Fixed-bed removal of Cs+ from aqueous solutions by microporous silicate ETS-4: Measurement and modeling of loading-regeneration cycles

Abstract

ETS-4 was prepared by hydrothermal synthesis and characterized by powder X-ray diffraction in order to assess its ion exchange capacity towards the removal of Cs+ from aqueous solutions in both batch and fixed-bed operation modes. Several assays were carried out to measure isotherm (8 experiments) and breakthrough curves (5 experiments); a set of loading-regeneration-loading experiments was also performed highlighting the ability of ETS-4 to be used in cyclic ion exchange. Powder X-ray diffraction showed that parent and Cs+-exchanged ETS-4 are isostructural. The Langmuir equation achieved good correlation results (average deviation of 6.58%), while the Nernst-Planck based model proposed for the fixed-bed assays fitted one breakthrough curve with 18.66% error, and was able to predict the remaining four experiments with 9.55% error. The Nernst-Planck parameters are the self-diffusion coefficients of Cs+ and Na+ in ETS-4, whose values (DCs+ = 3.193 x 10(-16) m(2) s(-1) and DNa+ = 6.088 x 10(-15) m(2) s(-1)) are consistent with the microporosity of ETS-4 framework and with the size of the counter ions. (C) 2016 Elsevier B.V. All rights reserved.