Remediation of Cr (VI) by inorganic-organic clay

Application of inorganic-organic clays (IOCs) for the remediation of hexavalent chromium (Cr (VI)) and the effect of bisphenol-A (BPA) were investigated. IOCs were better adsorbents for the removal of Cr (VI) than organoclay. Solution pH significantly affected the surface charge of IOCs and speciation of Cr in the solution; hence, the adsorption of Cr onto IOCs. Pseudo-second order model and Langmuir model were the best fit for the kinetics and equilibrium data, indicating chemisorption and formation of monolayer on homogenous adsorption sites, respectively. Cr (VI) adsorption by IOCs was driven by electrostatic interactions between positively charged IOC surfaces and HCrO₄^- anions. The IOC adsorption capacity for Cr (VI) correlates with the amount of loosely held ODTMA on the external surface of the clay. Involvement of an anion-exchange reaction was suggested in which the counter halide ions of the cationic surfactants were replaced by HCrO₄^- anions. Cr (VI) adsorption was not affected by the presence of BPA in the medium and two mechanisms for the adsorption of BPA and Cr (VI) were suggested. Partial reduction of Cr (VI) to Cr (III) was observed on the surface of IOC and the reducing agent responsible was suggested to be the Fe (II) in montmorillonite.