Investigation of alternative materials for BOF slag in landfill biogeochemical cover for carbon dioxide sequestration

Landfill gas (LFG), primarily composed of methane (CH₄) and carbon dioxide (CO₂), continues to escape from municipal solid waste (MSW) landfills despite mitigation strategies like gas collection systems and soil covers. A novel biogeochemical cover (BGCC), developed at the University of Illinois Chicago, aims to mitigate these fugitive emissions by incorporating a biochar-amended soil (BAS) layer for CH₄ oxidation and a basic oxygen furnace (BOF) slag layer for CO₂ sequestration. However, the limited availability of BOF slag near landfill sites presents a barrier to large-scale implementation, necessitating the identification of alternative CO₂-sequestering materials. This study evaluates four alkaline industrial wastes - concrete waste fines (CWF), class C fly ash (CCFA), grade 100 slag cement (SC), and cement kiln dust (CKD) - as potential substitutes for BOF slag. Batch experiments revealed that CKD exhibited the highest CO₂ sequestration capacity (225.1 mg/g), followed by CCFA (135.8 mg/g), SC (126.7 mg/g), and BOF slag (98.1 mg/g), with CWF demonstrating the lowest (66.4 mg/g). Column tests under continuous LFG flow further confirmed CKD's superior performance (134.1 mg/g), compared to BOF slag (55.8 mg/g) and CWF (51.8 mg/g). Although CKD demonstrated higher carbonation potential, its lower hydraulic conductivity suggests the need for alternative integration approaches in the BGCC system, such as CKD-amended sand, barrier soil, topsoil, or use as a standalone layer. These findings demonstrate the potential of waste-derived materials to enhance the environmental performance and scalability of BGCC systems, contributing to sustainable waste management and greenhouse gas mitigation through improved CO₂ sequestration.