Reduction of hematite

Some results of the reduction of hematite by graphite at 907 to 1,007°C in the presence of lithium oxide catalyst were correlated by the equation 1 — (1 — xY = kt. The reaction of solids ilmenite and carbon has the mechanism... 

The most important metallurgical process involving carbon is the reduction of hematite ore, which consists largely of iron(III) oxide, Fe203, mixed with silicon dioxide, Si02. Reduction occurs in a blast furnace (Figure 20.4a) typically 30 m high and 10 m in diameter. The... 

Fe(OH)2 exists as hexagonal plates as do the green rusts (Feitknecht Keller, 1950 Bernal et ak, 1959). The basic morphology of wiistite is cubic, but this compound is frequently obtained as very irregular particles. It is formed as irregular rounded crystals 20-100 (xm across by reduction of hematite with H2/H2O at 800 °C (Moukassi et al., 1984). 

Two sextets assigned to the A and B sites, can be fitted to a broadened Mossbauer spectrum. For maghemite formed via reduction of hematite to magnetite, followed... 

The reduction of hematite with H2 at 387-610 °C has been followed in situ using TEM and an environmental cell (Rau et al., 1987). The reduction reaction started at nudeation sites on the edge of the sample and as the reaction proceeded, a particle showed four reaction zones consisting of umeacted hematite, lamellar magnetite, porous magnetite and finally porous iron (the temperature was too low for wiistite). 

The rate controlling step was considered to be the reduction of magnetite to iron. During the reduction of hematite to magnetite there is an overall increase in volume due to dilation parallel to the c axis of hematite the dilation behaviour is dependent upon the reduction temperature (Husslage et al. 1999). 

Reduction of hematite at 400 °C in an atmosphere of 5% H2/95% Ar, saturated with water vapour and free from oxygen (Regazzoni et ak, 1981). 

Macedo, J. Bryant, R.B. (1989) Preferential microbial reduction of hematite over goethite in a Brazilian oxisol. Soil Sd. Soc. Am. J. 53 1114-1118... 

Write chemical equations that describe the following processes (a) the reduction of hematite in a blast furnace (b) the reduction of titanium tetrachloride to titanium metal (c) the removal of silica, Si02, from iron ore. 

The reduction of hematite was discussed in Section 7.6. We will use those results in describing methods of formation of ceramics here. 

Phosphate rock is calcined to remove carbonaceous material before being digested with sulfuric acid. Several different fluidization processes have been commercialized for the direct reduction of hematite to high-iron, low-oxide products. Foundry sand is also calcined to remove organic binders and release fines. 

The production of most of the steel manufactured in the United States begins with the reduction of hematite ore (mostly ferric oxide) with coke (carbon) in a blast furnace to obtain pig iron. The basic reaction is... 

In another example, five test cases were computed by PHREEQE and EQ3/6 and the same thermodynamic database was run for each program (INTERA, 1983) to test for any code differences. The five examples were speciation of seawater with major ions, speciation of seawater with complete analysis, dissolution of microchne in dilute HCl, reduction of hematite and calcite by titration with methane, and dedolomitization with gypsum dissolution and increasing temperature. The results were nearly identical for each test case. Test cases need to become standard practice when using geochemical codes so that the results will have better credibility. A comparison of code computations with experimental data on activity coefficients and mineral solubilities over a range of conditions also will improve credibility (Nordstrom, 1994). 

Carbothermic reactions are sohd-sohd reactions with carbon that apparently take place through intermediate CO and CO2. The reduction of iron oxides has the mechanism Fe Oy-H CO =>xFe-t C02, C02 + C=>2C0. The reduction of hematite by graphite at 907 to 1007°C in the presence of hthium oxide catalyst was correlated by the equation 1 — (1 — x) = kt. The reaction of sohd ihnenite ore and carbon has the mechanism FeH03-l- CO=>Fe -I-Ti02 + C02, CO2 + C = 2CO. A similar case is the preparation of metal carbides from metal and carbon, C -I- 2H2 CH4, Me -I- CH4 MeC -I- 2H2. 

This is a convenient parameter for a number of reasons. First, many oxidation reactions can be written to include molecular oxygen as a reactant, for example the reduction of hematite to magnetite. 

The ratio of oxidant to reductant (also called reduction factor, / ) in the process gas mixture has to be just optimal, in order to facilitate the reduction of hematitic to magnetitic phase and should not catalyze further reduction. In the present study R — A was utilized, where R = [(CO) + (H2)]/[(C02) + (H2O)]. 

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