Abstract: In an attempt to enhance the removal of Cadmium(Cd) from paddy field soil and meanwhile alleviate the influence on soil's pH value, we conducted electrokinetic removal test with CaCl₂-humic acid solution activating the mobility of Cd in soil. We observed the changes in the content of available Cd and the pH value of soil by changing the concentration of CaCl₂-humic acid and the time of activation. In addition, we examined the changes in the removed content of Cd, the total concentration of Cd , the concentration of available-state Cd, and the pH value of soil after activation and electrokinetic drainage. Results manifest that the solution with 0.5% CaCl₂ and 1% humic acid has an optimum activation effect on the Cd in soil, by raising the available-state Cd from 0.3 mg/kg to 0.44 mg/kg and cutting the pH value by only 0.4. After the drainage of the overlying water, Cd can be further removed by electrokinetic drainage. The electrokinetic removal content of Cd was about three times that in the overlying water. After both activation and electrokinetic drainage, the total content of Cd dropped from 1.72 mg/kg to about 1.20 mg/kg, the content of available-state Cd declined to 0.27-0.31 mg/kg, while the pH value of each section of the soil was relatively uniform and barely changed, ranging between 5.45 and 6.30. The present research method could maximize the removal of Cd in soil while reducing the impact on pH value, which ensures the safe production of crops.

Key words: cadmium in paddy soil, removal performance, CaCl₂-humic acid, activation, electrokinetic geosynthetics (EKG), electrokinetic drainage