Production of titanium dioxide

Claim 1

IN THE PROCESS FOR PRODUCING TITANIUM DIOXIDE FROM OXIDIC TITANIFEROUS MATERIALS CONTAMINATED BY AT LEAST ONE MATERIAL OF THE GROUP CONSISTING OF CHROMIUM, VANADIUM, NIOBIUM AND IRON IMPURITIES, WHICH PROCESS COMPRISES THE STEPS OF (A) DISSOLVING SAID OXIDIC TITANIFEROUS MATERIAL IN AQUEOUS SULFURIC ACID TO FORM AN AQUEOUS SOLUTION OF TITANYL SULFATE; (B) HYDROLYZING SAID TITANYL SULFATE SOLUTION TO FORM HYDROUS TITANIUM DIOXIDE; AND (C) RECOVERING AND CALCINING SAID HYDROUS TITANIUM DIOXIDE, THE IMPROVEMENT FOR SUBSTANTIALLY REDUCING THE AMOUNT OF SAID CONTAMINATION CARRIED OVER INTO THE FINAL PRODUCT WHICH COMPRISES THE ADDITIONAL STEPS OF (I) HEATING SAID SOLUTION FROM STEP (A) TO A TEMPERATURE AND FOR A TIME SUFFICIENT TO INITIATE PRECIPITATION OF TITANYL SULFATE; (II) ADDING AQEOUS SULFURIC ACID TO THE HEATED SOLUTION FROM STEP (I) AFTER COMMENCEMENT OF PRECIPITATION OF TITANYL SULFATE BUT PRIOR TO THE COMPLETION THEREOF TO PROFICE AN AQUEOUS ACIDIC SLURRY OF PRECIPITATED TITANYL SUFATE; (III) SEPARATING THE PRECIPITATED TITANYL SULFATE FROM THE MOTHER LIQUOR AFTER THE COMPLETION OF SAID PRECIPITATION; (IV) REDISSOLVING THE PRECIPITATED TITANYL SULFATE FROM STEP (III) IN AQUEOUS LIQUID TO PROVIDE A FRESH AQUEOUS SOLUTION OF TITANYL SULFATE OF SUBSTANTIALLY REDUCED CONTAMINATION; AND (V) EMPLOYING SAID TITANYL SULFATE SOLUTION OF STEP (IV) IN HYDROLYSIS STEP (B).