Bidentate and Monodentate Binding of Chromium (VI) on the Acid Scavenger Exchange Resin, MP-Carbonate, as a Function of pH

Abstract

Hexavalent chromium or Cr (VI) is a serious health risk that has been identified in drinking water and generally originates as industrial by-products and hazardous waste sites, although natural sources have been reported. Common methods to remove Cr (VI) employ adsorption, filtration, ion exchange technologies, and redox reactions. We report on a macro porous polystyrene anion exchange resin, a solid-supported equivalent of tetra-alkyl ammonium carbonate (Biotage® MP-Carbonate), to effectively remove Cr (VI) from synthetic wastewater with bidentate or monodentate binding modes of chromate, depending on the pH environment. Sorption capacity is pH dependent with 332, 161, and 163 mg CrO 4 2− per gram of MP-Carbonate adsorbed at pH 2, 6.8, and 10, respectively. Experimental data indicate an exergonic and endothermic adsorption process. Static vs. dynamic reaction conditions are discussed. Density functional theory calculations parallel the Gibbs free energy results of the bidentate binding of the large chromate ion compared to carbonate with the ammonium ions. These studies identify the potential uses of MP-Carbonate in the remediation of Cr (VI) wastewater unrelated to the pH of the water source.

Functionalization of magnetic chitosan microparticles for high-performance removal of chromate from aqueous solutions and tannery effluent

“…Many studies have demonstrated the potential of zero-valent iron [10], iron oxide [11], and magnetitebased sorbents [12] for the removal of chromate anions. Synthetic resins (chelating [13] or ion-exchange [14,15] have been frequently used for the recovery of chromate anions. Composite beads prepared by the interactions of alginate with polyethyleneimine have also been recently designed as beads for the effective recovery of Cr(VI) [16].…”