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2.
Denis Yu. Zezin Artashes A. Migdisov Anthony E. Williams-Jones 《Geochimica et cosmochimica acta》2007,71(12):3070-3081
The solubility of gold in H2S gas has been investigated at temperatures of 300, 350 and 400 °C and pressures up to 230 bars. Experimentally determined values of the solubility of Au are 0.4-1.4 ppb at 300 °C, 1-8 ppb at 350 °C and 8.6-95 ppb at 400 °C. Owing to a positive dependence of the logarithm of the fugacity of gold on the logarithm of the fugacity of H2S, it is proposed that the solubility of Au can be attributed to formation of a solvated gaseous sulfide or bisulfide complex through reactions of the type:
(A) 相似文献
3.
Emilie Pourtier Jean-Luc Devidal François Gibert 《Geochimica et cosmochimica acta》2010,74(6):1872-66
The solubility of synthetic NdPO4 monazite end-member was experimentally determined from 300 up to 800 °C, at 2000 bars in pure water, and in aqueous chloride or phosphate solutions. Both the classical weight-loss method and a new method based on isotope dilution coupled with thermal ionization mass spectrometer were used. In the range of temperature studied monazite showed a prograde solubility from 10−5.4 m at 300 °C up to 10−2.57 m at 800 °C. Experiments in H2O-H3PO4-NaCl-HCl solutions suggested Nd(OH)30 was the major species that was formed at high temperature and pressure. The equilibrium constants (log K) for the reaction:
4.
The solubility of molybdenum trioxide in liquid-undersaturated water vapour has been investigated experimentally at 300, 320, and 360 °C and 39-154 bars. Results of these experiments show that the solubility of MoO3 in water vapour is between 1 and 29 ppm, which is 19-20 orders of magnitude higher than the vapour pressure of MoO3(g). Molybdenum solubility increases exponentially with fH2O, suggesting the formation of a gaseous hydrated complex of the type MoO3·nH2O by the reaction:
(A.1) 相似文献
5.
Reaction between dissolved water and sulphide was experimentally investigated in soda-lime-silicate (NCS) and sodium trisilicate (NS3) melts at temperatures from 1000 to 1200 °C and pressures of 100 or 200 MPa in internally heated gas pressure vessels. Diffusion couple experiments were conducted at water-undersaturated conditions with one half of the couple being doped with sulphide (added as FeS or Na2S; 1500-2000 ppm S by weight) and the other with H2O (∼3.0 wt.%). Additionally, two experiments were performed using a dry NCS glass cylinder and a free H2O fluid. Here, the melt was water-saturated at least at the melt/fluid interface. Profiling by electron microprobe (sulphur) and infrared microscopy (H2O) demonstrate that H2O diffusion in the melts is faster by 1.5-2.3 orders of magnitude than sulphur diffusion and, hence, H2O can be considered as a rapidly diffusing oxidant while sulphur is quasi immobile in these experiments.In Raman spectra a band at 2576 cm−1 appears in the sulphide - H2O transition zone which is attributed to fundamental S-H stretching vibrations. Formation of new IR absorption bands at 5025 cm−1 (on expense of the combination band of molecular H2O at 5225 cm−1) and at 3400 cm−1 was observed at the front of the in-diffusing water in the sulphide bearing melt. The appearance and intensity of these two IR bands is correlated with systematic changes in S K-edge XANES spectra. A pre-edge excitation at 2466.5 eV grows with increasing H2O concentration while the sulphide peak at 2474.0 eV decreases in intensity relative to the peak at 2477.0 eV and the feature at 2472.3 eV becomes more pronounced (all energies are relative to the sulphate excitation, calibrated to 2482.5 eV). The observations by Raman, IR and XANES spectroscopy indicate a well coordinated S2− - H2O complex which was probably formed in the glasses during cooling at the glass transition. No oxidation of sulphide was observed in any of the diffusion couple experiments. On the contrary, XANES spectra from experiments conducted with a free H2O fluid show complete transformation of sulphide to sulphate near the melt surface and coexistence of sulphate and sulphide in the center of the melt. This can be explained by a lower H2O activity in the diffusion couple experiments or by the need of a sink for hydrogen (e.g., a fluid which can dissolve high concentration of hydrogen) to promote oxidation of sulphide by H2O via the reaction S2− + 4H2O = SO42− + 4H2. Sulphite could not be detected in any of the XANES spectra implying that this species, if it exists in the melt, it is a subordinate or transient species only. 相似文献
6.
