Microwave Technology in Metallurgical Applications
Microwave heating application in metallurgy metallurgy developed in recent years new technologies, some of the world's developed countries such as the United States, Britain, Germany, Japan, Canada , Australia, etc. are concerned about this new technology research, China is also eight 1910s began the research work in this field . Microwave heating application in metallurgy Although still in the development stage, but has made ​​a lot of very important research results , for example: microwave (2450MHz, 800W) and 17 kinds of carbon oxides and sulfides radiation, some of the compounds in a min can be heated to several hundred degrees Celsius .
Experimental results show: microwave heating can promote nickel oxide, cobalt oxide and manganese leaching before the pre- reduction , can promote molybdenum sulfide and chloride and rhenium sulfide roasting , almost all of the metal industry are treated by microwave . The late eighties , microwave heating is used for ore crushing, pretreatment of refractory gold from low grade ores and tailings recovery of gold from the ore extracted metals and heavy metals, iron ore and vanadium-titanium magnetite carbon thermal reduction , industrial waste treatment and so on.
Microwave heating and conventional heating type , he does not need outside to the inside of the heat conduction , but by microwave energy dissipation within the material to heat the material directly . According to the material properties ( conductivity, magnetic conductivity, permittivity) of different microwave can be directly and efficiently generates heat within the material in the whole .
Microwave in Metallurgy applications with the following conventional heating incomparable advantages :
( A ) selective heating of materials , heating rate, high heating efficiency ;
( 2 ) Microwave simultaneously promote endothermic and exothermic reactions , the catalytic reaction ;
( 3 ) When the microwave heating instead of conventional heating , melting , and other high-temperature chemical reaction may be at a very low temperature, i.e. microwave heating of reducing the effect of temperature chemical reaction ;
( 4) The microwave energy can make high-speed vibration atoms and molecules , the chemical reaction so as to create a more favorable thermodynamic conditions ;
( 5 ) it is easy to microwave polar liquid ( such as water, ethanol, various acid solution, etc. ) heating , microwave heating which can be used to facilitate dissolution of minerals in the solvent , the process of improving hydrometallurgical leaching rates and lower the process of energy ;
( 6 ) Microwave itself does not produce any gas to be purified only the reduction or oxidation reaction of the gas , and thus beneficial to the environment ;
( 7 ) Easy automatic control ; equipment is simple , there is no thermal inertia , according to the production process requires real-time control . The whole production line only 1 to 2 operatives .
Mineral warming in the microwave field performance
Metal ores usually refers to deposits mined from solid material , generally useful metallic minerals and associated gangue minerals , mineral aggregates . Microwave heating on mineral processing, its effect is often treated with mineral ( processed material ) itself conductive properties and material composition and structure.
1 , on the heating rate of conductance
Because microwave is between radio waves and light waves between the high ( typically frequency 100MHz ~ 100000MHz), therefore , the microwave heating of the heating rate of the material depends primarily on the material conductivity and penetration depth . Studies show that : the mineral insulator type conductivity is small (σ <10-81/Ωm), can hardly absorb the microwave , the microwave is transparent ; conductivity minerals have good electrical conductivity (σ> 1061/Ωm), microwave such a large energy loss in the mineral , but a small penetration depth , and thus the heating rate is not fast ; semiconductor -type minerals (σ = 10-81/Ωm ~ 1061/Ωm), the dielectric loss factor is large, while microwave penetration depth is large, which can well absorb the microwave , the heating rate is generally large .
2 , mineral components and structural impact on the heating rate
The results showed that: the heating rate effects mineral Another important factor is the composition and structure of the mineral , the heating rate of the mineral type of mineral ions , ionic radii , bond type and directly related impurities . Elemental basic elements can be microwave heating , microwave heating in which the carbon fastest heating rate , only the 60s it can be heated to 1556K, therefore , commonly used carbon as carbon thermal reduction of metal oxide additives. Most sulphide and sulfur has a large heating rate, which is mainly due to their frequencies in the microwave has a large dielectric constant. However , for different positive ions, minerals and compounds heating rate is different: containing Fe2 +, Co2 +, Ni2 +, Mo4 +, Cu +, Sn2 +, Pb2 + minerals and compounds have a faster heating rate , which contain Sb3 +, Zn2 +, Ag + is minerals and compounds are relatively slow heating rate , the fundamental reason is that the former type of transition bond -based, the latter mainly covalent bond type . Most of the oxide ore and oxide has a large heating rate , which contains Fe3 +, Fe2 +, Mn4 +, Cu +, Sn4 +, Pb2 +, Sb3 + oxidation and oxide ore with a heating rate of sulphide and sulphide similar . Oxysalt halide minerals and compared with other minerals and compounds under microwave heating rate is low. In addition to other mineral bond type , the heating rate is also related to the content with the mineral impurities , usually containing some impurities minerals and compounds have better heating rate , for example: tin cassiterite and compared to pure chlorine dioxide , although the chemical composition are SnO2, but the heating rate of cassiterite 19.7 (K / s), and a heating rate of pure tin dioxide was 4.75 (K / s).
Microwave heating of the ore microstructure
Ores usually contain various minerals ( including useful minerals and gangue minerals ) , when using the conventional heating method , the various minerals in the ore the same heating rate , they are heated to approximately the same temperature , the minerals will have a significant temperature difference , if the heating process is not crystal transformation , phase change or chemical change occurs , the microstructure of minerals usually do not change significantly due to heat . When heating with the microwave , the situation is quite different , since various mineral ores consisting of a different nature , are in the microwave heating field at different speeds , thus different minerals in the ore will be microwave heated to different temperatures , since the microwave can be heated most of the useful minerals , without heating the gangue minerals , which in the useful minerals and gangue minerals may form a distinct local temperature , so that the thermal stress generated between them , when such a large thermal stress a certain extent, it will interface between the mineral cracks , the cracks can effectively promote the useful minerals monomer dissociation and increasing the effective reaction area useful minerals , for reducing the cost of grinding ﹑ improve mineral recovery and accelerate the metallurgical reaction rate , has important practical significance. With a scanning electron microscope (SEM) of metal oxide ore to ore and curing stress rupture studies show that the microstructure of the ore before microwave radiation significantly different after microwave later, you can observe a thermal stress rupture ore , ore and gangue are separated .

