Manganese metallurgy review. Part III: Manganese control in zinc and copper electrolytes

Manganese is often associated with zinc and copper minerals, and can build up in the processing circuits. Part III of the review outlines the current practice and new developments to get a better understanding of manganese behaviour and control in electrowinning of zinc and copper, and identifies suitable methods and processes to control manganese.In zinc electrowinning, the presence of small amounts of manganese (1–5 g/L) can minimise the corrosion rate of the anodes and reduce the contamination of the cathodic zinc with lead, but excess manganese results in significant decreases in the current efficiency. The neutralized zinc feed solution that contains little acid is considered to be the best place to implement manganese control. Various methods and processes for manganese control in zinc electrowinning have been developed. Oxidative precipitation and solvent extraction are the most important methods. For the neutralized zinc solution at pH 5, oxidative precipitation using a strong oxidant such as Caro's acid and SO₂/O₂ can selectively precipitate manganese as insoluble MnO₂ or Mn(OOH), leaving other impurities, e.g., Mg, Cl⁻, F⁻, etc. in the circuit. Solvent extraction of zinc using D2EHPA (di-2-ethylhexyl phosphoric acid) can selectively recover zinc from the solution and leave other impurities including manganese in the raffinate.In copper solvent and electrowinning circuits, the problem of manganese is mainly associated with the decrease in the current efficiency and degradation of the solvent caused by the higher valent manganese species generated on the anode. The prevention or minimisation of Mn(II) oxidation during the electrowinning is critical. This can be achieved by adding ferrous ions or sulfur dioxide to control the cell potential.