HYDRATE STRENGTH — AGGLOMERATION, GROWTH AND OXALATE IMPACTS

Thomas D. and Armstrong L.

Hydrate strength is important to final alumina quality for smelters and to resist attrition during Bayer precipitation and calcination. Refiners rely largely on conditions during precipitation to achieve required particle strength. This paper outline results of laboratory precipitation test work to explore the importance of growth and agglomeration conditions on hydrate particle strength.

The particle bonds formed during agglomeration were found to be quite weak, with attrition testing of the agglomerates producing particles with a similar particle size to the seed material fed to agglomeration.

Particle growth at sufficiently high supersaturation rapidly strengthens these agglomerates, particularly if about 12 μm of particle growth at a supersaturation above about 1.4 (A/A*) can be achieved between the end of agglomeration and product removal.

The presence of solid phase oxalate (SPO) during growth led to significantly more rapid hydrate strengthening. However, generation of fine particles also increases. The supersaturation reduction required to offset this nullifies or perhaps even reverses the strengthening effect.