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1.
The solubility of molybdenum (Mo) was determined at temperatures from 500 °C to 800 °C and 150 to 300 MPa in KCl-H2O and pure H2O solutions in cold-seal experiments. The solutions were trapped as synthetic fluid inclusions in quartz at experimental conditions, and analyzed by laser ablation inductively coupled plasma mass spectrometry (LA ICPMS).Mo solubilities of 1.6 wt% in the case of KCl-bearing aqueous solutions and up to 0.8 wt% in pure H2O were found. Mo solubility is temperature dependent, but not pressure dependent over the investigated range, and correlates positively with salinity (KCl concentration). Molar ratios of ∼1 for Mo/Cl and Mo/K are derived based on our data. In combination with results of synchrotron X-ray absorption spectroscopy of individual fluid inclusions, it is suggested that Mo-oxo-chloride complexes are present at high salinity (>20 wt% KCl) and ion pairs at moderate to low salinity (<11 wt% KCl) in KCl-H2O aqueous solutions. Similarly, in the pure H2O experiments molybdic acid is the dominant species in aqueous solution. The results of these hydrothermal Mo experiments fit with earlier studies conducted at lower temperatures and indicate that high Mo concentrations can be transported in aqueous solutions. Therefore, the Mo concentration in aqueous fluids seems not to be the limiting factor for ore formation, whereas precipitation processes and the availability of sulfur appear to be the main controlling factors in the formation of molybdenite (MoS2). 相似文献
2.
Heat capacities of aqueous solutions of sodium hydroxide and water ionization up to 300 °C at 10 MPa
Simon Schrödle 《Geochimica et cosmochimica acta》2008,72(13):3124-3138
A commercial (Setaram C80) calorimeter has been modified to measure the heat capacities of highly caustic solutions at temperatures up to 300 °C and pressures up to 20 MPa. The improvements have allowed more accurate determination of the isobaric volumetric heat capacities of chemically aggressive liquids at high temperatures. Test measurements with aqueous solutions of sodium chloride showed a reproducibility of about ±0.1%, with an accuracy of ∼0.3% or better, over the whole temperature range. Heat capacities of aqueous solutions of sodium hydroxide at concentrations from 0.5 to 8 mol/kg were measured at temperatures from 50 to 300 °C and a pressure of 10 MPa. Apparent molar isobaric heat capacities of NaOH(aq) were calculated using densities determined previously for the same solutions by vibrating-tube densimetry. Standard state (infinite dilution) partial molar isobaric heat capacities of NaOH(aq) were obtained by extrapolation using an extended Redlich-Meyer equation. Values of the standard heat capacity change for the ionization of water up to 300 °C were derived by combining the present results with the literature data for HCl(aq) and NaCl(aq). 相似文献
3.
The behavior of ammonium, NH4+, in aqueous systems was studied based on Raman spectroscopic experiments to 600 °C and about 1.3 GPa. Spectra obtained at ambient conditions revealed a strong reduction of the dynamic three-dimensional network of water with addition of ammonium chloride, particularly at small solute concentrations. The differential scattering cross section of the ν1-NH4+ Raman band in these solutions was found to be similar to that of salammoniac.The Raman band of silica monomers at ∼780 cm−1 was present in all spectra of the fluid at high temperatures in hydrothermal diamond-anvil cell experiments with H2O ± NH4Cl and quartz or the assemblage quartz + kyanite + K-feldspar ± muscovite/tobelite. However, these spectra indicated that dissolved silica is less polymerized in ammonium chloride solutions than in comparable experiments with water. Quantification based on the normalized integrated intensity of the H4SiO40 band showed that the silica solubility in experiments with H2O + NH4Cl was significantly lower than that in equimolal NaCl solutions. This suggests that ammonium causes a stronger decrease in the activity of water in chloridic solutions than sodium.The Raman spectra of the fluid also showed that a significant fraction of ammonium was converted to ammonia, NH3, in all experiments at temperatures above 300 °C. This indicates a shift towards acidic conditions for experiments without a buffering mineral assemblage. The estimated pH of the fluid was ∼2 at 600 °C, 0.26 GPa, 6.6 m initial NH4Cl, based on the ratio of the integrated ν1-NH3 and ν1-NH4+ intensities and the HCl0 dissociation constant. The NH3/NH4+ ratio increased with temperature and decreased with pressure. This implies that more ammonium should be retained in K-bearing minerals coexisting with chloridic fluids upon high-P low-T metamorphism. At 500 °C, 0.73 GPa, ammonium partitions preferentially into the fluid, as constrained from infrared spectroscopy on the muscovite and from mass balance.The conversion of K-feldspar to muscovite proceeded much faster in experiments with NH4Cl solutions than in comparable experiments with water. This is interpreted as being caused by enhancement of the rate-limiting alumina solubility, suggesting complexation of Al with NH4. Nucleation and growth of mica at the expense of K-feldspar and NH4+/K+ exchange between fluid and K-feldspar occurred simultaneously, but incorporation of NH4+ into K-feldspar was distinctly faster than K-feldspar consumption. 相似文献
4.
