Abstract
The effect of UV light on the rate of dissolution of sphalerite, (Zn,Fe)S, has been investigated for samples from different sources. These different samples had different amounts of substitutional iron, ranging between 0.55 and 8.62%. It was found that the rate of dissolution of sphalerite is proportional to the content of substitutional iron, and that the rate of dissolution increased in the presence of UV light. Analysis of the data indicated that the effect of light was more pronounced for samples with lower iron content. A mechanism is described for the dissolution reaction that envisages that the oxidant preferentially accepts electrons from (or injects holes into) the d-band orbitals arising from the iron in substitutional positions in the lattice. The resulting hole in the d-band reacts with the surface causing the removal of the dissolution products from the surface. The effect of light was proposed to be due to the excitation of a valence band electron to the conduction band to create electron-hole pairs. The holes react with the surface, resulting in dissolution products, while the excited electrons are captured by the oxidant. Rate equations are derived that describe these mechanisms. These rate equations are shown to agree with the experimental data.
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