Study On Carbothermal Reduction Behavior And Mechanism Of Manganese Ore Powder In Microwave Field

Since the current ferroalloy production process has the disadvantages of long production cycle,low production efficiency,high energy consumption and serious pollution,it is very necessary to make research on the new technical production process of ferroalloy to realize better energy conservation,lower consumption and higher productivity.This paper took the raw material of South Africa manganese ore powder and coke in one domestic ferroalloy plant as the study object and carried out the reduction behavior and basis study of the microwave heating of coke contained manganese ore powder.Considering that there is few the basic theory study on the microwave heating process,this paper mainly studied on the four aspects:（1）Study on the material heating characteristics in microwave field;（2）Study on the micro morphology of mineral phase in the course of the microwave heating reaction;（3）Thermodynamic analysis of microwave electromagnetic field;（4）Dynamics study on the microwave heating of manganese ore powder contained coke.The following conclusions were drawn from the above research:（1）South Africa manganese ore power and the coke used in the industry manganese melting can be quickly heated up in a short time in the microwave field,which indicates the feasibility of the microwave heating for ferroalloy;It has certain relationship between the heating rate,the microwave power,material mass and the radiation area of the mixed raw material.The change of the dielectric constant,dielectric loss factor and the loss tangent of the single material and the mixed material from the room temperature to the 1000℃ indicates the single material and the mixed material have good absorption and storage capacity for microwave and also good dielectric loss capability.The penetration depth of the microwave is betweenl0.4-84cm,which is larger than the crucible diameter used in the experiment,and in this condition the material can absorb the microwave very well and achieve the uniform distribution of the temperature field,then realize the overall heating effect.（2）There is no metal phase precipitation when the manganese ore powder contained carbon is conventional heated under the temperature of 700-1100 ℃;however,when it is microwave heated,the metal phase is precipitated at the temperature of 700 ℃ and insoulated for10 minutes,which indicates the microwave heating reduces the carbothermal reduction temperature,the conventional thermodynamic calculation cannot meet the requirement of the thermodynamic analysis in the microwave field,and the thermodynamic analysis in the microwave field calls for developing and polishing.On the interface direct reduction reaction of the manganese ore powder and coke,CO and CO₂ are produced;CO₂ sets off a gasification reaction with coke and produces CO;CO sets off a gas-solid reaction with oxides;Oxides getting on with each other will rise thermal tearing,which brings convenience to the CO emit and oxides reduction reaction.The carbon in the slag phase becomes the thermal center,which creates good thermodynamic and dynamic condition for the carbon diffusion in the slag and gasification reduction reaction,above which can make the residue manganese oxide fully reduced and thus the metallization rate is greatly enhanced.（3）Establishing the thermosdynamics theories under the function of the microwave filed.Combine the classical thermodynamics with the electric field and the magnetic field to derive the thermodynamics in single field;Combine the electromagnetic compound field under the function of the microwave with classical thermodynamics to derive the thermodynamics under the function microwave electromagnetic field;The conclusion of the promotion or inhibition function of the microwave electromagnetic field on the chemical reaction was drawn by comparison of the chemical equilibrium constants in the presence or absence of the electromagnetic field function.（4）In the microwave heating condition,the reduction rate can be expedited by increasing C/O ratio and temperature.The reduction rate can also be expedited by reducing the particle size of manganese ore,however further reducing the particle size after the particle size has been reduced to 150 mesh will not expedite the reaction rate obviously.Thermal weight loss rate in the microwave heating condition is much larger than the conventional heating in the condition of the same temperature and insulation time;The rate increase factor Q is bigger than 1 between the temperature of 700-1110 ℃.which indicates that the microwave heating has a promote function on the carbothermal reduction reaction;The promote function of the microwave heating will be much more obvious at the low temperature and the later stage of the low temperature reaction.（5）The dynamics model under the function of the microwave filed was established based on the microstructure analysis and thermal gravimetric analysis of mineral phases and also the microwave heating,Overall reduction and thermal tearing structures were introduced into the dynamics model;The speed control segment of microwave heating reaction is CO gas internal diffusion,the microwave heating can also promote the interface chemical reaction,and the calculated apparent activation energy is 29.68 kJ·mol_-1;The speed control segment of conventional heating reaction is the interface chemical reaction,and the calculated apparent activation energy is 119.35 kJ·mol_-1;The above results indicates that the microwave heating can not only expedite the reaction rate but also reduce the reaction activation energy and improve the dynamics condition of the gas-solid reaction.The non-thermal effect of microwave heating of manganese ore powder containing carbon is verified from the view of dynamics.