Estimation of medium effects on equilibrium constants in moderate and high ionic strength solutions at elevated temperatures by using specific interaction theory (SIT): Interaction coefficients involving Cl, OH- and Ac-up to 200°C and 400 bars

Yongliang Xiong

doi:10.1186/1467-4866-7-4

Yongliang Xiong

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https://doi.org/10.1186/1467-4866-7-4

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Journal: Geochemical Transactions	Publication Date: May 23, 2006
Citations: 19	License type: cc-by

Affiliation: Sandia National Laboratories

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In this study, a series of interaction coefficients of the Brønsted-Guggenheim-Scatchard specific interaction theory (SIT) have been estimated up to 200°C and 400 bars. The interaction coefficients involving Cl- estimated include ε(H+, Cl-), ε(Na+, Cl-), ε(Ag+, Cl-), ε(Na+, AgCl2 -), ε(Mg2+, Cl-), ε(Ca2+, Cl-), ε(Sr2+, Cl-), ε(Ba2+, Cl-), ε(Sm3+, Cl-), ε(Eu3+, Cl-), ε(Gd3+, Cl-), and ε(GdAc2+, Cl-). The interaction coefficients involving OH- estimated include ε(Li+, OH-), ε(K+, OH-), ε(Na+, OH-), ε(Cs+, OH-), ε(Sr2+, OH-), and ε(Ba2+, OH-). In addition, the interaction coefficients of ε(Na+, Ac-) and ε(Ca2+, Ac-) have also been estimated. The bulk of interaction coefficients presented in this study has been evaluated from the mean activity coefficients. A few of them have been estimated from the potentiometric and solubility studies.The above interaction coefficients are tested against both experimental mean activity coefficients and equilibrium quotients. Predicted mean activity coefficients are in satisfactory agreement with experimental data. Predicted equilibrium quotients are in very good agreement with experimental values.Based upon its relatively rapid attainment of equilibrium and the ease of determining magnesium concentrations, this study also proposes that the solubility of brucite can be used as a pH (pcH) buffer/sensor for experimental systems in NaCl solutions up to 200°C by employing the predicted solubility quotients of brucite in conjunction with the dissociation quotients of water and the first hydrolysis quotients of Mg2+, all in NaCl solutions.

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Knowledge of medium effects on thermodynamics in concentrated solutions is fundamentally important to the thermodynamic modeling in many fields ranging from experimental systems in aqueous solutions to hydrothermal ore deposits of the natural systems
As the intent of this study is to provide a framework to treat medium dependence of equilibrium constants at elevated temperatures by using the specific interaction theory (SIT) model, the model verification is focused on testing whether interaction coefficients recommended by this study can pro
The Pitzer formalism is the preferred method in treatment of activity coefficients and other thermodynamic properties with high precision

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Knowledge of medium effects on thermodynamics in concentrated solutions is fundamentally important to the thermodynamic modeling in many fields ranging from experimental systems in aqueous solutions to hydrothermal ore deposits of the natural systems. Mean activity coefficients of SmCl3 solutions with concentrations of SmCl3 from 0.1 m to 1.0 m up to 65°C at 1 bar are reproduced according the temperature dependence relations of the Pitzer parameters from Roy et al [33].

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