Gold Leaching Without Cyanide
Without any doubt sodium cyanide is the best leaching reagent employed for extracting gold from different auriferous ores. It’s well known that cyanide gives acceptable gold recovery, is economical and can be neutralized in other to avoid environmental problems. However, the lack of amenable gold ores and the concern for the environment have motivated the search for new alternative leaching reagents. Probably, the first motivation is the psychological problem when the word cyanide is included in a new gold project.
No matter the existence of many gold operations around the world with detailed procedures respect to cyanide handling, some institutions make some observations to new gold projects and some of them have to be frozen. The right procedures made minimal the impact of cyanide on the environment, but the necessity of new extractive projects is an obligation. Other reason created for new leaching reagents for gold is based in the necessity of improving the leaching rate and reagents such as thiourea, bromine, iodine and thiosulphate have shown better results. Obviously, the application of new leaching reagents has an impact on metallurgy, investment and operative cost. Some of them are positive and others are negative.
Also, the search of new leaching reagents will make possible to treat gold deposits whose first leaching cyanidation tests didn’t give good recoveries. Perhaps, the best example is referred to the treatment of clayey ores which trend to increase the consumption of cyanide in the operation. The leaching of gold from resources, normally low grade ores is due to the low recoveries offered by gravimetric devices such as shaking tables, jigs, spirals or centrifugal devices, since flowsheet include stages to recover gold as soon as can be possible, tails from these stages present low content of precious metals, gold is not in the form of compounds of elements such as selenium. Other condition to leach gold ores is referred to the non-content of graphitic materials.
In general, the search for new leaching reagents is based on toxicity of cyanide during the extractive operation and its effects on the environment. Efforts have done, but the solution has not been obtained yet. There are only potential solutions.