Porphyry-type ore deposits sometimes contain fluid inclusion compositions consistent with the partitioning of copper and gold into vapor relative to coexisting brine at the depositional stage. However, this has not been reproduced experimentally at magmatic conditions. In an attempt to determine the conditions under which copper and gold may partition preferentially into vapor relative to brine at temperatures above the solidus of granitic magmas, we performed experiments at 800 °C, 100 MPa, oxygen fugacity () buffered by Ni-NiO, and fixed at either 3.5 × 10−2 by using intermediate solid solution-pyrrhotite, or 1.2 × 10−4 by using intermediate solid solution-pyrrhotite-bornite. The coexisting vapor (∼3 wt.% NaCl eq.) and brine (∼68 wt.% NaCl eq.) were composed initially of NaCl + KCl + HCl + H2O, with starting HCl set to <1000 μg/g in the aqueous mixture. Synthetic vapor and brine fluid inclusions were trapped at run conditions and subsequently analyzed by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Our experiments demonstrate that copper and gold partitioned strongly into the magmatic volatile phase(s) (MVP) (i.e., vapor or brine) relative to a silicate melt over the entire imposed range of . Nernst style partition coefficients between coexisting brine (b) and melt (m), Db/m (±1σ), range from 3.6(±2.2) × 101 to 4(±2) × 102 for copper and from 1.2(±0.6) × 102 to 2.4(±2.4) × 103 for gold. Partition coefficients between coexisting vapor (v) and melt, Dv/m range from 2.1 ± 0.7 to 18 ± 5 and 7(±3) × 101 to 1.6(±1.6) × 102 for copper and gold, respectively. Partition coefficients for all experiments between coexisting brine and vapor, Db/v (±1σ), range from 7(±2) to 1.0(±0.4) × 102 and 1.7(±0.2) to 15(±2) for copper and gold, respectively. Observed average Db/v at an of 1.2 × 10−4 were elevated, 95(±5) and 15 ± 1 for copper and gold, respectively, relative to those at the higher of 3.5 × 10−2 where Db/v were 10(±5) for copper and 7(±6) for gold. Thus, there is an inverse relationship between the and the Db/v for both copper and gold with increasing resulting in a decrease in the Db/v signifying increased importance of the vapor phase for copper and gold transport. This suggests that copper and gold may complex with volatile S-species as well as Cl-species at magmatic conditions, however, none of the experiments of our study at 800 °C and 100 MPa had a Db/v ? 1. We did not directly determine speciation, but infer the existence of some metal-sulfur complexes based on the reported data. We suggest that copper and gold partition preferentially into the brine in most instances at or above the wet solidus. However, in most systems, the mass of vapor is greater than the mass of brine, and vapor transport of copper and gold may become more important in the magmatic environment at higher , lower , or near the critical point in a salt-water system. A Db/v ? 1 at subsolidus hydrothermal conditions may also occur in response to changes in temperature, , , and/or acidity.Additionally, both copper and gold were observed to partition into intermediate solid solution and bornite much more strongly than into vapor, brine or silicate melt. This suggests that, although vapor and brine are both efficient at removing copper and gold from a silicate melt, the presence of Cu-Fe sulfides can sequester a substantial portion of the copper and gold contained within a silicate melt if the Cu-Fe sulfides are abundant. 相似文献
5.
