Potassium cobalthexacyanoferrate–gel beads for cesium removal: kinetics and sorption studies

Abstract

The hydrogel–sorbent composite beads of potassium cobalthexacyanoferrate (KCoHCF) were synthesized for separation of cesium from waste generated in the nuclear industry. Cross-linked sodium alginate, containing PVA, was used as a binding matrix for the synthesis of spherical beads of 2 mm diameter. The characterization of these beads was carried out, using TGA, SEM and BET surface area analysis techniques, which indicated the highly porous and hydrophilic nature of the beads. The sorption of cesium ions onto these synthesized beads was studied, using a radiotracer technique. To determine equilibrium sorption and kinetic parameters for different initial cesium ion concentrations, all the studies were conducted by a batch method. The experimental data were analyzed, using the different sorption isotherms, and found to be described the best by a Langmuir sorption isotherm. The monolayer capacity of KCoHCF–gel beads is found to be 15 mg g⁻¹ of the dry beads. Sorption kinetics data were analysed, using different kinetic models. The results show that the sorption follows pseudo second-order reaction kinetics. The initial sorption rate and the rate constants for the pseudo first-order, pseudo second-order and intraparticle diffusion were evaluated, and discussed for different initial concentrations in the range 1–20 mg L⁻¹. The mechanism of the sorption of cesium ions onto the synthesized beads was also investigated and film diffusion was found to be the rate determining step.