Abstract
This study presents a novel method for increasing the water/eluent migration amount based on the theory of repeated ice-segregation. It can improve the removal efficiency of freezing-thawing synergistic washing technology for heavy metal-contaminated clayey soil. Laboratory batch washing tests and freezing-thawing and washing tests were performed on clayey soil contaminated by Cd and Pb. EDTA with tartaric acid or citric acid were chose as the eluents. The removal rates of heavy metal with different test conditions and the changes of heavy metal speciation before and after freezing-thawing and washing tests were analyzed. Results show that comparing with the single freezing-water intake mode, the freezing-water intake based on repeated ice-segregation can enhance liquid-soil ratios. The eluent intake amount increased by 20%, and the removal efficiency of heavy metals Cd and Pb increased by 43.95% and 171.74%, respectively. The thawing front at a specific position of the soil column fluctuates under repeated ice-segregation, forming repeatedly freezing-thawing cycles, which increase the migration of the water/eluent and strengthen the contact reaction between eluent and heavy metals. These results provide a new idea for taking full advantage of freezing-thawing alternation to remediate heavy metal-contaminated clayey soil in seasonal frozen area.
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