The solubilities of the assemblages albite + paragonite + quartz and jadeite + paragonite + quartz in H2O were determined at 500 and 600 °C, 1.0-2.25 GPa, using hydrothermal piston-cylinder methods. The three minerals are isobarically and isothermally invariant in the presence of H2O, so fluid composition is uniquely determined at each pressure and temperature. A phase-bracketing approach was used to achieve accurate solubility determinations. Albite + quartz and jadeite + quartz dissolve incongruently in H2O, yielding residual paragonite which could not be retrieved and weighed. Solution composition fixed by the three-mineral assemblage at a given pressure and temperature was therefore bracketed by adding NaSi3O6.5 glass in successive experiments, until no paragonite was observed in run products. Solubilities derived from experiments bounding the appearance of paragonite thus constrain the equilibrium fluid composition. Results indicate that, at a given pressure, Na, Al, and Si concentrations are higher at 600 °C than at 500 °C. At both 500 and 600 °C, solubilities of all three elements increase with pressure in the albite stability field, to a maximum at the jadeite-albite-quartz equilibrium. In the jadeite stability field, element concentrations decline with continued pressure increase. At the solubility maximum, Na, Al, and Si concentrations are, respectively, 0.16, 0.05, and 0.48 molal at 500 °C, and 0.45, 0.27, and 1.56 molal at 600 °C. Bulk solubilities are 3.3 and 10.3 wt% oxides, respectively. Observed element concentrations are everywhere greater than those predicted from extrapolated thermodynamic data for simple ions, monomers, ion pairs, and the silica dimer. The measurements therefore require the presence of additional, polymerized Na-Al-Si-bearing species in the solutions. The excess solubility is >50% at all conditions, indicating that polymeric structures are the predominant solutes in the P-T region studied. The solubility patterns likely arise from combination of the large solid volume change associated with the albite-jadeite-quartz equilibrium and the rise in Na-Al-Si polymerization with approach to the hydrothermal melting curves of albite + quartz and jadeite + quartz. Our results indicate that polymerization of Na-Al-Si solutes is a fundamental aspect of fluid-rock interaction at high pressure. In addition, the data suggest that high-pressure metamorphic isograds can impose unexpected controls on metasomatic mass transfer, that significant metasomatic mass transfer prior to melting should be considered in migmatitic terranes, and that polymeric complexes may be an important transport agent in subduction zones. 相似文献
6.
Anne Verlaguet Fabrice Brunet William M. Murphy 《Geochimica et cosmochimica acta》2006,70(7):1772-1788
In order to quantify Al transfer in response to fluid-mineral equilibration under evolving metamorphic conditions, isobaric (0.7 GPa) experiments were conducted in the 350-550 °C range. Disequilibrium was induced (1) by holding initially pure water and natural minerals (kyanite + quartz ± muscovite enclosed in a perforated inner capsule) under isothermal conditions and (2) by stepwise temperature variations. In all experiments, secondary Al-bearing phases crystallized in the external tube of a “tube-in-tube” setup (SEM characterization); they are interpreted as witnesses of the evolution of the fluid composition (fluid reaction path). These reaction paths and the subsequent amount of secondary crystallizations were modeled using thermodynamic data from SUPCRT92 and estimates of both starting-mineral dissolution rates and elemental diffusion coefficients from the literature. A major result is that the amount of aluminum transferred to secondary phases is a thousand times larger than the calculated Al concentration in the fluid. Although the crystallization of Al-bearing phases was expected as a response to a temperature decrease, the stepwise temperature increase (20 °C/day) also led to aluminum transfer towards secondary phases. In the course of re-equilibration, the fluid first becomes saturated with respect to aluminosilicates and then reaches silica saturation, due to the low solubility of Al-minerals. Consequently, aluminosilicates partly recrystallize in response to a temperature increase. Crystallization of secondary Al-phases in the external tube implies that aqueous aluminum was efficiently transported from the inner capsule, even in the pure Al2O3-SiO2-H2O system. Therefore, mass balance calculations considering a constant Al reference frame, i.e., postulating Al immobility, should be regarded with caution. 相似文献
7.
