DETERMINATION OF THE PARAMETERS OF THE HOGFELDT MODEL FOR THE NITRATE-CHLORIDE ION-EXCHANGE ON DIFFERENT RESINS AND IN DIFFERENT MEDIA - VARIATION WITH THE WATER ACTIVITY OF THE SOLUTION

The Hogfeldt three-parameter model has been applied to nitrate-chlorid e ion exchange in diluted and in concentrated solutions. The three par ameters of the model have been calculated and their variation with the water activity of the solution, the crosslinking degree of the resin, and the nature of the co-ion (Li+, Na+, K+, and NH4+) has been determ ined. For a given resin and a given co-ion the results show that the H ogfeldt model can be applied to ion-exchange data in concentrated solu tions only if the variation of the parameters with the water activity of the solution is taken into account.