MODERN REFINERY DESIGN FOR QUALITY ALUMINA: A WORSLEY CASE STUDY

Newchurch, F.N. and Moretto, K.E.

The Worsley Alumina Refinery, brought on-line in 1984, incorporates a number of state-of-the art features. Of prime consideration in the design was the ultimate physical and chemical quality of the product. This paper presents an overview of the Refinery, highlighting some of these features.

Pre-desilication is employed and this results in very low (0.006%) SiO2 in product. High volume settlers are used to handle the high mud load created by the low grade Darling Range bauxite. Stringent performance criteria in settling and security filtration enable excellent Fe2O3 values (0.005%) to be maintained in the product. Control of lime inputs enables CaO and TiO2 to be controlled to acceptable levels, despite the high TiO2 content of the bauxite.

The three stage precipitation design, with an agglomerative first stage, enables good control of particle size and strength, while optimising yield. The original airlift precipitator agitation is currently being replaced with draft tube mechanical agitators, to improve tank utilisation and promote hydrate particle strengthening. Seed handling facilities are also being upgraded for similar reasons.

The presence of organics in the liquor, especially sodium oxalate, puts a limit on production capacity and quality. Options for improving this area are being actively pursued.

In its first six years of operation, the Worsley Refinery has steadily increased its productive capacity, while maintaining excellent quality criteria. Current expansion initiatives will continue this performance.