Copper electrowinning is based on the copper electrolysis principle which uses electrical power to reduce copper ions in solution to the copper metal on the cathode and to oxidize water on the anode in oxygen gas and hydrogen ions. The chemical equation ^(a) gives the copper electrolysis global chemical reaction.

2H₂O + 2CuSO₄ = 2Cu0 + O₂ + 2H₂SO₄^(a)

The copper electrowinning circuit of a plant having L/SX/EW configuration and using permanent cathode technology consists of a stainless steel cathode, an inert anode (lead alloy or titanium), and the copper electrolyte that contains Cu⁺², Fe⁺³, Fe⁺², Co⁺², and SO₄^-2 as major elements. The predominant reactions at the cathode are given by the chemical reactions ^(b) and ^(c) and the predominant reactions at the anode surface are given by the chemical reactions ^(d) and ^(e).

Cu⁺² + 2e⁻ = CuO ^(b)
Fe⁺³ + e⁻ = Fe^{+2 (c)}
H₂O = 2H⁺ + 1/2O₂ + 2^{e− (d)}
Fe⁺² = Fe⁺³ + e^{− (e)}

At the cathode, the mathematical expression gives the current density which is the sum of current densities used respectively for the chemical reactions ^(b) and ^(c).

The iron limiting current density is the maximum value of current density that uses to reduce Fe⁺³ to Fe⁺² in the cathode. The ion current density is limited by the diffusion of Fe⁺³ ions on the cathode surface.