Coupling of bioleaching and electrokinetic soil flushing for the in-situ removal of impurity from Pb-Zn mine tailings

This study combines bioleaching and electrokinetics (EK) for the in-situ removal of metals from polluted mine tailings collected from an abandoned Pb-Zn mine. The proposed treatment strategy consisted in the external production of an acid bioleaching (BL) medium in a bioreactor by means of autochthonous acidophilic microorganisms incubated from real mine tailings; next, the BL medium was subsequently used as anolyte and placed in contact in situ with the polluted soil, taking advantage of EK mechanisms r for dissolution and transport of metals to the cathode compartment. After obtaining a microbial culture capable of producing the bioleaching medium, lab-scale EK experiments were performed, and the influence of the voltage dosage (0.5, 1.0 and 1.5Vcm-1) was assessed. The results obtained showed that the BL medium improved the metal removal efficiency, and that the applied voltage gradient had a clear influence. Specifically, the combination of an electric current under 1.5Vcm-1 and the BL medium increased the metal removal rates by 17% (Fe), 4% (Cu), 2% (Zn), 12% (Mn), 12% (Ni), 1% (Cr) and 7% (Co), as compared to those without using BL. With this novel treatment, it was also possible to comply with the local regulatory requirements for most of the metals studied. This technology offers several advantages over other EK-bioleaching configurations previously reported. It was found that the limiting factor in the process was the voltage gradient applied, as higher voltages increased metal removal yields but also producing higher soil heating with the consequent energy losses.