Azone as a Green Extractant for Selective Uranium Recovery over Thorium: Extraction Behavior, Coordination Mechanism, and Comparison with TBP

Abstract

Azone, a commercially available amide compound widely used in pharmaceuticals and cosmetics, was investigated for its potential application in nuclear fuel separation. As a green extractant composed solely of carbon, hydrogen, oxygen, and nitrogen, it leaves no residue upon incineration. A comprehensive investigation was conducted to extract uranium selectively over thorium in nitric acid medium, using Azone as an extractant. The extraction behavior, kinetics, and thermodynamics of Azone were systematically examined and compared with those of tri-n-butyl phosphate (TBP). The results show that Azone in trimethylbenzene achieves uranium U(VI) extraction efficiency comparable to that of TBP, offering a significantly higher separation factor due to its near-zero extraction of Th(IV). Moreover, Azone exhibits favorable physicochemical properties, including higher thermal stability and a lower tendency for third-phase formation compared to TBP. The extraction mechanism was elucidated through UV-Vis titration and single-crystal X-ray diffraction, confirming coordination between the amide carbonyl oxygen and the uranyl ion. In conclusion, Azone represents a highly promising and efficient extractant for U(VI) recovery in thorium-based fuel cycles.