Recycling of Cr(VI) by membrane solvent extraction:: Long term performance with the mathematical model

This work focuses on the analysis of the long-term performance of a non-dispersive extraction process applied to the separation and concentration of hexavalent chromium contained in ground waters using Aliquat 336 as a extractant. Working with raw ground waters of high Cr(VI) concentration (700 mg/l), the influence of the temperature (20, 40 and 60 degrees C) and the influence of those interferences caused by the presence of competitive anions in the ground waters were studied in discontinuous mode. In continuous mode, the performance of the system for long periods of time was analysed and it was observed that the system is stable since the outlet concentration of Cr(VI) in the ground water and in the back-extraction solution (10-20 g/l) remains constant. Finally, the kinetic model of the separation is included at 40 degrees C and the value of the diffusivity and mass transport constants (K-m = 1.47 x 10(-7) m/s and D = 6.66 x 10(-11) m(2)/s) are calculated using equations from the literature and the values of the extraction equilibrium parameter (0.035) and repart constant in the back-extraction (13) were obtained by a comparison of experimental and simulated data. (c) 2006 Elsevier B.V. All rights reserved.