Carbothermal magnesium slag-derived self-stabilizing CaO-based sorbent for CO2 capture and its novel sintering-resistance mechanism

CaO-based looping (CaL) process has attracted substantial attention as another available CO₂ capture alternative. However, CaO-based sorbents are afflicted by severe capacity degradation over repeated carbonation/regeneration cycles. Currently, various modification approaches have been used to improve the anti-sintering property. However, these strategies are frequently associated with complex synthetic processing and expensive chemical agents, offsetting the cost gains of natural CaO resources. Herein, we developed a simple and cost-effective method to prepare self-stabilizing CaO-based sorbents via directly upcycling the CTMS only through hydration and calcination proceedings, without any additional chemical agents. Under mild conditions, CTMS-H-C exhibits an initial CO₂ uptake of 0.37 g_CO2 g_specimen⁻¹. After 10 carbonation/regeneration cycles, its capacity decline rate is 29.73 %, which is much lower than that of calcined limestone (75.13 %) and commercial CaO (67.87 %), highlighting the superior cyclic stability of CTMS-H-C. Moreover, the sorption kinetic analysis reveals that the degeneration of the sorption rate is correlated with the structural deterioration caused by thermal sintering of the sorbent after multiple cycles, especially at the kinetically-controlled state. By density functional theory calculations and TG/DTG characterizations, we provide a new perspective of the enhancement mechanism of MgO on cyclic CO₂ capture capability of CaO-based sorbents. The findings suggest that the incorporation of MgO can weaken the binding interaction of CO₂ with CaO, which is conducive to accelerating the desorption of CO₂, thereby avoiding sintering triggered by Ostwald ripening. Overall, the work not only provides a cost-effective route to CaO-based sorbent synthesis, but also offers a sustainable waste management method for magnesium smelting via vacuum carbothermal reduction by transforming CTMS to CaO-based sorbent.