Mechanistic study of active transport of silver(I) using sulfur containingnovel carriers across a liquid membrane

This work studies the mechanism of active transport of silver(I) through an immobilized liquid membrane (ILM) containing thiourea derivatives having s ulfur as donor atoms, namely (N-(N',N'-diethyl thiocarbamoyl)N "-phenylbenz amidine (TCBA) and 1,6-diethylcarbamoyl imino)-1,6-diphenyl-2,5 dithiahexan e (TCTH) dissolved in cumene as mobile carrier. An uphill transport model h as been described and equations have been derived taking into account aqueo us boundary layer diffusion and liquid membrane diffusion as simultaneous c ontrolling factors. In the present model, various separate cases were discu ssed using carrier TCBA and TCTH considering the possibility of each chemic al species and evaluating diffusional membrane resistance for lower and hig her concentration of extractants. The diffusion coefficients were observed to decrease with increase in the extractant concentration ranging from 1.0 x 10(-7) to 3.5 x 10(-6) mol cm(-3). Plotting [Ag](0)-[Ag](t) vs, time resu lted in a slope of [L-0]A/Delta(o)V taking into account both complexing spe cies, AgL and AgNO3L, in the membrane. The validity of this model was evalu ated with experimental data and found to be well in agreement with theoreti cal values. The mass transfer coefficient (Delta(a)(-1)), the diffusion coe fficient of the metal carrier species (D-o) and the thickness of the aqueou s boundary layer were calculated from the proposed model for TCBA and TCTH. The mathematical equation was derived to correlate the permeability flux w ith support characteristics such as porosity, tortuosity and thickness. (C) 1999 Elsevier Science B.V. All rights reserved.