Oxidation of Manganous and Chloride Ions on Mixed Metal Oxide Anodes

"In the present work, the oxidation of manganous and chloride ions on a mixed metal oxide (MMO) anode from a 40 ºC electrolyte containing 160 g/L sulfuric acid (H2SO4) with various concentrations of Mn2+ and Cl- was studied using cyclic voltammetry. These results indicated that Mn2+ concentration does not affect Cl2 evolution on a non-MnO2 coated MMO anode. However once MnO2 deposits on the MMO anode, Cl2 evolution is inhibited. The effects of manganous concentration and chloride concentration on the amount of MnO2 deposited in one hour were also evaluated. Cl- concentration did not affect the amount of MnO2 generated. Increasing Mn2+ concentration resulted in an increase in the amount of MnO2 deposited.INTRODUCTIONThe electrolytic recovery of zinc (Zn) is a well-known process and is estimated to produce approximately nine million tons of Zn per year worldwide (Recendiz, Nava, Lartundo-Rojas, Almaguer, & Gonzaleza, 2009). The Zn produced by this process is of high purity and has a wide range of applications, such as galvanizing (car body parts, pipes, metal wires, etc.), sacrificial anodes in offshore industries, casting alloys, alloying of brass, primary and secondary battery industries, etc.The electrochemical production of Zn employs aluminum cathodes and lead-silver anodes (Pb- Ag) (Recendiz et al., 2009). The Zn containing mineral (ZnS) is usually associated with other elements such as Mn, Mg, Ca, Cd, Cu, Cl, Fe, F, Co, Ni, Al, As, Sb, Si, Sn, Ge, Hg etc. (Nijjer, 2000). After processing of ZnS concentrates, the electrolyte obtained still contains residual metallic and non-metal impurities. Some of these impurities can impact the corrosion rate of Pb-Ag anodes."