RUI D H, YAO W F, NIE W J, et al.Toxicity leaching test of solidified Pb-Cd contaminated soil under an open-unidirectional freezing condition[J].Journal of Henan Polytechnic University(Natural Science) ,2026,45(1):189-196.

doi:10.16186/j.cnki.1673-9787.2024010004

Received:2024/01/02

Revised:2024/03/22

Published:2025-12-03

Toxicity leaching test of solidified Pb-Cd contaminated soil under an open-unidirectional freezing condition

Rui Dahu1,2, Yao Weifeng1, Nie Wenjun1, Zhang Jun1,2, Pan Weidong3

1.School of Civil Engineering， Henan Polytechnic University， Jiaozuo  454000， Henan， China；2.State Key Laboratory of Frozen Soil Engineering， Northwest Institute of Eco-Environment and Resources， Chinese Academy of Sciences， Lanzhou  730000， Gansu， China；3.Zhengzhou Metro Group Co.， Ltd.， Zhengzhou  450003， Henan， China

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/stabilize Pb-Cd composite contaminated soil. Freeze-thaw cycle tests and leaching toxicity  tests were conducted 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 freezing > 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%， respectively. The leaching concentrations of Pb and Cd in the open-unidirectional freezing group with stabilizer 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 significantly 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 improving the design of solidification/stabilization processes and evaluating the long-term stability of contaminated soil in shallow groundwater environments of seasonally frozen regions.

Key words:open-unidirectional freezing;solidification/stabilization;heavy metal-contaminated soil;leaching characteristic;degradation mechanism