Kinetics and Mechanism of Wet Milling Method Lead(II) Oxide Formation by the under Pressurized Oxygen

Abstract

Active leadan(II) oxide was formed by the oxidation of spherical granules (3---5 mm in diameter) of metallic lead with pressurized oxygen in the presence of the liquid medium at temperatures below about 60°C in the rotating mill. The effects of liquid medium, initial oxygen pressure, mill rotation speed, lead/liquid ratio, and temperature on the formation rate of the lead( II) oxide were investigated from various standpoints. It was found that water was indispensable for the reaction and the formation rate was the highest when pure water was used as the liquid medium. As the reaction mechanism, the following electrochemical reactions were proposed:
→PbO (Hydrolysis)
Pb→Pb²⁺+2e(Anode)
Pb→1/2O₂+HO₂+2e→2OH^- (Cathode)
The reaction rate was increased with increasing oxygen pressure, mill rotation speed and lead/liquid ratio, and with decreasing temperature. These effects on the reaction could be explained using the two film theory shown in Fig.3. The reaction rate was found to be first order with respect to the oxygen pressure, and the values of 0.6×10^-96.3×10^-9(kg-mol·m²/kg·h) were obtained as an overall oxygen transfer coefficient. It was also estimated that the diffusion of oxygen in gas and liquid phases was the rate-determining step in the reaction.