Effects of desilication and dealumination of NaA zeolite on uranium recovery from aqueous effluents

Abstract

Different processes for recovering uranium from raffinates and effluents generated throughout the nuclear fuel cycle are implemented. The adsorption process has been widely adopted in the uranium recovery from aqueous solution, due to its simplicity, rapid kinetics, wide applicability, cost-effectiveness and non-secondary contamination. Adsorption performance is directly determined by the appropriate adsorbents for the target compounds. Zeolite is one of the most commonly used materials for adsorption due to its low cost, high chemical and thermal stability. However, its relatively low sorption capacity limits its performance and feasibility. Many modification strategies have been used to improve its performance. Desilication and dealumination are among the processes that improve accessibility to active sites located inside the zeolite framework and can limit diffusion constraints through the creation of a secondary network of large pores (mesopores) connected to native micropores. In this study, the synthesized and modified NaA zeolite were characterized by powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR) and nitrogen adsorption-desorption analysis. Uranium adsorption capacities were found to be around 42 mg/g, 27 mg/g and 10 mg/g for desilicated NaA, NaA and dealuminated NaA respectively. The desilicated NaA material showed better selectivity compared to the starting material. The adsorption of UO22+ ions follows the Langmuir isotherm and the pseudo-second-order kinetic model. The values of uranium desorption 36%, 82% et 87% for NaA, desilicated NaA and dealuminated NaA have been reached using 1M HNO3 for one treatment cycle. The treatment of the real effluent with the three adsorbents showed a recovery of around 62% in uranium for NaA and desilicated NaA, for dealuminated NaA it was around 19% following the coadsorption of competing metal ions