Extraction of uranium from seawater by polymer-bound macrocyclic hexaketone

Abstract

THE energy crisis means that a petroleum substitute is urgently needed and a promising candidate is nuclear energy. Uranium, however, like petroleum, is distributed in small limited areas. These circumstances could be dramatically improved if uranium in seawater were to be utilised as a resource. Although its concentration is extremely low (3.3 parts per 10⁹), the total amount is huge, calculated at 4–4.5 × 10⁹ tons. We have recently synthesised a macrocyclic hexaketone (I) which is a very strong host of uranyl (UO²⁺₂) ion¹. Its noteworthy characteristics are: (1) six oxygen atoms can be directed towards the inside of the ring, if necessary, to form hexadentate coordination in near coplanarity which corresponds to the crystalline structure of various uranyl salts^2,3. (2) β-Diketone can easily be dissociated in seawater (pK_a is 8.95 for acetylacetone) to form a strong ligand, ketoenolate anion⁴. (3) The bound uranyl ion is readily liberated by the treatment with dilute aqueous acid. Here we report the successful extraction of uranyl ion directly from seawater using polymer-bound macrocyclic hexaketone.