Extraction of cadmium and copper using hollow fiber supported liquid membranes

Copper, cadmium and lead were extracted through a hollow fiber supported liquid membrane with Lix 84-i as copper extractant and Alamine 304-i as extractant for cadmium and lead. The mass transfer rate, expressed as permeability P, was limited by the diffusion through the aqueous stagnant films in the module for copper extraction. A characteristic permeability of 6.9 x 10^-6 m s^-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 on the tube side, these correlations predicted a three times higher permeability than was measured, while at the shell side, the permeabilities predicted from these accepted correlations were up to a factor of 8 lower than the measured ones. The extraction rate of cadmium from chloride solutions was limited by membrane diffusion. At 0.2 M Alamine 304-i, a permeability of 4·10^-6 m s^-1 was measured. Higher extraction 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 fact that the extractant had a lower affinity for lead.