title: Respective role of Fe and Mn oxide contents for arsenic sorption in iron and manganese binary oxide: an X-ray absorption spectroscopy investigation.
abstract: In our previous studies, a synthesized Fe-Mn binary oxide was found to be very effective for both As(V) and As(III) removal in aqueous phase, because As(III) could be easily oxidized to As(V). As(III) oxidation and As(V) sorption by the Fe-Mn binary oxide may also play an important role in the natural cycling of As, because of its common occurrence in the environment. In the present study, the respective role of Fe and Mn contents present in the Fe-Mn binary oxide on As(III) removal was investigated via a direct in situ determination of arsenic speciation using X-ray absorption spectroscopy. X-ray absorption near edge structure results indicate that Mn atoms exist in a mixed valence state of +3 and +4 and further confirm that MnOx (1.5 < x < 2) content is mainly responsible for oxidizing As(III) to As(V) through a two-step pathway [reduction of Mn(IV) to Mn(III) and subsequent Mn(III) to Mn(II)] and FeOOH content is dominant for adsorbing the formed As(V). No significant As(III) oxidation by pure FeOOH had been observed during its sorption, when the system was exposed to air. The extended X-ray absorption fine structure results reveal that the As surface complex on both the As(V)- and As(III)-treated sample surfaces is an inner-sphere bidentate binuclear corner-sharing complex with an As-M (M = Fe or Mn) interatomic distance of 3.22-3.24 Å. In addition, the MnOx and FeOOH contents exist only as a mixture, and no solid solution is formed. Because of its high effectiveness, low cost, and environmental friendliness, the Fe-Mn binary oxide would play a beneficial role as both an efficient oxidant of As(III) and a sorbent for As(V) in drinking water treatment and environmental remediation.
authors.affiliation: State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences (RCEES), Chinese Academy of Sciences (CAS) , Post Office Box 2871, Beijing 100085, People's Republic of China.
authors.forename: Gaosheng
authors.initials: G
authors.lastname: Zhang
authors.forename: Fudong
authors.initials: F
authors.lastname: Liu
authors.forename: Huijuan
authors.initials: H
authors.lastname: Liu
authors.forename: Jiuhui
authors.initials: J
authors.lastname: Qu
authors.forename: Ruiping
authors.initials: R
authors.lastname: Liu
mesh_terms: D000327:Adsorption; D001151:Arsenic / Q000302:isolation & purification*; D005290:Ferric Compounds / Q000737:chemistry*; D017895:Manganese Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry*; D012015:Reference Standards; D013696:Temperature; D056928:X-Ray Absorption Spectroscopy; D014965:X-Rays
chemical_list: D005290:Ferric Compounds; D017895:Manganese Compounds; D010087:Oxides; C000499:ferric oxide; C027424:manganese oxide; D001151:Arsenic