Solubility and stability of zeolites in aqueous solution; I, Analcime, Na-, and K-clinoptilolite

Publisher Website
Google Scholar
Abstract
The solubilities of analcime and clinoptilolite were determined in dilute, weakly alkaline, aqueous solutions below 300 degrees C and at vapor-saturated pressures. Analcimes used in this study were from Mont St. Hilaire, Quebec (an 1 , Si/Al = 2.02) and Wikieup, Arizona (an 2 , Si/Al = 2.55); clinoptilolite samples were from Castle Creek, Idaho (Si/Al = 4.50). The effects of alkali content (Na,K) on clinoptilolite solubility were determined by using cation-exchanged varieties of the Castle Creek material (cp 1 , cp 2 ). In neutral to weakly alkaline solutions, the dominant solubility-controlling reactions of these zeolites are NaAlSi 2 O 6 .H 2 O(an 1 ) + 5H 2 O(1) <--> Na (super +) + Al(OH) (super -) 4 + 2Si(OH) 4 (aq), Na (sub 0.85) Al (sub 0.85) Si (sub 2.15) O 6 . H 2 O(an 2 ) + 5H 2 O(1) <--> 0.85Na (super +) + 0.85Al(OH) (super -) 4 + 2.15Si(OH) 4 (aq), Na (sub 1.1) Al (sub 1.1) Si (sub 4.9) O 12 .3.5H 2 O(cp1) + 8.5H2O(1) <--> 1.1Na (super +) + 1.1A1(OH) (super -) 4 + 4.9Si(OH) 4 (aq), and K (sub 1.1) Al (sub 1.1) Si (sub 4.9) O 12 .2.7H 2 O(cp 2 ) + 9.3H 2 O(1) <--> 1.1K (super +) + 1.1Al(OH) (super -) 4 + 4.9Si(OH) 4 (aq). The logarithm of the equilibrium constants of these reactions were fit to the function: log K = A + BT + C/T + D log T. At 25 degrees C, log K 25 values for the Mont St. Hilaire analcime, Wikieup analcime, Na-clinoptilolite, and K-clinoptilolite are -16.1, -15.0, -26.5, and -28.1, respectively. These data were combined with the thermodynamic properties of the aqueous (aq) species Si(OH) 4 , Al(OH) (super -) 4 , Na (super +) , K (super +) , and liquid water (1) to determine standard Gibbs free energies of formation as a function of temperature. Values of Delta G 0f at 25 degrees C and 1 bar for the Mont St. Hilaire analcime and Wikieup analcime are -3089.2 and -3044.4 kJ/mol, respectively. The Delta G 0f values for hydrous Na-clinoptilolite and K-clinoptilolite, respectively, are -6267.9 and -6107.4 kJ/mol at 25 degrees C and 1 bar. The solubility data reported here, and results obtained from previous calorimetric studies, indicate that the aluminosilicate frameworks of analcime and clinoptilolite are stabilized by an increase in Al content.

This publication has 0 references indexed in Scilit: