Reduction of cobalt oxide with methane
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I. INTRODUCTION
COBALT is used extensively in superalloys for hightemperature applications such as turbine blades and rotary disks used in gas power generation plants and aircraft engines. Cobalt can be extracted from concentrates and occasionally directly from the ore itself by hydrometallurgical, pyrometallurgical, and electrometallurgical processes. Reduction of cobalt oxide with methane is one method for producing cobalt by pyrometallurgical route. Using methane as a reducing agent can be attractive especially in places where methane is available in abundance. The kinetics of reduction of cobalt oxide with hydrogen has been studied by Bustnes et al.[1] but for practical use, hydrogen is very expensive in comparison with methane, and frequently hydrogen is produced in metallurgical plants by methane reforming. Few studies are reported where methane has been employed directly for the reduction of metal oxides. Use of methane as a reducing agent has been reported by Ghosh et al.,[2] Qayyum and Reeve,[3] and Sparchez,[4] for iron oxide, and by Ale Ebrahim and Jamshidi,[5] for zinc oxide. The purpose of this work is to obtain kinetic parameters of reduction of cobalt oxide, CoO, with methane, toward assessing the feasibility of using methane to produce metallic cobalt. II. EXPERIMENTAL In this work, the thermogravimetric method was used in order to study the kinetics of the reduction reaction. A thermogravimeter (model TGH-1500 from Rheometric Scientific), which had a detection limit of 1 g, was used. In this equipment, a solid pellet was subjected to reaction with a continuous flow of gas containing methane (Air Products, 99.95 pct purity) as a reducing agent and the weight loss was recorded continuously. Experiments were carried out under isothermal conditions. Co3O4 (Merck, mean diameter 10.6 m, 98.8 pct purity) was used as the precursor material, which was made into flat pellets of different thicknesses and reduced in argon at 800 °C to CoO in 90 minutes. Reduction studies were conducted in a alumina tube of 2-cm diameter on CoO pellets with argon
B. KHOSHANDAM, PhD. Student, and E. JAMSHIDI, Professor, are with the Chemical Engineering Department, Amir-Kabir University of Technology (Tehran Polytechnic), Tehran, Iran 15914. R.V. KUMAR, University Lecturer, is with the Department of Materials Science and Metallurgy, Cambridge, CB2 3QZ United Kingdom. Contact e-mail: [email protected] Manuscript submitted January 16, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS B
(high-purity grade) as the carrier gas at a total flow rate of 100 to 120 cc/min for a mixture of argon and methane. At flow rate 100 cc/min, the reaction was dependent on flow rate, while at higher flow rate, the reaction was independent of flow rate. Experiments were carried out on the CoO pellets at atmospheric pressures in the temperature range of 800 °C to 950 °C. The geometry of the pellet was chosen to achieve a large diameter/thickness ratio in order to decouple the chemical reaction rate from diffusional resistance, such that the favored me
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