Method for recovering gold and silver in alkaline cyanide heap leaching solution - zinc precipitation
The zinc precipitation process, the Merrill-Claude process, is a very mature and well known technique. For the case where the amount of the leachate is small and the gold concentration is high, it is suitable to use zinc precipitation. The zinc precipitation process typically involves leachate precipitation, degassing, precious metal precipitation, and sediment filtration. The reaction of gold precipitation onto the zinc surface can be expressed by the following formula:
2Au(CN) 2 - +Zn 
2Au+Zn(CN) 4 2-
Zinc consumption is an important consideration when using the zinc powder (silver) precipitation process. The theoretical consumption of zinc by chemical formula should be 0.17 g of Zn∕gAu. In fact, the consumption of zinc varies greatly depending on the chemical nature of the solution. For dilute heap leaching, the zinc consumption per gram of gold precipitated varied from 10 to 30 g. The consumption of excess zinc is mainly due to impurities in the leachate and dissolved oxygen.
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