Manufacture of titanium dioxide

Claim 1

A PROCESS FOR THE MANUFACTURE OF TITANIUM DIOXIDE SUITABLE FOR INCORPORATION IN VITREOUS ENAMELS AND GLAZES, WHICH COMPRISES THE STEPS OF (A) PREPARING A HYDROUS TITANIUM DIOXIDE PRECIPITATE BY ADDING AN AQUEOUS SOLUTION OF TITANIUM SULPHATE HAVING A CONCENTRATION OF TITANIUM WITHIN THE RANGE OF 120 TO 180 GRAMS PER LITER CALCULATED AS TIO2, AND HAVING A TEMPERATURE WITHIN THE RANGE OF 40*C. TO 70*C., TO A PROPORTION OF HOT WATER SUCH THAT AFTER COMPLETE MIXING THE CONCENTRATION OF DISSOLVED AND UNDISSOLVED TITANIUM IS WITHIN THE RANGE OF 75 TO 95 GRAMS PER LITER CALCULATED AS TIO2, THE TEMPERATURE OF THE MIXTURE BEING MAINTAINED ABOVE 70*C. DURING MIXING AND FOR A PERIOD THEREAFTER SUFFICIENT TO COMPLETE THE HYDROLYSIS; (B) SEPARATING A MINOR PROPORTION OF THE PRECIPITATE SO FORMED; (C) PEPTIZING THE SAID MINOR PROPORTION OF THE PRECIPITATE, WHILE SUBSTANTIALLY FREE FROM SULPHATE ION, BY TREATING IT WITH HYDROCHLORIC ACID TO FORM A SUSPENSION HAVING A PH VALUE OF ABOUT 2; (D) MIXING THE PEPTIZED HYDROUS TITANIUM DIOXIDE WITH THE REMAINDER OF THE HYDROUS TITANIUM DIOXIDE PRECIPITATE; (E) WASHING (I) SAID REMAINDER AT LEAST AFTER PREPARATION OF SAID PRECIPITATE TO REMPVE LOOSELY BOUND SUPHURIC ACID AND(II) SAID MINOR PROPORTION AT LEAST AFTER PEPTIZING TO REDUCE MATERIALLY THE CONTENT OF CHLORIDE ION RESULTING FROM TREATMENT OF SAID MINOR PROPORTION WITH SAID HYDROCHLORIC ACID; AND (F) SUBJECTING THE MIXTURE TO CALCINATION, WHILE FREE FROM LOOSELY BOUND SULPHURIC ACID AND MATERIALLY REDUCED IN TIS CONTENT OF SAID CHLORIDE ION.