Selectivity in heterovalent anion exchange. Ion pairing vs. ion hydration

The values of the selectivity coefficients, K B / A , for heterovalent -2-2exchange with a strong-base resin and radiotracer Re04 ' Cr04 ' and W0 4 vs. -( ) 3-( 3-4-macro Cl , and radi otracer Cr CN 6 ' Co CN) 6 ' and Fe( CN) 6 Y. §.. •• macro CN have been determined.These results show that in such systems, contrary to early ideas on the nature of resin sele<;:tivity, the direction of the exchange is determined by the superior hydration of the ions in the dilute external aqueous phase over that in the resin phase, and not by ion pairing in the latter phase .