PRECIPITATION OF CALCIUM-CARBONATE FROM SOLUTIONS WITH VARYING CA2+ CARBONATE RATIOS/

The precipitation of calcium carbonate from solutions with the same in itial supersaturation and different initial [Ca](T)/([HCO3-]+[CO32-]) ratio, has been studied making unseeded and seeded experiments at T-25 -degrees-C. In unseeded experiments induction times (t(i)) varied in t he order. t(i)([Ca](T)/Sigma-C=1/4)>t(i)([Ca](T)/Sigma-C=1). In seeded experiments the higher growth rates correspond to runs where [Ca](T)/ Sigma-C=4, whereas the lower ones are observed in runs where [Ca](T)/S igma-C=1/4. The lower nucleation (high t(i)) and higher rate of growth observed when [Ca](T)/Sigma-C=4 can be explained, respectively, by th e formation of a lower concentration of ion pairs in the bulk solution and a higher concentration of pairs CaCO30 on the crystal surface.