Toxicity leaching test of solidified Pb-Cd contaminated soil under an open-unidirectional freezing condition
Rui Dahu
Yao Weifeng
Nie Wenjun
Zhang Jun
Pan Weidong
Abstract：Objectives This study aims to evaluate the leaching characteristics of solidified heavy metal-contaminated soil under an open-unidirectional freezing condition in the shallow groundwater environment of seasonally frozen regions.Methods Active magnesium oxide(MgO)and fly ash were used to solidify/sta-bilize Pb-Cd composite contaminated soil.Freeze-thaw cycle tests and leaching toxicity tests were con-ducted under two unidirectional freezing conditions:open(with external water replenishment)and closed(without external water replenishment).Scanning electron microscopy(SEM)was employed to investigate the deterioration mechanism of freeze-thaw cycles on the leaching characteristics of the solidified/stabilized Pb-Cd contaminated soil.Results The results showed that under different freezing conditions,the frost heave and the leaching concentrations of Pb and Cd followed the same trend:open-unidirectional freez-ing>closed unidirectional freezing>constant temperature freezing.After 11 freeze-thaw cycles,compared with the open-unidirectional freezing group without stabilizer,the frost heave of the closed unidirectional freezing group and the open-unidirectional freezing group with stabilizer decreased by 38%and 83%,re-spectively.The leaching concentrations of Pb and Cd in the open-unidirectional freezing group with stabi-lizer were 5.62 mg/L and 1.09 mg/L,which were 1.99 and 1.58 times those of the closed unidirectional freezing group,and 5.21 and 2.53 times those of the constant temperature freezing group,exceeding the limits specified in the national soil quality standards.Conclusions Freeze-thaw cycles reduced the content of hydration products and increased internal pore development within the solidified soil,thereby signifi-cantly weakening the immobilization effect of MgO-fly ash on Pb and Cd.The deterioration effect was more pronounced under the open-unidirectional freezing condition.These findings provide references for improv-ing the design of solidification/stabilization processes and evaluating the long-term stability of contaminated soil in shallow groundwater environments of seasonally frozen regions.
Keywords：open-unidirectional freezingsolidification/stabilizationheavy metal-contaminated soilleach-ing characteristicdegradation mechanism
Publication Date：2026-02-28
Online Publishing Date：2025-12-15(First online date of this platform, not the publication date of the document)
Pages：8( 189-196 )