Characterization of Resorcinol–formaldehyde Hydrogel As Adsorbent for Cesium Ion

We evaluated the performance of a resorcinol–formaldehyde (RF) hydrogel as an adsorbent for removing aqueous cesium ions (Cs+), by synthesizing cylindrical pellets of RF gels under different molar ratios (R/C) between resorcinol (R) and sodium carbonate (C) as the catalyst for the sol–gel polycondensation in the range from 2.5 to 400. The RF gel prepared at R/C = 2.5, containing the greatest amount of sodium ion (Na+), had the greatest Cs+ adsorption amount (0.660 mmol g−1), because Cs+ could be adsorbed on the network structure in the gel through exchange with Na+ at an equal molar ratio, but with the smallest effective diffusion coefficient of Cs+ (1.45 × 10–12 m2 s−1). Kinetic analyses based on the Dryden–Kay and intra-particle diffusion models revealed that the diffusivity of Cs+ in the RF gel depended strongly on the density of the network structure, which can be controlled by varying the R/C ratio.