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1.
The stability of yttrium-acetate (Y-Ac) complexes in aqueous solution was determined potentiometrically at temperatures 25-175 °C (at Ps) and pressures 1-1000 bar (at 25 and 75 °C). Measurements were performed using glass H+-selective electrodes in potentiometric cells with a liquid junction. The species YAc2+ and were found to dominate yttrium aqueous speciation in experimental solutions at 25-100 °C (log [Ac−] < −1.5, pH < 5.2), whereas at 125, 150 and 175 °C introduction of into the Y-Ac speciation model was necessary. The overall stability constants βn were determined for the reaction
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2.
Over the last decade, a significant research effort has focused on determining the feasibility of sequestering large amounts of CO2 in deep, permeable geologic formations to reduce carbon dioxide emissions to the atmosphere. Most models indicate that injection of CO2 into deep sedimentary formations will lead to the formation of various carbonate minerals, including the common phases calcite (CaCO3), dolomite (CaMg(CO3)2), magnesite (MgCO3), siderite (FeCO3), as well as the far less common mineral, dawsonite (NaAlCO3(OH)2). Nevertheless, the equilibrium and kinetics that control the precipitation of stable carbonate minerals are poorly understood and few experiments have been performed to validate computer codes that model CO2 sequestration.In order to reduce this uncertainty we measured the solubility of synthetic dawsonite according to the equilibrium: , from under- and oversaturated solutions at 50-200 °C in basic media at 1.0 mol · kg−1 NaCl. The solubility products (Qs) obtained were extrapolated to infinite dilution to obtain the solubility constants (. Combining the fit of these values and fixing  at 25 °C, which was derived from the calorimetric data of Ferrante et al. [Ferrante, M.J., Stuve, J.M., and Richardson, D.W., 1976. Thermodynamic data for synthetic dawsonite. U.S. Bureau of Mines Report Investigation, 8129, Washington, D.C., 13p.], the following thermodynamic parameters for the dissolution of dawsonite were calculated at 25 °C: , and . Subsequently, we were able to derive values for the Gibbs energy of formation (, enthalpy of formation ( and entropy ( of dawsonite. These results are within the combined experimental uncertainties of the values reported by Ferrante et al. (1976). Predominance diagrams are presented for the dawsonite/boehmite and dawsonite/bayerite equilibria at 100 °C in the presence of a saline solution with and without silica-containing minerals.  相似文献   

3.
The terrestrial mantle has a well defined Sb depletion of ∼7 ± 1 (Jochum and Hofmann, 1997), and the lunar mantle is depleted relative to the Earth by a factor of ∼50 ± 5 (Wolf and Anders, 1980). Despite these well defined depletions, there are few data upon which to evaluate their origin—whether due to volatility or core formation. We have carried out a series of experiments to isolate several variables such as oxygen fugacity, temperature, pressure, and silicate and metallic melt compositions, on the magnitude of . The activity of Sb in FeNi metal is strongly composition dependent such that solubility of Sb as a function of fO2 must be corrected for the metal composition. When the correction is applied, Sb solubility is consistent with 3+ valence. Temperature series (at 1.5 GPa) shows that decreases by a factor of 100 over 400 °C, and a pressure series exhibits an additional decrease between ambient pressure (100 MPa) and 13 GPa. A strong dependence upon silicate melt composition is evident from a factor of 100 decrease in between nbo/t values of 0.3 and 1.7. Consideration of all these variables indicates that the small Sb depletion for the Earth’s mantle can be explained by high PT equilibrium partitioning between metal and silicate melt . The relatively large lunar Sb depletion can also be explained by segregation of a small metallic core, at lower pressure conditions where is much higher (2500).  相似文献   

