The role of Fe(III) in enhancement of interaction between chitosan and vermiculite for synergistic co-removal of Cr(VI) and Cd(II)

Abstract Due to migration and the property of non-biodegradability, Cr(VI) and Cd(II) commonly coexist in water and soil, causing a synergistic toxic effect to humans. The interaction among metal ions, minerals and natural organic matter influences the migration process of heavy metals. This study focuses on the role that Fe(III) plays in the interaction between chitosan (CTS) and vermiculite (VMT) in regard to Cr(VI) and Cd(II) immobilization. Owing to the bridge bonding of Fe(III), a wrinkly film spread evenly on chitosan-Fe(III)-vermiculite composite (CTS-Fe-VMT-3). A fraction of the CTS enters the interlayer of the VMT. Relative to the VMT and CTS-VMT, the CTS-Fe-VMT-3 composite was found to have higher fixation capacity in the Cr(VI) and Cd(II) binary system. The findings verified the important role of Fe(III) in removal of Cr(VI) (102.740 mg g-1) and Cd(II) (59.524 mg g-1). A synergistic effect was also observed during adsorption by CTS-Fe-VMT-3 of the binary Cr(VI) and Cd(II) system. The synergistic removal mechanism involved complexation, electrostatic force, chelation, cation bridges, redox reaction and anion bridges. Moreover, the CTS-Fe-VMT-3 reduced part of Cr(VI) to Cr(III). Therefore, Fe(III) can significantly influence the migration and transformation of Cr(VI) and Cd(II) by affecting the interaction of CTS and VMT. This study provides a new idea for the treatment of combined heavy metal wastewater. To reveal the influence of the interaction of minerals and organic matter on the migration and transformation of heavy metals, the role of iron should be taken into consider.