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1.
Solution calorimetric measurements compared with solubility determinations from the literature for the same samples of gibbsite have provided a direct thermochemical cycle through which the Gibbs free energy of formation of [Al(OH) 4 aq?] can be determined. The Gibbs free energy of formation of [Al(OH) 4 aq?] at 298.15 K is ?1305 ± 1 kJ/mol. These heat-of-solution results show no significant difference in the thermodynamic properties of gibbsite particles in the range from 50 to 0.05 μm.The Gibbs free energies of formation at 298.15 K and 1 bar pressure of diaspore, boehmite and bayerite are ?9210 ± 5.0, ?918.4 ± 2.1 and ?1153 ± 2 kJ/mol based upon the Gibbs free energy of [A1(OH) 4 aq?] calculated in this paper and the acceptance of ?1582.2 ± 1.3 and ?1154.9 ± 1.2 kJ/mol for the Gibbs free energy of formation of corundum and gibbsite, respectively.Values for the Gibbs free energy formation of [Al(OH) 2 aq+] and [AlO 2 aq?] were also calculated as ?914.2 ± 2.1 and ?830.9 ± 2.1 kJ/mol, respectively. The use of [AlC 2 aq?] as a chemical species is discouraged.A revised Gibbs free energy of formation for [H 4SiO 4aq0] was recalculated from calorimetric data yielding a value of ?1307.5 ± 1.7 kJ/mol which is in good agreement with the results obtained from several solubility studies.Smoothed values for the thermodynamic functions CP0, ( , , ST0 - S00, kaolinite are listed at integral temperatures between 298.15 and 800 K. The heat capacity of kaolinite at temperatures between 250 and 800 K may be calculated from the following equation: CP0 = 1430.26 ? 0.78850 T + 3.0340 × 10 ?4T2 ?1.85158 × 10 ?4T2.The thermodynamic properties of most of the geologically important Al-bearing phases have been referenced to the same reference state for Al, namely gibbsite. 相似文献
2.
The synthetic chelating agent ethylenediaminetetraacetic acid (EDTA) has been used to evaluate the stoichiometric solubility product of galena (PbS) at 298°K: This method circumvents the possible uncertainties in the stoichiometry and stability of lead sulfide complexes. At infinite dilution, , and at an ionic strength corresponding to seawater ( ), . Using the value of at infinite dilution, and the free energies of formation of HS ? and Pb 2+ at 298°K (literature values), the free energy of formation of PbS at 298°K is computed to be . Galena is shown to be more than two orders of magnitude more soluble than indicated by calculations based on previous thermodynamic data. 相似文献
3.
The spectrophotometric measurements of chloro complexes of lead in aqueous HCl, NaCl, MgCl 2 and CaCl 2 solutions at 25°C have been analyzed using Pitzer's specific interaction equations. Parameters for activity coefficients of the complexes PbCl +, PbCl 20 and PbCl 3? have been determined for the various media. Values of , and were obtained for the cumulative formation constants. [ ]. These values are in reasonable agreement with literature data. The Pitzer parameters for the PbCl ion pairs in various media were used to calculate the speciation of Pb 2+ in an artificial seawater solution. 相似文献
4.
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/cm 2 total pressure.Complete solid solution of RbMg 3AlSi 3O 10(OH) 2 in KMg 3AlSi 3O 10(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 AlSi 3O 8 in KAlSi 3O 8 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 | 相似文献
6.
The carbonato and hydrogencarbonato complexes of Mg 2+ were investigated at 25 and 50° in solutions of the constant ClO 4? molality (3 M) consisting preponderantly of NaClO 4. The experimental data could be explained assuming the following equilibria: Mg 2+ + CO 2B + H 2O ag MgHCO +3 + H +, , Mg2+ + 2 CO 2g + 2 H 2Oag Mg(HCO 3) 02 ± 2 H +, , ?15.37 ± 0.39 (50°), Mg 2+ + CO 2g + H 2Oag MgCO 03 + 2 H +, ,?15.23 ± 0.02 (50°), with the assumption γMgCO30 = γMg(HCO3)02, ΔG0(I = 0) for the reaction MgCO 03 + CO 2g + H 2O = Mg(HCO 3) 02 was estimated to be ?3.9 1 ± 0.8 6 and 0.6 ± 2.4 kJ/ mol at 25 and 50°C, respectively. The abundance of carbonate linked Mg(II) species in fresh water systems is discussed. 相似文献
8.
The fractionation factors ( ) for the reduction of CO 2 to CH 4 by pure cultures of methane-producing bacteria are, for Methanosarcina barkeri at 40°C, 1.045 ± 0.002; for Methanobacterium strain M.o.H. at 40°C, 1.061 ± 0.002; and, for Methanobacterium thermoautotrophicum at 65°C, 1.025 ± 0.002. These observations suggest that the acetic acid used by acetate dissimilating bacteria, if they play an important role in natural methane production, must have an intramolecular isotopic fractionation ( ) approximating the observed fractionation. 相似文献
9.
