Cyanogenic Plants to Extract Gold: an Alternative for Artisanal MIners

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Worldwide, artisanal gold mining (AGM), in more than 70 countries, involves approximately 16 million people to produce 380-450 tonnes of gold annually. The main method used by these miners is the rudimentary amalgamation technique that consumes 1400 tonnes/a of elemental mercury and increasing. This is the world's largest source of man-made mercury pollution. The main alternative to amalgamation is cyanidation but many miners do not have adequate management skills or capital or even access to cyanide. A change in processing techniques used by artisanal miners implies in education and organization of the miners. Technology alone is not the only response to this dramatic picture of poverty and pollution, but affordable and simple techniques to replace mercury and Improve gold recovery is in the agenda of all International Agencies, Governments, NGOs and academics. If miners learn simple and affordable methods to extract gold with more efficiency than amalgamation (which usually extracts <30% of Au ), definitely they will adopt these techniques. More than 2000 vegetables contain glucosides that can be converted to cyanide by hydrolysis. Bamboo, sorghum and cassava are the main cyanogenic plants extensively cultivated in tropical and subtropical regions. Cassava is the stipple food of more than 0.5 billion people in the world and the accidental consumption of bitter cassava, with more than 2000 mg CN/kg, takes the lives of approximately 2000 people annually and hundreds of thousands suffer a devastating motor neurological damage called "kopnzo" due to the consumption of this cyanogenic root. Using bitter cassava and other cyanogenic plants as a source of cyanide for gold recovery process is a potential option to replace mercury in artisanal gold mines. The preliminary studies at UBC, being conducted with assistance of the Dept of Botany and Faculty of Land and Food Systems, as well as in close collaboration with the EMBRAPA, Brazil, resulted in extractions of 30% of gold from a gold flotation concentrate. There are many gaps in our knowledge about the gold extraction process using glycocyanide. The effect of pH, temperature, time, dissolved oxygen, and other catalysts must be further investigated generating a simple method to extract gold. The idea is to test in the lab the best conditions to extract gold from concentrates using cyanogenic plants and then apply this in a pilot study in the field in Colombia (or other country facing problems with Hg from AGM). A pre-feasibility study will complete the engineer design of a simple plant for cleaner production of gold using local vegetables.