Pure Wustite Research Articles

Hydrogen reduction of magnetite concentrate particles

ABSTRACT The reaction kinetics of hydrogen reduction of iron ore concentrate particles was studied in the present research work. Thermogravimetric analysis was used to study the reaction progress at temperature range of 700–900°C. Various methods were used to obtain the governing mechanism and reaction rate constant. It was resulted that, the reduction rate of ore concentrate was between the reduction rates of pure magnetite and pure wustite. The experimental work showed that, hydrogen reduction of magnetite to wustite has the greatest chance of occurrence at temperature range over 700°C. The reduction reaction can occur as a single-step reaction above 1000°C. The first-order reaction was a very important model for this reduction at the studied temperature range. Finally, the activation energy was obtained about 29.48 kJ.mol−1 .

Effect of Ca(II)-ion in Wüstite on its Reduction to Iron

Fired compacts of hematite doped with different contents of CaO (mass fractions were 3.5, 4.0, 4.5, 5.0 %) were isothermally reduced to wustite in a CO-CO 2 gas mixture at 1173K. It was found from X-ray diffraction investigation that the lattice parameters of wustite increased with CaO content dissolved in wustite crystal. The pure wustite as well as the wustite doped with CaO were reduced at different temperature. The results showed that the reductions were promoted with increasing CaO content. The higher the content of CaO dissolved in wustite crystal was, the larger the lattice parameter and the interplanar distances of wustite became. This expansion was helpful to the migration of Fe ions and enhanced the reduction. At the early stage, the reduction of pure and doped wustite compacts was controlled by the interfacial chemical reaction step. At the latter stage, the gaseous diffusion was the rate-determining step for both sample types.

Bulk moduli of magnesiowüstites from static compression measurements

The static compression of two magnesiowüstites with 60 and 80 mol % FeO has been measured up to 500 kbar under quasi‐hydrostatic conditions. Within the framework of a Birch‐Murnaghan equation of state, these and other data for magnesiowüstites are consistent with linear variations of the 1‐bar isothermal bulk modulus and of its 1‐bar pressure derivative, from pure wüstite (Ko = 1.545 ± 0.01 Mbar, Ko′ = 2.75 ± 0.3) to periclase (Ko = 1.600 ± 0.005 Mbar, Ko′ = 4.85 ± 0.2). The composition with 80% FeO, but not that with 60% FeO, exhibits a second‐order like phase change analogous to the magnetic transition already described for wüstite at around 150 kbar. The lack of a significant dependence of the bulk moduli on nonstoichiometry suggests that the effect of pressure on the defect structure is not as simple as assumed previously.

Electrical properties of manganese doped ferrous oxide at high temperatures

Electrical conductivity and thermoelectric power of Mn-doped ferrous oxide have been measured as a function of temperature (1070–1570 K) and oxygen pressure in the whole range of its stability. It has been shown that manganese changes the concentration of ionic defects in ferrous oxide and changes its electrical properties toward classic semiconductor; the complex defect structure characteristic for pure wustite, being observed up to 20–30% Mn. The metallic behavior found for highly defected pure wustite is also observed for Fe 1 − x Mn x O, containing 15–20% Mn, although the corresponding pressure range narrows and shifts toward the higher pressures.

Influence of potassium on the redox kinetics of wustite in its homogeneity range

In view of the numerous previous interpretations of the role of potassium in the reduction of wustite, experiments have been carried out under conditions that allow a more straightforward conclusion: instead of working with a diphasic solid (wustite partially reduced to iron), wustite single crystals were submitted to a series of redox cycles in CO-CO 2 at 890°C, inside its homogeneity range, with and without potassium. With pure wustite, the initial rate of the reaction was shown to be controlled by the surface chemical reaction, as it is linearly dependent on the total gas pressure. Such a conclusion seems valid for the main part of the reaction. Therefore, the chemical rate constant was derived as a function of the solid stoichiometry. Doping with 1 atom-% of potassium brings about an increase in the chemical rate constant which is multiplied by factors of roughly 5 and 10 for reduction and oxidation, respectively. However its behaviour as a function of the solid composition is more complicated. These results indicate that potassium acts directly on the surface exchange between wustite and a CO-CO 2 gas phase, and rule out several other interpretations.

The gaseous reduction of solid calciowustites in Co/Co2 and H2/H2O gas mixtures

The reduction of calciowustites has been carried out in CO/CO2 and H2/H2O gas mixtures at temperatures between 1073 and 1373 K. The effect of lime additions to the wustite is to extend considerably the range of gas conditions over which porous iron morphologies are observed compared to those found on reduction of pure wustite. The products obtained at low oxygen potentials consisted of porous iron containing a dispersion of CaO particles, at intermediate oxygen potentials a two phase structure consisting of porous iron and dicalcium ferrite was formed, and at high oxygen potentials a dense iron layer over the oxide surface is observed throughout reduction.

