Production of purified titanium dioxide pigment

Claim 1

AS A METHOD OF PRODUCING HIGHLY REFINED, PURIFIED TITANIA HYDROLYSATE SUBSTANTIALLY FREE OF PHOSPHATIC IMPURITIESD FROSM RELATIVELY PURE, WASHED TITANIA HYDROLYSATE CONTAINING PHOSPHATIC, IRON, VANADIUM AND CHROMIUM IMPURITIES IN TOTAL AMOUNT LESS THAN 1% BY WEIGHT CALCULATED ON THE TIO2 EQUIVALENT OF SAID HYDROLYSATE, WHEREIN SAID IMPURITIES ARE CONVERTED INTO ALKALI-SOLUBILIZED AND ACID-SOLUBILIZED FORMS AND ARE REMOVED BY WASHING WITH WATER, THE IMPROVED METHOD WHICH COMPRISES (1) CONVERTING SAID TITANIA HYDROLYSATE INTO AN INSOLUBLE METAL TITANATE AND SAID ALKALI-SOLUBILIZABLE IMPURITIES INCLUDING PHOSPHATIC IMPURITIES INTO WATER-SOLUBLE DERIVATIVES THEREOF, BY REACTING SAID HYDROLYSATE WITH A REACTIVE ALKALI COMPOUND CAPABLE OF SO-REACTISNG THEREWITH, AT AN ELEVATED TEMPERATURE UNTIL SAID REACTIONS ARE SUBSTANTIALLY COMPLETE; (2) SEPARATING THE INSOLUBLE METAL TITANATE FROM THE WATER-SOLUBLE CONSTITUENTS OF THE REACTION MIXTURE SO OBTAINED, INCLUDING THE PHOSPHATIC AND OTHER ALKALI-SOLUBILIZED IMPURITIES THEREOF, BY WASHING SAID MIXTURE WITH WATER; (3) DIGESTING THE SO-PURIFIED METAL TITANATE WITH CONCENTRATED SULFURIC ACID TO FORM SOLUBLE TITAMIUM SULFATE AND CONVERT THE ACID-SOLUBILIZABLE IMPURITIES INTO WATER-SOLUBLE DERIVATIVES THEREOF; (4) FORMING AN AQUEOUS SOLUTION OF THE TITANIUM SULFATE SO OBTAINED; (5) FILTERING THE TITANIUM SULFATE SOLUTION TO REMOVE IMPURITIES WHICH ARE NEITHER ALKALI-SOLUBILIZABLE NOR ACID-SOLUBILIZABLE AND ANY INSOLUBLE BY-PRODUCTS; (6) HYDROLYZING SAID TITANIUM SULFATE, IN SAID PURIFIED AQUEOUS SOLUTION TO FORM INSOLUBLE TITANIA HYDROLYSATE; AND (7) SEPARATING THE INSOLUBLE TITANIA HYDROLYSATE FROM THE ACID AND ACID-SOLUBILIZED IMPURITIES BY FILTERING AND WASHING WITH WATER; THE REFINED, PURIFIED TITANIA HYDROLYSATE SO OBTAINED BEING SUBSTANTIALLY FREE OF PHOSPHATIC IMPURITIES AND OTHER DELETERIOUS IMPURITIES AND BEING CAPABLE OF CONVERSION INTO TITANIUM DIOXIDE PIGMENTS HAVING EXCELLENT BRILLIANCE AND HIGH-TINTORIAL POWER.