Modelization of the transport of silver and copper in acidic thiourea medium through a supported liquid membrane

The facilitated co-transport of silver and copper in acidic thiourea medium through a supported liquid membrane (SLM) made of a flat-sheet polypropylene membrane support containing dibenzo- 18-crown-6 (DB18C6) as a carrier was studied. The permeability factors increased with increasing carrier concentration reaching a limiting value at greater than 1 mM. The calculation of the diffusion coefficients in membranes showed a lower diffusivity of DB18C6 complexes for copper than for silver. Both permeability and diffusion factors increase with the pH of the feed phase reaching a plateau at pH=1. An increase of temperature from 25 to 55°C drastically decreases the permeability and diffusion factors due to an evaporation of the organic phase from the membrane support. The diffusivity was significantly higher using a Celgard 2500 support with respect to Celgard 2400 and 2402 and Accurel PP. A theoretical model, applied elsewhere in the case of Donnan dialysis, has been applied for the first time to the case of facilitated transport, which has permitted evaluation of the effect of the diffusion of the carrier-metal-thiourea complexes inside the membrane support.