The Catalytic Activity Of Additives On Aluminum Using A Carbon Anode

Highly energy consumption and excessive carbon consumption are the prominent problems in aluminum electrolysis, Energy saving and carbon saving play an important role in aluminum production and are the primary object of this study. The effect of aluminum-containing additives (AlF3, A14C3, Al and A12O3) on the air/CO2 reactivity of carbon anode is studied with Isothermal-gravimetric method. Additionally, some relevant physical and chemical reactions are investigated with TG and XRD, to study the function mechanism of the aluminum-containing additives on structural aspect and chemical aspect.1) The airburn reactivity at 450℃ and carboxy reactivity at 970℃ of carbon anode are both found to decrease with Al-containing additives adding, and show a minimum with the amount of additives increasing. However, all Al-containing additives increase the airburn reactivity at 550℃ of carbon anode.2) It is proved that effect of Al-containing additives on the airburn reactivity and carboxy reactivity of carbon anode results from chemical factors and structural factors. Al-containing additives can lower the apparent activating energy for pyrogenation process of coal tar pitch, catalysis the pyrogenation reaction, increase the coke yield of binder pitch, so lower the air/CO2 reactivity of carbon anode. Simultaneously, the carbonization process of pitch is catalyzed by the continuous formation and decomposition of A14C3 or Al-C intermediates, therefore Al-containing additives increase the carbonization degree of binder coke, which lower the air/CO reactivity of binder coke and carbon anode. However, a-Al2O3 from Al-containing additives remains in the anode, a-Al2O3 serves as a catalyst during the oxidation process of carbon anode, so increase the Air/CO2 reactivity of binder coke and carbon anode.