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PROCESS ORIENTED CHARACTERIZATION OF OOLITIC IRON CONCENTRATE DURING
DEPHOSPHORISATION BY ROASTING AND LEACHING
K. IONKOV1, O. GOMES2, S. GAYDARDZHIEV1, A. CORREA DE ARAUJO3
Mineral Processing and Recycling Unit - GeMMe, University of Liege, Quartier Polytech 1, Allée de la
Découverte 9, 4000 Liège, Belgium
2
CETEM, Center for Mineral Technology, Av. Pedro Calmon, 900, Cidade Universitária, 21941-908, Rio
de Janeiro, Brasil
3
ArcelorMittal Mining & Mineral Processing Research Center, Voie Romaine, 57283, Maizières-lès-Metz,
France
1
ABSTRACT
Phosphorus in iron ores is considered as a deleterious component to iron making reflecting in cold
shortness of the produced steel. Quite often its removal by physical separation is impossible; the main
reason behind being fine dissemination of phosphorous minerals while in some limonitic ores phosphorous
is even met as phosphate groups inside the limonite structure. The present study investigates the
phosphorous removal mechanisms after thermal treatment (roasting) of a gravity-magnetic iron concentrate
of oolitic type, with low iron (~49%) and high phosphorus (~0.7 %) content. The roasting is followed by
aqueous and acidic leaching as part of an integrated dephosphorisation technology aiming at efficient
removal of phosphorous. The phosphorus migration pattern resulting from the thermal treatment has been
followed through focused mineralogical and microscopic (SEM-BSE) observations. Since phosphorous is
met as solid solution inside the oolites, when non-roasted concentrate is subjected to leaching its removal is
virtually impossible due to the restricted access of the acid. The results have shown that if roasting with
alkaline additives is done prior to leaching, the crystalline water is evaporated from the limonite and
restructuring of goethite towards hematite occurs, phenomena which drive phosphorus outside the core
towards the cracks or the interstices between crystals. Moreover, depending on the type of the alkaline
additives used in roasting, transition of limonite towards either goethite or magnetite has been detected
which results in different levels of dephosphorisation during the leaching. The mineralogical analysis of
the roasted with additives concentrate has indicated formation of mixed phases containing iron oxides,
silicates and ferrites as fine particles. Parallel to phosphorous, the exclusion of aluminum and silica from
the oolites has contributed to concomitant increase in iron, thus delivering after the leaching a final
concentrate with commercially acceptable iron grade.
Fig. Evolution of iron content in the concentrate as function of leaching time and acid concentration
KEYWORDS
Iron ore, dephosphorization, roasting, leaching, characterization