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A very important electrochemical process in which metal is electrolytically extracted from a salt of that metal in aqueous solution. It is usually used in conjunction with acid leaching of ore. Electrowinning only works for metals that are easier to reduce than water. Some common metals that meet this criterion include gold, silver, copper, iron, and zinc. It would not work for an active metal such as aluminum or sodium, because the water will reduce more readily than the metal oxide, making the process useless.

Usually, a metal oxide is leached with sulfuric acid to form a soluble sulfate, which is then electrowinned in an aqueous solution to make the metal. Here, copper is used as an example.

CuO + H2SO4 ----> CuSO4 + H2O

CuSO4 + H2O -(electricity)---> Cu + H2SO4

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