HPO42-和H2PO4-对蒙脱石-胡敏酸胶体凝聚的影响

为探究HPO₄^2-和H₂PO₄^-界面行为对土壤胶体凝聚的影响，以蒙脱石和胡敏酸胶体为研究对象，采用动态光散射技术比较研究HPO₄^2-和H₂PO₄^-引发胶体颗粒凝聚过程的差异.结果表明，随着电解质离子强度的升高，HPO₄^2-和H₂PO₄^-体系蒙脱石-胡敏酸混合悬液从慢速凝聚（线性增长）转化为快速凝聚（幂函数增长），但胶体凝聚过程对H₂PO₄^-体系离子强度的变化更敏感.HPO₄^2-和H₂PO₄^-作用下凝聚体有效粒径增长、总体平均凝聚速率（TAA）、临界聚沉离子强度（CCIS）和活化能均存在明显差异；其中，与HPO₄^2-相比，H₂PO₄^-体系中拥有更高的TAA、更低的CCIS和活化能，说明H₂PO₄^-离子引发蒙脱石-胡敏酸混合胶体凝聚的作用更强，HPO₄^2-体系中CCIS是H₂PO₄^-中的2.43倍.HPO₄^2-和H₂PO₄^-体系中离子特异性效应的差异（活化能差值）随离子强度的降低而增大，主要由强电场中离子非经典极化作用引发.胡敏酸的添加明显增加了HPO₄^2-体系中胶体的CCIS和活化能，而对H₂PO₄^-体系未产生明显影响；HPO₄^2-和H₂PO₄^-离子特异性效应的强弱在不同比例蒙脱石/胡敏酸体系中表现为96%蒙脱石+4%胡敏酸 >> 99%蒙脱石+1%胡敏酸 > 100%蒙脱石.以上结果表明HPO₄^2-和H₂PO₄^-对蒙脱石-胡敏酸混合胶体的凝聚存在强烈的离子特异性效应，胶体表面附近电场强度直接影响该效应的强弱.

Effects of HPO42- and H2PO4- on the aggregation of montmorillonite-humic colloidal particles

In order to investigate the effect of interfacial behaviors of HPO₄^2- and H₂PO₄^- on soil colloids aggregation, the aggregation kinetics of montmorillonite and humic colloids were monitored using a dynamic light scattering instrument. Results showed that the colloids aggregation in the HPO₄^2- and H₂PO₄^- systems transformed from slow aggregation (linear growth) to fast aggregation (power function growth) with increasing ionic strength of the electrolytes. In addition, the aggregation was more sensitive to the changes in ionic strength in H₂PO₄^- system. Significant differences of the growth of effective particle size, total average aggregation (TAA) rate, critical coagulation ionic strength (CCIS), and activation energy were observed in colloids aggregation in the HPO₄^2- and H₂PO₄^- systems. Compared with aggregation in HPO₄^2- system, aggregation in H₂PO₄^- system has a higher TAA rate, lower CCIS and lower activation energy, indicating that H₂PO₄^- has a stronger effect on initiating colloid aggregation. Besides, the CCIS of HPO₄^2- was 2.43 times as that of H₂PO₄^-. The difference of activation energies between the two systems increased with decreasing ionic strength, which might be caused by the ionic non-classical polarization in the strong external electric field. The addition of humic colloids significantly increased the CCIS and activation energy in HPO₄^2- system, but not in H₂PO₄^- system. The Hofmeister effects of HPO₄^2- and H₂PO₄^- on colloids aggregation followed the order of 96% montmorillonite+4% humic colloid >> 99% montmorillonite+1% humic colloid > 100% montmorillonite. These results indicated that there are strong Hofmeister effects of HPO₄^2- and H₂PO₄^- on the aggregation of montmorillonite-humic colloids, and the Hofmeister effects were directly dependent on the electric field strength near the surface of the colloids.