Cyanide and removal options from effluents in gold mining and metallurgical processes

Cyanide has been widely used as an essential raw material in several industries including textile, plastics, paints, photography, electroplating, agriculture, food, medicine and mining/metallurgy. Because of its high affinity for gold and silver, cyanide is able to selectively leach these metals from ores. Cyanide and cyanide compounds in wastewater streams are regulated. Residues and wastewater streams containing cyanide compounds have to be treated to reduce the concentration of total cyanide and free cyanide below the regulated limits. Natural degradation reactions can render cyanide non-toxic, resulting in carbon dioxide and nitrogen compounds. These natural reactions have been utilised by the mining industry as the most common means of attenuating cyanide. However, the rate of natural degradation is largely dependent on environmental conditions and may not produce an effluent of desirable quality in all cases year round. Technologies that include chemical, biological, electrochemical and photochemical methods have been developed to remove cyanide and cyanide compounds to below the regulated limits in wastewaters. This paper discusses commercially available and emerging methods for removing cyanide from waste streams, particularly from tailings and tailings reclaim waters that are generated in the gold mining processes.