Affinity of Cation-Exchange Membranes Towards Metallic Cations: Application in Continuous Electropermutation

The objective of this work was to correlate the separation process of the metallic cations (M(II)) by electropermutation (EP) of multications solution with the affinity of ion-exchange materials (IEMs). The obtained results show that the affinity order is similar for all tested IEMs and is as follows: Pb(II)>Cd(II)>Zn(II)>Mg(II). Furthermore, the order of the transfer flux (J) of metallic cations obtained with different tested cation-exchange membranes (CEMs) is identical to that encountered for the affinity order. Further analysis of the results demonstrated that the affinity of IEMs and the transfer flux change in reverse order of hydration ionic radius (r) of metallic cations: r_Mg(II)>r_Zn(II)≥r_Cd(II)>r_Pb(II). During the EP, the order of metallic cations transfer is as established previously when using different electro-regeneration cations (H⁺, Na⁺, NH₄⁺) and different co-ions (NO₃^?, Cl^?_, SO₄^2?). However, the extent of the transfer flux as a function of the nature of electro-regeneration cation follows the order: J_M(II)(H⁺)>J_M(II)(NH₄⁺)>J_M(II)(Na⁺). The removal rates of metallic cations vary in the range 89?99%. This work shows that the orders of the IEMs affinity and the transfer are mainly determined by the properties of metallic cations such as the hydration ionic radius. Nevertheless, the importance of the fixation and the transfer of metallic cations depend on the IEMs’ nature.