CALCIUM-CARBONATE CRYSTALLIZATION, AGGLOMERATION AND FORM DURING CONTINUOUS PRECIPITATION FROM SOLUTION

Experiments were carried out to study the precipitation of calcium carbonate resulting from the mixing of aqueous solutions of calcium nitrate and sodium carbonate in a continous-flow crystallizer at 25-degrees-C in the pH range 8.5 to 10.5, reagent concentration 0.025 to 0.2 mol/l and solution residence times of 5 to 20 min. The population balance model is used to estimate nucleation, growth and agglomeration rates. Under the conditions studied, agglomeration of individual, previously formed crystals largely determines particle size and at higher reagent concentrations results in a bimodal distribution. The crystal form depends on the concentration of reagents, pH and residence time.