Process for the purification of alkali metal bichromate

Claim 1

IN THE METHOD OF PREPARING SUBSTANTIALLY SULFATE-FREE ALKALI METAL BICHROMATE BY MIXING CHROME-BEARING ORE WITH ALKALI METAL CARBONATES AN ALKALI EARTGH METAL OXIDES ROASTING THE MIXTURE AT TEMPERATURES BETWEEN 2000* TO 2200*F., LEACHING THE MIXTURE WITH AN AQUEOUS MEDIA, SEPARATING THE LIQUID AND SOLID PORTIONS OF THE THUS-OBTAINED AQUEOUS MIXTURE, TREATING THE LIQUID PORTION OF SAID MIXTURE WITH AN ACID-BEARING SUBSTANCE THEREBY PRECIPITATING ALUMINA AND SILIC HYDRATE THEREFROM, FILTERING THE THUS-OBTAINED MIXTURE THEREBY REMOVING THE ALUMINA AND SILIC HYDRATE, TREATING THE FILTRATE WITH AN ACID-BEARING SUBSTANCE, THEREBY CONVERTING THE CHROMATE-CONTAINING FILTRATE TO A BICHROMATE LIQUOR CONTAINING ALKALI METAL SULFATE, CONCENTRATING THE BICHROMATE LIQUOR TO ABOUT 60* BE''., THEREBY CAUSING THE MAJOR PORTION OF THE ALKALI METAL SULFATE TO CRYSTALLIZE, AND SEPARATING THE ALKALI METAL SULFATE FROM THE BICHROMATE LIQUOR, THE IMPROVEMENT WHICH COMPRISES COOLING THE BICHROMATE LIQUOR FROM WHICH THE MAJOR PROPORTION OF THE SULFATE HAS BEEN REMOVED TO BELOW 20*F., THEREBY CO-CRYSTALLIZING ALKALI METAL SULFATE AND ALKALI METAL BICROMATE OUT OF THE BICHROMAE LIQUOR, AND SEPARATING THE ALKALI METAL SULFATE AND ALKALI METAL BICHROMATE FROM THE BICHROMATE LIQUOR, THEREBY OBTAINING A SULFATE CONTENT OF LESS THAN ABOUT 0.1% BY WEIGHT OF THE BICHROMATE LIQUOR.