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Section II: Phase Diagram Evaluations

Fe-Ga-S-Zn (Iron-Gallium-Sulfur-Zinc) V. Raghavan

Extraction of Ga from Fe-bearing sphalerite (or wurtzite) requires an understanding of the phase relationships in this quaternary system. In a series of papers [1991Uen, 1994Uen, 1995Uen, 1996Uen, 2002Uen], Ueno and Scott studied the phase equilibria of this quaternary system and the related ternary systems.

Binary Systems The Fe-Ga system [1993Oka] is characterized by the presence of a closed ␥ loop and several ordered forms of the Fe-based body-centered-cubic (bcc) solid solution (␣Fe). ␣⬘ has the CsCl type cubic structure. The structure of ␣⬙ is not known. ␣⵮ has the BiF3 type cubic structure. The intermediate phases of the system are: Fe3Ga, Fe6Ga5, Fe3Ga4, and FeGa3. The first two have high- and low-temperature modifications. For brief descriptions of the Fe-S, Fe-Zn, and Zn-S phase diagrams, see the Fe-S-Zn update in this issue. A partial phase diagram of the Ga-S system [Massalski2] depicts four intermediate phases: Ga2S, GaS, Ga4S5, and Ga2S3. The Ga-Zn phase diagram [Massalski2] is a simple eutectic system, with the mutual solid solubility between Ga and Zn of about 1 at.%. For crystal structure data, see [Pearson3].

Ternary Systems [1994Uen] determined two isothermal sections for the Fe-Ga-S system at 900 and 800 °C. Three ternary phases were found at these temperatures approximately along the FeS-Ga2S3 line. The phase denoted Z by [1994Uen] has the ZnS (sphalerite sp) type structure and a homogeneity range of Fe 3.4 Ga 37.7 S 58.9 -Fe 13.7 Ga 28.0 S 58.3 at 900 °C and Fe4.2Ga35.9S59.9-Fe13.9Ga28.4S57.7 at 800 °C. The phase denoted W by [1994Uen] is hexagonal [1981Par] and has an x-ray pattern similar to that of FeGa2S4 (low temperature modification, see [Pearson3]), but a different composition of Fe9Ga12S29. The third phase denoted X by [1994Uen] is tetragonal with the composition of Fe22Ga21S57. Ga4S5 was not found by [1994Uen]. GaS dissolves 0.1 at.% Fe and Ga2S3 dissolves 1.0-1.8 at.% Fe. Fe1−xS dissolves 0.4-0.5 at.% Ga. The phases along the Fe-Ga side found by [1994Uen] do not agree with the binary data accepted here. The isothermal section of [1994Uen] at 800 °C is redrawn in Fig. 1, omitting the tie lines to the Fe-Ga side. The section at 900 °C (not shown here) is very similar to the one at 800 °C. An update on the Fe-S-Zn phase diagram appears in this issue. There are no ternary phases in this system. ZnS dis-

Fig. 1 Fe-Ga-S isothermal section at 800 °C [1994Uen]. Narrow two-phase regions and tie lines to the Fe-Ga side are omitted.

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Journal of Phase Equilibria and Diffusion Vol. 25 No. 4 2004

Phase Diagram Evaluations: Section II

Fig. 2 Ga-S-Zn isothermal section at 800 °C [1995Uen]. Tie lines to the Fe-Ga side are omitted.

Fig. 3 Fe-Ga-S-Zn “pseudoternary” section FeS-GaS-ZnS at 800 °C [1996Uen]

solves a large amount of FeS. FeS, on the other hand, does not dissolve any ZnS. The Ga-S-Zn phase relations at 900 and 800 °C were determined by [1995Uen]. Two ternary

phases were found to lie approx