Gujie Qian Joël Brugger William M. Skinner Allan Pring 《Geochimica et cosmochimica acta》2010,74(19):5610-5443
We present the results of an experimental study into the sulfidation of magnetite to form pyrite/marcasite under hydrothermal conditions (90-300 °C, vapor saturated pressures), a process associated with gold deposition in a number of ore deposits. The formation of pyrite/marcasite was studied as a function of reaction time, temperature, pH, sulfide concentration, solid-weight-to-fluid-volume ratio, and geometric surface area of magnetite in polytetrafluoroethylene-lined autoclaves (PTFE) and a titanium and stainless steel flow-through cell. Marcasite was formed only at pH21°C <4 and was the dominant Fe disulfide at pH21°C 1.11, while pyrite predominated at pH21°C >2 and formed even under basic conditions (up to pH21°C 12-13). Marcasite formation was favored at higher temperatures. Fine-grained pyrrhotite formed in the initial stage of the reaction together with pyrite in some experiments with large surface area of magnetite (grain size <125 μm). This pyrrhotite eventually gave way to pyrite. The transformation rate of magnetite to Fe disulfide increased with decreasing pH (at 120 °C; pH120°C 0.96-4.42), and that rate of the transformation increased from 120 to 190 °C.Scanning electron microscope (SEM) imaging revealed that micro-pores (0.1-5 μm scale) existed at the reaction front between the parent magnetite and the product pyrite, and that the pyrite and/or marcasite were euhedral at pH21°C <4 and anhedral at higher pH. The newly formed pyrite was micro-porous (0.1-5 μm); this micro-porosity facilitates fluid transport to the reaction interface between magnetite and pyrite, thus promoting the replacement reaction. The pyrite precipitated onto the parent magnetite was polycrystalline and did not preserve the crystallographic orientation of the magnetite. The pyrite precipitation was also observed on the PTFE liner, which is consistent with pyrite crystallizing from solution. The mechanism of the reaction is that of a dissolution-reprecipitation reaction with the precipitation of pyrite being the rate-limiting step relative to magnetite dissolution under mildly acidic conditions (e.g., pH155°C 4.42).The experimental results are in good agreement with sulfide phase assemblage and textures reported from sulfidized Banded Iron Formations: pyrite, marcasite and pyrrhotite have been found to exist or co-exist in different sulfidized Banded Iron Formations, and the microtextures show no evidence of sub-μm-scale pseudomorphism of magnetite by pyrite. 相似文献
8.
Realistic simulations of fluid flow in geologic systems have severely been hampered by the lack of a consistent formulation for fluid properties for binary salt-water fluids over the temperature-pressure-composition ranges encountered in the Earth’s crust. As the first of two companion studies, a set of correlations describing the phase stability relations in the system H2O-NaCl is developed. Pure water is described by the IAPS-84 equation of state. New correlations comprise the vapor pressure of halite and molten NaCl, the NaCl melting curve, the composition of halite-saturated liquid and vapor, the pressure of vapor + liquid + halite coexistence, the temperature-pressure and temperature-composition relations for the critical curve, and the compositions of liquid and vapor on the vapor + liquid coexistence surface. The correlations yield accurate values for temperatures from 0 to 1000 °C, pressures from 0 to 5000 bar, and compositions from 0 to 1 XNaCl (mole fraction of NaCl). To facilitate their use in fluid flow simulations, the correlations are entirely formulated as functions of temperature, pressure and composition. 相似文献
9.
