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

Abstract

Numerous reagents for the elution of metal cyanide complexes from ion exchange resins have been proposed previously. However, a simple and cost-effective elution procedure has not been developed that is able to selectively strip metal cyanide complexes from the resin. The results of the current study 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 that 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 MgCl 2 eluant containing 200 mg/L free cyanide. Gold cyanide and zinc cyanide complexes were not eluted from any of the resins studied. Poor elution of metal cyanide complexes was observed when a concentrated MgSO 4 eluant containing 200 mg/L free cyanide was used. It is proposed that the chloride anion successfully competes with copper cyanide and iron cyanide complexes for active sites on the resin. Furthermore, the stereochemistry and degree of hydration of these complexes facilitate their selective elution by highly saline solutions. It is proposed that a highly saline elution stage followed by a conventional thiocyanate or zinc cyanide elution stage for strong base resins will produce a very simple and efficient elution procedure for the selective recovery of gold cyanide from strong base ion exchange resins. Furthermore, the selective elution procedure allows for the recycling of cyanide that is bound to the copper and iron cyanide complexes.