Sericite–chalcocite mineral particle interactions and hetero-aggregation (sliming) mechanism in aqueous media

Attractive particle interactions which lead to hetero-aggregation or “sliming” of gangue and valuable mineral particles are encountered in a number of hydrometallurgical and flotation processes. Sliming leads to poor recovery of the valuable, hydrophobic minerals and high recovery of hydrophilic gangue particles in flotation concentrates. In the present work, the influence of interfacial chemistry and dispersion conditions on particle interactions which underpin the mechanism of hetero-aggregation between sericite and chalcocite particles was investigated in the pH range 5–9 at 23 °C. Hetero-aggregation is shown to occur under aqueous dispersion conditions where the fluid shear rate was high and the individual chalcocite and sericite particles were negatively charged, as shown by the electrokinetic potential data. Continuous flow particulate adsorption and rheological studies revealed that the hetero-aggregation behaviour was strongly pH and oxidative environment dependant. Sliming was greater at lower than higher pH and under air saturation than N2 gas purge. The unexpected hetero-aggregation is ascribed to chalcocite (Cu(I)2S) surface oxidation and dissolution which accentuated with decreasing pH and Cu (II) ion hydrolysis effect. Specific adsorption of Cu (II) complexes onto the mix minerals’ surfaces had a striking impact on the interfacial chemistry, reflecting significantly enhanced dispersion shear yield stress. The attractive particles’ interactions are believed to be due to a combination of Cu(II)-mediated mechanisms including: electrostatic-charge patch attraction, van der Waals attraction, adsorbed ion–particle bridging, surface nucleation and cementation. Sliming mitigation was demonstrated by the use of N2 gas and higher pH, as evidenced by markedly lower sericite–chalcocite dispersion shear yield stress and greatly reduced particulate adsorption behaviour.