Arsenite Oxidation by a Poorly Crystalline Manganese-Oxide. 2. Results from X-ray Absorption Spectroscopy and X-ray Diffraction

• Published in: Environmental science & technology Vol. 44; no. 22; pp. 8467 - 8472
• Main Authors: Lafferty, Brandon J, Ginder-Vogel, Matthew, Zhu, Mengqiang, Livi, Kenneth J. T, Sparks, Donald L
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15.11.2010
• Subjects: Adsorption; Applied sciences; Arsenic; Arsenites - chemistry; Chemical reactions; Crystal structure; Crystallization; Diffraction; Environmental Processes; Exact sciences and technology; Manganese compounds; Manganese Compounds - chemistry; Minerals; Oxidation; Oxidation-Reduction; Oxides - chemistry; Pollution; Spectrum analysis; X-Ray Absorption Spectroscopy; X-Ray Diffraction; Oxidation reduction; XANES spectrometry; Arsenic; Arsenates; Pollutant behavior; X ray diffraction; EXAFS spectrometry; Heavy metal; Arsenites; Sorption; Trace element; Carcinogen; Manganese oxides; Pollution; X ray absorption spectrometry; Reaction mechanism; Simultaneous reaction; Poison; Oxidation
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es102016c

Arsenite (AsIII) oxidation by manganese oxides (Mn-oxides) serves to detoxify and, under many conditions, immobilize arsenic (As) by forming arsenate (AsV). AsIII oxidation by MnIV-oxides can be quite complex, involving many simultaneous forward reactions and subsequent back reactions. During AsIII oxidation by Mn-oxides, a reduction in oxidation rate is often observed, which is attributed to Mn-oxide surface passivation. X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) data show that MnII sorption on a poorly crystalline hexagonal birnessite (δ-MnO2) is important in passivation early during reaction with AsIII. Also, it appears that MnIII in the δ-MnO2 structure is formed by conproportionation of sorbed MnII and MnIV in the mineral structure. The content of MnIII within the δ-MnO2 structure appears to increase as the reaction proceeds. Binding of AsV to δ-MnO2 also changes as MnIII becomes more prominent in the δ-MnO2 structure. The data presented indicate that AsIII oxidation and AsV sorption by poorly crystalline δ-MnO2 is greatly affected by Mn oxidation state in the δ-MnO2 structure.