Computational Thermodynamics Modeling of Minor Element Distributions During Copper Flash Converting
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COPPER matte smelting was revolutionized in the 1960s by the advent of the Outokumpu flash furnace, but copper matte converting to blister copper is still dominated by Peirce-Smith converting, which is more than 100 years old. This technology is simple and reliable, but it has many well-documented disadvantages.[1] All the molten liquids are charged and discharged through the mouth of the converter, which requires the converter to be rolled out of its blowing position repeatedly. The result is that converting is a batch process, which requires frequent attention by ladle cranes, produces a waste gas stream that fluctuates in flow rate, temperature, and SO2 content, and it subjects the refractories to destructive temperature cycling. It also leads to the escape of fugitive SO2 emissions, which makes sulfur capture inefficient. These disadvantages have been overcome by the advent of continuous converting technologies such as the Mitsubishi bath converting process and the Kennecott flash converting process.[2] Both processes have a common feature in that they use lime (CaO) rather than silica as a flux, and calcium ferrite slag is produced. The properties of the calcium ferrite slag has been reviewed,[3] but of most interest is that it has a much lower viscosity than iron silicate slag, and so the risk of dangerous slag foaming is reduced greatly.[2] It is also basic in character and absorbs acidic oxides such as D.R. SWINBOURNE, Professor, is with the Extractive Metallurgy in the School of Civil, Environmental & Chemical Engineering, RMIT University, Melbourne, VIC 3001, Australia. Contact e-mail: drs@ rmit.edu.au T.S. KHO, Process Engineer, is with the Minerals & Metals Group, WorleyParsons, 145 South Terrace, Adelaide, SA 5000, Australia. Manuscript submitted November 18, 2011. Article published online March 23, 2012. METALLURGICAL AND MATERIALS TRANSACTIONS B
AsO1.5 and SbO1.5 better than the acidic iron silicate slag. However, it is also aggressive toward the magnesiachrome refractories used to line the furnaces,[4] which requires careful manipulation of slag composition to deposit a protective layer of magnetite on the furnace walls. The flash converting process developed by Kennecott Utah Copper Corporation (KUCC) and Outokumpu (now Outotec) was a response to increasingly restrictive air emission regulations and was designed to achieve more than 99.8 pct sulfur capture.[5] Production commenced in June 1995 with a design capacity of 1.0 million tons of copper concentrates per year, and in 2007, a second plant using the same technology, the Yanggu Xiang Guang Copper smelter in China began smelting.[6] The KUCC smelter has been described by Newman et al.[5] and recent improvements have been discussed by Walton et al.[7] A simplified flowsheet is given in Figure 1. The copper concentrates are blended with silica flux and flash converter recycle slag, dried, and then fed to a flash smelting furnace. Matte is granulated with water jets and stored, while the slag is slow cooled then processed for copper recovery. The smelter
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