Ion exchange equilibria between clinoptilolite and aqueous solutions of Na+/Cu2+, Na+/Cd2+ and Na+/Pb2+

Binary ion exchange equilibrium has been studied by the batch technique using the clinoptilolite as cation exchanger. The equilibrium zeolite loading data were generated for Na+ <----> Cu2+, Na+ <----> Cd2+ and Na+ <----> Ph2+ systems. Three different types of equations were used to predict experimental data: Freundlich, Langmuir and the thermodynamic equilibrium models. The last one was applied taking into account the following factors: (i) concentration of ions in solution and zeolite phase, (ii) activity of ions in solution and concentration in zeolite phase, (iii) activity of ions in solution and in zeolite phase. The Pitzer and Bromley models were used to calculate the activity coefficients of the solution phase. Wilson's approach was used to predict activity coefficient in zeolite phase. The results show that the agreement between calculated and real values was increasingly better as the concentrations were replaced by activities. To achieve good prediction of experimental data for binary systems, we may assume ideal behaviour of the zeolite phase, which allows us to reduce the complexity of mathematical calculations. On the other hand, the Wilson binary interaction parameters obtained from the model which considers activity coefficients in both phases can be applied for modeling multi-component systems equilibria. (C) 2003 Elsevier Inc. All rights reserved.