Metal recovery is the final step in a hydrometallurgical process, in which metals suitable for sale as raw materials are produced. Sometimes, however, further refining is needed to produce ultra-high purity metals. The main types of metal recovery processes are electrolysis, gaseous reduction, and precipitation.  For example, a major target of hydrometallurgy is copper, which is conveniently obtained by electrolysis. Cu ions are reduced to Cu metal at low potentials, leaving behind contaminating metal ions such as Fe and Zn.