1999 Volume 63 Issue 4 Pages 448-453
In order to determine the activities of components in the zinc-iron-sulfur ternary system, activity measurement of the iron-zinc binary system was carried out by employing an isopiestic method at temperatures of 1100 and 1200 K. Then the activities of components in the ternary system were calculated by applying the Gibbs-Duhem equations to the phase relation of metal-sulfide equilibrium. These data are of fundamental importance for discussing a new zinc distillation process with environmental consciousness proposed by the authors. In this process, zinc sulfide is directly reduced to zinc vapor with metallic iron, fixing sulfur as pyrrhotite. The results are summarized as follows:
(1) In the α-solid solution of the iron-zinc alloy, both the activities of iron and zinc exhibited considerable positive deviations from Raoult’s law. Both the activities of iron and zinc behave more ideal with increasing temperature. Activity coefficients were expressed by the following equations in the temperature range 1100 to 1200 K.
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Raoultian activity coefficients of zinc at infinite dilution, γZn(l)0, were obtained as 8.3 and 7.0 at 1100 and 1200 K, respectively.
(2) Relation between the equilibrium sulfur partial pressure and the composition of the condensed phase was determined. Using the equilibrium sulfur partial pressure and the activity of iron, the activity of FeS was obtained from the equilibrium constant of FeS formation reaction. Then the activity of ZnS was calculated by the Gibbs-Duhem relation.
(3) It was found from these results that the activity of FeS in the pyrrhotite which will be formed in the new zinc distillation process, can be regarded as almost unity. Zinc content in the pyrrhotite is therefore expected to be negligibly small, and the pyrrhotite can be utilized as a source of sulfuric acid or fuel for smelting processes for metals such as copper, nickel.
