Electrochemical and XAFS Studies of Effects of Carbonate on the Oxidation of Arsenite

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• 作者：Jaeshin Kim ; Gregory V. Korshin ; Anatoly I. Frenkel ; and Alexander B. Velichenko
• 刊名：Environmental Science & Technology
• 出版年：2006
• 出版时间：January 1, 2006
• 年：2006
• 卷：40
• 期：1
• 页码：228 - 234
• 全文大小：201K
• 年卷期：v.40,no.1(January 1, 2006)
• ISSN：1520-5851

文摘

Measurements of electrochemical (EC) arsenite oxidationdemonstrated that the arsenite oxidation current increasedin the presence of carbonate while the potential of the onsetof EC arsenite oxidation exhibited a strong shift towardless positive values. Examination of pH and total carbonateconcentration effects on the EC arsenite oxidationparameters showed that they were affected solely by theconcentration of carbonate ion CO₃^2-, which appearedto form relatively weak mono- and dicarbonate complexeswith arsenite. The EC activity of these complexes wasdetermined to be almost an order of magnitude higher thanthat of free arsenite. However, X-ray absorption fine-structure (XAFS) measurements did not show any changesin the properties of the As(III) inner complexation shellassociated with the presence of the bound carbonate ions.It was accordingly concluded that the strength of bondsbetween the bound carbonate and As(III) is close to that forAs(III)-OH^- interactions. The acceleration of the oxidationof carbonate-As(III) complexes was hypothesized tobe associated with an additional pathway of the formationof As(IV) intermediates, in which the carbonate grouppresent in the As(III) inner shell provides an electron toform a bound carbonate radical and also a good leavinggroup for facile cleavage from the transient As(IV) species.