Conc. titanium di:oxide suspension prodn. for use in paper mfr. - by dechlorinating slurry from chloride process without increasing polyvalent anion content and filtering without adding dispersant

摘要

Prodn. of TiO2 suspension (I) with a high solids content comprises converting finely-divided TiO2, produced by vapour phase oxidn. of TiCl4, in an aq. liquid with pH not over 4; adding dechlorinating agent(s) (II) and reducing the Cl2 and reducible Cl cpds. in the slurry; sepg. the TiO2 by filtration; making the filter cake fluid with a dispersant (III); and milling. The novel features are that (a) addn. of (II) causes no or limited increase in the concn. of polyvalent anions (IV) in the slurry; and (b) the slurry is filtered without using (III) or flocculant. The (IV) concn. is max. 3x10power-3 mole/l for press filtration and max. 5x10power-3 mole/l for suction filtration. With press filtration, pref. on a membrane filter press, the thixotropic filter cake is incorporated in portions in a suspension with a high solids content, which also contains the required (III), using shear. With suction filtration, pref. on a Moore filter, a solid filter cake is formed and this is made fluid by mixing with (III). (III) Is H2O2, NaHSO3 or a combination of these, H2O2 pref. being added before NaHSO3. The concn. of (I) may be increased by adding spray dried TiO2 and milling the mixt.. USE/ADVANTAGE - The process is suitable for producing (I) contg. 78 (wt.)% TiO2 or more. It is stable, has good transport and storage properties and gives excellent pigment.