Elsevier

Geochimica et Cosmochimica Acta

Volume 133, 15 May 2014, Pages 216-234
Geochimica et Cosmochimica Acta

Internal consistency in aqueous geochemical data revisited: Applications to the aluminum system

https://doi.org/10.1016/j.gca.2014.02.036Get rights and content

Abstract

Internal consistency of thermodynamic data has long been considered vital for confident calculations of aqueous geochemical processes. However, an internally consistent mineral thermodynamic data set is not necessarily consistent with calculations of aqueous species thermodynamic properties due, potentially, to improper or inconsistent constraints used in the derivation process. In this study, we attempt to accommodate the need for a mineral thermodynamic data set that is internally consistent with respect to aqueous species thermodynamic properties by adapting the least squares optimization methods of Powell and Holland (1985). This adapted method allows for both the derivation of mineral thermodynamic properties from fluid chemistry measurements of solutions in equilibrium with mineral assemblages, as well as estimates of the uncertainty on the derived results. Using a large number of phase equilibria, solubility, and calorimetric measurements, we have developed a thermodynamic data set of 12 key aluminum-bearing mineral phases. These data are derived to be consistent with Na+ and K+ speciation data presented by Shock and Helgeson (1988), H4SiO4(aq) data presented by Stefánsson (2001), and the Al speciation data set presented by Tagirov and Schott (2001). Many of the constraining phase equilibrium measurements are exactly the same as those used to develop other thermodynamic data, yet our derived values tend to be quite different than some of the others’ due to our choices of reference data. The differing values of mineral thermodynamic properties have implications for calculations of Al mineral solubilities; specifically, kaolinite solubilities calculated with the developed data set are as much as 6.75 times lower and 73% greater than those calculated with Helgeson et al. (1978) and Holland and Powell (2011) data, respectively. Where possible, calculations and experimental data are compared at low T, and the disagreement between the two sources reiterates the common assertion that low-T measurements of phase equilibria and mineral solubilities in the aluminum system rarely represent equilibrium between water and well-crystallized, aluminum-bearing minerals. As an ancillary benefit of the derived data, we show that it may be combined with high precision measurements of aqueous complex association constants to derive neutral species activity coefficients in supercritical fluids. Although this contribution is specific to the aluminum system, the methods and concepts developed here can help to improve the calculation of water–rock interactions in a broad range of earth systems.

Section snippets

Background and motivation

Ongoing research in the fields of equilibrium and kinetic geochemistry and their applications to many geologic processes, including hydrothermal crustal alteration (Seyfried et al., 2011), equilibrium isotope fractionation (Syverson et al., 2013), geologic CO2 utilization (Randolph and Saar, 2011) and storage (DePaolo et al., 2013), soil formation (Brantley and White, 2009), and others, have illustrated the importance of accurate calculations of equilibrium solubilities of rock-forming

Objectives and strategy

Aqueous geochemists require a database that provides an internally consistent means of calculating aluminum mineral and aqueous species thermodynamic properties over the wide range of crustal T and P, including not only the steam saturation curve, but also at the extreme conditions present in phase separation and hydrothermal alteration systems. In this study, we begin to develop this data set by taking advantage of both new and existing calorimetric measurements, phase equilibria, and aqueous

Methods

The standard states adopted in this study are a unit activity of an aqueous species in a hypothetical one molal solution referenced to infinite dilution, unit activity of pure minerals, and unit activity of pure liquid H2O at all temperatures and pressures. Mineral abbreviations utilized in this study follow the recommendations of Whitney and Evans (2010) (Table 1).

Anchor minerals: quartz, kaolinite, K-feldspar, and andalusite

Holland and Powell (1990) have shown that, for very large data sets, the relative size of the reaction matrix, R, and number of phases included in the vector g will reach a condition in which anchoring the matrix solution with input properties becomes unnecessary. However, the size of these data sets are much larger than the one presented here (e.g, >123 end-member phases (Holland and Powell, 1990)) and we therefore must employ anchor phases, as in their early studies (Powell and Holland, 1985,

Discussion

At its most basic level, the aluminum problem is truly a kaolinite problem, due to the improper reference state adopted by Helgeson et al. (1978) through Reaction (1) and the data shown in Fig. 1. By deriving and adopting thermodynamic data for 12 key Al minerals, including kaolinite, we have attempted to correct this longstanding problem. The ΔGf° we derive for kaolinite is 2.3 kcal/mol more negative than that reported by Helgeson et al. (1978), and, compared to the data provided here, the

