Extraction separation of rhenium(VII) with protic ionic liquids

Okamura, Hiroyuki   ; Kozai, Naofumi   

Technetium-99 is a long-lived anionic radionuclide and is also contained in radioactively contaminated water generated from the Fukushima Daiichi Nuclear Power Plant. However, there are few studies on the development of anion treatment technique compared to that of cation treatment technique. Therefore, it is desired to develop a novel technique capable of separating anionic radionuclides including technetium from an aqueous solution such as radioactively contaminated water with high efficiency. In this study, we focused on a protic ionic liquid ([TOAH][Cl]) consisting of a proton adduct of trioctylamine (TOA) and a chloride ion. The extraction system for perrhenate ion (ReO), which is an analog of technetium, was developed, and the extraction separation characteristics were evaluated. In the organic solvent system using TOA as an extractant, quantitative extraction was achieved only in the acidic region, whereas in the case of using [TOAH][Cl], ReO can be extracted into the ionic liquid phase with an extremely high distribution ratio of 10 or more even in the neutral region, which is the pH of radioactively contaminated water. Thus, it was suggested that the developed ionic liquid extraction system can efficiently separate technetium from neutral aqueous solutions such as radioactively contaminated water.