Copper fire refining can generally produce 99.0% to 99.8% of copper crude copper products, but still can not meet the requirements of the electrical industry on the nature of copper, other industries also need to use fine copper. Therefore, almost all modern crude copper is electrolytically refined to remove impurities that are difficult to remove by fire refining.

Electrolytic refining of copper, is the fire refining of copper cast into the anode plate, with pure copper thin as the cathode sheet, interphase into the electrolytic cell, with copper sulfate and sulfuric acid aqueous solution as the electrolyte, under the action of direct current, the anode copper and negative potential of the base metal dissolved into the solution, and precious metals and some metals (such as selenium, tellurium) insoluble, become the anode mud sunk at the bottom of the electrolytic cell.

The copper in the solution is preferentially precipitated on the cathode, while other base metals with negative potential cannot be precipitated on the cathode. It is removed when the electrolyte is regularly purified, so that the metal copper precipitated on the cathode is of high purity, which is called cathode copper or electrolytic copper, referred to as electric copper. Anode slime containing precious metals and rare metals such as selenium and tellurium is separately treated as a by-product of copper electrolysis in order to recover gold, silver, selenium, tellurium and other elements from it.

Base metal impurities gradually accumulate in the electrolyte, when it reaches a certain concentration, it will prevent the normal progress of the electrolysis process. For example, increasing the resistance and density of the electrolyte, slowing down the settling rate of the anode mud, and even discharging together with copper on the cathode, thus affecting the quality of the cathode copper, so it must be regularly extracted and purified quantitatively, and accordingly add new water and sulfuric acid to the electrolyte. In the purification process of the extracted electrolyte, valuable elements such as copper and nickel are often produced in the form of sulfate, and sulfuric acid is returned to the electrolytic system for reuse.

In the copper electrolysis workshop, there are usually hundreds or even thousands of electrolyzers, and each DC power supply series several of them into a system. The electrolyte in all electrolytic cells must be continuously circulated so that the electrolyte composition in the electrolytic cell is uniform. In the electrolyte circulation system, there is usually a heating device to heat the electrolyte to a certain temperature.