Equilibrium in the clinoptilolite-H{sub 2}O system
- Los Alamos National Lab., NM (United States)
A thermodynamic formulation for the sorption of H{sub 2}O in clinoptilolite has been obtained from analysis of equilibrium data collected by thermogravimetry on near endmember Ca-, Na-, and K-exchanged natural clinoptilolite (Fish Creek Mountains, Nevada). Temperature and pressure of the experiments ranged from 25 to 250 {degrees}C and 0.2 to 35 mbar H{sub 2}O vapor pressure. Equilibrium of three clinoptilolite species was successfully formulated with the following expression for the Gibbs free energy of hydration as a function of temperature and pressure: {Delta}{mu}{sub Hy}/T = {Delta}{mu}{sub Hy}{sup 0}/T{sub 0} + {Delta}H{sub Hy}{sup 0}(1/T - 1/T{sub 0}) - 3R[ln(T/T{sub 0}) + (T{sub 0}/T - 1)] + R ln[{theta}/(1 - {theta})P] + W{sub 1}/T{theta} + W{sub 2}/T{theta}{sup 2} where R is the gas constant, P is the vapor pressure of H{sub 2}O, W{sub 1} and W{sub 2} are the excess mixing parameters, and {theta} is the ratio H{sub 2}O/(maximum H{sub 2}O) with maximum water contents for the K, Na, and Ca end-members of 13.49, 15.68, and 16.25 wt%, respectively. The molar Gibbs free energy of hydration for calcium, sodium, and potassium clinoptilolite is -36.13 {plus_minus} 3.02, -29.68 {plus_minus} 3.77, and -25.53 {plus_minus} 1.37 kJ/mol H{sub 2}O, respectively. The molar enthalpy of hydration for these phases is -76.92 {plus_minus} 2.88, -74.19 {plus_minus} 3.46, and -67.78 {plus_minus} 1.25 kJ/mol H{sub 2}O. The thermodynamic formulation is applied to the occurrence of clinoptilolite at Yucca Mountain, Nevada, where the proposed emplacement of nuclear waste would lead to heating of clinoptilolite-bearing tuffs. Rock units with abundant clinoptilolite (or by analogy other hydrous phases) would remain significantly cooler than units with anhydrous minerals and would evolve a substantial volume of water. 21 refs., 11 figs., 5 tabs.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 468401
- Journal Information:
- American Mineralogist, Journal Name: American Mineralogist Journal Issue: 7-8 Vol. 81; ISSN AMMIAY; ISSN 0003-004X
- Country of Publication:
- United States
- Language:
- English
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