Insight into the strengthening mechanism of thiourea compounds in chalcopyrite bioleaching

The bioleaching kinetics of chalcopyrite remain too slow for large-scale industrial applications. Therefore, researchers have been exploring methods to boost the leaching rate of chalcopyrite bioleaching. Thiourea compounds have been found to be effective in enhancing chalcopyrite leaching. To clarify the effects and mechanisms of thiourea compound assisted chalcopyrite bioleaching, surface analyses, kinetic studies and microbial community tests of different compounds were carried out. The addition of these thiourea compounds accelerated the chalcopyrite leaching kinetics, and the promoting effect was enhanced with an increase in the dosage. Surface analyses using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) indicated that iron and copper, especially iron, were leached from chalcopyrite first. This was followed by the formation of polysulfide and elemental sulfur. It was demonstrated that thiourea compounds enhanced the leaching kinetics through multiple mechanisms. They reduced the redox potential, catalyzed the leaching of copper by chelating with the chalcopyrite surface, and eliminated the passive sulfur layer despite some negative impacts on the sulfur-oxidizing microbes in contact with the chalcopyrite surface. The results revealed the underlying mechanism of thiourea compounds in enhancing chalcopyrite bioleaching and their potential applications. Additionally, it pointed out the direction for identifying other potential ligands to assist in chalcopyrite leaching.