平衡常数的计算

配合物离解和矿物溶解等地球化学反应的平衡常数是地球化学计算最重要的热力学参数之一,它是由一定ｐＴ条件下实验测得的有关热力学数据计算出的,由于对各种反应的实验研究条件和程度不一,计算条件和精度要求各异,因此,对于每一具体应用应根据不同的需要和已有的热力学数据求取平衡常数,本文综述了不同条件下求取平衡常数的方法,并简要评述了平衡常数的可靠性。     

地球化学平衡的理论和计算

本文系统地回顾了多相组分化学平衡的理论基础和计算方法，重点分析了当今流行的平衡常数法和自由能量小法的异同，证明了这些方法在原则上的同一性同时也证明了反应平衡常数和物种自由能之间的可互换怀，并指出了互换的方法。     

300°～500℃锌在含氯、氟溶液中的溶解度

实验在300°～500℃,1Kb,用C-CO_2 Ni-NiO作缓冲剂控制fo_2条件下对ZnS在不同浓度、不同pH值的NaCl-H_2O和NaF-H_2O体系中的溶解度进行研究,同时对ZnCl_2在临界条件不同浓度NaCl溶液中迁移能力进行实验,通过实验结果热力学计算和分析,讨论了温度、介质种类、溶液浓度、pH值等影响Zn溶解度的各种主要因素:确定500C 1kb,Zn在含Cl溶液中主要以ZnCl_2~0形式存在.其标准生成自由能△G_(1.ZnCl_2~0)~0 =161.902kJ/mol;F~-对ZnS比Cl~-对ZnS的溶解能力大,在临界条件均一相中、ZnCl_2~0全部汽化迁移,依据实验数据,建立了Zn溶解度函数关系,使特定条件下的实验数据更具普遍意义.     

流体的热力学前缘研究

总结了当前国内外关于流体的热力学前缘研究领域如下：（１）流体体系的ｐ－Ｖ－Ｔ－ｘ相关系研究，主要对象是Ｈ２Ｏ－ＣＯ２－盐类多组分体系高温高压下相图的实验和理论研究。（２）矿物在流体中的溶解度及溶解后在流体中溶解类型的形式和热力学性质——平衡常数（或Ｇｉｂｂｓ自由能）及各种偏摩尔性质的研究。（３）流体热力学模型化研究，已研制出大量的计算机软件，包括多种矿物、溶解类型的热力学数据库和模拟热液平衡、矿物溶解性质、反应路径和水—岩相互作用的实用程序。（４）超临界流体的相关系和化学反应等有许多特殊的性质，对认识地球内部的演化将有重要意义。（５）新技术新方法的发展，使分析单个矿物包裹体成分变成了现实。     

高温高压下电解质溶液热力学性质的研究进展

高温高压下电解质溶液热力学性质的研究不仅对探讨地球内部流体的作用具有重要意义，而且在很多实际工业过程中也都有广泛应用。本综述了近10年来高温高压下电解质溶液热力学参数的实验测量和理论计算的进展，实验设备还有待进一步的改进和完善，以获得更高温度和压力下的数据，理论计算不仅有待于实验的发展，也与溶液的结构理论密切相关。     

基于假三元模型的透辉石-硬玉固溶体热力学性质计算

自然界中矿物多以固溶体形式存在,据其晶体化学特征计算热力学性质是开展矿物成因理论研究的基础。本文引入描述二元矿物固溶体热力学性质的假三元模型,计算得到了透辉石-硬玉固溶体系列的热力学性质。该模型通过构造一种高度有序的中间相,同时考虑长程和短程有序效应,基于热力学平衡态矿物固溶体自由能最低的规律,可以计算特定组分下矿物的平衡自由能、焓和熵等热力学参数。本文针对透辉石-硬玉固溶体体系,取绿辉石为其中间有序态,计算了其活度-成分关系和温度-组分相图等,发现绿辉石随温度升高的有序无序相变为一级相变,相变温度为1 148±25 K,与实验研究结果一致。本文获得的透辉石-绿辉石-硬玉体系的热力学参数可用于视剖面图方法研究MORB成分的岩石的榴辉岩相变质作用过程。     

