Oxidation kinetics of molten copper sulfide
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I.
INTRODUCTION
APPROXIMATELY 90 pct of the world's primary copper is extracted from sulfide ores by pyrometallurgical processes. The metallurgical flow sheet begins with the concentration of copper minerals by froth flotation then proceeds through roasting (an optional step), matte smelting (in blast, reverberatory, electric, or flash furnaces), and converting to blister copper. More recently, continuous reactors, the most prominent of which are the Noranda, Mitsubishi, and Isasmelt processes, have been developed for copper smelting and converting. In copper converting, upon which this study focuses, blister copper is produced by several cycles of matte oxidation. Copper converting proceeds in two stages: the slag-forming stage, during which the iron in the molten matte is oxidized and is fluxed with silica to form liquid fayalite slag according to the following reaction, 2((FeS))matte + 3(O2)air +
(SiO2)nux
= ((2(FeO)" SiO2))slag + 2(SO2)oef.gas
[1]
and the copper-making stage, which commences once the iron levels in the bath are reduced to about 1 wt pct. The metallurgy of the latter stage has not been fully resolved. From the literature, two different mechanisms of the copper-making stage have been proposed. Peretti t~l suggested that copper making proceeds in two steps. First, the melt is partially desulfurized until the sulfur content is lowered to about 19.4 pet as follows: ((Cu2S)) + x(O2) = ((Cu2Sl-x)) + x(SO2)
[2]
and during the second step, the sulfur-deficient (white metal) phase is oxidized to form the metal phase (blister copper) according to the following reaction: ((Cu2S)) + (02) = 2((Cu)) + (SO2)
[3]
A.H. ALYASER, Graduate Student, and J.K. BRIMACOMBE, Alcan Chair in Materials Process Engineering and Director, are with The Centre for Metallurgical Process Engineering, The University of British Columbia, Vancouver, BC, Canada V6T 1Z4. Manuscript submitted January 19, 1994. METALLURGICAL AND MATERIALS TRANSACTIONS B
King e t a / . , t21 on the other hand, suggested that the copper forms by the following reactions: 3 ((Cu2S)) + ~ (Oz) = (Cu20) + (S02) ((Cu2S)) + 2(Cu20) = 6((Cu)) + (SO2)
[4] [5]
which, when combined, yield Reaction [3]. The phenomena influencing the rate of the converting operation include mixing, accretion growth, heat transfer, and chemical reaction kinetics 13,41 not all of which are fully understood. Obviously, comprehension of the kinetics of both the slag-forming and copper-making stages rests also on the thermodynamics of the Cu-Fe-S-O system. Many thermodynamic studies have been conducted, tS-t~ but most of these have treated the reactants as neutral compounds whereas mattes are ionic in nature. Only a few investigations have addressed this question in depth. 19,~~ The present work focuses on the copper-making stage, specifically the kinetics of the oxidation of molten copper sulfide, and attempts to incorporate the ionic nature of the Cu-S-O system. II.
PREVIOUS WORK
Several experimental investigations have been conducted on the oxidation kinetics of molten cop
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