Evaluation of Calcium-Based Sorbents Derived from Natural Ores and Industrial Wastes for High-Temperature CO₂Capture

This study focuses on the investigation of potential calcium-based, low-cost sorbent materials for post-combustion CO2 capture via carbonate looping. Mineral limestone, carbide slag, and white mud were evaluated for their CO2 sorption activity, with the latter two being industrial wastes retrieved from chlor-alkali and paper pulp plants, respectively. Mineral magnesite was tested as a structural promoter in an attempt to improve the cyclic stability of the sorbents. Different methods consisting of hydration, acetic acid treatment, and a modified sol-gel autocombustion using glycerol as the combustion agent were applied to modify the structural and morphological characteristics of the mineral- A nd waste-derived CaO and improve their performance. Preliminary thermogravimetric analysis (TGA) tests proved the superiority of limestone and carbide slag treated with glycerol autocombustion over white mud. The addition of magnesite was considered more beneficial via the acetic acid treatment, since the promoted limestone and carbide slag presented adequate stability under 50 sorption/desorption TGA cycles, with a 43.2% and 34.2% deactivation, respectively. The most promising CaO-based sorbents were further evaluated in a bench-scale fluidized-bed reactor, with the promoted materials withstanding sintering more distinctly, even under more severe calcination conditions (880 °C, 50% CO2 concentration). Magnesite-promoted limestone exhibited an initial CO2 uptake of a11 mol CO2/kg of sorbent, which corresponds to a90% CaO conversion and <35% deactivation after 20 consecutive carbonation cycles, even under harsh calcination conditions. The superiority of the limestone promoted with magnesite was attributed to the enhancement of its pore network due to a reconstruction of its morphology in the presence of steam during the carbonation/calcination cycles.