The Improved Leaching Of Cu,Zn,Cd Contaminated Soil By Synergistic Effect Of Tea Saponin And EDTA

The tea saponin is a biological surfactant, which has been used in remedying the heavy metal contaminated soils, due to it's biodegradability and no secondary pollution. EDTA, as a synthetic organic chelator, could form stable complexes with most of heavy metals in a wide pH range, not only desorbing the adsorbed metals but also dissolving the insoluble metals. This paper selected the artificially polluted brown soil as the tested soil, and Cd, Cu, Zn as the desorbed objects. Through the oscillating extraction, the concentrations of the desorbed metals under the compound action of tea saponin and EDTA were optimized. Through the soil column leaching method, the optimal conditions of leaching of heavy metals under the compound action of tea saponin and EDTA were studied. Moreover, the effects of elution on the forms of heavy metals and the changes of soil enzymes were also studied to select the optimal restorative materials and provide theoretical basis for practical application. Experimental datas were fitted through Elovich equation, double constant equation and parabolic diffusion equation to found the optimal fitted equation. The results were as follows:(1) The tea saponin promoted the desorption of heavy metals in the soil when it was used alone. The concentration of tea saponin have an effect on the desorption rate. In 3%~5%, the desorption of heavy metals in the soil effected by the tea saponin was reached equilibrium. Desorption abilities of three heavy metals were Cd>Cu>Zn.(2) The compound action of tea saponin and low EDTA concentration has a remarkable effect on the desorption rate of Cu and Cd, and no effect on Zn. The compound action of tea saponin and high EDTA concentration could increase the desorption rate of heavy metals, while the desorption rate of heavy metals decreased with the increase of the concentration of tea saponin. (3) E>0, the effect of compound action of tea saponin and low EDTA concentration on the desorption of heavy metals was synergistic solubilization, and the synergistic solubilization was increased with the increase of E. E<0, the effect of compound action of tea saponin and high EDTA concentration on the desorption of heavy metals was antagonism, and the antagonism was increased with the increase of ? E ?.(4) In the teat range, EDTA was 0.2mmol/L, tea saponin was 5.00% and soil/liquid was 1:4could get good effects on the leaching.(5) After the leaching of soil under the compound action of tea saponin and EDTA, the desorption of the weak acid extracted heavy metals was the most effective, reduced heavy metals took second place. The oxidized and residual heavy metals were difficult to be leached. The decrease of the weak acid extracted and reduced heavy metals reduced the risk of environment.(6) The compound of low tea saponin concentration and EDTA, as eluent, has no obvious effect on the soil urease, without significant difference (p<0.05). With the increase of the concentration of tea saponin, the activity of urease increased and showed no significant difference (p<0.05) compared with control group. The activitis of catalase showed the trend of increased first and then decreased, and were all higher than the control group. Except for 0.10% tea saponin group, the difference of observation groups and control group were significant (P<0.05). The activities of invertase were increased gradually. Except for 0.10% tea saponin group, the activities were all higher than the control group. When the concentration of tea saponin was 7.00%, the activities of invertase were much higher than that of control group, and the difference were significant (P<0.05). The result shows that the leaching makes good for the maintain of soil fertile and growth of plants.(7) Experimental datas were fitted through Elovich equation, double constant equation and parabolic diffusion equation. The result shows that, the optimal equation to describe the effect of tea saponin and EDTA on the adsorption of heavy metals was Elovich equation, followed by double constant equation and parabolic diffusion equation. For this instance, the effect of tea saponin and EDTA on the adsorption of heavy metals was not a simple first order reaction.