Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Benning, L. G. Articles by Barnes, H. L. Search for Related Content GeoRef GeoRef Citation

Solubility and stability of zeolites in aqueous solution: II. Calcic clinoptilolite and mordenite

Liane G. Benning^*, Richard T. Wilkin and Hubert L. Barnes

Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, U.S.A.

The solubilities of Ca-exchanged clinoptilolite (Cpt-Ca) and Ca-exchanged mordenite (Mor-Ca) have been measured in aqueous solutions between 25 and 275 °C and at saturated water vapor pressures. Natural zeolites were cation exchanged to close to Ca end-member composition (90% for Cpt-Ca, and 98% for Mor-Ca). The controlling dissolution reactions may be written as:

These reactions are reversible as shown by equilibrium constants calculated for approach from under- and supersaturation. The log K_sp for Cpt-Ca increases from –26.9 at 25 °C to a maximum of –16.9 at 275 °C, whereas for Mor-Ca the equilibrium constant varies from –25.3 at 25 °C to –17.7 at 265 °C. The solubilities for both zeolites increase with increasing temperature showing a positive enthalpy for the dissolution reaction. At lower temperatures Cpt-Ca is slightly more soluble than Mor-Ca, which agrees with natural observations where mordenite and clinoptilolite commonly occur together spatially but mordenite is in general the higher-temperature phase. A comparison with other exchanged clinoptilolites indicates that Cpt-Ca is more stable than the Na, K, and Mg varieties. The results demonstrate that the exchanged cation has a large effect on the solubility behavior, and that divalently exchanged varieties are less soluble than monovalent varieties. From the solubility constants, the standard Gibbs free energies of formation for hydrous Cpt-Ca and Mor-Ca at 25 °C and 1 bar were determined to be –6387 ± 5 kJ/mol and –6275 ± 7 kJ/mol respectively. However, compared to the hydration states and the aluminosilicate structure, the effect of the cation on the Gibbs free energies of formation is small.

This article has been cited by other articles:

				T. Fridriksson, P. S. Neuhoff, B. E. Viani, and D. K. Bird Experimental determination of thermodynamic properties of ion-exchange in heulandite: Binary ion-exchange experiments at 55 and 85{degrees}C involving Ca2+, Sr2+, Na+, and K+ Am J Sci, April 1, 2004; 304(4): 287 - 332. [Abstract] [Full Text] [PDF]

				S. Yang, A. Navrotsky, and R. Wilkin Thermodynamics of ion-exchanged and natural clinoptilolite American Mineralogist, April 1, 2001; 86(4): 438 - 447. [Abstract] [Full Text] [PDF]

				R.T. Wilkin and H.L. Barnes Nucleation and growth kinetics of analcime from precursor Na-clinoptilolite American Mineralogist, October 1, 2000; 85(10): 1329 - 1341. [Abstract] [Full Text] [PDF]