Direct Conversion of Desiliconization Slag to a CaO-Mesoporous Silica Composite for CO<sub>2</sub> Capture: Effect of Acid Dissolution Agent

Abstract

Calcium looping (CaL) utilizing CaO-based adsorbent has been studied to reduce carbon dioxide emissions (CO2). 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 CO2 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), N2 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 CO2 adsorption capacity with 21.0 wt% per mass of adsorbent and the highest stability. The findings demonstrated that the mesoporous structure enhanced the CO2 adsorption and acetic acid is the best dissolution agent in synthesizing CaO-MS adsorbent by separating the crystalline CaO phase and SiO2 phase. Environmentally benign and economically viable CaO-based adsorbents synthesized from desiliconization slag can be used for CO2 capture, particularly in the iron and steel industry.