In one of the stages of the Merrill Crowe circuit in the gold recovery, after clarification and the removal of dissolved oxygen, precipitation with Zinc take place.
In this article we will briefly mention some of the characteristics of this part of the production process in the Merill Crowe plant.
It should be noted that the precipitation of Gold with Zinc, is one of the most widely used methods, since it is simple to operate, has a good efficiency, and once its dynamic equilibrium has been reached in the plants, it requires fewer personnel.
Zinc separates gold from the cyanide solution on an oxide-reduction reaction, since Zinc has a more electronegative potential than Gold, in this reaction Gold gains electrons (it is reduced to metal) and Zinc oxidizes (loses electrons).
This process to be carried out efficiently it is necessary that the greater amount of dissolved oxygen can be removed from the solution, since even very small amounts of oxygen can have a negative effect on precipitation.
As this chemical reaction is of a reducing nature, in the presence of dissolved oxygen the metal can be redissolved, increasing the consumption of zinc due to oxidation, and throwing a low quality precipitate, due to a high concentration of zinc.
Sometimes, in order to increase the efficiency of precipitation, small amounts of lead nitrate or lead acetate are added to the clarified solution (before zinc addiction).
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