Abstract: An improved process for the causticisation of Bayer liquors in an alumina refinery, the process including the steps of reacting lime with aluminate ions in a Bayer liquor within a primary reactor under controlled conditions of low to moderate temperature (between 70-80° C.) and agitation, to form substantially only a hydrocalumite species and hydroxyl ions; and a secondary reactor wherein the hydrocalumite species formed is subjected to heating in contact with a Bayer liquor under controlled conditions so as to cause the hydrocalumite species to react with the liquor to form calcium carbonate, aluminate ions and hydroxyl ions, whereby a causticised Bayer liquor is obtained and wherein the efficiency of lime utilization is substantially increased and/or alumina losses are minimized.

Abstract: A process for recovering alumina values from a first liquor having an initial concentration of aluminate ions and hydroxyl ions in solution is described. The first liquor is treated with a hydroxide of a metal other than aluminium to form an aluminium-bearing layered double hydroxide and produce a treated stream of first liquor, the treated stream of first liquor having a final concentration of aluminate ions less than the initial concentration of aluminate ions. The aluminium-bearing layered double hydroxide is separated from the treated stream of first liquor. Thereafter the clarified treated stream of first liquor is returned to a first location within an alumina refinery. The separated aluminium-bearing layered double hydroxide is contacted with a solution containing carbonate ions to form a slurry comprising an insoluble salt of the metal other than aluminium and a second liquor comprising aluminate ions released from the aluminium-bearing layered double hydroxide.

Abstract: An improved process for the causticisation of Bayer liquors in an alumina refinery includes a first step of reacting lime with aluminate ions in a Bayer liquor within a primary reactor operated at low to moderate temperature to form a hydrocalumite species and hydroxyl ions. In a second step, the hydrocalumite species is heated in contact with a Bayer liquor, which either includes or is a different liquor than the Bayer liquor of the first step, under controlled conditions to cause the hydrocalumite species to react with the liquor to form calcium carbonate, aluminate ions and hydroxyl ions. The principal advantages of the improved process include very high lime utilisation efficiencies (in excess of 90%) and a substantially increased C/S ratio (in excess of 0.955), allowing higher plant caustic concentrations and improved productivity. The loss of alumina due to the formation of unwanted calcium aluminate species is also greatly reduced.

Abstract: An improved process for the causticisation of Bayer liquors in an alumina refinery, the process including the steps of reacting lime with aluminate ions in a Bayer liquor within a primary reactor under controlled conditions of low to moderate temperature (between 70-80° C.) and agitation, to form substantially only a hydrocalumite species and hydroxyl ions; and a secondary reactor wherein the hydrocalumite species formed is subjected to heating in contact with a Bayer liquor under controlled conditions so as to cause the hydrocalumite species to react with the liquor to form calcium carbonate, aluminate ions and hydroxyl ions, whereby a causticised Bayer liquor is obtained and wherein the efficiency of lime utilization is substantially increased and/or alumina losses are minimized.

Abstract: A process for the removal of organic impurities in a Bayer process liquor in which wet and dry oxidation processes are linked together in a complementary way, such that the weaknesses of each individual organic removal process become a strength of the combined process. An organics-rich liquor stream is fed to a wet oxidation process to produce a first processed liquor which is depleted in organic compounds, but enriched in sodium carbonate and/or sodium oxalate. A feed slurry is fed to the dry oxidation process, typically including a liquor burner, where sodium compounds react to produce a discharge product. The first processed liquor and discharge product are directed into a leach tank, resulting in the formation of precipitated products including sodium carbonate and/or sodium oxalate. The precipitated products are separated from the leach tank and recycled in a mix tank providing the feed slurry to the liquor burner.