Alumina Vacuum Carbothermal Reduction - Mechanism And Experimental Study Of The Chlorination Process

Aluminum was used for many industries such as building, packaging, transportation, power, telecom, aerospace, national defense industry, machinery, petroleum chemical, culture and public health, metallurgy, agriculture and so on because of various excellent properties.This article gives a general comment on the following points:situation of bauxite resources, the present situation and the development of aluminum metallurgical industry and the recent research for new production methods ofaluminum metallurgy. Many problems which exist in the aluminum production by alumina carbothermic reduction- chlorination in vacuum have been investigated systemly, such as thermodynamics, the mechanisms, and the effect of additives.Thermodynamic calculations indicate that CO cannot react with Al4C3 and Al4O4C in the alumina carbothermic reduction process at 1573K～2073K and 100Pa. Reaction between Al4C3 and AlCl3(g) to produce AlCl(g) and C occurred below 1773K in 10-100Pa. Secondly, one important factor of affecting the method of aluminum vapor condensation was the temperature gradient in the condensation zone. When the system temperature dropped to the lowest temperature of liquid-gas transition, aluminum vapor would be condensed into solid-state directly. Thir ly, both reaction between Al and C to produce Al4C3 and reaction between Al and CO to produce Al4C3 and Al2O3 occurred below 973K at 10-100Pa. The beginning tempers ure of the reaction decreased with the concentration of CO in gas decreased in the rea:tion between Al and CO to produce Al4C3 and CO2. Lastly, SiC and Si can be pro luced by reaction between SiO2 and graphite, and then Al4SiC4 will be produced by Al3C4, Al4O4C and Al with SiC and Si which is produced in the carbothermic reduction p(?)cess and chloride reaction process.In the alumina carbothermic reduction and without AlCl3, Fe was produced at about 1273K; In the temperature range of 1473K～1623K, Fe3C was produced by Fe and C; Al3C4 and Al4O4C were generated by alumina and graphite at 1723K, because Al2O3 and C were packed by melts formed by Fe3C and Fe. All the temperatures of series reactions reacted with C are less than 800K except Fe react with C to produce Fe3C. With the rising of system tempreture, the more△G is negative, the more reactions are easy to ocuur. The temperatures of series reactions 2.32-2.36 of TiO2 reacted with C are not more than 1250K, and the preferential order of products is: Ti4O7, Ti3O5, Ti2O3, and TiC.Mechanism analysis for aluminum production by alumina carbothermic-chlorination shows that the content of CO in the gas decreased, but Al4O4C and Al4C3 increased with time during the alumina carbothermic reduction process. And Al4O4C are translated into Al4C3 gradually. Then, the content of CO in the gas is not increasing with time, and the reaction to produce CO doesn't exist in the chlorination process. The main reaction is that Al4C3 and AlCl3(g) to produce AlCl(g) and graphite (C). It implied the mechanism of alumina carbothermic reduction-chlorination process in vacuum involves three steps as follows:the carbothermic reduction of Al2O3 to produce Al4C3, the chlorination of Al4C3 by AlCl3(g) to produce AlCl(g), and the decomposition of AlCl(g) to produce Al(1). Secondly, aluminum bead was obtained in the condenser where the temperature gradient was about 1.4K/mm, and aluminum powder could be obtained where the temperature gradient was about 19.5K/mm through changed the temperature gradient in the condensation zone. Lastly, the main reason of Al4C3 produced was that the reaction between Al and CO to produce Al4C3 and CO2 occurred. The purity of aluminum increased with the concentration of CO in gas and the tempe ature decreased, and the upper purity of aluminum beads were generated after imp oving the experimental process.Firstly, in the carbothermic reduction process, SiC can be produced by reaction between SiO2 and graphite, and then it will react with Al3C4 which is generated by alumina and graphite to produce Al4SiC4. Because Al3C4 which will be (?)articipated the chlorination process is consumed by SiC, the recovery rate of aluminun will decrease indirectly. Secondly, in the alumina carbothermic reduction, Fe2O3 will rea(?)t with C to produce Fe and Fe3C.And then, Al2O3 and C are packed by melts formed by Fe3C and Fe, AI3C4 and Al4O4C are generated by alumina and graphite at 1723K.Fe2O3 decreased the reaction temperature of aluminum extracted from alumina by carbothermic reduction- chlorination process in vacuum, and then it increased the recovery rate of aluminum at 1723K especially adding 10% Fe2O3. Lastly, in the carbothermic reduction process, TiC was produced by C and TiO2, after TiO2 transformed from anatase into rutile gradually. In the range of 1763K～1783K, TiC unchanged before and after chlorination process. The experimental results illustrated that TiO2 don't participate in the alumina carbothermic reduction-chlorination process.