Investigation of High-Temperature Slag/Copper/Spinel Interactions
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TRODUCTION
IN primary and secondary copper smelting, the overall metal recovery is limited by copper losses in slags.[1] When pursuing an improvement of the process efficiency by limiting the metal losses, it is an absolute prerequisite to obtain a fundamental understanding of the characteristics and origin of these metal losses. It is well accepted, now, that copper losses in slags can be of chemical or mechanical nature.[2–4] Chemical copper losses refer to the dissolution of copper as sulfide or oxide during primary copper production and mainly as oxide during secondary production. This type of losses is determined by the system thermodynamics and is intrinsic to pyrometallurgical processes. The main influencing factors are temperature, oxygen partial pressure,[2,5–7] chemical activity of the metal,[2] and composition of the slag and matte.[2,5–7] Mechanically entrained metal refers to entrapped or floating unsettled droplets. In primary copper production, both metallic and matte droplets are entrained,
EVELIEN DE WILDE, formerly Ph.D. Student with the Department of Materials Science and Engineering, Ghent University, Technologiepark 903, 9052 Zwijnaarde, Ghent, Belgium, is now Project Leader with Umicore R&D, Kasteelstraat 7, 2250 Olen, Belgium. INGE BELLEMANS, Ph.D. Student, and KIM VERBEKEN, Professor, are with the Department of Materials Science and Engineering, Ghent University. Contact e-mail: Inge.Bellemans@ UGent.be MIEKE CAMPFORTS, Process Manager, is with Umicore R&D. MUXING GUO, Senior Researcher, BART BLANPAIN, and NELE MOELANS, Professors, are with the Department of Materials Engineering, KU Leuven, Kasteelpark Arenberg 44, bus 2450, 3001 Heverlee, Leuven, Belgium. Manuscript submitted October 21, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
while in secondary copper production, these losses are mainly metallic copper droplets. A variety of reasons are named in the literature to be responsible for this mechanical entrainment of droplets. Minto and Davenport[8] suggested a source for entrained Cu: SO2 bubbles, which originate at the bottom of the furnace, can elevate a surface film of matte into the slag.[8–10] A second important source is the dispersion of precipitated copper or matte, due to a decrease of the copper solubility in the slag. This variation in solubility is related to the process inhomogeneity due to, for example, zones with a locally lower temperature or a locally different oxygen partial pressure.[9] A third important cause is the entrapment of metal by manipulations such as charging or tapping. During tapping, mechanical entrainment can happen due to the rise of the underlying denser liquid phase, which can occur while flowing around obstacles in the vessel.[3] The physical dispersion of the denser layer into the slag by mixing can have several causes such as turbulence, mixing one phase into the other or injecting gas.[3,11] Additionally, the penetration of metallic copper into refractory can lead to metal losses.[12] There exists, however, an important additional source of mechanica
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