ELECTROMEMBRANE SYSTEMS IN CONDITIONS OF CONCENTRATION POLARIZATION -NEW DEVELOPMENTS IN THE ROTATING MEMBRANE DISK METHOD

The advantages of the rotating membrane disk (RMD) method, which allow s the examination of electromembrane system (EMS) polarization under c onditions of uniform availability of both surfaces of the membrane, ar e shown. To obtain accurate information on the values of membrane pote ntial (and thus on the solution concentration near the membrane surfac es), diffusional relaxation in combination with a RMD has been investi gated. Reversal regimes are studied while using the RMD. To calibrate the cell with flowing solution, an apparatus with a RMD is used. To de termine the selectivity value of ion-exchange membranes under limiting current density conditions, a method is developed whereby the rotatin g membrane allows a constant value of diffusion layers to be preserved . Different kinds of ion-exchange membrane (CMV, AMV, Neosepta, Flemio n, Ionac, Rhone-Poulenc, MC-40, MA-40, MF-4SC) have been studied. it i s found that, under limiting current density conditions, the selectivi ty value P in the majority of the membranes (except the hydrophobic pe rfluorinated membranes Flemion and MF-4SC) is considerably tower than it would be under equilibrium conditions. The effect on membrane selec tivity produced by excess hydrostatic pressure on one side of the memb rane disk is noted.