Removal of heavy metals from real mine tailings coupling electrokinetic soil flushing and Bioleaching

In the present work, polluted mine tailings from the abandoned Pb/Zn mine of San Quintín (Ciudad Real, Spain) have been treated by an innovative in-situ bioleaching process. Bioleaching uses the capacity of certain microorganisms of oxidizing iron and/or reduce sulphur which enhance the process of metal extraction due to the production of Fe3+ among other oxidizing agents. In-situ treatments, as electrokinetics (EK), allow the metal extraction and offer multiple advantages. EK use an electric field to mobilize species towards the soil thanks to the electromigration, electrophoresis and electroosmosis. The aim of this work is to evaluate the coupling of bioleaching and EK for the removal of heavy metals from the mine tailings. An acid leching medium, produced externally by acidophilic autochthonous microorganisms, was used as the anolyte in the EK cell. Thanks to the EK transport phenomena, the oxidizing medium was transported to the cathode, leaching the heavy metals of the soil, while simultaneously the leached metals were removed through the cathode due to electromigration. Different voltages were studied (0.5, 1 and 1.5 V/cm), the best results were for 1.5 V/cm, and it was clearly observed the positive influence of using the bioleaching culture compared to a single EK reference test.