2012-02-28_REVISION - M1980244 (78)

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0 013S Ill ioTH 1 SQUAW GULCH VALLEY LEACH FACILITY AND ADR PROCESS DESCRIPTION & DESIGN BASIS 1/25/2012 Page 2 of 3 neutralization tank and returned to the SGVLF in the barren solution. The carbon is then transferred to carbon stripping. CARBON STRIPPING OR ELUTION The loaded carbon is then transferred to a stripping vessel where a pre- treatment solution of hot water, sodium hydroxide and sodium cyanide strips or elutes the gold from the activated carbon. The stripped carbon is then introduced back into the CIC circuit or sent to the carbon regeneration kiln for re- activation. The stripped pregnant solution is pumped to electrowinning cells for further gold recovery. CARBON REGENERATION Stripped carbon is periodically regenerated in the carbon regeneration kiln. In the kiln, the carbon (at a feed rate of approximately 1,250_Ibs per hour) is heated 1,290 °F. In this elevated temperature the micro - cracks and fissures in the activated carbon are cleaned of fine particles and hydrocarbon residue. The exhaust from the kiln is cleaned through a scrubber (and /or carbon infiltration bed). The regenerated carbon is quenched and re- introduced back into the CIC circuit. ELECTROWINNING The stripped gold solution is introduced into electrowinning cells. In the electrowinning cells, an electrical current is passed through an anode submerged in the gold solution. Gold and silver are then plated onto the cathodes in the electrowinning cells. The cathodes are then cleaned and the gold /silver residue is pressure filtered and sent to the existing AGADR refinery for further refining. An electrowinning vent scrubber (and /or carbon infiltration bed) will clean any vapors that escaped the electrowinning cells during operation. BARREN PUMPING After the solution passes through the CIC carbon columns and all of the gold has been adsorbed onto the activated carbon, the solution is now known as barren solution. The barren solution is pumped through filters to remove any small carbon particles and then to a barren solution storage tank. From the barren solution storage tank, the amount of sodium cyanide and pH is adjusted in the solution and the solution is pumped to the SGVLF at a rate of approximately 17,000 gpm where it percolates through the ore material to again become pregnant solution. REAGENTS AT THE SGADR Sodium Cyanide System Sodium cyanide solutions allow the leaching of the gold from the gold ore. The SGADR will have a contained storage and mixing area for the preparation of the sodium cyanide leaching solution. Dry sodium cyanide briquettes are delivered by truck to the site in DOT approved