Thermodynamic Analysis and Reduction of Bismuth Oxide by Ethanol
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INTRODUCTION
BISMUTH (Bi) is a brittle metal with high density, low melting point, low thermal conductivity, and low toxicity. Because of these properties, Bi and its alloys have gained substantial attention in recent years for various applications such as dental prosthesis, automatic fire-extinguishing systems, lead-free solders, and ammunitions. Bismuth is usually obtained as a by-product of mining and refining of metals such lead and copper.[1] Bismuth can also be found in minerals such as bismuthinite (Bi2S3) and bismite (Bi2O3). In the case of bismuth sulfide ore, Bi2S3 is initially roasted in atmosphere containing oxygen to obtain Bi2O3. Bi2O3 is reduced by solid C to obtain metallic Bi.[2] The use of solid reducing agent, however, requires high temperatures and long reaction times owing to sluggish reaction rates between the solid reactants. Furthermore, the metallic product can be contaminated by solid carbon having impurities like Ca, Si, Fe, S, and P. Gas–solid reaction (gas-phase reduction) has received considerable attention because it is an efficient way to increase reduction rate at low temperatures owing to close contact between the reactants. Among the gaseous reducing agents, hydrogen is the most common one used for the reduction of metal oxides such as NiO,[3] Fe2O3.[4] But, it is relatively FATIH KORKMAZ, Graduate Student, SENOL CETINKAYA, Assistant Professor, and SERAFETTIN EROGLU, Professor, are with the Department of Metallurgical and Materials Engineering, Faculty of Engineering, Istanbul University, Avcilar, 34320 Istanbul, Turkey. Contact e-mail: [email protected] Manuscript submitted December 7, 2015 METALLURGICAL AND MATERIALS TRANSACTIONS B
expensive. In the present study, ethanol (C2H5OH) was used as an alternative reducing agent for Bi2O3 because it is renewable, increasingly available, easy to transport, biodegradable, low in toxicity, and produced in large quantities from various sources such as biomass, plants. To the best of our knowledge, no report has been published on metallic Bi production from Bi2O3 using C2H5OH as a reducing agent. The present study aims to investigate pyrometallurgical reduction behavior of Bi2O3 in a flowing atmosphere containing C2H5OH. Furthermore, thermodynamic analysis in the Bi2O3C2H5OH-Ar system was carried out in order to predict process parameters and to understand reaction pathways leading to the formation of metallic Bi.
II.
THERMODYNAMIC ANALYSIS
It has been carried out by the method of minimization of the Gibbs’ free energy of a system.[5] For a system of known input composition at a given pressure and temperature, both the equilibrium gas phase and condensed phase compositions can be computed by this method. It requires specifying all possible species and condensed phases known to exist in the temperature range of interest. In the present study, Bi2O3 and C2H5OH were used as input reactants. Ar was used as a carrier and diluting gas. Therefore, the computations were carried out in the Bi-O-C-H-Ar system at 1 atm. In this system, 70 species w
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