R. Álvarez, A. Ordóñez, and J. Loredo (Spain)
Gold mining, cyanide, passive treatments, constructed wetlands.
In the gold mining industry, wastes from cyanide leaching processes contain variable quantities of cyanide compounds; as wastes are transferred to a tailings pond for sedimentation and consolidation, the residual solution contains moderate cyanide levels. Most cyanide compounds in tailings ponds are in the free and “weak acid dissociable” (WAD) forms, being the majority of these as copper-cyanide complexes. Taking into account that natural degradation processes in tailing ponds reduce the toxicity of cyanide over time, the named passive systems can be considered as a potentially applicable treatment technology to detoxify leachates with residual cyanide content after the tailings ponds closure. Then, wetland-based passive systems have been experimented at laboratory and field scale at the site of a gold mine in northern Spain. At the laboratory scale, test included static aerobic cells, anaerobic dynamic columns, oxidation cascades and wetland. Average removal rates for Cu and other metals reached values in the range of 90-99%. A pilot scale passive system, constituted by aeration cascades and aerobic and anaerobic cells, has been constructed at the site of the mine. Results suggest that these technologies are able to detoxify leachates with residual cyanide concentrations in about 25% for dissolved cyanide and more than 90% for metals.
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