Alginate polyelectrolyte ionotropic gels

Abstract

The heterogeneous equilibrium for exchange of UO ²⁺₂ counter-ions in uranyl alginate exchange resin by H⁺ ions has been investigated using titrimetric and spectrophotometric techniques. The thermodynamic equilibrium constant was found to be 15.51±0.33 at 25 °C. The electrical conductivity of uranyl alginate in the form of circular discs has been examined as a function of temperature. The Arrhenius plot of log δ versus 1/T showed a complicated behaviour where three regions of conduction were separated by two distinct transition zones. This behaviour was interpreted by the transfer of electrons from alginate to the cross-linked uranyl ion with formation of free radicals and uranium ions of lower oxidation states in a sequence, followed by dimerization of these radicals in the final stages. The X-ray diffraction pattern indicated that the uranyl alginate complex is amorphous in nature. Infrared absorption spectra indicated the presence of UO ²⁺₂ chelated to the alginate macromolecular chains, and displayed γ_a CO ⁻₂ and γ_s CO ⁻₂ in the ranges of 1591 and 1410 cm⁻¹ respectively. Two geometrical structures for chelation of UO ²⁺₂ with the functional groups of alginate macromolecules have been suggested.