Recyclable glutaraldehyde cross-linked polymeric tannin to sequester hexavalent uranium from aqueous solution

Hydrophilicity of tannin limits its adsorbate retention potential. Herein, Acacia nilotica extracted polymeric tannin was immobilized by cross-linking with glutaraldehyde (nomenclature as polytannin glutraldehyde resin, PTGR) to enhance its water stability and tested in the removal of hexavalent uranium, U(VI). Fourier transform infra-red (FT-IR) bands confirmed the presence of phenolic functionalities (characteristic of tannin), while X-ray photoelectron spectroscopy (XPS) peaks at 284.6 and 530 eV showed the presence of C – C/C=C, C – OH, O – C – O, O – H, and. O – C – O functional groups on PTGR. Morphologically, PTGR particles (having an average particle size of 34 nm) were agglomerated with irregular geometry. The appearance of XPS peaks at 381.9 and 393.2 eV (due to U4f) confirmed the adsorption of U(VI), while shifting of FT-IR bands at 1610, 1389, 1100, and 1027 cm−1 to 1679, 1446, 1114 and 1056 cm−1 confirmed the involvement of C – O, C – H, CC groups present on cellulose and hemicellulose in U(VI) binding with PTGR. pH dependent U(VI) adsorption was found. Adsorption kinetics was rapid, accomplishing 60–90% adsorption within 15 min. The adsorption was exothermic. 90.7% of U(VI) adsorbed on PTGR was recovered with 0.1 M hydrochloric acid (HCl), while only 17% loss in PTGR adsorption potential was observed after four consecutive regeneration steps.