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1.
The Mars Global Surveyor, Mars Exploration Rover, and Mars Express missions have stimulated considerable thinking about the surficial geochemical evolution of Mars. Among the major recent mission findings are the presence of jarosite (a ferric sulfate salt), which requires formation from an acid-sulfate brine, and the occurrence of hematite and goethite on Mars. Recent ferric iron models have largely focused on 25 °C, which is a major limitation for models exploring the geochemical history of cold bodies such as Mars. Until recently, our work on low-temperature iron-bearing brines involved ferrous but not ferric iron, also obviously a limitation. The objectives of this work were to (1) add ferric iron chemistry to an existing ferrous iron model (FREZCHEM), (2) extend this ferrous/ferric iron geochemical model to lower temperatures (<0 °C), and (3) use the reformulated model to explore ferrous/ferric iron chemistries on Mars.The FREZCHEM model is an equilibrium chemical thermodynamic model parameterized for concentrated electrolyte solutions using the Pitzer approach for the temperature range from <−70 to 25 °C and the pressure range from 1 to 1000 bars. Ferric chloride and sulfate mineral parameterizations were based, in part, on experimental data. Ferric oxide/hydroxide mineral parameterizations were based exclusively on Gibbs free energy and enthalpy data. New iron parameterizations added 23 new ferrous/ferric minerals to the model for this Na-K-Mg-Ca-Fe(II)-Fe(III)-H-Cl-SO4-NO3-OH-HCO3-CO3-CO2-O2-CH4-H2O system.The model was used to develop paragenetic sequences for Rio Tinto waters on Earth and a hypothetical Martian brine derived from acid weathering of basaltic minerals. In general, model simulations were in agreement with field evidence on Earth and Mars in predicting precipitation of stable iron minerals such as jarosites, goethite, and hematite. In addition, paragenetic simulations for Mars suggest that other iron minerals such as lepidocrocite, schwertmannite, ferricopiapite, copiapite, and bilinite may also be present on the surface of Mars. Evaporation or freezing of the Martian brine led to similar mineral precipitates. However, in freezing, compared to evaporation, the following key differences were found: (1) magnesium sulfates had higher hydration states; (2) there was greater total aqueous sulfate (SO4T = SO4 + HSO4) removal; and (3) there was a significantly higher aqueous Cl/SO4T ratio in the residual Na-Mg-Cl brine. Given the similarities of model results to observations, alternating dry/wet and freeze/thaw cycles and brine migration could have played major roles in vug formation, Cl stratification, and hematite concretion formation on Mars.  相似文献   

2.
Pressure plays a critical role in controlling aqueous geochemical processes in deep oceans and deep ice. The putative ocean of Europa could have pressures of 1200 bars or higher on the seafloor, a pressure not dissimilar to the deepest ocean basin on Earth (the Mariana Trench at 1100 bars of pressure). At such high pressures, chemical thermodynamic relations need to explicitly consider pressure. A number of papers have addressed the role of pressure on equilibrium constants, activity coefficients, and the activity of water. None of these models deal, however, with processes at subzero temperatures, which may be important in cold environments on Earth and other planetary bodies. The objectives of this work were to (1) incorporate a pressure dependence into an existing geochemical model parameterized for subzero temperatures (FREZCHEM), (2) validate the model, and (3) simulate pressure-dependent processes on Europa. As part of objective 1, we examined two models for quantifying the volumetric properties of liquid water at subzero temperatures: one model is based on the measured properties of supercooled water, and the other model is based on the properties of liquid water in equilibrium with ice.The relative effect of pressure on solution properties falls in the order: equilibrium constants(K) > activity coefficients (γ) > activity of water (aw). The errors (%) in our model associated with these properties, however, fall in the order: γ > K > aw. The transposition between K and γ is due to a more accurate model for estimating K than for estimating γ. Only activity coefficients are likely to be significantly in error. However, even in this case, the errors are likely to be only in the range of 2 to 5% up to 1000 bars of pressure. Evidence based on the pressure/temperature melting of ice and salt solution densities argue in favor of the equilibrium water model, which depends on extrapolations, for characterizing the properties of liquid water in electrolyte solutions at subzero temperatures, rather than the supercooled water model. Model-derived estimates of mixed salt solution densities and chemical equilibria as a function of pressure are in reasonably good agreement with experimental measurements.To demonstrate the usefulness of this low-temperature, high-pressure model, we examined two hypothetical cases for Europa. Case 1 dealt with the ice cover of Europa, where we asked the question: How far above the putative ocean in the ice layer could we expect to find thermodynamically stable brine pockets that could serve as habitats for life? For a hypothetical nonconvecting 20 km icy shell, this potential life zone only extends 2.8 km into the icy shell before the eutectic is reached. For the case of a nonconvecting icy shell, the cold surface of Europa precludes stable aqueous phases (habitats for life) anywhere near the surface. Case 2 compared chemical equilibria at 1 bar (based on previous work) with a more realistic 1460 bars of pressure at the base of a 100 km Europan ocean. A pressure of 1460 bars, compared to 1 bar, caused a 12 K decrease in the temperature at which ice first formed and a 11 K increase in the temperature at which MgSO4·12H2O first formed. Remarkably, there was only a 1.2 K decrease in the eutectic temperatures between 1 and 1460 bars of pressure. Chemical systems and their response to pressure depend, ultimately, on the volumetric properties of individual constituents, which makes every system response highly individualistic.  相似文献   

