Electrorefining

Electrorefining is an electrochemical method used to purify metals. In a typical setup, an impure metal sample serves as the anode, a sheet of pure metal serves as the cathode, and an electrolyte containing ions of the refined metal completes the circuit. When current is applied, metal from the anode oxidizes and enters the solution as ions, migrates to the cathode, and reduces back to metal, depositing as high-purity product. Impurities largely remain in the electrolyte or concentrate as anode slime or dross around the anode.

Electrorefining is widely used for copper and nickel, and in various specialized applications for other metals. The electrolyte chemistry is chosen to support the target metal, promote efficient deposition, and manage byproducts. For copper refining, a copper sulfate-based electrolyte with sulfuric acid is common. Copper from the impure anode dissolves, the copper ions move to the cathode, and purified copper is deposited, while much of the impurities stay in solution or form the anode slime, which can contain precious metals.

Advantages of electrorefining include high metal purity, continuous operation, and scalable production. Limitations involve energy consumption, the need for corrosive or acidic electrolytes, and the management of anode slime that may contain valuable or hazardous impurities. The process is distinct from electroplating, which aims to deposit a thin coating of metal on a substrate rather than to purify an ingot.

In addition to copper and nickel refining, electrorefining appears in specialized contexts such as molten-salt refinements used in certain industrial and nuclear-processing schemes.