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Dissolution kinetics and solubility of calcium carbonate monohydrate

Calcium carbonate monohydrate (CaCO3xH2O) has been synthesized and the crystals were characterized by means of optical microscopy, FT-IR spectroscopy, X-ray diffractometry and thermogravimetry. The solubility was found by recording pH during the dissolution of the monohydrate in water, preventing contact with carbon dioxide from the air. The solubility product was calculated frm the final, equilibrium, pH value taking all the relevant calcium and carbonate species into account. In the temperature range 15-50 degrees C the solubility product Kso could be expressed by -log Kso=7.050+0.000159 theta2 where temperature is expressed in degrees C. The kinetics of dissolution of calcium carbonate monohydrate crystals in aqueous solution were studied at temperatures between 15 and 45 degrees C. The progress of dissolution was followed by recording pH as a function of time. It was found that the dissolution kinetics follow a second order rate equation with the rate constant k equal to 2.205x10-4, 6.190x10-4, 1.218x10-3 and 4.369x10-3 l mol-1 s-1/mg l-1 at 15, 25, 35, 45 degrees C respectively, and that the activation energy for dissolution was 73.3 kJ mol-1, suggesting a surface-controlled process.

Calcium carbonate monohydrate ; Dissolution kinetics ; Solubility product

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