Modeling the Viscosity of Silicate Melts Containing Lead Oxide
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INTRODUCTION
SILICATE slags containing lead oxide are formed during pyrometallurgical production of lead either from metal scrap or from ores. Of particular importance is the slag viscosity that quantifies the flow properties of the slag and affects the degree of refractory attack, the amount of entrained metal in the slag, the mass transfer at the slag–metal interface, and the heat transfer through the slag.[1] The viscosity of PbO-containing oxide melts is also of primary importance to the glass industry. Recently, we developed a new model for the viscosity of oxide melts.[2–4] In this model, the viscosity is related to the structure of the melt, which in turn is calculated from the thermodynamic description of the melt using the modified quasichemical model.[5,6] Most importantly, the model takes into account the formation of the silica network, which has a profound effect on the viscosity. The model predicts within experimental error limits the viscosity of multicomponent slags from just a few model parameters fitted to the viscosities of the binary and some ternary subsystems. In the present study, viscosity data are reviewed for melts formed by PbO with SiO2, Al2O3, CaO, MgO, Na2O, and K2O. A few model parameters are optimized to reproduce the viscosities of PbO, PbO-SiO2, and PbO-Al2O3-SiO2 melts. Then the available experimental viscosity data for other ternary and higher-order, PbOcontaining systems are compared with the viscosities calculated by the model without any additional adjustable model parameters. Lead-containing melts under WAN-YI KIM, formerly Ph.D. Student, with the Center for Research in Computational Thermochemistry, E´cole Polytechnique de Montre´al, Montre´al, QC H3C 3A7, Canada, is now Postdoctoral Fellow, with the Department of Mining and Materials Engineering, McGill University, Montre´al, QC H3A 2B2, Canada. ARTHUR D. PELTON, Emeritus Professor and Director, and SERGEI A. DECTEROV, Research Professor, are with the Center for Research in Computational Thermochemistry, E´cole Polytechnique de Montre´al. Contact e-mail: [email protected] Manuscript submitted May 6, 2011. Article published online December 7, 2011. METALLURGICAL AND MATERIALS TRANSACTIONS B
oxidizing conditions, where oxidation states higher than Pb2+ can be present, are not considered in the present article because of a lack of reliable experimental data on the viscosity and oxidation states of lead in these melts.
II.
VISCOSITY MODEL
For a more detailed description of the model, see the earlier articles.[2–4] A. Melts Formed by SiO2 and Basic Oxides MOx The structure of silicate melts is characterized by the bridging behavior of oxygen. An oxygen atom separating an M-M pair is a free oxygen, O2, an oxygen separating an M-Si pair is a nonbridging oxygen, O, and an oxygen separating a Si-Si pair is a bridging oxygen, O0. The silicon atoms in silicate melts are always tetrahedrally bonded to four oxygen ions. Basic silicate melts consist mainly of Men+, O2, and SiO4 4 ions. As the silica content increases above t
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