Phase Equilibrium and Minor Elements Distribution between Iron-Silicate Base Slag and Nickel-Copper-Iron Matte at 1573 K under High Partial Pressures of SO₂

Abstract

As a contribution to the understanding of oxygen-blowing smelting of the nickel-copper-iron matte, the phase equilibrium and the distribution of minor elements between the iron-silicate base slag saturated with silica and the Ni₃S₂–Cu₂S–FeS matte with a Ni:Cu molar ratio of 1 was investigated in a magnesia crucible under controlled partial pressures of SO₂ at 10.1, 50.7 and 101.3 kPa and 1573 K. At a given matte grade, the solubility of copper in the slag is found to be independent of p_SO2 while the solubility of nickel is dependent on p_SO2 and these behaviors are analyzed thermodynamically based on a concept of oxidic and sulfidic dissolutions of the components in the slag. The distribution ratio of X, L_X^s/m, is defined as (mass%X in slag)/{mass%X in matte}. At a fixed p_SO2, the distribution ratios of As and Sb decrease remarkably with increasing matte grade, and in the case of Bi, L_Bi^s/m decreases with increasing matte grade up to about 55 mass%Ni and then increases slightly in the higher range. When the matte grade is specified, the distribution ratios of As, Sb and Bi increase with increasing p_SO2. The results for the present Ni₃S₂–Cu₂S–FeS matte system were compared with those for the Cu₂S–FeS and Ni₃S₂–FeS matte systems.