TITLE:
Mineralogical Transformations in Altasteel Electric Arc Furnace Dust Roasted with Na2CO3 and Secondary Ferrite-Forming Additives
AUTHORS:
P. C. Holloway, T. H. Etsell
KEYWORDS:
Electric arc furnace dust, Phase transformations, Pyrometallurgy, Leaching, Sodium carbonate roasting
JOURNAL NAME:
Journal of Minerals and Materials Characterization and Engineering,
Vol.7 No.1,
March
20,
2008
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.