硅化作用形成机制的热力学研究──以锡矿山锑矿为例

应用热力学方法计算了不同温度和不同酸碱度条件下石英和水中的溶解度。结合地质资料对锡矿山锑矿硅化作用的形成机制进行了分析。研究表明：溶液在降温和酸化过程中均产生硅质沉淀，但温度降低起主要作用。     

水热体系中Na_2SO_4/K_2SO_4溶解度的热力学计算

硫酸盐流体是自然界中的常见热液,其盐度可以为成矿流体演化、成矿元素的迁移富集和矿床类型的划分等提供重要信息。但是现有文献报道的Na_2SO_4和K_2SO_4溶解度多是在饱和蒸气压条件或超临界条件下,而对于低温成矿热液体系的实验研究较少。热力学计算是研究流体性质的重要手段,特别是在实验结果较少的温压范围内起着重要作用,但是利用热力学模型来计算硫酸盐溶解度的工作却少有开展。使用Pitzer模型,利用Na_2SO_4和K_2SO_4溶液高温高压条件下的密度数据,使用非线性最小二乘法拟合,获得了压力对Na_2SO_4和K_2SO_4的活度系数及其溶解过程中的标准偏摩尔体积影响的模型参数,评价了压力对其活度系数和标准偏摩尔体积的影响。结合文献中饱和蒸气压下的相关参数,构建了温度范围为0～250oC,压力范围为0.1～40.0 MPa,Na_2SO_4和K_2SO_4溶解度的热力学计算模型。模型计算结果与文献数据吻合较好。计算结果还显示,压力对Na_2SO_4和K_2SO_4的平均活度系数和溶度积都有正向的促进作用,但是由于平均活度系数随压力的变化更大,导致Na_2SO_4和K_2SO_4的溶解度随压力的增大而降低,并且随着温度的升高这种降低的程度变得更大。     

基于广义热力学的超固结土本构模型

基于广义热力学基本理论,通过考虑塑性剪切变形产生的能量一部分以塑性自由能的形式储存,并且该部分自由能与超固结度相关,结合修正剑桥模型的热力学函数形式建立了适用于超固结土的自由能函数和耗散函数。该耗散函数与当前应力状态无关,相关联流动法则仍然适用。由建立的耗散函数和自由能函数,推导了弹塑性本构关系的屈服函数、流动法则、硬化定律。通过4种不同超固结土的试验结果和计算结果进行比较,验证了模型的合理性。     

300℃时钯和铂氯络合物稳定性的实验研究

在控制氧逸度和酸度的条件下测定了３０℃时钯和铂氯络合物溶解度，将溶解度资料作用，求得它们的氯络合物种类分别为ＰｄＣｌ＾２－４和ＰｔＣｌ＾２－４，计算了相应反应式的平衡常数及推导了平衡常数与温度从属关系表达式，讨论了实验结果的地质意义。     

Thermodynamics of concentrated electrolyte mixtures and the prediction of mineral solubilities to high temperatures for mixtures in the system Na-K-Mg-Cl-SO4-OH-H2O

Mineral solubilities in binary and ternary electrolyte mixtures in the system Na-K-Mg-Cl-SO₄-OH-H₂O are calculated to high temperatures using available thermodynamic data for solids and for aqueous electrolyte solutions. Activity and osmotic coefficients are derived from the ion-interaction model of Pitzer (1973, 1979) and co-workers, the parameters of which are evaluated from experimentally determined solution properties or from solubility data in binary and ternary mixtures. Excellent to good agreement with experimental solubilities for binary and ternary mixtures indicate that the model can be successfully used to predict mineral-solution equilibria to high temperatures. Although there are currently no theoretical forms for the temperature dependencies of the various model parameters, the solubility data in ternary mixtures can be adequately represented by constant values of the mixing term θ_ij and values of ψ_ijk which are either constant or have a simple temperature dependence. Since no additional parameters are needed to describe the thermodynamic properties of more complex electrolyte mixtures, the calculations can be extended to equilibrium studies relevant to natural systems. Examples of predicted solubilities are given for the quaternary system NaCl-KCl-MgCl₂-H₂O.     

