Phase transformations during the oxidation of fayalite (Fe2SiO4) are investigated for the recovery of iron from iron-rich nickel slag by oxidation-magnetic separation. The proportions of various phases calculated by FactSage 7.1 show that augite and spinel are the major phases in the FeO-SiO2-MgO-CaO-O2 system in air atmosphere. The decreased content of Fe2+shows that Fe2SiO4 is gradually oxidized into Fe3O4 with increasing oxidation time. XRD patterns demonstrate that Fe3O4and Ca(Mg,Fe)Si2O6 are the dominant phases after the oxidation. The Mössbauer spectrum indicates that 93.1 wt.% of iron in oxidized nickel slag is in magnetic minerals, while a limited amount of iron is contained in non-magnetic minerals. Ca(Mg,Fe)Si2O6 was formed during the heating stage in Ar atmosphere through the polymerization of SiO44-and also via peritectic reaction after the isothermal oxidation.
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