The Viscous Behavior of FeO t -Al 2 O 3 -SiO 2 Copper Smelting Slags
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THE use of low-quality raw materials and recycled glass has made the copper smelting process increasingly more complex and inefficient. In particular, there has been an increase in the concentration in the slag of Al2O3, which exists as gangue in the ores. As compositions change, the control of slag properties such as viscosity has become essential in maintaining the process efficiency and improving the separation between the slag and the matte. Al2O3, which is an amphoteric oxide, can behave as either a network breaker or a network former depending on the slag composition. When there is a high concentration of basic oxide components, Al2O3 can behave as a network-forming acidic oxide. When there is a high concentration of acidic oxide components, Al2O3 can behave as a network-breaking basic oxide.[1,2] According to studies done on copper smelting slags of starting composition CaO-41.8 pct, SiO2-7.6 pct, and Al2O3-25.3 pct FeO by Yazawa and Kameda,[3] Al2O3 additions of 7.6, 11, and 14.1 mass pct showed Al2O3 to behave as a network former when the content is more than 7.6 mass pct. Considering that copper smelting slags can have Al2O3 in excess of 15 mass pct, the effect HYUN-SHIK PARK, Research Assistant, and IL SOHN, Assistant Professor, are with the Department of Materials Science and Engineering, Yonsei University, Seoul 120-749, Korea. Contact e-mail: [email protected] SU SANG PARK, Principal Researcher, is with the Process Development Team, LS-Nikko Copper Inc, Ulju-gun, Ulsan 689-890, South Korea. Manuscript submitted November 27, 2010. Article published online April 12, 2011. 692—VOLUME 42B, AUGUST 2011
of Al2O3 over a wider composition range must be understood. Ro¨ntgen et al.[4] measured the viscosity of FeO-Al2O3SiO2 slags from 1473 K to 1723 K (1200 C to 1450 C) using an iron crucible. For FeO/SiO2 ratios of 2.39 and 3.0, additions of Al2O3 showed a characteristic V-shaped pattern. Initially, Al2O3 decreased the viscosity, reached a minimum, and increased subsequently with Al2O3 additions. Ro¨ntgen et al.[4] attributed this behavior to the primary phase change between fayalite and hercynite. However, at an FeO/SiO2 ratio of 1.85, the opposite behavior was observed, so that additions of Al2O3 produced a maximum in viscosity. Ducret and Rankin[5] studied the viscosities of the Fe-saturated FeO-Fe2O3SiO2 slags at 1573 K (1300 C) and found the viscosity to increase with the addition of SiO2. Higher concentrations of SiO2 were found to polymerize the slag melt and increase its viscosity. It was also found that the viscosity measurements of FeO-containing silicate melts varied widely among various researchers, indicating the difficulty of the experiment itself. In most cases, the discrepancies were a result of the difficulties encountered in the experimental methods employed. Specifically, the FeO in the melt reacted with the crucible, making it difficult to control the ionic states of Fe in the slag melts, which can affect the oxygen partial pressure. In studies by Lee et al.[6] done with ironmaking slags con
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