Dissolution Kinetics and Mechanism of Ulexite in Oxalic Acid Solutions
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The dissolution rates of ulexite in oxalic acid solutions were investigated statistically and graphically using homogeneous and heterogeneous reaction models at different stirring speeds, particle sizes, acid concentrations, and calcination and solution temperatures. It was found that the dissolution rate increased with increasing acid concentration and temperature and decreasing particle size, but was not affected by the stirring speed. The sample preheated at 140 degreesC had the highest dissolution rate. The activation energy for the process, E-d, was calculated to be 7.20 kcal mol(-1), which implies that the reaction rate was controlled by product-layer diffusion. The dissolution process correlated reasonably well with the product-layer-diffusion-controlled model.