Silica pigments and preparation thereof

Claim 2

A PROCESS FOR THE PRODUCTION OF SILICA PIGMENT WHICH COMPRISES A. MAINTAINING AN AQUEOUS SOLUTION OF ALKALI METAL SILICATE AT A FIRST AVERAGE TEMPERATURE WITHIN THE ;IQUID RANGE OF WATER DURING A FIRST STAGE OF ACIDULATION WHILE FEEDING CARBON DIOXIDE INTO THE SOLUTION IN AN AMOUNT SUFFICIENT TO FORM PRIMARY SILICA IN COLLOIDAL SUSPENSION IN THE SOLUTION AND TO PROVIDE THE APPEARANCE OF A TYNDALL EFFECT IN THE SOLUTION, THE TIME SPAN FROM THE COMMENCING OF THE FEEDING OF CARBON DIOXIDE UNTIL THE APPEARANCE OF THE TYNDALL EFFECT BEING 30 TO 300 MINUTES B. MAINTAINING THE COMPOSITION PRODUCED BY STEP (A) AT A SECOND, HIGER AVERAGE TEMPERATURE WITHIN THE LIQUID RANGE OF WATER DURING A SECOND STAGE OF ACIDULATION WHILE CONTINUING THE FEEDING OF CARBON DIOXIDE INTO THE COMPOSITION, SAID SECOND STAGE OF ACIDULATION BEGINNING WITH THE APPEARANCE OF THE TYNDALL EFFECT AND ENDING WHEN SUFFICIENT CARBON DIOXIDE HAS BEEN FED TO EFFECT PRECIPITATION AS PIGMENT OF ABOUT 10 PERCENT OF THE SILICA CONTENT OF THE COMPOSITION, SAID SECOND AVERAGE TEMPERATURE BEING AT LEAST 10*C, HIGHER THAN SAID FIRST AVERAGE TEMPERATURE, AND THE DURATION OF SAID SECOND STAGE BEING ABOUT 30 TO 300 MINUTES, C. CONTINUING THE PRECIPITATE OF THE SILICA BY CONTINUING THE FEEDING OF CARBON DIOXIDE INTO THE COMPOSITION PRODUCED BY STEP (B) UNTIL AT LEAST 90 PERCENT OF THE SILICA HAS PRECIPITATED AS PIGMENT, WHILE MAINTAINING THE TEMPERATURE OF THE COMPOSITION WITHIN THE LIQUID RANGE OF WATER, D. CONTINUING THE FEEDING TO CARBON DIOXIDE INTO THE COMPOSITION PRODUCED BY STEP (C) UNTIL AT LEAST ENOUGH THEREOF HAS BEEN FED TO CONVERT SUBSTANTIALLY ALL OF THE NA2O CONTENT OF THE COMPOSITION TO NA2CO3, AND E. RECOVERING THE PRECIPITATED SILICA PIGMENT FROM THE MOTHER LIQUOR.

Claim 3

The process of claim 1 wherein the alkali metal silicate is sodium silicate and the aqueous solution of sodium silicate in step (a), prior to being contacted with the carbon dioxide, contains a weight ratio of SiO2 to Na2O of less than 3.8 to 1.

Claim 4

The process of claim 1 wherein the average temperature of the solution in step (a) is maintained within the range of about 1* to 70* C.

Claim 5

The process of claim 1, wherein the average temperature of the composition in step (b) is maintained within the range of about 71* to 99* C.

Claim 6

The process of claim 1, wherein step (c) the pigment is removed as wet cake.

Claim 7

The process of claim 1, wherein, to form a dry product, in step (e) the pigment recovered from the mother liquor is filtered, washed and dried.

Claim 8

A process for the production of silica pigment which comprises a. maintaining an aqueous solution of alkali metal silicate at a first average temperature within the liquid range of water during a first stage of acidulation while feeding carbon dioxide into the solution in an amount sufficient to form primary silica particles in colloidal suspension in the solution and to provide the appearance of a Tyndall effect in the solution, the time span from the commencing of the feeding of carbon dioxide until the appearance of the Tyndall effect being 30 to 300 minutes. b. maintaining the composition produced by step (a) at a second, higher average temperature within the liquid range of water during a second stage of acidulation while continuing the feeding of carbon dioxide into the composition, said second stage of acidulation beginning with the appearance of the Tyndall effect and ending when sufficient carbon dioxide has been fed to effect precipitation as pigment of about 10 percent of the silica content of the composition, said second average temperature being at least about 20* C. higher than said first average temperature, and the duration of said second stage being about 30 to 300 minutes, c. continuing the precipitation of the silica by continuing the feeding of carbon dioxide into the composition produced by step (b) until at least 90 percent of the silica has precipitated as pigment, while maintaining the temperature of the composition within the liquid range of water, d. continuing the feeding of carbon dioxide into the composition produced by step (c) until at least enough thereof has been fed to convert substantially all of the Na2O content of the composition to Na2CO3, and e. recovering the precipitated silica pigment from the mother liquor.

Claim 9

A process for the production of silica pigment which comprises a. maintaining an aqueous solution of alkali metal silicate at a first average temperature within the liquid range of water during a first stage of acidulation while feeding carbon dioxide into the solution in an amount sufficient to form primary silica particles in colloidal suspension in the solution and to provide the appearance of a Tyndall effect in the solution, the time span from the commencing of the feeding of carbon dioxide until the appearance of the Tyndall effect being 30 to 300 minutes. b. maintaining the composition produced by step (a) at a second, higher average temperature within the liquid range of water during a second stage of acidulation while continuing the feeding of carbon dioxide into the composition, said second stage of acidulation beginning with the appearance of the Tyndall effect and ending when sufficient carbon dioxide has been fed to effect precipitation as pigment of about 10 percent of the silica content of the composition, said second average temperature being at least about 20* C. higher than said first average temperature, and the duration of said second stage being about 30 to 300 minutes, c. continuing the precipitation of the silica by continuing the feeding of carbon dioxide into the composition produced by step (b) until at least 90 percent of the silica has precipitated as pigment, while maintaining the temperature of the composition within the liquid range of water, d. continuing the feeding of carbon dioxide into the composition produced by step (c) until at least enough thereof has been fed to convert substantially all of the Na2O content of the composition to Na2CO3, and e. recovering the precipitated silica pigment from the mother liquor.