Sulfuric acid leaching of South African chromite. Part 1: Study on leaching behavior

The leaching behavior of chromite by sulfuric acid in the presence of oxidant was studied experimentally in this work, where most tests were carried out at 160 °C. The results indicated that magnesium and aluminum were leached out together from the silicate phase and porous amorphous silica was produced as a product layer, while the spinel phase gradually shrank with the duration of leaching. The separation of silicate and spinel phases had an influence both on the extraction yield of chromium and the leaching reaction rate by reducing the resistance presented by the silicon-rich phase. It was found that the erosion along the phase boundary was more severe than in other areas, and it can be speculated that groovy corrosion in the spinel phase occurred and developed at the grain boundary. The precipitation behavior of sulfate during the leaching process was also investigated at different temperatures up to 200 °C, showing that the sulfate precipitated in the silicon-rich phase at higher temperatures, while the main phase of the sulfate was chromium sulfate, coinciding with results reported by other researchers. All considered metal elements in the spinel phase leached out together in the experiments of this study.