4.
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   

5.
Chloride complexation of Cu+ controls the solubility of copper(I) oxide and sulfide ore minerals in hydrothermal and diagenetic fluids. Solubility measurements and optical spectra of high temperature CuCl solutions have been interpreted as indicating the formation of CuCl, , and complexes. However, no other monovalent cation forms tri- and tetrachloro complexes. EXAFS spectra of high temperature Cu-Cl solutions, moreover, appear to show only CuCl and complexes at T > 100 °C. To reconcile these results, I investigated the nature and stability of Cu-Cl complexes using ab initio cluster calculations and ab initio (Car-Parrinello) molecular dynamics simulations for CuCl-NaCl-H2O systems at 25 to 450 °C. Ab initio molecular dynamic simulations of 1 m CuCl in a 4 m Cl solution give a stable complex at 25 °C over 4 ps but show that the third Cl− is weakly bound. When the temperature is increased along the liquid-vapour saturation curve to 125 °C, the complex dissociates into and Cl−; only forms at 325 °C and 1 kbar. Even in a 15.6 m Cl brine at 450 °C, only the complex forms over a 4 ps simulation run.Cluster calculations with a static dielectric continuum solvation field (COSMO) were used in an attempt directly estimate free energies of complex formation in aqueous solution. Consistent with the MD simulations, the complex is slightly stable at 25 °C but decreases in stability with decreasing dielectric constant (ε). The complex is predicted to be unstable at 25 °C and becomes increasingly unstable with decreasing dielectric constant. In hydrothermal fluids (ε < 30) both the and complexes are unstable to dissociation into and Cl−.The results obtained here are at odds with recent equations of state that predict and complexes are the predominant species in hydrothermal brines. In contrast, I predict that only complexes will be significant at T > 125 °C, even in NaCl-saturated brines. The high-temperature (T > 125 °C) optical spectra of CuCl solutions and solubility measurements of Cu minerals in Cl-brines need to be reinterpreted in terms of only the CuCl and complexes.  相似文献   

6.
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7.
Comparative concentrations of carbonate and hydroxide complexes in natural solutions can be expressed in terms of reactions with bicarbonate that have no explicit pH dependence (). Stability constants for this reaction with n = 1 were determined using conventional formation constant data expressed in terms of hydroxide and carbonate. Available data indicate that stability constants appropriate to seawater at 25 °C expressed in the form are on the order of 104.2 for a wide range of cations (Mz+) with z = +1, +2 and +3. Φ1 is sufficiently large that species appear to substantially dominate MOHz−1 species in seawater. Evaluations of comparative stepwise carbonate and hydroxide stability constant behavior leading to the formation of n = 2 and n = 3 complexes suggest that carbonate complexes generally dominate hydroxide complexes in seawater, even for cations whose inorganic speciation schemes in seawater are currently presumed to be strongly dominated by hydrolyzed forms (). Calculated stability constants, and , indicate that the importance of carbonate complexation is sufficiently large that carbonate and hydroxide complexes would be generally comparable even if calculated Φ2 and Φ3 values are overestimated by two or more orders of magnitude. Inclusion of mixed ligand species in carbonate-hydroxide speciation models allows cation complexation intensities (MT/[Mz+]) to be expressed in the following form:
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8.
The effect of sulfur dissolved as sulfide (S2−) in silicate melts on the activity coefficients of NiO and some other oxides of divalent cations (Ca, Cr, Mn, Fe and Co) has been determined from olivine/melt partitioning experiments at 1400 °C in six melt compositions in the system CaO-MgO-Al2O3-SiO2 (CMAS), and in derivatives of these compositions at 1370 °C, obtained from the six CMAS compositions by substituting Fe for Mg (FeCMAS). Amounts of S2− were varied from zero to sulfide saturation, reaching 4100 μg g−1 S in the most sulfur-rich silicate melt. The sulfide solubilities compare reasonably well with those predicted from the parameterization of the sulfide capacity of silicate melts at 1400 °C of O’Neill and Mavrogenes (2002), although in detail systematic deviations indicate that a more sophisticated model may improve the prediction of sulfide capacities.The results show a barely discernible effect of S2− in the silicate melt on Fe, Co and Ni partition coefficients, and also surprisingly, a tiny but resolvable effect on Ca partitioning, but no detectable effect on Cr, Mn or some other lithophile incompatible elements (Sc, Ti, V, Y, Zr and Hf). Decreasing Mg# of olivine (reflecting increasing FeO in the system) has a significant influence on the partitioning of several of the divalent cations, particularly Ca and Ni. We find a remarkably systematic correlation between and the ionic radius of M2+, where M = Ca, Cr, Mn, Fe, Co or Ni, which is attributable to a simple relationship between size mismatch and excess free energies of mixing in Mg-rich olivine solid solutions.Neither the effect of S2− nor of Mg#ol is large enough by an order of magnitude to account for the reported variations of obtained from electron microprobe analyses of olivine/glass pairs from mid-ocean ridge basalts (MORBs). Comparing these MORB glass analyses with the Ni-MgO systematics of MORB from other studies in the literature, which were obtained using a variety of analytical techniques, shows that these electron microprobe analyses are anomalous. We suggest that the reported variation of with S content in MORB is an analytical artifact.Mass balance of melt and olivine compositions with the starting compositions shows that dissolved S2− depresses the olivine liquidus of haplobasaltic silicate melts by 5.8 × 10−3 (±1.3 × 10−3) K per μg g−1 of S2−, which is negligible in most contexts. We also present data for the partitioning of some incompatible trace elements (Sc, Ti, Y, Zr and Hf) between olivine and melt. The data for Sc and Y confirm previous results showing that and decrease with increasing SiO2 content of the melt. Values of average 0.01 with most falling in the range 0.005-0.015. Zr and Hf are considerably more incompatible than Ti in olivine, with and about 10−3. The ratio / is well constrained at 0.611 ± 0.016.  相似文献   

