Investigation of the Freeze-Lining Formed in an Industrial Copper Converting Calcium Ferrite Slag
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IUM ferrite slags are currently used in several commercial continuous copper converting technologies, such as the Mitsubishi downward lance converter, the Outokumpu flash converter, and the IsaConvert top submerged lance technology. In these low-silica calcium ferrite slags, it is the lime that fluxes the iron oxides generated during matte converting.[1,2] The typical concentrations of the lime and dissolved copper in the slag are reported to be 15 to 20 and 14 to 20 wt pct, respectively.[1] Compared to the iron-silicate-based slags, the benefits of calcium ferrite slags are their high fluidity, reduced ATA FALLAH-MEHRJARDI, Postdoctoral Research Fellow, and PETER C. HAYES, Professor in Metallurgical Engineering, are with the PYROSEARCH, School of Chemical Engineering, The University of Queensland, Brisbane, QLD, Australia. Contact e-mail: [email protected] JANI JANSSON, formerly Researcher with the Metallurgical Thermodynamics and Modelling Research Group, School of Chemical Technology, Aalto University, Espoo, Finland, is now Sales Support Specialist with the Application Development and Support, Outotec Oyj, Espoo, Finland. PEKKA TASKINEN, Professor, is with the Thermodynamics and Modelling Group, School of Chemical Technology, Aalto University. EVGUENI JAK, Professor in Pyrometallurgy, is with the PYROSEARCH, School of Chemical Engineering, The University of Queensland. Manuscript submitted June 17, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
slag volume, iron oxide solubility,[1,3] and improved ability to remove impurities, such as antimony and arsenic, from the molten copper.[3] Calcium ferrite slags are, however, highly aggressive to the refractory material of the reactor lining. In addition, pyrometallurgical coppermaking processes are operated under intensive process conditions, such as high process temperatures and vigorous bath agitation, to increase the kinetics of reactions and to achieve high smelter throughput. Consequently, increased refractory degradation and in extreme cases, premature shut-down of the smelter may result from thermal and chemical attack by these aggressive slags. One solution to this problem is the deliberate freezing of the slag on the cooled reactor wall; the direct contact between molten slag and the reactor wall is thereby avoided. The creation of a freeze-lining then protects the reactor wall from the harmful effects of thermal and chemical attack by the aggressive slag.[4–13] A critical challenge in using freeze-linings for the stable operation of these reactors is to be able to select and control the process conditions in such a way as to ensure the formation of a stable deposit with an optimum thickness. Thick layers may lead to drastic decreases of the reactor volume. Thin layers may result in excessive heat losses through the reactor walls,
frequent detachment of the freeze-lining from the reactor shell, and increased risk to the furnace integrity. Therefore, accurate prediction of deposit thickness for a given process condition is an imperative. Several heat transfer
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