Processes for the hydrothermal production of titanuim dioxide

A process comprising:

• f) mixing amorphous titanyl hydroxide with water to obtain a titanium-containing slurry;
• g) adding to the titanium-containing slurry 0.16 to 0.41 wt % of a free acid selected from the group consisting of HCl, HNO3, HF, H2C2O4.2H2O, and HBr to form an acidified titanium-containing slurry;
• h) adding to the acidified titanium-containing slurry 0.5 to 15 weight percent of a pigmentary rutile-directing additive to form a mixture;
• i) heating the mixture to a temperature of at least 220° C. but less than 374° C. for 24 hours or less in a closed vessel to form pigmentary rutile and a residual solution;
• and
• j) separating the pigmentary rutile from the residual solution.

A process comprising:

• a) mixing amorphous titanyl hydroxide with water to obtain titanium-containing slurry;
• b) adding to the titanium-containing slurry 0.3 to 20 weight percent of a free acid selected from the group consisting of HCl, H2C2O4.2H2O, HNO3, HF, and HBr to form an acidified titanium-containing slurry;
• c) adding 0.01 to 15 weight percent of a rutile-directing additive selected from the group consisting of the halides, oxalates, oxides, and hydroxides of zinc, tin, ammonium and the group I and group II metals to the acidified titanium-containing slurry to form a mixture;
• d) heating the mixture to a temperature of at least 150° C. but less than 250° C. for less than 24 hours in a closed vessel to form nano rutile and a residual solution;
• e) separating the nano rutile from the residual solution.

A process comprising:

• f) mixing amorphous titanyl hydroxide with water to obtain a titanium-containing slurry;
• g) optionally adding less than 0.16 wt % of an acid selected from the group consisting of HCl, HF, HBr, HNO3, and H2C2O4.2H2O or up to 20 wt. % of H2SO4 to the titanium-containing slurry to form an acidified slurry;
• h) adding 0.01-15 weight percent of an anatase-directing additive to the slurry to form a mixture;
• i) heating the mixture to a temperature of at least 150° C. but less than 374° C. for 24 hours or less in a closed vessel to form anatase and a residual solution;
• j) separating the anatase from the residual solution.

A process comprising:

• a) mixing amorphous titanyl hydroxide with water to obtain a titanium-containing slurry;
• b) adding a NH4OH/NH3 solution to the titanium-containing slurry such that the slurry has a pH greater than 9.0;
• c) adding to the slurry 0.01 to 15 weight percent of a brookite-directing additive to the titanium-rich slurry to form a mixture;
• d) heating the mixture to a temperature of at least 150° C. but less than the 374° C. for 24 hours or less in a closed vessel to form brookite and a residual solution;
• e) separating the brookite from the residual solution.