Yongliang Xiong Haoran Deng Martin Nemer Shelly Johnsen 《Geochimica et cosmochimica acta》2010,74(16):4605-4611
In this study, the solubility constant of magnesium chloride hydroxide hydrate, Mg3Cl(OH)5·4H2O, termed as phase 5, is determined from a series of solubility experiments in MgCl2-NaCl solutions. The solubility constant in logarithmic units at 25 °C for the following reaction,
Mg3Cl(OH)5·4H2O+5H+=3Mg2++9H2O(l)+Cl- 相似文献
7.
The ultraviolet spectra of dilute aqueous solutions of antimony (III) have been measured from 25 to 300 °C at the saturated vapour pressure. From these measurements, equilibrium constants were obtained for the following reactions:
H3SbO30 ? H+ + H2SbO3− 相似文献
8.
David Rickard 《Geochimica et cosmochimica acta》2006,70(23):5779-5789
The solubility of FeSm, synthetic nanoparticulate mackinawite, in aqueous solution was measured at 23 °C from pH 3-10 using an in situ precipitation and dissolution procedure and the solution species was investigated voltammetrically. The solubility is described by a pH-dependent reaction and a pH-independent reaction. The pH-dependent dissolution reaction can be described by
FeSm+2H+→Fe2++H2S 相似文献
9.
Charles A. Geiger Edgar Dachs Gilberto Artioli 《Geochimica et cosmochimica acta》2010,74(18):5202-5215
Armenite, ideal formula BaCa2Al6Si9O30·2H2O, and its dehydrated analog BaCa2Al6Si9O30 and epididymite, ideal formula Na2Be2Si6O15·H2O, and its dehydrated analog Na2Be2Si6O15 were studied by low-temperature relaxation calorimetry between 5 and 300 K to determine the heat capacity, Cp, behavior of their confined H2O. Differential thermal analysis and thermogravimetry measurements, FTIR spectroscopy, electron microprobe analysis and powder Rietveld refinements were undertaken to characterize the phases and the local environment around the H2O molecule.The determined structural formula for armenite is Ba0.88(0.01)Ca1.99(0.02)Na0.04(0.01)Al5.89(0.03)Si9.12(0.02)O30·2H2O and for epididymite Na1.88(0.03)K0.05(0.004)Na0.01(0.004)Be2.02(0.008)Si6.00(0.01)O15·H2O. The infrared (IR) spectra give information on the nature of the H2O molecules in the natural phases via their H2O stretching and bending vibrations, which in the case of epididymite only could be assigned. The powder X-ray diffraction data show that armenite and its dehydrated analog have similar structures, whereas in the case of epididymite there are structural differences between the natural and dehydrated phases. This is also reflected in the lattice IR mode behavior, as observed for the natural phases and the H2O-free phases. The standard entropy at 298 K for armenite is S° = 795.7 ± 6.2 J/mol K and its dehydrated analog is S° = 737.0 ± 6.2 J/mol K. For epididymite S° = 425.7 ± 4.1 J/mol K was obtained and its dehydrated analog has S° = 372.5 ± 5.0 J/mol K. The heat capacity and entropy of dehydration at 298 K are Δ = 3.4 J/mol K and ΔSrxn = 319.1 J/mol K and Δ = −14.3 J/mol K and ΔSrxn = 135.7 J/mol K for armenite and epididymite, respectively. The H2O molecules in both phases appear to be ordered. They are held in place via an ion-dipole interaction between the H2O molecule and a Ca cation in the case of armenite and a Na cation in epididymite and through hydrogen-bonding between the H2O molecule and oxygen atoms of the respective silicate frameworks. Of the three different H2O phases ice, liquid water and steam, the Cp behavior of confined H2O in both armenite and epididymite is most similar to that of ice, but there are differences between the two silicates and from the Cp behavior of ice. Hydrogen-bonding behavior and its relation to the entropy of confined H2O at 298 K is analyzed for various microporous silicates.The entropy of confined H2O at 298 K in various silicates increases approximately linearly with increasing average wavenumber of the OH-stretching vibrations. The interpretation is that decreased hydrogen-bonding strength between a H2O molecule and the silicate framework, as well as weak ion-dipole interactions, results in increased entropy of H2O. This results in increased amplitudes of external H2O vibrations, especially translations of the molecule, and they contribute strongly to the entropy of confined H2O at T < 298 K. 相似文献
10.
