Enhanced washing of HCB contaminated soils by methyl-beta-cyclodextrin combined with ethanol

The present study investigates the combined effect of cyclodextrin (CD) and cosolvent on the washing of hexachlorobenzene (HCB) from contaminated soils. Methyl-beta-cyclodextrin (MCD), ethanol, a natural soil (NS) and kaolin, were selected. Batch equilibrium experiments were conducted to quantify the performance of HCB solubilization and recovery by varied MCD/ethanol systems. Results show that with 30% or 50% of added ethanol, considerable synergistic effect on HCB solubilization was achieved in MCD/ethanol system. The formation of ternary MCD/ethanol/HCB complex is most likely responsible for the synergy. Similar synergy was further evidenced in the washing of HCB from kaolin and NS by MCD/ethanol system containing 30% ethanol. Unexpectedly, the combination of MCD and 50% ethanol exhibited negligible synergy of HCB recovery. The failure in promotion is probably due to a nonextractable fraction of HCB for NS, or a nearly complete HCB recovery from kaolin by 50% ethanol alone. Results also indicate that the synergistic effect of the MCD/ethanol system will be significantly hindered by a higher organic content and longer aging of the soil. Generally, our study suggests that compared to conventional CD or cosolvent-aided soil remediation, the combined use of CD and cosolvents would offer great superiority to the contaminant recovery.