Understanding the Extraction Mechanism in Ionic Liquids: UO₂²⁺/HNO₃/TBP/C₄-mimTf₂N as a Case Study

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

“…They are close to those we obtained previouslyf or as imilare xtraction experiment. [29] The shapes of the spectra of Samples Aa nd Ba re different, confirming the extractiono f two different uranyl species in the TBP/RTIL phase as afunction of the initial HNO 3 concentration.M oreover,t heir shape is very different to the one obtained in n-dodecane, which means that the extracted uranyl speciesa re of ad ifferent nature in RTIL and in the molecular solvent. Thus, as previously shown, we can rule out the extractiono fu ranyl in the RTIL as the neutral solvateUO 2 (NO 3 ) 2 (TBP) 2 .…”

“…[31] Those data are compared in Figure 1w ith those obtained by contacting the same aqueous phases with aT BP/RTIL phase ([TBP] = All these data werea cquired in the absence of U VI .A lthough some researchers have shown that large amounts of metal may influence the distribution of all compoundsi nb iphasic systems, [40] we consider our data to be applicable to Ue xtraction, because Uranium distribution coefficients (D U )v alues are identical from U = 10 À2 m down to trace amounts. [25,29] As am atter of fact, our uranyl extraction data published previously [29] were obtained for [UO 2 2 + ] eq,ini = 10 À3 m,w hereas the characterization of extracted species had to be acquired at higher uranium concentrations ([UO 2 2 + ] eq,ini = 10 À3 m), owing to the detectionl imits.…”

“…[29] We have investigated the composition of two RTIL extracted solutions, chosen from this uranium extraction curve.T he first one (Sample A) …”

“…. [29] The best fit of the experimental data is presented as aline. [UO 2 2 + ] = 10 À3 m. To obtain more information,w ec ompared the spectra of the extracteds peciesw itht hose of reference samples containing various ratios of nitrates and TBP (see Figure 5; see Figure S1 in the Supporting Information for spectrao fs amples containing only nitrates).…”

“…At low acid concentrations,b oth groups are in agreement about the extraction of the solvate [UO 2 À by an anion exchange with one RTIL anion at high acid concentrations. [29] However,this study did not consider the effect of TBP on the solubility of the RTIL ions in the aqueous phase during the extraction. Indeed,[ C n mim][Tf 2 N] has as light, but not negligible, solubility in water compared with organic molecular solvents.…”