The carbon mineralization of solid wastes enables the simultaneous achievement of efficient CO₂ capture and the activation enhancement of basic oxygen furnace (BOF) steel slag. However, the relatively low CO₂ concentration in industrial flue gas, the direct mineralization reaction between CO₂ on reaction of steel slag and the issue of low conversion efficiency should be concerned. This study was to employ a potassium glycinate (KG) solution to absorb and enrich CO₂ from flue gas. The CO₂-loaded KG solution was subsequently utilized to indirectly mineralize and modify BOF steel slag, thereby achieving both mineralization modification of steel slag powder and regeneration–recycling of the KG solution. The kinetic characteristics of the mineralization reaction between the CO₂-loaded KG solution and steel slag were investigated. The phase composition of mineralization products, the carbon sequestration capacity of steel slag, and the evolution of its reactivity were analyzed. Furthermore, a synergistic carbon capture approach integrating steel slag mineralization modification with carbonation curing of cement paste was explored, and its influence on the mechanical strength of cement was evaluated. This study could provide a technical support for CO₂ capture using steel slag and its high-value utilization in cement-based materials.

BOF steel slag with a CaO content of 37% was selected as a raw material. A 1 mol/L potassium glycinate (KG) solution was first carbonated to obtain a CO₂-loaded solution, which was subsequently used to mineralize the steel slag for different durations. The residual CO₂ loading in the mineralization filtrate was determined by acid-base titration. Combined with the measurements of pH value in the filtrate, the kinetic characteristics of steel slag mineralization at different reaction stages were elucidated, thereby identifying the optimal mineralization duration. X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were employed to quantify the carbon sequestration capacity and characterize the crystalline phases of both mineralized steel slag and carbonation-cured cement paste at different mineralization durations. Furthermore, the pozzolanic activity after mineralization was evaluated by a strength activity index method, based on a 30% replacement ratio and 28-d compressive strength. In addition, the mineralized steel slag was incorporated as a supplementary cementitious material into cement-based systems and subjected to synergistic carbonation curing in CO₂ atmosphere. The carbon sequestration efficiency and mechanical performance enhancement of mineralized steel slag under dual carbonation conditions were systematically assessed via compressive strength testing and microstructural phase analysis.

This study proposes and validates a complete collaborative process route, confirming that the mineral carbonation modification of steel slag with carbon-rich KG solution enhances its activity. The mineralized steel slag as an admixture can effectively improve the compressive strength of cement-based specimens. Compared with conventional organic amine solutions, the KG solution exhibits a faster CO₂ adsorption rate and a better adsorption efficiency. Also, the mineralization of steel slag with carbon-rich KG solution re-releases the CO₂ adsorption capacity of the KG solution, which, can effectively reduce the cost of indirect carbon mineralization of steel slag with respect to the CO₂ absorption effect in the first stage. The carbon mineralization product of steel slag contains calcite with an aragonite-like structure. The porous morphology of the product enhances its carbon sequestration capacity during the carbonation curing process of cement paste specimens. Furthermore, the metastable aragonite undergoes a dissolution-recrystallization effect during the curing process, effectively improving the early strength of cement-based materials.

This work evaluated the CO₂ capture and steel slag mineralization kinetics using KG solution, as well as the resource utilization effects. The results showed that the reaction rate between steel slag and carbon-rich KG solution could be rapid within the first 120 min, with the CO₂ reaction rate in KG reaching 92.8%. The calcium carbonate produced during the reaction encapsulated the steel slag particles, hindering the mineralization process, leading to a gradual slowdown of the reaction rate and stabilization in subsequent stages. After mineralization, the early activity of the steel slag was significantly enhanced, with a maximum 16.7% increase in 7-d compressive strength at a 10% dosage. Carbonation curing could effectively improve the early compressive strength of the steel slag cement paste. After 12 h of carbonation curing with 30% mineralized steel slag, the 7-d compressive strength was increased by 11.3%. The mineralization of steel slag with carbon-rich KG solution resulted in the formation of calcium carbonate with an aragonite crystal structure. The encapsulated calcium carbonate mineralization product on the steel slag provided nucleation sites for C-S-H gel in the cement hydration process, thereby accelerating the hydration process. Furthermore, the transformation of metastable aragonite into calcite during carbonation curing could enhance the cement matrix, leading to a cementitious strengthening effect. This method could have significant application prospects for the resource utilization of steel slag.