Pb²⁺ Leachability in the Cement-Based Solidified/Stabilized Contaminated Clay Under Saline and Alkaline Environments

ABSTRACT

Harsh environments such as saline and alkaline environments will affect solidification/stabilization quality, especially considering the long-term service cycle. To investigate the environmental influence on the leaching behavior of solidified/stabilized soils, the Pb²⁺ leaching behaviors of cement-stabilized contaminated clay (CSC) and ternary binder (CSG)-stabilized contaminated clay (CSGSC) under the endo/exogenous saline and alkaline attacking environment were discussed. Note that, the ternary CSG binder, consisting of cement, silica fume (SF), and desulfurization gypsum powder (DGP) in a ratio of 1:0.25:0.19, underwent pre-screening based on its unconfined compressive strength (UCS). Scanning electron microscopy was employed to reveal the environment-resisting mechanism. The leaching concentration of Pb²⁺ in the leachate from CSGSC was lower than that from CSC in both saline and alkaline environments with a same incorporation ratio (15%) to dry soils, indicating CSG’s efficiency. Under the exogenous environment, the Pb²⁺ cumulative leaching mass from the stabilized clays in saline environment was more than that in deionized water, while that under the endogenous environment was opposite. Microstructure analysis indicated that the SF and DGP in CSG facilitated the formation of calcium silicate hydrate and ettringite, resulting in a denser structure that greatly enhances the physical encapsulation and chemical fixation of Pb²⁺ cation. At the end, the different mechanism under endo/exogenous attacking environments was attributed to the cation influence on clay minerals and the formation of new substance. These findings provide a guidance for the remediation of contaminated soil in harsh environments.

KEYWORDS:

• Endo/exogenous attacking environments
• heavy metal contaminated clay
• solidification/stabilization
• leaching behavior
• micro-structure

Acknowledgments

This study was suppdorted by the National Key R&D Program of China (Grant No. 2019YFC1806004) and National Natural Science Foundation of China (Grant Nos. 42272322 and 51878159).

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Disclosure statement

No potential conflict of interest was reported by the author(s).

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Funding

The work was supported by the National Key Technologies Research and Development Program of China [2019YFC1806004]; National Natural Science Foundation of China [42272322 and 51878159].