Sustainable production of high-density magnesia from low-grade magnesite via a novel two-stage fluidized bed chlorination-sintering process

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 CaCl_2, 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.