How is electrolysis used in the purification of copper?

Electrolysis is used in the purification of copper by separating impure copper from its impurities using an electric current.

In the process of electrolysis for copper purification, an electric current is passed through a solution called an electrolyte. This electrolyte is usually copper (II) sulphate solution. The impure copper is made the anode (positive electrode) and a strip of pure copper is made the cathode (negative electrode). When the electric current is switched on, copper ions are dissolved at the anode, migrate towards the cathode and are deposited as pure copper.

The impurities in the copper anode, often silver and gold, fall to the bottom of the electrolysis tank as a sludge, leaving the copper ions free to migrate. This is because the impurities are less reactive than copper and do not dissolve in the electrolyte solution. They are often collected and used for other purposes due to their value.

The copper ions that migrate are positively charged and are attracted to the negatively charged cathode. Here, they gain electrons and are reduced to form pure copper atoms which are deposited on the cathode. The reaction at the cathode can be represented as Cu2+ + 2e- → Cu. This means that for every copper ion, two electrons are needed for it to be reduced to a copper atom.

The process continues until all the impure copper at the anode has been transferred to the cathode. The result is a layer of highly pure copper on the cathode. This method is highly effective in producing copper of high purity for use in electrical applications. It is also a sustainable method as it allows for the recycling of copper without loss of quality.