3.
Recent Mars missions have stimulated considerable thinking about the surficial geochemical evolution of Mars. Among the major relevant findings are the presence in Meridiani Planum sediments of the mineral jarosite (a ferric sulfate salt) and related minerals that require formation from an acid-salt brine and oxidizing environment. Similar mineralogies have been observed in acidic saline lake sediments in Western Australia (WA), and these lakes have been proposed as analogues for acidic sedimentary environments on Mars. The prior version of the equilibrium chemical thermodynamic FREZCHEM model lacked Al and Si chemistries that are needed to appropriately model acidic aqueous geochemistries on Earth and Mars. The objectives of this work were to (1) add Al and Si chemistries to the FREZCHEM model, (2) extend these chemistries to low temperatures (<0 °C), if possible, and (3) use the reformulated model to investigate parallels in the mineral precipitation behavior of acidic Australian lakes and hypothetical Martian brines.FREZCHEM is an equilibrium chemical thermodynamic model parameterized for concentrated electrolyte solutions using the Pitzer approach for the temperature range from <−70 to 25 °C and the pressure range from 1 to 1000 bars. Aluminum chloride and sulfate mineral parameterizations were based on experimental data. Aluminum hydroxide and silicon mineral parameterizations were based on Gibbs free energy and enthalpy data. New aluminum and silicon parameterizations added 12 new aluminum/silicon minerals to this Na-K-Mg-Ca-Fe(II)-Fe(III)-Al-H-Cl-Br-SO4-NO3-OH-HCO3-CO3-CO2-O2-CH4-Si-H2O system that now contain 95 solid phases.There were similarities, differences, and uncertainties between Australian acidic, saline playa lakes and waters that likely led to the Burns formation salt accumulations on Mars. Both systems are similar in that they are dominated by (1) acidic, saline ground waters and sediments, (2) Ca and/or Mg sulfates, and (3) iron precipitates such as jarosite and hematite. Differences include: (1) the dominance of NaCl in many WA lakes, versus the dominance of Fe-Mg-Ca-SO4 in Meridiani Planum, (2) excessively low K+ concentrations in Meridiani Planum due to jarosite precipitation, (3) higher acid production in the presence of high iron concentrations in Meridiani Planum, and probably lower rates of acid neutralization and hence, higher acidities on Mars owing to colder temperatures, and (4) lateral salt patterns in WA lakes. The WA playa lakes display significant lateral variations in mineralogy and water chemistry over short distances, reflecting the interaction of acid ground waters with neutral to alkaline lake waters derived from ponded surface runoff. Meridiani Planum observations indicate that such lateral variations are much less pronounced, pointing to the dominant influence of ground water chemistry, vertical ground water movements, and aeolian processes on the Martian surface mineralogy.  相似文献   

