Combined SECM and spectroscopy investigation of the interfacial chemistry of chalcopyrite during anodic oxidation

Hydrometallurgical copper extraction from chalcopyrite (CuFeS2), the most abundant copper-containing resource in the world, is always challenged by its passivation during industrial application, whose mechanisms are still not fully understood. In this study, the interfacial chemistry of chalcopyrite during the anodic oxidation was studied by combined Scanning Electrochemical Microscopy (SECM) and spectroscopic analyzes of Raman spectroscopy and X-ray absorption near-edge spectroscopy (XANES). Ex-situ SECM feedback mode was firstly used to detect and image the formation of passivating films. Then, the in-situ SECM substrate generation-tip collection (SG-TC) experiment by positioning the micro-platinum probe just above the chalcopyrite surface was conducted so that electrochemically active dissolution products can be deposited and monitored. Subsequently, Raman spectroscopy was performed on the SECM tip and the chalcopyrite substrate electrode respectively to identify the products that were released into the solution and then collected on the tip, as well as the ones left behind on the mineral surface. The SECM feedback mode mapping and approach curves demonstrated that under the passive and trans-passive potential regions, low conductive passivation films formed on the chalcopyrite surface, which contributed to the hindered dissolution of chalcopyrite due to the decreased electron transfer rate. In-situ SECM SG-TC results from the anodically oxidized chalcopyrite suggested that soluble sulfur species, most likely thiosulfate ions (S2O32?) were dissolved from the surface during the passivation films formation. The released S2O32? was evidenced by comparing with the pyrite anodic oxidation experiment and sulfur K-edge XANES analysis of the electrolytes collected after chalcopyrite anodic dissolution. In-situ Raman spectra of the oxidized chalcopyrite surface confirmed metal deficient layers were the passivation layers.