Preparation of phosphoryl-functionalized cycas leaves fiber adsorbent and performance in uranium extraction from seawater

<bold>Background</bold>The uranium reserves in seawater are approximately 4.5 billion tons, but extracting 1 kg of uranium from seawater requires processing about 300 million liters of seawater. Therefore, how to prepare adsorption materials that can maintain high adsorption capacity, long-term stability, and specific selectivity for uranium in the complex seawater environment is an urgent problem to be solved in the field of uranium extraction from seawater.<bold>Purpose</bold>This study aims to prepare a phosphorus-functionalized Cycas Leaves Fiber-PO₄ (P-CLF) with high adsorption performance for uranium in seawater using CLF as raw material.<bold>Methods</bold>The CLF was chemically modified with phosphate to prepare the P-CLF, and the effects of initial pH, temperature, contact time, initial concentration, and adsorbent dosage on the adsorption of uranium from seawater by P-CLF were experimentally investigated. Meanwhile P-CLF was characterized in experiments by Fourier Transform Infrared Spectrometer (FTIR), Scanning Electron Microscope and Energy Dispersive Spectrometer (SEM-EDS), and X-ray Photoelectron Spectroscopy (XPS).<bold>Results</bold>The experimental results show that the optimal pH for P-CLF to adsorb uranium is 5, and the equilibrium adsorption capacity at this pH could reach 1 218.05 mg·g^-1, which is one of the best fiber-based adsorbents known so far. After five adsorption-desorption cycles, the adsorption efficiency and desorption efficiency remain at 90.29% and 87.37%, respectively. When eight high-concentration interfering ions are added, the adsorption efficiency of P-CLF for a 5 mg·L^-1 uranium solution could reach over 99%. Moreover, the adsorption efficiency for simulated seawater with an initial uranium concentration of 5 mg·L^-1 is as high as 97.9%. The results show that a large number of phosphoric acid groups with strong coordination ability are successfully introduced onto the surface of P-CLF. The phosphoric acid groups coordinate with uranyl ions through the P=O bond to form complexes that are adsorbed on the surface of P-CLF.<bold>Conclusions</bold>Results of this study demonstrate that P-CLF has good recyclability and exhibits excellent uranium adsorption performance in high-salt, high-pH, and high-concentration ion interference environments, showing practical application potential in the field of uranium extraction from seawater.