The usual process of electrorefining copper consists of placing a copper anode (about 99.5–99.7% pure copper) in sulfuric acid (HSO) bath of copper electrolyte, together with a cathode, and passing a current between the anode and cathode through an external circuit. At the applied electropotential, copper and less noble elements dissolve in the electrolyte, while elements more noble than copper, such as gold (Au) and silver (Ag), do not. Under the influence of the applied electrical potential, copper ions migrate from the anode and deposit on the cathode, forming cathode copper.
The current IsaKidd technology represents the merger of the copper refining technologies developed by the two different organisations. The initial Isa Process development in the late 1970s, with its reusable stainless-steel cathode starter sheets, represented an advance on the previous technology of single-use starter sheets of pure copper, the production of which was a labour-intensive process.
The production of the single-use starter sheets involved laying down a sheet of copper by electrolysis on each side of a “mother plate”. Generating the sheet took a day, and thousands of sheets could be needed every day. Originally, the copper starter sheets were separated from the mother plate manually, but over time the process was automated. In addition, limitations associated with the use of copper starter sheets meant that it was difficult to meet the purity specifications of some new copper applications that were, in the 1970s and 1980s, demanding higher quality copper.