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RESEARCH PRODUCT

Batch-to-Melt Conversion Kinetics in Sodium Aluminosilicate Batches Using Different Alumina Raw Materials

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The batch-to-melt conversion in batches of sand, soda ash and corundum (C), alumina spinel (A), boehmite (B), or gibbsite (G) as Al2O3 carrier are studied using thermal analysis, X-ray diffraction, and 27Al nuclear magnetic resonance spectroscopy. Laboratory-scaled batches are either heated continuously or quenched from 1600°C in a series of increasing dwell times. The results show that the conversion from the raw materials to the fresh melt proceeds in two kinetic stages. During the first stage (3–5 min), fast conversion of nearly 95% by mass occurs and the conversion coefficient increases in the order G < C ≈ A < B. The second stage is controlled by the slow dissolution of intermediate crystal phases, such as cristobalite, carnegieite, sodium metasilicate, and diaoyudaoite, which leads to an increase in the total batch-to-melt turnover time of up to 10 min. No direct correlation between the kinetic parameters characterizing the first stage and the fraction and dissolution speed of intermediate crystals of the second stage could be established.