Solvent-Based Soil Washing of Mercury-Contaminated Soil with Eco-friendly Washing Agents

Mercury (Hg)-contaminated soils from anthropogenic activities pose significant challenges to ecosystems and their biotic and abiotic components. Among many treatment methods for the remediation of Hg-contaminated soils, soil washing has been practiced as an effective treatment. This study investigated Hg removal efficiencies by using different combinations of washing solutions, including organic acids (humic, citric, oxalic, tartaric acids), surfactants (Tween 80, sodium dodecyl sulfate (SDS)), and electrolyte solution (NaCl). Moreover, the optimal conditions of the soil-washing process also were pointed out. The results showed that the experiment performed by a combination of citric acid + Tween 80 with SDS provided the highest Hg removal efficiency (94%). Organic acids show potential in Hg-contaminated soil washing with relatively high removal efficiency, particularly humic acid, with a removal efficiency of 79%. Surfactants show a role in enhancing Hg removal efficiency when combined with organic acids. Surfactants have been shown to play a role in enhancing Hg removal efficiency, while electrolytes have not yet when combined with organic acids as the washing solutions. Therefore, further studies are needed when using electrolytes in soil-washing solutions. Mercury-contaminated soil washing is most effective at operating conditions of pH = 4, liquid-to-solid ratio = 5:1, and stirring speed = 1500 rpm. The liquid-to-solid ratio played a significant effect ( P < 0.05) on the Hg removal efficiency. The results from this study show the potential of green soil washing technology using less toxic, biodegradable, environmentally friendly, and low-cost chemicals.