Improvement of washing efficiency of heavy metal-contaminated clayey soils based on strong frost-heave characteristics of Akadama soil

The freeze-thaw synergistic chemical washing can remove heavy metal contaminants from clayey soils. However, the intake of eluent is low during the freezing process, resulting in low washing efficiency. Based on the idea of improving the frost heave of clayey soils and increasing water migration to improve the leaching efficiency, the freeze-thaw-leaching tests on soil columns are carried out by taking heavy metal-contaminated clayey soils as the research object and selecting strong frost-heave Akadama soil as the admixture. The results indicate that under the same freezing conditions, the frost-heave rate of Akadamas soil 124.48%, with the corresponding increase in the frost-heave amount and water intake of 5.85 times and 4.82 times that of clayey soils, respectively. This indicates an extremely strong frost-heave characteristic. The adsorption capacity of Akadama soil for Pb and Cd is weak, and it can be reused. After incorporating Akadama soil, the frost-heave amount and water intake of clayey soils significantly increase, with the maximum increments of 130.91% and 113.39%, respectively. After three freeze-thaw cycles, the removal rates of Pb and Cd reach 57.51% and 66.77%, respectively, representing an increase of 173.73% and 113.94% compared to those of the control group without Akadama soil. The SEM tests show that the structure of Akadama soil is severely broken and the number of pores increases, which is conducive to the migration and storage of water after freeze-thaw cycles. The method of using Akadama soil as an admixture soil to improve the freeze-thaw leaching efficiency has operability and universality in practical engineering applications. It provides a new approach for the remediation of heavy metal-contaminated clayey soils in seasonal frozen regions.