Alumina production

Claim 1

A PROCESS FOR THE PRODUCTION OF COARSE-GRAINED ALUMINA HYDRATE HAVING AT LEAST 70% BY WEIGHT OF PARTICLES PLUS 200 MESH, WHICH COMPRISES PRECIPITATING ALUMINA HYDRATE FROM A PORTION OF FRESH SUPERSATURATED ALUMINATE LIQUOR IN THE PRESENCE OF COARSE PARTICLES OF PREVIOUSLY PRECIPITATED AND CLASSIFIED HYDRATE FROM AN INITIALLY TREATED PORTION OF FRESH LIQUOR AS SEED AND IN THE SUBSTANTIAL ABSENCE OF PRECIPITATED FINE HYDRATE, THE AMOUNT OF SAID COARSE HYDRATE ADDED AS SEED BEING SUCH THAT THE ALUMINA-TOCAUSTIC WEIGHT RATIO OF THE LIQUOR ATTAINED AT THE END OF SELECTED PRECIPITATION TIME IS IN EXCESS OF ABOUT .350 AND UP TO ABOUT ,400, MAINTAINING THE COARSE PARTICLES IN SUSPENSION IN THE MIXTURE BY AGITATION TO PROMOTE PRECIPITATION AND FURTHER GROWTH OF THE COARSE SEED PARTICLES, CLASSIFYING THE HYDRATE PARTICLES PRODUCED BY DISCONTINUING AGITATION OF THE SLURRY AND PERMITTING THE COARSE AND FINE HYDRATE PARTICLES TO STRATIFY BY SETTLING, SEPARATING A SLURRY OF ENLARGED COARSER PARTICLES FROM THE RELATIVELY FINE HYDRATE PARTICLES BY TRANSFER OF THE FORMER TO QUIES CENT ZONE FOR FURTHER SETTLING, FURTHER SEPARATING AND REMOVING ADITIONAL FINE HYDRATE AS IVERFLOW IN THE QUIESCENT SETTLING ZONE, AND RECOVERING A CONCENTRATED SLURRY OF ENLARGED COARSE PARTICLES.