Effects of the spaces available for cations in strongly acidic cation-exchange resins on the exchange equilibria by quaternary ammonium ions and on the hydration states of metal ions.

The spaces (voids) available for cations in the five exchange resins with varying exchange capacities and cross-linking degrees were estimated, on the basis of the additivity of molar volumes of the constituents. Tetraalkylammonium ions (NR(4)(+); R: Me, Et, Pr) may completely exchange potassium ion on the resin having a larger void radius. In contrast, the ratio of saturated adsorption capacity to exchange capacity of the resin having a smaller void radius decreased with an increase in size of NR(4)(+) ions, due to the interionic contacts. Alkali metal ions could be exchanged quantitatively. While the hydration numbers of K(+), Rb(+), and Cs(+) were independent of the void radius, those of Li(+) and Na(+), especially Na(+), decreased with a decrease in void radius. Interionic contacts between the hydrated ions enhance the dehydration. Multivalent metal ions have the hydration numbers, comparable to or rather greater than those in water. A greater void volume available due to exchange stoichiometry released the interionic contacts and occasionally promoted the involvement of water molecules other than directly bound molecules. The close proximity between ions in the conventional ion-exchange resins having higher exchange capacities may induce varying interactions.

Coadsorption of trivalent metal ions and anions on strongly acidic cation-exchange resins by bridge bonding.

The effects of anions (P(V), P(III), P(I), Se(IV), OH(-), F(-), Cl(-), SCN(-), S(IV), and CH(3)COO(-)) on the adsorption of trivalent metal ions (Fe(3+), Al(3+), Ga(3+), In(3+), and Sc(3+)) to three strongly acidic cation-exchange resins (-S)(-) of different types (porous or gel) and different exchange capacities (4.55, 3.91, and 0.96 mmol g(-1)) were studied systematically. All these metal ions showed coadsorption of OH(-), irrespective of the resins. In contrast, coadsorption of P(V), P(III), P(I), and Se(IV) was observed on the resins of the higher exchange capacities but not on the resin of the lowest exchange capacity. Stoichiometric analyses and spectroscopic (Mossbauer and infrared) studies for Fe(3+) demonstrated the presence of the coadsorbed species: [(-S)(2)Fe(OH)] and [(-S)(2)(Fe-O-Fe)(S-)(2)] for OH(-), [(-S)(2)Fe(HPO(4))Fe(S-)(2)] for P(V), and [(-S)(2)FeX](j) (X(-) = H(2)PO(3)(-), H(2)PO(2)(-), HSeO(3)(-); j > 1) for P(III), P(I), and Se(IV). No coadsorption was observed for the other anions. These findings indicate that the bridge bonding of anions between the metal ions adsorbed on the resins of the higher exchange capacities plays a crucial role for the coadsorption. Some analytical implication was also discussed.