Removal of cadmium from contaminated soil using soapnut, shikakai, rhamnolipids and EDTA

This study investigates the operating variables of washing experiments involving four washing agents [Sapindus mukorossi (soapnut), Acacia concinna (shikakai), rhamnolipids and Ethylenediaminetetraacetic acid (EDTA)] for removal of cadmium (Cd) from contaminated soil in laboratory scale batch and column experiments. The operating variables included: time (2, 3, 4, 6, 8, 12, 24, 48 and 72 hrs), soil-solution ratio (1:10, 1:20, 1:30, 1:40 and 1:50), surfactant concentrations (1, 2, 3, 4, 5 and 6% by mass) and the pH of the washing solution (3, 3.5, 4, 4.5, 5 and 5.5). Results show that the removal efficiency increases with increase in surfactant concentration, soil-solution ratio as well as washing time, but decreases as pH increases.

It was also observed that the maximum removal efficiencies of 84.9% for soapnut, 87.4% for shikakai and 68.9% were obtained when 0.01M EDTA was mixed with biosurfactants at different concentrations. In column experiments, the highest removal efficiencies of 74.05%, 73.08%, 69.07%, 63.08% and 12.78% were obtained for EDTA, soapnut, shikakai, rhamnolipids and distilled water. The overall performance of the washing process indicates that saponin utilization in soil washing is much more effective than rhamnolipid.