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.