Solvent extraction of U(vi) by task specific ionic liquids bearing phosphoryl groups

Abstract

A novel class of hydrophobic ionic liquids based on quaternary ammonium cation and bearing phosphoryl groups was synthesized. The preliminary results of U(VI) extraction from aqueous solution into the ionic liquid are presented.Room-temperature ionic liquids (RTILs) are promising alternative solvents for organic synthesis, catalysis, electrochemistry and extraction. 1 Among industrial processes, extraction and separation of actinides and lanthanides from nuclear waste is one of the most challenging fields. 2,3 Ionic-liquid phases are suitable reception media for metallic radioactive species in liquid-liquid extraction processes as they show high stability under a and c irradiations 4-6 and enhanced safety towards criticality. 7 However, the partitioning of charged metallic species is limited by the fact that RTILs are usually not effective complexing agents, so the highly hydrated metal ions remain in the aqueous phase. 8 Improvements in the extraction efficiencies have been achieved by adding organic coordinating compounds which significantly increase the distribution ratios of metal ions between the ionic liquid and aqueous phases. 9 For example, Cocalia et al. 10 studied the extraction of U(VI) by dialkylphosphoric or dialkylphosphinic acids from aqueous solutions to the ionic liquid 1-decyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C 10 mim][Tf 2 N] and compared it to extraction into dodecane; partitioning measurements showed comparable patterns of distribution ratios for both the ionic liquid/ aqueous and dodecane/aqueous systems.In the industrial nuclear plutonium uranium extraction process 2 (PUREX) used worldwide, tri-n-butyl phosphate (TBP) is the uranyl extracting agent and is incorporated at 30% in dodecane. Giridhar et al. 11 reported on the extraction of U(VI) by TBP dissolved in RTIL [C 4 mim][PF 6 ] and compared its extraction ability when dissolved either in RTIL or in dodecane. The U(VI) distribution ratios are similar in the range of nitric acid concentration from 0.01 M to 4 M showing the interest of using such solvent. RTILs can be considered as alternative solvents, in replacement of the highly toxic and flammable kerosene mixtures that are used nowadays.Another very promising approach for metal extraction (and many other applications) lies in the concept of task-specific ionic liquids (TSILs). 12,13 These compounds, consisting of extracting entities grafted onto the cation of the ionic liquid, combine the properties of ionic liquids (e.g., non-volatility, non-flammability) with those of conventional extracting compounds. Upon grafting complexing substructures onto the organic cation of RTILs, the resulting TSILs behave both as the organic phase and the extracting agent, suppressing the problems encountered through extractant/solvent miscibility and facilitating species extraction and solvent recovery. Compared to the number of studies on the application of ILs in separations, TSILs have been the focus of relatively few studies. However, it has already been shown that TSILs bea...

Reprocessing of spent nuclear waste using ionic liquids

“…The possibility of using ILs instead of kerosene for extraction of uranium has been investigated. A series of studies were conducted by Giridhar et al for the extraction of uranium (U(VI)) from nitric acid (HNO 3 ) solution using TBP and ILs as diluents with direct electrodeposition of uranium from ILs phase [19][20][21][22][23][24][25] [23]. By using synthesized IL (1.1 M) in tri-n-butylmethyl ammonium bis(trifluoromethanesulphonyl) ([Me 3 NBu][Tf 2 N]), a remarkable distribution ratio for U(VI) (D U(VI) value of 170) was obtained.…”

Insights into the Mechanism of Extraction of Uranium (VI) from Nitric Acid Solution into an Ionic Liquid by using Tri‐n‐butyl phosphate

“…[13][14][15][16][17][18] However, they are expensive solvents and before any industrial applications can be envisioned, it is necessary to evaluate the exact contribution of RTILs compared with the "conventional" extraction systems. To do so, measurement of the extraction efficiency is just the first step.…”

Trialkylammoniododecaborates: Anions for Ionic Liquids with Potassium, Lithium and Protons as Cations

“…Ionic liquids are under serious scrutiny as potential alternative solvents for the separation of radioactive elements for reuse or disposal because their properties can potentially improve process safety and efficiency. [18] The isotope 10 B, present in 20 % natural abundance, has a very high thermal neutron-capture cross-section. Calculations [19] have shown that ionic liquids with sufficiently high natural boron concentrations can be used as nuclear-processing media as they are inherently safe with regards criticality accidents.…”