Bauxite Vacuum Carbon Thermal Reduction, The Experimental Study Of Chloride, And The Evaluation Of The Life Cycle

Aluminum is characteristic of light weight, good thermal and electrical conductivity, easy machining and so on. Aluminum is widely used in various sectors of national economy and is the largest amounts of production and consumption metal in non-ferrous metals. The electrolytic method to produce aluminum is a process of high cost, high energy, serious environmental pollution and high grade bauxite required as raw materials. Aiming at the shortcomings of the process, carbothermic reduction-chlorination of bauxite is put forward and carried out. The experiments and thermodynamic analysis in carbothermic reduction-chlorination of bauxite in vacuum are proceeded, and life cycle environmental impact of the process is evaluated.Thermodynamic calculations show that the hydrous minerals in bauxite dehydrate at623K under100Pa. In carbothermic process, When temperature is over873K, iron oxide and its reduction products react with titanium dioxide to give TiC eventually. Kaolinite reacts with carbon to give AI2O3and SiC over1373K. If TiO2converts into TiC completely, the reaction between remaining TiO2and SiC occurs below1473K and forms TiSi2. In1473K-1573K, mullite reacts with carbon to give Al2O3and silica. Through a series of reactions, iron oxide and silicon oxide finally form Fe3Si above1573K. The reactions occurred between SiO2and its reduction products generate silica in the temperature range of763K-1697K. At carbothermal reduction stage, Al2O3converts into Al4O4C, Al4SiC4and Al4C3.The results of carbothermic reduction-chlorination of bauxite in vacuum indicate that diasporite and boehmite dehydrate completely and kaolinite starts to decompose into mullite and amorphous silicon dioxide at1373K. When the temperature increased to1573K, the quartz-type silica is formed, followed by transformation into silicon carbide. Mullite converts into Al2O3and SiC in temperature range of1473～1573K. At1673K, A14CO4. Al4SiC4and Fe3Si are generated. The compounds of titanium and silicon are not detected. TiC, SiC and Fe3Si are not involved in chlorination process. The products of the process are aluminum and silicon. Anhydrous aluminum chloride reacts with Al4CO4to give aluminum. Silicon is generated by the decomposition of Silicon monoxide. The results of life cycle assessment for carbothermic reduction-chlorination of bauxite in vacuum show that the main consumption in the process are bauxite and power energy, the most amounts of emissions is CO2, followed by CO and SO2. After characterized, the largest environmental damage type is GWP, followed by AP and HTP. Environmental impact type is GWP, AP and POCP in turn, ADP is the minimum damage type after standardized. Considering the weight of every environmental type, the most effect environmental type is GWP, followed by POCP and the minimal damage type is HTP. The development of the process is manily limited by electricity consumption in aluminum extraction process. The measures can be adopted to decrease the consumption of electrical energy such as reducing temperature and holding time (especially in chlorination phase), improving the recovery of metal aluminium, expanding experiment equipment and improving the structure of coal-fired power and energy efficiency, et al.