Intrinsic kinetics of the oxidation of chalcopyrite particles under isothermal and nonisothermal conditions
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INTRODUCTION
THEoxidation of chalcopyrite has received wide attention in the past, due to the development of roasting as a unit process in the recovery of copper from chalcopyrite ore. Knowledge of the rate of oxidation and its dependence on oxygen pressure, temperature, and particle size are of considerable importance in ensuring that desired phases occur as final products and that industrially feasible rates of roasting are achieved. Most of the previous work at understanding the mechanism and kinetics of chalcopyrite oxidation was limited to roasting temperatures of practical interest--below 973 K. At temperatures around 773 K, cupric sulfate and ferric oxide were the final roasting products, whereas, at around 923 K, cupric and cuprous oxides were observed. 2-5 Bumazhnov and Lenchev 3 extended their work to higher temperatures and reported ferrite formation at temperatures above 973 K. Yazawa 6 and Rosenqvist 7 have analyzed the process thermodynamically by constructing predominance area diagrams and reported that the observed phases agree with their analysis. Leung 8 has suggested that oxidation in commercial roasters occurs through two p a t h s - - t h e direct oxidation of chalcopyrite to Fe304 and by oxidation of pyrrhotite resuiting from the decomposition of chalcopyrite. Other workers 2'4 believe that bornite forms first followed by magnetite formation. Razouk et al. 9 suggest that, below 673 K, covellite forms first and is then oxidized to oxide and sulfate. At higher temperatures, CuSO4 results from the interaction between CuO and Fe2(SO4) 3. Above 873 K, both copper and iron sulfate decompose, and the resulting oxides react above 1173 K to form ferrites. Thornhill and Pidgeon l~ conducted a micrographic study of the roasting process at 923 K and concluded that the formation of digenite and P.C. CHAUBAL, Graduate Student, and H.Y. SOHN, Professor, are with the Department of Metallurgy and Metallurgical Engineering, University of Utah, Salt Lake City, UT 84112-1183. Manuscript submitted September 7, 1984.
METALLURGICALTRANSACTIONS B
covellite was the key and accounted for the selective oxidation of the iron component of chalcopyrite. Few investigators have attempted a basic kinetic study of the oxidation process. Bumazhnov and Lenchev 3 found that the nucleation and growth kinetics by Erofeev" described their data obtained using particles in the size range 50 to 250 microns. They observed three regions; between 673 K and 789 K, the activation energy was 176 kJ/mol, between 789 K and 973 K it was 113 kJ/mol, and above 973 K they obtained a value of 42 kJ/mol. Agarwal and Gupta ~2used a shrinking-core model to describe the oxidation of pelletized agglomerates between 773 K and 973 K and obtained an activation energy of 50 kJ/mol. The studies mentioned above used a fluidized-bed reactor to carry out the tests. The elimination of mass transfer effects is usually quite difficult in such reactors. Hence such data cannot be used to study the kinetics in reactors where fluid dynamics are different from t
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