Removal of heavy metals from abandoned smelter contaminated soil with poly-phosphonic acid: Two-objective optimization based on washing efficiency and risk assessment

Abstract

Abstract Soil washing is a feasible technology to achieve rapid remediation and reuse of contaminated sites. However, there is still a need to seek eco-friendly and low-cost washing reagents. In this study, a two-objective optimization method has been proposed to investigate the removal efficiencies of eluents and risk of migration (risk assessment code, RAC) of residual metal simultaneously when soil Cd and Pb washed by polyamino polyether methylene phosphonate (PPMP) and bis (hexamethylene triamine penta (methylenephosphonic acid)) (BHMT). The coefficients of determination of the equations proved that D-optimal mixture design could be used for optimizing and modeling of the two objectives during soil washing. And their single-factor (concentration, solution pH, or contact time) and interaction effects indicated that PPMP react with Cd and Pb through chelation at strong acid in soil, whereas acid dissolution effect would convert the stable form of soil Pb into unstable form. BHMT could rapidly remove more acid-soluble fractions of Cd and Pb through the electric double layer adsorption, and is favorable under neutral conditions. Moreover, the optimum removal efficiencies of soil Cd and Pb were 83.98 and 41.29%, and RACs were 45.1 and 5.16% respectively in PPMP washing; accordingly, 69.31 and 28.11% of optimum removals and 32.45 and 0.98% of RACs for soil Cd and Pb were obtained in BHMT leaching. Therefore, PPMP and BHMT are two feasible remediation reagents of the abandoned industrial soils contaminated by heavy metals.