| Summary: | 博士 === 國立成功大學 === 化學工程學系 === 102 === This study demonstrates the abilities of negatively charged biosurfactants, surfactin and rhamnolipid, to remove adsorbed copper ions from sand surfaces with a continuous solution flushing technique. The surfactin with purity about 90% and rhamnolipid with purity of 62.75% were applied to remove adsorbed copper ions from sand surfaces. A popular anionic surfactant, sodium dodecylsulfate (SDS), was used in the flushing experiments for the comparison purpose. The interfacial properties of surfactin and rhamnolipid were identified first. Contamination of sand was performed through adsorption processes with different drying operations. Type I sand was dried in a drying column by N2 gas, which mainly resulted in adsorption with the inner-sphere interaction. Type II sand was dried in an oven. The adsorption densities of Cu ion contaminant were 13.45 mg/kg and 26.78 mg/kg for type I and II sands, respectively.
The surfactin solution flushing approach for both types of sands, low removal efficiency of 2-15% for copper ions was detected due to the contact of surfactin with copper ions mainly occurring in the inter-particle pore regions. Increasing the surfactin concentration could increase the dynamic foaming capacity and lead to improved removal efficiency up to 40%. The results demonstrated that the foam-enhanced solution flushing approach was efficient with a low usage of surfactin. For rhamnolipid solution, when using a flushing technique without foam, the removal efficiency could be improved by increasing the concentration. The cumulative removal efficiencies were gradually increased to 5%, 6%, and 12% with 24-PV effluent of rhamnolipid solutions with concentrations of 1x, 2.5x, and 5x cmc, correspondingly. For the residual type sand, higher removal efficiencies were found with 19%, 21%, and 23 %, correspondingly. By using a foam-enhanced flushing technique with rhamnolipid, the removal efficiency for the inner-sphere type and residual type sand could be further increased to ~25% and ~49%, respectively, under the corresponding conditions.
Rhamnolipid has excellent potential to remove metal ion contaminants, even those adsorbed with the inner-sphere interaction type. The physical properties of rhamnolipid made it a good candidate for applications as a surfactant. However, surfactin has a lower ability to remove adsorbed metal ions. Compared to surfactin, SDS possesses properties similar to rhamnolipid. The foam-enhanced solution flushing technique improved the migration of surfactant molecules and delivered more N2 gas with higher pressure as it increased the ability of biosurfactant monomers to spread and penetrate into the pores. The foam-enhanced solution flushing technique thus significantly improved the removal efficiency of adsorbed metal ions on sand surfaces.
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