Characterization of the solid leach residues from the iodine-assisted chalcopyrite leaching in ferric sulfate media

Chalcopyrite dissolution in ferric sulfate media at ambient conditions is slow. The addition of iodide has been found to significantly improve chalcopyrite leaching in the potential range where triiodide (I₃⁻) or diiodine (I₂) is the predominant species. In the iodine-assisted chalcopyrite leaching process, elemental sulfur was proposed to be the form of sulfur product while iron precipitation was also observed. Given the potential impact of elemental sulfur and iron precipitates on chalcopyrite leaching, this study analyzed the solid leach residues collected from the iodine-assisted chalcopyrite leaching using different solid characterization techniques. The X-ray diffraction analysis of the bulk residues shows that elemental sulfur was the product of chalcopyrite leaching and that pyrite was unreactive. The cross-sectional analysis by a mineral liberation analyzer (MLA) shows that thick layers of jarosite and elemental sulfur coated the surfaces of the solid particles. Further analysis by X-Ray photoelectron spectroscopy (XPS) with a depth resolution of <10 nm confirmed that elemental sulfur was formed and that the formation of jarosite was favored at 40 and 45 °C. Despite the formation of elemental sulfur and iron precipitates, a near complete dissolution of chalcopyrite could be achieved. Further research is required to understand how the presence of iodine changes chalcopyrite leaching in such a way that surface passivation does not occur.