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CYANIDE HEAP BIOLOGICAL DETOXIFICATION - PHASE II
BLESS, D. R., P. J. CLARK, AND D. M. JORDAN. CYANIDE HEAP BIOLOGICAL DETOXIFICATION - PHASE II. Presented at Batelle's 9th International in-Situ and On-Site Bioremediation Symposium, Baltimore, MA, May 07 - 10, 2007.
To inform the public.
Many active mine sites, mines in the closure stage and some abandoned mines are and have utilized cyanidation to remove and recover precious metals. Discharges from these sites normally contain significant amounts of metal cyanide complexes and concentrations of thiocyanate, soluble heavy metals and ammonia, nitrate and sulfate. Chemical, physical and biological processes have been developed to attempt to clean up seeps and discharges. Strong oxidants such as hydrogen peroxide, chlorine dioxide, Caros Acid, ozone and sulfur dioxide have shown effectiveness in some applications. Biological processes, alkaline chlorination, reverse osmosis and ion exchange have been effective in removing thiocyanate, cyanides and heavy metals. Typically, biological processes incur lower capital costs at substantially lower operational costs while producing a treated effluent that is compatible with receiving waters and the environment. Environmental health pressures are being brought to bear on the mining companies worldwide. Viable treatment technologies must therefore, be highly efficient in terms of cost and reduction of contaminants to very low concentrations while producing an environmentally benign effluent. In a previous demonstration through the Mine Waste Technology Program (MWTP), Cyanide Heap Biological Detoxification, four biological technologies were evaluated in large-scale column testing as to their effectiveness in reducing cyanide and heavy metals to at or below regulatory limits within an acceptable timeframe and with low operational costs. Phase II of this demonstration (the technology which showed significant reduction of cyanide and heavy metals within 120 days) was emplaced in the fall of 2004 at a cyanide heap leach pad located at the Cortez Mine in Crescent Valley, Nevada. The progress of the heap detoxification was monitored through November of 2005. The results of this demonstration will be presented and discussed.