The development of a flow injection analysis method for the quantification of free cyanide and copper cyanide complexes in gold leaching solutions

The quantification of free cyanide, Cu(CN)2− and Cu(CN)32−, is essential in investigating the leaching of copper–gold ores in cyanide solutions. A flow injection analysis (FIA) method has been developed for this purpose which utilizes a flow-through electrochemical cell containing silver and platinum electrodes. The basis of this method is that the measured charge due to either silver oxidation or copper reduction at an applied potential is related to the species concentration. A potential of −150 mV was chosen for free cyanide measurement, at which the measured charge due to silver oxidation is related to the free cyanide concentration. While silver oxidation at 100 mV and copper reduction at −650 mV were used for Cu(CN)32− and Cu(CN)2− analysis, respectively. For the solution containing both free cyanide and Cu(CN)32−, a two-step analysis technique was developed for the quantification of each of these species. A pretreatment method was also developed to remove the interference of sulfide ions. The versatility of the FIA method developed in this study is demonstrated by measuring the cyanide species formed during the leaching of both Cu2O and Cu2S in cyanide solutions.