低价氯化铝法从氧化铝直接碳还原炼铝的机理分析

Direct Extraction of Aluminum from Alumina by Carbonthermic Reaction-Chlorination and Possible Mechanisms

碳热过程的热力学分析表明，系统压力为100Pa时，生成Al4O4C与Al4C3以及Al4O4C与c结合生成Al4G的初始温度分别为1690，1711，1472K；碳热一氯化过程的热力学分析表明，在101Pa，1500K时，氧化铝直接碳热一氯化的吉布斯自由能为-20．041kJ；系统压力为100Pa时，Al4O4C，Al4C3以及A1203联合Al4O4C，Al4c3参与氯化反应的初始温度分别为1459，1378，1416K。实验结果显示：碳热过程在50～100Pa、高于1693K时，Al4O4C与Al4C3开始生成且含量随着温度的升高而增加；随着温度的继续升高或系统压力的减小，Al2O3及Al4O4C碳热转化为Al4C3。在50—100Pa，1693K时进行了实验，证明了该过程没有发生碳热一氯化反应。在70～150Pa，1753—1853K的范围时进行实验，均得到金属铝，说明要发生碳热一氯化反应必须先发生氧化铝与碳的碳热反应，即生成Al4O4C与Al4C3。

A novel technique was developed to directly extract aluminum from alumina by carbonthennic reaction- chlorination. The impacts of the extraction conditions, including the pressure and temperature, on the carbonthermic reaction and carbonthennic chlorination were analyzed based on thermodynamics. The calculated results show that at 100 Pa, the initial formation temperatures of Al4O4C and Al4C3, and the phase transition temperature from Al4O4C to Al4C3 by bonding of C,are 1690, 1711 and 1472 K, respectively. At 101 Pa and 1500 K,the Gibbs free energy in carbonthennic chlorination of Al2O3 with C and AlCl3 is -20. 041 kJ. At 100 Pa, the initial formation temperatures of MCl in chlorination of Al4O4C and Al4C3 and/or in their chlorination involving M2O3, are 1459, 1378 and 1416 K, respectively. The experi- mental results show that at 50 to 100 Pa and at a temperature higher than 1693 K, the formation rates of Al4O4C and Al4C3 increase with an increase of temperature;as the temperature goes up or the pressure drops down,Al2O3 and Al4O4C turn into Al4C3. Moreover, no carbonthermic chlorination occurs at 1693 K at 50 - 100 Pa. The fact that M metal was obtained at 1853 K shows that the carbonthermic reaction of Al2O3 and C, i. e. the formation of Al4O4C and Al4C3, initiates earbonthemaic chlorination.