Microwave heating decomposition of minerals
Smelting process for ore more by various compounds, important compounds are carbonates, oxides, sulfides and chlorides . Compounds when heated to a certain temperature , it can be decomposed into a simpler compounds and gases. Thermal decomposition of the compound to absorb a lot of heat , the reaction rate is usually controlled by the heat . Conventional heating method , the heat is not effectively transmitted to the inner surface of the compound , resulting in low rates of decomposition process , high energy consumption . As the microwave can generate heat internally of the compound , and therefore can effectively accelerate the rate of decomposition of the compound and lower the energy consumption of the process .
1 , the microwave thermal decomposition of manganese dioxide
In the aluminum thermal reduction manganese from manganese oxide production when , Mn3O4 in MnO2, Mn2O3, Mn3O4 and MnO has the best oxygen . It can ensure an appropriate reaction rate to produce a sufficient temperature , but also to ensure the safety of the process . Oxygen content is too high will lead to a risk of explosion or cause loss of control of the process , while the oxygen content is too low will cause the reaction heat is not enough to melt the material , resulting in metal and slag are not well separated . Thus, in order to smoothly carry out the process , the oxide must be adjusted or the oxygen content of the ore . One way of adjusting the oxygen content in the 1273 ~ 1373K through the thermal decomposition temperature of the MnO2 into Mn3O4. Replace the traditional microwave heating to facilitate conduction heating MnO2 into Mn3O4, will increase the reaction rate and lower the energy consumption of the process .
MnO2 used is chemically pure chemical reagent ( 98.5% ) . Mn3O4 and 1273K in the air atmosphere under the conditions of decomposition of MnO2 system taken by X -ray diffraction (XRD) analysis confirmed that decomposition products composed entirely of Mn3O4 , MnO2 , and Mn3O4 of particle size less than 0.087mm. Before the experiment , MnO2 and Mn3O4 was dried at 378K 12h, the weight of each test sample 15g, in an air atmosphere , the decomposition experiment 2450MHz, 650W microwave and heated silicon carbide tube furnace . Experiment, the powder sample was placed in the quartz crucible (15cm × Ø5cm), and hung on the electronic balance to determine the weight loss of the sample . The weight loss of microwave heating of the sample is applied to the microwave energy from the start the measurement , the thermal decomposition of the traditional weight loss is measured at a constant temperature .
MnO2 and Mn3O4 were used in an air atmosphere under microwave radiation. The temperature they reach a function of time , as shown in Table I. Obviously , MnO2 with fast heating rate , and can be heated almost Mn3O4 . Therefore, the microwave energy can be effectively used instead of heating the MnO2 Mn3O4, thereby reducing the energy consumption of the process . MnO2 and Mn3O4 microwave heating for selective decomposition of MnO2 very favorable.
Table MnO2 and Mn3O4 microwave heating heating rate
t (min) T (K) ΔT / Δt (K / min)
MnO2 Mn3O4 MnO2 Mn3O4
0298298 __
19203052207
210503121127
31000320768
5112333522 7.5
712,503,480 6.5
111170372-306
151050380-342
Above table shows that , in the initial heating , MnO2 heating rate (ΔT / Δt) increases with time and decreases rapidly when the heating time is reached 7min , the heating rate to zero , and thereafter, the heating rate becomes negative, that the sample began to cool . This indicates that the microwave radiation occurred during the MnO2 to Mn3O4 changes will affect the rate of warming , can be discussed as follows:
If we consider the radiation heat loss and the thermal effect of the reaction , the sample in the microwave field in the heating rate formula is:
= ( 1 )
Where : T is the temperature , t is time , Cp is the heat capacity , is the vacuum dielectric constant , the dielectric loss factor of the microwave frequency , the electric field strength , the heat radiation coefficient of the sample , the Stefan Boltzmann constant , surface area of ​​the sample , the sample volume per unit volume in the sample group to the molar number of the thermal effect of the reaction , the reaction conversion rate .

 

 

●微波加热原理       http://www.weiboshebei.cn/yingyong-neiye-17.html

 

●微波杀菌原理       http://www.weiboshebei.cn/yingyong-neiye-18.html

 

●微波设备定做流程   http://www.weiboshebei.cn/yingyong-neiye-19.html