A model is developed for the calculation of coupled phase and aqueous species equilibrium in the H2O-CO2-NaCl-CaCO3 system from 0 to 250 °C, 1 to 1000 bar with NaCl concentrations up to saturation of halite. The vapor-liquid-solid (calcite, halite) equilibrium together with the chemical equilibrium of H+, Na+, Ca2+, , Ca(OH)+, OH−, Cl−, , , CO2(aq) and CaCO3(aq) in the aqueous liquid phase as a function of temperature, pressure, NaCl concentrations, CO2(aq) concentrations can be calculated, with accuracy close to those of experiments in the stated T-P-m range, hence calcite solubility, CO2 gas solubility, alkalinity and pH values can be accurately calculated. The merit and advantage of this model is its predictability, the model was generally not constructed by fitting experimental data.One of the focuses of this study is to predict calcite solubility, with accuracy consistent with the works in previous experimental studies. The resulted model reproduces the following: (1) as temperature increases, the calcite solubility decreases. For example, when temperature increases from 273 to 373 K, calcite solubility decreases by about 50%; (2) with the increase of pressure, calcite solubility increases. For example, at 373 K changing pressure from 10 to 500 bar may increase calcite solubility by as much as 30%; (3) dissolved CO2 can increase calcite solubility substantially; (4) increasing concentration of NaCl up to 2 m will increase calcite solubility, but further increasing NaCl solubility beyond 2 m will decrease its solubility.The functionality of pH value, alkalinity, CO2 gas solubility, and the concentrations of many aqueous species with temperature, pressure and NaCl(aq) concentrations can be found from the application of this model. Online calculation is made available on www.geochem-model.org/models/h2o_co2_nacl_caco3/calc.php. 相似文献
11.
The solubility of crystalline Mg(OH)2(cr) was determined by measuring the equilibrium H+ concentration in water, 0.01-2.7 m MgCl2, 0.1-5.6 m NaCl, and in mixtures of 0.5 and 5.0 m NaCl containing 0.01-0.05 m MgCl2. In MgCl2 solutions above 2 molal, magnesium hydroxide converted into hydrated magnesium oxychloride. The solid-liquid equilibrium of Mg2(OH)3Cl·4H2O(cr) was studied in 2.1-5.2 m MgCl2. Using known ion interaction Pitzer coefficients for the system Mg-Na-H-OH-Cl-H2O (25°C), the following equilibrium constants at I = 0 are calculated:
12.
Göril Möschner Barbara Lothenbach Andrea Ulrich Ruben Kretzschmar 《Geochimica et cosmochimica acta》2008,72(1):1-18
The solubility of Fe-ettringite (Ca6[Fe(OH)6]2(SO4)3 · 26H2O) was measured in a series of precipitation and dissolution experiments at 20 °C and at pH-values between 11.0 and 14.0 using synthesised material. A time-series study showed that equilibrium was reached within 180 days of ageing. After equilibrating, the solid phases were analysed by XRD and TGA while the aqueous solutions were analysed by ICP-OES (calcium, sulphur) and ICP-MS (iron). Fe-ettringite was found to be stable up to pH 13.0. At higher pH-values Fe-monosulphate (Ca4[Fe(OH)6]2(SO4) · 6H2O) and Fe-monocarbonate (Ca4[Fe(OH)6]2(CO3) · 6H2O) are formed. The solubilities of these hydrates at 25 °C are: 相似文献
13.
K.U. Rempel A.E. Williams-Jones A.A. Migdisov 《Geochimica et cosmochimica acta》2008,72(13):3074-3083
The solubility and speciation of the assemblage MoO2-MoO3 in water vapour were investigated in experiments conducted at 350 °C, Ptotal from 59 to 160 bar and fHCl from 0 to 3.4 bar (0-2.0 mol%). Measured solubility at these conditions ranges from 22 to 2500 ppm (∑fMo from 4.4 × 10−4 to 6.5 × 10−2 bar). The concentration of Mo in the vapour at fHCl below 0.1 bar is similar to that in pure water vapour, but increases by two orders of magnitude at fHCl above 0.1 bar. The fugacity of gaseous Mo species is independent of chloride concentration at fHCl below 0.1 bar, but increases with increasing fHCl above this pressure. The dominant Mo species at fHCl below 0.1 bar is interpreted to be the same as it is in pure water vapour, and to form as a result of the reaction
(A1) 相似文献
14.
