Removal of heavy metals from contaminated soil and sediments using the biosurfactant surfactin

The feasibility of using a biodegradable surfactant, surfactin from Bacillu s subtilis, for the removal of heavy metals from a contaminated soil (890 m g/kg zinc, 420 mg/kg copper, 12.6% oil and grease) and sediments (110 mg/kg copper, 3300 mg/kg zinc) was evaluated. Results showed that after one end five batch washings of the soil, 25 and 70% of the copper, 6 and 25% of the zinc, and 5 and 15% of the cadmium could be removed by 0.1% surfactin with 1% NaOH, respectively. From the sediment, 15% of the copper and 6% of the zinc could be removed after a single washing with 025% surfactin/1% NaOH. T he geochemical speciation of the heavy metals among the exchangeable, oxide , carbonate, organic, and residual fractions was determined by selective se quential extraction procedure. For both matrices, the exchangeable fraction s were minimal, while the carbonate and the oxide fractions accounted for o ver 90% of the zinc present and the organic fraction constituted over 70% o f the copper. Results after washing indicated that surfactin with NaOH coul d remove copper from the organic fraction, zinc from the oxide, and cadmium from the carbonate fractions. The residual fraction remained untouched. Th ese experiments indicate that the sequential extraction studies could be us eful in designing soil-washing procedures.