The separation of nickel and cadmium from highly concentrated solutions by means of non-dispersive solvent extraction (NDSX) has been studied in this work. Extraction and back-extraction processes were carried out simultaneously in a batch mode using two parallel modules and the organic phase flowing in a closed circuit. Starting with concentrations of 0.37 M of Cd and 0.37-0.68 M of Ni in the feed aqueous phase, 1 M of H2SO4 in the back-extraction phase, and using D2EHPA as extractant, the viability of the separation-concentration of Cd from that mixture has been confirmed. Under the experimental conditions, the separation process was run at a constant rate of mass transport, thus leading to a selectivity factor in the concentration step rho=67 mol Cd/mol Ni.