Investigation of carbon sequestration and water–gas transport parameters of steel slag–bentonite mixture

The utilisation of steel slag, as a final cover material for municipal landfills, has attracted growing interest. However, research on the patterns of carbon sequestration by steel slag in landfill environments and the impermeable barrier performance of the slag layer before and after sequestration (abbreviated as BC and AC, respectively) remains scarce. This study investigated the effects of constant pressure (CP) and non-constant pressure (NP) conditions, initial CO2 concentration (cin, vol%), water content (w, wt%) and bentonite content (wb, wt%) on the carbon sequestration capacity of steel slag through incubation tests. Concurrently, flexible-wall tests were conducted to evaluate bentonite content and the degree of compaction (DOC) on the gas permeability (kg), gas diffusion coefficient (Dg) and hydraulic conductivity (ks) before and after carbonation. Results demonstrated that cin significantly enhances the carbon sequestration capacity of steel slag. Increasing the DOC (i.e. from 85% to 95%) or wb (i.e. from 5% to 15%) reduced the kg,Dg and ks by over 56%. After carbonation, these parameters decreased by a further 20% or more, while ks remained consistently below 1 × 10−7 cm/s.