The Research On Adsorption Behavior And Electrokinetic Removal Of Cd In Red Soils

Soil contaminated by heavy metals is one of the environmental problems that should be resolved urgently. To remedy the contaminated soils, understanding the adsorption behavior of heavy metals in soils is very important. In this paper, cadmium and red soils were, respectively, taken as the target pollutant and experimental soils. Then, the adsorption behavior of cadmium(Experiment I) in red soil and the feasibility of electrokinetic remediation on the removal of cadmium from cadmium-contaminated red soils(Experiment II) were investigated. The results are given as follows.Experiment I showed that the curve of cadmium adsorbed vs pH showed three stages, namely, the adsorption amount increasing slowly at low pH, then increasing quickly with the rise of pH, and reaching the maximum amount at high pH. According to the specific adsorption reaction between cadmium( II ) and soils, a linear equation relating to the relationship between the partition coefficient of Cadmium( II ) in soils and pH was established. The experimental data with regard to the partition coefficients of cadmium( II ) and pH values were fitted to the above-mentioned equation. The results showed that the correlation coefficients increased significantly with the rise of pH. Meanwhile, it indicated that the specific adsorption reaction between cadmium (II) and the red soils used in this study intensified remarkably with the rise of pH. The result of theoretical analysis on precipitation reactions indicated that the precipitation reaction was controlled by carbonate until pH was a little higher than 11. The adsorption data at different pH values and initial cadmium( II ) concentrations were fitted, by a linear least squares technique, to the Langmuir, Frundlich and Temkin adsorption isotherms and the results showed that the Langmuir isotherm was the best one to well describe the adsorption behavior of Cadmium in studied red soils. Judged from the changes of parameters in Langmuir equation, both were pH-dependent. At last, by substituting the fitting results obtained from experimental data for the parameters in Langmuir equation, a pH-dependent model of adsorption isotherms of Cadmium in studied red soils was established under the experimental conditions.Experiment II showed that: (1) Soil pH was the major factor affecting the efficiency of electrokinetic remediation. Low pH was helpful to the desorption and...