Selective elution of copper and iron cyanide complexes from ion exchange resins using saline solutions

Numerous reagents for the elution of metal cyanide complexes from ion excha nge resins have been proposed previously. However, a simple and cost-effect ive elution procedure has not been developed that is able to selectively st rip metal cyanide complexes from the resin. The results of the current stud y show that highly saline solutions can be used to selectively elute copper cyanide and iron cyanide complexes from a variety of anion exchange resins containing different quaternary ammonium functional groups. It was found t hat for most resins an elution efficiency of greater than 80% copper and 99 % iron was achieved within 12 bed volumes (BV) of a concentrated KCl or MgC l2 eluant containing 200 mg/L free cyanide. Gold cyanide and zinc cyanide c omplexes were not eluted from any of the resins studied. Poor elution of me tal cyanide complexes was observed when a concentrated MgSO4 eluant contain ing 200 mg/L free cyanide was used. It is proposed that the chloride anion successfully competes with copper cyanide and iron cyanide complexes for ac tive sites on the resin. Furthermore, the stereochemistry and degree of hyd ration of these complexes facilitate their selective elution by highly sali ne solutions. It is proposed that a highly saline elution stage followed by a conventional thiocyanate or zinc cyanide elution stage for strong base r esins will produce a very simple and efficient elution procedure for the se lective recovery of gold cyanide from strong base ion exchange resins. Furt hermore, the selective elution procedure allows for the recycling of cyanid e that is bound to the copper and iron cyanide complexes. (C) 2000 Elsevier Science B.V. All rights reserved.