Mechanical properties and microscopic mechanisms of Zn2+-contaminated soil stabilized by cement and lime

Abstract

[Objective] The solidification effect of cement and lime on Zn²⁺ contaminated red clay was investigated. [Methods] Taking Guilin red clay as the research object, the effects of different cement and lime contents on the strength characteristics, conductive behavior, heavy metal migration law, and microstructure of contaminated soil were systematically studied through unconfined compressive strength test, conductivity test, soil column leaching test, and microscopic analysis. [Results] The results show that increased curing agent content significantly enhances the curing effect, and the optimum proportion is 6% of cement and 6% of lime. The curing treatment significantly improves the unconfined compressive strength of Zn²⁺ contaminated red clay, and the resistivity is negatively correlated with stress-strain. The soil column leaching test showed that Zn²⁺ gradually migrated downward under the action of rainwater, resulting in pollution of the lower soil layer. The leaching concentration increased with the increase in rainwater volume. The microstructure analysis showed that the immobilization of Zn²⁺ was mainly due to the C-S-H gel and Ca(OH)₂ generated by the hydration reaction of cement and lime. These products filled the soil pores and formed stable compounds with Zn²⁺, effectively inhibiting heavy metal migration. [Concluion] Cement and lime can effectively immobilize Zn²⁺ and inhibit ion migration. The recommended cement 6%+lime 6% ratio is applied in the remediation project of heavy metal-contaminated red clay in Guilin. The research result provide micro-mechanism support and process parameter optimization for the treatment of heavy metal-contaminated soil.

Keywords

heavy metal pollution / strength / cement / lime / red clay / mechanical properties / microstructure