This UV spectrophotometric study was aimed at providing precise, experimentally derived thermodynamic data for the ionisation of molybdic acid (H2MoO4) from 30 to 300 °C and at equilibrium saturated vapour pressures. The determination of the equilibrium constants and associated thermodynamic parameters were facilitated by spectrophotometric measurements using a specially designed high temperature optical Ti-Pd flow-through cell with silica glass windows.The following van’t Hoff isochore equations describe the temperature dependence of the first and second ionisation constants of molybdic acid up to 300 °C:
10.
The dissolution rate of illite, a common clay mineral in Australian soils, was studied in saline-acidic solutions under far from equilibrium conditions. The clay fraction of Na-saturated Silver Hill illite (K1.38Na0.05)(Al2.87Mg0.46Fe3+0.39Fe2+0.28Ti0.07)[Si7.02Al0.98]O20(OH)4 was used for this study. The dissolution rates were measured using flow-through reactors at 25 ± 1 °C, solution pH range of 1.0-4.25 (H2SO4) and at two ionic strengths (0.01 and 0.25 M) maintained using NaCl solution. Illite dissolution rates were calculated from the steady state release rates of Al and Si. The dissolution stoichiometry was determined from Al/Si, K/Si, Mg/Si and Fe/Si ratios. The release rates of cations were highly incongruent during the initial stage of experiments, with a preferential release of Al and K over Si in majority of the experiments. An Al/Si ratio >1 was observed at pH 2 and 3 while a ratio close to the stoichiometric composition was observed at pH 1 and 4 at the higher ionic strength. A relatively higher K+ release rate was observed at I = 0.25 in 2-4 pH range than at I = 0.01, possibly due to ion exchange reaction between Na+ from the solution and K+ from interlayer sites of illite. The steady state release rates of K, Fe and Mg were higher than Si over the entire pH range investigated in the study. From the point of view of the dominant structural cations (Si and Al), stoichiometric dissolution of illite occurred at pH 1-4 in the higher ionic strength experiments and at pH ?3 for the lower ionic strength experiments. The experiment at pH 4.25 and at the lower ionic strength exhibited lower RAl (dissolution rate calculated from steady state Al release) than RSi (dissolution rate calculated from steady state Si release), possibly due to the adsorption of dissolved Al as the output solutions were undersaturated with respect to gibbsite. The dissolution of illite appears to proceed with the removal of interlayer K followed by the dissolution of octahedral cations (Fe, Mg and Al), the dissolution of Si is the limiting step in the illite dissolution process. A dissolution rate law showing the dependence of illite dissolution rate on proton concentration in the acid-sulfate solutions was derived from the steady state dissolution rates and can be used in predicting the impact of illite dissolution in saline acid-sulfate environments. The fractional reaction orders of 0.32 (I = 0.25) and 0.36 (I = 0.01) obtained in the study for illite dissolution are similar to the values reported for smectite. The dissolution rate of illite is mainly controlled by solution pH and no effect of ionic strength was observed on the dissolution rates. 相似文献
11.
A modified commercial (Setaram C80) calorimeter has been used to measure the isobaric volumetric heat capacities of concentrated alkaline sodium aluminate solutions at ionic strengths from 1 to 6 mol kg−1, with up to 40 mol.% substitution of hydroxide by aluminate, at temperatures from 50 to 300 °C and a pressure of 10 MPa. Apparent molar heat capacities for the mixtures, Cp?, derived from these data were found to depend linearly on the aluminate substitution level, i.e., they followed Young’s rule. These quantities were used to estimate the apparent molar heat capacities of pure, hypothetical sodium aluminate solutions, Cp? (‘NaAl(OH)4’(aq)). Slopes of the Young’s rule plots were invariant with ionic strength at a given temperature but depended linearly on temperature. The heat capacities of ternary aqueous sodium hydroxide/aluminate mixtures could therefore be modelled using only two parameters in addition to those needed for the correlation of Cp? (NaOH(aq)) reported previously from these laboratories. An assessment of the standard thermodynamic quantities for boehmite, gibbsite and the aluminate ion yielded a set of recommended values that, together with the present heat capacity data, accurately predicts the solubility of gibbsite and boehmite at temperatures up to 300 °C. 相似文献
12.
