Effect of P 2 O 5 and Fe t O on the Viscosity and Slag Structure in Steelmaking Slags
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NTRODUCTION
IN 2013, China’s crude steel production reached 0.779 billion tons, which accounted for nearly half of the world’s total output. This unavoidably generates a large amount steelmaking slags as by-products out of which only a small part can be recycled as soil conditioners, fertilizers, recovery of metals or recovered in iron- and steelmaking process, etc.[1] Among these recycling methods, the reuse of spent steelmaking slags in the iron- and steelmaking process is considered as the most effective way.[2–4] However, the increased dephosphorization in steelmaking processes or the use of high phosphoruscontaining iron ores resulted in the large amount of steelmaking slags containing high content of phosphorous.[2,4] Recycling these P-bearing steelmaking slags in blast furnace (BF) process would result in the enrichment of phosphorus in the liquid iron, which subsequently increases the burden of further dephosphorization.[2] This prevents the reuse of P-bearing steelmaking slags. Furthermore, P-bearing steelmaking slags cannot be used to prepare phosphatic fertilizer using the Thomas method due to low phosphorus content.[4] It is therefore necessary to explore other Z.J. WANG, Doctoral Candidate, Q.F. SHU, M. ZHANG, and M. GUO, Professors, are with the Department of Physical Chemistry of Metallurgy, University of Science and Technology Beijing, Beijing 100083, P.R. China. S. SRIDHAR, Professor, is with the WMG, International Digital Laboratory, University of Warwick, Coventry, CV4 7AL, UK. Z.T. ZHANG, Professor, is with the Department of Energy and Resources Engineering and Beijing Key Laboratory for Solid Waste Utilization and Management, College of Engineering, Peking University, Beijing 100871, P.R. China. Contact e-mail: [email protected] Manuscript submitted September 19, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
utilization methods. Selective crystallization and phase separation (SCPS) method was put forward to recycle the phosphorous in steelmaking slags, and has been investigated extensively. [5,6] During the SCPS process, the selective crystallization is the key step to successfully extract phosphorous. Many researchers considered that n(2CaOÆSiO2-3CaOÆP2O5) (nC2S-C3P) solid solution as the enriched phosphorous phases, and they extensively studied the selective crystallization behaviors of nC2S-C3P in the steelmaking slags through modifying the slags using Al2O3,[3] CaF2,[4] SiO2,[7] etc. The selective precipitation of slags is determined by many variables, such as the chemical composition, cooling rate, transfer mechanism for both mass and heat, and interfacial kinetics.[8] The viscosity of the slags is a critical property since it governs the mass transfer and the crystallization behavior of the molten slag. It is well known that the macroscopic physical and chemical properties of slags are primarily determined by the microscopic structures. Thus, an understanding the relation between the viscosity and structure of steelmaking slag is crucial. Considering the chemical compositions of P-
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