4.
复杂卤水组分对于石盐流体包裹体均一温度的影响尚不明确,文章基于NaCl-X-H_2O(X=KCl, MgCl_2,CaCl_2, Na_2SO_4)三元卤水体系,尝试探讨K~+、Mg~(2+)、Ca~(2+)、SO_4~(2-)对石盐流体包裹体均一温度测试结果的影响。不同卤水体系最大均一温度分析结果表明,K~+、Mg~(2+)、Ca~(2+)的存在总体上会导致石盐流体包裹体均一温度偏大,SO_4~(2-)的存在对均一温度的影响很小。以NaCl-H_2O体系为参照,NaCl-Na_2SO_4-H_2O体系平均均一温度较之要低,而NaCl-KCl-H_2O、NaCl-MgCl_2-H_2O和NaCl-CaCl_2-H_2O体系与其相反。NaCl-KCl-H_2O体系中的KCl浓度与平均均一温度呈现负相关关系,NaCl-MgCl_2-H_2O、NaCl-CaCl_2-H_2O、NaCl-Na_2SO_4-H_2O体系中的w(MgCl_2)、w(CaCl_2)和w(Na_2SO_4)与平均均一温度则呈现正相关关系。平均和最大均一温度分析结果都显示出复杂卤水体系中不同离子及其浓度对石盐流体包裹体均一温度会产生影响。本研究对于具有复杂化学组分卤水结晶析出石盐均一温度的研究具有重要的参考价值。  相似文献   

5.
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6.
稀土元素在矿石中有多种不同的赋存形式,主要有离子吸附型和矿物晶格型,稀土不同赋存形态对其本身准确分析测定有很大的影响。本文从稀土元素在矿石中不同赋存形态的角度出发,探讨了不同前处理方法对稀土准确测试结果的影响,采用盐酸-硝酸-氢氟酸-高氯酸(四酸)敞开酸溶、盐酸-硝酸-氢氟酸-高氯酸-硫酸(五酸)敞开酸溶、氢氟酸-硝酸封闭压力酸溶、氢氧化钠-过氧化钠碱熔四种方法对离子吸附型和矿物晶格型两类赋存类型的稀土矿石样品进行前处理,电感耦合等离子体发射光谱法测定其中的15种稀土元素。结果表明:对于离子吸附型的稀土矿石标准物质(GBW 07161、GBW 07188),四酸敞开酸溶法测定的结果明显偏低,15种稀土元素大都偏低10%~20%,五酸敞开酸溶法、封闭压力酸溶法和碱熔法的测定值与标准值吻合;而对于稀土以离子化合物及类质同象置换的形式赋存于矿物晶格中的白云鄂博轻稀土矿石样品,三种酸溶法结果较碱熔法均偏低,其中四酸敞开酸溶法偏低最多,约偏低20%左右,五酸敞开酸溶法和封闭压力酸溶法偏低5%~15%。本文提出,对于离子吸附型稀土矿,五酸敞开酸溶法和封闭压力酸溶法可以代替传统操作复杂的碱熔法,但对于稀土以离子形式赋存于矿物晶格型的稀土矿,目前最合适的前处理法是传统的碱熔法。  相似文献   

7.
Equilibrium chlorine-isotope (37Cl/35Cl) fractionations have been determined by using published vibrational spectra and force-field modeling to calculate reduced partition function ratios for Cl-isotope exchange. Ab initio force fields calculated at the HF/6-31G(d) level are used to estimate unknown vibrational frequencies of 37Cl-bearing molecules, whereas crystalline phases are modeled by published lattice-dynamics models. Calculated fractionations are principally controlled by the oxidation state of Cl and its bond partners. Molecular mass (or the absence of C-H bonds) also appears to play a role in determining relative fractionations among simple Cl-bearing organic species. Molecules and complexes with oxidized Cl (i.e., Cl0, Cl+, etc.) will concentrate 37Cl relative to chlorides (substances with Cl−). At 298 K, ClO2 (containing Cl4+) and [ClO4]− (containing Cl7+) will concentrate 37Cl relative to chlorides by as much as 27‰ and 73‰, respectively, in rough agreement with earlier calculations. Among chlorides, 37Cl will be concentrated in substances where Cl is bonded to +2 cations (i.e., FeCl2, MnCl2, micas, and amphiboles) relative to substances where Cl is bonded to +1 cations (such as NaCl) by ∼2 to 3‰ at 298 K; organic molecules with C-Cl bonds will be even richer in 37Cl (∼5 to 9‰ at 298 K). Precipitation experiments, in combination with our results, provide an estimate for Cl-isotope partitioning in brines and suggest that silicates (to the extent that their Cl atoms are associated with nearest-neighbor +2 cations analogous with FeCl2 and MnCl2) will have higher 37Cl/35Cl ratios than coexisting brine (by ∼2 to 3‰ at room temperature). Calculated fractionations between HCl and Cl2, and between brines and such alteration minerals, are in qualitative agreement with both experimental results and systematics observed in natural samples. Our results suggest that Cl-bearing organic molecules will have markedly higher 37Cl/35Cl ratios (by 5.8‰ to 8.5‰ at 295 K) than coexisting aqueous solutions at equilibrium. Predicted fractionations are consistent with the presence of an isotopically heavy reservoir of HCl that is in exchange equilibrium with Cl−aq in large marine aerosols.  相似文献   

