东北草甸棕壤的零电荷点和界面酸-碱反应特征平衡常数

分别采用电势滴定(Potentiometric titration)法, 质量滴定(Mass titration)法和惰性电解质滴定(Inert electrolyte titration)法测定了荷结构负电荷的东北草甸棕壤的零净电荷点(PZNC), 研究表明荷结构负电荷的土壤依然存在与电解质浓度无关的零净电荷点, 三种方法的实验结果分别为2.9, 5.0和3.3. 相比较而言, 电势滴定法和惰性电解质滴定法的结果相近, 而质量滴定法的结果偏高. 对文献中推算表面质子活性位密度(N_s)的方法进行了改进, 得到东北草甸棕壤样品的N_s为2.5 mmol?g^－1. 根据实验测定的pH_PZNC, N_s和结构电荷密度(σ_st)值直接计算得出东北草甸棕壤样品的界面反应特征平衡常数即1-pK模型中的pK, 2-pK模型中pK_a1^int和pK_a2^int, 分别为3.37, 2.42和4.32, 与文献报道的沉积物和蒙脱土的值相吻合.

Point of Zero Charge and Intrinsic Surface Reaction Equilibrium Constants of Meadow Brown Soil in Northeast of China

The point of zero net charge (PZNC) for the meadow brown soil in northeast of China with structural negative charges was measured by three methods: potentiometric titration, mass titration and inert electrolyte titration, showing that for the meadow brown soil which possesses structural negative charges, a PZNC independent of electrolyte concentration exists, and the values of pH_PZNC obtained by the above three methods are 2.9, 5.0 and 3.3, respectively. It was found that the values of pH_PZNC determined by potentiometric titration and inert electrolyte titration were very close while that determined by mass titration was relatively high. The estimating method of the total density of surface proton-active sites (N_s) in literatures was improved to obtain the N_s value of the meadow brown soil in northeast of China, which is 2.5 mmol? g^－1. According to the values of pH_PZNC, N_s and structural negative charge density (σ_st) measured, the intrinsic surface reaction equilibrium constants, pK of 1-pK model, pK_a1^int and pK_a2^int of 2-pK model, were directly calculated to be 3.37, 2.42 and 4.32, respectively, for the meadow brown soil in northeast of China.