Transport of zinc complexes through an anion exchange membrane

The transport of zinc complexes ions through an anion exchange membrane was evaluated by the treatment of solutions with and without cyanide. The ionic transport was analyzed as a function of the applied current density and of the cyanide and hydroxyl concentration. Experimental results showed that the ionic transfer in electrodialysis was mainly affected by concentration. There is an ideal molar relationship among the concentration of the cyanide ions, hydroxyl and zinc ions, in solution, in which the zinc transport is maximized. For values above or below this, the transport decreases. Zinc extraction from solution containing CN! was more effective when the current density of 29 mA.cm!2 was applied. The current–voltage curves (CVC) of the anion exchange membrane show that the electrical resistance of the AMV membrane increases with the presence of the zinc–cyanide complex in the solution.

The results presented in this paper allowed us to identify and to relate important parameters that influence the zinc ion complex transport through the AMV anionic membrane. The results also show that zinc extraction by means of electrodialysis is linked to the CN! and OH! concentration in the solutions. The transport in cyanidric media (NaCN) is larger than the transport in alkaline media (NaOH) and in the mixture of these two media (NaOH + NaCN). There is an ideal molar relationship among the concentration of the cyanide, hydroxyl and zinc ions, in the solution. For values above or below this relationship the transport decreases. However, from CVC it can be observed that the solutions with NaCN present a membrane potential larger than the solutions with NaOH. The presence of the zinc ions complex with cyanide increases considerably the membrane potential when compared to the membrane potentials equilibrated without this complex. The results show that electrodialysis can be an alternative to the recovery of the cyanide ions. Changes on the AMV membrane were observed by SEM. The membrane material lost its plasticity with the use, turning into a breakable material.