title: Oxidation of Cr(III) on birnessite surfaces: The effect of goethite and kaolinite.
abstract: Oxidation of Cr(III) by manganese oxides may pose a potential threat to environments due to the formation of toxic Cr(VI) species. At present, it was still unclear whether the extent of Cr(III) oxidation and fate of Cr(VI) would be changed when manganese oxides co-exist with other minerals, the case commonly occurring in soils. This study investigated the influence of goethite and kaolinite on Cr(III) oxidation by birnessite under acidic pH condition (pH3.5) and background electrolyte of 0.01mol/L NaCl. Goethite was found not to affect Cr(III) oxidation, which was interpreted as the result of overwhelming adsorption of cationic Cr(III) onto the negatively-charged birnessite (point of zero charge (PZC)<3.0) rather than the positively-charged goethite (PZC=8.8). However, more Cr(VI) would be retained by the surface with the increase in addition of goethite because of its strong ability on adsorption of Cr(VI) at low pH. Moreover, either Cr(III) oxidation or distribution of the generated Cr(VI) between the solid and solution phases was not affected by kaolinite (PZC<3.0), indicating its low affinity for Cr species. Reactions occurring in the present mixed systems were suggested, which could be partly representative of those in the soils and further indicates that the mobility and risk of Cr(VI) would be decreased if goethite was present.
authors.affiliation: Department of Resources and Environmental Sciences, College of Agriculture, Guangdong Ocean University, Zhanjiang 524088, China. Electronic address: zjzhly@126.com.
authors.forename: Laiyuan
authors.initials: L
authors.lastname: Zhong
authors.affiliation: Department of Resources and Environmental Sciences, College of Agriculture, Guangdong Ocean University, Zhanjiang 524088, China; Stockbridge School of Agriculture, University of Massachusetts, Amherst, MA 01003, USA.
authors.forename: Jiewen
authors.initials: J
authors.lastname: Yang
authors.affiliation: Department of Land Resources Management, College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China. Electronic address: lm_liu@126.com.
authors.forename: Liming
authors.initials: L
authors.lastname: Liu
authors.affiliation: Stockbridge School of Agriculture, University of Massachusetts, Amherst, MA 01003, USA.
authors.forename: Baoshan
authors.initials: B
authors.lastname: Xing
mesh_terms: D002857:Chromium / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D058085:Iron Compounds / Q000737:chemistry*; D007616:Kaolin / Q000737:chemistry*; D008903:Minerals / Q000737:chemistry*; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D058085:Iron Compounds; D008903:Minerals; D010087:Oxides; C505018:birnessite; D002857:Chromium; C094886:goethite; D007616:Kaolin
keywords: Birnessite; Cr(III) oxidation; Goethite; Kaolinite