Abstract

The effect of secondary additives, such as CaCO₃ and MnCO₃, on the mineralogical transformations in Altasteel EAF dust (9.4% Zn, 31.9% Fe) during roasting with Na₂CO₃, and metal extractions during hot water and H₂SO₄ leaching of the roasted residues, was studied using a combination of techniques, including Design of Experiments testing, x-ray diffraction, scanning electron microscope/energy dispersive xray analysis and chemical analysis. The research objective was to promote the formation of acid insoluble metal ferrites during roasting to try to lower iron extractions during acid leaching. Neither additive was effective in reducing iron extractions due to the unexpected mineralogical changes caused during roasting by the addition of these secondary additives to this poorly crystalline EAF dust. Low CaCO₃ or MnCO₃ additions promoted the formation of manganese rich iron oxides (e.g., Mn₂FeO₄), instead of MnFe₂O₄, which caused more iron to be available to react with Na₂CO₃ during roasting to form acid soluble NaFeO₂. Increased CaCO₃ additions further increased iron extractions, by further increasing the formation of Mn₂FeO₄ ferrites, but increased MnCO₃ additions at roasting temperatures above 950°C led to the formation of a ZnFe₂O₄-MnFe₂O₄ solid solution. While this resulted in lower iron extractions, lower overall zinc recoveries during acid leaching were also observed.

Keywords

Electric arc furnace dust, Phase transformations, Pyrometallurgy, Leaching, Sodium carbonate roasting

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Conflicts of Interest

The authors declare no conflicts of interest.

References