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MacArthur-Forrest Process:


(A) Extraction of Gold:
In the Mac Arthur process, solid gold reacts with sodium cyanide to form a soluble gold complex. The impurities are filtered out of the solution and the gold is reduced back to elemental gold with a reactive metal such as zinc.
(B) Extraction of Silver:
Metallic Ag is dissolved from its ore in dilute NaCN solution, and the solute so obtained is treated with scrap Zn when Ag is precipitated. Air is blown into the solution oxidize Na2S. Leaching the metals like silver, gold with CN- is an oxidation reaction
Here Zn act as reducing agent
Leaching has been practiced for many years and often results in the contamination of streams and rivers with cyanide. New alternatives, using the thiosulfate ion (S2O3-) , are being investigated to replace it.
(C) Extraction of Copper:

Different acid, base, and salt solutions are sometimes used to selectively separate out metal-bearing minerals. For example, sulfuric acid is used to separate the copper and iron from the mineral chalcopyrite, CuFeS2, and a sodium chloride solution is used to separate the lead from the insoluble mineral anglesite, PbSO4.

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