Recovery of metals by Donnan dialysis with ion exchange textiles

Donnan Dialysis is an adequate process to recover metals from dilute solutions, however, when the enrichment is needed, the osmosis phenomenon occurs and reduces the efficiency of the operation. Moreover, a lot of ion exchange membranes are so far from the ideal permselectivity. In this work, the combination of ion exchange membranes with an ion exchange textile is used to perform separation – concentration of copper and silver by means of an unconventional Donnan dialysis. The results obtained have shown a great reducing of the osmosis phenomenon and a good yield for the concentration of the metallic ions. Hypotheses about the transfer mechanism through the system composed by ion exchange membranes and the ion exchange textile are emitted. A correlation between the ion hydration and their ability to cross through the proposed system is established.

In this work, it was shown again that the osmosis phenomenon becomes an important inconveniece for classical Donnan dialysis. However, the method can be improved by the combination of ion exchange membranes with a cation exchange textile. The hydrophilic properties of the textile allow decreasing the water flux and enhancing the transfer of ions, which are weakly hydrated. In the case of copper and silver, this hybrid process has improved the selectivity, increased the enrichment factors and it has given rise to a very efficient separation, concentration process applied to two ions, which are often found in the same effluent. Acknowledgments We want to thank Professor Claude Gavach (CNRS Montpellier – France) who has furnished us with the cation exchange textile from the Institute of Textile of France (ITF) and with whom we have collaborate during a long time in the membrane area.