| China produces 57.80%of the world's steel,and consumes nearly 1.054 billion tons of iron ore raw materials annually.However,due to my country's low iron ore grade and poor endowment,domestic iron ore output is far from meeting the demand for steel production,and the degree of foreign dependence is higher than 80%.Therefore,the efficient development and utilization of low-grade refractory iron ore is of great significance for ensuring the stable supply of basic raw materials for my country's basic iron and steel industry and transforming my country's rich iron ore reserves into output.Generally speaking,compared with strong magnetic magnetite,weak magnetic iron-bearing minerals such as hematite,siderite,are difficult to efficiently enrich through simple weak magnetic separation.The iron recovery rate of traditional beneficiation technology is low,which increases production.Cost has also caused a lot of waste of resources.Among them,siderite has 1.834 billion tons of reserves in my country,and its theoretical grade is low.Traditional gravity separation,magnetic separation,flotation and their combined processes are difficult to raise the concentrate grade to more than 45%.At present,the magnetized roasting process is recognized as the most effective technical method for processing low-grade refractory iron ore and achieving efficient and economic recovery of iron resources.The basic principle is to change the weak magnetic iron-containing phase to the strong magnetic magnetite phase through the roasting reaction,so that high-grade and high-recovery iron concentrate can be produced by simple weak magnetic separation.Traditional shaft furnaces and rotary kilns failed to fully utilize the advantages of the magnetized roasting process due to the limitation of the reactor's principle.Based on the principle of fluidized roasting,the fluidized bed reactor has the outstanding advantages of low reaction temperature,high reaction efficiency,high conversion rate,low energy consumption,and easy large-scale equipment.Accordingly,this thesis takes siderite,one of the main refractory iron ore species,as the research object,based on the advanced fluidization reaction principle,combined with industrial production reaction conditions,the magnetic roasting process of low-grade refractory mixed siderite is studied.With reaction characteristics,a new process method of siderite oxidation-ultra-low temperature reduction has been developed to realize the high-magnetization conversion and high-efficiency weak magnetic separation of refractory mixed siderite.Following results has been achieved:Based on siderite in Shaanxi province as the research object,by Yunnan siderite and Liaoning hematite as control group,with the background of industrial gas,siderite fluidized roasting-magnetic separation was studied.Through XRD phase analysis,explores the siderite phase transition in the process of magnetization roasting and the generation of FeO.Base these,oxidation-reduction magnetization roasting-magnetic separation technology was developed.(1)It reveals the phase transition and the generation path of wustite in the process of siderite reduction roastingThe phase transition during siderite fluidized direct reduction magnetization roasting was studied,and the influence of time and temperature on the phase transition during roasting was explored,as well as the generation path of wustite FeO during siderite reduction roasting.The results show that under the condition R0.45,T<570?,the products of siderite roasting are Fe3O4 and FeO,and the content of wustite FeO increasing with the increase of temperature and time,which does not completely follow the CO reduction balance curve of iron oxide.The production of wustite FeO may be the particularity of the roasting of siderite FeCO3.The intermediate product of roasting decomposition is FeO.Due to the balance of CO and CO2,part of FeO cannot be completely converted,and the transformation into Fe3O4 after CO2 oxidation is not stable enough,and it is easy to be overreduced by CO to FeO.(2)The process of siderite preoxidation-ultralow temperature reduction magnetization roasting was developedFor weak magnetic material appeared in the process of direct reduction magnetization roasting wustite affect weakly magnetic separation index,but hematite reduction completely obey the reduction law of thermodynamics,the preoxidation-reduction magnetization roasting was put forward.The phase transition during the process of oxidation and reduction was studied,to realize the FeO-free fluidization magnetization roasting of siderite,and to obtain strong magnetic roasting ore for subsequent magnetic separation.At the same time,the path of FeO generation in the process of preoxidation-reduction roasting was revealed.Results show that the siderite under 610? oxide product for hematite ?-Fe2O3 and maghemite y-Fe2O3,oxidation reduction potential in 0.45 after reduction gas under the condition of reduction roasting under 560?,500?.When transformation of magnetic roasting product completed,FeO started to appear,and the content of FeO increased with the increase of temperature and time,which may be due to the ?-Fe2O3 reduction of Fe3O4 unstable and easy to overreduced.However,at 450?,there has been no wustite FeO in the product,which may be due to the decrease of temperature and the increase of stability of Fe3O4,which is not easy to be overreduced.The pre-oxidation and ultra-low temperature reduction process of 610? oxidation followed by 450?reduction can avoid the generation of weakly magnetic wustite FeO in the magnetization roasting process of siderite and obtain the strongly magnetic roasting products.(3)Low intensity magnetic separation of roasted oreThe effects of magnetic field strength grinding particle size and different roasting conditions on low intensity magnetic separation index were investigated.The results show that a concentrate with a grade of 62.07%and a recovery of 88.26%can be obtained after oxidizing siderite at 610? and reducing the roasting ore at 450?,grinding the ore to-30?m with a particle size of 82.75%through two low intensity magnetic separation processes of 1100Gs and 1300Gs.However,the magnetized roasted ore directly reduced at 560? for 5 min was subjected to low magnetic separation under the same conditions.Due to the presence of low magnetic FeO,the total iron recovery was only 49.54%,which further verified the excellent effect of pre-oxidation-ultra-low temperature fluidized magnetized roasting.In this paper,the phase transformation and magnetic changes in the process of siderite roasting were studied,and a low temperature FeO-free magnetic roasting system for siderite was established to provide theoretical guidance for industrial magnetic roasting and magnetic separation of siderite. |
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