Kinetics of Reduction of CaO-FeO x -MgO-PbO-SiO 2 Slags by CO-CO 2 Gas Mixtures
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INTRODUCTION
THE emerging intensive smelting and slag cleaning processes have resulted in a growing interest in development of an improved understanding of the kinetics of reactions between slags and carbonaceous reactants. Published studies on the kinetics of redox reactions involving lead slags are limited and deal mainly with iron-free melts,[1–4] although a few recent studies on slags containing iron oxide have been published.[5–8] Studies by Masson et al.[1] and Sasabe et al.[9] demonstrated some of the factors that have a marked influence on the electrochemical transport of oxygen in lead silicates. It follows from their findings that the presence of transition metal ions (e.g., Fe2+ and Fe3+) in metallurgical slags will promote electronic conductivity; as a consequence, transporting oxygen ions and maintaining electroneutrality in such slags should be sufficiently fast for other kinetic barriers to become important in redox reactions. In earlier publications by the present authors,[5,6] findings from a series of investigations on the reduction kinetics of lead and zinc containing industrial slags by a
number of reductants were reported. In these studies, it was shown that when carbonaceous reductants are used, the rate of formation of CO2 at the gas-slag interface can play an important role with respect to the rate-controlling step. Subsequent work by Kinaev et al.[8] showed that when solid carbonaceous reductants are used, the reduction rate of slags containing lead and iron oxides are almost independent of carbon reactivity, slag basicity, and sulfur content of the slag. Their deduced first-order rate constant was found to be in good agreement with those deduced from the reduction of similar slags with CO-CO2 gas mixtures.[5,6] The present study was aimed at quantifying the effects of slag chemistry, its oxidation state, and temperature on the kinetics of reactions between synthetic magnesia slags and saturated CaO-FeOx-MgO-PbO-SiO2 CO-CO2 gas mixtures under conditions where mass transfer in the gas or liquid phases is unlikely to be the rate-limiting step. The planned work had a specific focus on determining the effects of iron oxide content of the slag on the mechanism and interfacial rate constant.
II. SHARIF JAHANSHAHI is with Meta-Logical Solutions, Armadale, VIC 3143, Australia, and also with University of New South Wales, Sydney, NSW 2052, Australia. Contact emails: [email protected], [email protected] STEVEN WRIGHT is with CSIRO Mineral Resources, Clayton. Manuscript submitted November 22, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS B
EXPERIMENTAL DETAILS
The experimental arrangement used for the present work is shown in Figure 1. The experiments were carried out in a vertical tube furnace heated with silicon carbide heating elements and controlled to ±2 K (±2 C) by a proportional band controller. Temperature measurements were made with a Pt/Pt-13 pct Rh
thermocouple located at the base of the recrystallized magnesia crucible, which was about 30-mm high with internal diameter of 16 mm.
