Mixing variables for prebaked anodes used in aluminum production

Abstract

The quality of anode electrode used in aluminum electrolysis industry and its dependence on the production parameters are studied in this work. Using a calcined petroleum coke and a coal tar pitch, anode pastes were made at laboratory scale at four mixing temperatures and four mixing times. The pastes were compacted in a cylindrical mold at a maximum pressure of 60 MPa. The green samples were then baked at 1130 °C for 12 h. Measurement of density variations as well as porosity and pore size distribution was carried out on the green and baked samples as a function of mixing temperature and time. For the setup used, an optimum mixing time and temperature were suggested, resulting in a better mixing effectiveness, maximum density, and minimum air permeability and specific surface area. Green and baked anode samples were characterized to study the influence of mixing time and temperature on the anode properties. Increasing mixing temperature from 158 °C to 178 °C decreases the percentage of open porosity that improves the green apparent density. In addition, the maximum size of medium pores decreases from 26 μm at 158 °C towards 11 μm at 188 °C. ► Mixing temperature and time influence mixing effectiveness and anode properties. ► There is a density gradient along the height of the pressed samples. ► Better mixing results in a more homogeneous paste with dispersed porosity. ► Smaller pores are filled by pitch using optimum mixing variables. ► Optimum mixing parameters result in the maximum density and minimum permeability.