Liquid Iron Oxide Research Articles

Semiconductivity and physicochemical properties of iron oxide-containing slags

Solid and liquid iron oxides exhibit characteristics of semiconductors. The semiconductive behavior also features in some slags containing iron oxide. This paper aims at highlighting some of the experimental indications of the role of semiconductivity in electrical conduction, the chemical diffusion and in reaction kinetics at slag surfaces. It is not a thorough review of the subject matter but an attempt at shedding some light on the connection between these properties.

Catalytic H2S Conversion and SO2 Production over Iron Oxide and Iron Oxide/γ-Al2O3 in Liquid Sulfur

A stirred-glass autoclave containing liquid sulfur and solid iron oxide catalyst was used to study low-tonnage sulfur recovery from H2S-containing gas streams. The objectives were to test the feasibility of using both liquid sulfur as a reaction medium and iron oxide as a direct oxidation catalyst for prolonged H2S conversion. Using a 1.60% H2S and 0.80% O2 (balance N2) feed gas, fresh iron oxide acted primarily as a scavenger for bulk H2S removal from the inlet gas stream. Following the scavenging phase, the steady-state iron oxide/sulfide was able to maintain low catalytic activity (30% conversion). The steady-state catalyst did, however, have a strong ability to generate significant amounts of SO2 in the presence of inlet feed O2. Data showed that this SO2 production resulted from the oxidation of the liquid sulfur over the steady-state iron oxide/sulfide. The rate of SO2 formation was shown to be directly proportional to the concentration of O2 in the inlet feed gas. Although H2S conversions over stea...

｀１８´Ｏを含むＣＯ‐ＣＯ２気体質量分析によるガス‐溶融酸化鉄間の酸素交換反応速度測定

Reaction between molten oxide containing iron oxide and CO-CO2 gas is the essential reaction in numerous metallurgical smelting processes and the refining speed depends on this reaction rate. Therefore, the mechanism and kinetics for this reaction give us important information for the analysis, simulation and control of processes, and development of new refining systems. Many investigations have been done for clarification of reaction mechanisms between molten oxide containing iron oxide and CO-CO2 gas, however the direct measurement of oxygen exchange rate controlled by chemical reaction has not been conducted because of experimental difficulties. In the present work, oxygen exchange reaction rate between molten iron oxide and CO-CO2 gas has been measured by means of isotope exchange technique using C18O2-enriched CO2 gas. Isotope exchange technique is a useful method because the chemical reaction rate between gas and liquid phases could be measured directly without any influence of mass transfer in gas or liquid phases. The effects of temperature and CO2/CO ratio on the exchange rate have been investigated. It was clarified that the exchange rate was determined by interfacial reactions at first, and then by diffusion of 18O in liquid iron oxide.

The Mixing Efficiency of an Eccentric‐Disc Kneading Zone in Intermeshing Co‐ and Counter‐Rotating Twin‐Screw Extruders

AbstractThe distributive mixing efficiency of a twin‐screw extruder kneading zone consisting of eccentric disc elements was measured using an online video technique. Both co‐ and counter‐rotation were examined. Viscous Newtonian silicone oil was used as model liquid and black iron oxide pigment served as tracer substance. Under isoviscous, creeping flow and non‐diffusive conditions and for a fixed flow rate ratio of the colored and uncolored feed streams, the intensity of segregation S is only a function of the kinematic parameter Λ (the ratio of the imposed extruder throughput and the throughput at zero axial pressure gradient). The measured dependency of S on Λ is in qualitative agreement with the results of Pawlowski for a single screw extruder. The data was also plotted against the dimensionless speed of rotation, i.e. the product of the screw speed and the average residence time within the mixing section. This brings the abscissa ranges for mixers with different conveying capacity closer together, and differences in mixing efficiency between the tested configurations can be better interpreted. The energetic efficiency of the mixers investigated is compared by applying the concept of specific action. This helps to decide which mixer geometry and operating conditions produce a given homogeneity with the lowest amount of work done by viscous forces.

