Detailed study on reduction of hazardous Cr(VI) at acidic pH using modified montmorillonite Fe(II)-Mt under ambient conditions

Contamination of groundwater and soil by high levels of hexavalent chromium directly affects the environment and human health as a serious pollutant. Remediation by reduction, i.e., Cr(VI) Cr(III), using a variety of reducing agents and/or processes has been explored for many years. In the present study, application of Fe(II)-Montmorillonite [a dioctahedral smectite, Fe(II)-Mt] containing interlayer Fe(II) ions as an environmentally benign clay mineral for reduction of Cr(VI) in acidic pH from aqueous solution was investigated. Fe(II)-Mt was reacted at stoichiometric excess [Fe(II)-Mt: 0.32g; Cr(VI): 1mM, 100mL] in K2Cr2O7 solution at pH of 5.5 and 3.0. The decrease of Cr(VI) was monitored spectrophotometrically, and the results were corrected for the anion exclusion effect, i.e., the electrostatic interaction of HCrO- ions with the negatively charged surface of the clay mineral. Stoichiometric reduction of Cr(VI) was achieved in short time; at pH 5.5, 20% reduction was achieved in the first 10min, after which the reduction proceeded gradually to consume all of the interlayer Fe(II) ions at about 6h. On the other hand, at pH 3.0, the reaction completed in about 15min. Moreover, Fe(II)-Mt clay mineral can be conveniently prepared and handled in large amounts, making this method feasible even for remediation of Cr(VI) contamination over large areas in real applications.