Process for leaching of alumina from aluminous material

Claim 1

IN A PROCESS FOR LEACHING ALUMINA FROM FINELY DIVIDED ALUMINOUS MATERIAL BY DIGESTION WITH AQUEOUS SODIUM HYDROXIDE SOLUTION, THE CONCENTRATION OF SAID SODIUM HYDROXIDE VARYING FROM ABOUT 40 GRAMS TO ABOUT 400 GRAMS NAOH PER LITER AT DIGESTION TEMPERATURE OF ABOUT 225* F. TO ABOUT 450*F. THAT IMPROVEMENT CONSISTING OF ADDING AN ALKALI METAL BORON COMPOUND SOLUBLE IN SAID AQUEOUS SODIUM HYDROXIDE DIGESTION SOLUTION, SAID ALKALI METAL BORON COMPOUND BEING A MEMBER OF THE CLASS CONSISTING OF ALKALI METAL METABORATE, ALKALI METAL TETRABORATE AND ALKALI METAL PERBORATE, THE AMOUNT OF SAID ALKALI METAL BORON COMPOUND VARYING FROM ABOUT 10 GRAMS PER LITER TO ABOUT 400 GRAMS PER LITER OF DIGESTION SOLUTION AND SAID DIGESTION IS CARRIED OUT FOR A PERIOD OF ABOUT 1/2 HOUR TO ABOUT 1 HOUR WHEREBY THE EXTRACTION OF A ALUMINA FROM SAID ALUMINOUS MATERIAL IS INCREASED OVER THE AMOUNT WHICH WOULD BE EXTRACTED IN THE TIME FOR EXTRACTING METAL BORON COMPOUND AND THE TIME FOR EXTRACTING ALUMINA FROM THE ALUMINOUS MATERIAL IS SHORTENED UNDER THE STATED TEMPERATURE CONDITIONS OF SAID DIGESTION.