土壤矿质胶体对镉的吸附-解吸热力学与动力学研究

通过等温吸附-解吸热力学与动力学实验,研究了土壤胶体对镉的吸持特性.结果表明,吸附等温线拟合以Freundlich方程最优,其次是Langmuir方程.按对镉的吸附量由大到小顺序胶体依次是:紫色土矿质胶体(8 216.34 mg/kg)、黄壤矿质胶体(6 468.11 mg/kg)、紫色土去铁矿质胶体(4 963.13 mg/kg)和黄壤去铁矿质胶体(2 342.83mg/kg).而吸附强度则相反,按解吸率大小胶体依次是:紫色土去铁矿质胶体(8.7%～33.9%)、黄壤去铁矿质胶体(2.2%～25.4%)、紫色土矿质胶体(6.8%～18.9%)和黄壤矿质胶体(0.6%～17.7%).由动力学实验得出:土壤矿质胶体对镉的等温吸附-解吸过程分为开始时的快速反应阶段和随后的慢速反应阶段,吸附和解吸过程中两阶段划分时间点分别为4 h和12 h,动力学过程以双常数方程描述最佳.

Research on the thermodynamics and kinetics of adsorption-desorption of cadmium on the different soil colloids

This paper aims to introduce the authors' study of the characteristics of adsorption-desorption process of cadmium on the soil colloid through experiments in the case of keeping stable temperature. And the results of our study reveal that the isotherms of cadmium adsorption by soil colloids could be best described by Freundlich model, with Langmuir model followed. The order of the maximum adsorption of different soil colloids is the mineral colloid of the purple soil ( 8 216.34 mg/kg), that of the yellow soil(6 468.11 mg/kg), the de-ironed mineral colloid of the purple soil(4 963.13 mg/kg )and the de-ironed mineral colloid of the yellow soil. However, the adsorption intensity of the four soil colloids proves to be different from the adsorption capacities, while the desorption ratio of the four soil colloids indicates the de-ironed mineral colloid of the purple soil(8.7%-33.9%) > de-ironed mineral colloid of the yellow soil(2.2%-25.4%)> mineral colloid of the purple soil(6.8%-18.9%)>mineral colloid of the yellow soil(0.6%-17.7%). We have also found that the collusions from the dynamic experiments that the adsorption-desorption process of cadmium on the four soil colloids can be divided into the fast stage, i.e. some time span from the beginning of the reaction, and the slow stage, i.e. for the long time after the fast stage. In addition, the time separating the two stages in the progress of adsorption-desorption usually lasts 4 hours and 12 hours, and their kinetic isotherm could be thus the best described by the Double-constant model.