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Removal of Cu, Cd, Pb and Zn from Contaminated Soil by Using Plant-Based Surfactants, Sapindus mukorossi L (Soapnut) and Acacia Concinna (Shikakai)

The performance of two plant-based surfactants in the removal of heavy metals (Cu, Cd, Pb and Zn) from soil was studied ex-situ. Experimental parameters were: six soil-solution ratios (1:10, 1:20, 1:30, 1:40, 1:50 and 1:60), six surfactant concentrations (0, 1, 2, 3, 4, 5 and 6% by mass), seven washing times (2, 3, 4, 6, 8, 24, and 48 hr) and four pH values of the washing solution (3, 4, 5 and 6). In general, removal efficiency increased with an increase in surfactant concentration, time and soil-solution ratio but decreased with increase in the pH of washing solution. The removal of heavy metals was in the following range: Cu, Cd, Zn and Pb for both surfactants reaching up to 90%, 80%, 53% and 52% respectively. The overall performance of the batch washing process indicates that both surfactants were very effective in soil washing. The effectiveness of these surfactants is due to their ability to form micelles and subsequent removal of heavy metals from the soil surface by reducing the interfacial tension. Both surfactants have the advantages of being environment-friendly and cost effective.