A THERMODYNAMIC MODEL OF CHEMICAL WEATHERING OF FLOTATION TAILINGS OF PGE–Cu–Ni SULFIDE ORES

We present a thermodynamic model of the interaction between surface water and the flotation tailings of PGE–Cu–Ni sulfide ores from the studied ore district in the Krasnoyarsk Territory. The urgency of the study is determined by the need to assess the long-term stability of mineral assemblages. The aim of the study is to elucidate the regularities of transformation of mineral assemblages during long-term storage. The mineral and chemical compositions of samples from two pits and the chemical composition of aqueous extracts served as initial data. Calculations were carried out in the solid–water–gas system with varying Eh values to simulate different degrees of the system openness to atmospheric oxygen (standard P–T conditions, pCO2 gas = 10–3.5 atm). Based on the modeling results, it has been established that pyrrhotite remains stable under extremely reducing conditions (pO2 gas = 10–79 atm), in which the dissociation of water into atomic oxygen and hydrogen is possible. In general, the obtained models reflect the transition from sulfide to oxide–silicate assemblages, accompanied by a decrease in the number of mineral phases as oxidation progresses. The modeled assemblages are consistent with the parageneses observed in the polished sections. It is shown that the material largely retains its primary mineralogical features even after decades of storage, which is explained by the high content of rock-forming minerals within a dense clay matrix that prevents penetration of oxygen and moisture in amounts sufficient for intense oxidation. The results obtained can be used in the development of technological schemes for the recovery of potentially valuable metals from flotation tailings of PGE–Cu–Ni sulfide ores.