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Loaded carbon must be desorbed in order to recover the gold absorbed. There are sev
eral methods that use caustic soda or alcohol working temperatures between 70 to 140 oC. Caustic soda has the advantage of low cost and reduces the time required for desorbing the gold.
A typical stripping solution contains 20-25% by weight of ethylene or propylene glycol and 2% by weight of caustic soda. Sodium cyanide is sometimes added to the solution, but is frequently unnecessary. The solution is heated about 190 oF and pumped through the carbon stripping vessel at a flow rate of about two bed volumes per hour. Gold and silver are recovered from the pregnant solution by electrowinning, and the barren electrolyte solution is reheated and recycled through the stripping vessel. Stripping is typically continued for 24 hours and results in stripped carbon having gold values of less than 3 oz/tc of carbon.
Stripping solution consumption is typically in the range of 20-40 us gal/st of carbon stripped, but this may be reduced via the use of a recovery system. Plant testing has indicated that carbon activity is not adversely impacted by stripping solution.
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