In this chapter the mass transfer during liquid-liquid plug flow in small channels is presented. The extraction of dioxouranium(VI) ions from nitric acid solutions into TBP/IL mixtures (Table 3.2), relevant to spent nuclear fuel reprocessing was investigated. A schematic of the experimental set-up used for the extraction of dioxouranium(VI) ions from nitric acid solutions by TBP dissolved in ionic liquids is depicted in Fig. 3.2 (Sect. 3.4).The effects of initial nitric acid concentration, residence time, flow rate ratio, mixture velocity, and ionic liquid type are discussed. In addition, the effects of scaling up on the mass transfer performance of the extractor are examined. The overall mass transfer coefficients (k L α) obtained for the three different channel sizes varied between 0.049 and 0.312 s −1 . Finally, the possibility of industrial application of the intensified extraction units is discussed.
Extraction of Dioxouranium(VI) at EquilibriumAll equilibrium extractions were carried out at room temperature with 1:1 ionic liquid to aqueous phase ratio. The ionic liquid in its pure state absorbs a small amount of water depending on the initial nitric acid concentration that can vary from 17000 to 25000 ppm for 0.01 to 3 M nitric acid concentration, respectively. In the experiments a solution of 30 % (v/v) TBP in ionic liquids was prepared and equilibrated with the nitric acid solution at the required concentration by mechanical shaking at various time lengths. Saturation was confirmed by measuring the viscosity for both pure and saturated ionic liquid with a digital Rheometer DV-III Ultra (Brookfield). It was found that the ionic liquid was saturated after about 45 min shaking. Then, the two phases were separated and the pre-equilibrated