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.