Synthesis of potassium copper hexacyanoferrate - magnetic hydrogel composite beads for effective cesium adsorption

Abstract

The potassium copper hexacyanoferrate-immobilized magnetic hydrogel bead (HCF-bead) was synthesized via a double cross-linking with $Fe_{3+}$ ions and freeze-thaw for $Cs_+$ adsorption from contaminated environments. The hydrogel was composed of poly(vinyl alcohol) (PVA) and carboxymethyl cellulose (CMC), in which the citric acid functionalized $Fe_3O_4$ was incorporated to facilitate the dispersion of KCuHCF nanoparticles and magnetic separation of the used adsorbent. The HCF-bead can remove moderately high $Cs_+$ up to 69.2 mg/g. Rapid kinetics enables 99% $Cs_+$ uptake within 4 h from the $Cs_+$ solution (10.5 ppm, V/m = 1000 mL/g). Above all, the HCF-bead exhibits remarkable $Cs_+$ sorption performances in terms of selectivity and stability. The adsorbent still maintains its impressive performances even in seawater with considerably high distribution coefficient Kd value of $1.09 \times 104$ mL/g at an extremely low $Cs_+$ concentration (1.05 ppm). Furthermore, the HCF-bead reveals outstanding pH stability with $Cs_+$ removal efficiency >99.5 % across a broad pH range from 4 to 11. The form of bead allows simultaneous application to the continuous column operation and the batch mode operation for magnetic separation after $Cs_+$ removal. From capable and practical perspectives, the HCF-bead is a highly effective and promising adsorbent for the selective removal of $Cs_+$.