Ion-exchange Behaviour

Two factors are of importance and are best discussed separately. First, we need to examine the nature and ionic composition of the metal solutions used to irnpregnate the support and secondly, the nature and concentration 

Let us therefore review in general terms what is known about ionic absorption on surfaces. 

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Studies of the solubility of polonium(IV) in formic, acetic, oxalic and tartaric acids have provided evidence of complex formation,48 with the acetato complex emerging as more stable than the hexachloro anion. Other studies of the solubility of polonium(IV) hydroxide in carbonate49 and nitrate50 solution, together with investigations51 of the ion exchange behaviour of polonium(IV) at high nitrate ion concentration, have been discussed in terms of the formation of anionic complex species. 

Thiocyanate. — On the basis of /-orbital hybridization Diamond [351] predicted the formation of stronger actinide complexes with thiocyanate ion than for the rare earths. Subls and Chopfin [352] have studied the ion exchange behaviour of many actinide and rare earth thiocyanate complexes and have shown that europium is eluted much sooner than americium from Dowex-1 with ammonium thiocyanate. The stability constants for the formation of MSCN2+ and M(SCN)2 complexes for Nd3+, Eus+, Pu3+, Am3+, Cm3+, and Cf34 have been measured [353] and are tabulated in Table 25. It is apparent from the table that the formation... 

Fig. 7. Ion-exchange behaviour of 1 a) Pb, Cu groundwater simulant, and b) Cu and Cd ion removal from the Ringer solution.

Therefore it is important to understand that the weak/strong terminology is generic in referring to the parent acid form of the resin. Equations 4.9-4.13 illustrate the dissociation and ion exchange behaviour of ideal weakly acidic cation exchange resins where a short equilibrium arrow denotes an unfavourable direction of exchange. 

The Ca + ions of CaHAP can be rather readily replaced by other metal ions, so that there have been many studies on the ion-exchange behaviour of CaHAP [16-22]. However, to our knowledge, there seem to be few investigations on the surface structure and nature... 

Dybcz3mski R., Hubicki Z., Kulisa K. Ion exchange behaviour of 23 elements and amphoteric properties of chelating resin Duolite ES 346 containing amidoxime groups. Solvent Extraction and Ion Exchange 1988 6 699-724. 

Wide-line and n.m.r. measurements led to a value of 1.87 A for the H P distance in Zr(HP04)2 values for all other H H distances are also given. The ion-exchange behaviour of ctystalline zirconium phosphates depends on the method of preparation, and the details of the sodium-potassium exchange on this material have been investigated by two groups. The ion-exchange properties of chromium phosphates similarly... 

Comans, R.N.J., Hilton, J., Cremers, A., Bonouvrie, P.A. Smith, J.T. Predicting radiocesium ion-exchange behaviour in freshwater sediments (submitted for publication). 

Both specific adsorption and ion exchange mechanisms may operate to remove lead from solution onto suspended or even settled sediments. The fine fraction of waterborne sediments can show a considerable cation exchange capacity. Hem [27] has applied a theoretical model to the ion exchange behaviour of lead in natural waters, and finds that the proportion of lead associated with sediment depends upon the pH and the cation exchange capacity of the sediment (Fig. 3.7). The cation exchange capacities shown in Fig. 3.7 are probably typical of those for a suspended sediment concentration of somewhere between 1 and 100 mg dmf. These results suggest that a significant proportion of lead in water may be reversibly adsorbed on suspended sediments. 

The Monomer The chemical properties such as the ion exchange behaviour or die ability to undergo hydrophobic interactions arc influenced by die choice of the monomer. For example polyaniline has been shown to be less hydrophobic then polypyrrole (7,8). The electrochemical properties are also affected. Bodi... 

CLEARFIELD, A., STYNES, j.A.,The preparation of crystalhne zirconium phosphate and some observations on its ion exchange behaviour,/. Inorg. Nucl. Chem., 1964, 26,117. 

Origin and Nature of Ion Exchange Behaviour in Molecular Sieves... 

If, therefore, conventional ion exchange remains an important post-synthesis preparative technique, and the materials have in addition major direct applications as ion exchangers, why have the number of fundamental studies decreased It is certainly not because ion exchange behaviour of molecular sieves is sufficiently well understood and predictable to render further fundamental research studies unnecessary. Two causes are su ested to explain this decline ... 

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