9.
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   

10.
The electrical conductivities of aqueous solutions of Li2SO4 and K2SO4 have been measured at 523-673 K at 20-29 MPa in dilute solutions for molalities up to 2 × 10−2 mol kg−1. These conductivities have been fitted to the conductance equation of Turq, Blum, Bernard, and Kunz with a consensus mixing rule and mean spherical approximation activity coefficients. In the temperature interval 523-653 K, where the dielectric constant, ε, is greater than 14, the electrical conductance data can be fitted by a solution model which includes ion association to form , , and , where M is Li or K. The adjustable parameters of this model are the first and second dissociation constants of the M2SO4. For the 673 K and 300 kg m−3 state point where the Coulomb interactions are the strongest (dielectric constant, ε = 5), models with more extensive association give good fits to the data. In the case of the Li2SO4 model, including the multi-ion associate, , gave an extremely good fit to the conductance data.  相似文献   

11.
The solubility of carbon in Fe and Fe-5.2 wt.% Ni melts, saturated with graphite, determined by electron microprobe analysis of quenched metal melts was 5.8 ± 0.1 wt.% at 2000 °C, 6.7 ± 0.2 wt.% at 2200 °C, and 7.4 ± 0.2 wt.% at 2410 °C at 2 GPa, conditions relevant for core/mantle differentiation in a shallow magma ocean. These solubilities are slightly lower than low-pressure literature values and significantly beneath calculated values for even higher pressures [e.g., Wood B. J. (1993) Carbon in the core. Earth Planet. Sci. Lett.117, 593-607]. The trend of C solubility versus temperature for Fe-5.2 wt.% Ni melt, within analytical uncertainties, is similar to or slightly lower (∼0.2-0.4 wt.%) than that of pure Fe. Carbon content of core melts and residual mantle silicates derived from equilibrium batch or fractional segregation of core liquids and their comparison with our solubility data and carbon content estimate of the present day mantle, respectively, constrain the partition coefficient of carbon between silicate and metallic melts, in a magma ocean. For the entire range of possible bulk Earth carbon content from chondritic to subchondritic values, of 10−4 to 1 is derived. But for ∼1000 ppm bulk Earth carbon, is between 10−2 and 1. Using the complete range of possible for a magma ocean at ∼2200 °C, we predict maximum carbon content of the Earth’s core to be ∼6-7 wt.% and a preferred value of 0.25 ± 0.15 wt.% for a bulk Earth carbon concentration of ∼1000 ppm.  相似文献   

