The decomposition, reduction and reoxidation of oxides are an important part of the chemical reaction in the sintering process. It affects the mineral composition of the sintered ore and the formation of the liquid phase, thus affecting the quality of the sintered ore. For example, the sintering atmosphere is appropriately controlled to reduce the reduction process of iron oxide, promote the formation of Fe 2 O 3 and reduce the formation of FeO, which is advantageous for the improvement of the reduction property of the sintered ore.
(A) decomposition of the iron oxide compound sintered many oxides, iron or manganese compound mainly iron oxide, magnesium calcium oxide in the flux, if these oxide decomposition reaction during the sintering process is determined by Usually the metal oxide decomposition their chemical reaction equilibrium constant (Kp) and other changes in pressure level ([Delta] Z) can be represented by the following formula:
2MeO=2Me+O 2
If MeO and Me are present in a solid phase without melting each other, the reaction equilibrium constant of the above formula is equal to the decomposition pressure:
K p =P o2
The relationship between the decomposition pressure and the standard isostatic position of the reaction is:
ΔZo=-KTlnP o2
When the partial pressure of oxygen in the gas phase is P' o2 , then
When P o2 >P' o2 , ΔZ<0 oxide decomposes,
When P o2 <P' o2 , the ΔZ>0 reaction proceeds in the direction in which the oxide is formed;
When P o2 = P' o2 , the ΔZ = 0 reaction tends to equilibrium.
In the atmosphere P' o2 = 0.21 and most metal oxides have a much lower decomposition pressure than 0.21 gas, so most metal oxides are relatively stable in the atmosphere.
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The decomposition pressure of MnO 2 , Mn 2 O 3 and Fe 2 O 3 is relatively large, the partial pressure of MnO 2 at 460 ° C is 0.21, the partial pressure at 550 ° C is 1.0 atm (98066.5 Pa), and Mn 2 O 3 reaches the corresponding partial pressure. The temperature is 927 ° C and 1100 ° C. Therefore, the advanced oxide of iron and manganese (that is, the oxide with high degree of oxidation) begins to decompose even in the drying zone or pre-tropical zone during the sintering process, and Fe 2 O 3 is at 1383 ° C. The decomposition pressure is 0.21, and the decomposition pressure at 1.052 ° C is 1.0, which is more difficult to decompose than the advanced oxide of manganese. Under sintering conditions, the actual pressure of the gas in the sintering zone is 0.9 atm (0.9×98066.5 Pa), so the partial pressure of oxygen is 0.18-0.19 atm (0.9×98066.5 Pa); the pre-tropical exhaust gas contains 8-10% oxygen. The partial pressure of oxygen is 0.072-0.09 atm (×98066.5 Pa), and the sintering temperature in the combustion zone can reach 1350~1450 °C. The partial pressure of oxygen near the carbon particle is lower than that of the pre-tropical zone, so Fe 2 O 3 Decomposition or violent decomposition occurs. Magnetite Fe 3 O 4 is only 10 - 7.5 at 1500 ° C (×98066.5 Pa), so decomposition under sintering conditions is impossible. However, in the presence of SiO 2 , the temperature is higher than 1300 to 1350 ° C, which can be decomposed as follows:
2Fe 3 O 4 +3SiO 2 =3(FeO) 2 · SiO 2 +O 2
Thermal decomposition of the floc body (Fe x O) is not possible under sintering conditions because its decomposition pressure is lower than Fe 3 O 4 at the same temperature.
The decomposition temperature of FeO can be calculated by the following formula:
Therefore, FeO cannot be decomposed under sintering conditions. There are also many oxides in the sinter, which have a lower decomposition pressure than FeO, and therefore require a higher decomposition temperature. The greater the negative value of ΔZ°, the greater the affinity of metal and oxygen, that is, the less the metal oxide is decomposed. The calcium and magnesium oxides are seen from the figure, and the ΔZ° is the smallest, so it does not occur under the sintering temperature and atmosphere. Any decomposition.
(II) Reduction of iron oxide During the sintering process, there are reducing gas CO and red hot fuel particles near the fuel particles, so there is a strong reducing atmosphere, so the oxide and liquid phase of iron, manganese and the like in the sintered material The iron and manganese oxides in the medium will be reduced.
That is, A, B, C, and D are the stable regions of Fe 2 O 3 , Fe 3 O 4 , FeO, and Fe, respectively. See Fig. 2, when there is excess fixed carbon, the reduction reaction products of various oxides of iron are determined. The equilibrium curve of the gasification reaction is CO 2 + C = 2CO, as shown in Figure 3.
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