An Investigation on the Removal Efficiency for Metal Ions From Porous Sand-Packed Columns by a Biosurfactant with the Foam-Enhanced Flushing Technique
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This study investigated the potential application of a biosurfactant, surfactin, for metal ion removal in the contaminated soil remediation. Sand was contaminated by copper and cadmium ions with concentrations of 13.45 and 5.84 mg/kg, respectively, with the model of inner sphere adsorption. Dynamic foam capacity of surfactin was evaluated at a concentration of 5 times critical micelle concentration. The zeta potential of surfactin micelles was evaluated by a zeta sizer. An experimental column containing metal ioncontaminated sand was then used to evaluate the removal efficiency for the metal ions by using the biosurfactant solution and foam-enhanced flushing approaches. When the sand-packed columns containing metal ions were flushed by surfactin solutions, the removal efficiency was not over than 4% for copper ion and 14% for cadmium ion, respectively. When the sand-packed columns were flushed by surfactin solutions with foams, the removal efficiency was increased to 15% and 24% for copper and cadmium ions, respectively. The foam-enhanced flushing approach could apparently increase the removal efficiency for the metal ions. The less removal efficiency for the metal ions by surfactin might be related to the porous structures of the sand and the metal ion-sand interaction with the inner sphere sorption model. The copper ion is more water soluble and it is found that pure water has higher removal efficiency for the copper ions than the surfactin solution. However, the foam-enhanced approach could be applied to decrease the channeling effect in the sand-packed column and thus to improve the removal efficiency for the metal ions.