Conclusion

Ongoing aqueous geochemical research has shown the critical significance of accurate calculations of rock-forming mineral solubilities, which, in turn, form the foundation of models of kinetically controlled mineral–fluid reactions. These calculations require a thermodynamic data set that is internally consistent with respect to both minerals and aqueous species. In this contribution, we have exhibited a method for deriving internally consistent thermodynamic data with estimates of

Disclaimer

Dr. Saar has a royalty and equity interest in, and serves as the Chief Scientific Officer for, Heat Mining Company, LLC, a company which may commercially benefit from the results of this research. Dr. Saar and the University of Minnesota have financial interests arising from the rights to receive royalty income under the terms of a license agreement with Heat Mining Company LLC. These relationships have been reviewed and managed by the University of Minnesota in accordance with its conflict of

Acknowledgments

We gratefully acknowledge support from the Department of Energy (DOE) Geothermal Technologies Program under Grant Number EE0002764 for this contribution and related research. W.E.S. wishes to acknowledge funding from NSF MGG-OCE under grant numbers 0751771 and 0813861. M.O.S. also thanks the George and Orpha Gibson endowment for its generous support of the Hydrogeology and Geofluids Research Group. The authors also thank the anonymous reviewers, Associate Editor Gleb Pokrovski, and Executive

References (142)

  • H. Haselton et al.

    Experimental study of muscovite stability in pure H2O and 1 molal KCl–HCl solutions

    Geochim. Cosmochim. Acta

    (1995)
  • H. Hellevang et al.

    The dissolution rates of dawsonite at pH 0.9 to 5 and temperatures of 22, 60 and 77 °C

    Appl. Geochem.

    (2010)
  • B.S. Hemingway et al.

    Revised values for the Gibbs free energy of formation of [Al(OH)4aq-], diaspore, boehmite and bayerite at 298.15 K and 1 bar, the thermodynamic properties of kaolinite to 800 K and 1 bar, and the heats of solution of several gibbsite samples

    Geochim. Cosmochim. Acta

    (1978)
  • P.C. Ho et al.

    Ion association of dilute aqueous potassium chloride and potassium hydroxide solutions to 600 °C and 300 MPa determined by electrical conductance measurements

    Geochim. Cosmochim. Acta

    (1997)
  • W.-L. Huang

    Stability and kinetics of kaolinite to boehmite conversion under hydrothermal conditions

    Chem. Geol.

    (1993)
  • E. Königsberger et al.

    The boehmite solubility gap

    Hydrometallurgy

    (2011)
  • A.C. Lasaga et al.

    Chemical weathering rate laws and global geochemical cycles

    Geochim. Cosmochim. Acta

    (1994)
  • K. Maher et al.

    The role of reaction affinity and secondary minerals in regulating chemical weathering rates at the Santa Cruz Soil Chronosequence, California

    Geochim. Cosmochim. Acta

    (2009)
  • H. May et al.

    Aqueous dissolution, solubilities and thermodynamic stabilities of common aluminosilicate clay minerals: kaolinite and smectites

    Geochim. Cosmochim. Acta

    (1986)
  • H.M. May et al.

    Gibbsite solubility and thermodynamic properties of hydroxy-aluminum ions in aqueous solution at 25 °C

    Geochim. Cosmochim. Acta

    (1979)
  • E. Merino

    Diagenesis in Tertiary sandstones from Kettleman North Dome, California–II. Interstitial solutions: Distribution of aqueous species at 100 °C and chemical relation to the diagenetic mineralogy

    Geochim. Cosmochim. Acta

    (1975)
  • K.L. Nagy et al.

    Dissolution and precipitation kinetics of gibbsite at 80 °C and pH 3: The dependence on solution saturation state

    Geochim. Cosmochim. Acta

    (1992)
  • E.H. Oelkers et al.

    Calculation of activity coefficients and degrees of formation of neutral ion pairs in supercritical electrolyte solutions

    Geochim. Cosmochim. Acta

    (1991)
  • D.A. Palmer et al.

