Synergistic leaching of Cd and Pb from contaminated soil using Sapindus saponins and citric acid

Taking the heavy metals contaminated soil in an abandoned lead-zinc mining area as the research object,Cd and Pb in the contaminated soil were synergistically leached using Sapindus saponin and citric acid (CA).A compound leaching agent was prepared with the water extract of 20 g/L soapberry peel and 0.3 mol/L CA.After adding CA to the extract,the removal rate of Pb in the soil was effectively improved.Under conditions of volume ratio of extract to CA 1∶3,leaching agent pH 5 and leaching time 12.0 h,the removal rate of Cd and Pb was 75.2% and 41.6%,respectively.Both the double constant equation and the Elovich equation can describe the leaching process of Cd and Pb in contaminated soil by the compound leaching agent,indicating that the desorption of Cd and Pb is mainly a heterogeneous diffusion process.The compound leaching agent can effectively reduce the content of exchangeable state of Cd and Fe-Mn oxidation state of Pb in the soil,and can promote the transformation of heavy-metal speciation.