(490c) CO2 Mineralization and Hydrogen Production through Sodium Carbonate Looping for Cementitious Materials

To reverse global warming, advancements to drive a net-negative carbon economy are essential; many current approaches to capture and store CO₂ from industrial flue gas and the atmosphere are expensive and have significant energy requirements. We propose a novel thermochemical sodium carbonate (Na₂CO₃) looping process utilizing steel slags for reactive CO₂ capture and simultaneous conversion of the slags into supplementary cementitious materials (separate amorphous silica and carbonated slag). The slag is aqueously carbonated at mild conditions (25-70°C, 1 atm) by exothermic reactions. This process was demonstrated on BOF steel slags and achieved high capture rates of 79% and 90% for 4% and 343ppm CO₂, respectively, sequestering up to 4.1 mmol CO₂ per gram of slag. Compared to a slag and water mixture baseline case, the looping scenarios mineralized 2-5 times more CO₂. XRD, ICP-OES, SEM, and EDS analyses confirmed the effectiveness of the Na₂CO₃ looping process in converting CO₂ and slags to stable carbonates and silica. Additionally, reacting the slag with steam at high temperature can produce up to 1.02 mmol H₂ per gram of slag. Overall, the whole process can be driven by steelmaking waste heat and small amounts of renewable energy, and there is no chemical consumed. Technoeconomic analysis indicates economic viability, with costs of $107.16 and $31.40 per ton of CO₂ for DAC and point source capture resulting in 40-80% cost reduction compared to the baseline case.