XPS Analysis and Mechanism of Pyrite Biooxidation

The dissolution of pyrite was controlled by the surface chemical reaction, which was the key factor affecting the dissolution process. X-ray photoelectron spectroscopy (XPS) was an advanced surface analysis technique in study of mineral dissolution process, and a change in the chemical state of element on the surface less 5 nm could be observed by XPS, which could be good reference for understanding mechanisms and kinetics for bioleaching of pyrite. In this paper, XPS analysis was used to analyze the changes of chemical state on mineral surface during the biological leaching of pyrite at room temperature. The results showed that the surficial layer was made up of both the sulphur-bearing and the iron-bearing products, the sulphur-bearing group was comprised of pyrite, sulphate, cysteine and polysulphide, while the iron-bearing group was comprised of goethite and ferric complex. The results showed that dissolution of pyrite was related to surficial sulphur speciation. In the pyrite dissolution process, the Fe-S bond broke first, and then the surficial iron and sulphur were rapidly oxidized by bacteria and oxygen, after that the reaction interface migrated deeper into the pyrite body, and the iron hydroxides and oxides were the final remaining phase on the surface of pyrite. The pyrite was bio-degraded via thiosulfate mechanism, and multiple patterns of bioleaching coexisted, including “indirect” and “direct” leaching. To a certain extent, these stable iron hydroxides and oxides accelerated electron transfer on the surface of pyrite, and promoted the electrochemical oxidation of pyrite. © Editorial Office of Chinese Journal of Rare Metals. All right reserved.