8.
铬铁矿中亚铁的测定方法   总被引：5，自引：3，他引：2  
杨林  黄宝贵  陈述 《岩矿测试》2010,29(6):719-722
采用硫-磷混合酸微波消解对难溶的钒钛磁铁矿进行前处理,用5-溴-PADAP-过氧化氢分光光度法测定矿样中的钒,优化了微波消解的实验条件。加入浓磷酸和40 g/L氟化钠溶液分别消除了共存常量元素铁和钛的干扰。方法检出限为0.004μg/mL,线性范围为0.01~1.0μg/mL。应用于实际钒钛磁铁矿样品中钒的测定,重现性好,检出限较低,灵敏度较高,能够满足简单、快速、批量分析的要求。  相似文献   

9.
During Li recovery from salar brines, Li concentration is typically increased to about 60,000 mg L?1 by evaporation. We investigated the concentration changes of Li, Na, K, Mg, Cl, SO4, and B during evaporation of both natural Uyuni and artificial Atacama brines. The Uyuni brine exhibited a maximum Li concentration of 6810 mg L?1 at 31 days of evaporation, at which point the majority of the Na and K in the brine was removed. The Li concentration decreased with further evaporation due to precipitation as Li2SO4, such that the level at the 56 day mark was approximately 4130 mg L?1. In contrast, the artificial Atacama brine showed no pronounced Li precipitation, even after 54 days, at which point the Li concentration was 21,800 mg L?1. The initial concentrations of Na and K in the Atacama brine were higher than those in the Uyuni brine, and the Atacama solution still retained K after 54 days of evaporation. The order of precipitation of cation species during the evaporation of both brines was: Na, followed by K, Mg, and Li. Thus, Li precipitation in the Atacama brine might be prevented due to the more favored precipitations of Na and K, such that significant Li removal did not occur in this brine.  相似文献   

10.
The mineral solubility model of Harvie and Weare (1980) is extended to the eight component system, Na-K-Mg-Ca-H-Cl-SO4-OH-HCO3-CO3-CO2-H2O at 25°C to high concentrations. The model is based on the semi-empirical equations of Pitzer (1973) and co-workers for the thermodynamics of aqueous electrolyte solutions. The model is parameterized using many of the available isopiestic, electromotive force, and solubility data available for many of the subsystems. The predictive abilities of the model are demonstrated by comparison to experimental data in systems more complex than those used in parameterization. The essential features of a chemical model for aqueous electrolyte solutions and the relationship between pH and the equilibrium properties of a solution are discussed.  相似文献   

11.
Solubilities of methane in multisalt solutions at 550 psia and 25°C can be predicted from single-salt salting coefficients. The ionic strength contribution of the ith salt, Ii, is multiplied by its molal salting coefficient, kmi, in the following summation over all salts:
logMoMs = ∑i kmiIi
where mo and ms are molal methane solubilities in distilled water and the salt solution, respectively, at the T, P and methane fugacity of interest.This equation predicts methane solubility in multisalt brines containing Na+, K+, Mg+2, Ca+2, Cl?, SO4?2 and CO3?2 ions. kmi values reported by Stoessell and Byrne (1982b) can be used in solubility predictions in brines at earth surface conditions. Prediction in reservoir brines would require determination of kmi, for the different salts at reservoir temperatures and pressures.  相似文献   

