The Kinetics of the Reduction of Lead Monoxide by Hydrogen

Abstract

The rate of reduction of fused lead monoxide particles in a differential reactor with H₂-N₂ and H₂-H₂O mixtures has been measured by absorbing the H₂O of reaction or chemically analysing the product, Pb-PbO. After falling from a high initial value, the reduction rate remains virtually constant until 40-50% of the PbO has been reduced, and then slowly declines. The rate of reduction is independent of the gas flow rate from 5-151. S.T.P./min and not markedly influenced by variations in particle size from -36+52 to -7+10 mesh B.S.S. With H₂-N₂ mixtures the rate of reduction of PbO at 575 and 675 °C is proportional to p_H2, and with H₂-H₂O mixtures at 575 °C it is proportional to p_H2/(1+0.5p_H2O), where p_H2, and p_H2O are the partial pressures of H₂ and H₂O, respectively. The activation energy for reduction with H₂-N₂ and H₂-H₂O mixtures over the temperature range 475-775 °C is 39 kcal/g-mole. Chemisorption of H₂ on the PbO appears the most likely rate controlling step at the Pb-PbO interface. Rates of reduction over the steady rate period, k₀, are correlated by the expression k₀=f(R)[p_H2/(1+0 5 p_H2O)] exp(-39 000/RT), where f(R) is a parameter related to particle shape and size.