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 m 2 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. Graphic abstract