Cu2+和Zn2+在土壤电场中的极化对黑土胶体凝聚的影响

金属离子在土壤胶体固-液界面上的行为差异引起土壤胶体絮凝过程的差异,并深刻影响土壤溶液中养分或污染物的迁移转化。为明确Cu~(2+)和Zn~(2+)两种金属离子界面行为对土壤胶体凝聚的影响,本文选取黑土胶体为研究对象,利用动态/静态光散射技术研究专性吸附离子Cu和Zn体系中不同离子浓度条件下黑土胶体的凝聚行为。结果表明:(1)Cu~(2+)和Zn~(2+)两种金属离子引发黑土胶体凝聚的机制相似,均是低浓度下的慢速凝聚和高浓度下的快速凝聚,达到快速凝聚机制后,胶体的总体平均凝聚速率受离子种类影响较小。(2)Cu~(2+)对黑土胶体聚沉能力大于Zn~(2+),Zn~(2+)的临界聚沉浓度是Cu~(2+)的3.51倍,在黑土胶体的凝聚过程中存在强烈的离子特异性效应。(3)两种离子体系中颗粒间相互作用的活化能差异随离子浓度的降低而增大。此两种离子在凝聚作用的较大差异性源于Cu~(2+)较Zn~(2+)对有机配位体有较强的亲和力,以及黑土胶体表面附近强电场对离子的强烈极化作用扩大了两种离子本身的微小差异。

Effects of Cu2+ and Zn2+ polarization by electric fields on the colloid aggregation of black soil

The behavior of metal ions at the solid-liquid interfaces of soil considerably affects the aggregation of soil colloids, which subsequently influences the movement and transformation of nutrients and contaminants in soil solutions. To analyze the effects of interfacial behaviors by Cu²⁺ and Zn²⁺ on soil colloid aggregation, the aggregation kinetics of black soil colloids were monitored using a dynamic/static light scattering instrument. The aggregate process was induced by specifically adsorbed Cu²⁺ and Zn²⁺ ions. The aggregation of black soil colloids was induced by Cu²⁺ and Zn²⁺ through similar mechanisms. The soil colloids underwent reaction-limited cluster aggregation at low electrolyte concentrations and diffusion-limited cluster aggregation(DLCA) at high electrolyte concentrations. In the DLCA regime, the total average colloid aggregation rate was relatively unaffected by ion species. Strong ion-specific effects were observed for Cu²⁺ and Zn²⁺ during the aggregation of black soil colloids. The critical coagulation concentration of Zn²⁺ was 3.51 times higher than that of Cu²⁺, and the difference between the two systems'' activation energies increased with declining electrolyte concentrations. Two explanations were proposed for the observed differences in the aggregation behaviors of soil colloids induced by Cu²⁺ and Zn²⁺. Cu²⁺ had a stronger affinity for organic ligands than Zn²⁺. Moreover, the strong polarization of ions by strong electric fields at the surface of black soil colloids amplified the minor differences in the structure of the two ions.