Thermodynamic Calculation of Solubility of Na2SO4/K2SO4 in Hydrothermal Fluids

Sulfate fluids are common fluids in nature, and their salinity studies can provide important information for the evolution of ore-forming fluids, migration and enrichment of ore-forming elements, and the classification of deposit types. Considerable research has been carried out to investigate the solubility of Na₂SO₄ and K₂SO₄ in hydrothermal fluids, however most of the literature reported experimental data were under saturated vapor pressure or the water supercritical region. A few data have been reported for the low temperature hydrothermal mineralization region. Thermodynamic model is a useful method to study the properties of hydrothermal geofluids, especially for mineral solubility. Pitzer interaction model is one of the most widely used model to calculate the thermodynamic properties of hydrothermal fluids, but few work have ever been carried out to calculate the solubility of sulfate at high temperature and pressure. With Pitzer specific interaction model, using the literature reported density data of Na₂SO₄ and K₂SO₄ solutions at high temperature and pressure, the pressure effect on Pitzer activity coefficient of sulfate and the standard partial molar volume change during sulfate dissolution process were evaluated and related parameters were obtained. The standard partial molar volumes of Na₂SO₄ and K₂SO₄ calculated with these parameters agreed well with those reported in the literature. Combined with the relevant parameters in the literature under saturated vapor pressure, a thermodynamic model for Na₂SO₄ and K₂SO₄ solubility calculation with temperature up to 250 ℃ and pressure up to 40 MPa was developed. The model gave very good agreement with the experimental solubility data. With this model, Na₂SO₄ and K₂SO₄ solubility was calculated at high temperature and pressure. The calculation results showed that pressure had a positive effect on both the average activity coefficient and solubility product of Na₂SO₄ and K₂SO₄, but the solubility of Na₂SO₄ and K₂SO₄ decreased with pressure due to the larger change of the average activity coefficient with pressure. And as the temperature increased, the degree of such reduction became larger. The results herein can provide instructions for the compositional analysis of sulfate fluid inclusions.     

Predicted equilibrium constants for solid and aqueous selenium species to 300 °C: applications to selenium-rich mineral deposits

In this study, an attempt has been made to assess aqueous speciation of selenium and solubility product constants of common selenides at elevated temperatures (up to 300 °C) by using various extrapolation methods. This study predicts that reduced selenium species are dominant species in many geological processes even under relatively oxidized conditions such as those dictated by the magnetite–hematite buffer. On the basis of extrapolated equilibrium constants and solubility product constants for common Se-bearing mineral phases, critical ∑Se/∑S ratios (molal ratios) in mineralizing fluids are proposed for independent selenium mineralization. The minimum ∑Se/∑S ratios in mineralizing fluids for independent selenium mineralization should be at least 10⁻⁶, 10⁻⁵ and 10⁻⁴ at 100, 200 and 300 °C, respectively. For giant independent selenium deposits such as the La'erma and Qiongmo Au–Se deposits in the western Qingling mountains, and Yutangba Se deposits in Hubei Province, China, the mineralizing fluids have reached much higher ∑Se/∑S ratios ranging from 10⁻¹ to 10⁻³ at 200 °C. This study also suggests that the equilibrium assemblage of pyrite–ferroselite among the common ore minerals requires the highest ∑Se/∑S ratios in mineralizing fluids, followed in decreasing order by the assemblages of stibnite–antimonselite, galena–clausthalite, cinnabar–tiemannite, and acanthite/argentite–naumannite. The assemblage of pyrite–ferroselite can also be formed under relatively oxidizing conditions where [∑H₂Se]/[∑H₂S] ratios can be high enough for the formation of independent ferroselite.     

交互四元体系Li~+,Mg~(2+)//SO_4~(2-),B_4O_7~(2-)-H_2O 288K时相平衡研究

采用等温溶解平衡法研究了288K时Li+,Mg2+//SO42-,B4O72--H2O四元体系的固液相平衡关系,测定了该四元体系在288K时平衡液相的溶解度和密度。依据实验测定的平衡溶解度数据及对应的平衡固相,绘制了该四元体系的平衡相图及密度组成图。研究结果表明:交互四元体系Li+,Mg2+//SO42-,B4O27--H2O288K时平衡相图中有2个共饱点,5条单变量曲线,4个结晶区对应的平衡固相分别为Li2B4O7.3H2O,Li2SO4.H2O,MgB4O7.9H2O和MgSO4.7H2O。     

An improved model for the calculation of CO2 solubility in aqueous solutions containing Na, K, Ca, Mg, Cl, and SO4

