Adsorption mechanism of Cd2+ on solid waste–based PRB composite filler and pore structure dynamic evolution laws

Abstract

In this study, a composite granular filler (CGF) was prepared primarily using steel slag, fly ash, and desulphurization gypsum to remedy the default of expensive, passivation, and ease of failure for the traditional permeable reactive barrier (PRB). The adsorption characteristics of the CGF on Cd2+ were investigated by the static adsorption, and the strength loss and scatter ratio were clarified with an immersion test. Dynamic adsorption and visualization modeling were used to determine the primary factors influencing adsorption and the evolution laws of material corrosion and pore clogging. Various characterization methods were used to research the adsorption mechanism. The results showed that the CGF fit with the pseudo-second-order kinetic model and Langmuir model, and the optimal adsorption capacity reached 8.64 mg/g; the minimum ratio of scatter and strength loss were 4.95% and 6.16%, respectively. The pump speed greatly influenced the breakthrough curves. The maximum dynamic adsorption capacity reached 1.81 mg/g, and the Thomas model described the adsorption behavior well. After adsorption, the porosity increased by 7.79%, and clogging in the middle of the column was not serious. The connected pores still accounted for 99.48%, and the pore network model (PNM) maintained excellent connectivity. Hydration products generated in the CGF ensured strength and durability, and they also benefited the adsorption of Cd2+ through ion exchange, co-precipitation, and surface adsorption. This research provides a new solid-waste resource utilization method for heavy metal removal in groundwater and a theoretical basis for the long-term purification of PRB with good potential for application and economic benefits.