DISSOLUTION KINETICS AND SOLUBILITY OF CALCIUM-CARBONATE MONOHYDRATE

Calcium carbonate monohydrate (CaCO3H2O) has been synthesized and the crystals were characterized by means of optical microscopy, FT-IR spec troscopy, X-ray diffractometry and thermogravimetry. The solubility wa s found by recording pH during the dissolution of the monohydrate in w ater, preventing contact with carbon dioxide from the air. The solubil ity product was calculated from the final, equilibrium, pH value takin g all the relevant calcium and carbonate species into account. In the temperature range 15-50 degrees C the solubility product K-SO could be expressed by - log K-SO = 7.050 + 0.000159 theta(2) where temperature is expressed in degrees C. The kinetics of dissolution of calcium car bonate monohydrate crystals in aqueous solution were studied at temper atures between 15 and 45 degrees C. The progress of dissolution was fo llowed by recording pH as a function of time. It was found that the di ssolution kinetics follow a second order rate equation with the rate c onstants k equal to 2,205 x 10(-4), 6.190 x 10(-4), 1.2,18 x 10(-3) an d 4.369 x 10(-3) 1 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.