Other Electromembrane Separation Processes

In addition to the processes discussed so far there are two more electromembrane separation processes in which the driving force is not an externally applied electrical potential but a concentration gradient. The processes are referred to as diffusion dialysis and Donnan dialysis. Diffusion dialysis is utilizing anion- or cation-exchange membranes only to separate acids and bases from mixtures with salts. Donnan dialysis can be used to exchange ions between to solutions separated by an ion-exchange membrane. Both processes have so far gained only limited practical relevance [4] and will not be discussed in this chapter. 

1 Spiegler, K.S. (1956) Electrochemical operations, in Ion-Exchange- Technology (eds F.C. Nachod and J. Schubert), Academic Press, New York. 

2 Wilson, J.R. (ed.) (1960) Demineralization by Electrodialysis, Butterworth Scientific Publications, London. 

3 Schaffer, L.H. and Mintz, M.S. (1966) Electrodialysis, in Principles of Desalination (ed. K.S. Spiegler), Academic Press, 

4 Strathmann, H. (2004) Ion-Exchange Membrane Separation Processes, Elsevier, Amsterdam, The Netherlands. 

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In conclusion, a greater knowledge of the effect of the key controlling parameters of this powerful separation technique, as well as improvement in membrane life time of the currently available commercial electromembranes and reduction in their costs, would ensure further growth beyond desalination and salt production and foster ED applications in the food sector, as well as in the chemical, pharmaceutical, and municipal effluent treatment areas. This will of course need extensive R D studies and will highly likely result in hybrid processes combining ED to other separation techniques, such as NF, IE, and so on, so as to shorten present downstream and refining procedures. 

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