Magnetic fines from the Kaali impact-site (Holocene, Estonia): Preliminary SEM investigation

The Kaali crater field (1 sq. kilometre, 9 craters) offers a unique opportunity to recover large amounts of magnetic fines still partly preserved from late-stage weathering. SEM studies of these materials reveal an unusually wide spectrum of derivatives from the initial iron meteorite body, including minor amounts of unmelted metal fragments, and an abundance of more evolved products resulting from primary oxidation processes. Most of these products are sprays and splashes of liquid iron oxides, and some particles may be ascribed to oxide condensates from a vapor phase, as a result of both atmospheric ablation and vaporization upon impact. This wide range reflects varied impact conditions, due to variable masses and velocities of fragments after atmospheric disruption of the original meteoritic body. The large spectrum of magnetic fines from Kaali should provide an excellent probe into the chemical- and isotopic-fractionation of elements over a range of impact processes, from atmospheric entry to post-impact alteration. Magnetic fines from other sites of multiple impacts may have the same potential, and deserve more systematic attention.

The chemical diffusivity of oxygen in liquid iron oxide and a calcium ferrite

Measurements have been made of the chemical diffusion coefficient of oxygen in liquid iron oxide at temperatures from 1673 to 1888 K and in a calcium ferrite (Fe/Ca = 2.57) at temperatures from 1573 to 1873 K. A gravimetric method was used to measure the oxygen uptake during the oxidation of the melts by oxygen or CO2-CO mixtures. The rate was shown to be controlled by mass transfer in the liquid melt. The chemical diffusivity of oxygen in liquid iron oxide at oxygen potential between air and oxygen was found to be 4.2±0.3 × 10−3 cm2/s at 1888 K. That in iron oxide at oxidation state close to iron saturation was established to be given by the empirical expression log D=−6220/T + 1.12 for temperatures between 1673 and 1773 K. For the calcium ferrite (Fe/Ca=2.57) at oxygen potential between air and oxygen, the diffusivity of oxygen was found to be given by log D=−1760/T−1.31 for temperatures between 1673 and 1873 K.

Rate of interfacial reaction between liquid iron oxide and CO-CO2

The interfacial reaction rate between liquid iron oxide and CO-CO2 was determined using a thermogravimetric technique. The measured rates were controlled by the chemical reactions at the gas-slag interface. The apparent first-order rate constant, for the oxidation of liquid iron oxide by CO2, decreased sharply with the equilibrium CO2/CO ratio. The rate of reduction of liquid iron oxide by CO showed a slight increase with the oxidation state of the melt. At 1773 K, the apparent first-order rate constants are given by k=4.0×10−5(CO2/CO)−0.8 and k=4.0 × 10−5(CO2/CO)0.18 mol cm−2 s−1 atm−1 for the oxidation and reduction, respectively. The addition of basic oxides, such as BaO and CaO, resulted in an increased reaction rate, while the addition of acidic oxide, such as SiO2, decreased the rate. The results are consistent with the dissociation or formation of the CO2 molecule, involving the transfer of two charges, being the rate controlling mechanism of the reactions.

Interfacial kinetics of hydrogen with liquid slag containing iron oxide

Interfacial kinetics on the hydrogen reduction of liquid Fe t O in Fe t O-M x O y slag (M x O y = CaO, SiO2, Al2O3, and TiO2) has been studied at 1673 K. Because the rate of hydrogen reduction was very fast, the rate was controlled by gas-phase mass transfer under most of the experimental conditions. The effect of CaO or SiO2 addition on the interfacial chemical reaction rate of hydrogen reduction was empirically evaluated as a function of the ferrous-ferric ratio in the slag. The observed interfacial chemical reaction rates in Fe t O-CaO and Fe t O-SiO2 slags showed reasonable agreement with the estimated values. Most of the available literature data on the reduction rate of liquid iron oxide by solid carbon, hot metal, and reducing gases were also reviewed and compared with the results of the present work. It was found that the rate of hydrogen reduction of liquid iron oxide slag is much faster than that with other reducing agents such as solid carbon, carbon dissolved in the liquid iron, and CO gas.

The Solubility of Oxygen in Liquid Iron Oxide During the Combustion of Iron Rods in High-Pressure Oxygen

The combustion of pure iron rods in oxygen is characterized by excess oxygen in the molten products. The amount of oxygen dissolved in the molten mass exceeds that required for stoichiometric haematite, Fe2O3, the highest oxidation state for solid iron oxide. Oxygen mass-balance calculations and post-test product analysis suggest that the average oxygen-to-iron molar ratio of the molten oxide product is as high as 2.1 and possibly higher. This corresponds to an increase in oxygen solubility in the molten iron oxide (over that of molten iron metal), which is compatible with the existence of various forms of ferrite ions such as FeO2−1, Fe2O5−4, FeO3−3, and Fe2O7−8. The presence of this excess oxygen confirms the proposed heterogeneous mechanism for the burning of iron, that is, that primary oxidation takes place at an interface between liquid iron and the molten combustion products containing the excess oxygen.

