Experimental connections between aqueous–aqueous and aqueous–ionic liquid biphasic systems

Abstract

Aqueous-ionic liquid (A-IL) biphasic systems containing deuterated water, deuterated nitric acid (10 À2 M to 7 M) and either [C 1 C 4 im + ][Tf 2 N À ], [C 1 C 10 im + ][Tf 2 N À ] or [Me 3 BuN + ][Tf 2 N À ] have been examined in terms of water and acid solubilities in the IL-rich phase and in terms of IL cation and anion solubilities in the waterrich phase. Other experiments focused on the IL cation and anion solubility in the water-rich phase upon addition of either [C 1 C 4 im + ][Cl À ] or [Li + ][Tf 2 N À ]. The results evidence a complex interplay between all negatively and positively charged ions of the samples that could be described following the usual approach used for aqueous-aqueous (A-A) biphasic systems. Other examples from the literature are discussed and demonstrate that the frontier between A-A and A-IL systems is questionable. Predictions are made for the extraction of metallic ions by use of biphasic systems in this work that are successfully compared to literature data.

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

“…[32] In our previous work, [29] our model was built on the assumption that the concentrationso fb oth [Tf 2 N À ]a nd [C 4 mim + ]i ons, which intervene in the two extraction equilibria shown in Equations (3) and (4), N À ]v ariations are strongly dependento nb othT BP and nitric acid concentrations, and that the RTIL cation and anion behave in adifferent way.W e, thus, need to take this fact into accounti no ur new model.Considering the intricate ion exchanges in such biphasic systems, [31,33] we limit ourselves to an empiricalm athematicald escription of the concentration data, by use of ad hoc analytical expressions between [HNO 3 ] = 0a nd 7 m as Equations (7) and (8):…”

“…[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.…”

“…In one of our previous studies, we pinpointed the important mutual solubilities of all components of such systems (water,H + ,m ineral acid counter-anion, and the RTIL cations and anions) showing that both phases could be qualified as "aqueous". [31] Therefore, in the strictest sense, it would be better to name the phases by using the terms "upper phase" and "lower phase". Nevertheless, we will use the terms "aqueous" and "RTIL" phases to refer to the initial phases, prior to mixing, and to the upper and lower phases, respectively,a fter mixing, as commonly delineated in the field.…”

“…[31].I nbrief, an aliquot of the internal standard solution was added to an aliquot of the aqueous phase containing RTIL ions and then the total volume was adjusted with deuterium oxide. Sodium citrate and sodium trifluoroacetate were used as internal standards quantitative for 1 Ha nd 19 FN MR measurements, respectively.N MR spectra were acquired using aB ruker Avance-I 300 MHz spectrometer at 298 K.…”

“…Indeed,[ C n mim][Tf 2 N] has as light, but not negligible, solubility in water compared with organic molecular solvents. [30] During liquid-liquide xtraction, the presence of am ineral acid in the aqueous phase results in as ignificant increase of the aqueouss olubility of the IL;t his solubility is not only dependent on the nature and concentration of the acid, [31,32] buta lso on the RTIL structure. [33] It has also been shown that the introductiono fv ariousn eutral organophosphorus extractantsi nto the IL phase significantly increases the solubility of [C 5 mim][Tf 2 N] in 1 m HNO 3 .…”