An eco-friendly approach to purify natural magnesite and to densify sintered magnesia

Abstract

High-grade raw magnesite ore for DBM97 production became rare in China after a mining frenzy for over 30 years. However, the demand for high-purity sintered magnesia grows in high-temperature industries that accompany volatile components. The developed process starts from the flotation of low-grade natural magnesite, executes the flash calcination in a suspension calciner, and ultimately accomplishes sintering in an extraordinary high-temperature shaft kiln. But it is hard to densify such magnesia. In this work, a novel eco-friendly approach is studied in a pilot plant with a capacity of 40 t/d input, to calcine natural magnesite grading as low as 40 % MgO, to carry out three levels of watering treatments removing Si-, Fe- and Ca-components and hydrating MgO (gaining >90 % Mg(OH)2), to calcine magnesium hydroxide for active MgO in the suspension calciner, and finally to burn high purity magnesia to high densification. The MgO hydration process is highlighted with the pivotal parameters of hydrating duration and temperature, which is believed to be an eco-friendly beneficiation. The calcined caustic magnesia obtained has a high activity of < 20 s with citric acid. While such CCM compacts are sintered at ordinary high temperatures, the bulk density of > 3.4 g/cm3 reached in industrial potential of dead burnt magnesia with the purity of > 97.5 % MgO.