Sulfide capacities of fayalite-base slags
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I.
INTRODUCTION
S U L F U R is an element that occurs in many metal extraction processes, and it is also of critical importance in understanding the formation of magmatic sulfide deposits. In view of this, extensive measurements of sulfur solubility in a wide variety of metallurgical slags tl-8j and in complex synthetic and natural oxide systemstg,l~ have been reported during the last 40 years. In spite of this, a literature review indicated that only limited data are available for sulfur solubility in fayalite slags m and, furthermore, these are not available in the temperature region of interest for nonferrous pyrometallurgical processing of sulfide concentrates of copper and nickel. This information is necessary to gain insight into the understanding of copper and nickel losses in fayalite slag. Pay metal losses can occur both as chemically dissolved species and as entrained sulfide matte. Knowledge of the amount of sulfur present as solution in the homogeneous liquid slag phase can be used to determine the amount of sulfur entrained as sulfide. Information is available on the sulfur content of the slags from matte-slag equilibrium measurements both from industrial practice 12~ and from laboratory studies. I16.241There is a large scatter in both the laboratory data and industrial data. This is probably due to sulfide entrainment, as different levels of matte entrainment in slags have been reported. In order to have a better understanding of the entrainment problems, the sulfide capacity of fayalite-base (FeOSIO2) slags was determined by gas-slag equilibria in the present study in the temperature range of interest to copper and nickel smelting, namely, 1473 to 1623 K. In addition, the influence of A1203, MgO, and CaO additions to fayalite slags was investigated, as these oxides are generally present in commercial slags. Oxygen p0tentials of 10- 95" to I0- 11 MPa and sulfur potentials of 10 -3 tO 10 -4.5 MPa were employed in this study, since these ranges represent the conditions existing in industrial smelting furnaces. S.R. SIMEONOV, Postdoctoral Fellow, R. SRIDHAR, Senior Research Associate, and J.M. TOGURI, INCO/NSERC Professor, are with the Department of Metallurgy and Materials Science, University of Toronto, Toronto, ON, Canada, M5S 1A4. Manuscript submitted May 23, 1994. METALLURGICAL AND MATERIALS TRANSACTIONS B
II.
THERMODYNAMIC CONSIDERATIONS
In the case of a gas-slag reaction, the sulfur-oxygen exchange equilibrium is given by Eq. [1]: 1 1 2 S2 (gas) + 02- (slag) = ~ 02 (gas) + S 2- (slag)
[1]
The sulfide capacity, as originally defined by Fincham and Richardson, till is given by Eq. [2]: Cs2 = (mass pct S 2-) a [ - o 2 _ ~t~tps~
KI
• ao2
•
[2]
fs ~-
where Cs :- is the sulfide capacity of slag (mass pet S z-) is mass pet of sulfur in the slag, Po2 and Ps2 are the respective partial pressures of oxygen and sulfur in the gas phase in equilibrium with the slag, and Kt, ao2_, and fs2_ represent the equilibrium constant for Eq. [1], the activity of 02- in the slag, and activity coefficient of S
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