鐵酸鈣與赤鐵礦非等溫還原動力學

李剛; 丁成義; 宣森煒; 呂學偉; 吳珊珊

doi:10.13374/j.issn2095-9389.2018.11.005

鐵酸鈣與赤鐵礦非等溫還原動力學

doi: 10.13374/j.issn2095-9389.2018.11.005

1) 重慶大學材料科學與工程學院, 重慶 400044;
2) 重慶大學機械傳動國家重點實驗室, 重慶 400044

基金項目:

重慶市鐵礦石超聲波輔助燒結技術研究資助項目(cstc2014kjrc-qnrc90001)

國家自然科學基金資助項目(51544203)

詳細信息

中圖分類號: TF521+.1
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出版歷程
- 收稿日期: 2017-11-15

Non-isothermal reduction kinetics of calcium ferrite and hematite

1) College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China;
2) State Key Laboratory of Mechanical Transmissions, Chongqing University, Chongqing 400044, China

摘要

摘要: 采用非等溫熱重的方法,在30% CO+70% N₂(體積分數)氣氛下,以10 K·min^-1升溫至1123 K的過程中,比較了鐵酸鈣與赤鐵礦的逐級還原過程及其還原動力學.結果表明:鐵酸鈣和赤鐵礦開始還原溫度分別為873 K和623 K;由反應速率與反應度的關系及分階段X射線衍射物相分析發現,鐵酸鈣還原過程為兩段式反應(CaO·Fe₂O₃→2CaO·Fe₂O₃→Fe),而赤鐵礦還原過程為傳統的三段式反應(Fe₂O₃→Fe₃O₄→FeO→Fe).通過Freeman-Carroll法計算得知鐵酸鈣和赤鐵礦的還原平均活化能分別為49.88和43.74 kJ·mol^-1;鐵酸鈣還原過程符合隨機成核隨后生長模型,動力學模式函數為Avrami-Erofeev方程,其積分形式為[-ln (1-α)]ⁿ;而赤鐵礦還原過程動力學機理分為兩部分,在還原度α為0.1~0.5時,為三級化學反應模型,模式函數積分形式為1-(1-α)³;在α為0.5~0.9時,符合二維圓柱形擴散模型,動力學模式函數為Valensi方程,其積分形式為α+(1-α)ln (1-α).
- 鐵酸一鈣 /
- 三氧化二鐵 /
- 非等溫還原 /
- 動力學 /
- 模式函數
Abstract: The reduction behaviors of sinter and lump ores, which account for 90% of the raw materials charged into blast furnace process, are important to coke reduction in the ironmaking industry. The isothermal reduction behaviors of sinter and lump ores have been extensively studied; however, non-isothermal conditions, which are more consistent with the temperature change characteristics in a blast furnace, have been rarely investigated in terms of their reduction processes. Studies on the reduction behaviors of calcium ferrite and hematite, which are individually contained in sinter and lump ores, can provide more significant guidance to the practical operation. Comparisons of the reduction behaviors of calcium ferrite and hematite involves thermodynamic parameters such as the starting reduction temperature and kinetic parameters such as activation energy and model function. Considering reduction processes, hematite has been clearly explored by numerous works to an extent far more than calcium ferrite. In addition, in studying the reduction behaviors of calcium ferrite and hematite, pellet samples of 1-100 mm were the focus in the past and rarely micron-sized powder samples (1-100 μm). However, nowadays, micron-sized particles are extensively applied on iron ores reduction in fluidized bed process and non-blast furnace process, such as FINEX^® method; therefore, in this study, calcium ferrite and hematite were compared, considering their reduction routes and reduction kinetics. Non-isothermal reduction experiments of powdery calcium ferrite and hematite heated up to 1123 K with a rate of 10 K·min^-1 in a continuous stream of 30% CO and 70% N₂ were conducted through thermo-gravimetric analysis. The results show that the reduction processes of calcium ferrite and hematite begin at 873 K and 623 K, respectively. Reduction rate analysis and subsequent X-Ray diffraction measurements at various stages reveal that the reduction of calcium ferrite can be divided into two steps:CaO·Fe₂O₃ → 2CaO·Fe₂O₃ → Fe, whereas that of hematite mainly comprises three steps:Fe₂O₃ → Fe₃O₄ →FeO → Fe. The activation energy was calculated by Freeman-Carroll method, and the average values of calcium ferrite and hematite reduction are 49.88 and 43.74 kJ·mol^-1, respectively. The reduction of calcium ferrite can be described by random instant nucleation and two-dimensional growth of nuclei model; its corresponding model function is Avrami-Erofeev equation with an integral form of[-ln(1-α)]ⁿ, whereas the reduction of hematite was initially expressed by a tertiary chemical reaction model (reduction degree α=0.1~0.5) with an integral form of 1-(1-α)³, and subsequently by a two-dimensional cylindrical diffusion model (α=0.5~0.9) with an integral form of α+(1-α) ln(1-α).
- calcium ferrite /
- hematite /
- non-isothermal reduction /
- kinetics /
- model function

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參考文獻(29)

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