A proposed mechanism for nitrate and thiocyanate elution of strong-base ion exchange resins loaded with copper and gold cyanocomplexes

The use of ion exchange resins for the recovery of gold cyanide and other base metal cyanocomplexes has been hindered by poor elution, among other factors. To overcome this drawback, saline solutions have been proposed as an eluant for the loaded cyanocomplexes, with nitrate and thiocyanate being the most promising. In the present work, the elution of gold- and copper-cyanocomplexes from polyacrylic- and polystyrene-based resins at 50 °C was studied. The results showed that copper cyanide was easily eluted from polyacrylic- and polystyrene-based ion exchange resins using either 1 mol/L SCN− or NO3-. However, there was poor elution of the gold cyanide complex from the polystyrene-based resins using nitrate solutions, reflecting the higher affinity that gold cyanide presents for the latter. Conversely, gold elution reached 90% using thiocyanate. Therefore, the separation of gold and copper is possible using polystyrene resins, eluting first with nitrate and then with thiocyanate. Raman spectra have shown the presence of gold and also copper complexes in the resin beads, as well as in the eluate produced during elution of both the resins, suggesting that elution takes place by an ion exchange mechanism. The better performance observed using thiocyanate, as compared to nitrate, is discussed, based on the features of both ions.