Electron spin-echo study on the hydration structure of transition metal ions on cation exchangers

Abstract

Abstract Electron spin-echo modulation studies of paramagnetic transition metal ions, Cu 2+ , Mn 2+ and Cr 3+ , adsorbed on cation exchangers, SiO 2 , TiO 2 and cross-linked polystyrenesulfonic acid, hydrated by D 2 O have been carried out at 4.2 K for elucidating the hydration structure of cations on the exchangers. Analysis of the deuterium electron spin-echo modulation by D 2 O coordinated to the metal ions shows that the hydration numbers are two, four and three for Cu 2+ , Mn 2+ and Cr 3+ , respectively. Comparison of these hydration numbers with those for the fully hydrated metal ions in aqueous solutions indicates that ion associations take place on the exchangers, at least at low temperatures. It is concluded that the adsorption of fully hydrated metal ions of the valency n and the hydration number m , M n+ (H 2 O) m , onto the cation exchangers with the exchange groups Ex-O − is generally expressed by the reaction M n + (H 2 O) m + n (Ex−O − )⇋M n + (H 2 O) m ---(Ex−O) n ⇋M n + (H 2 O) m − n (Ex−O) n ⇋ M n + (H 2 O) m − n (Ex−O) n + n H 2 O .