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 (d(j) = 0.25 and 0.5 mm), and different operating conditions, i.e. residence time (tau = 1-9 s), total jet velocity (u(tot) = 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%.