GB854933A - Seed for production of rutile titanium dioxide pigment and process - Google Patents

Abstract

A cured aqueous mixture of colloidally dispersed hydrated titanium oxide, a source of fluoride ions and hydrochloric, hydrobromic hydriodic or nitric acid may be employed as seed material in hydrolysing titanium sulphate solutions to give a rutile-forming precipitate. The mixture may be prepared by peptising washed and purified orthotitanic acid with the other components, heating the mixture directly or indirectly with steam to form the dispersed seed and curing the mixture by allowing to stand at room temperature or by heating at or near the boiling point. In the examples the orthotitanic acid is prepared by precipitation by adding titanium sulphate solution prepared from metatitanic acid to a sodium carbonate solution, filtering and washing. The invention permits the formation of stable seed material having concentrations up to 180 g./l. TiO2. Hydrochloric acid if used may be present as 20-50% wt. of the TiO2 and corresponding proportions of the alternative acids may be used: hydrofluoric acid if used as the fluoride source may comprise 0.1-5% wt. of the TiO2. Other sources of fluoride ions are alkali metal and alkaline earth metal fluorides. In hydrolysing a sulphate liquor 0.5-1.5% of the seed material by weight of hydrolysable TiO2 in said liquor may be used, and the seed material may be employed as such or after coagulation e.g. by ammonium hydroxide, and washing to remove halides. In the examples 0.4% Na2CO3, 0.075% Li2CO3 and 0.2% NH4H2PO4 were added to the washed filter cake prior to calcination.