12.
We have measured apatite solubility in calcic carbonatitic liquids and determined apatite/melt partition coefficients for a series of trace elements, including the rare earth elements (REE), high field strength elements (HFSE), Rb, Sr, U-Th-Pb. Experiments were performed between 4 and 6 GPa, from 1200 to 1380 °C, using the multianvil apparatus. Trace element concentrations were determined by laser ablation ICP-MS and electron microprobe. In addition, a specific protocol was designed to measure carbon concentration in the apatites, using the electron microprobe. Two starting apatite samples were used in order to test for the effect of apatite chemistry on partitioning behavior.Apatite solubility is lower in calcitic melts by a factor 3-5 compared to dolomitic melts (3-5.5 vs. 10-18 wt.% P2O5 in melt). We interpret this difference in terms of solubility product in the liquid and propose an empirical model for apatite saturation that takes into account melt calcium content. We conclude that calcitic melts that may form by melting of carbonated eclogites could be saturated with residual apatite, contrary to dolomitic melts formed in carbonated peridotites.Compatibility behavior of the REE depends on apatite silica content: REE are compatible in apatites containing 3.5-5 wt.% SiO2, with values between 1.5 and 4, whereas REE are incompatible in apatites containing 0.2 wt.% SiO2. HFSE, U, Th, and Y are compatible in silica-rich apatite, with while . Strontium is always retained in the melt, with of the order of 0.5. Lead appears to be incompatible in apatite, although this finding is weakened by almost complete Pb loss to sample container. High silica concentration favors REE incorporation in apatite by allowing for charged balanced coupled substitution. Sulfur and carbonate may also favor REE incorporation in apatite. Our results allow to reconcile previously published experimental determinations of REE partitioning. We use our experimentally determined partition coefficients to investigate the impact of residual apatite during partial melting of recycled carbonated material (eclogite + sediments) and discuss how the chemical characteristics of the produced liquids can be affected by residual apatite.  相似文献   

13.
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):
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14.
The adsorption of phosphate onto calcite was studied in a series of batch experiments. To avoid the precipitation of phosphate-containing minerals the experiments were conducted using a short reaction time (3 h) and low concentrations of phosphate (?50 μM). Sorption of phosphate on calcite was studied in 11 different calcite-equilibrated solutions that varied in pH, PCO2, ionic strength and activity of Ca2+, and . Our results show strong sorption of phosphate onto calcite. The kinetics of phosphate sorption onto calcite are fast; adsorption is complete within 2-3 h while desorption is complete in less than 0.5 h. The reversibility of the sorption process indicates that phosphate is not incorporated into the calcite crystal lattice under our experimental conditions. Precipitation of phosphate-containing phases does not seem to take place in systems with ?50 μM total phosphate, in spite of a high degree of super-saturation with respect to hydroxyapatite (SIHAP ? 7.83). The amount of phosphate adsorbed varied with the solution composition, in particular, adsorption increases as the activity decreases (at constant pH) and as pH increases (at constant activity). The primary effect of ionic strength on phosphate sorption onto calcite is its influence on the activity of the different aqueous phosphate species. The experimental results were modeled satisfactorily using the constant capacitance model with >CaPO4Ca0 and either >CaHPO4Ca+ or > as the adsorbed surface species. Generally the model captures the variation in phosphate adsorption onto calcite as a function of solution composition, though it was necessary to include two types of sorption sites (strong and weak) in the model to reproduce the convex shape of the sorption isotherms.  相似文献   

15.
Ammonium fixed in micas of metamorphic rocks is a sensitive indicator both of organic-inorganic interactions during diagenesis as well as of the devolatilization history and fluid/rock interaction during metamorphism. In this study, a collection of geochemically well-characterized biotite separates from a series of graphite-bearing Paleozoic greenschist- to upper amphibolite-facies metapelites, western Maine, USA, were analyzed for ammonium nitrogen () contents and isotopic composition (δ15NNH4) using the HF-digestion distillation technique followed by the EA-IRMS technique. Biotite separates, sampled from 9 individual metamorphic zones, contain 3000 to 100 ppm with a wide range in δ15N from +1.6‰ to +9.1‰. Average contents in biotite show a distinct decrease from about 2750 ppm for the lowest metamorphic grade (∼500 °C) down to 218 ppm for the highest metamorphic grade (∼685 °C). Decreasing abundances in are inversely correlated in a linear fashion with increasing K+ in biotite as a function of metamorphic grade and are interpreted as a devolatilization effect. Despite expected increasing δ15NNH4 values in biotite with nitrogen loss, a significant decrease from the Garnet Zones to the Staurolite Zones was found, followed by an increase to the Sillimanite Zones. This pattern for δ15NNH4 values in biotite inversely correlates with Mg/(Mg + Fe) ratios in biotite and is discussed in the framework of isotopic fractionation due to different exchange processes between or , reflecting devolatilization history and redox conditions during metamorphism.  相似文献   

