Improving washing efficiency of heavy metal-contaminated clayey soils based on repeated ice-segregation in seasonal frozen areas

The scheme to improve the washing efficiency of heavy metal-contaminated clayey soil is proposed by using the repeated ice-segregation based on the theory of "repeated segregation mechanism of thick ground ice". The laboratory batch washing tests and freezing-thawing and washing tests are performed on Cd- and Pb-contaminated clayey soils with EDTA, tartaric acid as eluents. Subsequently, the removal effects of heavy metals under different working conditions are analyzed. The results show that it provides advantages for water migration in thawing soils and repeated ice-segregation by controlling the thawing rate. Compared with that of the single freezing-water intaking mode, the eluent intaking amount of the freezing-thawing and washing tests with repeated ice-segregation increases by about 20%. The repeated fluctuations of the freezing-thawing interface will promote the eluent to fully contact with the heavy metal in the soils. Their synergistic effects can effectively increase the removal effeciency of heavy metals. The removal efficiency of Cd and Pb increases by 43.95% and 171.74%, respectively. It is of certain reality and universality in practical engineering application and provides a new idea for the remediation of heavy metal-contaminated clayey soils in seasonal frozen areas.