Reduction of iron-silicon-oxysulfide by CO gas injection
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I. INTRODUCTION
THE reduction of iron oxides in the temperature range below the melting point of iron appears to be a potential production route for high-purity iron. It has been reported that metallic iron is produced from Fe-S-O melts by CO gas rejection at 1200 8C,[1–4] which is lower than the melting point of iron (1535 8C). Impurities are limited because the solid solubility of impurities in metallic iron is very low at the given temperature. For example, sulfur dissolves in liquid iron over 0.1 wt pct at 1535 8C, but the solubility of sulfur in iron at 1200 8C is only 0.02 wt pct.[5] A value of 2.0 3 1025 g-O/cm2 s was observed to be the maximum reduction rate at 1200 8C.[3] The sulfur emissions were not a serious problem because the reduction rate of sulfur was low. The most important advantage of this oxysulfide bath is that the Fe-S-O system exhibits a liquid-phase field at a very low temperature, with a eutectic at 920 8C, permitting a low smelting temperature compared to the conventional processes. This would result into a high output per unit volume of the reactor, a low energy consumption, and the production of pure metallic iron. The present study was carried out to extend the investigation to the Fe-Si-S-O system. Very few studies of the reduction behavior in the Fe-Si-S-O system are described in the literature. The purpose of this article is to report the reduction behavior of Fe-Si-S-O melts by CO gas injection.
injection was not performed. The gas inlet of the furnace also allowed the system to be flushed with argon during fusion of the matte and between experiments. The gas train supplied the high-purity (99.9 pct purity) CO and Ar inlet gases. The CO and Ar-CO gas mixtures (PCO 5 0.5 and 0.3 atm, respectively) were used as an injection gas. The CO gas was injected in most experiments (PCO 5 1 atm). The matte charges were blends of commercially produced FeO, FeS, and SiO2. The Matte composition used in this study is shown in Table I. The amount of FeO, FeS, and SiO2 was calculated to obtain a 1 kg Fe-Si-S-O melt. The temperature of the matte inside the coil was monitored by inserting a Pt-10 pct Rh-Pt alloy wire thermocouple inside the alumina tube. Once the desired temperature inside the coil had been reached, each matte was isothermally held for 30 minutes. During this time, Ar was flushed through the system at a flow rate of 2 L/min. The reduction reaction was studied at the temperatures of 1150 8C and 1250 8C. At these temperatures, the liquid oxysulfide melt was obtained. After confirming that the gas composition in the furnace was pure argon, the tip of the alumina injection tube was set 3 cm below the melt surface. When the injection gas was changed from Ar to CO, a digital stopwatch was switched on. Subsequently, the exit-gas composition was analyzed by the mass spectrometer. The reduction rate was calculated from data of the exit-gas composition after CO injection.
II. EXPERIMENTAL
III. RESULTS AND DISCUSSION
The equipment used in the experimental setup consisted of a sealed furnace
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