Purification of alkali metal halides

Claim 1

IN A PROCESS FOR PURIFICATION OF ALKALI METAL HALIDES TO A STATE OF PURITY IN RESPECT TO HEAVY METALS AND ALKALINE EARTH METALS EXCEEDING THAT OF U. S. P. OR C. P. ALKALI METAL HALIDES, THE STEPS OF CONTACTING AN AQUEOUS SOLUTION, SUBSTANTIALLY FREE OF SULFATE ION, OF AN ALKALI METAL HALIDE OF THE CLASS CONSISTING OF ALKALI METAL CHLORIDES, BROMIDES AND IODIDES, SAID AQUEOUS SOLUTION BEING ALREADY OF RELATIVELY HIGH PURITY, BUT CONTAINING VERY SMALL QUANTITIES OF METAL COMPOUNDS AS IMPURITIES, IN EQUIPMENT HAVING AN ALUMINUM-CONTAINING GLASS SURFACE IN CONTACT WITH THE SOLUTION, WITH A QUANTITY OF THE CARBONATE OF THE ALKALI METAL BEING PURIFIED AMOUNTING TO AT LEAST 0.4% OF THE WEIGHT OF THE SALT AND NOT EXCEEDING 10% THEREOF, PERCENTAGES BEING BY WEIGHT, DRY BASIS, SEPARATING THE RESULTING INSOLUBLE CARBONATE PRECIPITATE FROM THE SOLUTION, ADDING A QUANTITY OF ACID HAVING THE SAME ANION AS THE SALT BEING TREATED, IN QUANTITY MORE THAN ONE MOL BUT LESS THAN TWO MOLS PER MOL OF PREVIOUSLY ADDED CARBONATE, WHEREBY DISSOLVED ALUMINA IS PRECIPITATED IN THE FORM OF AN ALUMINUM-CONTAINING FLOC AND SOME OF SAID CARBONATE REMAINS IN THE FORM OF BICARBONATE, SEPARATING THE RESULTING PRECIPIATE, ADDING SUFFICIENT OF SAID ACID TO REACT WITH ALL SAID BICARBONATE AND CRYSTALLIZING OUT THE ALKALI METAL HALIDE BEING PURIFIED.