A method for predicting ion exchange equilibria in ternary ion exchange systems

• Published in: Reactive polymers, ion exchangers, sorbents ion exchangers, sorbents, 1985-01, Vol.3 (3), p.207-215
• Main Authors: Bichkova, Valentina A., Soldatov, Vladimir S.
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Exchange resins and membranes; Forms of application and semi-finished materials; Polymer industry, paints, wood; Technology of polymers
• ISSN: 0167-6989; 1878-3201
• DOI: 10.1016/0167-6989(85)90006-6

A method for computing the ionic composition of an equilibrium phase, either solution or resin, at a given composition of the other has been suggested for multiionic systems. Application of the method requires a knowledge of selectivity coefficients as a function of exchanger phase composition for binary systems. The equivalent fractions of exchangeable ions in the resin or solution have been found by solving a set of equations composed of n−1 equations of selectivity coefficients of pseudobinary equilibria and an equation of mass balance. Knowledge of the dependence of selectivity coefficients of pseudobinary exchanges on resin ionic composition is required for the calculation. It has been found in an analytical form using the theoretical approach suggested in a previous paper [1]. The equations have been tested with five ternary systems exhibiting strong deviations from ideal behaviour (ion exchange equilibria of monovalent ions on highly cross-linked sulfonic resins). Three approximations have been used for theoretical calculations. In the first approximation, the system was treated as ideal (constant selectivity coefficient). In the second case, the function In k j i = f( x j was approximated by straight lines (regular system) situated on the plane In k j i = f( x i , x j ). In the third approximation, a second-power equation valid for irregular statistic systems was used for the function ln k j i = f( x i , x j ). The first approximation was shown to give results on highly cross-linked resins that are in disagreement with the experimental data. On the other hand, the third approximation gave results in excellent agreement with the experimental data.