This work reports the application of thermodynamic models, including equations of state, to binary (salt-free) CH4-H2O fluid inclusions. A general method is presented to calculate the compositions of CH4-H2O inclusions using the phase volume fractions and dissolution temperatures of CH4 hydrate. To calculate the homogenization pressures and isolines of the CH4-H2O inclusions, an improved activity-fugacity model is developed to predict the vapor-liquid phase equilibrium. The phase equilibrium model can predict methane solubility in the liquid phase and water content in the vapor phase from 273 to 623 K and from 1 to 1000 bar (up to 2000 bar for the liquid phase), within or close to experimental uncertainties. Compared to reliable experimental phase equilibrium data, the average deviation of the water content in the vapor phase and methane solubility in the liquid phase is 4.29% and 3.63%, respectively. In the near-critical region, the predicted composition deviations increase to over 10%. The vapor-liquid phase equilibrium model together with the updated volumetric model of homogenous (single-phase) CH4-H2O fluid mixtures (Mao S., Duan Z., Hu J. and Zhang D. (2010) A model for single-phase PVTx properties of CO2-CH4-C2H6-N2-H2O-NaCl fluid mixtures from 273 to 1273 K and from 1 to 5000 bar. Chem. Geol.275, 148-160), is applied to calculate the isolines, homogenization pressures, homogenization volumes, and isochores at specified homogenization temperatures and compositions. Online calculation is on the website: http://www.geochem-model.org/. 相似文献
15.
James D. Prikryl 《Geochimica et cosmochimica acta》2008,72(18):4508-4520
The dissolution and growth of uranophane [Ca(UO2)2(SiO3OH)2·5H2O] have been examined in Ca- and Si-rich test solutions at low temperatures (20.5 ± 2.0 °C) and near-neutral pH (∼6.0). Uranium-bearing experimental solutions undersaturated and supersaturated with uranophane were prepared in matrices of ∼10−2 M CaCl2 and ∼10−3 M SiO2(aq). The experimental solutions were reacted with synthetic uranophane and analyzed periodically over 10 weeks. Interpretation of the aqueous solution data permitted extraction of a solubility constant for the uranophane dissolution reaction and standard state Gibbs free energy of formation for uranophane ( kJ mol−1). 相似文献
16.
The speciation of cobalt (II) in Cl− and H2S-bearing solutions was investigated spectrophotometrically at temperatures of 200, 250, and 300 °C and a pressure of 100 bars, and by measuring the solubility of cobaltpentlandite at temperatures of 120-300 °C and variable pressures of H2S. From the results of these experiments, it is evident that CoHS+ and predominate in the solutions except at 150 °C, for which the dominant chloride complex is CoCl3−. The logarithms of the stability constant for CoHS+ show moderate variation with temperature, decreasing from 6.24 at 120 °C to 5.84 at 200 °C, and increasing to 6.52 at 300 °C. Formation constants for chloride species increase smoothly with temperature and at 300°C their logarithms reach 8.33 for , 6.44 for CoCl3−, 4.94 to 5.36 for , and 2.42 for CoCl+. Calculations based on the composition of a model hydrothermal fluid (Ksp-Mu-Qz, KCl = 0.25 m, NaCl = 0.75 m, ΣS = 0.3 m) suggest that at temperatures ?200 °C, cobalt occurs dominantly as CoHS+, whereas at higher temperatures the dominant species is . 相似文献
17.
The solubility of KFe(CrO4)2·2H2O, a precipitate recently identified in a Cr(VI)-contaminated soil, was studied in dissolution and precipitation experiments. Ten dissolution experiments were conducted at 4–75°C and initial pH values between 0.8 and 1.2 using synthetic KFe(CrO4)2·2H2O. Four precipitation experiments were conducted at 25°C with final pH values between 0.16 and 1.39. The log KSP for the reaction
相似文献
18.
