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USE OF ION EXCHANGE RESINS WITH NONAQUEQUS AND MIXED SOLVENTS 0. D. BONNER University of South Carolina, Columbia, South Carolina
A ~ ~ ~many u results G Hof
ion exchange experiments
in aqueous media have been published, there are few
literature references to the use of ion exchangers in nonaqueous media or in mixed solvents. Articles describing the use of synthetic cation or anion exchange resins in nonaqueous or mixed solvents have been published principally within the past five or six years. This review is not intended to be exhaustive but will cover some of the recent developments in the use of synthetic ion exchangers for three types of separations: (1) the separation of ionic substances in nonaqueous or mixed solvents, (2) the separation of nonionic substances in nonaqueous or mixed solutions, and (3) the separation of ionic from nonionic materials in solutions. All data which will be presented were obtained from experiments using the styrenedivinylbenzene copolymer type exchangers with strong acid or strong base exchange sites. Dowex 50 and Amberlite IR-120 have sulfonic acid (RSOs-) exchange sites while Dowex 2 has quaternary ammonium [RN+(CH3)2C2HIOH]exchange sites.
for the exchange of a given pair of ions are greater for resins of higher DVB content. It has been demonstrated further that the values of the salectivity coefficients for exchanges between various ions may be combined into a selectivity scale. Since the lithium ion is the least preferred, the selectivity of the resin for it is taken as unity. This selectivity scale ( 2 ) for the common univalent ions in aqueous solution is shown in Table 1. I t may be noted that the affinity of the resin for the ions is inversely related to their hydrated size. TABLE 1 Selectivity Scale for t h e Removal of Ions from Aqueous Solution by Dowex 50 Resins
4%
I)V R
8% DVR
16%
DV B
ION EXCHANGE IN AQUEOUS SOLUTIOX
As a preface to the discussion of ion exchange in mixed solvents, a review of some results in aqueous media should be of interest. Without regard to solvent, the exchange of univalent ions may be regarded as a metathetical reaction which may he represented by the equation (A+),
+ (B+)i = (A+)
