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Gold + Copper + Cadmium separation

Hi - We have some old cyanide solutions of Gold + Copper + Cadmium (~ 4 g/L gold) from which we would like to recover the precious metal. First we added KOH to increase pH to 14 then we added zinc powder to precipitate gold. After neutralization by chlorhydric acid, we obtain a brown powder we investigated by X-ray fluorescence. The analysis revealed the presence of Gold + Copper + Cadmium. How to separate these three metals to have pure gold powder. Is there a better solution to recover gold from these old cyanide solutions ? Thanks in advance ;)

François Pignon
Plating shop employee - France
February 23, 2009

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February 25, 2009

Heat the metal powder in nitric acid. That will dissolve the Cu and Cd and leave the gold.

In the future, try plating the gold out. Proper manipulation of the current density will leave the Cu and Cd in solution. An additional cyanide add might help.

Dave Wichern
Consultant - The Bronx, New York

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February 26, 2009

Francois

The only practical way to convert old gold solutions into something useful is to contact your supplier of gold salts. They will normally analyse the solution and give you the option of paying cash or returning the gold in the form of pure gold salts.
The supplier will normally retain a small percentage of the gold as payment for the analysis, extraction and conversion.
They should give you the opportunity of agreeing the analysis before deciding.
As you have found, doing the job yourself is not simple and if you succeed, there is always the problem of what to do with the gold.
Trading in gold metal is controlled in most countries and conversion to potassium gold cyanide is even more difficult than extracting pure gold.

Geoff Smith
Hampshire, England