Study on sodium roasting kinetics of vanadium removal slag of titanium tetrachloride
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摘要: 基于非等温热重分析研究Na2CO3添加量和升温速率对含钒尾渣氧化的影响规律，采用Kissinger-Akahira-Sunose(KAS)法计算了含钒尾渣氧化过程活化能和指前因子，并通过Coats-Redfem法推断机理函数并建立不同阶段所适用的动力学方程。结果表明：含钒尾渣完全氧化的温度为700 ℃，随Na2CO3添加量增加，表观活化能逐渐降低，氧化速率提高；当Na2CO3添加量超过20%后，钒渣在氧化焙烧过程中出现玻璃相，产生烧结现象，表观活化能开始逐渐增大，氧化速率降低。钠化焙烧过程分为四个阶段，其动力学方程分别为：第一阶段二维扩散dα/dT=exp(−72.03/RT)4(1−α)1/2[1−(1−α)1/2]20.022/β，第二阶段三维扩散dα/dT=exp(−23.7/RT)3/2(1−α)4/3[(1−α)−1/3−1]−10.014/β，第三阶段化学反应dα/dT=exp(−27.91/RT) (1−α)20.06/β，第四阶段形核与长大dα/dT=exp(−12.09/RT)2(1−α)[−ln(1−α)]1/20.14/β。Abstract: Based on non-isothermal thermogravimetric analysis, the influences of Na2CO3 addition and heating rate on oxidation of vanadium removal slag of titanium tetrachloride (vanadium-containing tailings) were studied. The Kissinger-Akahira-Sunose (KAS) method was used to calculate the activation energy and pre-exponential factor of the oxidation process of vanadium-containing tailings. Through the Coats-Redfem method, the mechanism function was inferred and the kinetics equations of different stages were established. The results show that the temperature for complete oxidation of the vanadium-containing tailings is 700 ℃. With the increase of Na2CO3 addition, the apparent activation energy gradually decreases and the oxidation rate increases. While the Na2CO3 addition exceeds 20%, the glassy phase appears during the oxidation roasting process which results in sintering, and the apparent activation energy gradually increases with the oxidation rate decreased consequently. The sodium roasting process can be divided into four stages and the kinetics equations are as follows: the first stage of two-dimensional diffusion with dα/dT=exp(−72.03/RT)4(1−α)1/2[1−(1−α)1/2]20.022/β, the second stage of three-dimensional diffusion with dα/dT = exp (−23.7/RT)3/2(1−α)4/3[(1−α)−1/3−1]−10.014/β, the third stage of chemical reaction with dα/dT=exp(−27.91/RT)(1−α)20.06/β and the fourth stage of nucleation and growth with dα/dT=exp(−12.09/RT)2(1−α)[−ln(1−α)]1/20.14/β.
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图 1 四氯化钛除钒尾渣XRD图谱
Figure 1. XRD pattern of vanadium removal slag of crude titanium tetrachloride
图 2 不同升温速率下钒渣氧化的TG/DTG曲线
Figure 2. TG/DTG curves of oxidation of vanadium containing slag at different heating rates
图 3 不同Na2CO3添加量下表观活化能与转换率的关系
Figure 3. The relationship between apparent activation energy and conversion rate with different addition amount of Na2CO3
图 4 四氯化钛除钒尾渣钠化焙烧反应速率与转化率的关系
Figure 4. The relationship between the reaction rate and conversion rate of sodium calcination of the vanadium removal slag of titanium tetrachloride
图 5 升温速率为10、15、20 K/min下ln(G(α)/T2)−1/T关系
Figure 5. Relationship of ln(G(α)/T2)−1/T at heating rate of 10 K/min, 15 K/min, and 20 K/min
表 1 粗四氯化钛精制尾渣的主要化学成分
Table 1. Main chemical compositions of vanadium removal slag of crude titanium tetrachloride
% Cl Fe2O3 TiO2 Al2O3 V2O5 ZrO2 C SiO2 Cr2O3 31.95 19.18 15.39 8.64 11.17 6.77 2.68 1.86 0.81 
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表 2 四氯化钛除钒尾渣添加20%Na2CO3钠化焙烧在不同阶段的表观活化能和指前因子
Table 2. Apparent activation energy and pre-exponential factor in different stages for sodium roasting of vanadium removal slag of titanium tetrachloride with 20% Na2CO3
阶段 不同升温速率时的活化能 活化能/(kJ·mol−1) 指前因子/min−1 10 K/min 15 K/min 20 K/min 活化能/(kJ·mol−1) 拟合度 活化能/(kJ·mol−1) 拟合度 活化能/(kJ·mol−1) 拟合度 第一阶段 77.66 0.99 71.98 0.99 66.44 0.99 72.03 0.022 第二阶段 24.81 0.99 21.78 0.99 24.51 0.98 23.7 0.014 第三阶段 33.67 0.98 26.04 0.99 24.03 0.99 27.91 0.06 第四阶段 13.43 0.98 10.21 0.99 12.64 0.99 12.09 0.14
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