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微波場下的釩渣氯化動力學

Kinetics of chlorination of vanadium slag by microwave heating

  • 摘要: 研究了微波加熱條件下(500~800 ℃),AlCl3氯化釩渣中有價金屬Fe、Mn、V和Cr變溫動力學。通過X射線衍射和掃描電鏡能譜表征了氯化產物隨時間的物相演變和形貌變化,考察了AlCl3/釩渣的質量比和熔鹽配比對氯化提取率的影響。結果表明,AlCl3/釩渣的質量比為1.5、(NaCl-KCl)/AlCl3熔鹽質量比為1.66∶1時Fe、Mn、V和Cr的提取率最佳,分別為91.66%、92.96%、82.67%、75.82%和63.14%,微波加熱30 min,5種元素的提取率達到或者超過常規加熱方式6 h的氯化提取效果。通過熱力學和動力學分析,橄欖石相優先于尖晶石相發生氯化反應。而且V和Cr的氯化反應速度小于Fe和Mn。Fe和Mn氯化過程為擴散控制,其非等溫擴散活化能為17.02和17.10 kJ·mol?1, V和Cr在氯化過程中的限制性環節為界面化學反應,其表觀活化能分別為40.00和50.92 kJ·mol?1;微波與熔鹽耦合強化氯化反應的機理可以描述為擴散作用增強和局部化學反應增強。

     

    Abstract: Microwave heating was used in this study to chlorinate the extraction of Fe, Mn, V, and Cr from vanadium slag using AlCl3 molten salt at a temperature range from 500 to 800 °C. Microwave heating chlorination kinetics was studied in a non-isothermal mode. The effects of the AlCl3/vanadium slag mass ratio and molten salt ratio on the extraction rate of chlorination peoducts were investigated. The structure and morphology evolution of microwave heating chlorination products were characterized by X-ray diffraction and scanning electron microscope with energy dispersive spectrometer. The results show that the highest extraction rate of the five elements (Fe, Mn, V, Cr, and Ti) can be achieved as 91.66%, 92.96%, 82.67%, 75.82% and 63.14%, when the mass ratios of AlCl3/vanadium slag and NaCl–KCl/AlCl3 are 1.5 and 1.66, respectively. These extraction rates in the microwave heating mode for 30 min are reached and exceeded by 6 h in the conventional heating method. Microwave heating will minimize the chlorination time and reduce the volatilization of AlCl3. Based on the thermodynamics and kinetic analysis, the different phases of vanadium slag can be chlorinated using AlCl3 in the range from 400 to 800 °C, and the olivine phase is superior to the spinel phase in chlorination. In addition, the chlorination rates of V and Cr are slower than those of Fe and Mn, and increasing the reaction time is advantageous for the chlorination of V and Cr. The chlorination of Fe and Mn is controlled by diffusion, and the non-isothermal diffusion activation energies of Fe and Mn are 17.02 and 17.10 kJ·mol?1, respectively. In contrast, the chlorination of V and Cr is limited in the interfacial chemical reaction step, for whom the activation energies give 40.00 and 50.92 kJ·mol?1, respectively. The combination effect of the microwave and molten salt on the chlorinating vanadium slag can be attributed to the enhancement of the diffusion and local chemical reaction.

     

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