Selective Separation of Fe-Concentrates in EAF Slags Using Mechanical Dissimilarity of Solid Phases
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RECLAMATION of high-valued metal species in industrial waste slag produced from ironmaking and steelmaking processes has been of growing interests for energy saving and environment-friendly process development. Most blast furnace slags are reprocessed as commercial materials applied to asphalt concrete, concrete, road bases, and especially an additive to or a partial replacement for ordinary Portland cement (OPC) because of its cementitious properties.[1–4] However, the majority of electric arc furnace (EAF) slags are disposed of in landfills or partially used as low-valued materials for road construction and is limited for use as OPC due ustite to its high Fe content existing as FetO because w€ (FeO) phase formed in the Fe-rich EAF slag has no cementitious properties and inhibits formation of hydraulic phases which enhances cement properties.[5,6] The landfilled EAF slag contains noxious inorganics such as heavy metals including Cr, Ni, Ti, and Zn that could be leached into the ecosystem, even though they are present in a minimal amount. Therefore, efforts are being made to reduce the total Fe contents in EAF waste slags for the production of basic metals to increase metal SUNG SUK JUNG, Graduate Student, and IL SOHN, Associate Professor, are with the Department of Materials Science and Engineering, Yonsei University, Seoul 120-749, Korea. Contact e-mail: [email protected] KEEYOUNG JUNG, Senior Researcher, is with the Research Institute of Industrial Science and Technology, Pohang 790-600, Korea. Manuscript submitted March 23, 2016. Article published online November 15, 2016 METALLURGICAL AND MATERIALS TRANSACTIONS A
recovery and recycle otherwise wasted calcium-silicate oxide material as a higher value-added OPC, which requires a significantly lower Fe content than that presently available.[6–10] Approximately 15 wt pct of Fe content remains in the slag after metallic iron chips are magnetically separated.[5] As of 2014, the unreclaimed total Fe loss via the EAF slag is estimated to be as much as 9 million tons globally.[11] In the EAF, Al-dross (Al-70 pct Al2O3) additions to the high Fe-containing oxide melts can lower the Fe content; however, these additions are limited because of the increased Al2O3 content that can result in excessively high viscosity.[12] Thus, lowering the Fe content below 10 wt pct in the waste slag for OPC use within the EAF would not be practical. In a past study[13] on Fe redistribution of EAF slags using controlled cooling including isothermal crystallization period, the primary spinel phase in the Fe-rich slag could be selectively concentrated with Fe, whereas the amorphous phase was deficient in Fe. This resulted in differences in the magnetic behavior of the primary crystalline spinel and amorphous phases. Furthermore, these noticeable differences in the magnetism between the crystalline and amorphous phases resulted in relatively efficient separation of the solidified slag, allowing Fe contents of amorphous waste oxides to be controlled at approximately 10 wt pct. However, this efficie
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