Evaluation of carbon sequestration by iron-rich slag materials

Mining and metalliferous alkaline waste offer an opportunity for carbon sequestration by trapping carbon dioxide (CO 2 ) through hydration, sorption, or precipitation. The objective of this paper was to determine the feasibility of two iron-rich slag materials for use as a substrate to sequester injected CO 2 . The physical, chemical and mineralogical characteristics of both samples were analyzed showing a larger particle size, smaller surface roughness, and higher porosity for S2 than S1. Both samples were injected with 10% v /v CO 2 in airtight media bottles that were agitated for 24 h with various initial moisture conditions. Both wastes exhibited high potential for carbon trapping with up to 92.5% and 99.5% CO 2 removal for samples S1 and S2, respectively. Through qualitative and quantitative analysis, results showed that both samples showed precipitates of minor carbonate phases. S1 precipitated calcium carbonate (CaCO 3 ) and S2 precipitated CaCO 3 , magnesite (MgCO 3 ), and siderite (FeCO 3 ) achieving mineral trapping. However, the majority of solid phase CO 2 removal was attributed to chemical adsorption onto the metal-based surfaces of iron-rich slag materials. At 10% ( v /v) CO 2 , solid phase CO 2 trapping has the potential to remove 1000 and 1073 g CO 2 per tonne of S1 and S2, respectively. The results are promising for carbon trapping using metalliferous waste at low moisture conditions. • CO 2 capture by titanium slag achieved up to 99.5% CO 2 removal • CO 2 trapping achieved was up to 98.5% in the solid phase primarily via adsorption • Mineral trapping was as CaCO 3 and Fe 6 (OH) 12 CO 3 ∙ H 2 O • Liquid phase CO 2 removal was via solubility and mineral trapping