DISSOLVED FORMS OF COPPER IN VANYUKOV FURNACE SLAGS: A STRUCTURAL BASIS DERIVED FROM THE IONIC CONSTITUTION OF THE SLAG MELT

Copper losses in Vanyukov furnace slags are largely determined by copper chemically dissolved in the melt, which cannot be recovered by settling. The dissolution of copper in fayalite-type iron-silicate melts, which form the basis of these slags, is examined from the perspective of the ionic structure of the slag melt. Mössbauer spectra of quenched sulphur-containing glasses were analysed in conjunction with data on the anionic density and surface tension of the melts. In glasses containing up to 3% sulphur, Fe²⁺ ions occupy three non-equivalent octahedral sites. A sulphide anion replaces one of the six oxygen atoms in the coordination environment of Fe²⁺, while the coordination number of sulphur with respect to iron is 4–5. S²⁻ and Fe³⁺ ions form stable associations, as indicated by the precipitation of pyrite and sulphur-rich pyrrhotite during crystallisation and by the composition-dependent variations in anionic density and surface tension. The equilibrium constant for the exchange reaction between FeO and the hypothetical component FeS₁.₅ is approximately 1.5 at 1250 °C. CaO additions induce distortions in the oxygen octahedron surrounding Fe²⁺, similar to those caused by sulphur. Accordingly, the sulphidic and oxidic forms of dissolved copper are attributed to Cu⁺ ions associated with Fe²⁺O₅S and Fe³⁺O₆ complexes, respectively. These structural considerations provide a basis for limiting the magnetite content, reducing the concentration of dissolved sulphur, and optimising CaO fluxing conditions to minimise copper losses with Vanyukov furnace slags.

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