Physicochemical properties, metal availability and bacterial community structure in heavy metal-polluted soil remediated by montmorillonite-based amendments

Clay materials are commonly used in remediation techniques for heavy metal contaminated soil. In this study, a magnesium (Mg(OH)(2)/MgO)-montmorillonite was proposed to be utilized for heavy metals immobilization in contaminated soil, with the remediation efficiency evaluated through the toxicity characteristic leaching procedure (TCLP) and the community bureau of reference sequential extraction procedure (BCR). The addition of magnesium-montmorillonite resulted in lower TCLP extractability for the heavy metals (Cu, Pb, Zn and Cd) in soil as it promoted their conversion from acid soluble fraction to residual fraction. Meanwhile, MM raised the soil pH and water-soluble organic carbon (WSOC). It was demonstrated that the immobilization of heavy metal in the presence of magnesium-montmorillonite was primarily induced by electrostatic attraction, precipitation and chelation with water-soluble organic carbon. Interestingly, a decreased bacterial community diversity was observed in soil treated by magnesium-montmorillonite (MM). The presence of pure magnesium-montmorillonite promoted the relative abundance of Proteobacteria, Actinobacteria and Firmicutes but reduced that of Bacteroides and Acidobacteria. Our results suggest that integrating the biochar into montmorillonite-based amendments can alleviate the damage to soil microorganisms by weakening the negative correlation between the two factors (content clay and WSOC in soil) and soil bacteria. (C) 2020 Elsevier Ltd. All rights reserved.