Investigation of Reactive Origin for Attachment of Cu Droplets to Solid Particles
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NTRODUCTION
THE presence of copper droplets in the slag is one of the causes that the overall metal recovery in primary and secondary copper production is limited.[1] Preventing these metal losses requires a fundamental understanding of their characteristics and origin. Copper losses in slags are in literature generally subdivided into chemical and mechanical losses.[2–4] Chemical copper losses represent the formation and dissolution of copper sulphide and/or copper oxide and are intrinsically present in pyrometallurgical processes. The chemical losses are linked to the system’s thermodynamics, i.e., the oxygen partial pressure,[2,5–7] the temperature, the composition of the slag and matte[2,5–7] and the chemical activity of the metal oxide or sulphide.[2]
INGE BELLEMANS, LISA CLAEYS, TIM DE SERANNO, and KIM VERBEKEN are with the Department of Materials, Textiles and Chemical Engineering, Ghent University, Technologiepark 903, Zwijnaarde, 9052 Ghent, Belgium. Contact e-mail: [email protected] EVELIEN DE WILDE is with the Department of Materials, Textiles and Chemical Engineering, Ghent University and also with the Umicore R&D, Kasteelstraat 7, 2250 Olen, Belgium. MIEKE CAMPFORTS is with the Umicore Precious Metals Refining, Adolf Greinerstraat 14, 2660 Hoboken, Belgium. BART BLANPAIN and NELE MOELANS are with the Department of Materials Engineering, KU Leuven, Kasteelpark Arenberg 44, Bus 2450, Heverlee, 3001 Louvain, Belgium. Manuscript submitted November 8, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS B
Mechanical copper losses refer to entrapped or floating unsettled droplets. In primary copper production, these include both matte and metal droplets, whereas mainly metallic droplets are entrapped in secondary copper production. One of the causes of the mechanical entrainment of the droplets is the precipitation of copper or matte due to a decrease in the solubility of copper in the slag.[8] A second cause of the mechanical losses is the dispersion of metal into the slag by gas-producing reactions. Minto and Davenport[9] suggested that rising SO2 bubbles that nucleated at the bottom of the furnace can elevate an interfacial film of matte into the slag.[8–10] Operational actions performed in pyrometallurgical processes, such as tapping or charging, are another possible cause for mechanical droplet losses. During tapping, the denser liquid can rise when flowing around obstacles in the vessel and hence mechanical losses can take place.[3] Moreover, gas injections, turbulence or pouring of one phase into the other can cause the physical dispersion of the denser layer into the slag.[3,11] Furthermore, metallic copper can penetrate the refractory, which in turn can also lead to metal losses.[12] These causes were already examined and discussed extensively in literature, but another possible source for the mechanical losses of copper droplets is often not specified: the attachment of droplets to solids in slags, hampering their sedimentation by a mechanical or physical stabilization of the metal droplet slag mixture.
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