A critical evaluation of the thermodynamic data for boron ions,ion pairs,complexes, and polyanions in aqueous solution at 298.15 K and 1 bar

Energy related industrial development, municipal waste treatment processes and some natural sources, contribute to B (being present) in the environment in elevated concentrations. Boron forms numerous aqueous ion pairs and complexes, some of which would not normally exist in significant concentrations under typical baseline environmental conditions. A complete understanding of the aqueous chemistry of B depends on an accurate evaluation of the thermodynamic data for these species.Equilibrium constants for 29 inorganic complexes, ion pairs, and polyanions of B have been critically evaluated. Apparent equilibrium constants have been extrapolated to zero ionic strength, and the selected thermodynamic values are tabulated. Gibbs free energies of formation for the aqueous species have been computed; these are presented with entropy and enthalpy values where available     

用线性自由能关系预测金属络合物的热力学性质

Sverjensky与Molling提出的线性自由能关系是根据金属阳离子的热力学性质来预测等结构系列中固体相的标准生成自由能。本文研究结果证实,水溶液中金属络合物与简单金属阳离子之间也存在类似的相关关系,预测值与实验值的差异通常小于1．5kcal／mol或小于一个log单位,这一线性自由能关系对于预测自然环境中重金属的水溶物种的配分、迁移和毒性具有非常重要的应用价值。     

The solubility of calcite in seawater solutions of various magnesium concentration, It = 0.697 m at 25 °C and one atmosphere total pressure

Stoichiometric solubility constants of calcite in initially supersaturated solutions of various magnesium to calcium concentration ratios but identical ionic strength were determined at 25°C and one atmosphere total pressure.The thermodynamic solubility constant of calcite is used with ion pairing equations to interpret the data reported in this study. Results indicate that even though magnesian calcites, rather than pure calcite, precipitate from seawater solutions containing magnesium ions, the incorporation of MgCO₃ in the calcite crystal lattice does not extensively alter the equilibrium calcium carbonate activity product.The equilibrium activity of the ionic species in solution and the composition of magnesian calcite overgrowths precipitated from solutions of similar composition are used to calculate the solubility of magnesian calcites. The values for magnesian calcite solubilities obtained by this approach are lower than those obtained from the dissolution kinetics of biogenic carbonates.     

The elastic solid solution model for minerals at high pressures and temperatures

Non-ideality in mineral solid solutions affects their elastic and thermodynamic properties, their thermobaric stability, and the equilibrium phase relations in multiphase assemblages. At a given composition and state of order, non-ideality in minerals is typically modelled via excesses in Gibbs free energy which are either constant or linear with respect to pressure and temperature. This approach has been extremely successful when modelling near-ideal solutions. However, when the lattice parameters of the solution endmembers differ significantly, extrapolations of thermodynamic properties to high pressures using these models may result in significant errors. In this paper, I investigate the effect of parameterising solution models in terms of the Helmholtz free energy, treating volume (or lattice parameters) rather than pressure as an independent variable. This approach has been previously applied to models of order–disorder, but the implications for the thermodynamics and elasticity of solid solutions have not been fully explored. Solid solution models based on the Helmholtz free energy are intuitive at a microscopic level, as they automatically include the energetic contribution from elastic deformation of the endmember lattices. A chemical contribution must also be included in such models, which arises from atomic exchange within the solution. Derivations are provided for the thermodynamic properties of n-endmember solutions. Examples of the use of the elastic model are presented for the alkali halides, pyroxene, garnet, and bridgmanite solid solutions. Elastic theory provides insights into the microscopic origins of non-ideality in a range of solutions, and can make accurate predictions of excess enthalpies, entropies, and volumes as a function of volume and temperature. In solutions where experimental data are sparse or contradictory, the Helmholtz free energy approach can be used to assess the magnitude of excess properties and their variation as a function of pressure and temperature. The formulation is expected to be useful for geochemical and geophysical studies of the Earth and other planetary bodies.     

