title: Manganese(II)-catalyzed and clay-minerals-mediated reduction of chromium(VI) by citrate.
abstract: Unlike lower valent iron (Fe), the potential role of lower valent manganese (Mn) in the reduction of hexavalent chromium (Cr(VI)) in soil is poorly documented. In this study, we report that citrate along with Mn(II) and clay minerals (montmorillonite and kaolinite) reduce Cr(VI) both in aqueous phase and in the presence of dissolved organic carbon (SDOC) extracted from a forest soil. The reduction was favorable at acidic pH (up to pH 5) and followed the pseudo-first-order kinetic model. The citrate (10 mM) + Mn(II) (182.02 μM) + clay minerals (3% w/v) system in SDOC accounted for complete reduction of Cr(VI) (192.32 μM) in about 72 h at pH 4.9. In this system, citrate was the reductant, Mn(II) was a catalyst, and the clay minerals acted as an accelerator for both the reductant and catalyst. The clay minerals also serve as a sink for Cr(III). This study reveals the underlying mechanism of the Mn(II)-induced reduction of Cr(VI) by organic ligand in the presence of clay minerals under certain environmental conditions.
authors.affiliation: CERAR-Centre for Environmental Risk Assessment and Remediation, Building X, University of South Australia , University Boulevard, Mawson Lakes, SA 5095, Australia.
authors.forename: Binoy
authors.initials: B
authors.lastname: Sarkar
authors.forename: Ravi
authors.initials: R
authors.lastname: Naidu
authors.forename: Gummuluru S R
authors.initials: GS
authors.lastname: Krishnamurti
authors.forename: Mallavarapu
authors.initials: M
authors.lastname: Megharaj
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry*; D001546:Bentonite / Q000737:chemistry; D002384:Catalysis; D002857:Chromium / Q000032:analysis / Q000737:chemistry*; D019343:Citric Acid / Q000737:chemistry*; D000077215:Clay; D052918:Environmental Restoration and Remediation / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D007616:Kaolin / Q000737:chemistry; D007700:Kinetics; D008345:Manganese / Q000737:chemistry*; D010084:Oxidation-Reduction; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis*
chemical_list: D000538:Aluminum Silicates; D012987:Soil; D012989:Soil Pollutants; D002857:Chromium; D001546:Bentonite; C074702:chromium hexavalent ion; D007616:Kaolin; D019343:Citric Acid; D008345:Manganese; D000077215:Clay