土壤表面电荷与离子间的相互作用对可变电荷体系电导的影响

Effects of Interactions Between Surface Charges and Ions on Conductance of Variably Charged Soil

近年来,电导在土壤研究中有着非常广泛的应用,它可能作为揭示土壤胶体颗粒表面与离子之间相互作用的一种有效工具.在该研究中,将不同浓度的KNO3分别加入土壤胶体悬液和水体系后测定体系电导率和pH值,研究了土壤表面电荷与离子间的相互作用对悬液电导的影响,结果发现:1)随体系电解质浓度增加,胶体表面可变负电荷的数量增加,胶粒电导增加;2)KNO3的水解使得加入的KNO3浓度越高,悬液体系的pH值越低;3)决定可变电荷体系表面负电荷多少的关键并不是H+的活度的高低,而是表面静电吸附中H+与盐基阳离子的相对竞争力的强弱,即低的pH值并不一定导致表面负电荷数量降低;4)在研究电解质对可变电荷胶体表面电荷的影响时,不能忽略离子水解对表面电荷性质影响的间接效应.

Conductance determination has been widely applied to the study of soil science and may become a useful approach to revealing the interactions between colloidal particle surface and solution ions. Through the determination of electrical conductivities and pH in soil suspensions and aqueous solutions at different KNO3 concentrations, some interesting interaction effects, between the particle surface of a variably charged soil and solution ions were observed. The number of variably negative charges on the soil particle surface increased with increasing electrolyte concentration in soil colloidal suspension and, as a result, the suspension conductance increased. Because of the hydrolysis of KNO3, the higher the KNO3 concentration was, the lower pH values would be in the soil colloidal suspension. It seemed that the key factor influen- cing the numbers of negative charges for variably charged particles was not pH but the relative competition between H＋ and base ions physically adsorbed on the particle surface. In other words, lower pH did not necessarily lead to a decrease in the number of negative charges on the soil particle surface. Therefore, the indirect effects of the hydrolysis of the electrolyte on the surface charges should not be neglected in the study of the effect of electrolyte on surface charges of variably charged particles.