The effect of surfactants on the interfacial rates of reaction of CO2 and CO with liquid iron oxide

The 14CO2-CO isotope exchange technique has been used to measure the rates of dissociation of CO2 on liquid iron oxide containing the surface active components P2O5 or Na2O, principally at 1673 K. The apparent first-order rate constant is found to decrease monotonically with small additions of P2O5 up to a factor of about 4 at 3.5 mol pct. Vaporization losses prevented detailed studies of the effect of Na2O, but it is shown that there is probably a twofold increase in the rate constant at a concentration of about 0.2 wt pct and a fivefold increase at a concentration between 0.5 and 1.6 wt pct. A smoothed surface potential model, based upon the Vol’kenshtein model for catalysis by semiconductors, is developed, and it is shown that the required surface potential changes due to the segregation of P2O5 and Na2O are physically reasonable.

The influence of oxygen pressure and P2O5 on the surface tension of liquid iron oxide at 1435 °C

The influence of oxygen pressure and P2O5 on the surface tension of liquid iron oxide at 1435 °C

Determination of the chemical diffusion of oxygen in liquid iron oxide at 1615 °c

The chemical diffusion of oxygen in liquid iron oxide has been studied by the oxidation of a melt in a long capillary at 1615 °C. When pure oxygen was used as the oxidizing agent, the surface composition of the slag was found to be in close agreement with the expected gas-slag equilibrium, suggesting that diffusion is the controlling step. This was not the case when air, 5 pct oxygen in argon or pure CO2 was used to oxidize the slag. The deviation of the surface composition from the expected equilibrium was in accordance with a mechanism of mixed control by both the gas-slag reaction and diffusion in the bulk. The average value of the chemical diffusivity of oxygen (or iron) in liquid iron oxide with Fe2+/FeT between 0.25 and 0.77 was established to be 3(±1) × 10-7 m2/s. This value is one to two orders of magnitude higher than those from earlier studies. There seems to be a reasonable correlation between the chemical and the ionic self-diffusivities through the Darken equation. A quantitative analysis in this respect and on the role of electron hole migration depends on the availability of data on the ionic conductivity and the tracer diffusivities.

Photoelectric measurement of the foaming process in the reduction of slags containing iron oxide

A measuring method for determining foaming volume is being developed. The volume increase and the progress of the foaming process can be continuously determined and quantified by optical means through evaluation of brightness differences. The influences of various reducing agents on the foaming process are considered. CO evolution resulting from the reaction between liquid iron oxide and carbon constitutes the decisive factor for foaming of this type. In contrast, the temperature-dependent formation of O2 which occurs during conversion of haematite to magnetite only produces a small increase in volume during the melting process. No foaming is observed during reduction by the gas phase at the surface of the specimen. The foaming behaviour of slags in the basic FeOn-CaO-SiO2 system is investigated. Maximum foaming occurs in the moderate basicity range. Similarly, foaming may also be maximized with moderate gangue contents in the oxide melt. Relatively high volume increases are likewise achieved within certain temperature ranges. The rate of gas formation constitutes the main criterion determining the foaming intensity. The highest volume increase values observed lie in the region of 1100% related to the initial volume. The foaming process always exhibits a reliable degree of reproducibility. Eine Meßmethode zur Bestimmung des Schaumvolumens wird entwickelt. Über die Erfassung von Helligkeitsunterschieden können optisch die Volumenzunahme und der Verlauf des Schäumens quantitativ und kontinuierlich bestimmt werden. Es werden die Einflüsse verschiedener Reduktionsmittel auf das Schäumen betrachtet. Die CO-Entwicklung bei der Reaktion zwischen flüssigem Eisenoxid und Kohlenstoff ist der entscheidende Faktor für derartiges Schäumen. Dagegen ruft die temperaturbedingte O2-Abspaltung aus dem Hämatit nur eine geringfügige Volumenzunahme während des Schmelzvorgangs hervor. Bei einer Reduktion durch die Gasphase an der Oberfläche der Probe wird kein Schäumen beobachtet. Das Schäumverhalten von Schlacken des Grundsystems FeOn-CaO-SiO2 wird untersucht. Ein Schäummaximum tritt im Bereich mittlerer Basizität auf. Ebenfalls kann ein Maximum bei mittleren Gangartanteilen in der Oxidschmelze beobachtet werden. In bestimmten Temperaturbereichen werden ebenfalls höhere Volumenzunahmen erreicht. Für die Stärke des Schäumens spielt die Gasbildungsgeschwindigkeit die wichtigste Rolle. Die höchsten beobachteten Werte für die Volumenzunahme liegen bei 1100%, bezogen auf das Ausgangsvolumen. Der Schäumvorgang zeigt stets eine aussagekräftige Reproduzierbarkeit.

