The effect of thiourea as a complexing agent on the separation of metallic ions through cation exchange membranes by Donnan dialysis

Donnan dialysis has been investigated in this work in the order to exhibit the influence of the composition of solution on the performance of commercial cation exchange membrane toward metallic ions. Transference fluxes have been determined either as experimental values or calculated according to theoretical models. A good agreement between theoretical and experimental flows has been obtained principally in the case of CMV membrane which presents a lower thickness. It has been demonstrated that addition of thiourea causes an increase of separation properties of membrane. The separation is mainly due to the complex formation between Ag⁺ and Cu⁺ ions and thiourea. Monovalent copper ion is obtained after reduction of Cu²⁺ and oxidation of thiourea and formation of bisulfide of formamidine which constitute a barrier to monovalent complex transference.