12.
This paper describes a chemical model that calculates solute and solvent activities and solid-liquid equilibria in the H-Na-K-OH-Cl-HSO4-SO4-H2O system from dilute to high solution concentration within the 0° to 250°C temperature range. All binary and ternary subsystems are included in the model parameterization. The model is validated by comparing predictions with experimental data, primarily in higher order systems, not used in the parameterization process. Limitations of the model due to data insufficiencies are discussed.The Harvie and Weare (GCA44, 981, 1980) solubility modeling approach, incorporating their implementation of the concentration-dependent specific interaction equations of Pitzer (J. Phys. Chem.77, 268, 1973), is employed. This model expands the variable temperature Na-K-Cl-SO4-H2O model of Greenberg and Moller (GCA53, 2503, 1989) by including acid (H2SO4, HCl) and base (NaOH, KOH) species. Temperature functions for the chemical potentials of 5 acidic (sodium bisulfate, sodium sesquisulfate, mercallite, potassium sesquisulfate and misenite) and 6 basic (4 sodium hydroxide hydrates and 2 potassium hydroxide hydrates) solid phases are determined.  相似文献   

13.
At T > 100°C development of thermodynamic models suffers from missing experimental data, particularly for solubilities of sulfate minerals in mixed solutions. Solubilities in Na+-K+-Ca2+-Cl−-SO42−/H2O subsystems were investigated at 150, 200°C and at selected compositions at 100°C. The apparatus used to examine solid-liquid phase equilibria under hydrothermal conditions has been described.In the system NaCl-CaSO4-H2O the missing anhydrite (CaSO4) solubilities at high NaCl concentrations up to halite saturation have been determined. In the system Na2SO4-CaSO4-H2O the observed glauberite (Na2SO4 · CaSO4) solubility is higher than that predicted by the high temperature model of Greenberg and Møller (1989), especially at 200°C. At high salt concentrations, solubilities of both anhydrite and glauberite increase with increasing temperature. Stability fields of the minerals syngenite (K2SO4 · CaSO4 · H2O) and goergeyite (K2SO4 · 5 CaSO4 · H2O) were determined, and a new phase was found at 200°C in the K2SO4-CaSO4-H2O system. Chemical and single crystal structure analysis give the formula K2SO4 · CaSO4. The structure is isostructural with palmierite (K2SO4 · PbSO4). The glaserite (“3 K2SO4 · Na2SO4”) appears as solid solution in the system Na2SO4-K2SO4-H2O. Its solubility and stoichiometry was determined as a function of solution composition.  相似文献   

14.
Modern rift zone hydrothermal brines are typically CaCl2-bearing brines, an unusual chemical signature they share with certain oil field brines, fluid inclusions in ore minerals and a few uncommon saline lakes. Many origins have been suggested for such CaCl2 brines but in the Reykjanes, Iceland, geothermal system a strong empirical case can be made for a basalt-seawater interaction origin. To examine this mechanism of CaCl2 brine evolution some simple mass balance calculations were carried out. Average Reykjanes olivine tholeiite was “reacted” with average North Atlantic seawater to make an albite-chlorite-epidotesphene rock using Al2O3 as the conservative rock component and Cl as the conservative fluid component. The excess components released by the basalt to the fluid were “precipitated” at 275° C as quartz, calcite, anhydrite, magnetite and pyrite to complete the conversion to greenstone. The resulting fluid was a CaCl2 brine of seawater chlorinity with a composition remarkably similar to the actual Reykjanes brine at 1750 m depth. Thus, the calculations strongly support the idea that the Reykjanes CaCl2 brines result from “closed system” oceanic basalt-seawater interaction (albitization — chloritization mechanism) at greenschist facies temperatures. The calculation gives a seawater: basalt mass ratio of 3∶1 to 4∶1 (vol. ratio of 9∶1 to 12∶1), in keeping with experimental results, submarine vent data and with ocean crust cooling calculations. The brine becomes anoxic because there is insufficient dissolved or combined oxygen to balance all the Fe released from the basalt during alteration. Large excesses of Ca are released to the fluid and precipitate out in the form of anhydrite which essentially sweeps the brine free of sulfate leaving an elevated Ca concentration. The calculated rock-water interaction basically involves Na + Mg + SO4 ? Ca + K, simulating chemical differences observed between oceanic basalts and greenstones from many mid-ocean ridges.  相似文献   

