Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich , CH-8092 Zurich, Switzerland.
Environ Sci Technol. 2013 Oct 1;47(19):10912-21. doi: 10.1021/es4024095. Epub 2013 Sep 19.
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 9.5-600 mmol kg(-1). 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.
腐殖物质的阳离子结合和电子转移反应决定了氧化还原动力学系统中铜的形态，但缺乏腐殖物质与 Cu+结合的定量研究。我们在 pH 7.0 的透析细胞实验中研究了 Cu2+的还原和 Cu+的结合，使用还原和氧化的土壤腐殖酸 (HA) 作为还原剂和吸附剂，铜负载量为 9.5-600 mmol kg(-1)。这些数据用于定量解释在存在 HA 的情况下，阳离子结合和电子转移过程之间的相互作用，这些过程决定了缺氧和有氧条件下铜的形态。将 Cu2+加入还原的 HA 中，在 1 小时内几乎完全还原为 Cu(I)。在有氧条件下也有明显的还原作用。Cu(I)分数的缓慢下降归因于基于热力学考虑形成的 Cu(0)。与其他亲硫阳离子（如 Ag+或 Cd2+）相比，发现 Cu+与 HA 的结合很强。我们的结果表明，Cu+和 Cu2+的等温线表现出氧化还原电位依赖性交点。根据 Cu+和 Cu2+结合的差异，发现 HA 的存在将 Cu(II)的稳定场扩展到中等还原条件，并由于 Cu(I)配合物的形成而降低 Cu(0)的稳定场。
