HyClass™ Technology for Improvement of Trihydrate Classification in the Bayer Process

The classification section in the Bayer plants is a critical part of the process. The final separation of the finest hydrate particles from the spent liquor takes place in the tertiary thickener vessels. Efficient capture of trihydrate particles in the classification circuit is essential to improve the productivity of the Bayer process. It is widely accepted that the efficiency of the classification circuit can be improved by the use of additives. Nalco is continually developing new polymer chemistries to improve the efficiency of trihydrate flocculation. A novel hydrate classification technology, HyClass™, was developed by Nalco and field evaluated in the tertiary thickener units of Noranda Alumina. HyClass technology significantly improves the flocculation performance against an industrial standard 85700 with respect to increased hydrate capture, improved settling dose-response, higher underflow densities and most importantly, further improved slurry rheology. The lab development and field evaluation work is summarized in this paper.