FILTRATION OF PREGNANT HOT SLURRIES WITH HIBAR FILTRATION - A KEY FOR INNOVATING THE DIGESTION PROCESS

Bott, R., Langeloh, T., Hahn, J.

Alumina refineries are permanently looking to increase the extraction yield of the digestion process but also to optimize and to reduce the operational costs. The focus of the experts is also on the sustainability of the operation of alumina refineries, and as a consequence the long term disposal and liability costs of the bauxite residue (in most cases considered to be hazardous waste). The extraction yield of the digestion process has been a major focus for decades and is coming again to the foreground. During the downstream thickening and washing process, some percentages of alumina are lost due to the long residence time, the lower operating temperature and the lower caustic concentration of the liquid phase and mud. If it was possible to separate the very hot, highly caustic and over-saturated digestion suspension just after the autoclave or tube digestion reactor, a lot of extractable alumina could be saved. More advanced digestion processes like ILTD (Improved Low Temperature Digestion) Process offer attractive options.