Bioleaching and electrochemical property of marmatite by Sulfobacillus thermosulfidooxidans

Bioleaching and electrochemical experiments were conducted to evaluate marmatite dissolution in the presence of pure S. thermosulfidooxidans. The effects of particle size, pH controlling and external addition of Fe3+ ions on the zinc extraction were investigated. The results show that in the bioleaching process the best particle size range is 0.043–0.074 mm and adjusting pH regularly to the initial value has a profound effect on obtaining high leaching rate. External addition of Fe3+ ions could accelerate the bioleaching, while the concentration of additional Fe3+ over 2.5 g/L weakens the positive effect, and even hinders the dissolution of marmatite. SEM and XRD analyses of the leaching residues reveal that a product layer composed of elemental sulfur and jarosite is formed on the mineral surface, which results in a low leaching speed at later phase. The results of electrochemical measurements illustrate that additional Fe3+ ions could increase the corrosion current density, which is favorable to zinc extraction. The EIS spectra show that rate-limiting step does not change when Fe3+ ions are added.