Evaluation of Cs+ and Sr2+ sorption behaviour of synthetic NaA and NaP zeolite modified with graphene oxide

NaP and NaA zeolites are the promising materials for removal of cesium (Cs⁺) and strontium (Sr²⁺) from nuclear waste, and the effective utilisation of these relies on the appropriate modification to enhance their ion exchange properties. In this aim, zeolite (NaZ) containing both NaA and NaP zeolites, and the composite of zeolite and graphene oxide (GO-NaZ), were synthesised by hydrothermal process and characterized by varieties of techniques, like XRD, Raman spectroscopy, scanning electron microscopy (SEM), gas adsorption, and small angle X-ray scattering (SAXS). Presence of both NaP and NaA phases was confirmed from XRD and Raman spectroscopy. SEM, SAXS and gas adsorption studies indicated presence of extensive macropores and rough surfaces in the samples. The sorption behaviours of the samples were studied using solutions of radioactive tracer or inactive ions, and the sorption efficiencies were evaluated by equilibrium and kinetic studies. Equilibrium studies indicated that the composites have higher Cs⁺ exchange capacity than the pristine NaZ. However, opposite trend was observed for Sr²⁺ ions. Kinetic studies revealed that the Sr²⁺ and Cs⁺ uptake follow pseudo-2nd order kinetic model. It was also revealed that GO-NaZ composite shows better selectivity for Cs⁺ over Na⁺ at lower concertation of Cs⁺, and hence it can be a promising material for site decontamination.