Activated Carbon for Gold Recovery
It has been widely known that activated carbon can be use to adsorb gold from cyanide leach solutions but activated carbon, as a media for recovery of gold, did not gain wide acceptance in the gold industry until the 1970's, with the requirement of heap leaching for vast quantities of low grade gold ores.
It is now the most common method used for the recovery of gold from a cyanide leach solution.
GOLD RECOVERY METHODS
Gold Recovery from cyanide leach solutions can be done by three main methods, Carbon in Pulp (CIP), Carbon in Leach (CIL) and Carbon Columns in which CIP and CIL are nearly same technique.
CIL and CIP are continuous processes where activated carbon can be use in a cascade of large agitated tanks (as mentioned in below figure). The main difference between CIL and CIP processes is that in CIP, leaching and adsorption occur simultaneously where as in CIL, leaching and adsorption done at the same time. CIL is being used when organic present in the ore is high.
In CIP, Activated carbon is mixed with the cyanide leach solution and ore in the leach tanks while the gold is being dissolved. This process ensure fast interface between the carbon and the gold loaded cyanide solution. The carbon is then removed by screening allowing the liquid and finely ground ore to pass through easily and retaining carbon on the screen.
Because of this, Hardness of activated carbon is very much important factor. If activated carbon has low hardness then it will be cracked during agitation process and small particles of activated carbon containing gold will wash through with liquid and ore and this will be loss of precious metal.
The CIP method is only used when tank leaching is utilized for the recovery of gold from the ores and this is not the case with most large gold mines today, since heap leaching is the lowest cost method for recovering gold from ores containing from a few grams to 5 or 6 grams per ton.
Occasionally, carbon columns will be used with tank leaching operations, also, especially if the mine has a dual leach system, heap leach of low grade and tank leach of high grade.
Carbon columns consist of large columns charged with activated carbon. The pregnant cyanide solution flows through the carbon columns, which are generally situated in step fashion, so that the overflow from the highest column will gravity flow to the next column, alleviating the requirement for pumping. The gold adsorbs onto the surface of the carbon. The loaded carbon is periodically removed from the columns, and sent to the stripping circuit.
The stripping circuit is generally subjected to a heated solution (90 deg to 120 deg C) of (1%) sodium hydroxide and (0.1%) cyanide and the gold is re-dissolved and removed from the carbon surface. At this point, the sodium hydroxide / cyanide solution is sent to electro winning cells, where the gold is plated onto stainless steel cathodes. The gold is removed from the cathodes by either using a high pressure water spray, sometimes shaking the cathode, and in some cases, the stainless steel cathode is placed into a melting furnace and heated to 1100 deg C, to melt the gold from the cathode and most will wash the gold "sponge" from the cathodes. The fine, powdered gold is then melted and poured into dore bars.
Having in-depth knowledge of Gold Recovery process, we have specifically manufactured Puraqua CNB AuM and Puraqua CNB AuH range of activated carbon for Gold recovery process. They exhibit very high hardness (min. 98%) with very less platelet content (max. 3%). They also represent excellent gold loading and gold adsorption capacity.
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