Metals and Equilibria: Extracting Metals Using Carbon

Before extracting a metal from its ore, the ore must first be mined and then processed (concentrated). This involves removing unwanted materials such as soil, rock, and other minerals, followed by heat treatment.
The extraction method depends on the reactivity of the metal. For metals higher than carbon in the reactivity series (like zinc, iron, tin, lead), carbon is used to extract these metals from their ores. This process is called reduction.
Reduction is the loss of oxygen from a substance. In a metal ore, reduction involves removing oxygen from the metal oxide to leave the pure metal. For example, in extracting iron from iron(III) oxide (Fe2O3), the equation would be: Fe2O3 + 3C -> 2Fe + 3CO.
Carbon is an ideal reducing agent for this process as it is more reactive than many metals but less reactive than others. It reacts with the oxygen in the metal oxide to form carbon dioxide, thus removing the oxygen from the metal in the process.
The reduction process is usually conducted in a blast furnace. Here, the carbon in the form of coke (a type of fuel) is burnt with hot air to produce carbon dioxide. This carbon dioxide then reacts with more carbon to produce carbon monoxide. This carbon monoxide then reacts with the metal oxide to produce pure metal.
For metals that are low in the reactivity series (like silver, gold), the reduction process does not require a reducing agent. These metals can simply be heated in the presence of air to remove any excess oxygen.
The extraction process is both cost-effective and energy efficient. However, it also contributes to carbon dioxide emissions, which are harmful to the environment.
It’s important to recycle metals where possible to limit the need for mining and extraction, reducing the environmental impact of these processes.