5. Detoxification of effluents and tailings from the cyanide process

Over the last few decades, cyanidation has often come under attack as a polluting process. It is certainly a dangerous process, and in the plant, free cyanides are monitored hourly, both in the circuits and in the effluents and solid discharges. Copper cyanides pose the most acute problems, as they are much more stable than sodium cyanide. Ruptured tailings dams have caused disasters at Omai (Guyana) and Baia Mare (Romania), where copper cyanides spread 2,000 km to the Danube estuary [68]. However, copper (II) in the absence of free cyanide can act as an oxidant, and if sufficient ammonia is added, copper (II) can be stabilized and prevented from reacting with the copper (I) cyanide complex