text: The final stage in the production of copper is refining. Refining is achieved by electrolysis, which exploits the easy (low potential) and selective conversion of copper(II) solutions to the metal. The anodes cast from processed blister copper are placed into an aqueous solution of 3–4% copper sulfate and 10–16% sulfuric acid. Cathodes are thin rolled sheets of highly pure copper or, more commonly these days, reusable stainless steel starting sheets (as in the IsaKidd process). A potential of only 0.2–0.4 volts is required for the process to commence. In industrial plants current densities up to 420 A/m are possible.
  At the anode (oxidation reaction), copper and less noble metals dissolve. More noble metals and less soluble elements such as silver, gold, selenium, and tellurium settle to the bottom of the cell as anode slime, which forms a salable by-product. Copper(II) ions migrate through the electrolyte to the cathode. At the cathode (reduction reaction),  ions are reduced in copper metal and Cu plates out, but less noble constituents such as arsenic and zinc remain in solution unless a higher voltage is used.
  The reactions involving metallic copper and  ions at the electrodes are the following: