Palladium Recycling from Spent Nuclear Fuel: Is Kinetics a Valuable Way to Improve Selective Extraction?

In a few countries, uranium and plutonium are recovered from spent nuclear fuel by the PUREX process. Although already robust, this process still suffers from a few drawbacks, among them the coextraction of some fission products, including Pd(II). Because new extraction steps could hardly integrate the process to remove it beforehand, the transfer kinetics was considered a potential means to enhance the selectivity between Pd(II) and U(VI). Thus, an investigation of mass-transfer kinetics of palladium extraction by 30% - TBP in dodecane from nitrate media was carried out using the single-drop technique in order to better understand the phenomena governing the palladium transfer during the extraction step. Global mass-transfer coefficients for Pd (II) were also compared to reference studies on uranyl nitrate. This article reports the distribution coefficient of Pd (II) extracted from 0 to 3 mol.L−1 HNO3 by TBP, as well as the overall mass-transfer coefficient at 3 mol.L−1 HNO3. The effect of temperature on the kinetics was also measured, leading to the conclusion of a mixed (diffusion and chemistry) regime governing the palladium extraction.