15.
Recent isopiestic studies of the Fe2(SO4)3-H2SO4-H2O system at 298.15 K are represented with an extended version of Pitzer’s ion interaction model. The model represents osmotic coefficients for aqueous {(1 − y)Fe2(SO4)3 + yH2SO4} mixtures from 0.45 to 3.0 m at 298.15 K and 0.0435 ? y ? 0.9370. In addition, a slightly less accurate representation of a more extended molality range to 5.47 m extends over the same y values, translating to a maximum ionic strength of 45 m. Recent isopiestic data for the system at 323.15 K are represented with the extended Pitzer model over a limited range in molality and solute fraction. These datasets are also represented with the usual “3-parameter” version of Pitzer’s model so that it may be incorporated in geochemical modeling software, but is a slightly less accurate representation of thermodynamic properties for this system. Comparisons made between our ion interaction model and available solubility data display partial agreement for rhomboclase and significant discrepancy for ferricopiapite. The comparisons highlight uncertainty remaining for solubility predictions in this system as well as the need for additional solubility measurements for Fe3+-bearing sulfate minerals. The resulting Pitzer ion interaction models provide an important step toward an accurate and comprehensive representation of thermodynamic properties in this geochemically important system.  相似文献   

16.
There is now evidence that naturally occurring acid–water is more abundant than previously thought and that it has been important in the geologic past. Understanding the processes leading to the formation of such systems is required to appreciate the role of acid systems in geologic processes and to develop indicators for recognizing the geologic/environmental importance of these systems in the past. This paper characterizes the hydrogeology, hydrogeochemistry, microbial biogeochemistry and landscape attributes of acid–groundwater surface water systems in Australia with an emphasis on a well studied playa-lake system, Lake Tyrrell, Murray Valley. A model for the origin of these acid brines is presented and the importance of acid-brine producing systems is speculated upon. Data include porewater and groundwater geochemical measurements (collected during a 10 day field campaign) and results from geochemical modeling and graphics (e.g., Piper diagrams and x–y plots of seawater evaporation trajectories). Key characteristics of the system are (1) aquifer materials have low acid buffering capacities, (2) saline groundwater flowing onto playa surfaces is an oxic, H2SO4 solution, (3) authigenic minerals include combinations of jarosite [KFe3(SO4)2(OH)6], alunite [KAl3(SO4)2(OH)6] and Fe oxides that can form as evaporite minerals, (4) a source for solutes can be marine aerosols and (5) the formation of ironstones. Groundwater acidification by various processes including sulfide oxidation and ferrolysis, and at many different times, are the unique aspects for evolution of these acid brines and they can be considered another end member of the Eugster–Jones–Hardie model for the evolution of brines in closed basins. Acid–hypersaline groundwater and playa systems such as Lake Tyrrell may be an example of expected changes in the hydrogeochemistry of terrestrial water during late-stage continental denudation under arid conditions. Historically these systems may have been integral to the formation of opal, bauxite, some low temperature ore deposits, of authigenic K-feldspars, and continental redbeds. Natural acid saline systems, such as those in Australia, may also be representative of acid saline systems on Mars.  相似文献   

17.
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   

18.
A general Equation of State (EOS), which we previously developed for pure nonpolar systems, is extended to polar systems such as water and to mixtures in this study. This EOS contains only two parameters for each pure component and two additional parameters for each binary mixture (no higher order parameters are needed for more complicated mixture systems). The two mixing parameters can be eliminated for nonaqueous mixtures with a slight loss of accuracy in both total mole volume and in excess volume (or nonideal mixing). Comparison with a large amount of experimental PVTX data in pure systems (including H2O) and in the mixtures, H2O-CO2, CO2-N2, CH4-CO2, and N2-CO2-CH4 results in an average error of 1.6% in density. Comparison with commonly used EOS for supercritical fluids shows that the EOS of this study covers far more T-P-X space with higher accuracy. We believe that it is accurate from supercritical temperature to 2000 K and from 0 to 25,000 bar or higher with an average error in density of less than 2% for both pure members and mixtures in the system H2O-CO2-CH4-N2-CO-H2-O2-H2S-Ar and possibly with additional gases. Comparison with the published simulated data suggests that this EOS is approximately correct up to 300,000 bar and 2800 K.We also simulated the PVTX properties of a number of supercritical fluid mixtures using molecular dynamics (MD) simulation. These results and those of other authors are well predicted by the EOS of this study.  相似文献   

