A Microscopic study of the transformation of sphalerite particles during the roasting of zinc concentrate |
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Authors: | J W Graydon D W Kirk |
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Affiliation: | (1) Department of Chemical Engineering and Applied Chemistry, University of Toronto, M5S 1A4 Toronto, ON, Canada |
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Abstract: | The formation of zinc ferrite (ZnFe2O4) during the roasting of iron-bearing zinc concentrates requires substantial additional processing to recover the zinc from
this compound by leaching and to eliminate the iron from the leachate. The phase changes that occur in the particles of a
typical industrial zinc sulfide concentrate during roasting in a fluidized bed at 1223 K were investigated by the use of light
microscopy, electron microprobe analysis, and SEM with EDS. The processes which the iron undergoes during its eventual transformation
into ferrite have been clarified by examination of the phases and the morphology of partially roasted marmatitic sphalerite
particles (Zn, Fe)S, and by reference to the known phase equilibria involved in the Zn-Fe-S-0 system. The oxidation of ironbearing
sphalerite occurs in three stages. The first involves the selective diffusion of most of the iron to the particle surface
resulting in the formation of an iron oxide shell enclosing a largely unreacted zinc sulfide kernel. In the second stage,
this kernel is oxidized to form a solid solution of zinc oxide and iron oxide. The iron is initially present in the ferrous
state but, with the disappearance of the sulfide kernel, is oxidized to ferric iron. In the final stage, this dissolved iron
oxide and the iron oxide shell react with the surrounding zinc oxide to form the refractory spinel zinc ferrite. |
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