Study On Magnetization Roasting Reaction Behaviors Of Various Iron Minerals

Magnetization roasting can realize the efficient development and utilization of complex refractory iron ore resources,and its industrial application has made some progress.However,due to the complex composition of iron ore,there are often a variety of iron minerals,and the reaction behavior of different iron minerals in the process of magnetization roasting is different.At present,it is difficult to achieve accurate control of phase transformation of iron minerals,so the development of magnetization roasting technology is limited.In this paper,hematite,limonite and siderite,which are the main iron minerals in complex refractory iron ores,are taken as the research objects to carry out magnetization roasting experiments.The isothermal magnetization roasting kinetic mechanism of different iron ore systems is determined.Chemical composition analysis,X-ray diffraction analysis(XRD),BET analysis,comprehensive thermal analysis and Scanning electron microscope with energy dispersive spectrometer(SEM-EDS)analysis are used.The phase transformation and reaction behaviors of iron minerals during magnetization roasting were studied.During the magnetization roasting of hematite-limonite,limonite in the system is first dehydrated and transformed into hematite with porous structure.The cracks and pores in the particles make it easier for CO to enter into the particles and react with the newly formed hematite,so limonite is easier to be reduced to magnetite during magnetization roasting.The higher the limonite content in the system,the higher the porosity of the sample,and the shorter the time needed to complete the magnetization roasting.After magnetization roasting,the weak magnetic hematite and limonite are transformed into strong magnetic magnetite.The isothermal magnetization roasting kinetics study shows that the most probable mechanism functions of hematite,limonite and hematite-limonite system are A2 random nucleation and subsequent growth model,whose integral form is G(α)=[-ln(1-α)]1/2.The activation energy and preexponential factor of hematite-limonite system are between hematite and limonite single system,indicating that the higher the limonite content in the system,the easier the magnetization roasting reaction proceeds.The experimental results of magnetization roasting of hematite-siderite system show that in N2 atmosphere,the siderite is first decomposed by heating to form FeO and CO2.FeO and CO2 react rapidly to form Fe3O4 and CO,and then CO will reduce hematite to magnetite.Therefore,siderite can be used as a reductant for hematite.At the same time,the decomposition product of siderite is also magnetite in this process,so the magnetization roasting of hematitesiderite system is realized.After magnetization roasting,many pores and cracks appeared in the sample particles,and the magnetic properties of the sample were greatly improved.The isothermal kinetics of magnetization roasting shows that the kinetic model of hematite-siderite system is D6 diffusion model,whose integral form is G(α)=[1-(1-α)1/3]2.The activation energy and pre-exponential factor of the reaction are far less than those of hematite and siderite,which indicates that the magnetization roasting reaction between hematite and siderite is very easy to proceed.Siderite is an efficient reductant for the magnetization roasting of hematite.The magnetization roasting experiment results of the limonite-siderite system show that in N2 atmosphere,the limonite is first heated to remove the bound water and crystal water,and transformed into hematite with higher porosity.Then the siderite in the system is heated and reacts to form Fe3O4 and CO in two steps,and then CO reacts with the newly formed hematite to form magnetite.After magnetization roasting,the strongly magnetic magnetite is the main iron mineral in the roasted products and has a high porosity.The magnetization roasting isothermal kinetics study shows that the kinetic model of the limonite-siderite system is the D6 diffusion model,and its integral form is J(α)=[1-(1-α)1/3]2.Compared with the single systel of limonite and siderite,the reaction activation energy and pre-exponential factor of the binary system are smaller,indicating that the magnetization roasting reaction of limonite and siderite is easy to proceed.In addition,the reaction activation energy and exponential factor of the limonite-siderite system are also smaller than that of the hematite-siderite system.This is because the porosity of the hematite produced by the dehydration of the limonite is higher than that of the natural hematite.The CO generated by the decomposition of siderite is more likely to enter the inside of the particles and react.The research results reveal the reaction behaviors and phase transformation of different iron minerals in the process of magnetization roasting,which provides a theoretical basis for the control and industrial application of complex refractory iron ore magnetization roasting process.