Magnetite reduction

Fig. 14. Fluidized-bed reactor for SASOL I (M. W. Kellogg) having process conditions of an alkaline, reduced high grade magnetite, reduction degree 95% ...

It should be noted that the choice of Fe0 950 (wustite) rather than FeO in the preceding reactions is not arbitrary [10]. The steam-iron reaction would produce very little hydrogen at these temperatures if magnetite were reduced to FeO instead of Fe095O. Hacker et al. [55] determined that the activation energy of magnetite reduction with H2 and CO is equal to 95 and 98 kj/mol, respectively. The energy of activation of wustite oxidation with steam was found to be 29 kj/mol. 

Hematite Magnetite Reduction Reduction-dissolution reprecipitation Reducing gas Alkaline solution with N2H4... 

Replacement of Cr with Al has been investigated extensively in recent times. Several groups concluded that Cr can be successfully replaced with Al. In 2000 Araujo and Rangel [33] first time ever reported Fe-Al-Cu catalysts for WGS reaction. They prepared Fe-Al, Fe-Cu, Fe-Al-Cu catalysts by coprecipitation. They maintained the iron to dopant molar ratio of 10. Addition of Al to the iron oxide increases the catalytic activity of iron oxide slightly. However, addition of both Al and Cu to the iron oxide increases the WGS activity tremendously (34 x lO" mol g h ). The catalyst with both dopants showed higher activity than a chromium- and copper-doped commercial catalyst (25 X lO" mol g h ). This sample produces the active phase more easily than the other catalysts and shows resistance to a further magnetite reduction. 

Activation of the catalyst is carried out in a H2/N2 mixture at moderate pressure. The process must be carefully controlled in order to ensure the development of maximum surface area. The rate of reduction is controlled by adjusting the temperature the lower the reduction rate, the better the development of the micro porous structure (r = 100 to 150 A). Exposure to water/steam of the reduced part of the catalyst will cause sintering and loss of activity and counter-diffusion of water should be minimised by operating at highest possible gas velocities. Water is also reported to inhibit the magnetite reduction rate (15). It is removed by condensation before the exit gas is... 

Shoesmith et al. has made an extensive study of oxide-covered iron electrodes in EDTA and citric acid solutions. Three distinct potential regions were observed. In Region I ( > -100 mV vs. SCE), little Fe + was released, and there was only minor oxide dissolution. This is considered the induction period for pore formation. In Region II (-450 mV < E < -100 mV), potential values were between those of magnetite reduction (reductive dissolution) and metal dissolution, suggesting that autoreduction. 

Figure 2.8. The mechanism of magnetite reduction (a) describes the reducibility of a magnetite brick under standard conditions as a function of its porosity. In the range of poor reducibility the reaction is topotactic and leads to a core and shell structure visible in an optical microscope and shown schematically in (b). Section (c) describes the situation at the wustite-magnetite interface as can be seen in an electron microscope.

Key Words Vanadium-Titanium Magnetite, Reduction Swellability, Low Temperature Reduction Disintegration, Oxidized Pellets... 

Rudolph M, Erler J, Peuker UA (2012) A TGA-FTIR perspective of fatty acid adsorbed on magnetite nanoparticles—decomposition steps and magnetite reduction. CoUoids Surf A... 

The reduction of iron ore is accompHshed by a series of reactions that are the same as those occurring in the blast furnace stack. These include reduction by CO, H2, and, in some cases soHd carbon, through successive oxidation states to metallic iron, ie, hematite [1309-37-17, Fe202, is reduced to magnetite [1309-38-2], Fe O, which is in turn reduced to wustite [17125-56-3], FeO, and then to metallic iron, Fe. The typical reactions foUow. 

Coal pipelines have been built in countries such as France (8.8 km), and Russia (61 km), and pipelines are also used for transporting limestone, copper concentrates, magnetite, and gHsonite in other parts of the world. The first coal pipeline, built in Ohio, led to freight rate reductions. The pipeline stopped operation after introduction of the unit train, used exclusively to transport coal from the mine to an electric power generation station. 

The principal cathodic reaction on the upper surface of the membrane is the reduction of Cu " that is formed by the reaction of Cu with dissolved oxygen in the water these Cu ions are provided partly from the diffusion through the pores in the oxide membrane from within the pit and partly from those produced by cathodic reduction (equation 1.154). Lucey s theory thus rejects the conventional large cathode small anode relationship that is invoked to explain localised attack, and this concept of an electronically conducting membrane has also been used by Evans to explain localised attack on steel due to a discontinuous film of magnetite. 

In this process the reduction of the ferric components of the scale is coupled to oxidation of the base metal, both reactions yielding ferrous species readily soluble in the acid. For magnetite the processes are as shown in equations 11.1 and 11.2. 

In general there does not appear to be any direct correlation between the rate of the chemical dissolution of oxides and the rate of scale removal, although most work on oxide dissolution has concentrated on magnetite. For example, Gorichev and co-workers have studied the kinetics and mechanisms of dissolution of magnetite in acids and found that it is faster in phosphoric acid than in hydrochloric, whereas scale removal is slower. Also, ferrous ions accelerate the dissolution of magnetite in sulphuric, phosphoric and hydrochloric acid , whereas the scale removal rate is reduced by the addition of ferrous ions. These observations appear to emphasise the importance of reductive dissolution and undermining in scale removal, as opposed to direct chemical dissolution. 

At the even higher temperatures found in HP industrial process or power generating boilers, the oxidation of iron is accomplished by the reduction of hydrogen ions supplied by the HW. The magnetite film is thus formed directly. 

If hardness breakthrough occurs and goes undetected for any length of time, the treatment reserve is swamped and quickly becomes depleted. This loss of treatment is serious because calcium carbonate scaling can result. The reduction in alkalinity also can permit silicate scaling to occur and prevent adequate maintenance of the magnetite film, which protects the waterside metal surfaces from corrosion. 

Iron has been the dominant structural material of modem times, and despite the growth in importance of aluminum and plastics, iron still ranks first in total use. Worldwide production of steel (iron strengthened by additives) is on the order of 700 million tons per year. The most important iron ores are two oxides, hematite (Fc2 O3) and magnetite (Fc3 O4). The production of iron from its ores involves several chemical processes that take place in a blast furnace. As shown in Figure 20-22. this is an enormous chemical reactor where heating, reduction, and purification all occur together. 

Reduction of monocyclic aromatic nitro compounds has been demonstrated (a) with reduced sulfur compounds mediated by a naphthoquinone or an iron porphyrin (Schwarzenbach et al. 1990), and (b) by Fe(II) and magnetite produced by the action of the anaerobic bacterium Geobacter metallireducens (Heijman et al. 1993). Quinone-mediated reduction of monocyclic aromatic nitro compounds by the supernatant monocyclic aromatic nitro compounds has been noted (Glaus et al. 1992), and these reactions may be signihcant in determining the fate of aromatic nitro compounds in reducing environments (Dunnivant et al. 1992). 

Aluminothermic reduction is one among the few pyrometallurgical processes where the actual process closely follows the route theoretically predicted from thermodynamic data. This characteristic, coupled with the simplicity associated with the whole process, makes it well suited for demonstration experiments. The reduction of magnetite by aluminum is a suitable example in this context. 

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