The removal of radioactive strontium ions from aqueous solutions by isotopic exchange using strontium decavanadates and corresponding mixed oxides

Abstract

Two types of strontium decavanadate samples (A and B) were synthesized conductometrically in different pH ranges of 6.7-5.6 and 4.2-3.5, respectively. The samples were used as isotope exchangers after heat treatment at 333, 378 and 573 K for the removal of Sr-90 radionuclide from the aqueous solution which is one of the most important fission products of uranium. The content of crystalline water in the exchangers was determined by thermo-gravimetric analysis (TGA). They were characterized using the X-ray diffraction (XRD), diffuse reflectance infrared Fourier-transforms (DRIFT) and the energy dispersive spectral (EDS) analysis. The SEM micrographs showed that sample A dried at 333 K has an urchin-like structure but it decomposes as annealed at 573 K. Sample B dried at 333 K is composed of quadrangular-prism like micro-rods but nano-sized platelets also formed at 573 K. The time-dependent studies conducted at three different molar ratios of strontium ions in the exchanger to the solution showed that Sr2+ ions completely exchanged at the ratio of 3.5 and 2.0 for the samples A and B annealed at 573 K, respectively. The kinetic data were analyzed using McKay, Nernst Planck, and Paterson's models and correlated to structural characteristics of the exchangers. The Sr-removal capacities of the exchangers evaluated by applying the Langmuir isotherm model increased with the annealing temperature. The results revealed that radioactive Sr2+ ions can be selectively removed by the exchangers annealed at 573 K from real wastewater because the exchange fractions are not significantly affected by the pH changes and the common coexisting cations.