Chin, L.A.D.

Aluminium smelters are unanimous in their specification of low-dustiness as one of the desired properties of Smelter-Grade Alumina (SGA). A common practice of alumina plants, even those which produce sandy-type SGA, is to return dusts collected by electrostatic precipitators (ESP) used as the final dust collection stages on alumina calciners, and the dusts collected in the dust collectors in the calcined alumina handling systems, to the SGA product shipped to the smelters. This dust disposal practice is reconsidered in this paper. These dust streams should be minimised by the appropriate technologies and practices in the precipitation, hydrate classification, hydrate washing and calcination systems, the unavoidable dust collected regarded as undesired fine material removed from the SGA product, and alternative disposal practices developed. The fine ESP dust can be (a) returned to the precipitation circuit and mixed with Fine Seed to be agglomerated, (b) redigested in caustic soda solution to manufacture sodium aluminate solution and/or White Aluminium Hydroxide, (c) redigested in acid solutions to manufacture aluminium salts, such as aluminium sulphate, or (d) calcined to produce Special Aluminas for ceramic, abrasive and refractory applications. The hot-end dusts can be used as feedstock for the manufacture of sodium aluminate solution, white aluminium hydroxide, and of Special Aluminas as in (b),(c) and (d) above, or (e) be used as an alumina source for manufacture of glasses.