Mössbauer spectra of 57Fe in ion exchange resins

Abstract

Mössbauer spectra have been recorded for different cation exchange resins containing Fe 2+ and Fe 3+ ions. The resins studied are both of the polystyrene sulfonic acid type with varying degrees of crosslinking and of the polyphenol sulfonic acid type. Great care was taken in the preparation of the resins to avoid the formation of iron chloride and hydroxide complexes. The width of the absorption lines was found to be more than three times larger than the width generally observed in crystalline substances. From a discussion of different line-broadening mechanisms it is concluded that the broadening is probably caused by variations in the value of the electric field gradient tensor in the different cationic sites in the noncrystalline lattice. In the case of Fe 3+ ions simulataneous variations in the chemical shift may also contribute to the line broadening. Absorption of water in the resins containine Fe 2+ ions was accompanied by a decrease of the intensity of the Mössbauer absorption. This was interpreted as a “solvation” effect weakening the bond between the ions of opposite charge. The experimental results indicate that at water contents < 6 H 2O per anionic group, the water is mainly adsorbed at the ionic groups in the polystyrene type resins, while in the polyphenolic resin water adsorption probably also occurs at the oxygen bridges in the polymer.