Study On Column Leaching Of Cadmium From Contaminated Soil Using Composite Reagents

In this paper, leaching of Cd soil was studied by several kinds of commonly used type of reagents in single or mixed solution using soil column leaching method. The concentration of the reagents and washing time, flow rate and volume ratio of those reagents were chosen to research the optimal conditions, then compared the chemical forms of Cd before and after co-leaching by mixed solution.(1)The research indicates that the removal efficiency was gradually improved as a function of leaching time. After 24h under the flow rate of 1.0 mL ·min-1, the removal rate was 88.89%,83.95%,71.22%,70.22%,23.00% for the HC1, EDTA, citric acid, tannic acid and rhamnolipid, at the concentration of 2.0 mol·L-1,0.1 mol·L-1,0.8 mol·L-1,10 mmol·L-1,1.5%, respectively.(2) Best effect was obtained in 24 hours. The removal of Cd was experimented by composite leaching of citric acid and tannic acid, and the optimum concentrations was 10.0 mmol·L-1 and 0.6 mol·L-1 respectively. When the volume ratio of co-leaching reagents was 3:1, the removal rates of Cd achieved 96.66%. Otherwise, the speed of removal rate was decreased with the passage of the time.(3)The data of the experiment were fitted through Elovich equation, double constant equation and first-order linear. We found that the Elovich equation is the best equation to describe the effect of citric acid and tannic acid on the adsorption of Cd. Also, these results showed that this effect of co-leaching on the adsorption of Cd was not a simple first order reaction.(4) Co-leaching removed the acid extractable, organic-bound states of Cd effectively.98.45% and 90.98% of acid extractable, organic-bound states of Cd have been removed. The decrease of the acid extracted reduced the risk of environment. For the distance, with the increase of soil depth, the concentration of Cd showed a rising trend. The Geo-accumulation index method was proposed to evaluate the effect of the eluent on the remediation of Cd.The result showed that, the content of heavy metal Cd in soil is greatly reduced, and the effect of soil remediation is remarkable.