Zinc Adsorption Effects on Arsenite Oxidation Kinetics at the Birnessite-Water Interface

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• 作者：Laura E. Power ; Yuji Arai ; and Donald L. Sparks
• 刊名：Environmental Science & Technology
• 出版年：2005
• 出版时间：January 1, 2005
• 年：2005
• 卷：39
• 期：1
• 页码：181 - 187
• 全文大小：166K
• 年卷期：v.39,no.1(January 1, 2005)
• ISSN：1520-5851

文摘

Arsenite is more toxic and mobile than As(V) in soil andsediment environments, and thus it is advantageous to explorefactors that enhance oxidation of As(III) to As(V). Previousstudies showed that manganese oxides, such as birnessite(-MnO₂), directly oxidized As(III). However, these studiesdid not explore the role that cation adsorption has onAs(III) oxidation. Accordingly, the effects of adsorbed andnonadsorbed Zn on arsenite (As(III)) oxidation kineticsat the birnessite-water interface were investigated usingbatch adsorption experiments (0.1 g L^-1; pH 4.5 and 6.0;I = 0.01 M NaCl). Divalent Zn adsorption on synthetic -MnO₂in the absence of As(III) increased with increasing pHand caused positive shifts in electrophoretic mobility valuesat pH 4-6, indirectly suggesting inner-sphere Zn adsorptionmechanisms. Arsenite was readily oxidized on birnessitein the absence of Zn. The initial As(III) oxidation rate constantdecreased with increasing pH from 4.5 to 6.0 and initialAs(III) concentrations from 100 to 300 M. Similar pH andinitial As(III) concentration effects were observed insystems when Zn was present (i.e., presorbed Zn prior toAs(III) addition and simultaneously added Zn-As(III)systems), but As(III) oxidation reactions were suppressedcompared to the respective control systems. Thesuppression was more pronounced when Zn was presorbedon the -MnO₂ surfaces as opposed to added simultaneouslywith As(III). This study provides further understandingof As(III) oxidation reactions on manganese oxide surfacesunder environmentally applicable conditions wheremetals compete for reactive sites.