Phase equilibrium and minor-element distribution between Ni 3 S 2 -FeS matte and calcium ferrite slag under high partial
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INTRODUCTION
THE conventional pyrometallurgical process of nickel sulfide ores consists of two stages of smelting and converting. The concentrates are oxidized in the smelting stage to produce the Ni-Cu-Fe-S matte with 10 to 50 wt pct Ni and the iron-silicate–based slag. The smelting furnace matte is further oxidized in the converting stage to produce the Ni-Cu-S matte, which has a very small content of iron of less than 1 wt pct and high contents of nickel and copper, with 40 to 75 wt pct Ni and 5 to 50 wt pct Cu.[1] The contents of nickel and copper in the converting matte are dependent solely on their contents in the concentrate. The combination of intensive reactors with the use of oxygen or oxygen-enriched air has provided improved nickel smelting and converting processes such as the INCO-Flash, Outokumpu Flash, and Top blowing rotatory converter (TBRC). The use of oxygen or oxygen-enriched air necessarily affords the exhaust gas with a high content of SO2. Hence, when the previous processes are discussed from the standpoint of thermodynamics, the equilibrium studies for the nickel matte and the slag under a high partial pressure of SO2 (PSO2) are of practical importance. However, very few data have been reported on the equilibrium and the distribution of minor elements between the nickel matte and slag phases. Hence, the authors[2–5] have conducted a series of experimental studies on the phase equilibrium and the distribution of minor elements between the Ni3S2-FeS or Ni3S2-Cu2S-FeS matte and the iron-silicate–based slag at the oxygen smelting condition, with PSO2 values of 10.1, 50.7, and 101.3 kPa and controlled partial pressures of O2 and S2. J.M. FONT, Associate Researcher, is with the Institute for Advanced Materials Processing, CODELCO-Chile, Milla´n 1200 Rancaqua-Chile. M. HINO, Associate Professor, and K. ITAGAKI, Professor, are with the Institute for Advanced Materials Processing, Tohoku University, Sendai 980-8577, Japan. Manuscript submitted August 24, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS B
Although the use of a CaO-FeOx slag (calcium ferrite slag) has been successfully practiced in the converting furnace of the Mitsubishi continuous copper-making process, no attempt has been reported on its use in the nickel converting process. The authors consider that there will be the possibility to make use of this slag in making a new process of nickel converting. Therefore, it is of interest to compare the results for the phase equilibrium and the distribution of minor elements between the traditional iron-silicate–based slag and the calcium ferrite–based slag. In the present study, the phase equilibrium and the distribution of minor elements between the Ni3S2-FeS matte corresponding to the iron-free matte and the CaO-FeOx –based slag (containing about 2 wt pct MgO) in a magnesia crucible were investigated at 1523 K under controlled partial pressures of S2, O2, and SO2 of 10.1, 50.7, and 101.3 kPa. The important byproduct elements of Ag, Co, and Cu and the detrimental elements of As, Sb, and Bi we
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