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

Abstract

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.

Diverse Secondary Interactions between Ions Exchanged into the Resin Phase and Their Analytical Applications

“…5. 21 The nM values of monovalent ions were substantially equal to those on CG-4×8 (Fig. 2) and were independent of the resin type whether gel or porous.…”

“…1). 21 Quantitative exchange was observed for all QA on CG-1×2 but only for TMA + on CG-4×2 and on CG-4×8. The maximum exchange reached 98% for TEA + and 92% for TPA + on CG-4×2, and 82% for TEA + and 60% for TPA + on CG-4×8.…”

“…2. 21 At this humidity, only strongly bound water molecules remained. The nM values of weakly hydrating ions like K + , Rb + , and Cs + were around 2 on all resins.…”

“…Their performances were compared with those of conventional resins, so as to highlight the diverse secondary interactions shown in Scheme 1. [21][22][23][24] In addition, the earlier studies on the reactions of …”

Synergistic effect of temperature and background counterions on ion-exchange equilibria

“…It has been reported that the number of water molecules hydrated to some ions such as Na + and H 2 PO 4 À decreases with an increase in the ion-exchange capacity and the cross-linking degree and this experimental result can be ascribed to dehydration of the ion by a decrease in the void space for the ions in the ion-exchange resins. [22][23][24][25][26] The difference in the distribution coefficients of alkali metal ions between Naon, MCI GEL CK02A and MCI GEL CK10S may also be attributed to differences in the ion-exchange capacity and crosslinking degree of these resins (Table 1). Since Cs + has relatively large ionic size and its concentration is larger in MCI GEL CK 10S than in CK02A and Naon, the remaining void space should be smaller than in the other two resins.…”