Impacts of coexisting mineral on crystallinity and stability of Fe(II) oxidation products: Implications for neutralization treatment of acid mine drainage

The neutralization treatment of acid mine drainage involves the oxidation of Fe(II), but little is known about effects of co-existing minerals on the oxidation and hydrolysis of Fe(II) to iron oxides. Here we investigated transformation of fresh and heated Fe(II) oxidation coprecipitates, which were synthesized in the presence and the absence of five co-existing minerals (montmorillonite, kaolin, quartz (SiO2), aluminium oxide (Al2O3) and calcium carbonate (CaCO3)). In the FeSO4 system with montmorillonite or kaolin, the formation of lepidocrocite was inhibited with the increase of clay mineral contents. In the same system, heated coprecipitates of mont-morillonite were mainly comprised of amorphous ferrihydrite and its transformation was retarded by the excess montmorillonite. In the FeCl2 system with SiO2, Al2O3 or CaCO3, akaganeite formation was inhibited with increase in the corresponding mineral contents. In the same system, goethite formation was blocked by either CaCO3 or Al2O3 and the growth of lepidocrocite was inhibited by CaCO3 or SiO2. However, magnetite formation was enhanced by addition of CaCO3. These findings are important for predicting products of abiotic Fe(II) oxidation during the neutralization of acid mine drainage and for better understanding the transformation of amorphous iron oxides in the complicated environmental matrix.