Phase equilibrium and minor element distribution between FeO x -SiO 2 -MgO-based slag and Cu 2 S-FeS matte at 1573 K und
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INTRODUCTION
A combination of intensive reactors, with the use of oxygen or oxygen-enriched air as the blowing gas, has provided a number of improved copper smelting processes such as the INCO-flash, Outokumpu-flash, and Mitsubishi-continuous processes. Phase equilibrium studies for slag and copper matte phases under high partial pressure of SO2 are of practical importance for thermodynamically evaluating the behaviors of the related components, such as the solubility of copper in the slag phase and the distribution of valuable or detrimental minor elements between the matte and slag phases. A series of experimental studies[1–4] have already been conducted in a limited range of conditions for pSO2 around 10.1 kPa, which corresponds to smelting with air blowing. However, there remain very few data on the phase equilibrium under higher pressures of SO2. Tavera and Davenport[5] studied the phase equilibrium between the matte and fayalite slag phases under partial pressures of SO2 controlled at 10.1 to 101.3 kPa, but without controlling the partial pressures of sulfur and oxygen. A potential diagram[6] for the Cu-FeS-O-SiO2 system at 1523 to 1573K suggests that the partial pressure of S2 equilibrated with the matte and the fayalite slag with saturated SO2 under high SO2 pressure is considerably high at 10 to 1000 Pa. This condition must require controlling of pS2 as well as pSO2 in the equilibrium experiments; otherwise, the equilibrium condition may be hardly attained due to the continuous flushing of sulfur from the system. The objective of the present work was to extend the phase equilibrium studies from the air-blowing conditions around G. ROGHANI, Research Fellow, is with the Department of Mining, Minerals & Materials Engineering, University of Queensland, QLD 4072, Brisbane, Australia. Y. TAKEDA, Associate Professor, is with the Department of Materials Science and Technology, Faculty of Engineering, Iwate University, Morioka 020-0066, Japan. K. ITAGAKI, Professor, is with the Institute for Advanced Materials Processing, Tohoku University, Sendai 980-8577, Japan. Manuscript submitted June 2, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS B
10.1 kPa pSO2 into the oxygen-smelting condition with pSO2 greater than 10.1 kPa, with the partial pressures controlled by means of a liquid sulfur reservoir. Following the studies[7,8] for the copper matte/calcium ferrite slag equilibria, the phase equilibrium and the distribution ratio of minor elements such as silver, lead, arsenic, antimony, and bismuth between the Cu2S-FeS matte and the SiO2-saturated FeOXSiO2 –based slag containing 5 to 10 wt pct MgO were investigated at 1573 K in oxygen-smelting conditions, with pSO2 values of 10.1, 50.7, and 101.3 kPa. The SiO2-saturated fayalite slags form the basis of the industrial slags in copper converting as well as copper matte smelting, which are mainly composed of iron oxide and SiO2 with the additional components of CaO, Al2O3, and MgO. The MgO content of the present slag is considerably higher than that of the industrial slag
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