Microbial Leaching of Iron from Hematite: Direct or Indirect Elution

Exiguobacterium oxidotolerans was found to be effective for dissolving Fe2+ from hematite via reduction under alkaline conditions. However, the possible mechanism for bacterial reduction of hematite in seawater is still unclear. The present work has investigated the reductive dissolution of iron by the bacteria in two elution systems, namely direct and indirect elution systems. Greater than 30 mg L−1 of Fe was dissolved and measured in a direct elution system. Fourier transform infrared (FTIR) and field-emission scanning electron microscopy (FE-SEM) revealed the surface oxidation and particle aggregation in our direct elution system. The obtained results suggest that direct interaction of bacterial cells with hematite facilitates iron elution, probably due to electron transfer to hematite via the cell membrane, resulting in reductive elution of hematite.