Method of precipitating microfine silica using phosphate

Claim 3

The method of claim 1, wherein the phosphate salt is selected from the group consisting of sodium trimetaphosphate, sodium tripolyphosphate and sodium hexametaphosphate.

Claim 4

The method of claim 1, wherein the heating temperatures recited in steps (b) and (c) is between 85° and 98° C.

Claim 5

In the process for producing precipitated silica particles from an alkali metal silicate by addition of a precipitating agent, filtering, reslurrying the precipitate with an aqueous washing agent, filtering, washing and drying; the improvement whereby, the silica particles have surface phosphate ions thereon, and are characterized by a particle size between 20 and 800 mμ, loss on ignition between 6.5 and 10.5%, loss at 105° C between 3.0 and 5.0%, pH value between 6.5 and 10, void volume of 1.3 to 5.0 cc/g, surface area of 25 to 600 m 2 /g and pore volume of 0.01 to 0.4 cc/g and comprising the steps of: a. forming a dilute solution of sodium silicate having a weight ratio of 1.5 to 4.0 SiO 2 /1.0 Na 2 O, and containing 0.01 to 0.05 g of Na 2 O/cc; b. heating said solution to a temperature between 80° and 100° C; c. adding sufficient phosphate salt to said heated solution to obtain 0.7 to 1.2 equivalents of phosphate salt per equivalent of Na 2 O, while maintaining the temperature between 80° and 100° C for a period of 1.0 to 3.5 hours, thereby producing a slurry of silica; d. filtering, washing and reslurrying the silica with aqueous NH 3 , and then e. filtering, rewashing and drying to obtain the product.

Claim 6

In the process for producing precipitated silica particles from an alkali metal silicate by addition of a precipitating agent, filtering, reslurrying the precipitate with an aqueous washing agent, filtering, washing and drying; the improvement whereby, the silica particles have surface phosphate ions thereon, and are characterized by a particle size between 20 and 800 mμ, loss on ignition between 6.5 and 10.5%, loss at 105° C between 3.0 and 5.0%, pH value between 6.5 and 10, void volume of 1.3 to 5.0 cc/g, surface area of 25 to 600 m 2 /g and pore volume of 0.01 to 0.4 cc/g and comprising the steps of: a. forming a dilute solution of sodium silicate having a weight ratio of 1.5 to 4.0 SiO 2 /1.0 Na 2 O, and containing 0.01 to 0.05 g of Na 2 O/cc; b. heating said solution to a temperature between 80° and 100° C; c. adding sufficient phosphate salt to said heated solution to obtain 0.7 to 1.2 equivalents of phosphate salt per equivalent of Na 2 O, while maintaining the temperature between 80° and 100° C for a period of 1.0 to 3.5 hours, thereby producing a slurry of silica; d. filtering, washing and reslurrying the silica with aqueous NH 3 , and then e. filtering, rewashing and drying to obtain the product.

Claim 7

The process of claim 4, wherein the phosphate salt is selected from the group consisting of sodium trimetaphosphate, sodium tripolyphosphate and sodium hexametaphosphate.

Claim 8

The process of claim 4, wherein the heating takes place between 85° and 98° C.