Oxidation of pyrrhotite particles falling through a vertical tube
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I.
INTRODUCTION
IN the
Outokumpu type flash smelter, fine particles of copper sulfide concentrate are fed from the top of the reaction shaft together with siliceous flux and preheated oxygen-enriched air. During descent through the shaft, sulfide particles are partly oxidized. They are melted due to the heat of oxidation. The oxidation rate of the particles is extremely high, and the residence time in the shaft is supposed to be less than a second. Jorgensen et al. ~ oxidized chalcopyrite particles of 37 to 53 p,m size in the air stream and reported that most of the reaction took place in less than 50 ms. Mineralogical examination revealed that the oxidation product was copper ferrite because of excess supplied oxygen as compared with the calculated amount from the feeding rate of chalcopyrite particles. Jorgensen 23 also carried out the combustion experiments of pyrite particles and proposed that the reaction proceeded through the following three stages: heating to the ignition temperature (870 K), decomposition to pyrrhotite (970 K), and formation of Fe-S-O melt with rapid elevation of the particle temperature. The maximum temperature of the droplets was reported to be 1880 to 2630 K depending on the oxygen partial pressure of the gas stream. In the analysis of flash smelting process, it is important to elucidate the progress of oxidation and fusion of the sulfide concentrate during the descent in the shaft. The major constituent of copper sulfide concentrate is chalcopyrite, of which iron is preferentially oxidized during the oxidation? 5 However, the oxidation mechanism of chalcopyrite is rather complicated, especially under the condition of nonisothermal oxidation. On the other hand, many studies 467 have been made on the oxidation of iron sulfide, and the reaction mechanism is simple. It is intended in the present work to study the progress of oxidation and fusion of pyrrhotite particles falling in a mixed O2-N: gas stream. A mathematical model was developed to calculate the progress of oxidation and fusion. Z. ASAKI, Assocmte Professor, and Y KONDO, Professor. are with the Department of Metallurgy. Kyoto Umverslty, K3oto 606, Japan S. MORI, former Student at Kyoto Umverslty, is now with Ool Power Station, Kansal Electric Company Ltd., Fukui 919-21, Japan. M IKEDA, former Student at Kyoto Umverslty. ~s now at Osaka Branch, Sa~tama Bank, Osaka 541, Japan Manuscript submitted July 3, 1984
METALLURGICALTRANSACTIONS B
II.
EXPERIMENTAL
Pyrite lumps mined at Yanahara Mine, Okayama, Japan, were decomposed and melted in a carbon crucible to prepare pyrrhotite. The resulting pyrrhotite lumps were crushed and screened into 115 to 250 and 250 to 325 mesh size. The mean particle diameter was 88 and 51 /xm, respectively. The chemical assay of the synthesized pyrrhotite particles is shown in Table I, and the composition of pyrrhotite is calculated as Fe097S assuming that the minor constituents of Cu, Zn, and Pb are in the form of Cu2S, ZnS, and PbS, respectively. The experimental apparatus is shown schematically in
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