Innovative seawater uranium recovery agent based on low-cost polyacrylonitrile fibers

An innovative seawater uranium adsorbent was prepared from the low-cost and commercially-available polyacrylonitrile (PAN) fibers. The optimum condition to synthesize the adsorbent was to irradiate the PAN fibers with 100 kGy gamma ray, amidoximate in 3 (w/v)% hydroxylamine hydrochloride solution for 75 min at 75 °C, yielding the PAN nitrile group conversion of approximately 60%. At 100 kGy, the degree of crystallinity of the irradiated fibers was also highest at 79.1%. The performances of the adsorbent in seawater samples were excellent. By submersion in the seawater sample spiked with 250 ppb of uranium for 4 weeks, the prepared fibers exhibited the adsorption capacity of 32.28 mg/g adsorbent. By submersion in seawater samples spiked with 76.5 ppm of uranium for 1 week and 945 ppm of uranium for up to 4 weeks, the fibers exhibited the adsorption capacities of 111.25 and 200.07 mg/g adsorbent, respectively. The adsorbent showed a uranium adsorption capacity of 0.11 mg/g adsorbent for 8 weeks of soaking in brine concentrate from a seawater reverse osmosis plant. The kinetics of seawater absorption by the adsorbent was quite rapid, reaching the equilibrium swelling ratio of approximately 300% in 5 min or less. Another important finding was that the prepared PAN fibers exhibit the characteristics of a superabsorbent material (equilibrium swelling ratio in DI water of 5,550%). The low cost and the ease of preparation of the fibers offer a novel environmental remediation process to adsorb uranium ions released into seawater following a nuclear accident.