Robert C. Newton 《Geochimica et cosmochimica acta》2006,70(22):5571-5582
Solubilities of corundum (Al2O3) and wollastonite (CaSiO3) were measured in H2O-NaCl solutions at 800 °C and 10 kbar and NaCl concentrations up to halite saturation by weight-loss methods. Additional data on quartz solubility at a single NaCl concentration were obtained as a supplement to previous work. Single crystals of synthetic corundum, natural wollastonite or natural quartz were equilibrated with H2O and NaCl at pressure (P) and temperature (T) in a piston-cylinder apparatus with NaCl pressure medium and graphite heater sleeves. The three minerals show fundamentally different dissolution behavior. Corundum solubility undergoes large enhancement with NaCl concentration, rising rapidly from Al2O3 molality (mAl2O3) of 0.0013(1) (1σ error) in pure H2O and then leveling off to a maximum of ∼0.015 at halite saturation (XNaCl ≈ 0.58, where X is mole fraction). Solubility enhancement relative to that in pure H2O, , passes through a maximum at XNaCl ≈ 0.15 and then declines towards halite saturation. Quenched fluids have neutral pH at 25 °C. Wollastonite has low solubility in pure H2O at this P and T(mCaSiO3=0.0167(6)). It undergoes great enhancement, with a maximum solubility relative to that in H2O at XNaCl ≈ 0.33, and solubility >0.5 molal at halite saturation. Solute silica is 2.5 times higher than at quartz saturation in the system H2O-NaCl-SiO2, and quenched fluids are very basic (pH 11). Quartz shows monotonically decreasing solubility from mSiO2=1.248 in pure H2O to 0.202 at halite saturation. Quenched fluids are pH neutral. A simple ideal-mixing model for quartz-saturated solutions that requires as input only the solubility and speciation of silica in pure H2O reproduces the data and indicates that hydrogen bonding of molecular H2O to dissolved silica species is thermodynamically negligible. The maxima in for corundum and wollastonite indicate that the solute products include hydrates and Na+ and/or Cl− species produced by molar ratios of reactant H2O to NaCl of 6:1 and 2:1, respectively. Our results imply that quite simple mechanisms may exist in the dissolution of common rock-forming minerals in saline fluids at high P and T and allow assessment of the interaction of simple, congruently soluble rock-forming minerals with brines associated with deep-crustal metamorphism. 相似文献
19.
Bjorn O. Mysen 《Geochimica et cosmochimica acta》2007,71(7):1820-1834
Solubility and solution mechanisms of H2O in depolymerized melts in the system Na2O-Al2O3-SiO2 were deduced from spectroscopic data of glasses quenched from melts at 1100 °C at 0.8-2.0 GPa. Data were obtained along a join with fixed nominal NBO/T = 0.5 of the anhydrous materials [Na2Si4O9-Na2(NaAl)4O9] with Al/(Al+Si) = 0.00-0.25. The H2O solubility was fitted to the expression, XH2O=0.20+0.0020fH2O-0.7XAl+0.9(XAl)2, where XH2O is the mole fraction of H2O (calculated with O = 1), fH2O the fugacity of H2O, and XAl = Al/(Al+Si). Partial molar volume of H2O in the melts, , calculated from the H2O-solulbility data assuming ideal mixing of melt-H2O solutions, is 12.5 cm3/mol for Al-free melts and decreases linearly to 8.9 cm3/mol for melts with Al/(Al+Si) ∼ 0.25. However, if recent suggestion that is composition-independent is applied to constrain activity-composition relations of the hydrous melts, the activity coefficient of H2O, , increases with Al/(Al+Si).Solution mechanisms of H2O were obtained by combining Raman and 29Si NMR spectroscopic data. Degree of melt depolymerization, NBO/T, increases with H2O content. The rate of NBO/T-change with H2O is negatively correlated with H2O and positively correlated with Al/(Al+Si). The main depolymerization reaction involves breakage of oxygen bridges in Q4-species to form Q2 species. Steric hindrance appears to restrict bonding of H+ with nonbridging oxygen in Q3 species. The presence of Al3+ does not affect the water solution mechanisms significantly. 相似文献
20.
Jun Li 《Geochimica et cosmochimica acta》2011,75(15):4351-4376
A thermodynamic model is developed for the calculation of both phase and speciation equilibrium in the H2O-CO2-NaCl-CaCO3-CaSO4 system from 0 to 250 °C, and from 1 to 1000 bar with NaCl concentrations up to the saturation of halite. The vapor-liquid-solid (calcite, gypsum, anhydrite and halite) equilibrium together with the chemical equilibrium of H+,Na+,Ca2+, , , and CaSO4(aq) in the aqueous liquid phase as a function of temperature, pressure and salt concentrations can be calculated with accuracy close to the experimental results.Based on this model validated from experimental data, it can be seen that temperature, pressure and salinity all have significant effects on pH, alkalinity and speciations of aqueous solutions and on the solubility of calcite, halite, anhydrite and gypsum. The solubility of anhydrite and gypsum will decrease as temperature increases (e.g. the solubility will decrease by 90% from 360 K to 460 K). The increase of pressure may increase the solubility of sulphate minerals (e.g. gypsum solubility increases by about 20-40% from vapor pressure to 600 bar). Addition of NaCl to the solution may increase mineral solubility up to about 3 molality of NaCl, adding more NaCl beyond that may slightly decrease its solubility. Dissolved CO2 in solution may decrease the solubility of minerals. The influence of dissolved calcite on the solubility of gypsum and anhydrite can be ignored, but dissolved gypsum or anhydrite has a big influence on the calcite solubility. Online calculation is made available on www.geochem-model.org/model. 相似文献