Suspension-calcined dolomite with ultrahigh reactivity for silicothermic magnesium production

Calcined dolomite (CaO⋅MgO) is a critical feedstock for silicothermic magnesium production, and its reactivity significantly influences the primary magnesium yield. However, conventional industrial stacked-state calcination of lump dolomite often requires long residence times and results in non-uniform reactivity due to surface over-calcination and core under-calcination. While suspension calcination of powdered dolomite offers a potential route for obtaining high-reactivity feedstock at lower temperatures and shorter times, its ultimate reactivity and effectiveness in silicothermic reduction remain insufficiently explored. Here, we develop a suspension calcination route for dolomite powders and evaluate its feasibility for magnesium metallurgy through coupled simulations, laboratory experiments, and ton-scale pilot validation. Under optimized gas-solid conditions, dolomite decomposes within 8∼12 s at ∼1100 °C, producing calcined dolomite with a near-theoretical reactivity of 36.07%. This significantly outperforms typical industrial rotary kilns requiring hours of processing. This exceptional reactivity originates from a refined CaO⋅MgO microstructure featuring abundant mesoporosity and nanocrystalline grains. Crucially, this high-reactivity feedstock drastically improves reduction efficiency by lowering the pellet-to-magnesium mass ratio. These results demonstrate a scalable and energy-efficient pathway to produce highly reactive calcined dolomite for magnesium manufacturing.