Solvent-free synthesis of hydroxycancrinite zeolite microspheres during the carbonation process of blast furnace slag

CO₂ mineralization is a technological solution to reduce anthropogenic CO₂ emissions. It is more cost-effective to use industrial wastes as feedstock than natural minerals and eliminate some of the energy-consuming operations, to recover various value-added byproducts. In this study, hydroxycancrinite zeolite was synthesized by a solvent-free method during the carbonation of blast furnace slag (BFS) as the waste feedstock. The effects of various process factors such as the alkaline dosage, crystallization temperature, and crystallization batch time on the synthesis of hydroxycancrinite were systematically investigated. A well-crystallized spherical hydroxycancrinite was obtained by mixing with NaOH solid and then crystallizing at 100 °C for 4 h. The as-synthesized products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscope, thermogravimetric analysis, and Brunauer-Emmett-Teller analysis. The results revealed that pure microspheres of hydroxycancrinites are obtained with a diameter of ∼1 μm and a surface area of 37.2 m²/g. Based on the material balance and preliminary economic evaluation, 361 kg CO₂/t BFS can be stored by calcium and magnesium components, whereas almost all of the silicon and aluminum are recovered as value-added zeolites, which significantly improve the process economy.