Biosurfactants have oil and water amphiphilic properties and commonly used for leaching heavy metals in soil.In order to further improve the removal rate of Cd in soil,ethylenediamine tetramethyl phosphonic acid(EDTMPA),polyamide acid(PAA)and citric acid(CA)were respectively combined with biosurfactants.The leaching characteristics of single leaching agent and composite materials on Cd contaminated soil were investigated by a horizontal experiment method,and the leaching parameters were optimized by response surface methodology.The leaching efficiency and the removal effect of soil Cd pollution between composite leaching and single leaching,different composite materials and leaching sequence were compared.The results showed that the removal rate of Cd by bio-surfactant was<16.69%.The removal rate of heavy metals by EDTMPA and saponin mixed leaching was significantly improved,and the removal rate of Cd was 49.28%higher than that by saponin alone.The optimization results of response surface model showed that the leaching time,mixing ratio,and temperature have a significant impact on the leaching effect,with the order of influence being leaching time>mixing ratio>temperature>pH,and there is interaction between the two factors.The optimum parameters of EDTMPA and saponin mixed leaching are:complex ratio 1.3∶1,pH of 7,temperature of 22℃,and leaching time of 240 min.Under these conditions,the removal rate of Cd is 65.16%.
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