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

Donnan dialysis is anion exchange membrane process that can be used for the purification and concentration of diluted solutions. In this work, the beh aviour of gold, silver and copper in cyanide medium is examined. Flux of cy anide complexes and corresponding free cyanide are determined using five co mmercial anion exchanger membranes (AMV, ACS, RAI 5035, ADP and ADS). The r esults show that the rate transfer depends upon the nature of the anion exc hanger membrane. It is observed that the species number in the feed solutio n influences the transfer selectivity of metal ion complex against free cya nide Thus, gold which forms only one stable species with cyanides is transf erred 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 d ialysis is proposed. A three compartment Donnan dialysis is performed to im prove the separation between the studied metals. Decyanidation is also exam ined and separation factors are calculated. It is shown that Donnan dialysi s can be an efficient technique for the separation of cyanides complexes of copper, gold and silver when parameters such as anion exchange membrane an d the number of compartments are optimised. An advantage of this technique is also the possibility of recycling all reactants with a good impact on th e environment. (C) 2000 Elsevier Science B.V. All rights reserved.