The decay constant 87Rb has been redetermined by measuring the amount of radiogenic 87Sr produced over a period of 19 years, in 20 g samples of purified RbClO 4, using isotope dilution techniques. The rubidium sample was spiked with 84Sr and the nanogram quantities of strontium separated by coprecipitation with Ba(NO 3) 2. Analyses were carried out on a 25cm, 90° sector mass spectrometer equipped with a Spiraltron electron multiplier. Measurement of three independent ratios permitted continuous monitoring of the ion beam fractionation. The average of nine determinations gives a value for the decay constant of . [ .] 相似文献
10.
Potentiometric measurements in dilute sodium borate solutions with added alkali earth chlordie salts yield the following expressions for the dissociation constants of alkali earth borate ion pairs from 10 to 50°C: where T is in °K. Enthalpies for the dissociation reactions at 25°C are less than 1 kcal./mole for all the alkali earth borate ion pairs.Values for p K(NaH 2BO 3°) from 5 to 55°C computed from the experimental data of Owen and King are in good agreement with those determined potentiometrically. The average value from both methods is 0.22 ± 0.1 at 25°C.Application to seawater of computed p K's for MgH 2BO 3+, CaH 2BO 3+ and NaH 2BO 30 yields an apparent dissociation constant for boric acid of 8.73 vs. 8.70 measured by Lyman, 8.68 by Buch and 8.73 by Byrne and Kester. 相似文献
11.
The South Mountain batholith of southwestern Nova Scotia is a large, peraluminous, granodiorite-granite complex which intrudes mainly greenschist facies metasediments of the Cambro-Ordovician Meguma Group. Using Rb-Sr isochrons constructed from whole rocks and mineral separates, the present study shows a variation in age and initial ratios of the intrusive phases of the batholith as follows: biotite granodiorite (371.8 ± 2.2 Ma, ( ranges from 0.7076 ± 0.0003 to 0.7090 ± 0.0003, with the average = 0.7081); adamellite (364.3 ± 1.3 Ma, ); porphyry (361.2 ± 1.4 Ma, ); using λ87Rb = 1.42 × 10 ?11yr?1.A suite of Meguma country rock samples showed a variation of at the time of intrusion of the batholith. A number of xenoliths of this material occurring in the marginal granodiorite had partially equilibrated isotopically with the granodiorite at a higher ratio than elsewhere in the granodiorites. This evidence demonstrates that isotopic (and probably some accompanying bulk chemical) contamination by the Meguma rocks has been an important factor in determining the ultimate chemical composition and mineralogy of the South Mountain batholith.The of the early granodiorites indicates that the parent magma of the South Mountain batholith was derived from a source unlike the Meguma Group. The precise nature of the source region cannot be determined by Rb-Sr work unless the degree of contamination with Megumalike material is known. 相似文献
13.
A linear correlation exists between the standard Gibbs free energies of formation of calcite-type carbonates (MCO 3) and the corresponding conventional standard Gibbs free energies of formation of the aqueous divalent cations (M 2+) 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 Helgeson et 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
15.
The tracer-diffusion coefficient of ions in water, Dj0, and in sea water, , differ by no more than zero to 8 per cent. When sea water diffuses into a dilute solution of water, in order to maintain the electro-neutrality, the average diffusion coefficients of major cations become greater but of major anions smaller than their respective or Dj0 values. The tracer diffusion coefficients of ions in deep-sea sediments, Dj,sed., can be related to by , where θ is the tortuosity of the bulk sediment and a a constant close to one. 相似文献
16.
High precision mass spectrometric determination of calcium isotope ratios allows the 40K → 40Ca radioactive decay to be used for dating a much broader range of geologic materials than is suggested by previous work. is used to monitor enrichments in 40Ca and can be measured to ±0.01% (2σ) using an exponential mass discrimination correction (Russell et al., 1978) and large ion currents. The earth's mantle has such a low (～0.01) that it has retained “primordial” ± 0.011 (normalized to ), as determined by measurements on two meteorites, pyroxene from an ultramafic nodule, metabasalt, and carbonatite. ratios can be conveniently expressed relative to this value as ?Ca in units of 10 ?4. To test the method for age dating, a mineral isochron has been obtained on a sample of Pikes Peak granite, which has been shown to have concordant KAr, RbSr, and UPb ages. Plagioclase, K-feldspar, biotite, and whole rock yield an age of 1041 ± 32 m.y. (2σ) in agreement with previous age determinations ( λK = 0.5543 b.y. ?1, , 40K = 0.01167%). The initial of 151.024 ± 0.016 ( ?Ca = +0.5 ± 1.0), indicates that assimilation of high K/Ca crust was insufficient to affect calcium isotopes. Measurements on two-mica granite from eastern Nevada indicate that the magma sources had K/Ca ≈ 1, similar to intermediate-composition crustal rocks. These results show that the KCa system can be used as a precise geochromometer for common felsic igneous and metamorphic rocks, and may prove applicable to sedimentary rocks containing authigenic K minerals. The relatively short half-life of 40K, the non-volatile daughter, and the fact that potassium and calcium are stoichiometric constituents of many minerals, make the KCa system complementary to other dating methods, and potentially applicable to a variety of geologic problems. 相似文献
17.
