Chemical process for extracting monohydrate alumina containing materials

Claim 1

IN THE WET ALKALI ALUMINATE PROCESS FOR THE PRODUCTION OF ALUMINA FROM ALUMINOUS MATERIALS CONTAINING CAUSTIC SOLUBLE MONOHYDRATE ALUMINA, WHEREIN THE ALUMINA IS EXTRACTED BY PRESSURE DIGESTION OF THE ALUMINOUS MATERIAL IN RECYCLED SPENT CAUSTIC ALUMINATE LIQUOR LEAVING AN INSOLUBLE RESIDUE, THE PREGNANT LIQUOR IS DEPRESSURIZED AND FLASH COOLED AND WATER IS REMOVED THEREFROM BY FLASH STEAM GENERATION, THE SPEND LIQUOR IS DILUTED BY INJECTION STEAM IN HEATING TO DIGESTION TEMPERATURE, THE PREGNANT LIQUOR IS DILUTED BY ADDITION OF WASH WATER USED IN WASHING OF SAID INSOLUBLE RESIDUES, AND AN AMOUNT OF WATER EQUIVALENT TO THE NET DILUTION IS REMOVED THEREFORM BY EVAPORATION IN EACH CYCLE, THE IMPROVED PROCESS FOR TOTAL EXTRACTION OF THE CAUSTIC SOLUBLE ALUMINA WITH SUBSTANTIALLY REDUCED HEAT INPUT, WHICH COMPRISES PRESSURE DIGESTING THE ALUMINOUS MATERIAL IN THE DILUTED SPENT LIQUOR FROM WHICH NOT MORE THAN A MINOR FRACTION OF THE NET DILUTION WATER IS REMOVED, LIMITING DIGESTION DILUTION BY INCREASING THE SPENT LIQUOR TEMPERATURE BY AN AMOUNT IN EXCESS OF 200*F. AND AT LEAST TO WITHIN 100*F. OF THE DIGESTION TEMPERATURE BY INDIRECT HEAT EXCHANGE WITH THE FLASH STEAM GENERATED BY FLASH COOLING THE PREGNANT LIQUOR, THE DIGESTION BEING CONDUCTED AT A TEMPERATURE SUFFICIENTLY ABOVE THE ATMOSPHERIC BOILING POINT OF SAID DILUTED LIQUOR SUCH THAT ON DEPRESSURIZING AND FLASH COOLING THEREOF AT LEAST THE MAJOR PORTION OF THE NET DILUTION WATER IS REMOVED BY FLASH STEAM GENERATION, AND DEPRESSURIZING THE PREGNANT LIQUOR TO SUBSTANTIALLY THE ATMOSPHERIC BOILING POINT THEREOF.