Synthesis and characterization of amidoxime modified chitosan/bentonite composite for the adsorptive removal and recovery of uranium from seawater.

A novel amidoxime functionalized adsorbent, poly(amidoxime)-grafted-chitosan/bentonite composite [P(AO)-g-CTS/BT] was prepared by in situ intercalative polymerization of acrylonitrile (AN) and 3-hexenedinitrile (3-HDN) onto chitosan/bentonite composite using ethylene glycol dimethacrylate (EGDMA) as cross linking agent and potassium peroxy disulphate (K2S2O8) as free radical initiator. The adsorbent was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS), BET surface area analyser and X-ray photoelectron spectroscopy (XPS). Nitrile groups from two monomers converted to amidoxime groups and therefore, increases the adsorption efficiency of uranium(VI) [U(VI)] from seawater. The optimum pH for U(VI) adsorption was found to be 8.0. The adsorbent dosage of 2.0 g/L was sufficient for the complete removal of U(VI) from seawater. The kinetic data fitted well with pseudo-second-order kinetic model which assumes the presence of chemisorption. The equilibrium attained within 60 min and well agreement of equilibrium data with Langmuir adsorption model confirms monolayer coverage of U(VI) onto P(AO)-g-CTS/BT. The maximum adsorption capacity was found to be 49.09 mg/g. Spent adsorbent was effectively regenerated using 0.1 N HCl. Six cycles of adsorption-desorption experiments were conducted to study the practical applicability and repeated use of the adsorbent. The feasibility of the adsorbent was also tested using natural seawater. The results show that P(AO)-g-CTS/BT is a promising adsorbent for the removal of U(VI) from seawater.