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.

Sheet Metal Stamping

A sheet metal stamping operation is one in which sheet metal is cut and formed into a desired shape or profile. Although a sheet metal stamping process may utilize numerous types of special machines, three basic items are essential: the sheet metal from which the part is to be made; the stamping press; and the stamping die.

With the exception of a specialized sheet metal stamping process commonly referred to as hot stamping, most sheet metal stamping operations involve cold forming. This essentially means that no heat is intentionally introduced into the die or the sheet material. However, keep in mind that although stamping is a cold-forming process, heat is generated. Cutting or forming sheet metal creates friction between the die and the metal-much like the friction and heat that occur when you rub your hands together.