Remediation of Pb–Cd contaminated soil using coal bottom ash-based geopolymer and coir: Soil remodeling and mechanism

Abstract

Stabilizing heavy metal-contaminated soil with solid waste-based materials is a sustainable approach. This study synthesized a coal bottom ash-based geopolymer and coir for the treatment of Cd- and Pb-contaminated soil. The results demonstrated that adding 10% geopolymer stabilized over 95% of Cd and Pb in contaminated soil, with the maximum compressive strength of soil reaching 634 kPa after curing. Geochemical model simulations revealed that Pb and Cd primarily converted to precipitated mineral forms (Cd<inf>4</inf>(OH)<inf>6</inf>SO<inf>4</inf>, Pb<inf>4</inf>(OH)<inf>6</inf>SO<inf>4</inf>, Litharge, and larnakite) when the system pH exceeded 5. From a mechanical perspective, the combination of coir and coal bottom ash-based geopolymers effectively solidified heavy metals while improving soil frost resistance, compression resistance, and shear resistance. The mineral recombination of coal bottom ash was successfully achieved, and it was prepared as an amorphous cementitious material. This study unveils the mechanism of geopolymer-cemented heavy metals and their structural strengthening, providing new technologies for addressing land resource pollution and realizing the green, sustainable, and clean reuse of industrial solid waste.