Sequestration of Landfill Gas Emissions Using Basic Oxygen Furnace Slag: Effects of Moisture Content and Humid Gas Flow Conditions

Fugitive methane (${\mathrm{CH}}_4$) and carbon dioxide (${\mathrm{CO}}_2$) emissions from municipal solid waste (MSW) landfills constitute one of the major anthropogenic sources of greenhouse gas (GHG) emissions. In this regard, several researchers have focused on developing biocovers that are primarily aimed at reducing ${\mathrm{CH}}_4$ emissions from MSW landfills. Although these studies have been successful in reducing ${\mathrm{CH}}_4$ emissions, the continuous ${\mathrm{CO}}_2$ emissions due to microbial ${\mathrm{CH}}_4$ oxidation and MSW decomposition remain a major concern. In this study, the ${\mathrm{CO}}_2$ sequestration potential of basic oxygen furnace (BOF) steel slag subjected to simulated landfill gas (LFG) conditions was examined to remove ${\mathrm{CO}}_2$ emissions from landfills while also promoting the beneficial use of BOF slag. Several series of batch experiments were performed at typical ambient conditions with varying moisture contents to evaluate the ${\mathrm{CO}}_2$ removal capacity of BOF slag. Small-scale column experiments were also performed simulating various LFG flow conditions, such as dry and humid LFG, and continuous and intermittent LFG flow into the column. The results from the batch experiments showed that moisture is requisite for the initiation of carbonation reactions in BOF slag; however, there was no definitive trend or an optimum moisture content that could be defined for the range of moisture contents tested. The ${\mathrm{CO}}_2$ removal rate appeared to have a two-step mechanism: initial rapid ${\mathrm{CO}}_2$ removal followed by gradual removal of ${\mathrm{CO}}_2$. The ${\mathrm{CO}}_2$ removal capacity of BOF slag was found to be 350 and $155\mathrm{mg}/\mathrm{g}$ of ${\mathrm{CO}}_2$ under humid and dry LFG conditions, respectively. The total residual lime/portlandite, which is readily available at the slag surface, appears to be responsible for the instantaneous carbonation of ${\mathrm{CO}}_2$. In the long term, ${\mathrm{CO}}_2$ removal exceeded the theoretical capacity of total residual lime/portlandite content, which was likely associated with the leaching of other reactive minerals such as larnite (${\mathrm{Ca}}_2{\mathrm{SiO}}_4$). Substantial ${\mathrm{CH}}_4$ removal by BOF slag (120 and $40\mathrm{mg}/\mathrm{g}$ under humid and dry conditions, respectively) was observed.