Remediation of cadmium and pyrene co-contaminated soil by washing with biodegradable chelating surfactant LED3A

In this study, sodium N-lauroyl ethylenediamine tetriacetate (LED3A), a biodegradable chelating surfactant, was used as washing agent to remove cadmium (Cd) and pyrene (Pyr) co-contaminants from soils by batch experiments. The effects of washing time, LED3A concentration, temperature, pH value, water-soil ratio and ionic strength on the removal efficiencies were extensively explored. In addition, the forms of Cd and Pyr in soil before and after washing were analyzed. The results indicated that LED3A could simultaneously removal of Cd and Pyr from the contaminated soil. The pseudo-second order kinetics model was most suitable for describing the desorption processes of the two kinds of pollutants. Compared with the corresponding single contaminated soil, the interaction of coexistence of Cd and Pyr reduced their equilibrium removal rates with 5.13% and 9.91%, respectively. The removal efficiencies of Cd and Pyr were both increased with the increasing of LED3A concentration (0~15000mg/L), temperature (15~35°C) and water-soil ratio (10:1~60:1). Under the optimal (cost-effective) conditions (12000mg/L, 25°C, 30:1water-soil ratio), the removal rates of Cd and Pyr were 57.66% and 51.07%, respectively. The pH value of the soil-solution system was preferably maintained at alkaline conditions (pH=11). Appropriate ionic strength (0.1mol/L Na+ or 0.005mol/L Ca2+) could significantly promote the removal effect. The contents of exchangeable and reducible fractions of Cd as well as the non-desorbing and desorbing fractions of Pyr decreased with 61.09%, 26.35%, 17.26% and 68.44%, respectively, compared with their contents before washing. The residual fraction analysis of contaminants in soil demonstrated that the proportion of bio-available fractions of Cd and Pyr was significantly decreased. Correspondingly, soil environmental hazards and ecological risk induced by co-contaminants could be effectively reduced by the proposed approach. Remediation of heavy metal and organic co-contaminated soil by washing with biodegradable LED3A could be a promising green remediation method. © 2023 Chinese Society for Environmental Sciences. All rights reserved.