Mineralization regeneration of NH3–CO2 absorption solution and crystalline phase transition pathways of calcium carbonate

Conventional carbon capture technologies often suffer from high energy demands during the desorption stage, whereas mineralization-assisted desorption provides a promising alternative to mitigate this challenge. This study investigates the mineralization-regeneration process of the NH 3 –CO 2 absorption system, with particular emphasis on the influence of CaCl 2 on desorption performance and the underlying reaction mechanisms. The work further examines the phase transition behavior and doping regulation of calcium carbonate, and introduces steel slag as a practical calcium source to evaluate its feasibility for large-scale applications.Results indicate that the desorption efficiency of the NH 3 –CO 2 absorption system is strongly dependent on the calcium dosage and reaction temperature. At a CO 2 /Ca 2+ molar ratio of 1.0:1.0, pH 9, and a reaction temperature of 25 °C, the desorption rate reached 93.55%. The purity of the mineralized calcium carbonate exceeded 99.84%. Moreover, in the presence of NH 3 and Mg 2+ , a distinct crystalline phase transition pathway was identified. Without Mg 2+ , the transformation proceeded along the aragonite → calcite pathway, whereas higher Mg 2+ concentrations (molar ratio of 0.4) promoted the formation of clustered calcite structures. The leachate reacted with the NH 3 –CO 2 absorption solution to achieve a desorption rate of 80.50%, producing calcium carbonate with 98.74% aragonite content, and demonstrating superior stability compared to the CaCl 2 -based system over multiple cycles. Collectively, these findings confirm the viability of indirect mineralization-assisted desorption in the NH 3 –CO 2 absorption system and highlight the potential of industrial solid wastes, particularly steel slag, as alternative calcium sources for carbon capture applications.