Abstract
High-purity, densified magnesia (HPDM) is a crucial refractory material for various high-temperature industrial applications. However, the naturally occurring high-grade magnesite ores required for HPDM production are rapidly depleting due to their overconsumption over the years. For the sustainable HPDM production, this study proposes an innovative two-stage fluidized bed process to produce HPDM from currently abundant low-grade magnesite ores. The first fluidized bed reactor operates at 700 °C using hydrogen chloride (HCl) as the fluidizing gas. This stage removes iron (Fe) by selectively chlorinating it into volatile chlorides (FeCl3), while converting calcium (Ca) into CaCl2, which remains with MgO in the chlorinated intermediates. These intermediates are subsequently dechlorinated and sintered in the second fluidized bed at 1600 °C to produce HPDM. Thermodynamic analysis was performed to guide optimization of reaction conditions, which was subsequently validated by experiments. Results reveal that HCl preferentially reacts with CaO and Fe₂O₃ at 700 °C. When a higher-purity magnesite flotation concentrate is used as raw material, the final HPDM product is found to meet industrial standards for high-performance magnesia, characterized by greater than 98% MgO purity and more than 98% densification. This work establishes a feasible and efficient route for valorizing low-grade magnesite, offering significant economic and environmental advantages over conventional methods.