Total dialysis coefficient

Diffusion dialysis was initially applied in viscose rayon production to recover caustic soda using parchment paper as a membrane. Today the largest industrial utilization of diffusion dialysis is to recover acids or alkalis from waste acids and alkalis using anion or cation exchange membranes. Figure 6.28 shows the principle of diffusion dialysis for acid recovery from waste acid solution. The process and membrane performance are evaluated on the basis of the flux of acids or alkalis (dialysis coefficient) and the ratio of the flux of metal salt to that of acids or alkalis (separation coefficient). The total dialysis coefficient [molh-1 m 2 (moll-1)], Uo, is defined by... 

Table 3.4 shows the dialysis coefficients (Um) and separation coefficients of an anion exchange membrane, NEOSEPTA AFN, for acid recovery in mixed solutions of salts and various acids. Dialysis coefficients of hydrochloric acid and nitric acid are high, which are suitable for recovery by diffusion dialysis. However, results shown in Figure 6.30, Tables 3.4 and Figure 6.7 correspond to Um in Eq. (6.12) and U should be considered in the practical utilization of the membrane. Even though Um of the membrane increases with improvement and modification of the membrane, the total dialysis coefficient, U0, does not always increase due to an increase in Uv... 

The two ion gradients that develop in the dialysis experiment are conveniently quantitated in terms of interaction coefficients. A histogram (Fig. 21. IB) diagrams the ion concentrations in a similar experiment as cartooned in Fig. 21.1 A. The total number of KC1 ion pairs that migrates across the membrane as equilibrium is established, when normalized by the number of RNA molecules present, becomes the interaction coefficient rkci- Another way to find the same number is to count the total number of KC1 ion pairs on each side of the membrane at equilibrium... 

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