Process for accelerating the digestion and sedimentation steps on the Bayer alumina process

An improved process for accelerating the digestion procedure of bauxite containing diaspore or goethite processed according to the Bayer technology at a temperature of from 180.degree.-300.degree. C. with the aid of an aluminate liquor having a sodium oxide concentration of from 80-300 g/liter for increasing the alumina yield, for converting goethite into hematite and for recrystallizing the resulting finely dispersed hematite wherein the improvement comprises carrying out the digestion with the addition of a hydrogarnet catalyst having a composition of

• A.sub.3 B.sub.2 /SiO.sub.4 /.sub.3-x /(OH).sub.4 /.sub.x
• in an amount corresponding to 5-20% by weight calculated on the dried weight of the bauxite where A is Ca.sup.2+, Mg.sup.2+, Mn.sup.2+ or Fe.sup.2+ and B is Al.sup.3+, Fe.sup.3+ or Cr.sup.3+ or Al.sup.3+ yFe.sup.3+, in which y is 0.05 to 0.5, and x is from 0 to 3.