    Aqueous high-temperature solubility studies. I. The solubility of boehmite as functions of ionic strength (to 5 molal, NaCl), temperature (100–290 °C), and pH as determined by in situ measurements

    Geochim. Cosmochim. Acta

    (2001)
  • D.A. Palmer et al.

    Aluminum speciation and equilibria in aqueous solution: II. The solubility of gibbsite in acidic sodium chloride solutions from 30 to 70 °C

    Geochim. Cosmochim. Acta

    (1992)
  • E. Althaus et al.

    An experimental re-examination of the upper stability limit of muscovite plus quartz

    Neues Jahrb. Mineral. Monatsh.

    (1970)
  • G.M. Anderson et al.

    Thermodynamics in Geochemistry: The Equilibrium Model

    (1993)
  • Apps J. A., Neil J., Jun C. -H. (1988) Thermochemical properties of gibbsite, bayerite, boehmite, diaspore, and the...
  • S. Arnórsson et al.

    Assessment of feldspar solubility constants in water in the range of 0° to 350 °C at vapor saturation pressures

    Am. J. Sci.

    (1999)
  • R. Barany et al.

    Heats and free energies of formation of gibbsite, kaolinite, halloysite, and dickite US Dept. of the Interior

    Bureau of Mines

    (1961)
  • R.L. Bassett et al.

    Critical review of the equilibrium constants for kaolinite and sepiolite

  • P. Bénézeth et al.

    Mineral solubility and aqueous speciation under hydrothermal conditions to 300 °C – the carbonate system as an example

    Rev. Mineral. Geochem.

    (2013)
  • R.G. Berman

    Internally-consistent thermodynamic data for minerals in the system Na2O–K2O–CaO–MgO–FeO–Fe2O3–Al2O3–SiO2–TiO2–H2O–CO2

    J. Petrol.

    (1988)
  • Bethke C. M. and Yeakel S. (2012) The Geochemist’s Workbench Release 9.0 Reaction modeling guide. Aqueous Solutions...
  • S.L. Brantley et al.

    Approaches to modeling weathered regolith

    Rev. Mineral. Geochem.

    (2009)
  • O.P. Bricker et al.

    Mineralogic factors in natural water equilibria

  • N.D. Chatterjee

    The upper stability limit of the assemblage paragonite + quartz and its natural occurrences

    Contrib. Mineral. Petrol.

    (1972)
  • N.D. Chatterjee et al.

    The system CaO–Al2O3–SiO2–H2O: New phase equilibria data, some calculated phase relations, and their petrological applications

    Contrib. Mineral. Petrol.

    (1984)
  • D. De Ligny et al.

    Energetics of kaolin polymorphs

    Am. Mineral.

    (1999)
  • Geochemistry of geologic CO2 sequestration

    Rev. Mineral. Geochem.

    (2013)
  • K. Ding et al.

    Activity coefficients of H2 and H2S in NaCl solutions at 300–425°C, 300–500 bars with application to ridge crest hydrothermal systems

    Eos

    (1990)
  • Drummond S. E. (1981) Boiling and mixing of hydrothermal fluids: chemical effects on mineral precipitation. Ph.D....
  • M.J. Ferrante et al.

    Thermodynamic data for synthetic dawsonite

    Rep. Invest.

    (1976)
  • C.-I. Fialips et al.

    New thermochemical evidence on the stability of dickite vs. kaolinite

    Am. Mineral.

    (2003)
  • C.-I. Fialips et al.

    Crystal properties and energetics of synthetic kaolinite

    Am. Mineral.

    (2001)
  • E. Franck

    Hochverdichteter wasserdampf I. Elektrolytische Leitfähigkeit in KCl–H2O–Lösungen bis 750 °C

    Z. Phys. Chem.

    (1956)
  • J.D. Frantz et al.

    Electrical conductances and ionization constants of salts, acids, and bases in supercritical aqueous fluids: I. Hydrochloric acid from 100 to 700 °C and at pressures to 4000 bars

    Am. J. Sci.

    (1984)
  • C. Frink et al.

    The solubility of gibbsite in aqueous solutions and soil extracts

    Soil Sci. Soc. Am. J.

    (1962)
  • R. Garrels et al.

    Reactions of feldspar and mica with water at low temperature and pressure

  • R.M. Garrels et al.

    Solutions, Minerals, and Equilibria

    (1965)
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