Donnan dialysis of copper, gold and silver cyanides with various anion exchange membranes

Abstract

Donnan dialysis is an ion exchange membrane process that can be used for the purification and concentration of diluted solutions. In this work, the behaviour of gold, silver and copper in cyanide medium is examined. Flux of cyanide complexes and corresponding free cyanide are determined using five commercial anion exchanger membranes (AMV, ACS, RAI 5035, ADP and ADS). The results show that the rate transfer depends upon the nature of the anion exchanger membrane. It is observed that the species number in the feed solution influences the transfer selectivity of metal ion complex against free cyanide Thus, gold which forms only one stable species with cyanides is transferred faster through an ACS membrane than copper which forms three species. However, this result is not verified when an ADS membrane is used. A model of the complex transfer through anion exchange membranes based on Donnan dialysis is proposed. A three compartment Donnan dialysis is performed to improve the separation between the studied metals. Decyanidation is also examined and separation factors are calculated. It is shown that Donnan dialysis can be an efficient technique for the separation of cyanides complexes of copper, gold and silver when parameters such as anion exchange membrane and the number of compartments are optimised. An advantage of this technique is also the possibility of recycling all reactants with a good impact on the environment.