Thermodynamic properties of analcime solid solutions

Abstract

Analcime (Na x Al x Si 3-x O 6 ⅐ [(3-x)/2]H 2 O, where x varies from ϳ ϳ0.78 to ϳ ϳ1.06) is one of the most common rock-forming zeolites. It forms in a wide range of geologic environments that span a range of temperature and pressure from ambient to magmatic conditions. Cluster variation method analysis of 29 Si magic angle spinning nuclear magnetic resonance spectra indicates 1) the presence of at least two distinct states of short range Si/Al disorder [low (less disordered) and high (more disordered) analcime], and 2) that configurational entropy associated short-range Si-Al disorder within each of these states increases regularly with increasing Si content. Hydrofluoric acid (HF) solution calorimetry at 50°C was used to determine the enthalpy of formation of five pure analcime samples of varying composition (range of x approximately 0.95 to 1.05) and Si-Al disorder. Enthalpies of formation from the elements at 25°C (⌬H f ) for these samples fall on a linear trend, except for one sample of high analcime for which ⌬H f was about 6.1 ؎ 3.0 kJ/mol less stable than a low analcime of the same composition. Comparison with the results of previous calorimetric studies indicates negligible excess enthalpies of mixing in both low and high analcime solid solutions (that is, the solid solutions are athermal). The configurational entropies derived from cluster variation analysis were in turn used to derive activity-composition relationships for low analcime solid solutions whose compositions are bounded by an aluminous endmember (Na 1.05 Al 1.05 Si 1.95 O 6 ⅐ 0.975H 2 O) and a siliceous endmember (Na 0.75 Al 0.75 Si 2.25 O 6 ⅐ 1.125H 2 O). These relationships were used to retrieve thermodynamic properties for the endmembers from experimental observations of equilibria between analcime, albite, and aqueous solutions. Retrieved values of ⌬H f are in excellent agreement with the calorimetric results of this study. Comparative analysis of equilibrium observations in the literature indicate that one sample of analcime from the Mont St. Hilaire alkaline intrusive complex used for analcime solubility measurements is high analcime. The Gibbs energy of disordering at 298.15 K, 1 bar consistent with the retrieval calculations is ϳ ϳ 6 kJ/mol. The thermodynamic properties of disordering for analcime indicate that hydrated low analcime is stable with respect to hydrated high analcime everywhere in Earth's crust. Phase relations between low analcime, quartz, albite, and aqueous solutions calculated from the retrieved thermodynamic data indicate that at quartz equilibrium, low analcime should become more Si-rich with increasing temperature and pressure and that the composition of analcime is a sensitive function of the chemical potential of SiO 2 . Stable equilibrium between analcime, albite, quartz and H 2 O occurs at much lower temperatures than suggested by earlier phase equilibrium experiments. The breakdown of analcime plus quartz to form albite in geologic systems probably reflects metastable equilibrium in which the composition of...

ThermoChimie database developments in the framework of cement/clay interactions

“…The thermodynamic properties of zeolites have been the subject of numerous experimental studies either using calorimetry or solution equilibria (Johnson et al, 1982(Johnson et al, , 1983(Johnson et al, , 1985(Johnson et al, , 1991(Johnson et al, , 1992Belitsky et al, 1982;Hemingway and Robie, 1984;Donahoe et al, 1990;Kiseleva et al, 1996Kiseleva et al, , 2001Shim et al, 1999;Drebushchak et al, 2000;Ogorodova et al, 2003;Neuhoff et al, 2004;Neuhoff and Wang, 2007). However, problems arise with the completeness of the thermodynamic datasets, for example with DH 0 f and S 0 (J mol À1 K À1 ) measured on minerals displaying slightly different compositions.…”

“…Scheme illustrating the process for completing the thermodynamic data sets for cement minerals. Neuhoff et al (2004) were able to explain these differences by considering variations in compositions and in the Si/Al ordering state. For entropy, the only direct measurement of the parameter is given by Johnson et al (1982): 226.75 and 171.71 J/mol K for the hydrated and anhydrous phases, respectively.…”

“…Its composition field is rather narrow: according to Neuhoff et al (2004) the number of Si atoms ranges from 1.8 to 2.3 for six oxygen atoms. A considerable amount of work has been devoted to the thermodynamic properties of analcime.…”

“…For entropy, the only direct measurement of the parameter is given by Johnson et al (1982): 226.75 and 171.71 J/mol K for the hydrated and anhydrous phases, respectively. This measurement could be extended to different Si/Al ratios by Neuhoff et al (2004) by using a solid solution model. They also provide configurational entropies for various compositions.…”

Middle Miocene zeolite-bearing turbidites, Abrămuţ Basin (Pannonian Basin), NW Romania

“…In this case, the tem per a ture val ues are lower -be tween 21 to 34°C at the bound ary between zone I and II, and be tween 37 to 51°C at the bound ary be tween zones II and III. Neuhoff et al (2004) plot ted compositional and ther mo dy namic data for analcime with thermo-bar o met ric isograds. The au thors dis cuss the sta bil ity of analcime with var i ous chem i cal com po si tions in the sys tem analcime-quartz-al bite-H 2 O.…”