The Influence And Reacitive Crystallization Kinetics Of Nesquehonite

In this thesis, precipitation of magnesium carbonate hydrates was investigated by the reaction of MgSO4 with Na2CO3. In the reaction, the influenced factors such as reaction temperature, titration speed and initial concentration on the crystal growth and morphology of production were studied. When the reaction temperation was below 313 K, the needle-like nesquehonite (MgCO3·3H2O) was synthesized. When the temperature was up to 323 K, the spherical-like crystals were obtained, and with the temperature increasing, the diameter of crystals increased. The production also were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results showed that the initial concentration and titration speed also had significant effect on the crystal growth and the crystals size of MgCO3·3H2O besides reaction temperature. As the preceding state of mading MgO, the crystal size of nesquehonite has an important relation to the active of magnesia. The reactive crystallization kinetics of nesquehonite were investigated in a continous mixed-suspension mixed-product removal (MSMPR) crystallizer. We found that the growth rate of product crystal was size-dependent by analyzing experimental data. Based on the theory of population balance, the Bransom, CR, ASL, MJ2 and MJ3 size-dependent growth rate models were discussed in details. Using the non-linear least squares method, the parameters of three growth rate models were determined by fitting the experimental data of population density obtained in steady state. By comparison of experimental population density data and population density data that calculated from five size-dependent growth rate models by using a objective function Sy, it was found that the MJ3 model was the best one for predicting the growth of nesquehonite. That's more, the growth rate equation was determined by using the model of MJ3.