CRYSTAL GROWTH MODIFICATION: PRACTICAL AND THEORETICAL CONSIDERATIONS FOR THE BAYER PROCESS
Roe, W.J., Owen, D.O. and Jankowski, J.A.
Producers of sandy alumina in today's marketplace generally tend to push for yield to the point where further stress would result in diminished alumina quality, with regard to impurity content and/or crystal size distribution. A chemical additive is now being used in a number of Bayer plants, which is capable of coarsening the yield of alumina trihydrate product in precipitation. Parts-per-million dosages are seen to measurably shift the size distribution profile of the hydrate, as well as promote a radical coarsening and morphology change in precipitated sodium oxalate. These additive-induced effects then can provide new freedom to push for higher yields, by way of stressing the system in ways which prior to treatment would have been impossible.
Laboratory tests show that the additive induces hydrate coarsening in clean liquor, as well as in liquors purposely spiked with a sodium humate contaminant. The results of these tests have provided additional clues to the mechanism by which the crystal growth modifier works.