Enhancement of arsenopyrite bioleaching by different Fe(III) compounds through changing composition and structure of passivation layer

Ferric iron has a significant effect on the bioleaching of arsenopyrite, the most efficient way for pretreatment of arsenopyrite-bearing gold ores. Up to date, the differential effect of Fe(III) compounds on that process was rarely studied. Herein, FeCl3, Fe(NO3)3 and Fe2O3 were addressed to unravel their different promotion effects during arsenopyrite biooxidation by Sulfobacillus thermosulfidooxidans, in which the As/Fe/S speciation transformation were comprehensively analyzed mainly with synchrotron radiation-based X-ray diffraction (SR-XRD) and Fe L- and As/S K-edge X-ray absorption near edge structure (XANES) spectroscopy to detect the elimination of passivation, besides the changes in the morphology and the leaching parameters of the mineral. The results showed that, the bioleaching of arsenopyrite was efficiently promoted under addition of the Fe(III) compounds (0.6 g/L), for instance, the extraction rates of As were increased from 55% to 64–77%, the surface of arsenopyrite suffered more serious corrosion and covered with a loose and porous structure, the intermediates S0, thiosulfate and orpiment significantly decreased, and jarosites and schwertmannite increased, the remaining content of arsenopyrite was decreased from 31.5% to 21.7–5.3%. Those results indicated that, the iron/sulfur oxidation activity was enhanced and the transformation of those intermediates was accelerated by the Fe(III) compounds added. Such change intension accompanied with the promotion effect observes the order FeCl3 > Fe(NO3)3 > Fe2O3. These results reveale that the adding Fe(III) compounds, especially for FeCl3, can efficiently promote the biooxidation through removal of some intermediates from the surface of the arsenopyrite and thus optimize the pretreatment of arsenopyrite-bearing gold ores.