Study On Carbothermal Reduction Reaction Behavior Of Niobium Concentrate In Microwave Field

As an important rare metal,niobium is widely used in the fields of national defense technology,aerospace,electronic devices and medical devices because of its high melting point,high ductility,good electrical conductivity,high corrosion resistance and superconductivity.However,at this stage,the utilization process of niobium resources in Bayan Obo has problems such as complex process flow,serious environmental pollution,high energy consumption and low economic efficiency,thus limiting the further development of niobium smelting to a certain extent.Microwave heating is a new type of heating means,with the advantages of avoiding cold center,easy automatic control,environmental protection and no pollution.It is often used in the reduction process of complex minerals.In this thesis,a microwave carbon thermal reduction study of niobium concentrate was conducted for the comprehensive utilization of niobium minerals,and the behavior of microwave carbon thermal reduction reaction and strengthening mechanism of niobium concentrate were explored to provide new ideas for niobium concentrate smelting.In this thesis,the microwave carbon thermal reduction process of niobium concentrates was investigated and the results showed that:As the reduction temperature rises,niobium concentrate metallization is the first to increase rapidly,and the metallization rate is still increasing after reaching 1200℃,but the rate of increase slows down;The metallization rate of niobium concentrate increases with the increase of holding time and then decreases,reaching 94.84%at 30 min of holding time and only 93.26%at 60 min;The metallization rate increased with the increase of the carbon matching ratio,and was 93.26%when the carbon matching ratio was 1:1,and 95.48%when the carbon matching ratio reached 1:1.2.And with the increase of carbon matching ratio,the excess carbon may wrap the metallic iron and unreacted iron oxide,which hinders the further reaction.The optimal process conditions for the carbon thermal reduction of niobium concentrate in microwave field were finally derived as a reduction temperature of 1100℃,a holding time of 30 min,and a carbon matching ratio of 1:1.In this thesis,the reduction process of Nb and Ti in the microwave carbothermal reduction reaction of niobium concentrates is investigated,and the results show that,Nb C starts to be generated at 900℃;At 1100℃,the reduction of niobium oxide is nearing its end and the reduction of titanium oxide begins,the niobium-titanium products are mainly Nb C and（Ti,Nb）C.At 1300℃,the titanium dioxide carbon thermal reduction reaction is carried out in large quantities,and the products are mainly in the form of Ti C and（Ti,Nb）C.In this thesis,the kinetic mechanism of the carbon thermal reduction process of niobium concentrates was explored by means of non-isothermal thermal analysis kinetics,modified C-R method as a way to fit with 15 mechanistic function models to investigate the reaction fraction versus temperature profiles during the reaction,and the results show that,The carbon thermal reduction reaction of niobium concentrate in the microwave field conforms to the three-dimensional diffusion model with the equation y=1-（2/3）α-（1-α）^2/3,and the apparent activation energy Ea=131.654 kj/mol is much smaller than Ea=376.732 kj/mol under conventional heating.