Calcium-Rich Industrial Wastes as Potential Sorbents for Cyclic CO2 Capture in the Gas–Solid Carbonation–Calcination Looping

Calcium-rich industrial wastes may serve as low-cost sorbents for near-source CO2 capture, but their practical potential depends on the reactive calcium species and cyclic stability. This study compares steel slag (SS), air pollution control residue (APCr), and cement kiln dust (CKD) under controlled thermogravimetric analysis (TGA) conditions for direct gas–solid carbonation and calcination looping. X-ray diffraction identified Ca(OH)2 in SS, CaClOH in APCr, and calcite-derived CaO in the calcined CKD as the principal reactive calcium species, corresponding to theoretical CO2 sequestration capacities of 117.0, 58.2, and 365.2 g CO2 kg−1 waste, respectively, based on the reference intensity ratio method. After the isothermal carbonation for 1 h, experimental carbon sequestration capacities or CO2 uptakes were 84, 39, and 201 g CO2 kg−1 waste, equivalent to conversion rates of 71.8, 67.0, and 55.0%. The CO2 uptake curves showed that the carbonation kinetics of these wastes obeys a two-stage regime featuring an initial rapid carbonation stage followed by a slower one restricted by the product-layer diffusion of CO2. Among the investigated industrial wastes, CKD exhibited the highest cyclic uptake of CO2 and the lowest observed cyclic deactivation, whereas the lower cyclic performance of SS and APCr was largely limited by the calcium encapsulation and chloride-induced high-temperature sintering, respectively. This study provides an alternative solution for the valorization of industrial solid waste according to the “waste-for-waste” concept.