The following equation has been previously developed for the drag coefficient of a sphere. In this work the authors propose a power series expansion for C0 in terms of the Reynolds number: A fifth-order polynomial permits obtaining the drag coefficient and the settling velocity of a sphere, up to a Reynolds number of 3 × 10 5, with an average relative error of about 2%. 相似文献
18.
Natural malachite is a well defined solid demonstrating reproducible solubility behavior over a wide range of pH. The following equilibrium constants associated with the malachite dissolution equilibrium at 25°C, 1 atm were determined: (infinite dilution) (0.72 ionic strength) (36.9‰ salinity seawater). The temperature dependence of a “mixed” equilibrium constant, Ksp+, of the form: has been measured at I = 0.72, yielding the relationship: within a 5–25°C temperature range. The effect of pressure on the solubility of malachite in water and seawater was estimated from partial molar volume and compressibility data. For 25 °C at infinite dilution and in seawater .Comparison of stoichiometric and apparent malachite equilibrium constants has been used to estimate the extent of copper(II) ion interaction at the ionic strength of seawater. In dilute carbonate medium (total alkalinity, TA = 2.4 meq/kg H2O, pH 8.3), 2.9% of total dissolved copper exists as the free copper(II) ion and in seawater ( S = 36.9%., TA = 2.3 meq/kg H2O, pH = 8.1), is 3.1%.Total dissolved copper levels of approximately 450–750 nMol/Kg are necessary to attain malachite saturation conditions in the open ocean. Observations of malachite particles suspended in seawater must be explained by precipitation or solid phase substitution reactions from localized environments rather than by direct precipitation from bulk seawater. 相似文献
19.
Calculations based on approximately 350 new measurements (Ca T-PCO 2) of the solubilities of calcite, aragonite and vaterite in CO 2-H 2O solutions between 0 and 90°C indicate the following values for the log of the equilibrium constants KC, KA, and KV respectively, for the reaction CaCO 3(s) = Ca 2+ + CO 2?3: where T is in oK. At 25°C the logarithms of the equilibrium constants are ?8.480 ± 0.020, ?8.336 ± 0.020 and ?7.913 ± 0.020 for calcite, aragonite and vaterite, respectively.The equilibrium constants are internally consistent with an aqueous model that includes the CaHCO +3 and CaCO 03 ion pairs, revised analytical expressions for CO 2-H 2O equilibria, and extended Debye-Hückel individual ion activity coefficients. Using this aqueous model, the equilibrium constant of aragonite shows no PCO 2-dependence if the CaHCO +3 association constant is between 0 and 90°C, corresponding to the value logKCahco+3 = 1.11 ± 0.07 at 25°C. The CaCO 03 association constant was measured potentiometrically to be between 5 and 80°C, yielding logKCaCO03 = 3.22 ± 0.14 at 25°C.The CO 2-H 2O equilibria have been critically evaluated and new empirical expressions for the temperature dependence of KH, K1 and K2 are , and logK2 = ?107.8871 ? 0.03252849 T + 5151.79/ T + 38.92561 logT ? 563713.9/ T2 which may be used to at least 250°C. These expressions hold for 1 atm. total pressure between 0 and 100°C and follow the vapor pressure curve of water at higher temperatures.Extensive measurements of the pH of Ca-HCO 3 solutions at 25°C and 0.956 atm PCO 2 using different compositions of the reference electrode filling solution show that measured differences in pH are closely approximated by differences in liquid-junction potential as calculated by the Henderson equation. Liquid-junction corrected pH measurements agree with the calculated pH within 0.003-0.011 pH.Earlier arguments suggesting that the CaHCO +3 ion pair should not be included in the CaCO 3-CO 2-H 2O aqueous model were based on less accurate calcite solubility data. The CaHCO +3 ion pair must be included in the aqueous model to account for the observed PCO 2-dependence of aragonite solubility between 317 ppm CO 2 and 100% CO 2.Previous literature on the solubility of CaCO 3 polymorphs have been critically evaluated using the aqueous model and the results are compared. 相似文献
20.
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 Al 3+ 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 Al 3+ 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
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