How are metals purified after extraction?

Metals are purified after extraction through processes like electrolysis, distillation, or zone refining, depending on the metal's properties.

After metals are extracted from their ores, they often contain impurities that affect their quality and usefulness. Therefore, they need to be purified. The method of purification depends on the metal's properties and the nature of the impurities.

One common method of purification is electrolysis. This process uses an electric current to drive a non-spontaneous chemical reaction. In the case of metal purification, the impure metal is made the anode (positive electrode) in an electrolytic cell. The metal ions are oxidised at the anode and dissolve into the electrolyte. They are then reduced at the cathode (negative electrode), depositing pure metal. This method is often used for metals like copper and aluminium.

Distillation is another method used to purify metals, especially those with low boiling points like zinc and mercury. The impure metal is heated until it vaporises. The vapour is then condensed, leaving behind the impurities.

Zone refining is a method used to purify metals with very high melting points, like silicon and germanium. A small section of the impure metal rod is melted with a circular heater. As the heater is slowly moved along the rod, the impurities move with the molten zone and concentrate at one end of the rod. The rest of the rod is left with pure metal.

In some cases, metals are purified using a combination of these methods. For example, copper is first purified by electrolysis, and then any remaining oxygen is removed by heating in a reducing atmosphere. The choice of purification method depends on the specific requirements of the metal's intended use.