Direct Synthesis of a Regenerative CaO–Fe3O4–SiO2 Composite Adsorbent from Converter Slag for CO2 Capture Applications

The iron and steel industry produces large volumes of iron and steel-making slags as mineral residues and a massive volume of carbon dioxide (CO2) due to the consumption of raw materials, such as iron ore, lime, and coke. Converter slag, produced during the refining of pig iron to produce steel in steel-making furnaces, is a complex oxide composed of CaO, FeO, SiO2, and other minor oxides. The scope for recycling of converter slag is rather limited compared with that of blast furnace slag due to the unique chemical composition. Herein, we report a facile route to convert converter slag into a CaO–Fe3O4–SiO2 composite (Cslag–CFS) which possesses a high CO2 adsorption performance. A composite composed of crystalline CaO particles, Fe3O4 particles, and mesoporous SiO2 (mean surface area 64 m2/g) was synthesized using converter slag as the sole source material and formic acid as a leaching agent via a facile dissolution–hydrothermal process. Owing to the formation of a crystalline CaO phase, the composite exhibited a CO2 uptake of 23.4 wt % per mass of adsorbent and may be used as an efficient and regenerative solid adsorbent for CO2 capture. This study offers an alternative approach that may provide solutions to both recycling of waste slag and recovery of CO2 gas that the iron and steel-making industry is currently confronting.