Hydrogen Reduction of Liquid Iron Oxide Fines in Gas-conveyed Systems.

A laboratory scale fine particles-gas conveyed system was utilized to measure the reduction rates of liquid wustite with hydrogen at high temperatures. N2-H2 mixtures having various flow rates and compositions were flowed downward through a cylindrical reactor maintained at a constant temperature of 1723 to 1823 K. A batch of pure spherical wustite particles (mean dia.; 58μm) was concurrently fed into the reactor at a small constant rate and reduced in a hot zone. The reduction process was found to proceed in such a manner that metallic iron particles were enclosed inside a wustite droplet. Rate analysis was made of one dimensional mass balance equations for particle taking the shrinkage into consideration. Under relatively small reducing potentials, it was concluded that the major fraction of overall reaction resistance is attributable to chemical reaction. However, under higher reducing potentials, the reduction process was estimated to include an appreciable diffusion resistance within the liquid phase. >From the temperature dependence of forward chemical reaction rate constants, the activation energy was evaluated to be 110 kJ/mol.

The solubility of copper in lime-saturated and calcium ferrite-saturated liquid iron oxide

The solubility of copper in lime-saturated and calcium ferrite-saturated liquid iron oxide has been measured at 1300 °C by equilibrating copper-gold alloys with the melts in CO-CO2 atmospheres of oxygen potentials 10−7, 10−8, 10−9, and 10−10 atm. It was found that copper exhibits Henrian behavior in the oxide melts and that the solubility is given by $$wt pct Cu = 17.6a_{CuO_{0.5} } $$

溶融酸化鉄の還元速度

溶融酸化鉄の還元速度

溶融酸化鉄のCOによる還元反応速度に及ぼす添加物の影響

溶融酸化鉄のCOによる還元反応速度に及ぼす添加物の影響

On the interfacial rate of reaction of CO2 with a calcium ferrite melt

Measurements of the rate of dissociation of CO2 have been made by the14CO2-CO isotope exchange technique on calcium ferrite melts with Ca/Fe = 0.30 at 1300 °C. Studies have also been made of the interfacial rates of oxidation of calcium ferrite melts with an average CaO content of 19.45 wt pct (CaJFe ≃0.33) in CO2-CO atmospheres at 1362 °C. It is shown that the rates of oxidation are consistent with the rates of isotope exchange, indicating a common rate determining step. Measurements of the equilibrium Fe3+/Fe2+ ratio as a function of the CO2/CO ratio for 19.3 wt pct CaO melts at 1360 °C and for 28.7 and 18.6 wt pct CaO melts at 1300 °C are found to be in close agreement with the deductions of Takeda, Nakazawa, and Yazawa. Combination of the equilibrium data with the results of the isotope exchange studies indicate that the apparent first order rate constant for the dissociation of CO2 is inversely proportional to the square of the Fe3+JFe2+ ratio of the melt, as has been previously found for liquid iron oxide, lime-saturated calcium ferrites, silicasaturated iron silicates, and an equimolar “FeO”-CaO-SiO2 melt.

Reduction of Liquid Iron Oxide

Previous kinetic studies on the reduction of liquid iron oxide or iron oxide contained in liquid slag were reviewed, being focussed on experimental procedures.Reduction of liquid wustite with carbon dissolved in liquid iron proceeds faster than with carbon monoxide or solid carbon.Previous works have given much valuable information to understand the complicated reactions, and to show still some problems remained to be solved.

溶融酸化鉄の還元

溶融酸化鉄の還元