THE INFLUENCE OF THE OPERATIONAL CONDITIONS ON THE PRECIPITATION PROCESS

A study of the precipitation processes for sparingly soluble substance s was performed with the two systems of CaSO4 . 2H(2)O and CaCO3. A co ntinuous as well as a batch DTB-crystallizer were investigated in orde r to describe the influence of different operational conditions on the kinetic parameters, on the median crystal size and on the crystal mod ification. Besides the mode of operation the location of the feed poin t, the reactant concentration, the power input and the residence time were examined. The experimental results are discussed under special co nsideration of the mixing conditions. With the help of data from liter ature the results of the examined DTB-crystallizer were transferred to other types of crystallizer and to other operating conditions. In the batch experiments agglomeration and phase transformation processes pl ay an important role. Due to the high initial supersaturation an unsta ble amorphous precursor was built in the case of CaCO3, which, at the end of the experiment, transferred to stable crystalline modifications . The small particle size and the high supersaturation encourage the a gglomeration process compared to the continuous process.