-energetic scenario has changed with respect to the conditions under which the plants and operating philosophies were formerly conceived. As copper grades have decreased, larger volumes must be treated to keep production constant, and the percentage of the feed comprising fines has increased, as liberation sizes of the copper minerals have become progressively smaller. Typically, the mitigating procedure to deal with high turbidity in supernatants, caused by non-sedimenting fines, involves increasing flocculant doses, thus impacting operational costs. Recovery of process water for recirculation is crucial, since the cost of adding extra fresh water may be a strong economic constraint. In the present work, we evaluate the effect of the presence of clays in the solid-liquid separation of copper sulphide synthetic tailings, quantifying the impact on separation efficiency, with the purpose of obtaining different practical solutions for solid-liquid separation with the presence of clays. First, we characterize the impact of clay presence in the solid-liquid separation stage considering sedimentation rate, supernatant turbidity, and Zeta Potential. Based on the results obtained in the previous stage, we analyse the performance of flocculation in sulphide tailings with the presence of clays. Finally, we compare and estimate technical solutions to treat tailings with different types of clays. Different effects on sedimentation efficiency can be distinguished according to the type of clay and the water in which it operates: while in the case of tailings with the presence of kaolinitic clays, the highest sedimentation efficiency occurs in the case of flocculation in water continental, at the same time, salinity decreases it. In the case of tailings with the presence of bentonite clays, the sedimentation efficiency increases as there is a higher concentration of cationic salts; In the case of distilled water, the flocculation efficiency is very low, so it is recommended to add a cationic additive, also considering the low economic cost that these imply. In the case of tailings with the presence of quartz clays, it was not possible to distinguish a clear effect in the increase or decrease of the sedimentation efficiency with the addition of flocculants, coagulants or when operating in seawater.