Abstract: A process for the preparation of an improved quality TiO.sub.2 pigment by hydrolysis of titanyl sulphate, isolation of the hydrolysis product form the waste acid produced during the hydrolysis, washing of the hydrolysis product and calcination of the hydrolysis product to form the TiO.sub.2 pigment, wherein the hydrolysis of the titanyl sulphate is carried out using separately produced hydrolysis nuclei which have been produced by a reaction of titanium salts with alkaline reagents, and in which waste acid and/or wash liquid containing waste acid is added after at least 50% of the total duration of the hydrolysis process.

Abstract: In the preparation of titanium dioxide comprising autothermically digestion a titanium-containing raw material with sulphuric acid to form a solid relatively easily soluble digestion cake containing titanyl sulphate, extracting metal sulphates from this cake by water or dilute sulphuric acid, separating the undissolved residues and, optionally after crystallization of iron sulphate heptahydrate, hydrolyzing the titanyl sulphate to produce titanium oxide hydrate, and calcining the titanium oxide hydrate to titanium dioxide, the improvement which comprises adding to the raw material a metal sulphate and effecting the autothermic decomposition with sulphuric acid of about 80 to 88% concentration. Advantageously the acid is obtained by mixing dilute acid with concentrated sulphuric acid or oleum, some of the dilute acid and metal sulphate coming from a by-product filter cake produced in the course of the process.