Study On The Reduction Reaction Behavior On The Surface Of Hematite During Magnetization Roasting

Magnetized roasting is one of the effective methods for efficient utilization of complex refractory iron ore resources,and a major breakthrough has been made in technology and equipment.However,further in-depth research is still needed in the regulation of phase transformation to promote the further development of magnetized roasting technology.Therefore,this thesis mainly focuses on CO and H2 during the magnetization roasting process to study the reduction reaction behavior of hematite during the magnetization roasting process,and systematically and in-depth study the hematite mineral phase transformation process,the magnetic change law and hematite during the magnetization roasting process.Surface reduction reaction behavior,the research results enrich the theoretical system of refractory iron ore magnetization roasting to a certain extent.This paper takes hematite as the research object,CO and H2 as reducing gases,and systematically investigates the influence of different reduction conditions on the reduction of hematite.With the help of thermodynamic analysis,X-ray diffraction,X-ray photoelectron spectroscopy,and transmission electron microscope,the law of phase evolution and surface valence state change of hematite during magnetization roasting was systematically studied.With the help of VASP and Material Studio software,the physicochemical properties of iron mineral crystals and surface structure were studied from the microscopic level based on first principles,and the reduction behavior of CO and H2 on the Fe2O3 surface was described.Combined with the analysis of thermodynamics,XRD and VSM,the reduction of hematite under the atmosphere of CO and H2 is carried out in the order of Fe2O3→Fe3O4→FeO.Under the action of CO reducing agent,the best process parameters for the reduction of hematite into magnetite by magnetic roasting are temperature 560℃,CO reducing agent concentration 30%,reduction time 8 min,and the calcined product TFe grade is 71.71%,FeO content is 31.12%.Under the action of H2 reducing agent,the magnetization reduction effect of hematite is stronger than that of CO as reducing agent.Under the roasting conditions of temperature 560℃,H2 reducing agent concentration 30%and reduction time 8 min,the TFe grade of the roasted product is 71.81%,FeO content is 31.99%.XPS results show that the binding energy of Fe2p3/2 shifts to the left as the temperature increases during the hematite magnetization roasting process;when the temperature is 560℃ the characteristic peak position of Fe2p3/2 is at 710.78 eV,indicating that the surface has become Magnetite:As the temperature continues to rise,the characteristic peak continues to shift to the left,and FeO is generated by over-reduction.Based on first-principles calculations,the reaction of different amounts of CO and H2 molecules at different positions on the Fe2O3(001)plane and Fe2O3(111)plane is studied,and the structure before and after the reaction has changed in charge density,state density and bond length.Aspect analysis.When a CO molecule acts on the surface of hematite,CO combines with surface oxygen atoms to form CO2,forming oxygen vacancies on the surface,the position of the surface atoms changes,FeT1 and FeT2 get electrons from positive trivalent to positive divalent,and the surface structure changes;After two CO molecules react with the surface of hematite,two CO2 molecules are formed,and two oxygen atom vacancies are generated on the surface.Analysis of the physical and chemical properties of the structure shows that the surface structure has been partially transformed into magnetite inverse spinel.Trends in structure.The action of H2 molecules on the surface of hematite is carried out in two steps.First,one H2 is cracked on the surface,and two hydrogen atoms combine with surface oxygen atoms to form a hydroxyl group;two H2 molecules react with the surface of hematite to form two H2O Molecules,oxygen vacancies are formed on the surface,and the surface structure obviously has a tendency to change to the magnetite structure.The research results of this paper deepen the understanding of the phase transformation of hematite to magnetite during the magnetization roasting process,enrich the theoretical system of iron ore magnetization reduction,and have a good guiding significance for controlling the precise phase transformation of iron ore.