| The siderite resources is very rich in China,but the separation technology of siderite is a worldwide problem,the technical indexes of iron grade 40%?55%and recovery 50%?60%are obtained by traditional physical separation method.At present,magnetizing roasting technology,as a relatively efficient and reasonable technology for the treatment of siderite resources,has attracted much attention.However,problems of high roasting temperature or long roasting time still exist in shaft furnace,rotary kiln and fluidized magnetizing roasting system.Aiming at solving these problems,the related theoretical and experimental research on fluidized magnetizing roasting process of siderite is carried out to explore the technical ways of reducing roasting temperature,shortening reaction time and improving roasting effect,and the feasibility of applying blast furnace gas to magnetizing roasting system.The main results are as follows:(1)By studying the technological mineralogy of the siderite materials,the detailed characteristics of the intercalation relationship between this type of siderite and other iron-bearing minerals and gangue minerals are obtained,the aim is to provide technical basis for selecting the processing technology of this type of siderite and predicting the separation and enrichment effect.The results show that:the iron grade of siderite is 37.29%and the gangue content is high,of which the SiO2 content is as high as 13.02%.Iron is mainly distributed in carbonate,it is the main component for smelting,and the slag-making component is mainly SiO2.The intercalation of siderite with gangue minerals,calcite and other substances is complex,and most CaO,MgO and MnO exist in carbonate minerals as homogeneity and closely symbiosis with iron.The conventional physical separation process is difficult and the recovery rate is low,so an efficient fluidized magnetizing roasting process should be studied.(2)Thermodynamic analysis of fluidized magnetizing roasting material system is carried out to investigate the feasibility of fluidized magnetizing roasting of siderite at low temperature.The results show that:in the temperature range of siderite magnetizing roasting,the main reaction is the reduction of iron ore and the formation and reduction of complex iron compounds.The reaction of FeCO3 decomposition to Fe3O4 is the dominant reaction,and it is severe in 500?700°C temperature range,and then is stable.Other non-dominant elements(silicon,calcium,magnesium,aluminum)are also involved in the reaction.Solid-solid reaction may occur.When the temperature is 450°C,it begins to generate a small amount of FeSiO3 and Fe2SiO4.When the temperature is 550?,it begins to generate small amounts of FeAl2O4,CaSiO3,CaFe2O4,MgSiO3 and MgFe2O4.Therefore,the fluidized magnetizing roasting process,in which the solid material is suspended,may shorten the reaction time,reasonably reduce the reaction temperature,and reduce the energy consumption and iron loss.(3)The pore structure and fractal characteristics of siderite,its particles after preheating and its functional rule in fluidized magnetizing roasting are studied by image analysis method.The results show that:the preheating process can promote the formation of cracks and pores,increase the volume and specific surface area of particle holes,and expose the material interior to the reaction atmosphere.The degree and depth of particle crack increased with preheating time,the porosity,pore spindle,pore shape factor and average pore diameter of the material particles are improved to different degrees,and the pore shape is developing towards irregularity.As a result,the whole material is more sparse and porous,which is conducive to strengthening the reaction between reducing gas and material.Therefore,it is suggested that the mechanism of pore and reaction surface can be increased through the preheating process to strengthen the magnetizing roasting reaction.(4)The effects of different content and types of reducing gases in fluidized magnetizing roasting of siderite are explored and analyzed,and the reducing gas dosage and the coupling of different gases strengthen the reaction process and reduce the reaction temperature are studied,the feasibility of using blast furnace gas in the roasting process is also investigated.The researches show that:the reduction reaction rate can be increased by increasing the concentration of reducing gas and using mixed CO and H2 gas,blast furnace gas can be used in magnetizing roasting system.Kinetic research shows that:when the reaction temperature are 500 and 550°C,the initial stage of fluidized magnetizing roasting reaction is mainly controlled by chemical reaction,and the late stage is mainly controlled by internal diffusion.When reaction temperature is 600 and 650?,the initial stage of the reaction is controlled by chemical reaction,and the late stage is controlled by a combination of internal diffusion and chemical reaction.The apparent reaction activation energy of fluidized magnetizing roasting of H2 reducing gas is 37.7KJ/mol,and the result of CO+H2 is 15.9KJ/mol,which makes the reaction less difficult.The synergistic strengthening effect of CO+H2 mixed gas is better than that of alone,which can effectively reduce the reaction temperature and reaction time of fluidized magnetizing roasting.(5)The distribution of particle in fluidized magnetizing roaster in laboratory is analyzed by numerical simulation,the effects of particle size and shape on particle distribution are obtained,the influence mechanism of particles in fluidized magnetizing roasting process of siderite and the effect on enhancing magnetizing roasting process and reducing reaction temperature are explored.The results show that:optimization of particle size can effectively enhance the effect of fluidized magnetizing roasting.The finer the grain,the shorter the time needed for complete decomposition.On the contrary,the time required will be correspondingly longer.When siderite particles are added into the reactor,effects of suspension and particle size stratification will occur,the bottom layer is large-size particle,the middle layer is intermediate size,and the top layer is small size.Particle size composition is different,the height of suspension layer is different.With the same particle size,the higher the shape factor,the higher the suspension height and the worse the uniformity of particle distribution.On the contrary,the smaller the shape factor,the better the particle distribution uniformity.When the particle size composition is P80=92.45?m and the shape factor is 1.2,the distribution uniformity of siderite particles in fluidized magnetizing roaster is the best.(6)The effects of magnetizing roasting before and after strengthening measures are compared,the results show that the process of fluidized magnetizing roasting of siderite can be enhanced by preheating,increasing the concentration of reducing gas and their coupling effect,and enhancing the effect of particle size.The reaction temperature can be decreased from 700°C to 550°C,while the reaction time can be reduced from 100s to 90s.Under the condition of optimized process,the conversion rate of fluidized magnetizing roasting is 88.42%,and the iron grade and recovery are 62.57%and 89.21%respectively,it is better than the magnetizing roasting of siderite raw ore without strengthening measures.At the same time,the energy consumption of the system can be reduced and the obtained technical data can provide reference for the development of new fluidized magnetizing roasting system in the future. |
PDF Full Text Request