Preparation of anatase titanium dioxide

A process for the preparation of anatase titanium dioxide comprising precipitating hydrous titanium oxide from an aqueous solution of a titanium sulphate in the absence of added nuclei and subjecting the hydrous titanium oxide to calcination wherein the titanium sulphate solution has a concentration equivalent to from 200 to 300 grams TiO.sub.2 per liter and a ratio by weight of sulphate to titanium between 1.6:1 and 2.2:1 expressed as H.sub.2 SO.sub.4 :TiO.sub.2, the precipitation of hydrous titanium oxide is induced by the addition of water to the titanium sulphate solution in an amount between 5 and 35 parts of water per 100 parts of titanium sulphate solution by weight, the precipitated hydrous titanium oxide is separated from the aqueous solution and subjected to calcination in the presence of a potassium compound and a phosphorus compound, the potassium compound being present in an amount equivalent to between 0.20 and 0.60 percent by weight potassium oxide calculated as K.sub.2 O with respect to TiO.sub.2 and the phosphorus compound being present in an amount equivalent to between 0.15 and 0.55 percent by weight phosphorus oxide calculated as P.sub.2 O.sub.5 with respect to TiO.sub.2, the thermal profile of the calcination being such that the titanium oxide is introduced initially into a first calcination zone having a gas temperature in the range 460.degree. C. to 600.degree. C. and subsequently passed to a second calcination zone having a gas temperature in the range 650.degree. C. to 700.degree. C., is heated by passing through the first zone and the second zone to a temperature in the range 650.degree. C. to 700.degree. C. over a period between 220 and 260 minutes, is further heated in a third zone to a temperature in the range 740.degree. C. to 800.degree. C. over a period between 20 and 60 minutes, is further heated in a fourth zone to a temperature in the range 845.degree. C. to 900.degree. C. over a period between 50 and 90 minutes, is further heated in a fifth zone to a temperature in the range 900.degree. C. to 950.degree. C. over a period between 30 and 70 minutes and is finally heated in a sixth zone to a temperature in the range 930.degree. C. to 1020.degree. C. over a period between 70 and 130 minutes.