Removal of arsenic from contaminated soil by washing with amino acid-derived ionic liquids: Remediation effects and potential mechanisms

It is a challenging task to find an environmentally friendly and effective washing agent for the remediation of contaminated soil. In this study, the remediation effect of 15 amino acid-derived ionic liquids (AA-ILs) on arsenic (As)-contaminated soil was evaluated, and the best washing agent was selected to optimize the washing conditions. The results showed that 1.0 mol/L [Ala][H2PO4] (Ala represents alanine) exhibited the highest As removal efficiency of 90.1 % at a liquid-soil ratio of 4:1 and a washing time of 480 min. The results of kinetic studies showed that the As removal process by [Ala][H2PO4] washing followed a second-order kinetic model. After washing, residual As was the main form of As in soil, which inhibited the bioavailability and toxicity of As. In addition, the soil type remained unaltered, the content of nutrient elements increased, but the soil pH and mineral content decreased. The potential mechanisms of As removal by [Ala][H2PO4] included acid dissolution, ion exchange and coordination reactions. In conclusion, [Ala][H2PO4] can be used as a green washing agent for efficient remediation of As-contaminated soil.