During refining the blister copper produced in the converter is processed to high-grade anode copper with a purity of over 99% in fire or anode furnaces. Firstly, residues of less noble elements are oxidised and removed as slag (“oxidation phase"). In the subsequent “pole phase“ natural gas, methane, propane or an ammonia-containing gas mixture is added to reduce the oxygen content.
Various types of furnaces, such as rotary drum or hearth are used. For the production of copper anodes for electrolysis, the copper is cast into an anode mold at the end of refining.