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1.
Frank J Millero 《Geochimica et cosmochimica acta》1982,46(1):11-22
The effect of presure on the solubility of minerals in water and seawater can be estimated from In where the volume (ΔV) and compressibility (ΔK) changes at atmospheric pressure (P = 0) are given by Values of the partial molal volume () and compressibilty () in water and seawater have been tabulated for some ions from 0 to 50°C. The compressibility change is quite large (~10 × 10?3 cm3 bar?1 mol?1) for the solubility of most minerals. This large compressibility change accounts for the large differences observed between values of ΔV obtained from linear plots of In Ksp versus P and molal volume data (Macdonald and North, 1974; North, 1974). Calculated values of for the solubility of CaCO3, SrSO4 and CaF2 in water were found to be in good agreement with direct measurements (Macdonald and North, 1974). Similar calculations for the solubility of minerals in seawater are also in good agreement with direct measurements (Ingle, 1975) providing that the surface of the solid phase is not appreciably altered. 相似文献
2.
Dimitri A Sverjensky 《Geochimica et cosmochimica acta》1984,48(5):1127-1134
A linear correlation exists between the standard Gibbs free energies of formation of calcite-type carbonates (MCO3) and the corresponding conventional standard Gibbs free energies of formation of the aqueous divalent cations (M2+) at 25 °C and 1 bar ΔGMCO30 = m(ΔGf,M2+0) ? 141,200 cal · mole?1 where m is equal to 0.9715. This relationship enables prediction of the standard free energies of formation of numerous hypothetical carbonates with the calcite structure. Associated uncertainties typically range from about ± 250 to 600 cal · mole?1. An important consequence of the above correlation is that the thermodynamic equilibrium constant for the distribution of two trace elements M and N between carbonate mineral and aqueous solution at 25 °C and 1 bar is proportional to the free energy difference between the corresponding two aqueous ions: In Combination of predicted standard free energies, entropies and volumes of carbonate minerals at 25°C and 1 bar with standard free energies of aqueous ions and the equation of state in Helgesonet al. (1981) enables prediction of the thermodynamic equilibrium constant for trace element distribution between carbonates and aqueous solutions at elevated temperatures and pressures. Interpretation of the thermodynamic equilibrium constant in terms of concentration ratios in the aqueous phase is considerably simplified if pairs of divalent trace elements are considered that have very similar ionic radii (e.g., , ). In combination with data for the stabilities of complex ions in aqueous solutions, the above calculations enable useful limits to be placed on the concentrations of trace elements in hydrothermal solutions. 相似文献
3.
Frank J Millero 《Geochimica et cosmochimica acta》1979,43(10):1651-1661
The apparent constants (K'i) for the ionization of carbonic acid in seawater at various salinities (S,%.) have been fit to equations of the form ln whereKi is the thermodynamic ionization constant in water, Ai, and Bi are adjustable parameters. The temperature dependence (TK) of Ki, Ai and Bi were of the form, a0 + a1/T + a3 ln T. Equations of similar forms have been used to analyze the ionization constants for water and boric acid and the solubility product of calcite in seawater. The effect of pressure on the apparent constants () have been fit to equations of the form ln where the volume (ΔV) and compressibility (ΔK) changes are polynomial functions of temperature. The equations generated for various açids in seawater have been used to examine the carbonate system in seawater. Equations relating the NBS and Tris pH scales have been derived as well as equations of pH as a function of temperature and pressure. The equations from Hansson (1972, Ph.D. Thesis, University of Göteborg, Sweden) and Mehrbachet al. (1973, Limnol. Oceanogr.18, 897–907) have been used to examine the components of the carbonate system. At a fixed total alkalinity and total carbon dioxide, differences of ±0.01 m-equiv kg?1 in HCO?3 and CO2?3 were found; however, the [CO2] and Pco2 are nearly the same. The contribution of borate ion, B(OH)?4 determined from the equations of Hansson (1972, Ph.D. Thesis, University of Göteborg, Sweden) and Lyman (1957, Ph.D. Thesis, University of California, Los Angeles) differ by ±0.01 m-equiv kg?1 for waters with the same salinity and temperature. 相似文献
4.
