Joint Effect Of Sapindus Saponins Water Extract And Chelating Agent In Remediation Of Cadmium Contaminated Soil

Cadmium(Cd),a kind of heavy metal pollutant,can enter the food chain though soil,dust,and crops.As a staple crop in China,rice can easily enrich Cd from soil,which can represent a health risk to consumers.Cadmin(Cd)contaminated soil is among the large amount of soils polluted by heavy metals.It will be of significant meaning if remediated soils can meet the high demand of reused effectively.Heavy metals do not undergo microbial degradation,and persist for a long time afer their introduction to soil.soil washing can effectively and rapidly get rid of the heavy metals from contaminated soils.In order to achieve the purpose of high-efficiency removal,this article selected Sapindus saponins,mixture of EDTA and Sapin.dus saponins andmixture of EDTA and Sapindus saponins to be made washing agents for repairing the Cd polluted soils.Exploring the influence of solution concentration and pH and washing time on removal efficiency.To compare the variation of metal fractions soils before and after washing,and further analyzed the concentrations of organic matter and nutrients in soil.The main conclusions showed as followed:(1)Cd removal efficiencies increased with growing concentrations.From 3.03 to 8.03 of solution pH,the removal efficiency linearly decreased for the Sapindus saponins.The highest removal efficiency of Cd was 37.87%,respectively under the removal conditions of concentration of Sapindus saponins of 35 g·L-1,pH of 4.83,and leaching time of 240min.The leaching process of the Sapindus saponins with fitting data were better curved Elovich model(R2=0.947)and the pseudo second order kinetics(R2=0.917).(2)The effect of compound action was synergistic-effect which EDTA and Sapindus saponins desorbed Cd in soil.With the concentration increasing,the synergistic effect always was becoming smaller.The Cd washing rate of 87.63%was obtained under the optimum conditions of Sapindus saponins mass concentration 20g·L-1,EDTA concentration 1mmol·L-1,volume ratio of Sapindus saponins solution to EDTA solution 1:1,liquid-to-soil ratio of 15:1,pH of 5.07,and leaching time of 1440min.The effect of compound action was synergistic-effect which MGDA and Sapindus saponins desorbed Cd in soil.With the concentration increasing,the synergistic effect always was becoming smaller.It even manifests antagonistic effect.The Cd washing rate of 84.37%was obtained under the optimum conditions of Sapindus saponins mass concentration 10g·L-1,MGDA concentration 1 mmol·L-1,volume ratio of Sapindus saponins solution to MGDA solution 1:1,liquid-to-soil ratio of 15:1,pH of 5.45 and leaching time of 720min.Increasing the ratio of liquid to soil and prolonging,the washing time are beneficial to increase the washing rate of cadmium.(3)Under the condition of low concentration,the combined eluent can achieve better elution effect than single elution.The Elovich model could better describe the combined washing process.The results showed that the washing of heavy metals between the combined solution and soil was mainly diffusion and heterogeneous diffusion.(4)The fractionation results of Cd from contaminated soil before and after washing showed as follow:the desorption effect of Cd forms used Sapindus saponins,mixture of EDTA and Sapindus saponins,mixture of MGDA and Sapindus saponins showed acid-soluble state>reducible state>oxidizable state>residual state.The content of cadmium in acid-soluble state and reducible state was obviously reduced by combined washing.(5)Sapin.dus saponins water extract has little damage to the soil nutrients,and the solution remaining in the soil contains nutrients,so it can be used as the supplement of soil nutrients.The combined elution of MGDA(EDTA)and saponins could slow down the washing loss of organic matter and basic nutrients in soil.