Phase and microstructure of FeO–SiO2–CaO–MgO system in oxidizing atmosphere

Abstract

To improve the enrichment and recycling of iron in iron-rich copper slag, the phase and microstructure of FeO–SiO₂–CaO–MgO system in oxidizing atmosphere were studied after adding MgO and CaO to the iron-rich copper slag. Thermodynamic calculations by FactSage software show that the addition of MgO favors the formation of magnetite (Fe₃O₄) in the FeO–SiO₂–CaO–MgO system and the formation of hematite (Fe₂O₃) is limited. The formed Fe₃O₄ can exist stable above 1657K in air atmosphere. The calculations are proved by XRD patterns when Fe₃O₄ is the only iron oxide in the oxidized system. Quantitative analysis by Mössbauer spectrum indicated that 96.29% iron was enriched in Fe₃O₄ and MgFe₂O₄ in the quaternary system, while Fe distributed in FeSiO₃ and Ca(Mg,Fe)Si₂O₆ were 0.39% and 3.32%, respectively. The magnetite and bar-shaped wollastonite crystalized in molten slag were surrounded by augite formed in the solidification processing. The growth characteristics of magnetite were investigated to improve the enrichment of iron in the modified copper slag. Results show that iron was enriched in the flakes, scattered particles, and dendrite magnetite particles, which favors the iron-recycling from copper slag by magnetic-separation.