Kinetics of Hydrogen Reduction of Chalcopyrite Concentrate RITAYAN CHATTERJEE and DINABANDHU GHOSH A Ghatshila chalcopyrite concentrate (average particle size, 50 lm) containing primarily CuFeS 2 and SiO 2 (Cu 16 pct) was reduced by a stream of hydrogen in a thermogravimetric analyzer (TGA) at selected temperatures [1173 K to 1323 K (900 °C to 1050 °C)], hydrogen flow rates, partial pressures of hydrogen (0.33 9 101.3 to 101.3 kPa), and sample bed heights. The product was a mixture of Cu (26 pct), SiO 2 , CuFeO 2 , and Fe. The rate equations for the three typical controlling mechanisms, namely, gas film diffusion (mass transfer), pore diffusion, and interfacial reaction, have been derived for the system geometry under study and applied to identify the rate-controlling steps. The first stage of the reduction, which extended up to the first 13 minutes, was rate controlled by the interfacial reaction. The last stage, which spanned over the last 60 to 120 minutes and accounted for a small percentage of reduction, was controlled by pore diffusion through the built-up Cu (and Fe) layer. The activation energy in the first stage was 101 kJ mol 1 and that in the second stage was 76 kJ mol 1 . Subsequent acid leaching with 1 M HCl solution of the reduction product removed all soluble species, leaving a Cu (53.3 pct) + SiO 2 mixture, with a small concentration (2.7 pct) of Cu 2 O in it. This result compares well with the predicted final mixture of Cu (59 pct)-SiO 2 based on a mass balance on the starting concentrate. A follow-up heating at 1523 K (1250 °C) produced a sintered Cu-SiO 2 composite with spherical copper particles of 400 lm diameter embedded in a silica matrix. Elemental chemical analyses were carried out by energy-dispersive X-ray spectroscopy/atomic absorption spectroscopy. The phase identification and microstructural characterization of Cu- SiO 2 mixtures were carried out by X-ray powder diffraction and optical microscopy. DOI: 10.1007/s11663-015-0419-6 Ó The Minerals, Metals & Materials Society and ASM International 2015 I. INTRODUCTION THE majority of copper ores currently available around the world are in the form of sulfides, especially chalcopyrite (CuFeS 2 ) and to a lesser extent chalcocite (Cu 2 S). [1] The conventional pyrometallurgical method of copper extraction from these ores has several steps: roasting, smelting, converting, fire refining, and elec- trorefining. The steps involve the oxidation of sulfides which results in the generation of polluting sulfur dioxide gas. An alternative to this environment-un- friendly, lengthy process may be the reduction of sulfides by hydrogen or other reducing agents. Although this alternative seems to be attractive for its simplicity, its major problem is its unfavorable thermodynamics with a small equilibrium constant. To overcome this barrier, lime, which is a suitable material to fix the produced hydrogen sulfide gas in the form of solid calcium sulfide, has been successfully used by many researchers. [2–6] However, the addition of lime, which is a strongly hygroscopic material, introduces handling problem and imposes an additional task of separating the solid waste of calcium sulfide from the produced metal. Still another simple method to overcome the thermodynamic barrier is to accept the poor utilization of the reducing gas and use sufficiently large quantity of it. [7,8] The excess cost thus involved may be considerably offset by the saving caused by doing away with the lime; in addition, the copper produced will be much cleaner. Notably, in the previous studies of sulfide reduction, pure, synthetic materials were used and the possible role of gangue minerals was not considered. The reduction of sulfide ores or concentrates could be a more challenging and industrially important study. Accordingly, the main objective of the current work was to study the kinetics of hydrogen reduction of chalcopyrite concentrate, without adding lime to the system. In addition, it was intended to synthesize copper-silica composite, a valuable com- mercial product, by acid leaching of the reduction product, followed by sintering. Further separation of copper from silica, which would complete the making of copper from chalcopyrite concentrate, could not, how- ever, be taken up in the current study. Different methods of synthesis of Cu-SiO 2 composite, as have been reported in the literature, include gamma- ray irradiation, [9] electrodeposition, [10] microemulsion processing, [11] ambient drying, [12,13] and doping of Cu in RITAYAN CHATTERJEE, formerly Graduate Student with the Department of Metallurgical and Materials Engineering, Jadavpur University, Kolkata 700032, India, is now Assistant Professor with the Department of Applied Sciences, Haldia Institute of Technology, Haldia 721657, West Bengal, India. DINABANDHU GHOSH, Professor, Department of Metallurgical and Materials Engineering, Jadavpur University. Contact e-mail: dbghosh100@yahoo.com Manuscript submitted February 27, 2015 Article published online July 22, 2015. 2692—VOLUME 46B, DECEMBER 2015 METALLURGICAL AND MATERIALS TRANSACTIONS B