Characteristic And Kinetics Of Magnetization Roasting Of Siderite In Micro Fluidized Bed Reaction Analyzer

With the development of national economy,the demand for steel is gradually increasing in China.Siderite is one of the most important iron resources in China,the main component of which is ferrous carbonate(Fe CO₃).Due to the low content of iron,it is difficult to be directly used in ironmaking in blast furnace.They must be calcined to remove carbon dioxide(CO₂)to generate iron oxide before used.Siderite can be decomposed to generate Fe₃O₄in inert atmosphere,and Fe₃O₄can be maintained in a relatively stable state.Although there are many studies on the decomposition characteristics of siderite in inert atmosphere,siderite decomposition in inert atmosphere can be divided into two steps,the first step is Fe CO₃?Fe O+CO₂,and the second step is 3Fe O+CO₂?Fe₃O₄+CO.However,the total reaction rate can only be obtained by thermogravimetric analyzer(TGA),and the reaction rate of step-by-step reaction can not be obtained.Therefore,the mechanism and kinetic parameters are still of great significance.In order to solve the above problems,the reaction characteristics and kinetics of siderite decomposition in inert atmosphere(Ar)were studied using micro fluidized bed reaction analyzer(MFBRA),and the step-by-step reaction kinetics was obtained,which was compared with the results measuring by TGA.Then,the influence of different atmospheres on siderite decomposition was studied by thermogravimetry.The results are as follows:(1)In TGA,only one endothermic peak can be found during the process of siderite decomposition in N₂atmosphere.The activation energy of the total reaction is 112.1 k J/mol,the pre-exponential factor is 2.8×10⁹s^-1,the mechanism model is random nucleation followed by growth model F1:G(x)=-ln(1-x).The main solid product is Fe₃O₄,and a small amount of Fe O.(2)Compared with the results measured by TGA,it has been found that the gas product CO₂is produced earlier to CO in inert atmosphere in MFBRA,which proves that the decomposition of siderite is a two-step reaction.With the increase of temperature,the complete decomposition time of siderite becomes less and less.It only takes a few seconds to complete decomposition above700°C,and the time interval of CO₂and CO produced increases from 0.02 s(450°C)to 1.3 s(700°C).According to the time series curves of CO₂and CO gas products,the apparent activation energy of the first step is 77.2 k J/mol,the apparent activation energy of the second step is 99.5 k J/mol,the average activation energy of the overall reaction is 96.8 k J/mol,and the pre exponential factors lg A are 3.7×10⁸s^-1,3.4×10⁸s^-1,2.0×10¹⁰s^-1,respectively.the reaction of the first step follows the same mechanism model as the total reaction.Both of them follow random nucleation and growth model F1:G(x)=-ln(1-x);the reaction of the second step follows the phase boundary model R2:G(x)=1-(1-x)^1/2.(3)Air and CO₂in the reaction atmosphere have an important influence on the decomposition of siderite.Compared with the results in N₂,the existence of CO₂seriously inhibits the decomposition of siderite,and the decomposition temperature increases by about 50°C.The activation energy increased to about 400 k J/mol.The siderite decomposition in air is endothermic at the beginning stage,then become exothermic at higher temperature,which is different from that siderite decomposition in air is endothermic in N₂and CO₂.However,the initial decomposition temperature is similar between N₂and air.The activation energy is reduced to 92.2 k J/mol,the pre-exponential factor is 6.5×10⁸s^-1,and the main solid product is?-Fe₂O₃.The mechanism model followes random nucleation and growth model F1:G(x)=-ln(1-x).