Cs+ ion exchange over lanthanide silicate Eu-AV-20: Experimental measurement and modelling

• Microporous Ln-silicate Eu-AV-20 was used for the first time as ion exchanger.
• Eu-AV-20 was synthesised and characterized by PXRD, PLS, SEM and ICP-MS.
• Equilibrium and kinetic experiments were performed to study the uptake of Cs+.
• Photoluminescent spectrum of Eu-AV-20 is modified by ion exchange with Cs+.
• Ion exchange data was modelled using Langmuir and Maxwell–Stefan equations.

The ion exchange of Cs+ from aqueous solutions was studied using for the first time a microporous lanthanide silicate with photoluminescence properties, Eu-AV-20. It was prepared by hydrothermal synthesis, characterized by SEM, PLS, PXRD and ICP-MS, and several batch ion exchange experiments were performed to measure isotherm and removal curves. Additional curves were measured to evaluate the competition with Na+. The results evidenced the great selectivity of Eu-AV-20 towards Cs+ since cesium removal was slightly modified even for Na+/Cs+ concentrations ratio of 190. The emission photoluminescent spectra of native and Cs+-exchanged Eu-AV-20 were also determined for the first time, and significant modifications were detected, which discloses the potential of Eu-AV-20 for Cs+ sensing purposes.The Langmuir equation provided a good fit to the equilibrium data, with average error of 5.3%, and the Maxwell–Stefan based model adopted to represent the kinetic curves (i.e., concentration versus time) achieved a deviation of 19.0%. An analysis of variance confirmed that the model was statistically significant to represent the uptake curves.The Maxwell–Stefan based model comprises three parameters, namely, the diffusion coefficients associated to the interactions of Cs+ and Eu-AV-20, Na+/K+ and Eu-AV-20, and Cs+ and Na+/K+, whose fitted values were 2.706 × 10−15, 5.713 × 10−15 and 9.446 × 10−17 m2 s−1. Such low values evidenced that the intraparticle mass transport mechanism is surface diffusion. This fact is ascribed to the small pores of the Eu-AV-20 crystal, 5.8 × 6.8 Å, because the counter ions never escape from the force field of the framework co-ions, mainly due to the strong and long range nature of the electrostatic interactions.

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