Investigating the interaction of thiol collectors and collector mixtures with sulphide minerals using thermochemistry and microflotation

In order to recover minerals by flotation, the sub-processes of collector adsorption onto the valuable minerals followed by bubble-particle attachment should occur efficiently. This paper investigates both of these sub-processes for various thiol collectors and their mixtures onto base metal sulfide minerals. The aim of the work was to investigate whether there is a correlation between the strength of the collector interaction with the mineral and the subsequent bubble-particle attachment. The collector-mineral interaction was measured experimentally using an isothermal titration calorimeter in order to determine the molar enthalpy of adsorption for each collector-mineral system. The bubble-particle attachment was measured using a microflotation device which essentially determines the hydrophobicity of the mineral. Sodium ethyl xanthate (SEX) and sodium diethyl dithiocarbamate (diethyl-DTC) and mixtures thereof were used as collectors with either single minerals or binary mixtures of pyrite and chalcopyrite, respectively. The adsorption enthalpies of the collectors were interpreted with reference to the chemical structure of the collector molecule and showed that the greater the positive inductive effect of the collector, which may be qualitatively related to their pKa values, the greater their affinity for the mineral surface. When mixtures of collectors were used there was clear evidence of synergistic effects in enhanced enthalpies of interaction between collectors and the mineral surface and in increased microflotation recoveries. When mixtures of pyrite and chalcopyrite were used the flotation recovery and enthalpy of adsorption of SEX onto the individual pyrite particles in the mixture also increased substantially compared to the case of pyrite alone. Mechanisms are proposed to interpret these observations.