Effect of thiourea on the facilitated transport of silver and copper usinga crown ether as carrier

Facilitated co-transport of both silver and copper ions in acidic-thiourea medium has been studied. Thiourea can form successive complexes, which are less mobile than the free metal cation. Tn fact, the mass-transport fluxes of both silver and copper ions decrease when the concentration of thiourea in the feed phase increases. The results obtained have been confirmed by th e partition of the different species in the feed aqueous phase Versus the c oncentration of thiourea by means of a conditional calculation which showed that Ag+ and Cu2+ species predominate at very low thiourea concentration ( 10(-5)-10(-4) M) and are substituted by complexes M(Tu)(n)(+) (M = Ag, Cu w ith n = 1-4) with increasing Tu concentration. The fundamental parameters i nfluencing the transport of silver and copper ions have also been determine d: Thiourea concentration in the feed phase, pH of the feed-solution, silve r and copper concentration in the feed phase, crown-ether concentration in the membrane phase and the membrane support characteristics. It was possibl e to take advantage of the different chemical characteristics of Ag+ and Cu 2+ in presence of thiourea. Working in the right conditions the selectivity of the transport (JAg(+)/JCu(2+)) increased from 1.6 to 5.5 with increasin g Tu concentration from zero to 10(-1) M. (C) 2001 Elsevier Science B.V. Al l rights reserved.