The kinetics of the reduction of lead from lead oxide slags
Abstract
Global environmental concerns have created great interest in the development of new low emissions techniques for obtaining lead bullion from the principal lead bearing ore, galena. The QSL reactor is reviewed as a promising new process; investigation into the kinetics of the process may improve its productivity. Previous research performed on the kinetics of the oxidation and reduction of lead from lead oxide slags is reviewed. Appropriate techniques for examining the reduction process and describing the kinetics of the reactions of interest are presented. The reduction of lead from the PbO-SiO$\sb2$ and the PbO-FeO$\rm \sb{n}$-SiO$\sb2$ systems at 900 and 1250$\sp\circ$C, respectively, was studied by eliminating gas phase mass transfer as the rate-controlling step, and subsequently observing the variation of the extent of the reduction reaction with time. The reduction in the PbO-SiO$\sb2$ was controlled by a surface reaction. Rate constants were obtained for p$\rm \sb{CO\sb2}/p\sb{CO}$ = 7 to 25 reducing gases. The temperature dependence of the surface reaction was determined at a constant oxygen potential of 1.86 $\times$ 10$\sp{-14}$ atm, and the activation energy was found to be 353 kJ/mole. The reduction of lead in the PbO-FeO$\rm \sb{n}$-SiO$\sb2$ system was observed under liquid phase mass transport control with p$\sb{\rm O\sb2}$ = 10$\sp{-9}$ to 10$\sp{-14}$ atm reducing gases. The kinetics of the reduction reaction was described using both semi-infinite and finite boundary conditions. The interdiffusivity for Pb$\sp{++}$ was found to be 9.05 $\times$ 10$\sp{-9}$ m$\sp2$ s$\sp{-1}$. Values for the concentration of PbO at the surface of the melts for these reducing gases were determined. The Fe$\sp{+++}$/Fe$\sp{++}$ ratios in the samples were measured, but could not be directly correlated to the reaction kinetics.
Degree
Ph.D.
Advisors
Gaskett, Purdue University.
Subject Area
Materials science|Metallurgy
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