A suite of programs,OptimA, OptimB,OptimC, and OptimS compatible with the Unitherm database,for deriving the thermodynamic properties of aqueous species from solubility,potentiometry and spectroscopy measurements

This paper describes four programs for Windows, designed to obtain the thermodynamic properties of aqueous species from experimental data and reporting them in the Unitherm database format (HCh software package). Programs OptimA and OptimS allow users to derive the standard Gibbs free energies of aqueous species from the results of chemical experiments (e.g., potentiometry or solubility) and from ultraviolet–visible (UV–Vis) absorption spectra, respectively; programs OptimB and OptimC enable optimization of the parameters of the revised Helgeson–Kirkham–Flowers equation of state and the modified Ryzhenko–Bryzgalin electrostatic model, respectively, for an aqueous species from its standard Gibbs free energy or stability constant as a function of temperature and pressure.     

A thermodynamic model for the solubility of barite and celestite in electrolyte solutions and seawater to 200°C and to 1 kbar

This paper describes a model for barite and celestite solubilities in the Na–K–Ca–Mg–Ba–Sr–Cl–SO₄–H₂O system to 200°C and to 1 kbar. It is based on Pitzer's ion interaction model for the thermodynamic properties of the aqueous phase and on values of the solubility products of the solids revised in this work. It is shown how barite and celestite solubilities in electrolyte solutions can be accurately predicted as a function of temperature and pressure from previously determined Pitzer's parameters. The equilibrium constant for the BaSO₄(aq) ion pair dissociation reaction is calculated from recently reported barite solubility in Na₂SO₄ solutions from 0 to 80°C. Pressure corrections are evaluated through partial molal volume calculations and are partially validated by comparing model predictions to measured barite and celestite solubilities in pure water to 1 kbar and in NaCl solutions to 500 bars. The model is then used to investigate the tendency of ion pairing of Ca, Sr and Ba with sulfate in seawater. Finally, the activity coefficient of aqueous barium sulfate in seawater is calculated for temperature, pressure and salinity values found in the ocean and compared to published values.     

Magnesian calcite stabilities: A reevaluation

Equilibrium constants at stoichiometric saturation with respect to various magnesian calcite compositions were measured using free-drift dissolution rate data and inverse time plots to estimate equilibrium pH. The equilibrium constants determined for two ultrasonically cleaned and annealed biogenic magnesian calcites (12 and 18 mole % MgCO₃) in CaCl₂ + MgCl₂ media at two Mg:Ca molar ratios (1:5 and 5:1) are about three times smaller than those previously reported by Plummer and Mackenzie (1974). These equilibrium constants are not affected by changes in initial pH value, solid:solution ratio, or solution Mg:Ca molar ratio when the ion activity product is expressed in the fractional exponent form. Other models for expression of the equilibrium ion activity product fail to yield consistent values in solutions of different Mg:Ca molar ratios.Experiments performed using crushed samples not ultrasonically cleaned and annealed yield equilibrium constants which vary with solid:solution ratio. Those performed at high solid:solution ratios yield values which approach those previously reported. Submicron size particles and crystal strain induced by crushing the biogenic carbonates may cause more rapid dissolution rates and, hence, overestimation of the solubility of samples not prepared so as to minimize these effects. Thus, the large range in reported solubilities of magnesium calcites may be a result of differences in sample preparation procedure.The results of these measurements shift the thermodynamic equivalence point of aragonite and magnesian calcite from 7.5 mole % MgCO₃ up to 12 mole % MgCO₃ and prompt a reassessment of models for carbonate diagenetic reactions in natural environments.