Simultaneous removal of lindane and heavy metals from contaminated soils by rhamnolipids enhanced washing

In this study,the effect of rhamnolipids on the simultaneous removal of one representative organochlorine pesticide( OCPs),lindane,and two heavy metals,Pb and Cd,from simulated soils was investigated.Capacity and influencing factors of rhamnolipids to solubilize lindane and complex Pb and Cd in aqueous solutions were explored.Furthermore,speciation analysis of heavy metals in soils before and after washing was conducted.Results showed that lindane solubility increased with elevated ionic strength,while decreased as pH rose from 5.0 to 10.0.The complexation of Pb with rhamnolipids was stronger than that of Cd.The higher the rhamnolipids concentration was,the larger the complexed concentration of Pb and Cd.However,as pH rose from 5.5 to 10.0,the complexation of Pb and Cd with rhamnolipids was inhibited and promoted,respectively.The sorption of rhamnolipids to soil can be fitted using a linear isotherm.In addition,significant removal of lindane and heavy metals from soils was achieved when rhamnolipids concentration was above 5000 mg·L-1.Particularly,the desorption rate was 76.9%,18.0% and 100% for lindane,Pb and Cd,respectively,at rhamnolipids concentration of 40000 mg·L-1,and the optimal pH value was 7.0.It was also suggested that the removal efficiency of Pb and Cd by rhamnolipids was strongly related to their speciation in soils,and metals in exchangeable stage could be removed more effectively.