Remediation of Cd- and Pb- contaminated clay soils through combined freeze-thaw and soil washing.

To improve the washing efficiency for low-permeability clay, the method of freeze-thaw synergistic chemical washing was put forward to study the cadmium (Cd)-and lead (Pb)- real-site contaminated soils as the research object and ethylene diaminete traacetic acid (EDTA) was selected as the eluent to conduct a soil column washing test of heavy metal-contaminated clay soil. Results show that repeated freeze-thaw of soil can destroy the original structure of soil particles, help the eluent fully interact with pollutants, and thus improve washing efficiency. Cd was showed the best removal effect after supplying 0.1 mol/L EDTA twice and deionized water thrice by freeze-thaw and washing, and the removal rate reached 88.07%. Pb was also showed the better removal effect after three times of 0.1 mol/L EDTA and four times of deionized water through freeze-thaw and washing, and the removal rate reached 37.78%. Combined freeze-thaw and chemical washing can effectively remove the reducible and residual fractions of Cd and Pb in the clay soils. Moreover, freeze-thaw synergistic chemical washing can remove Cd and Pb at low liquid/soil ratios. The conclusions obtained in the study are of important theoretical value and technical support for the similar engineering.