Thermodynamic Analysis and Reduction of Bismuth Oxide by Ethanol FATIH KORKMAZ, SENOL CETINKAYA, and SERAFETTIN EROGLU In this study, ethanol (C 2 H 5 OH) was used as an alternative reducing agent for Bi 2 O 3 because ethanol is renewable, increasingly available, and low in toxicity. Thermodynamic analysis was performed to predict experimental conditions for Bi formation in the Bi 2 O 3 -C 2 H 5 OH-Ar system at Ar/C 2 H 5 OH molar ratio of 10.5. Ar was used as a carrier gas for ethanol. Bi 2 O 3 reduction kinetics was investigated at 600 K to 800 K (327 °C to 527 °C) at Ar flow rate 85 sccm. Ar flow rate was also varied at 600 K and 800 K (327 °C and 527 °C) in order to clarify the mechanism controlling the process. Mass measurements and XRD analyses were carried out to determine the extent of reduction. Fractional conversion increased with time and temperature. Full reduction time decreased from ~180 minutes at 600 K (327 °C) to ~30 minutes at 700 K and 800 K (427 °C and 527 °C). The reduction process was external mass transfer limited (Q a = 7.2 kJ/mole) above 700 K (427 °C). It was controlled by intrinsic chemical kinetics (Q a = 54.7 kJ/mole) below 700 K (427 °C). In the mass-transport-controlled regime, the extent of reduction increased with flow rate as predicted by a mass-transport theory. Possible reaction pathways were discussed using the thermodynamic and experimental results. DOI: 10.1007/s11663-016-0686-x Ó The Minerals, Metals & Materials Society and ASM International 2016 I. 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, auto- matic 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 (Bi 2 S 3 ) and bismite (Bi 2 O 3 ). In the case of bismuth sulfide ore, Bi 2 S 3 is initially roasted in atmosphere containing oxygen to obtain Bi 2 O 3 . Bi 2 O 3 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 reac- tants. Among the gaseous reducing agents, hydrogen is the most common one used for the reduction of metal oxides such as NiO, [3] Fe 2 O 3 . [4] But, it is relatively expensive. In the present study, ethanol (C 2 H 5 OH) was used as an alternative reducing agent for Bi 2 O 3 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 Bi 2 O 3 using C 2 H 5 OH as a reducing agent. The present study aims to investigate pyrometallurgical reduction behavior of Bi 2 O 3 in a flowing atmosphere containing C 2 H 5 OH. Furthermore, thermodynamic analysis in the Bi 2 O 3 - C 2 H 5 OH-Ar system was carried out in order to predict process parameters and to understand reaction path- ways 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 con- densed 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, Bi 2 O 3 and C 2 H 5 OH 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 were considered to be as the constituents of the gas phase. They include H 2 ,H 2 O, CO, CO 2 , CH 3 , CH 4 , C 2 H 4 , C 2 H 6 , CH 2 O, CH 4 O, C 2 H 2 O 2 , Bi, Bi 2 , and BiH 3 . Condensed equilibrium phases were assumed to be Bi 2 O 3 , Bi, and C. Input 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: senol-c@istanbul.edu.tr Manuscript submitted December 7, 2015 METALLURGICAL AND MATERIALS TRANSACTIONS B