Formation mechanism of manganese compounds in acidic electrolytes of copper

The formation mechanism of manganese compounds in acidic electrolytes (180 g/1 of H2SO4) was studied by potentiostatic experiments at 50 deg C. In the oxide layer on a PbCaSn anode, amorphous MnOOH was formed. XRD showed that anodic slimes collected from the cell bottom after 3 h was made up of: gamma-MnO2 and epsilon-MnO2. It was proved that the epsilon type oxide was formed by an electrochemical process and the gamma type oxide was formed by a pure chemical precipitation, the last one depends on the MnO4 concentration in the electrolyte. The electrochemical formation of MnOOH only depends on the concentration of Mn3+ in the electrolyte, and this amorphous compound is the intermediate specie for generating epsilon-MnO2. Fe2+, in the presence of Mn2+, inhibited the formation of both MnO2 oxides, and in the anode interfase reduces PbO2 to PbSO4, that repots in the anodic slime. Furthermore, the presence of ferrous ion resulted in a better distribution of the manganese compounds and originates PbSO4 precipitates, which report on the slime.