What material is commonly used to displace copper from solutions in the extraction process?

In the extraction process of metals, certain materials can react with metal ions in solution, leading to the displacement of the metal. In the case of copper, scrap iron is the most commonly used material for this purpose.

When scrap iron is introduced into a solution containing copper ions, a chemical reaction occurs wherein the iron, being more reactive than copper, displaces the copper from the solution. This process is based on the reactivity series of metals, where less reactive metals can be displaced by more reactive ones. As a result, copper is precipitated out of the solution while the iron goes into solution as iron ions.

This principle of using a more reactive metal to displace a less reactive metal is commonly applied in metallurgical processes, particularly in extraction methods used in the mining and recycling industries. Other options like coal, gold, and aluminum do not effectively perform this function in the context of copper extraction, as they do not share the same level of reactivity necessary for the displacement reaction to occur.