19.
Interstitial brines from the Temblor and the McAdams sandstones at Kettleman are essentially NaCaCl solutions with subsidiary SO4 and the total salinities are roughly 30,000 and 10,000 ppm, respectively. Activities of H+ and all other aqueous species have been calculated for 100°C (the in situ temperatures of the brines) from chemical analyses of the brines and 100-degree dissociation constants alone. The brine alkalinities measured at surface temperature appear to be too low when comparing them against alkalinities calculated from the measured pHs of the brines. Consequently, alkalinities calculated for 25°C were substituted for the measured ones in the calculation of the distribution of aqueous species at 100°C.Although the brines are nearly neutral (pH 6·3–d7·9) at surface temperature, their pHs calculated for 100°C range from 8·1 to 8·7 (± 0·35). These pHs and the 100-degree activities of the other aqueous species permit graphic representation of the brines on activity diagrams. Most brines fall at or near the boundaries between the stability fields of quartz, albite, microcline, mica, montmorillonite and anhydrite. Because these minerals are present as authigenic phases in the sandstones, the calculations suggest that the minerals are in stable equilibrium with the brines. By contrast, the calculations suggest that the brines are supersaturated by about three orders of magnitude with respect to calcite, also present in the sandstones. One possible explanation for this is kinetic inhibition of calcite crystallization by Mg2+ and SO42? ions in the brines. Phosphatic pellets, glauconite and probably dolomite, pyrite and some kaolinite are early authigenic minerals preserved in the sandstones and they are not now in equilibrium with the brines, which are supersaturated with respect to dolomite and pyrite. The chemical relationship between the brines and the diagenetic minerals laumontite and sphene, also present in the Temblor Formation, cannot be assessed reliably until the thermodynamic properties of laumontite and of aqueous titanium complexes are well known.  相似文献   

20.
Perennial ice covers on many Antarctic lakes have resulted in high lake inorganic carbon contents. The objective of this paper was to evaluate and compare the brine and CO2 chemistries of Lake Vida (Victoria Valley) and West Lake Bonney (Taylor Valley), two lakes of the McMurdo Dry Valleys (East Antarctica), and their potential consequences during global warming. An existing geochemical model (FREZCHEM-15) was used to convert measured molarity into molality needed for the FREZCHEM model, and this model added a new algorithm that converts measured DIC into carbonate alkalinity needed for the FREZCHEM model. While quite extensive geochemical information exists for ice-covered Taylor Valley lakes, such as West Lake Bonney, only limited information exists for the recently sampled brine of >25 m ice-thick Lake Vida. Lake Vida brine had a model-calculated pCO2 = 0.60 bars at the field pH (6.20); West Lake Bonney had a model-calculated pCO2 = 5.23 bars at the field pH (5.46). Despite the high degree of atmospheric CO2 supersaturation in West Lake Bonney, it remains significantly undersaturated with the gas hydrate, CO2·6H2O, unless these gas hydrates are deep in the sediment layer or are metastable having formed under colder temperatures or greater pressures. Because of lower temperatures, Lake Vida could start forming CO2·6H2O at lower pCO2 values than West Lake Bonney; but both lakes are significantly undersaturated with the gas hydrate, CO2·6H2O. For both lakes, simulation of global warming from current subzero temperatures (?13.4 °C in Lake Vida and ?4.7 °C in West Lake Bonney) to 10 °C has shown that a major loss of solution-phase carbon as CO2 gases and carbonate minerals occurred when the temperatures rose above 0 °C and perennial ice covers would disappear. How important these Antarctic CO2 sources will be for future global warming remains to be seen. But a recent paper has shown that methane increased in atmospheric concentration due to deglaciation about 10,000 years ago. So, CO2 release from ice lakes might contribute to atmospheric gases in the future.  相似文献   

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