Arsenite Oxidation by a Poorly Crystalline Manganese-Oxide 1. Stirred-Flow Experiments

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• 作者：Brandon J. Lafferty ; Matthew Ginder-Vogel ; Donald L. Sparks
• 刊名：Environmental Science & Technology
• 出版年：2010
• 出版时间：November 15, 2010
• 年：2010
• 卷：44
• 期：22
• 页码：8460-8466
• 全文大小：263K
• 年卷期：v.44,no.22(November 15, 2010)
• ISSN：1520-5851

文摘

Manganese-oxides (Mn-oxides) are quite reactive, with respect to arsenite (As^III) oxidation. However, studies regarding the pathways of As^III oxidation, over a range of time scales, by poorly crystalline Mn-oxides, are lacking. In stirred-flow experiments, As^III oxidation by δ-MnO₂ (a poorly crystalline form of hexagonal birnessite) is initially rapid but slows appreciably after several hours of reaction. Mn^II is the only reduced product of δ-MnO₂ formed by As^III oxidation during the initial, most rapid phase of the reaction. There seems to be evidence that the formation of Mn^III observed in previous studies is a result of conproportionation of Mn^II sorbed onto Mn^IV reaction sites rather than from direct reduction of Mn^IV by As^III. The only evidence of arsenic (As) sorption during As^III oxidation by δ-MnO₂ is during the first 10 h of reaction, and As sorption is greater when As^V and Mn^II occur simultaneously in solution. Our findings indicate that As^III oxidation by poorly crystalline δ-MnO₂ involves several simultaneous reactions and reinforces the importance of studying reaction mechanisms over time.