1989-10-10_REVISION - M1988112 (12)

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solution to remove calcium carbonate scale and other impurities. In the second step the gold is removed from the carbon using the Zadra elution procedure. Elution or desorption is accomplished by contacting the carbon with a caustic/cyanide solution at elevated temperatures. The vessel is operated under pressure to ensure the desired temperatures. The desorption vessel is operated in closed- circuit with the electrowinning cell. The final step in this process is to reactivate or regenerate the carbon by passing the carbon through a kiln. The regenerated carbon is returned to the adsorption circuit. The gold will be plated from the desorption solution or electrolyte by electrowinning. Electrowinning is an electrolysis procedure that utilizes an insoluble anode. Stainless steel anodes and steel wool cathodes will be used. The gold is plated onto the steel wool cathode. The steel wool cathodes are removed periodically and smelted in a dore furnace. The iron and other impurities are slagged off and a dore bar containing the precious metals is poured. The slurry will be removed from the leach tanks for treatment. Treatment will use sulfuric acid to lower solution pH levels to below 9.0 to promote precipitation of some of the salt and metal levels and to allow liberation and volatilization of the cyanide. The relationship between cyanide and pH is shown on the enclosed Figure 0.5-1. As shown on this figure, approximately 10X of the cyanide can be volatilized by pH control. The reactions will be initiated in an agitated vessel. The pH level will be measured during the treatment process to ensure that the proposed pH levels are achieved prior to disposal. Additional volatization will occur as a result of the proposed thin layer disposal method and the exposure of the beach area to ultraviolet light fora period of time until the next layer is deposited. The mill design will include an internal curbing and collection system within the mill to ensure that in the event of a tank rupture ;~ or leak all solutions are collected and contained within the mill. d=16