By stirring polyacrylonitrile fibers with a length of 5mm 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 (0.8-1.3cm) and apparent densities (0.1-0.2g/cm
3). 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 (T
s). The shape stability of AO-spheres in 1M NaOH-5% NaCl correlates with the treatment time with 1M hydroxylamine (T
AO); the treatment time with the alkaline solution (T
A1) for the loss of fibers less than 1wt% is less than 24h for AO-spheres obtained with T
AO=2h, less than 16h for those with T
AO=4h,and less than 8h for those with T
AO=8h. Adsorption rates of uranium on AO-spheres from seawater exhibit constant maximums for T
s<5h and decrease with an increase in T
s>5h, due tothe greater difficulty of uranium diffusion into AO-spheres prepared under T
s>5h. The AO-spheres obtained under the condition of T
s=5h, T
AO=8h, and T
A1=8h show the adsorptivity toward uranium in seawater of 0.72mg/g after 21days, which is almost equal to that with nonformed AO-fibers. Uranium on AO-spheres is readily eluted with 1M HCl
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