APPLICATION OF EMULSION LIQUID MEMBRANES TO RECOVER COBALT IONS FROM A DUAL-COMPONENT SULFATE-SOLUTION CONTAINING NICKEL IONS

Emulsion liquid membranes (ELMs) containing 2-ethylhexyl phosphonic ac id mono-2-ethylhexyl ester (PC-88A) have been applied to recover cobal t II ions from a dilute sulphate solution containing equal amounts of nickel II ions (0.16 g/l). We focused on the study to develop an effec tive technique to recover cobalt as a target metal. It is found that p olyamine (PX 100) membranes allow better permeation rates of cobalt io ns than sorbitan monooleate (Span 80) membranes. The separation factor (beta(Co/Ni)) in polyamine membranes averaged 70 at a carrier concent ration of 12 mol/m(3) and feed solution pH 5.5. The permeation rate of Co IIwas found to increase proportionately with feed pH while for Ni II it decreased substantially at pH above 5.5 indicative of slower int erfacial reaction rate. We found that short contact time (4-6 min) of feed solution and emulsion improved separation factor (beta(Co/Ni)) at feed pH above 5.5 and also minimized chances of emulsion break up. We have also observed that Span 80 membranes are hydrolyzed readily in a moderate acidic sulphate solution (pH 4.0-5.5) to form viscous gels. Results have shown that excess carrier [(HR)(2)] affects the stability of emulsion and thus the separation factor. The critical ratio of car rier to emulsifier [(HR)2]/[C-sf] was found to be approximately 0.5. T his paper concludes with a discussion on the prospects of ELM system i n practical use. (C) 1998 Elsevier Science B.V, All rights reserved.