The ionization quotients of aqueous carbon dioxide (carbonic acid) have been precisely determined in NaCl media to 5 m and from 50° to 300°C using potentiometric apparatus previously developed at Oak Ridge National Laboratory. The pressure coefficient was also determined to 250°C in the same media. These results have been combined with selected information in the literature and modeled in two ways to arrive at the best fits and to derive the thermodynamic parameters for the ionization reaction, including the equilibrium constant, activity coefficient quotients, and pressure coefficients. The variation with temperature of the two fundamental quantities and were examined along the saturation vapor pressure curve and at constant density. The results demonstrated again that for reactions with minimal electrostriction changes the magnitudes and variations of and with temperature are small and, in addition, and are approximately independent of salt concentration.The results have also been applied to an examination of the solubility of calcite as a function of pH (in a given NaCl medium) for the neutral to acidic region both for systems with fixed CO2 pressure and systems where the calcium ion concentration equals the concentration of carbon. The pH of saturated solutions of calcite with PCO2 of 12 bars increases from 5.1 to 5.5 between 100° and 300°C. 相似文献
5.
Stability constants of hydroxocomplexes of Al(III):Al(OH)2+ and A1(OH)4? have been measured in the 20–70°C temperature range by reactions involving only dissolved species. The stability constant of the first complex ion is studied by measuring pH of solutions of aluminium salts at several concentrations. of aluminate ion is deduced from equilibrium constants of the reaction between the trioxalato aluminium (III) complex ion and Al3+ in acid medium, and between the same complex ion and A1(OH)4? in alkaline medium. The K values and the associated ΔH are and ΔH1 = 11.8 Kcal; and ΔH4 = 42.45 Kcal. These last results are not in agreement with the values of recent tables for and of Al3+ and Al(OH)4?. We suggest a consistent set of data for dissolved and solid Al species and for some aluminosilicates. 相似文献
6.
Howard M. May Philip A. Helmke Marion L. Jackson 《Geochimica et cosmochimica acta》1979,43(6):861-868
Solubility curves were determined for a synthetic gibbsite and a natural gibbsite (Minas Gerais, Brazil) from pH 4 to 9, in 0.2% gibbsite suspensions in 0.01 M NaNO3 that were buffered by low concentrations of non-complexing buffer agents. Equilibrium solubility was approached from oversaturation (in suspensions spiked with Al(NO3)3 solution), and also from undersaturation in some synthetic gibbsite suspensions. Mononuclear Al ion concentrations and pH values were periodically determined. Within 1 month or less, data from over-and undersaturated suspensions of synthetic gibbsite converged to describe an equilibrium solubility curve. A downward shift of the solubility curve, beginning at pH 6.7, indicates that a phase more stable than gibbsite controls Al solubility in alkaline systems. Extrapolation of the initial portion of the high-pH side of the synthetic gibbsite solubility curve provides the first unified equilibrium experimental model of Al ion speciation in waters from pH 4 to 9.The significant mononuclear ion species at equilibrium with gibbsite are Al3+, AlOH2+, Al(OH)+2 and Al(OH)?4, and their ion activity products are , , and . The calculated standard Gibbs free energies of formation (ΔG°f) for the synthetic gibbsite and the A1OH2+, Al(OH)+2 and Al(OH)?4 ions are ?276.0, ?166.9, ?216.5 and ?313.5 kcal mol?1, respectively. These ΔG°f values are based on the recently revised ΔG°f value for Al3+ (?117.0 ± 0.3 kcal mol?1) and carry the same uncertainty. The ΔG°f of the natural gibbsite is ?275.1 ± 0.4 kcal mol?, which suggests that a range of ΔG°f values can exist even for relatively simple natural minerals. 相似文献
7.
A.E. Beswick 《Geochimica et cosmochimica acta》1973,37(2):183-208
K and Rb distributions between aqueous alkali chloride vapour phase (0.7 molar) and coexisting phlogopites and sanidines have been investigated in the range 500 to 800°C at 2000 kg/cm2 total pressure.Complete solid solution of RbMg3AlSi3O10(OH)2 in KMg3AlSi3O10(OH)2 exists at and above 700°C. At 500°C a possible miscibility gap between approximately 0.2 and 0.6 mole fraction of the Rb end-member is indicated.Only limited solid solution of Rb AlSi3O8 in KAlSi3O8 has been found at all temperatures investigated.Distribution coefficients, expressed as in solid/(Rb/K) in vapour, are appreciably temperature-dependent but at each temperature are independent of composition for low Rb end-member mole fractions in the solids. The determined values and their approximate Rb end-member mole fraction () ranges of constancy are summarized as follows: (°C)
(°C)T | ||||
500 | 0–0.2 | 0–0.07 | ||
700 | 0–0.2 | 0–0.1 | ||
800 | 0–0.2 | 0–0.1 |