A direct conversion of blast furnace slag to a mesoporous silica–calcium oxide composite and its application in CO2 captures

Abstract

In the iron manufacturing industry, it is unavoidable to produce large volumes of blast furnace slag (BFS) as a mineral residue from the preparation of pig iron in blast furnaces as well as to discharge a high volume of carbon dioxide (CO₂) gas as a result of the consumption of coke. These byproducts potentially lead to environmental problems such as ground pollution and global warming unless they are treated. BFS is a complex oxide mainly composed of CaO, MgO, SiO₂ and Al₂O_3. The former two have the ability to react with CO₂, and SiO₂ is a major component of mesoporous silica (MS). Herein, we report a direct route to convert BFS into a mesoporous silica-calcium oxide composite (slagCaO-MS) possessing high CO₂ adsorption performance. A composite composed of SBA-15-like mesoporous silica with a pore diameter of 12.3 nm and crystalline CaO particles (mean surface area = 128 m² g⁻¹) was synthesized from BFS via a facile dissolution-hydrothermal process using formic acid as a dissolving agent, while the use of mineral acids (HNO₃ and HCl) resulted in the formation of ill-defined low-surface-area materials with less CO₂ adsorption capacities. The composite synthesized under optimum conditions was found to have a CO₂ uptake value of 18.8 wt% per mass of adsorbent, and could be regenerated for at least 10 cycles. The green and low-cost adsorbent originating from BFS with high CO₂ adsorption ability and reusability is advantageous for mitigating CO₂ emissions discharged from the iron manufacturing industry, and will surely contribute to the sustainable development of the iron manufacturing industry.