Sulfide capacities of CaO-CaF 2 -CaCl 2 melts
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I.
INTRODUCTION
I N recent years, the physical chemistry of halide melts has become of increasing interest to the metallurgist, because the fundamental knowledge of their physicochemical behavior is still relatively unknown. This is particularly the case with C1 - and F -containing melts, whose capabilities of holding elements like S and P have been the object of a few investigationsJ 1-41 This article reports on a study of the sulfide capacities of CaO-CaC12-CaF 2 melts, in the temperature range of 1000 ~ to 1300 ~ for different slag compositions. In addition, the obtained thermodynamic data are of direct metallurgical importance for the selecting of proper refining reagents in iron and steelmaking processes. II.
THERMODYNAMIC
1 [s] + 0 2 - = S2- + 2 02
[1]
Based on Reaction [2], the sulfide capacity was originally defined as Eq. [3] by a gas-slag reaction: Is~ 1
1 S 2- ..~ _ 0 2
2
2
Cs2- = (pct Ssl~g)" .~/Po~ ~/Ps,
[2]
[3]
It can also be expressed in terms of the sulfur partition, as in Eq. [5], by considering the dissolution of sulfur into a metal (Eq. [4]): 1 2 $2 (g) = [S] [4] Cs 2-
As seen in Eq. [5], the sulfide capacity can be obtained by chemical analysis of the slag and metal and is dependent on slag composition and temperature. Because the Cs-'- does not depend on the nature of the metal, pure silver was used as metal in this study. The values of K4 and fs in Eq, [5] for silver were calculated from the experimental data published by Fukatsu and Kozuka t61 and Rosenqvist, rvl respectively.
CONSIDERATIONS
As is well known, sulfur in molten iron and steel is removed as a sulfide according to Eq. [1]:
52 --~ 0 2 - :
where [pct S] = wt pct of S in a metal; (pct S) = wt pct of S in a slag; fs = the activity coefficient of S in a metal; and K4 = the equilibrium constant for Reaction [4].
( p c t S)
----'(po) [pct S]
1/2 K4 "--
fs
[51
SIMEON SIMEONOV, formerly Visiting Research Fellow, Institute of Industrial Science, University of Tokyo, is Lecturer, Sofia Technological University, Sofia, Bulgaria. TOSHIHIKO SAKAI, formerly Research Fellow, Institute of Industrial Science, University of Tokyo, is with the Hitachi Works, Hitachi, Nippon Mining Company. M A S A F U M I MAEDA, Associate Professor of Metal Source Technology, is with the Institute of Industrial Science, University of Tokyo, Tokyo 106, Japan. Manuscript submitted June 10, 1991. METALLURGICAL TRANSACTIONS B
III.
EXPERIMENTAL
PROCEDURE
Approximately 5 g of silver and 1.5 g of slag from the (CaO-CaF2-CaCI2) system were equilibrated in a nickel crucible. In each experiment, three crucibles were set in a nickel boat which was then placed in the hot zone of a horizontal furnace. The first crucible contained only slag with a higher content of CaC12 (68 mol pct) to keep the CI potential in the reaction tube approximately constant during the experimental trials. The next two crucibles were placed in such a manner as to obtain the required equilibration sulfur distribution between the slag, of given composition, and the molten silve
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