Aqueous oxidation of galena by hydrogen peroxide in hydrochloric acid

Abstract

ABSTRACT The aqueous oxidation of galena by hydrogen peroxide (H2O2) at an initial pH 2.0 and at a temperature of 30 °C was studied using potentiodynamic polarisation, Electrochemical impedance spectroscopy, aqueous batch experiments, Fourier transform infrared spectroscopy, Raman spectroscopy and quantum chemical calculations. It has been found that H2O2 is an effective oxidant of galena. The rate of the aqueous oxidation of galena is strongly dependent on the concentration of H2O2 ([H2O2]). The apparent reaction order with respect to [H2O2] is 1.05. The experimental results can be interpreted as follows. Sulphur breaks from the galena surface and is subsequently oxidised in solution to SO4 2− (aq). Such an oxidation mechanism is also supported by quantum calculations that show that breaking sulphur from the galena surface and its subsequent oxidation is energetically privileged in relation to the direct oxidation of the PbS surface. During the oxidation there are precipitated a series of species, such as PbO·PbSO4, S(0) etc. Experimental observations show that as the [H2O2] increases, the amount of species precipitated decreases, and the rate of oxidation increases. Taking this relationship into account, we could identify the optimal conditions in which lead and sulphur can be extracted efficiently and ecologically from galena-bearing ores.