Abstract: The invention relates to a process for the reduction of sodium hydroxide losses of the Bayer-cycle by modified causticization of red mud which comprisessubjecting an optionally previously concentrated red mud slurry led off from the red mud washing line by ramification and containing a liquid phase which has a concentration of 5-40 g. caustic Na.sub.2 0/1. caustification by adjusting the lime content expressed as CaO through addition of lime or lime milk to 1-3.2 moles per mole Al.sub.2 O.sub.3, preferably to 2-2.5 moles per mole Al.sub.2 O.sub.3, related to the total Al.sub.2 O.sub.3 content of the slurry;stirring the slurry for 0.3-5 hours at a temperature of 70.degree.-110.degree. C., preferably at 80.degree.-100.degree. C.;adding to the slurry 3-4 moles, preferably 3.2-3.4 moles, of soda related to 1 mole of the originally dissolved Al.sub.2 O.sub.3, and continuing the stirring for 1-4 hours at 80.degree.-100.degree. C., preferably at a temperature of 90.degree.-95.degree. C.

Abstract: An improved process for accelerating the digestion process in the Bayer alumina process is provided which promotes both the goethite-hematite conversion and a more perfect and quick dissolution of the diaspore. The above is achieved by carrying out the digestion in the process of 5-20% by weight calculated on the dry weight of the bauxite of a novel hydrogarnet catalyst.

Abstract: The invention relates to an improved process for the production of alumina according to the Bayer technology, of bauxites containing goethite and especially of boehmitic or diasporic bauxites, for the acceleration of the digestion process, for the transformation of goethite into hematite, for the increase of alumina yield and for the reduction of the caustic soda losses, the essence of which consists in carrying out the digestion in the presence of 2-6% CaO and 0.2-2.0% Mg.sup.++, Fe.sup.++, Mn.sup.++ Co.sup.++ ions based on the weight of the dry bauxite or of compounds or ores containing these ions in the indicated quantities.

Abstract: A method for processing bauxites according to the Bayer technology, with an increased yield in Al.sub.2 O.sub.3 and with decreased caustic soda losses, starting particularly from goethite bauxites of boehmite and/or diaspore type and carrying out the digestion at 180.degree.C to 300.degree.C using an aluminate liquor containing Na.sub.2 O.sub.caustic in a concentration of 80 to 300 g./l. The digestion is carried out in the presence of a calcium compound in an amount corresponding to 2 to 6 % of CaO calculated for the dry weight of bauxite and of a sulfate salt in an amount corresponding to 1.0 to 7.0 g./l. of sulfate ion concentration, whereby the goethite content of the bauxite is converted into hematite. The process provides advantageous conditions for the complete dissolution of the boehmite and diaspore content of bauxite in the vicinity of the equilibrium molar ratio, and enables to recover efficiently the caustic soda losses in the Bayer process itself, requiring no supplementary operation.