Voltammetric Investigation on Uranyl Sorption by Alginate Based Material. Influence of Hydrolysis and pH Dependence

Abstract

The removal of U(VI) as uranyl (UO22+) from aqueous solutions was investigated by sorption onto alginate based material. The hydrolysis of uranyl ion was always taken into account in the calculations of free (22UO) ion in aqueous solution, in the experimental pH range considered, as well as the acid-base properties of alginate polymer. The sorption process follows a pseudo-second order kinetic model and the sorption rate decreases when the pH value increases. In addition to the classical Langmuir and Freundlich models, the equilibrium data were fitted by using a modified multi-component equilibrium model, never tested before. Differential Pulse Voltammetry (DPV) and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) measurements were carried out in NaNO3 aqueous solutions for the kinetic and equilibrium studies, respectively. Direct measurements of uranyl by DPV were carried out without using complexing agent, as usually reported in the literature; this allowed us to know the free UO22+ concentration and the hydrolyzed species formed in the ~ 2.0 to 5.0 pH range investigated. The physical structure and morphology of biomaterials was investigated by Scanning Electron Microscopy (SEM) analysis and Energy Dispersive X-ray spectroscopy (EDX) measurements.