| Microwave as heating energy has been successfully applied in the fields of drying and food processing due to its numerous advantages such as voluminal heating, rapid heating, selective heating and quick start-up and stopping. But for the high energy consumption industry of metallurgical, microwave heating shows a slow progress in its metallurgy engineering application, and the replicated and promoted engineering application of its are rarely reported. The main reasons may be that materials researched in previous studies were relatively dispersed and lack of organic intrinsic relations, and the pertinency about the smelting of specific ore and specific metallurgy processing were not strong and inadequated in systematicness. Furthermore, many methods were adopted to characterize the interactions between materials and microwave. However, the correlation, difference, and suitability of the results from different characterizing methods were lack of research. Therefore, it was difficult to form the effective support for engineering application of microwave metallurgy.In this paper, aiming to solve these problems above, according to the categorization principles by chemical elements, four typical metallurgical raw materials such as iron-containing material, manganese material, sulfide ore, and carbonaceous material were selected as the research object. And microwave heating rate, electromagnetic parameters, and energy absorbing method were used to characterize the microwave absorbing properties of above materials. Systematical studies were carried out to compare the difference of microwave absorbing properties and microwave effect among the different components in the same raw material, together with the correlation, difference, and suitability of the results from different characterizing. And the processing mechanism of mixing various materials or phase change occurred in microwave metallurgical process was revealed to provide theoretical foundation for correctly selecting and controlling raw material, process adjustment, and predicting results in the application of microwave metallurgy. Based on the above studies, microwave roasting, microwave carbothermal reduction and microwave assisting grinding were studied and the effects of procedure parameters and mechanism were revealed. The conclutions can be drawn as following:(1) Three methods such as microwave heating rate, electromagnetic parameters, and energy absorbing methods were used to characterize the interaction properties of microwave and materials from different perspectives, which show different connotation. The correlations of characterization results were associated with the materials. Each of above methods had specific test equipment and requirement, along with its own advantage, disadvantage and adaptability. Although each method focused on different target, there were theoretical correlations among them. According to the classification principles by chemical elements, microwave absorbing characteristics of different types of materials were studied. According to the energy absorption results under a shorter microwave radiating time, the microwave absorbing properties of different materials were sorted by classification. For iron bearing material: FM-3(Fe3O4)>FM-4(Fe3O4)>FM-2(FeS2)>FM-8(Fe)>FM-1(FeS2)>FM-5(Fe2O3) >FM-6(Fe2O3)>FM-7(Fe2O3); for manganese bearing materials:M-1 (MnO2)>M-2(MnO2)>M-3(Mn)>M-4(MnO); for sulphide ore:S-1(Pb4Fe Sb6S,4)>S-2(Fe S2)>S-3(CuFeS2)>S-4(PbS)>S-5(ZnS); for carbonaceous materials:graphite> activated carbon>coke>coal-HS>wood chips>charcoal>coal-LS.Based on the test results attained under the condition of sequentially microwave radiating and preferentially absorbing microwave, the microwave absorbing properties of materials could vary with microwave heating, and its trend was related with the materials themselves. Intial microwave absorbability of FM-5(Fe2O3), FM-6(Fe2O3), M-2(MnO2), S-3(CuFeS2), S-4(PbS) and S-5(ZnS) were weak, and then became stronger when microwave heating temperature rose to certain tempaerature. Intial microwave absorbability of magnetite, pyrite and iron powder were strong and became weak as temperature increased. The ability of M-4(MnO) and FM-7(Fe2O3) in absorbing microwave were the weakest and can not be heating to high temperature by microwave. Microwave absorbability of coarse iron scrap is stronger than that of fine iron scrap, and fine pyrite and reduced iron powders in absorbing microwave are stronger than coarse. By comparing the measured temperature with the simulation of electromagnetic field distribution in a single mode waveguide (BJ26 type), it was verified that there were several different microwave losing mechanisms for materials tested.(2) The microwave roasting effect and behavior of pyrite concentrate were significantly influenced by the microwave roasting equipment and the parameters of roasting process. During the roasting of pyrite concentrate, microwave not only acted as a heat source, but also strengthened the microwave roasting behavior by coupling with the newly formed material which was strongly absorbing microwave. In multimode cavity, nonuniform distributions of electromagnetic fields resulted in uneven roasting and produced local sintering material under high temperature, which leaded to worse roasting effect and removal of S reduce to 4%. Microwave roasting time could be shorten half by mixing segmented roasting, the removal of S was 99.34% after microwave roasting for 100 min, which is similar to that roasting for 200 min with unsegmented roasting.(3) In microwave carbothermal reduction of pyrite cinder, pyrite cinder and carbonaceous reductant belonged to two kinds of materials with different microwave absorbing properties. They were coupled with each other in microwave field through adsorbing microwave and able to strengthen carbothermal reduction reaction. Fe recovery with 5%wood chips was 99%. The reducing effect of 3% coal,3% coke and 3% charcoal was similar, with Fe recovery 95.When increasing microwave power or power density, the microwave carbothermic reducting effect of sulfuric acid residue and microwave utilization were improved.(4) Due to microwave selective heating and voluminal heating, the pre-treatment of cassiterite polymetallic sulphide ore with microwave heating was carried out. By this way, in grinding product coarse size (-3.2+2、-2+1 mm) decreased significantly, and middle size (-0.425+0.15 mm) and fine size (-0.074 mm) increased. Metallic distribution increased in -0.425 mm size fraction, and thus more metallic minerals were crushed preferentially. Fe-bearing minerals were crushed preferentially significantly, and preferential crush of Sn, Pb and Zn were relatively weak. Rough calculation of energy consumption showed that microwave heating pretreatment needed only 1/20 time of traditional heating. The Bond work index of microwave treated ore was 8.2% lower than that of untreated ore.In a word, the above research results have good guidance and high academic value for microwave metallurgical equipment design, material selection, process control and mechanism research. |
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