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

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.