Coarsening of partially calcined alumina dust

In an operation wherein a primary stream of a filtered Bayer pregnant liquor is cooled to precipitate alumina trihydrate therefrom, the improvement which comprises withdrawing a secondary stream of filtered Bayer pregnant liquor from said primary stream, adding to said secondary stream of Bayer pregnant liquor an aqueous admixture or slurry consisting essentially of partially calcined alumina dust recovered during the calcincing of alumina trihydrate to alumina, said partially calcined alumina dust exhibiting a loss on ignition of about 12-20% by weight after 1 hour at 1000.degree. C. and being comprised of a mixture of .alpha.-Al.sub.2 O.sub.3, .gamma.-Al.sub.2 O.sub.3, Al.sub.2 O.sub.3.H.sub.2 O and Al.sub.2 O.sub.3.3H.sub.2 O, said Al.sub.2 O.sub.3.H.sub.2 O being present in said mixture in an amount of about 5% up to about 20% by weight, said mixture having a particle size such that at least 80-90% by weight is less than 44 microns, and finely divided calcium carbonate or calcite, cooling the resulting secondary stream of Bayer pregnant liquor now containing the added aqueous admixture or slurry therein to precipitate alumina trihydrate and introducing the resulting treated secondary stream into admixture with said primary stream of said Bayer pregnant liquor and precipitated additional alumina trihydrate therefrom.