The promotion effect of FeS₂ on Sb₂S₃ bioleaching and Sb speciation transformation

Stibnite (Sb₂S₃) is an important but difficult to biologically leach mineral, so it is important to find a potential scheme for improving the bioleaching rate of Sb₂S₃. In this study, by combining experiments and first-principles density functional theory (DFT) calculations, the impact and related mechanisms of pyrite (FeS₂) on stibnite (Sb₂S₃) bioleaching were studied for the first time. The bioleaching results revealed that FeS₂ obviously improved the Sb₂S₃ bioleaching rate, and in the 0.5FeS₂:0.5CuFeS₂ system, the bioleaching rate of Sb₂S₃ increased from 2.23 to 24.6%, which was the best mass mixing ratio. The XPS and XANES results revealed that during the bioleaching process, Sb₂S₃ was transformed to Sb₂O₃ and Sb₂O₅. The electrochemical results revealed that after FeS₂ was mixed, a FeS₂-Sb₂S₃ galvanic cell formed, which promoted the electron transfer efficiency and redox reaction of Sb₂S₃. The DFT results show that between the Sb₂S₃ (0 1 0) and FeS₂ (1 0 0) surfaces, S-Fe, S-S, S-Sb, and Sb-Fe bonds are formed, and the direction of electron transfer is from Sb₂S₃ to FeS₂; the work functions for Sb₂S₃ after addition of FeS₂ decrease, implying that faster electron transfer occurs; Fe(III)-6H₂O derived from FeS₂ adsorbs on the surface more easily than does glucose, which is the major component of the extracellular polymeric substances in bacteria, indicating that during the bioleaching process, Fe(III)-6H₂O plays an important role; after mixing, both Fe(III)-6H₂O and glucose adsorb on the Sb₂S₃ (0 1 0) surface more easily, with stronger bonds and larger adsorption energies, which are in good agreement with the experimental results.