Case Study: Bacterial Cyanide Detoxification during Closure of the Green Springs Gold Heap Leach Operation

The U.S. Bureau of Mines, U . S . Department of the Interior, demonstrated the viability of using bacterial cyanide oxidation for decommissioning a heap leach operation. The field demonstration was conducted under a CRADA with USMX during the decommissioning of USMX's Green Springs gold operation near Ely, NV. The test objective was to bacterially oxidize the cyanide in the process solution using the carbon adsorption tanks as bioreactors and then to rinse residual cyanide from the spent heaps using the biotreated process solution. 'Results are presented from the initial laboratory tests designed to (1) determine the effectiveness of cyanide -oxidizing bacteria, previously isolated and tested at the SLRC, in Green Springs solutions, (2) determine the cyanide oxidizing potential of the indigenous bacteria, (3) determine the most cost effective nutrient, and (4) simulate actual operating conditions at the site. Results from the field test are presented showing that the bacteria destroyed a portion of the cyanide using the carbon tanks as bioreactors at flow rates of 50 and 300 gal/min. Data indicated that bacterial cyanide oxidation is a function of retention time and nutrient concentration. A flowsheet is presented depicting the circuit. Biohydrmkllwg iad Techdog MS Edited by A.E. Tormo, M L Ape1 and C.L. Brierlay The Minerals, MO~IS d Matetiah Sociev, IO93