Prediction of the limit of the metastable zone in the CaCO3-CO2-H2O system

The surpassing of the solubility product of the anhydrous forms of calcium carbonate - calcite, aragonite, and vaterite - is not sufficient to induce spontaneous precipitation. The existence of a metastable zone, in the nucleation of the calcium carbonate, is still an experimental phenomenon. A thermodynamic demarcation of the metastable zone in the CaCO 3 -CO 2 -H 2 O system, where only a secondary nucleation can occur, has been delimited for the first time. Through experimental exploration of a large supersaturation field, results obtained by the bubbling method are treated with the use of thermodynamic data of different varieties of CaCO 3 . At temperatures ranging between 25 and 60°C, a primary nucleation (spontaneous precipitation) occurs when the ionic activity product of the calco-carbonic solution surpasses the solubility product of CaCO 3 .H 2 O. No spontaneous nucleation occurs when the ionic activity product stabilizes between the solubility products of calcite and monohydrated calcium carbonate, which means that the solution remains in a metastable state. The metastability can be broken by seeding with calcium carbonate crystals (aragonite in this case) and then the germination is a secondary one. A model for the prediction of the limit of the metastable zone, presented in this report, is in agreement with experimental results.

[1]  R. Rosenbauer,et al.  The Solubility and Stabilization of Ikaite (CaCO3·6H2O) from 0° to 25°C: Environmental and Paleoclimatic Implications for Thinolite Tufa , 1993, The Journal of Geology.

[2]  H. Elfil,et al.  Role of hydrate phases of calcium carbonate on the scaling phenomenon , 2001 .

[3]  W. Chien,et al.  Crystal growth kinetics of calcite in a dense fluidized‐bed crystallizer , 1999 .

[4]  A. Mersmann,et al.  How to predict the metastable zone width , 1998 .

[5]  J. Gal,et al.  Mechanisms of scale formation and carbon dioxide partial pressure influence. Part I. Elaboration of an experimental method and a scaling model. , 2002, Water research.

[6]  I. Greenwald.  THE DISSOCIATION OF CALCIUM AND MAGNESIUM CARBONATES AND BICARBONATES , 1941 .

[7]  A. E. Nielsen,et al.  Electrolyte crystal growth kinetics , 1984 .

[8]  Michael J. Hounslow,et al.  Growth and aggregation rates for calcite and calcium oxalate monohydrate , 1999 .

[9]  Å. Oskarsson,et al.  Solubility of calcium carbonate hexahydrate , 1993 .

[10]  L. Brečević,et al.  Dissolution kinetics and solubility of calcium carbonate monohydrate , 1995 .

[11]  R. Sheikholeslami.  Nucleation and kinetics of mixed salts in scaling , 2003 .

[12]  Takeshi Ogino,et al.  The formation and transformation mechanism of calcium carbonate in water , 1987 .

[13]  J. Rieger,et al.  Study of Precipitation Reactions by X-ray Microscopy: CaCO3 Precipitation and the Effect of Polycarboxylates , 2000 .

[14]  C. Kontoyannis,et al.  Precipitation of calcium carbonate in aqueous solutions , 1984 .

[15]  J. Johnston.  The several forms of calcium carbonate , 1916 .

[16]  E. Dana.  On a crystal of andalusite from Delaware County, Pennsylvania , 1872, American Journal of Science.

[17]  L. N. Plummer,et al.  The solubilities of calcite, aragonite and vaterite in CO2-H2O solutions between 0 and 90°C, and an evaluation of the aqueous model for the system CaCO3-CO2-H2O , 1982 .

[18]  H. Roques.  Kinetics of the formation conditions of carbonate tartars , 1974 .

[19]  P. Panine,et al.  Formation and Growth of Amorphous Colloidal CaCO3 Precursor Particles as Detected by Time-Resolved SAXS , 2002 .

[20]  J. Ulrich,et al.  Some aspects of the importance of metastable zone width and nucleation in industrial crystallizers , 2002 .

[21]  G. H. Nancollas,et al.  The crystallization of calcium carbonate , 1971 .