Recovery of uranium from natural seawater by moored adsorption bed packed with fibrous amidoxime adsorbent

A high-performance fibrous adsorbent with amidoxime group was synthesized by using a PAN fiber of 6 denier as the starting material. The activation energy of uranium adsorption was 38 kJ·mol-1, and the intrinsic adsorption rate of uranium from natural seawater at 23.8degC was about 300 mg of uranium per kg of dry fiber per day. The adsorbent was packed in cells of 10-mm thick honeycomb stages backed with a plastic net, and the stages were assembled into a block of 15 cm height. The adsorbent was also packed in spherical shells of 20 mm diam., made of a plastic net, and the balls were packed in a column of 15 cm length. The honeycomb block and packed column were fixed in a cage of 80 cm diam. and 15 cm thickness. Then the cage was moored outside Imari bay for eight hours per day in an experimental period of five days. The amount of adsorbed uranium per unit volume of the bed showed a maximum at an optimum void fraction of the packed bed and was not much changed by the type of beds used. Pitch and roll motions were as effective as the sea current velocity for promoting penetration of seawater through the beds. The price of uranium recovered by the proposed system was estimated as yen 100,000 per kg. (author)