IMPURITY MATERIALS BALANCE IN ALUMINA REDUCTION CELLS

Kvande, H.

There are two main reasons for the study of materials balances for impurities in alumina reduction cells:

- to produce pure, high-quality aluminium

- to meet increasingly stringent fluoride emission standards

A general problem with impurity materials balances is that they depend on differing raw materials, cell operating strategies and hooding efficiencies. Thus, the results will be more or less specific to each individual smelter. Even so, the available literature data for materials balances agree reasonably well for the elements Fe, Si, Ga, Ti and Zn. On the other hand, there is still some uncertainty in the data for V, P, Cu, Ni and Pb. More work is needed to study minor impurity elements like Sn, Mn, Cr, B, S and others.

The present contribution gives special attention to the effects of the use of secondary alumina on the impurity content of the aluminium produced. Furthermore, materials balances for Li, Mg and Ca are discussed, since these have received little attention previously.