Development for recovery technology for useful rare metals from seawater by radiation graft nonwoven fabric

Aiming to secure stable energy resources in future, development of an effective recovery system for metals in seawater was attempted using radiological techniques and useful rare metals such as uranium and vanadium were successfully recovered at higher performance. Gamma ray or electron beam was exposed to a felting nonwoven fabric composed of polyethylene fibers and a radical species that allows the initiation of graft polymerization was produced. Then, polymerization of acrylonitryl group and conversion of cyanyl group to amidoxim one became possible. Since the recovery fabric was made of hydrophobic polyethylene, the functional group to contact with seawater was present merely on the side chain produced by graft polymerization. Therefore, this fabric was highly durable to a long-term immersion into seawater. The performance test was made in the test apparatus moored in a region 7 km off the coast of Mutsu in Aomori. The fabric was taken from the system after the immersion for 20 days and the amounts of metals trapped on the fabric were determined. One gram of uranium was collected for 20 days using one kg of the trapping fabric. The concentration of uranium on the fabric was 0.1-0.2%, which was similar to the concentration of uranium ore. The recovery of uranium using the fabric was more than ten times higher than that of the conventional material of hydrous titanium oxide. A high purity of uranium and vanadium powders could be obtained by the present recovery system with the trapping fabric. (M.N.)