ALUMINA QUALITY SURVEY

Welch, B.J.

Analysis of the results of the survey arranged by the Organising Committee of this workshop show that smelters requirements for quality alumina are dominated by environmental issues in the pot rooms. Properties that affect the working environment, especially dust, and the fluoride adsorption capacity are seen as the most important ones. When viewed by the cell technologies, it is seen a greater dissatisfaction is experienced by Soderberg cell operators than in smelters operating prebake cells.

With the higher performance point fed prebake cells the emphasis on alumina quality shifts to factors influencing the economic performance, namely aluminium fluoride consumption (through sodium content especially), and the efficiency of cells (through phosphorus, vanadium and silicon impurity levels). Alumina solubility is considered more important for point fed cells than those fed on longer break and feed cycles where it is now recognised that sludge tends always to form. The alumina properties that influence the quality of anode cover become more important for prebake technologies that do not have point feeders.