Abstract

The formation mechanism of manganese compounds in acidic electrolytes (180 g/1 of H 2SO 4) was studied by potentiostatic experiments at 50°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: ?-MnO 2 and ?-MnO 2. It was proved that the ? type oxide was formed by an electrochemical process and the ? type oxide was formed by a pure chemical precipitation, the last one depends on the MnO 4 - concentration in the electrolyte. The electrochemical formation of MnOOH only depends on the concentration of Mn 3+ in the electrolyte, and this amorphous compound is the intermediate specie for generating ?-MnO 2. Fe 2+, in the presence of Mn 2+, inhibited the formation of both MnO 2 oxides, and in the anode interfase reduces PbO 2 to PbSO 4, that repots in the anodic slime. Furthermore, the presence of ferrous ion resulted in a better distribution of the manganese compounds and originates PbSO 4 precipitates, which report on the slime.