Preparation of spherically formed fibers containing amidoxime groups and their ability to adsorb uranium in seawater

By stirring polyacrylonitrile fibers with a length of 5 mm and a diameter of 5 deniers in a methanolic solution of hydroxylamine, spheres having amidoxime groups (AO-spheres) have successfully been formed. The resulting spheres have well-controlled diameters (0.8-1.3 cm) and apparent densities (0.1-0.2 g/cm3). The yield of AO-spheres depends on the stirring speed, the ratio of the fiber weight to the solution volume, and the fiber length. The water content and apparent density of AO-spheres are affected predominantly by the stirring time (TS). The shape stability of AO-spheres in 1 M NaOH-5% NaCl correlates with the treatment time with 1 M hydroxylamine (TAO); the treatment time with the alkaline solution (TA1) for the loss of fibers less than 1 wt% is less than 24 h for AO-spheres obtained with TAO=2 h, less than 16 h for those with TAO=4 h, and less than 8 h for those with TAO=8 h. Adsorption rates of uranium on AO-spheres from seawater exhibit constant maximums for TS<5 h and decrease with an increase in TS>5 h, due to the greater difficulty of uranium diffusion into AO-spheres prepared under TS>5 h. The AO-spheres obtained under the condition of TS=5 h, TAO=8 h, and TA1=8 h show the adsorptivity toward uranium in seawater of 0.72 mg/g after 21 days, which is almost equal to that with nonformed AO-fibers. Uranium on AO-spheres is readily eluted with 1 M HCl. (author)