Reduction roasting (2)

Relationship between composition and carbon monoxide gas phase equilibrium temperature when reducing metal oxide shown in Figure 3, when the reduction reaction is exothermic (â–³ H <O), the reaction equilibrium constant K _P decreases with increasing temperature, equilibrium case The %CO in the gas phase will increase; otherwise, the %CO in the equilibrium gas phase will decrease. At a certain temperature, the relationship between the gas phase composition and the reaction direction can be judged by the following formula:

When solid carbon is used as the reducing agent, the reduction reaction is called direct reduction, and the reduction reaction is:
MO+CO=M+CO ₂
+)CO ₂ +C=2CO
MO+C=M+CO
The equilibrium gas phase composition at this time has a relationship with temperature as shown in Fig. 4. The two curves intersect at point a, and the gas phase composition and temperature corresponding to point a are the equilibrium state of the direct reduced body at a given pressure, and other points are It is not balanced. If the system is at point c, T _h >T _o , the reaction (1) is in equilibrium, but excess CO ₂ will promote the gasification of the solid carbon, increase the %CO in the system, and promote the reduction of the metal oxide. This process continues. Until all metal oxides are reduced. The gasification of carbon causes the gas phase composition to move toward point b, and finally reaches equilibrium at point b. Conversely, if the system is at point d, it will cause the metal to be oxidized, causing the gas phase composition to move toward point e. The process proceeds until all of the metal is oxidized and finally reaches equilibrium at point e. Therefore, the temperature corresponding to point a is the onset reduction temperature (ie, the theoretical onset reduction temperature) of the solid carbon-reduced metal oxide at this pressure. Since the gasification of carbon is related to pressure, the theoretical starting reduction temperature also varies with pressure. The higher the pressure, the higher the initial reduction temperature; the more stable the metal oxide, the higher the initial reduction temperature.

In addition to being in a pure state, metal oxides are often present in a bound state. Since the bound metal oxide is more stable than the pure state, it is more difficult to be reduced and must be reduced under higher temperature conditions.
The reduction roasting method is currently mainly used for the treatment of refractory mineral raw materials such as iron , manganese , nickel , copper , tin and antimony , so that the target mineral is converted into a state that is easily enriched by physical beneficiation or easily leached.

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