Critical evaluation of the thermochemical properties of lead sulfates
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I. I N T R O D U C T I O N T H E thermochemical properties of the four lead sulfates--PbSOq, PbOPbSO4, (PbO)2PbSO4, ( P b O ) 4 P b S O a - that are stable at elevated temperatures are of importance to understanding and controlling pyrometallurgical lead processes. Despite numerous studies of equilibria involving these sulfates, the equilibrium data have yet to be evaluated critically to yield acceptable values for the properties of the lead sulfates. This study attempts to fill that need insofar as the available data permit. The selected thermochemical properties developed herein are in excellent agreement with the measurements of Esdaile tll and good agreement with the measurements of Kellogg and Basu t21 as modified by Lloyd t31 and Fukatsu and Kozuka.[41 The work also suggests minor changes in the heat of formation of PbO(c, yellow) and PbS(c), both of which are well within the uncertainty of the values listed in critical data compilations. Kellogg and Basu t21 were the first to establish that the system Pb-S-O is characterized by eight stable univariant equilibria and two invariant points in the temperature range 600 to 1 100 K (Table I). They employed a static manometric technique to measure the equilibrium pressure of SO2 for five of these equilibria (no.'s 1, 2, 4, 5, and 8) as a function of temperature. In a subsequent study from the same laboratory, Lloyd t3] measured Eq. [6] for the first time and remeasured Eqs. [5] and [8]. His values for Eq. [8] differed markedly from those of Kellogg and Basu, 12~ and he showed that their earlier results were in error. Esdaile ~lJ measured all eight equilibria using the same basic method as Kellogg and Basu tEj and Lloyd, I3~but he employed unusual precautions to degas his samples prior to pressure measurement, special checks to establish attainment of equilibrium, and X-ray analysis to prove the nature of the stable phases in each equilibrium. His resuits agree well with those of Kellogg and Basu as extended and modified by Lloyd, but there is little doubt that his data are superior to the earlier w o r k - - l e s s scatter, more data points, and measurement over larger temperature ranges. It is unfortunate that his high-quality equilibrium data have been overlooked by more recent
HERBERT H. KELLOGG is Stanley-Thompson Professor of Chemical Metallurgy, Henry Krumb School of Mines, Columbia University, New York, NY 10027. Manuscript submitted April 22, 1988. METALLURGICAL TRANSACTIONS B
investigators of the system Pb-S-O, probably because of its nonarchival Australian publication. The eight univariant equilibria and two invariant points are given in Table I, and their interrelations are illustrated in Figure 1. The expanded scales used in Figure 1 do not permit showing the full range of Esdaile's experimental points, except for Eq. [4]. The various equilibria shown divide the diagram into areas within which unique pairs of condensed phases are stable. The data for the eight univariant equilibria afford a unique opportunity to evaluate the thermochemical properties
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