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
13.
Ammoniojarosite [(NH4,H3O)Fe3(OH)6(SO4)2], a poorly soluble basic ferric sulfate, was produced by microbiological oxidation of ferrous sulfate at pH 2.0-3.0 over a range of concentrations (5.4-805 mM) and temperatures (22-65 °C). Ammoniojarosites were also produced by chemical (abiotic) procedures in parallel thermal (36-95 °C) experiments. At 36 °C, schwertmannite [ideally Fe8O8(OH)6(SO4)] was the only solid product formed at <10 mM concentrations. Between 11.5 and 85.4 mM , a mixed product of ammoniojarosite and schwertmannite precipitated, as identified by X-ray diffraction. In excess of 165 mM , ammoniojarosite was the only solid phase produced. An increase in the incubation temperature using thermoacidophiles at 45 and 65 °C accelerated the formation of ammoniojarosite in culture solutions containing 165 mM . Both the biogenic and chemical ammoniojarosites were yellow (2Y-4Y in Munsell hue), low surface area (<1 m2/g), well crystalline materials with average co and ao unit cell parameters of 17.467 ± 0.048 Å and 7.330 ± 0.006 Å, respectively. Strong positive correlations were observed between unit cell axial ratios (co/ao) and increasing synthesis temperature in both biotic and abiotic systems. All samples were N deficient compared to stoichiometric ammoniojarosite, and both chemical and X-ray data indicated partial replacement of by H3O+ to form solid solutions with 0.14-0.24 mole H3O+ per formula unit. The morphology of the biogenic jarosites included aggregated discs, pseudo-cubic crystals and botryoidal particles, whereas the chemical specimens prepared at 36-95 °C were composed of irregular crystals with angular edges. Morphological information may thus be useful to evaluate environmental parameters and mode of formation. The data may also have application in predicting phase boundary conditions for Fe(III) precipitation in biogeochemical processes and treatment systems involving acid sulfate waters. 相似文献
14.
In order to (1) explain the worldwide association between epithermal gold-copper-molybdenum deposits and arc magmas and (2) test the hypothesis that adakitic magmas would be Au-specialized, we have determined the solubility of Au at 4 kbar and 1000 °C for three intermediate magmas (two adakites and one calc-alkaline composition) from the Philippines. The experiments were performed over a fO2 range corresponding to reducing (∼NNO−1), moderately oxidizing (∼NNO+1.5) and strongly oxidizing (∼NNO+3) conditions as measured by solid Ni-Pd-O sensors. They were carried out in gold containers, the latter serving also as the source of gold, in presence of variable amounts of H2O and, in a few additional experiments, of S. Concentrations of Au in glasses were determined by LA-ICPMS. Gold solubility in melt is very low (30-240 ppb) but increases with fO2 in a way consistent with the dissolution of gold as both Au1+ and Au3+ species. In the S-bearing experiments performed at ∼NNO−1, gold solubility reaches much higher values, from ∼1200 to 4300 ppb, and seems to correlate with melt S content. No systematic difference in gold solubility is observed between the adakitic and the non-adakitic compositions investigated. Oxygen fugacity and the sulfur concentration in melt are the main parameters controlling the incorporation and concentration of gold in magmas. Certain adakitic and non-adakitic magmas have high fO2 and magmatic S concentrations favorable to the incorporation and transport of gold. Therefore, the cause of a particular association between some arc magmas and Au-Cu-Mo deposits needs to be searched in the origin of those specialized magmas by involvement of Au- and S-rich protoliths. The subducted slab, which contains metal-rich massive sulfides, may constitute a potentially favorable protolith for the genesis of magmas specialized with respect to gold. 相似文献
15.
