title: Co2+-exchange mechanism of birnessite and its application for the removal of Pb2+ and As(III).
abstract: Co-containing birnessites were obtained by ion exchange at different initial concentrations of Co(2+). Ion exchange of Co(2+) had little effect on birnessite crystal structure and micromorphology, but resulted in an increase in specific surface areas from 19.26 to 33.35 m(2)g(-1), and a decrease in both crystallinity and manganese average oxidation state. It was due to that Mn(IV) in the layer structure was reduced to Mn(III) during the oxidation process of Co(2+) to Co(III). The hydroxyl groups on the surface of Co-containing birnessites gradually decreased with an increase of Co/Mn molar ratio owing to the occupance of Co(III) into vacancies and the location of large amounts of Co(2+/3+) and Mn(2+/3+) above/below the vacant sites. This greatly accounted for the monotonous reduction in Pb(2+) adsorption capacity, from 2538 mmol kg(-1) for the unmodified birnessite to 1500 mmol kg(-1) for the Co(2+) ion-exchanged birnessite with a Co/Mn molar ratio of 0.16. The amount of As(III) oxidized by birnessite was enhanced after ion exchange, but the apparent initial reaction rate was greatly decreased. The present work demonstrates that Co(2+) ion exchange has great influence on the adsorption and oxidation behavior of inorganic toxic metal ions by birnessite in water environments.
authors.affiliation: Key Laboratory of Subtropical Agricultural Resources and Environment, Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, PR China.
authors.forename: Hui
authors.initials: H
authors.lastname: Yin
authors.forename: Fan
authors.initials: F
authors.lastname: Liu
authors.forename: Xionghan
authors.initials: X
authors.lastname: Feng
authors.forename: Mingming
authors.initials: M
authors.lastname: Liu
authors.forename: Wenfeng
authors.initials: W
authors.lastname: Tan
authors.forename: Guohong
authors.initials: G
authors.lastname: Qiu
mesh_terms: D000327:Adsorption; D001152:Arsenicals / Q000302:isolation & purification*; D003035:Cobalt / Q000737:chemistry*; D004785:Environmental Pollutants / Q000302:isolation & purification*; D007474:Ion Exchange; D007854:Lead / Q000302:isolation & purification*; D008345:Manganese / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry*; D056951:Photoelectron Spectroscopy; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties
chemical_list: D001152:Arsenicals; D004785:Environmental Pollutants; D010087:Oxides; C505018:birnessite; D007854:Lead; D003035:Cobalt; D008345:Manganese