Process for the production of durable titanium dioxide pigment

Claim 2

In a process for preparing durable titanium dioxide pigment by depositing in a slurry of TiO 2 a dense silica coating upon said TiO 2 followed by precipitating alumina into said slurry, the improvement which comprises: A. maintaining the TiO 2 slurry at a temperature of from 80° C. to 100° C. during the silica deposition, B. adjusting the slurry to a pH of from 9 to 10.5, C. rapidly adding sufficient sodium silicate to provide from 1.5 to 15% silica, based upon the TiO 2 , as a dense, amorphous, substantially continuous coating upon the TiO 2 , D. adjusting the pH of the slurry to from 9 to 10.5 and maintaining said pH at a temperature of from 80° C. to 100° C. for from 15 to 60 minutes, E. adjusting the slurry to a pH of about 8, F. rapidly adding sodium aluminate and acid simultaneously to the slurry while maintaining the pH of the slurry from 7 to 9, and G. filtering, washing and drying the treated TiO 2 .

Claim 3

The process of claim 1 in which the slurry is maintained at a temperature of from 85° C. to 95° C. and the pH is from 9 to 10.5 for from 30 to 60 minutes following silica addition.

Claim 4

The process of claim 1 in which the acid employed is selected from the group consisting of HCl and H 2 SO 4 .

Claim 5

In a process for preparing durable titanium dioxide pigment by depositing in a slurry of TiO 2 a dense silica coating upon said TiO 2 followed by precipitating alumina into said slurry, the improvement which comprises: A. heating and maintaining the TiO 2 slurry at a temperature of from 80° C. to 100° C., B. rapidly adding sufficient sodium silicate to provide from 1.5 to 8% silica, based upon the TiO 2 , as a dense, amorphous, substantially continuous coating upon the TiO 2 , C. adjusting the pH of the slurry to from 9 to 10.5 and maintaining said adjusted slurry at a temperature of from 85° C. to 95° C. for from 15 to 60 minutes, D. rapidly and simultaneously adding sodium aluminate and an acid selected from the group consisting of HCl and H 2 SO 4 , said sodium aluminate and acid being in proportion to maintain the slurry at a pH of from 8 to 9, E. curing the slurry for up to 30 minutes, and F. adjusting the slurry to pH 7 and filtering, washing and drying.

Claim 6

In a process for preparing durable titanium dioxide pigment by depositing in a slurry of TiO 2 a dense silica coating upon said TiO 2 followed by precipitating alumina into said slurry, the improvement which comprises: A. heating and maintaining the TiO 2 slurry at a temperature of from 80° C. to 100° C., B. rapidly adding sufficient sodium silicate to provide from 1.5 to 8% silica, based upon the TiO 2 , as a dense, amorphous, substantially continuous coating upon the TiO 2 , C. adjusting the pH of the slurry to from 9 to 10.5 and maintaining said adjusted slurry at a temperature of from 85° C. to 95° C. for from 15 to 60 minutes, D. rapidly and simultaneously adding sodium aluminate and an acid selected from the group consisting of HCl and H 2 SO 4 , said sodium aluminate and acid being in proportion to maintain the slurry at a pH of from 8 to 9, E. curing the slurry for up to 30 minutes, and F. adjusting the slurry to pH 7 and filtering, washing and drying.

Claim 7

In a process for preparing durable titanium dioxide pigment by depositing in a slurry of TiO 2 a dense silica coating upon said TiO 2 followed by precipitating alumina into said slurry, the improvement which comprises: A. maintaining the TiO 2 slurry at a temperature of from 80° C. to 100° C. during the silica deposition, B. adjusting the slurry to a pH of from 9 to 10.5, C. rapidly adding sufficient sodium silicate to provide from 1.5 to 15% silica, based upon the TiO 2 , as a dense, amorphous, substantially continuous coating upon the TiO 2 , D. adjusting the pH of the slurry to from 9 to 10.5 and maintaining said pH at a temperature of from 80° C. to 100° C. for from 15 to 60 minutes, E. rapidly adding sodium aluminate and acid simultaneously to the slurry while maintaining the pH of the slurry from 7 to 9, and F. filtering, washing and drying the treated TiO 2 .

Claim 8

In a process for preparing durable titanium dioxide pigment by depositing in a slurry of TiO 2 a dense silica coating upon said TiO 2 followed by precipitating alumina into said slurry, the improvement which comprises: A. maintaining the TiO 2 slurry at a temperature of from 80° C. to 100° C. during the silica deposition, B. adjusting the slurry to a pH of from 9 to 10.5, C. rapidly adding sufficient sodium silicate to provide from 1.5 to 15% silica, based upon the TiO 2 , as a dense, amorphous, substantially continuous coating upon the TiO 2 , D. adjusting the pH of the slurry to from 9 to 10.5 and maintaining said pH at a temperature of from 80° C. to 100° C. for from 15 to 60 minutes, E. rapidly adding sodium aluminate and acid simultaneously to the slurry while maintaining the pH of the slurry from 7 to 9, and F. filtering, washing and drying the treated TiO 2 .

Claim 9

The process of claim 5 in which the slurry is maintained at a temperature of from 85° C. to 95° C. and the pH is from 9 to 10.5 for from 30 to 60 minutes following silica addition.

Claim 10

The process of claim 5 in which the acid employed is selected from the group consisting of HCl and H 2 SO 4 .

Claim 11

In a process for preparing durable titanium dioxide pigment by depositing in a slurry of TiO 2 a dense silica coating upon said TiO 2 followed by precipitating alumina into said slurry, the improvement which comprises: A. maintaining the TiO 2 slurry at a temperature of from 80° C. to 100° C. during the silica deposition, B. rapidly adding sufficient sodium silicate to provide from 1.5 to 15% silica, based upon the TiO 2 , as a dense, amorphous substantially continuous coating upon the TiO 2 , C. adjusting the pH of the slurry to from 9 to 10.5 and maintaining said pH at a temperature of from 80° C. to 100° C. for from 15 to 60 minutes, D. rapidly adding sodium aluminate and acid simultaneously to the slurry while maintaining the pH of the slurry from 7 to 9, and E. filtering, washing and drying the treated TiO 2 .

Claim 12

In a process for preparing durable titanium dioxide pigment by depositing in a slurry of TiO 2 a dense silica coating upon said TiO 2 followed by precipitating alumina into said slurry, the improvement which comprises: A. maintaining the TiO 2 slurry at a temperature of from 80° C. to 100° C. during the silica deposition, B. rapidly adding sufficient sodium silicate to provide from 1.5 to 15% silica, based upon the TiO 2 , as a dense, amorphous substantially continuous coating upon the TiO 2 , C. adjusting the pH of the slurry to from 9 to 10.5 and maintaining said pH at a temperature of from 80° C. to 100° C. for from 15 to 60 minutes, D. rapidly adding sodium aluminate and acid simultaneously to the slurry while maintaining the pH of the slurry from 7 to 9, and E. filtering, washing and drying the treated TiO 2 .

Claim 13

The process of claim 8 in which the slurry is maintained at a temperature of from 85° C. to 95° C. and the pH is from 9 to 10.5 for from 30 to 60 minutes following silica addition.

Claim 14

The process of claim 8 in which the acid employed is selected from the group consisting of HCl and H 2 SO 4 .