16.
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17.
Lead speciation in many aqueous geochemical systems is dominated by carbonate complexation. However, direct observations of Pb2+ complexation by carbonate ions are few in number. This work represents the first investigation of the equilibrium over a range of ionic strength. Through spectrophotometric observations of formation at 25 °C in NaHCO3-NaClO4 solutions, formation constants of the form were determined between 0.001 and 5.0 molal ionic strength. Formation constant results were well represented by the equation:
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18.
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19.
Synthesis, characterization and thermochemistry of a Pb-jarosite   总被引：1，自引：0，他引：1  
The enthalpy of formation from the elements of a well-characterized synthetic Pb-jarosite sample corresponding to the chemical formula (H3O)0.74Pb0.13Fe2.92(SO4)2(OH)5.76(H2O)0.24 was measured by high temperature oxide melt solution calorimetry. This value ( = −3695.9 ± 9.7 kJ/mol) is the first direct measurement of the heat of formation for a lead-containing jarosite. Comparison to the thermochemical properties of hydronium jarosite and plumbojarosite end-members strongly suggests the existence of a negative enthalpy of mixing possibly related to the nonrandom distribution of Pb2+ ions within the jarosite structure. Based on these considerations, the following thermodynamic data are proposed as the recommended values for the enthalpy of formation from the elements of the ideal stoichiometric plumbojarosite Pb0.5Fe3(SO4)2(OH)6:  = −3118.1 ± 4.6 kJ/mol,  = −3603.6 ± 4.6 kJ/mol and S° = 376.6 ± 4.5 J/(mol K). These data should prove helpful for the calculation of phase diagrams of the Pb-Fe-SO4-H2O system and for estimating the solubility product of pure plumbojarosite. For illustration, the evolution of the estimated solubility product of ideal plumbojarosite as a function of temperature in the range 5-45 °C was computed (Log(Ksp) ranging from −24.3 to −26.2). An Eh-pH diagram is also presented.  相似文献   

20.
The influence on olivine/melt transition metal (Mn, Co, Ni) partitioning of substitution in the tetrahedral network of silicate melt structure has been examined at ambient pressure in the 1450-1550 °C temperature range. Experiments were conducted in the systems NaAlSiO4-Mg2SiO4- SiO2 and CaAl2Si2O8-Mg2SiO4-SiO2 with about 1 wt% each of MnO, CoO, and NiO added. These compositions were used to evaluate how, in silicate melts, substitution and ionization potential of charge-balancing cations affect activity-composition relations in silicate melts and mineral/melt partitioning.The exchange equilibrium coefficient, , is a positive and linear function of melt Al/(Al + Si) at constant degree of melt polymerization, NBO/T. The is negatively correlated with the ionic radius, r, of the M-cation and also with the ionization potential (Z/r2, Z = electrical charge) of the cation that serves to charge-balance Al3+ in tetrahedral coordination in the melts. The activity coefficient ratio, (γM/γMg)melt, is therefore similarly correlated.These melt composition relationships are governed by the distribution of Al3+ among coexisting Q-species in the peralkaline (depolymerized) melts coexisting with olivine. This distribution controls Q-speciation abundance, which, in turn, controls (γM/γMg)melt and . The relations between melt structure and olivine/melt partitioning behavior lead to the suggestion that in natural magmatic systems mineral/melt partition coefficients are more dependent on melt composition and, therefore, melt structure the more alkali-rich and the more felsic the melt. Moreover, mineral/melt partition coefficients are more sensitive to melt composition the more highly charged or the smaller the ionic radius of the cation of interest.  相似文献   

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