EXTRACTION OF CADMIUM AND COPPER USING HOLLOW-FIBER SUPPORTED LIQUID MEMBRANES

Copper, cadmium and lead were extracted through a hollow fiber support ed liquid membrane with Lix 84-i as copper extractant and Alamine 304- i as extractant for cadmium and lead. The mass transfer rate, expresse d as permeability P, was limited by the diffusion through the aqueous stagnant films in the module for copper extraction. A characteristic p ermeability of 6.9x10(-6) ms(-1) was measured at a flow rate of 0.076 m s(-1) through the fibers. The measured permeabilities were compared to generally accepted mass transfer correlations. For a feed flowing o n the tube side, these correlations predicted a three times higher per meability than was measured, while at the shell side, the permeabiliti es predicted from these accepted correlations were up to a factor of 8 lower than the measured ones. The extraction rate of cadmium from chl oride solutions was limited by membrane diffusion. At 0.2 M Alamine 30 4-i, a permeability of 4.10(-6) m s(-1) was measured. Higher extractio n rates were found when cadmium was extracted from chloride-containing mixtures of phosphoric and sulfuric acid. The extraction rate of lead was a factor of 20 lower than that of cadmium. This was due to the fa ct that the extractant had a lower affinity for lead. (C) 1998 Publish ed by Elsevier Science B.V. All rights reserved.