Study On Roasting Mechanism And Reasonable Granular Upper Limit Of Fluidized Magnetization

The theoretic grade of siderite is low. Even used in sinter as ore-proportiongning, the evolution of CO2 will significantly affect the sinter strength. Thus, magnetic roasting becomes the only suitable process for siderite beneficiation. Multi-stage circular fluidization and magnetization roasting offset the defects in conventional shaft furnace, rotary kiln and furnacein fluidized bed, such as poor heat and mass transfer rate, uneven surface and interior roasted quality,as well as high energy consumption. Previous researches on the mechanism of fluidization and magnetization roasting on siderite is few, and the upper limit on granularity of this technology has not been proposed. In this paper, X-ray diffraction, mineralogical microscope, TG-DTA and other modern detection technologies are applied to conduct the research on phase change of siderite with isomorphism of Mg,Mn and dynamics mechanism in fluidization and magnetization roasting. Through orthogonal test, the interrelation between particle granularity, roasting temperature and roasting time were analyzed. And the upper limit on granularity suitable for fluidization and magnetization roasting on siderite was proposed.Thermodynamic analysis shows isomorphism of Mn CO3,Mg CO3 in siderite and Ca CO3 containing in siderite ore has no inhibiting effect on Fe CO3 thermal decomposition. On the contrary, when temperature is higher than 570℃, the evolution of CO2 is conducive to Fe O oxidized into Fe3O4,which is good for Fe CO3 thermal decomposition into Fe3O4.Phase change research results show Fe CO3 decomposed into Fe3O4 at 550℃,600℃and 650℃; and at these temperature, Fe O did not appeared. When the temperature reaches 700℃,750℃ and 800℃, Fe CO3 decomposed into Fe3O4 and Fe O at first,then Fe O changed into Fe3O4 with longer roasting time, and finally, Fe CO3 decomposed into Fe3O4 in all.Isothermal kinetics research results show that siderite fluidization magnetic roasting thermal decomposition kinetics is in accord with three-level chemical reaction control mechanism, when the activation energy is 156.23KJ/mol, which means that pre-exponential factor lg A is 7.60;Research results on fluidization characteristics of siderite show that fluidizing gas velocity apparently increased when particle size is larger than 0.5mm, and the effect of fluidization gets bad.The orthogonal test shows that temperature is the main effecting factor for siderite fluidization magnetic roasting conversion rate, followed by size and the time. Roasting time should be more than 107 s to keep the conversion rate of +0.30 mm particles of siderite fluidization magnetic roasting higher than 85% at 850℃.The residence time of particles in fluidization magnetic roasting device with circulation of 400Kg/h is 90-100 s. Thus,the upper limit on granularity suitable for this device is 0.30 mm. At the same time the upper limit on granularity in fluidization magnetic roasting device with circulation of 0.6 mt/a is 0.30 mm by prediction.