In isolation of which one of the following metals from their ores, the use of cyanide salt is commonly not involved?

Silver is commonly extracted using the MacArthur-Forrest cyanide process. In this method, metallic silver reacts with sodium cyanide in the presence of water and oxygen to form the soluble complex sodium dicyanoargentate. This reaction can be represented as follows: $$ 4Ag + 8NaCN + 2H_2O + O_2 \rightarrow 4Na[Ag(CN)_2] + 4NaOH $$ Once the silver is in solution, zinc dust is added to precipitate pure silver metal, which demonstrates that silver extraction does involve cyanide.

Similarly, gold extraction employs the cyanide process, in which gold metal reacts with sodium cyanide, water, and oxygen to yield sodium dicyanoaurate as the soluble complex: $$ 4Au + 8NaCN + 2H_2O + O_2 \rightarrow 4Na[Au(CN)_2] + 4NaOH $$ The precipitated gold metal is then recovered by adding zinc dust, confirming that gold extraction also involves cyanide.

Although zinc is typically obtained by roasting zinc sulfide ore (ZnS) to zinc oxide followed by carbon reduction, certain hydrometallurgical methods utilize cyanide. In these processes, zinc forms the soluble complex $$[Zn(CN)_4]^{2-}$$, showing that cyanide can participate in zinc extraction under specific conditions.

In contrast, copper extraction does not rely on cyanide. Copper is obtained from ores such as copper pyrite ($$CuFeS_2$$) through a sequence of roasting, smelting with silica flux in a blast furnace, Bessemerisation to produce blister copper, and electrolytic refining to yield pure copper. Because copper(I) cyanide is insoluble, cyanide leaching is unsuitable for copper.

The correct answer is Option D: copper.