Aluminum Electrolytic Carbon Anode Electrochemical Activity

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 electrochemical reactivity of carbon anode are investigated widely and deeply. The following factors influencing the overvoltage of carbon anode are studied with a modified current interruption technique: pitch content and butt content in the raw material prescription of industrial prebaked anodes, anode additives (A1F3 and compound oxides), composition of electrolyte, carbon dust, aluminum addition and CO bubbling et al. On the basis, the mechanism of anode process in aluminum electrolysis is elementary discussed. The mainly conclusions and findings can be summarized as follows:1) The current interruption technique in aluminum electrolysis is modified. This technique can give more exact, reliable and reproducible overvoltage results than previous literature reported method, whose standard deviation is less than 0.01 IV. The improved current interruption technique is a reliable method to characterize the electrochemical reactivity of carbon anode and to study the anodic process mechanism in aluminum electrolysis. This method can also be used for electrode process in other molten salt systems.2) Some factors in industrial prebaked anode production are found be able to lower the anodic overvoltage. These factors include pitch content increase, butt addition, and sulfur elimination during the high temperature baking.3) Some anode additives are found be able to lower the anodic overvoltage. A1F3 and Al-Mg compound Oxides (added by dipping) both can lower the anodic overvoltage, the anode baking temperature and the MgO/Al2O3 ratio has an effect on their electrocatalysis activity. Lowering the baking temperature can increase their electrocatalysis activity. The closer the ratio is to the spinel composition MgAl2O4, the more effective it is in decreasing the anodic overvoltage. Mechanical doped MgAl2O4 can also lower the anodic overvaltage of carbon anode,at 1A/cm2 current density, compared with the identical undoped anode, the doped anode baked at 970 C lower anodic overvoltage for 63mV, the doped anode baked at 1200C lower anodic overvoltage for 28mV.4) Carbon dust, Al addition and CO bubbling are found be able to lower the anodic overvoltage of carbon anode, and MgAl2O4 is found be able to lower the negative effect of CO. The added Al and carbon dust react with the anode product CO2 and form CO, CO is easy to adsorb on the surface of carbon anode. Consequently, the anode process is blocked and the anodic overvoltage increase.5) The anodic overvoltage is found to increase with increasing amount of A1F3 and CaF2 in electrolyte. The reason may be that CaF2 and A1F3 increase the wetting angle of electrolyte on carbon anode, increase the real anodic current density, so increase the anodic overvoltage.