Impact of coke calcination levels on the microstructure and consumption of carbon anodes in aluminum electrolysis

Carbon anodes for aluminum electrolysis were made of different calcination levels of coke as an aggregate and coal pitch as a binder. The porous structure parameters of carbon anode materials were characterized by using laser confocal scanning microscopy and the image analysis method. The anodic reaction and electrolysis consumption were also investigated in a lab scale aluminum electrolysis cell. The results demonstrate that the micropores gradually extend to crack-like macropores along the aggregate-binder interface with increasing coke calcination levels. The porosity,aspect ratio and connectivity first decrease and then increase,while the specific surface area decreases. It is appropriate to reduce the crystallite height of calcined cokes to 1.9 nm,so that the corresponding anodes can have the air reactivity of 9.6%,the CO₂ reactivity of 3.0%,and the anode consumption of 355.4 kg per ton aluminum. The excessive consumption mechanism for the low calcined anode cokes may change from selective consumption of the binder to co-consumption of both the aggregate and the binder,which can reduce the carbon dust and the total carbon consumption in aluminum electrolysis.