Design Of Adsorbents Based On Natural Biomass For Rapid Uranium Extraction From Seawater

To withstand the complex natural environment and ecological system in ocean,the adsorbents with high strength,mass transfer,and antifouling ability are urgently needed for uranium extraction.Polypropylene amidoxime（PAO）adsorbents have been widely studied because of its extremely high adsorption capacity though its mechanical strength and adsorption rate are slow.Herein,instead of the traditional polyacrylamidoxime（PAO）structures,we choose benzamidoxime as the functional ligand to design a small molecule oxime functionalized natural sponge（sponge-oxime）by a two-step process.Furtherly,we design an anti-adhesive adsorbent（Anti-LS/SA）by conjugating functional ligands of salicylaldoxime（SA）and hyaluronic acid（HA）on the micro-channeled biomass via a facile one-step process.The sponge-oxime adsorbent showed good uranium adsorption capacity,and the equilibrium adsorption capacity reached 406 mg-U/g-Ads in uranyl ion aqueous solution with an initial concentration of 32 ppm and p H=6,while adsorption equilibrium time was 6-8hours.In addition,in the presence of many competitive ions,the adsorbent showed strong selectivity.After 7 adsorption-elution cycles,the adsorption capacity of the adsorbent in 8ppm uranium aqueous solution still reached 219 mg-U/g-Ads,where the elution efficiency was 78.68%.The strong effect of functional ligands on uranium was verified by comparative experiments of different samples,and the binding mechanism between the adsorbent and uranyl ions was also analyzed by XPS data.On the premise of ensuring a high adsorption capacity,the sponge-oxime also improved the adsorption rate,and the good mechanical properties of natural sponge also increased the number of recycling of adsorbents and the possibility of uranium adsorption in real seawater.As for Anti-LS/SA,the interconnected microchannels of LS can accelerate the seawater transport,plus the micromolecular uranium-adsorbing ligand,endowing the Anti-LS/SA with very fast uranium adsorption process;the average adsorption rates reach up to 131±1.8 mg g^-1 hour^-1（in the uranium spiked seawater with concentration of 8 ppm）and 0.1176 mg g^-1day^-1（in the natural seawater）in the main adsorption stages,which exceed almost currently oxime-based uranium adsorbents.Owing to the high hydration of HA,the adsorbents exhibit excellent hydrophilicity and anti-bacterial adhesion properties,which are demonstrated by the bacteria adhesion testing.In addition,the Anti-LS/SA displays long service life and very high tensile strength of 62.63 MPa to withstand the strong ocean waves.Kinetics models and XPS data have analyzed its extraction mechanisms.Considering its high efficiencies,structural advantages,as well as the facile and massive construction,we believe the Anti-LS/SA will be a promising candidate for the large-scale uranium extraction from seawater.