Tetrasodium iminodisuccinate as a biodegradable complexing agent for remediating metal-contaminated soil

Soil washing is a rapid and cost-effective method to treat contaminated soils. However, conventional chelating agents exhibit adverse environmental effects. Tetrasodium iminodisuccinate (IDS) is a new type of amino carboxyl chelating agent, which exhibits strong chelating performance, high solubility in aqueous solution, and is environmentally friendly in soil. In this study, batch washing of Cu, Pb, and Cd removal from simulated contaminated soil and real project-scale soil of a Pb-polluted field was explored to evaluate the application of IDS in the remediation of potentially toxic metal-contaminated soil. The effects of the IDS solution pH, concentration, reaction temperature, liquid/soil (L/S) ratio, number of washing cycles, and contact duration were investigated, and the optimal conditions were identified as follows: pH 7, IDS concentration 10 mmol center dot L-1, L/S ratio 10:1; 25 degrees C; and 24 h. Almost 80.6% of Cu, 71.1% of Pb, and 59.1% of Cd were removed from simulated contaminated soil under optimal conditions. The primary potentially toxic metal removal mechanisms were analyzed by potentially toxic metal state detection before and after IDS washing. Real project-scale Pb-polluted field washing was demonstrated under the same conditions in addition to the IDS concentration of 4.5 mmol center dot L-1. The Pb concentration was reduced from 460 to 86.8 mg center dot kg(-1) (mean value), which is below the threshold identified in the 'Risk Assessment of Soil Environmental Health in Shanghai' (Residential Area, 140 mg center dot kg(-1)). The results confirm that IDS is a promising soil washing agent that can effectively remove potentially toxic metals from contaminated soil and minimize environmental risks.