Dialysis Donnan

Donnan dialysis is an ion exchange process in which an ion exchange membrane is placed between two solutions, i.e., the feed (I) and receiver (II) solutions. The membrane is permeable to counter-ions and excludes co-ions. The ionic strength of the feed solution is relatively low compared with that of the receiver electrolyte solution. At equilibrium, if concentrations are used instead of activities, there is the following Donnan relationship, 

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Many related processes use charged membranes and/or EMF. Electrodialytic water dissociation (water splitting), diffusion dialysis, Donnan dialysis, and electrolysis are related processes. Electrowsis (chlorine-caustic) is a process of enormous importance much of which is processed through very special membranes. 

Donnan Dialysis Another nonelectrical process using ED membranes is used to exchange ions between two solutions. The common application is to use H to drive a cation from a dilute compartment to a concentrated one. A schematic is shown in Fig. 20-85. In the right compartment, the pH is 0, thus the H+ concentration is lO higher... 

FIG. 20-85 Schematic of Donnan dialysis using a cation-exchange membrane. 

Nolan A.L., McLaughlin M. J., Mason S.D. Chemical speciation of Zn, Cd, Cu and Pb in pore waters of agricultural and contaminated soils using donnan dialysis. Environ Sci... 

Determination of trace metals in seawater represents one of the most challenging tasks in chemical analysis because the parts per billion (ppb) or sub-ppb levels of analyte are very susceptible to matrix interference from alkali or alkaline-earth metals and their associated counterions. For instance, the alkali metals tend to affect the atomisation and the ionisation equilibrium process in atomic spectroscopy, and the associated counterions such as the chloride ions might be preferentially adsorbed onto the electrode surface to give some undesirable electrochemical side reactions in voltammetric analysis. Thus, most current methods for seawater analysis employ some kind of analyte preconcentration along with matrix rejection techniques. These preconcentration techniques include coprecipitation, solvent extraction, column adsorption, electrodeposition, and Donnan dialysis. 

Also, discussions of a number of applications of Nafion are not included in this document and are, at most, mentioned within the context of a particular study of fundamental properties. A number of these systems are simply proposed rather than in actual commercial applications. Membranes in fuel cells, electrochemical energy storage systems, chlor-alkali cells, water electrolyzers, Donnan dialysis cells, elec-trochromic devices, and sensors, including ion selective electrodes, and the use of these membranes as a strong acid catalyst can be found in the above-mentioned reviews. 

Gulf South Research Institute J. K. Smith RO-Donnan dialysis... 

Concentration Method. The concentration procedure that was developed and evaluated was a RO-Donnan dialysis system (4). The initial objective during method development was to conduct membranescreening tests to evaluate the suitability of various RO and ion-exchange membranes. The four membranes considered for final evaluation on the basis of solute rejection, chlorine stability, and artifact production were the cellulose acetate and FT-30 (Film Tec) RO membranes, the Nafion cation-exchange membrane, and the ION AC MA 3475 anion-exchange membrane. 

Figure 4. Major components of an RO concentration-Donnan dialysis organic recovery system.

Three other processes using ion exchange membranes (Donnan dialysis, diffusion dialysis and piezodialysis) are covered in Chapter 13. 

Now the major application of dialysis is the artificial kidney and, as described in Chapter 12, more than 100 million of these devices are used annually. Apart from this one important application, dialysis has essentially been abandoned as a separation technique, because it relies on diffusion, which is inherently unselec-tive and slow, to achieve a separation. Thus, most potential dialysis separations are better handled by ultrafiltration or electrodialysis, in both of which an outside force and more selective membranes provide better, faster separations. The only three exceptions—Donnan dialysis, diffusion dialysis and piezodialysis—are described in the following sections. 

One dialysis process for which the membrane does have sufficient selectivity to achieve useful separations is Donnan dialysis. If salt solutions are separated by a membrane permeable only to ions of one charge, such as a cation exchange membrane containing fixed negatively charged groups, then distribution of two different cations M+ and N+ across the membrane can be expressed by the Donnan expression... 

Figure 13.3 Illustration of a Donnan dialysis experiment to separate and concentrate uranyl nitrate, U02(N03)2, after Wallace [5]...

Although Donnan dialysis membranes can perform interesting separations, these membranes are a solution to few industrially important applications. Consequently, Donnan dialysis remains a solution in search of a problem. 

Kasthurikrishnan, N. and Koropchak, J.A. (1993) Flow injection donnan dialysis preconcentration of trace metal cations for inductively coupled plasma atomic emission spectrometry. Anal. Chem., 65, 857-862. 

Berggren, D. (1990) Speciation of cadmium(II) using Donnan dialysis and differential-pulse anodic stripping voltammetry in a flow-injection system. Int. J. Environ. Anal. Chem., 41, 133-148. 

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. 

The example shown in Fig. 39 illustrates the treatment of an aluminum anodizing bath waste stream by Donnan dialysis. Sulfate ions and protons freely permeate from a feed stream of aluminum sulfate and sulfuric acid across... 

FIGURE 39 Donnan dialysis application to the separation of sulfuric acid from aluminum sulfate. AI2(S04)3 designated byo and... 

H. Garmes, F. Persin, J. Sadeaur, G. Pourcelly, M. Mountadar, Defluoridation of groundwater by a hybrid process combining adsorption and Donnan dialysis, Desalination 145 (2002) 287-291. 

M. Hichour, F. Persin, J. Sandeaux, C. Gavach, Fluoride removal from waters by Donnan dialysis, Sep. Purif. Technol. 18 (2000) 1-11. 

In Eq. (65), the prime indicates the salt concentration in the reference chamber of the Donnan dialysis experiment with T and P held fixed. 

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