THEORETICAL-ANALYSIS OF NEUTRALIZATION DIALYSIS IN THE 3-COMPARTMENT MEMBRANE CELL

A theoretical model of the kinetics of neutralization dialysis across ideally selective ion exchange membranes is suggested. The model is ba sed on the use of the Nernst-Planck equations describing ion transport through both the membranes and adjacent unstirred layers (ULs) of sol ution. Special emphasis is made on the kinetics of change in pH of the desalinated solution. The character of this change with time is shown to depend essentially on the solution concentration. At sufficiently high concentration of the solutions in the three compartments, the pre sence of the ULs can be neglected in the model, and the pH value in th e desalination compartment is determined only by the relationship betw een the intrinsic permeabilities of the membranes. In this case, the m odel predicts the pH to be in either the acidic or the alkaline range of values during most of the desalination experiment, so that the pass age of the pH through neutrality, if it occurs at all, is ''leaplike'' . In contrast, in solutions of sufficiently low concentration,, the ex change of counterions between the compartments is controlled by mass t ransfer through the ULs. For this limiting case, a rigorous relationsh ip linking the concentrations in the three compartments is derived und er which the pH of the desalinated solution assumes the neutral value. Finally, at intermediate concentration of the solutions, the model is found to describe satisfactorily the data of auxiliary experiments wi th appropriate choice of parameters.