New Methods To Calculate Activity Coefficients Of Chloride Salt Aqueous Solutions

ABSTRACT:Electrolyte solution can be used as excellent media for many inorganic and organic reactions and has huge potential application in fields like biology, pharmacy, hydrometallurgy, chemistry and chemical engineering, material synthesis, environmental management and energy. Activity coefficient of electrolyte solution is one of the most important parameters in solution thermodynamics and reflects the interaction among ions and solvent molecules, which is of great significance in research on ion salvation, ion association and solution structure. As chloride solutions widely exist in seawater, salt lake and other chemical engineering fields, their thermodynamic properties are prerequisite for understanding component behavior in chloride solutions and guiding practice and exploitation of salt lake efficiently. The primary content in this work is described as follows:(1) Surface tension of the binary systems CoCl2-H2O、NiCl2-H2O、CuCl2-H2O、NaCl-H2O and KCl-H2O have been determined at298.15K and atmospheric pressure in the wide ionic strength by maximum bubble pressure method. Empirical formulas of surface tension as a function of concentration have been constructed for the measured systems by regression. Results show that there is good linear correlation between surface tension and concentration in the experimental concentration range and the linear dependence relation is more rigorous at low concentration.(2) Based on the Gibbs adsorption isotherm and adsorption formula at the gas-liquid interface, the correlation between surface tension and activity with2parameters related to the system temperature and property was derived for the first time. A new model with5parameters to calculate activity coefficient has been proposed and regressed based on experimental values to obtain the5parameters with satisfactory results.(3) In order to test the applicable scope and accuracy of the proposed model, Pitzer model and the model proposed in this work were selected to calculate and compare the activity coefficient of the chosen systems at certain concentration with literature data. Results demonstrate that activity coefficient calculated by Pitzer model agree well with literature data except CuCl2-H2O system. The model in this work can predict the activity coefficient of the binary systems CoCl2-H2O、NiCl2-H2O and NaCl-H2O with good results, which can be concluded that the new model provides a new approach to calculate activity coefficients (or activity) of electrolyte solutions with a relatively high precision by measuring the surface tension. However, large errors exist when the proposed model was adopted to predict the activity coefficient of CUCl2-H2O and KCl-H2O binary systems.(4) Compared with the commonly used isopiestic methods and electromotive force (emf) methods, it is easier to calculate the activity coefficient of solutions by measuring the surface tension with a relatively high precision, which can be applied to engineering fields successfully.