Comparison of liquid membrane processes for the removal of cadmium from wet phosphoric acid

The viability of the cadmium removal from wet phosphoric acid by means of t hree liquid membrane processes (emulsion liquid membranes, supported liquid membranes and non-dispersive solvent extraction) has been demonstrated in previous works where the kinetics of cadmium removal were successfully stud ied [A.I. Alonso, A.M. Urtiaga, S. Zamacona, A. Irabien, I. Ortiz, J. Membr . Sci. 130 (1997) 193; J.A. Daoud, S.A. El-Reefy, H.E Aly, Sep. Sci. Techno l. 33 (1998) 537; T Gallego, E.S. Perez de Ortiz, Separation of cadmium fro m phosphoric acid containing Cu2+ and Cd2+ using surfactant liquid membrane s, in: D.M. Maron, Begell (Ed.), Int. Symp. on Liquid-Liquid Two Phase Flow and Transport Phenomena, Antalya, Turkey, 3-7 November 1997, Begell House, New York, 1998, pp. 301-310]. This work has been focused on the comparison of the three liquid membrane technologies for the removal of Cd, working w ith cadmium initial concentrations in the range of 1.8 x 10(-4)-4.45 x 10(- 3) M and using Cyanex 302 as organic extractant in the concentration range 0.025-0.63 M. The comparison has been made in terms of the values of mass t ransfer flux. The mass transfer models and the corresponding mass transport parameters provided the system tools for the quantitative comparison. By s imulation of the cadmium flux and of the evolution of the cadmium concentra tion with time it was concluded that the rate of Cd removal and the values of mass transfer flux under the studied conditions varied in the order NDSX > ELM > SLM. (C) 2000 Elsevier Science B.V. All rights reserved.