Carbon-Dioxide and Hydrogen-Sulfide Removal from Simulated Landfill Gas Using Steel Slag

Municipal solid waste landfills are a source of major greenhouse gases such as methane (${\mathrm{CH}}_4$) and carbon dioxide (${\mathrm{CO}}_2$) and emit a trace amount of hydrogen sulfide (${\mathrm{H}}_2\mathrm{S}$). Recently, steel slag has extensively been used for mineral ${\mathrm{CO}}_2$ sequestration to minimize the ${\mathrm{CO}}_2$ releases to the atmosphere. This study explores the potential of basic oxygen furnace (BOF) steel slag to simultaneously remove ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2\mathrm{S}$ from landfill gas (LFG). Various batch and column tests were conducted to evaluate the ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2\mathrm{S}$ removal potential of the BOF slag under various conditions such as moisture content and particle size of the BOF slag. The three different particle sizes of BOF slag (coarse, as-is, and fine) were exposed to continuous flow of a synthetic LFG [50% ${\mathrm{CO}}_2$, 48.25% ${\mathrm{CH}}_4$, and 1.75% ${\mathrm{H}}_2\mathrm{S}$ by volume ($\mathrm{v}/\mathrm{v}$)] in a column reactor to evaluate the effect of particle size on ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2\mathrm{S}$ removal capacity of the slag. Similarly, the BOF slag was exposed to synthetic LFG as well as 20% ($\mathrm{v}/\mathrm{v}$) of ${\mathrm{H}}_2\mathrm{S}$ alone in batch reactors at varying moisture contents (10%–30% by weight) to evaluate the effect of moisture content on the ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2\mathrm{S}$ removal capacity of the slag. A significant ${\mathrm{H}}_2\mathrm{S}$ removal of $27\mathrm{g}{\mathrm{H}}_2\mathrm{S}{\mathrm{kg}}^{-1}$ BOF slag and ${\mathrm{CO}}_2$ removal of 76 g ${\mathrm{CO}}_2{\mathrm{kg}}^{-1}$ BOF slag were obtained in the batch reactor. The fine BOF slag ($<0.106\mathrm{mm}$) showed the maximum ${\mathrm{CO}}_2$ removal (300 g ${\mathrm{CO}}_2{\mathrm{kg}}^{-1}$ BOF slag) and ${\mathrm{H}}_2\mathrm{S}$ removal (38 g ${\mathrm{H}}_2\mathrm{S}{\mathrm{kg}}^{-1}$ BOF slag) upon exposure to continuous synthetic LFG flow in the column reactor. The quantitative X-ray diffraction (QXRD) analysis showed the highest increase in carbon ($77.5\mathrm{g}\mathrm{C}{\mathrm{kg}}^{-1}$ BOF slag) and sulfur ($28\mathrm{g}\mathrm{S}{\mathrm{kg}}^{-1}$ BOF slag) contents in the fine BOF slag, which was consistent with the mass balance of carbon and sulfur from ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2\mathrm{S}$ uptake in column tests. The major reaction product with ${\mathrm{H}}_2\mathrm{S}$ was elemental sulfur depicted by the significant increase in the sulfur content in the X-ray fluorescence analysis. The key minerals involved in carbonation reactions were lime, portlandite, and larnite, as these minerals showed significant reduction in weight percentage (100%, 82%, and 80%, respectively) in the QXRD analysis. Overall, BOF slag showed promising results in mitigating ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2\mathrm{S}$ from LFG.