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
16.
B.E. Etschmann W. Liu H. Müller O. Proux J. Brugger 《Geochimica et cosmochimica acta》2010,74(16):4723-2827
Chloride and hydrosulfide are the principal ligands assumed to govern transport of copper in hydrothermal fluids. Existing solubility experiments suggest that Cu(I)-hydrosulfide complexes are dominant compared to chloride complexes at low salinities in alkaline solutions (H2S(aq)/HS− pH buffer), and may be important in transporting Cu in low density magmatic vapors, potentially controlling the liquid-vapor partitioning of Cu. This study provides the first in situ evidence of the solubility of copper sulfides and the nature and structure of the predominant Cu species in sulfur-containing fluids at temperatures up to 592 °C and pressures of 180-600 bar. XANES and EXAFS data show that at elevated T (?200 °C), Cu solubility occurs via a linear Cu complex. At 428 °C in alkaline solutions, Cu is coordinated by two sulfur atoms in a distorted linear coordination (angle ∼150-160°). This geometry is consistent with the species predicted by earlier solubility studies. In addition, in situ measurements of the solubility of chalcocite in 2 m NaHS solutions performed in this study are in remarkably good agreement with the solubilities calculated using available thermodynamic data for Cu(I)-hydrosulfide complexes, also supporting the interpretation of speciation in these studies and validating the extrapolation of low-T thermodynamic properties for to high P-T. Data on phase separation for the 2 m NaHS solution show that while significant amounts of copper can be partitioned into the vapor phase, there is no indication for preferential partitioning of Cu into the vapor. This is consistent with recent partitioning experiments conducted in autoclaves by Pokrovski et al. (2008a) and Simon et al. (2006). XANES data suggest that the species present in the low density phase is very similar to that present in the high density liquid, i.e., , although Cu(HS)(H2S)0 cannot be excluded on the basis of XAS data. 相似文献
17.
The structure of silicate melts in the system Na2O·4SiO2 saturated with reduced C-O-H volatile components and of coexisting silicate-saturated C-O-H solutions has been determined in a hydrothermal diamond anvil cell (HDAC) by using confocal microRaman and FTIR spectroscopy as structural probes. The experiments were conducted in-situ with the melt and fluid at high temperature (up to 800 °C) and pressure (up to 1435 MPa). Redox conditions in the HDAC were controlled with the reaction, Mo + H2O = MoO2 + H2, which is slightly more reducing than the Fe + H2O = FeO + H2 buffer at 800 °C and less.The dominant species in the fluid are CH4 + H2O together with minor amounts of molecular H2 and an undersaturated hydrocarbon species. In coexisting melt, CH3 - groups linked to the silicate melt structure via Si-O-CH3 bonding may dominate and possibly coexists with molecular CH4. The abundance ratio of CH3 - groups in melts relative to CH4 in fluids increases from 0.01 to 0.07 between 500 and 800 °C. Carbon-bearing species in melts were not detected at temperatures and pressures below 400 °C and 730 MPa, respectively. A schematic solution mechanism is, Si-O-Si + CH4?Si-O-CH3+H-O-Si. This mechanism causes depolymerization of silicate melts. Solution of reduced (C-O-H) components will, therefore, affect melt properties in a manner resembling dissolved H2O. 相似文献
18.
The solubility of ZnS(cr) was measured at 100 °C, 150 bars in sulfide solutions as a function of sulfur concentration (m(Stotal) = 0.02-0.15) and acidity (pHt = 2-11). The experiments were conducted using a Ti flow-through hydrothermal reactor enabling the sampling of large volumes of solutions at experimental conditions, with the subsequent concentration and determination of trace quantities of Zn. Prior to the experiments, a long-term in situ conditioning of the solid phase was performed in order to attain the reproducible Zn concentrations (i.e. solubilities). The ZnS(cr) solubility product was monitored in the course of the experiment. The following species were found to account for Zn speciation in solution: Zn2+ (pHt < 3), (pHt 3-4.5), (pHt 5-8), and ZnS(HS)− (pHt > 8) (pHt predominance regions are given for m(Stotal) = 0.1). Solubility data collected in this study at pHt > 3 were combined with the ZnS(cr) solubility product determined at lower pH to yield the following equilibrium constants (t = 100 °C, P = 150 bars):
19.
