No abstract

Calcium looping (CaL) utilizing CaO-based adsorbent has been studied to reduce carbon dioxide emissions (CO 2 ). Synthesis of the CaO-based adsorbents from waste slags has captured the interest of the iron and steel industry, which is dealing with intensive amounts of waste slag produced. The drawback of using CaO-based adsorbents is their low regenerative ability during cyclic CO 2 adsorption. In this study, aiming to synthesize a CaO-based adsorbent with better cyclic stability, we used desiliconization slag as a raw material, which is produced during the steel purification process by minimizing the silicon concentration. We synthesized a CaO and mesoporous silica (CaO-MS) composite from desiliconization slag using P123 as an organic template and several organic acids, including formic acid (FA), acetic acid (AA), and citric acid (CA) as dissolution agents. The structure and performance of the adsorbents were investigated using X-ray diffraction analysis (XRD), N 2 adsorption-desorption, transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), and thermogravimetric analysis (TG). Compared to the samples synthesized with other organic acids, the slag-derived adsorbent synthesized with acetic acid (DSslag-CaO-MS(AA)) displayed the optimum CO 2 adsorption capacity with 21.0 wt% per mass of adsorbent and the highest stability. The findings demonstrated that the mesoporous structure enhanced the CO 2 adsorption and acetic acid is the best dissolution agent in synthesizing CaO-MS adsorbent by separating the crystalline CaO phase and SiO 2 phase. Environmentally benign and economically viable CaO-based adsorbents synthesized from desiliconization slag can be used for CO 2 capture, particularly in the iron and steel industry.

Utilizing a reversible reaction between CaO and CO 2 , namely the calcium looping (CaL) process, is among the CO 2 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 CO 2 uptake (0.78 gram of CO 2 per gram of CaO), its CO 2 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-Ca 12 Al 14 O 33 (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 SiO 2 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 Ca 12 Al 14 O 33 via thermal decomposition. According to the TGA study, the synthesized adsorbent produced with nitric acid (BFS-CaO-CAO(NO 3 )) had better adsorption of CO 2 (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 (Ca 12 Al 14 O 33 ) in the adsorbent, which acted as an inert binder, effectively prevented the sintering and agglomeration of CaO particles. A lowcost, ecologically viable regenerative CO 2 -adsorbent synthesized from BFS is advantageous for lowering CO 2 emissions.