NUCLEATION OF CALCIUM-CARBONATE AT DIFFERENT INITIAL PH CONDITIONS

The precipitation of calcium carbonate from mixing calcium chloride an d potassium bicarbonate/carbonate solutions at 25 degrees C has been s tudied doing unseeded batch pH-drift experiments. The record of pH has been used to determine induction times. The pH and pCa measurements w ere used for calculations of species concentration and supersaturation . SEM indicated that vaterite was the predominant phase formed. The de pendence of the induction time on supersaturation was analyzed with di fferent models. The results indicate that a good fit is obtained from the plot of In t(i) versus 1/1n(2) beta but the small size of the crit ical nucleus indicates that an atomistic model is more realistic. The nucleation parameters have been determined using an empirical expressi on of the growth rate of vaterite taken from the literature, together with the experimentally measured induction times.