CO₂ Adsorption on a CaO–Ca₁₂Al₁₄O₃₃ Composite Synthesized from a Blast Furnace Slag and its Regenerative Ability

Abstract

Utilizing a reversible reaction between CaO and CO₂, namely the calcium looping (CaL) process, is among the CO₂ adsorption and sequestration techniques that have been intensively studied over the years. While CaO-based sorbents offer numerous advantages, such as broad accessibility, low cost, and relatively high theoretical CO₂ uptake (0.78 gram of CO₂ per gram of CaO), its CO₂ capture capability during cyclic operation degrades substantially, which has remained an important issue for commercial CaL process applications. To address the aforementioned problem, in this study, we synthesized a CaO–Ca₁₂Al₁₄O₃₃ (BFS-CaO-CAO) composite from blast furnace slag (BFS) by using two types of inorganic acid, nitric acid, and hydrochloric acid. Acid-leaching and the subsequent separation of SiO₂ content from BFS resulted in a formation of Ca–Al-based layered double hydroxide, which was then transformed into a mixed oxide of CaO and Ca₁₂Al₁₄O₃₃ via thermal decomposition. According to the TGA study, the synthesized adsorbent produced with nitric acid (BFS-CaO-CAO(NO₃)) had better adsorption of CO₂ (13 wt% per mass of adsorbent) and regenerative ability compared to an analog synthesized with hydrochloric acid (BFS-CaO-CAO(Cl)). Moreover, the presence of mayenite (Ca₁₂Al₁₄O₃₃) in the adsorbent, which acted as an inert binder, effectively prevented the sintering and agglomeration of CaO particles. A low-cost, ecologically viable regenerative CO₂-adsorbent synthesized from BFS is advantageous for lowering CO₂ emissions.