New Amidoxime-Based Material TMP-g-AO for Uranium Adsorption under Seawater Conditions

A novel amidoxime-based adsorbent of titanium-molybdopyrophosphate-g-amidoxime (TMP-g-AO) was prepared by chemical coprecipitation and subsequent chemical modifications. The successful grafting of acrylonitrile group and the subsequent conversion of acrylonitrile group to amidoxime groups were characterized by scanning electron microscopy-energy dispersive spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, N2–BET, and thermal analysis. The adsorption behavior of uranium(VI) on TMP-g-AO was investigated for low concentration uranium solution by batch experiments at a fixed pH of 8.2 ± 0.1. It is found that the adsorption rate of uranium from solution was 99.77% when the uranium concentration was 42.3 μg/L, pH = 8.2 ± 0.1, temperature = 298.15 K, and the adsorbent dosage = 0.05 g. The kinetic data follow the pseudo-second-order model, and adsorption equilibrium data fit the Langmuir model well. The thermodynamics parameters (ΔS, ΔH, and ΔG) indicate that the adsorption process is spontaneous and endothermic. The functional TMP-g-AO adsorbent exhibits good selectivity and affinity for uranium ions under coexisting multimetal ions except for Fe3+ and Co2+. Desorption was performed, and the adsorption rate of uranium by TMP-g-AO only decreased 1.42% after five consecutive adsorption–desorption cycles. In order to evaluate the potential application of TMP-g-AO for uranium extraction from seawater, the experiments on adsorption of uranium(VI) from natural seawater and the uranium-doped seawater were conducted, and the adsorbent exhibited a high adsorption rate of uranium(VI). The results show that TMP-g-AO could be a very promising adsorbent for uranium extraction from seawater.