Copper Redox Transformation and Complexation by Reduced and Oxidized Soil Humic Acid. 2. Potentiometric Titrations and Dialysis Cell Experiments

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• 作者：Felix Maurer ; Iso Christl ; Beate Fulda ; Andreas Voegelin ; Ruben Kretzschmar
• 刊名：Environmental Science & Technology
• 出版年：2013
• 出版时间：October 1, 2013
• 年：2013
• 卷：47
• 期：19
• 页码：10912-10921
• 全文大小：433K
• 年卷期：v.47,no.19(October 1, 2013)
• ISSN：1520-5851

文摘

Cation binding and electron transfer reactions of humic substances determine copper speciation in redox-dynamic systems, but quantitative studies for Cu⁺ binding to humic substances are lacking. We investigated reduction of Cu²⁺ and binding of Cu⁺ at pH 7.0 in a dialysis cell experiment using reduced and reoxidized soil humic acid (HA) as reductant and sorbent at copper loadings of 9.5鈥?00 mmol kg^鈥?. The data were used to quantitatively explain the interaction between cation binding and electron transfer processes that determine copper speciation in the presence of HA under anoxic and oxic conditions. Addition of Cu²⁺ to reduced HA resulted in almost complete reduction to Cu(I) within 1 h. Reduction was also significant under oxic conditions. The slow decrease of the Cu(I) fraction was attributed to formation of Cu(0) based on thermodynamic consideration. Cu⁺ binding to HA was found to be strong compared to other chalcophile cations like Ag⁺ or Cd²⁺. Our results indicate that Cu⁺ and Cu²⁺ isotherms exhibit a redox potential-dependent intersection point. According to the differences in Cu⁺ and Cu²⁺ binding, the presence of HA was found to extend the stability field of Cu(II) to moderately reducing conditions and to reduce the stability field of Cu(0) due to the formation of Cu(I) complexes.