Abstract

In Chile, copper concentrate production through mineral flotation is increasing while production through hydrometallurgical processes is decreasing due to the depletion of oxidized ores. Using the idle capacity of hydrometallurgy plants for acid pretreatment of sulfate ores before the leaching stage is an attractive alternative; however, a deeper understanding of the process and the products of such treatment is required. In this study, the mineral species formed during acid pretreatment are characterized to identify new mineralogical species. Pretreatment was conducted at 50 °C with 210 kg/t H2SO4 over 15 days on a copper concentrate mainly composed of enargite (35.93%). The characterization techniques used were X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), and X-ray Photoelectron Spectroscopy (XPS). XRD identified copper sulfate (CuSO4) formation and the disappearance of chalcocite/digenite (Cu2S) and bornite (Cu5FeS4), indicating their transformation into sulfates. FESEM showed that enargite particles were oxidized, suggesting they did not form copper sulfates. The XPS results confirmed the presence of copper in species such as sulfides and sulfates. The results indicate that chalcocite and bornite transformed into copper sulfates, while chalcopyrite and enargite were only superficially oxidized. The combination of techniques allowed for a detailed identification of mineral transformations during pretreatment. © 2025 by the authors.