Abstract
The mass transfer performance of confined impinging-jets (CIJs) contactors was investigated for metal separations. In particular, the extraction of uranium(VI) from aqueous nitric acid solutions (3 M) into 30% v/v TBP/Exxsol D80, relevant to spent nuclear fuel reprocessing, was studied for different cell geometries, i.e. main chamber size (D = 2 and 3.2 mm) and jet diameter (dj = 0.25 and 0.5 mm), and different operating conditions, i.e. residence time (τ = 1–9 s), total jet velocity (utot = 2.6–8.6 m/s), and reactor length (L = 7–85 cm). For all conditions investigated, the aqueous phase was the dispersed one. Drop sizes were also measured with high-speed imaging. It was found that the extraction efficiency increased by increasing residence time for a constant total jet velocity regardless of the chamber size. At a constant residence time, higher extraction efficiency was achieved at high total jet velocities, which are associated with larger interfacial areas (smaller drops). The extraction efficiency reached 70% in most of the cases investigated in less than 2 s. In addition, high overall volumetric mass transfer coefficients (up to 1 s−1) were obtained at short residence times. Using regression analysis, a correlation for the overall volumetric mass transfer coefficient was developed from the experimental data with an average deviation of 9%.
Highlights
Impinging-jets contactors, where two liquid streams collide at high velocities, have attracted significant research interest in recent years and have been found to benefit heat and mass transfer applications [1,2,3,4,5]
The mass transfer performance of intensified confined impingingjets (CIJs) contactors was investigated for uranium(VI) separations relevant to spent nuclear fuel reprocessing
Higher extraction efficiency was achieved by increasing the residence time; this increase was almost linear for the first 2 s, whilst as the residence time increased further, the efficiency increased at a slower rate
Summary
Impinging-jets contactors, where two liquid streams collide at high velocities, have attracted significant research interest in recent years and have been found to benefit heat and mass transfer applications [1,2,3,4,5]. Immiscible liquids have been used in either open or confined environments, where the resulting jet is enclosed in a channel. The liquid jets collide in small cells generating high energy dissipation rates within small volumes, which can significantly increase heat and mass transfer rates, and in the case of immiscible liquids, the interfacial areas. The presence of the channel walls can change substantially the flow dynamics during collision and results for constrained and unconstrained streams cannot be directly related to each other. Confined impinging-jets approaches have found applications in crystallization [8,9], nanoparticle synthesis using liquid precipitation [10,11] and micromixing [12,13]
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