Carbon dioxide- and salt-bearing solutions are common in granulite, ore-forming and magmatic environments. The presence of CO2 affects mineral solubilities, fluid miscibility, and viscosity and wetting properties, and is expected to affect salt speciation. EXAFS measurements of RbBr-H2O-CO2 fluids contained in corundum-osed synthetic fluid inclusions (SFLINCs) have been used to investigate the effect of CO2 on salt speciation at temperatures to 579 °C and pressures to around 0.26 GPa.Forward modelling indicates that solute dehydration is difficult to distinguish from up to around 40% of Rb-Br ion-pairing, so results refer to the total number of nearest neighbours, which are likely to be mostly O present in waters of hydration, but may also include Br, if ion pairing is present. Additionally, results relate to the number of well-ordered neighbours in the first shell, because nearest neighbours with a high degree of disorder may be present but contribute minimally to the EXAFS signal. Analysis of the EXAFS results at the Rb edge for the CO2-free solution is consistent with previous work and shows that the number of nearest neighbours for Rb in CO2-free solutions decreases from 6 ± 0.6 to 1.4 ± 0.1 as temperature increases from 20 to 534 °C. The decrease is accompanied by a decrease in Rb-x bondlengths of 0.05 Å, where x is the first shell scatterer. Results for the CO2-bearing solution are different to those for the CO2-free solution. The number of nearest neighbours is 16 and 22% less than for the CO2-bearing solution at 312 and 445 °C respectively. Changes in the numbers of nearest neighbours correlate well with calculated changes in the bulk solution dielectric constant; CO2-bearing and CO2-free solutions lie on the same trend, which suggests that it may be possible to calculate the number of nearest neighbours from dielectric constant. Rb-x bondlengths for the CO2-bearing solution are statistically indistinguishable to those for the CO2-free inclusions. Results for Br are worse quality than for Rb so EXAFS analysis could not be completed, however XANES spectra for CO2-free and CO2-bearing solutions are consistent with solute dehydration similar to that recorded by the Rb spectra. The conclusions of this study provide support for the notion that CO2 has a fundamental effect on the mechanics of solubility, and that these effects should be incorporated into conceptual and quantitative thermodynamic models. 相似文献
20.
Thomas Fockenberg Michael Burchard Walter V. Maresch 《Geochimica et cosmochimica acta》2006,70(7):1796-1806
The solubility of natural, near-end-member wollastonite-I (>99.5% CaSiO3) has been determined at temperatures from 400 to 800 °C and pressures between 0.8 and 5 GPa in piston-cylinder apparatus with the weight-loss method. Chemical analysis of quench products and optical monitoring in a hydrothermal diamond anvil cell demonstrates that no additional phases form during dissolution. Wollastonite-I, therefore, dissolves congruently in the pressure-temperature range investigated. The solubility of CaSiO3 varies between 0.175 and 13.485 wt% and increases systematically with both temperature and pressure up to 3.0 GPa. Above 3.0 GPa wollastonite-I reacts rapidly to the high-pressure modification wollastonite-II. No obvious trends are evident in the solubility of wollastonite-II, with values between 1.93 and 10.61 wt%. The systematics of wollastonite-I solubility can be described well by a composite polynomial expression that leads to isothermal linear correlation with the density of water. The molality of dissolved wollastonite-I in pure water is then
log(mwoll)=2.2288-3418.23×T-1+671386.84×T-2+logρH2O×(5.4578+2359.11×T-1). 相似文献