Thermodynamics of brine-salt equilibria—I. The systems NaCl-KCl-MgCl2-CaCl2-H2O and NaCl-MgSO4-H2O at 25°C |
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Authors: | James R. Wood |
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Affiliation: | The Johns Hopkins University, Baltimore, Maryland 21218, U.S.A. |
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Abstract: | A thermodynamic model for concentrated brines has been developed which is capable of predicting the solubilities of many of the common evaporite minerals in chloro-sulfate brines at 25°C and 1 atm. The model assumes that the behaviour of the mean stoichiometric ionic activity coefficient in mixtures of aqueous electrolytes can be described by the Scatchard deviation function and Harned's Rule. In solutions consisting of one salt and H2O, the activity coefficient is described by the expression where and B? salt specific parameters obtained from data regression. In a mixture of n electrolytes and H2O, B? for the ith component is given by where αij is a (constant) mixing parameter characterizing the interaction of the i and j components and yj is the ionic strength fraction of the jth component. The activity of H2O is obtained from a Gibbs-Duhem integration and does not require any additional parameters or assumptions. In this study, parameters have been obtained for the systems NaCl-KCl-MgCl2-CaCl2-H2O and NaCl-MgSO4-H2O at 25°C and 1 atm. Computed solubility curves and solution compositions predicted for invariant points in these systems agree well with the experimental data. The model is flexible and easily extended to other systems and to higher temperatures. |
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