Solid-solute phase equilibria in aqueous solution: II. A potentiometric study of the aragonite-calcite transition

Königsberger, Erich; Bugajski, Jerzy; Gamsjäger, Heinz

doi:10.1016/0016-7037(89)90158-0

Cited by 18 publications

(4 citation statements)

References 9 publications

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“…Our solid medium apparatus 1 experiments are in reasonable agreement with Johannes and Puhan 's [1971] gas apparatus and piston‐out experiments given that probable ∼70 MPa inaccuracy for the piston‐cylinder brackets of Johannes and Puhan [1971]. If we include the theoretical 298 K equilibrium pressure of 0.299 GPa calculated by Königsberger et al [1989] on the basis of their measurements of Δ r G ° and Δ r S °, all the gas apparatus data and our new high‐pressure data can be fit by the equation: P (GPa) = 2.4 × 10 −6 * ( T − 298) 2 (K) − 7.4 × 10 −4 * ( T − 298) (K) + 0.299, indicated by the solid line in Figure 1a.…”

Section: Resultssupporting

confidence: 76%

The calcite → aragonite transformation in low‐Mg marble: Equilibrium relations, transformation mechanisms, and rates

Hacker

2005

J. Geophys. Res.

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[1] Experimental transformation of a rather pure natural calcite marble to aragonite marble did not proceed via the expected straightforward polymorphic replacement. Instead, the small amount of Mg in the starting material (0.36 wt %) was excluded from the growing aragonite and diffused preferentially into the remaining calcite grains, producing Mg-rich calcite rods that persisted as relicts. Nucleation of aragonite occurred exclusively on grain boundaries, with aragonite [001] oriented subparallel to calcite [0001]. The aragonite crystals preferentially consumed the calcite crystal on which they nucleated, and the reaction fronts developed preferentially along the {010} and {110} planes of aragonite. Each aragonite neoblast that grew was nearly free of Mg (typically <0.1 wt %). The excess Mg was taken up by the calcite grains in between, stabilizing them and causing a few volume percent rodlike relicts of Mg-enriched calcite (up to 10 wt % MgO) to be left behind by the advancing reaction front. The aragonite growth rates are approximately linear and range from $3 Â 10 À11 m s À1 at 600°C to $9 Â 10 À9 m s À1 at 850°C, with an apparent activation enthalpy of 166 ± 91 kJ mol À1 . This reaction mechanism and the resultant texture are akin to cellular precipitation reactions in metals. Similar transformation textures have been reported from high-Mg marbles in Japan and China that disproportionated to low-Mg calcite and dolomite.

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Section: Resultssupporting

confidence: 76%

The calcite → aragonite transformation in low‐Mg marble: Equilibrium relations, transformation mechanisms, and rates

Hacker

2005

J. Geophys. Res.

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“…The differences between the chemical potentials of calcite and other calcium carbonate phases such as aragonite or vaterite can be measured by galvanic cells without. liquid junction equipped with hydrogen or glass electrodes [33]. When these carbonates were equilibrated with CaClz solutions of the same molality and COZ atmospheres of the same compositions the measured e.m.f.…”

Section: Experimental Met Hodsmentioning

confidence: 99%

“…The thermostatted vessel used in these equilibrium studies operated on a similar principle to that of the solubility cells described above [33].…”

Section: Experimental Met Hodsmentioning

confidence: 99%

Solubilities of metal carbonates

Gamsjäger¹,

Königsberger²,

Preis³

1998

Pure and Applied Chemistry

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Solubilities in aqueous media of sparingly-soluble metal carbonates play an important role in chemical processes whether they occur in a laboratory, on an industrial scale, or in the geologic environment. Solubility phenomena (i.e. dissolution and precipitation reactions) of metal carbonates control procedures for preparing, separating and purifying chemicals. Moreover, the interactions of the hydrological cycle with the cycle of carbonate rocks, the naturally occurring dissolution of carbonate minerals in water as well as their precipitation on the ocean floor and in the sediments of rivers and lakes can be described by the principles of solubility, although gigantic quantities of material may be involved.The experimental methods for the determination of carbonate solubilities are reviewed and the results are discussed within the frame-work of equilibrium thermodynamics. It will be shown that Gibbs functions of pure stoichiometric carbonate phases can be determined by accurately measuring solubilities in aqueous electrolyte systems. In cases where solid-solid phase transformations and recrystallisations are kinetically inhibited, the methods developed were successfully applied to metastable equilibria. Occasionally, solubility data were even employed to estimate activity coefficients of components forming a series of carbonate solid solutions.Whenever possible the activity coefficients of the reacting species were controlled by use of a constant ionic medium. Solubility constants obtained at various fixed ionic strengths were fitted to the Pitzer equations and extrapolated to infinite dilution. Provided the standard potentials of the respective metal ion/metal electrode are known over a range of ionic strengths the values of solubility constants at infinite dilution can be calculated independently. In any case the optimised thermodynamic constants were incorporated in a comprehensive computer model which permits a wide variety of solubility calculations. These are illustrated by a case study of a multicomponent system with industrial relevance.

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“…Königsberger et al [42] investigated the ∆ r G°of the aragonite-calcite transition, and obtained a value of -830 ± 20 J mol -1 . The present analysis with the original Pitzer parameters and the new para-…”

mentioning

confidence: 99%

Consistency issues of aqueous solubility data and solution thermodynamics of electrolytes

Visscher

Vanderdeelen

2005

Pure and Applied Chemistry

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For the calculation of aqueous solubility of electrolytes, thermodynamic data from different sources are required. This can lead to errors if the data are inconsistent. This study reveals that some often-used semi-empirical equations for CO2 solubility and other equilibria are inconsistent with CODATA (Committee on Data for Science and Technology) key thermodynamic data. The equations were recalculated to make them consistent with CODATA. Combining standard thermodynamic data of NaCl with the Pitzer model leads to significant deviations from the accepted experimental value at 25 °C. Owing to the inadequacy of the Pitzer model at molalities exceeding 6 mol kg–1, this model leads to poor predictions of the HCl vapor pressure in equilibrium with highly concentrated aqueous HCl solutions. A long-standing inconsistency problem is related to the solubility of calcium carbonate. The main problem is disagreement on the existence of the CaHCO3+ ion pair. It is shown that the inconsistency largely disappears if it is assumed that the CaHCO3+ exists at low ionic strength, but becomes less stable at higher ionic strength.

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Solid-solute phase equilibria in aqueous solution: II. A potentiometric study of the aragonite-calcite transition

Cited by 18 publications

References 9 publications

The calcite → aragonite transformation in low‐Mg marble: Equilibrium relations, transformation mechanisms, and rates

The calcite → aragonite transformation in low‐Mg marble: Equilibrium relations, transformation mechanisms, and rates

Solubilities of metal carbonates

Consistency issues of aqueous solubility data and solution thermodynamics of electrolytes

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