Development of the Adsorbent at the Takasaki Research Laboratory

　Scientists at the Takasaki Research Laboratory are carrying out a research program for radiation graft polymerization as one way to make use of radiation. In this process, a high polymer reacts with other molecules while being bombarded with radioactive rays and some branches are consequently attached to the polymer. Until now, this radiation technology has been applied to the improvement of the diaphragm of a button-type battery, and production of a deodorizer for cleaning air and a highly efficient filter for producing pure water.
　As a part of this research program, research has been conducted to recover heavy metals from seawater. This process used an nonwoven fabric made of polyethylene, graft-polymerized with acrylonitrile under the application of radioactive rays and then, using a reaction with hydroxyamine, introduced to the amidoxime group. It was found that the polymer thus obtained can selectively adsorb particular metals. This method was applied to recovery of rare metals dissolved in seawater in laboratory experiments which found that the polymer can simultaneously adsorb vanadium, uranium, cobalt, and titan. Fig. 1 and Fig. 2(a) show a method for synthesizing the adsorbent and mechanism of adsorbing the metals, respectively. And Fig. 2 (b) shows its pilot model.
　Preliminary adsorption tests were conducted in the sea off the Sekine coast near the JAERI Mutsu Workplace in 1996 and 1997. Adsorption of the rare metals was confirmed by a test conducted in 1996 in which the adsorbent was moored in the sea for 20 to 60 days. After this, the adsorbent was treated with hydrochloric acid to recover the vanadium and uranium. As shown in Fig. 3, the amount of the adsorbed rare metals increased with the duration of mooring.
　In 1997, the equipment shown in Fig. 4 was used to achieve rare metal adsorption. Each 1 to 2 kg of adsorbent (7 to 15 m² wide nonwoven fabric was cut into 15 cm² wide sheets and piled) was enclosed in containers made of wire netting. These were moored in seawater at a depth of 10 to 30m for 20 days. The test was repeated eight times, and 20g of vanadium oxide and 16g of uranium oxide were recovered in all (Fig. 5).