Abstract
The reaction kinetics of the dissolution of pure scheelite (CaWO4) particles in aqueous Na4EDTA solutions were studied at atmospheric pressure. As expected, the dissolution rate increased with decreasing initial particle size and with increasing temperature and Na4EDTA concentration. Further, the dissolution rate decreased as the initial solid-liquid ratio and the ionic strength of the solution were increased. The experimental results do not support the conventional shrinking-core model for a single irreversible reaction. A new shrinking-core model for multiple reactions, composed of a noninstantaneous reversible reaction (scheelite dissociation into the ions Ca2+ and WO 2−4 ) and an instantaneous irreversible reaction (formation of Ca-EDTA complex), was presented. The observed dependency of the dissolution rate on the relevant operating variables was the same a the theoretical predictions based on the present shrinking-core model. The activation energy was 49800 J mol−1. These findings justify the validity of the assumed kinetic model with the multiple reactions as the rate-controlling step. The dissolution rate expression was obtained as a function of the initial particle size, initial solid-liquid ratio, Na4EDTA concentration, temperature, and ionic strength of the solution.
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Konishi, Y., Katada, H. & Asai, S. Kinetics of the dissolution of scheelite in aqueous Na4EDTA solutions. Metall Trans B 18, 331–337 (1987). https://doi.org/10.1007/BF02656151
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DOI: https://doi.org/10.1007/BF02656151