EPC alluvial/placer/river gold washing plant

After the gold in cyanide solution is adsorbed by activated carbon, a reversible equilibrium state is established in the cyaniding system between the gold on the surface of gold-loaded carbon and the gold in cyanide solution. The gold-loaded carbon is also in the similar equilibrium state when it is desorbed. When adding CN- or OH- to the desorption system, as these anions are more easily adsorbed by the activated carbon, Au(CN-)2 already adsorbed will be recovered, and the reversible equilibrium of gold adsorption is interrupted and develops adversely against gold adsorption. This is gold desorption. The process of gold desorption is shown as follows:

We can presume that desorption of gold from gold-loaded carbon is essentially trying to destroy the equilibrium of activated carbon adsorption, and causing the process to develop adversely against gold adsorption. Therefore, increasing the cyanide density, increasing alkalinity, raising the temperature, boosting the pressure or adding organic solvent will accelerate desorption of gold from the activated carbon.

Principle of electrolysis

The pregnant solution obtained through desorption of gold-loaded carbon contains gold undoubtedly. The gold contained in pregnant solution can be recovered by electrolytic method. Because no new substance is added into the solution in the process of electrolysis, pure gold sediments can be obtained, which facilitates the further treatment. Therefore, electrolytic method is adopted by most of the gold mines.

Gold exists in the desorbed pregnant solution in the form of Au (CN-) 2. Precipitation of gold, silver and little copper is done by the cathode in the electrolysis process, and so it is with hydrogen due to water deoxidization. Oxygen is separated out by the anode, resulting in ionic oxidation, where carbon dioxide and nitrogen are separated.

Here are the reactions:

Cathode reactions:

Anode reactions:

Reactions of bulk solution:

Technological flow

Used in the following gold CIP/CIL flowchart.

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