An improved model is presented for the calculation of the solubility of carbon dioxide in aqueous solutions containing Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, and SO₄²⁻ in a wide temperature–pressure–ionic strength range (from 273 to 533 K, from 0 to 2000 bar, and from 0 to 4.5 molality of salts) with experimental accuracy. The improvements over the previous model [Duan, Z. and Sun, R., 2003. An improved model calculating CO₂ solubility in pure water and aqueous NaCl solutions from 273 to 533K and from 0 to 2000 bar. Chemical Geology, 193: 257–271] include: (1) By developing a non-iterative equation to replace the original equation of state in the calculation of CO₂ fugacity coefficients, the new model is at least twenty times computationally faster and can be easily adapted to numerical reaction-flow simulator for such applications as CO₂ sequestration and (2) By fitting to the new solubility data, the new model improved the accuracy below 288 K from 6% to about 3% of uncertainty but still retains the high accuracy of the original model above 288 K. We comprehensively evaluate all experimental CO₂ solubility data. Compared with these data, this model not only reproduces all the reliable data used for the parameterization but also predicts the data that were not used in the parameterization. In order to facilitate the application to CO₂ sequestration, we also predicted CO₂ solubility in seawater at two-phase coexistence (vapor–liquid or liquid–liquid) and at three-phase coexistence (CO₂ hydrate–liquid water–vapor CO₂ [or liquid CO₂]). The improved model is programmed and can be downloaded from the website http://www.geochem-model.org/programs.htm.     

The Chemical Speciation of Fe(III) in Freshwaters

Dialysis and chemical speciation modelling have been used to calculate activities of Fe³⁺ for a range of UK surface waters of varying chemistry (pH 4.3–8.0; dissolved organic carbon 1.7–40.3 mg l⁻¹) at 283 K. The resulting activities were regressed against pH to give the empirical model: . Predicted Fe³⁺ activities are consistent with a solid–solution equilibrium with hydrous ferric oxide, consistent with some previous studies on Fe(III) solubility in the laboratory. However, as has also sometimes been observed in the laboratory, the slope of the solubility equation is lower than the theoretical value of 3. The empirical model was used to predict concentrations of Fe in dialysates and ultrafiltrates of globally distributed surface and soil/groundwaters. The predictions were improved greatly by the incorporation of a temperature correction for , consistent with the temperature dependence of previously reported hydrous ferric oxide solubility. The empirical model, incorporating temperature effects, may be used to make generic predictions of the ratio of free and complexed Fe(III) to dissolved organic matter in freshwaters. Comparison of such ratios with observed Fe:dissolved organic matter ratios allows an assessment to be made of the amounts of Fe present as Fe(II) or colloidal Fe(III), where no separate measurements have been made. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

含HCI四元水盐体系溶解度预测及其在工艺上的应用：Pitzer混合参数对HCI—MgCI2—H2O体系25℃时溶解度预测的影响

计算了HCl-MgCl2-H2O体系25°C时溶解度以及θ     

Solid-liquid Equilibria for the System KBr–K2SO4–H2O at 348 K

正1 Introduction The underground brine resources distributing widely in Sichuan Basin,China have drawn worldwide attention due to their unusual element abundance and excellent quality.     

Na+, K+, Mg2+//NO3-, Cl-, SO42--H2O体系 25 ℃热力学模型和溶解度预 测Ⅳ:四元体系K+, Mg2+//NO3-, Cl--H2O的Pitzer混合参数及其应用

前三篇文章我们获得并讨论了用于六元体系溶解度计算合理的单独电解质Pitzer参数,及Na+,K+//Cl-,NO3--H2O四元体系混合参数和它们的应用。本文报道对K+,Mg2+//NO3-,SO42--H2O四元体系混合参数的研究及其在体系溶液热力学性质和溶解度预测中的应用。     

锂盐水溶液的热力学性质研究

本文用Ｍｅｉｓｓｎｅｒ公式、Ｂｒｏｍｌｅｙ公式、Ｃｈｅｎ公式、Ｐｉｔｉｅｒ公式及经作者改进的平均球近似（ＭＳＡ）方法对锂盐水溶液（最大浓度达２０ｍｏｌ／ｋｇ）的离子平均活度系数进行了计算和比较，结果表明改进后的ＭＳＡ方法的计算精度最高。另外，本文还应用改进的ＭＳＡ法，使用由单一电解质水溶液离子平均活度系数得到的参数，不用任何混合参数，预测了２９８．１５ｋ时ＬｉＣｌ＋Ｌｉ２ＳＯ４和ＬｉＣｌ＋ＫＣｌ水溶液的等温溶解度图．其结果与文献实验值基本一致。