Flocculation of kaolin slurries with phosphoric acid

Claim 2

IN THE METHOD FOR PRODUCING HIGH GRADE KAOLIN CLAY PRODUCTS WHICH COMPRISES LEACHING A DISPERSED KAOLIN CLAY WATER SLURRY WITH ABOUT 3 TO ABOUT 10 POUNDS, PER TON OF CLAY, OF A LEACHING AGENT CAPABLE OF REDUCING THE INSOLUBLE SALTS PRESENT IN SAID SLURRY AS IMPURITIES TO THEIR SOLUBLE FORM, FLOCCULATING SAID SLURRY WITH A FLOCCULATING AGENT, AND DEWATERING THE RESULTANT SLURRY MIXTURE TO REMOVE SAID SOLUBLE SALTS, THE IMPROVEMENT COMPRISING: ADDING PHOSPHORIC ACID AS A FLOCCULATING AGENT TO SAID SLURRY DURING THE LEACHING STEP, SAID PHOSPHORIC ACID BEING ADDED IN AN AMOUNT SUFFICIENT TO REDUCE THE PH OF THE SLURRY TO BETWEEN ABOUT 2.5 TO ABOUT 4.5, TO THEREBY OBTAIN A FINISHED CLAY PRODUCT THAT UPON DISPERSION, POSSESSES IMPROVED LOW VISCOSITY AND SLURRY STABILITY CHARACTERISTICS.

Claim 5

The method in accordance with claim 2, wherein said leaching agent is a compound selected from the group consisting of sodium dithionite and zinc dithionite.

Claim 6

The method in accordance with claim 2, wherein said phosphoric acid is added in an amount sufficient to lower the pH of the slurry leaching agent mixture to between about 3.5 to about 4.5.

Claim 7

The method in accordance with claim 2, wherein said phosphoric acid is added at least about 5 minutes after the beginning of the leaching step to thereby obtain maximum brightness of the finished clay product as well as said improved viscosity and slurry stability.

Claim 8

A method in accordance with claim 2, wherein said phosphoric acid is added in an amount of from about 1/2 to about 15 pounds phosphoric acid per ton of the kaolin clay.

Claim 9

The method in accordance with claim 2, wherein said slurry contains from about 10 to 35 percent clay solids, by weight.

Claim 10

The method in accordance with claim 2, wherein said phosphoric acid is employed as said flocculant in combination with a flocculant selected from the group consisting of aluminum sulfate, sulfuric acid, or hydrochloric acid.

Claim 11

The method in accordance with claim 8, wherein said phosphoric acid is added during the leaching step in combination with aluminum sulfate.

Claim 12

A method in accordance with claim 9, wherein at least about twenty-five percent by weight of said phosphoric acid-aluminum sulfate mixture is phosphoric acid.

Claim 13

A high grade kaolin clay product which, upon dispersion, possesses improved low viscosity and slurry stability during storage in an aqueous solution, said kaolin clay product being prepared by the method comprising the steps of: a. forming an aqueous slurry of a finely divided kaolin clay; b. contacting said clay water slurry with from about 3 to about 10 pounds, per ton of clay, of a leaching agent capable of reducing the insoluble salts present in said slurry to their soluble form, said leaching agent being selected from the group consisting of sodium dithionite and zinc dithionite; c. adding phosphoric acid as a flocculant to the slurry during the leaching step in an amount sufficient to lower the pH thereof to between about pH 2.5 to about pH 4.5, said acid being added after the leaching step begins; and d. dewatering the resultant mixture to thereby obtain a finished clay product that, upon dispersion, possesses low viscosity and improved slurry stability.

Claim 14

A high grade kaolin clay product which, upon dispersion, possesses improved low viscosity and slurry stability during storage in an aqueous solution, said kaolin clay product being prepared by the method comprising the steps of: a. forming an aqueous slurry of a finely divided kaolin clay; b. contacting said clay water slurry with from about 3 to about 10 pounds, per ton of clay, of a leaching agent capable of reducing the insoluble salts present in said slurry to their soluble form, said leaching agent being selected from the group consisting of sodium dithionite and zinc dithionite; c. adding phosphoric acid as a flocculant to the slurry during the leaching step in an amount sufficient to lower the pH thereof to between about pH 2.5 to about pH 4.5, said acid being added after the leaching step begins; and d. dewatering the resultant mixture to thereby obtain a finished clay product that, upon dispersion, possesses low viscosity and improved slurry stability.