気孔率の異なるウスタイトペレットの硫化水素含有水素ガスによる高温還元挙動

In order to understand the effect of sulphur in reducing gas on the reduction behavior of iron oxides, the reduction experiments were conducted in H2-H2S mixtures with various sulphur activities at 1 000 and 1 200°C. Macroscopic reduction patterns of pure wustite pellets can be divided into seven types, depending on the porosity of pellets and the activity of sulphur in the gas. This classification is slightly modified by the addition of MgO and CaO. The reduction of pellets with low porosity is retarded greatly due to the formation of iron-oxysulphide liquid. The retardation of reduction does not occur with pellets of high porosity even under the high sulphur activity to form FeS. However, the reduction is retarded provided that the sufficient amount of the liquid to fill up the pores is formed. The activity of sulphur in equilibrium under iron, wustite and iron-oxysulphide liquid was determined experimentally. MgO in wustite raises the sulphur activity and CaO lowers it. Sulphur in the gas without the formation of sulphides causes the topochemical reduction pattern, independently of the presence of foreign oxides.

Hydrogen reduction of wustite single crystals doped with Mg, Mn, Ca, Al, and Si

In order to investigate the reduction mechanism of wustite in the presence of impurities usually met in the ironmaking industry, single crystals have been prepared with Mg, Mn, Ca, Al, and Si as dopants. The amounts of dopant in the lattice is around 4,4,2.5,0.5, and 0.01 mol pct, respectively, at 800 ‡C. For reduction with pure hydrogen, from 600 to 950 ‡C, Ca is the most efficient for accelerating the process at high degrees of reduction (75 pct) Mg and Mn are also active in this respect. Al has only a slowing down effect. Si also slows down the reaction at temperatures between 600 850 ‡C. In the presence of 20 torrs of water vapor in the gas, Mg and Mn are less efficient and unable to prevent the same slowing down of reaction observed with pure wustite at around 850 ‡C and classically called the ‡rate minimum‡. Our interpretation of these results is mainly based upon the observations of microstructures of partly reduced crystals which show a change in the texture of the iron produced which can be correlated with the reduction rate. These observations lead to a possible explanation in terms of the role of inclusions of impurity oxides on the sintering process of the metal, correlated with their ability to dissolve into the wustite lattice. However, this suggestion cannot apply in the case of Si at low temperatures, and this element is therefore supposed to play a role in the stages of reaction associated with the surface of the crystals.

A study of the mechanism of reduction with hydrogen of pure wustite single crystals

A study of the mechanism of reduction with hydrogen of pure wustite single crystals

A study of the mechanism of reduction with hydrogen of pure wustite single crystals

Many economic studies have shown that iron ore reduction could be an important use of hydrogen, provided that its price was low enough. With this in mind, it was important to clarify the reasons of the significant slowing down, observed between 700 °C and 900 °C, in many experimental investigations of iron ore (or oxide) reductions with hydrogen and attributed to very different reasons. The experiments reported here have been designed with wustite single crystals so that safer conclusions may be derived than with the more complex situation encountered with iron ores. TGA, coupled with microstructure investigations, has shown conclusively that the slowing down is connected with the iron texture evolution toward a layer more impermeable to diffusion in the pores. Such a behavior is still increased in wet hydrogen by the blocking of active sites on wustite by water vapor. Another result is worth stressing: the very irregular shape of the reaction interface, quite different from the classical topochemical model.

Diversity and complexity of the wustite solid solutions II - some properties connected with the localized electron state

The electron state for any wustite solid solution is derived from the distance criterion and graphically outlined as a function of the substituant oxidation number, ionic radius and cationic fraction. The electrical properties of wustite and of some solid solutions are reviewed. For pure wustite, attention is drawn to the non-intervention of the interstitial iron, and to possible preferential paths for electronic holes with some consequences for the Seebeck coefficient. For wustite solid solutions, the behaviour in diluted systems is in agreement with the defect formation equations; concentrated solutions display complex and varied properties. Data on the Néel temperature variations are rather well documented and explained thanks to Smart's modification of the Molecular Field Theory, except for monovalent substituants due to the complicated situation provided by the controlled valence mechanism.

Al<SUB>2</SUB>O<SUB>3</SUB>, CaO, MgOを含むマグネタイトおよびウスタイトの還元によつて生成する還元鉄の気孔径分布

The pore-radius distributions in the reduced iron from magnetite and wustite containing several foreign oxides were measured by the mercury penetration method, and the cross sections of the wustite grains in the partially reduced samples were observed.The following results were obtained.(1) Wustite grains reduced from magnetite containing Al2O3 are reduced nontopochemically and the micro pores are formed in the reduced iron. However, this behavior is not observed when the wustite as a starting material contains Al2O3.(2) Wustite grains which are reduced from magnetite and wustite containing CaO are reduced nontopochemically and the pore radius becomes larger with increasing the quantities of CaO.(3) Wustite grains containing MgO are reduced topochemically as in the case of pure wustite grains and the addition of MgO gives little effect to the pore-adius of reduced iron.(4) It is concluded that those effects of Al2O3 and also CaO can be found when the compounds of the foreign oxides with iron oxides are precipitated in wustite during the reduction.