Method for bleaching gray kaolin clay

Claim 1

The method of claim 1 wherein ozone is the sole bleaching reagent that is employed in brightening said clay.

Claim 3

A method for improving the brightness of gray domestic sedimentary kaolin clay containing an organic impurity and ferruginous impurity which is not removable from the clay by leaching with acid which comprises providing a fluid dispersed aqueous slip of said clay, incorporating ozone into said slip in the form of small bubbles until substantial bleaching takes place and, without removing discrete ferrinous matter, flocculating the slip of clay by adding acidic material, removing water from the flocs and recovering bleached kaolin clay which is brighter than the clay was before ozone treatment but which has essentially the same iron analysis as the clay had before the ozone treatment.

Claim 4

A method for improving the brightness of sedimentary gray-colored domestic kaolin clay containing an organic impurity and a ferruginous impurity which is not removable from the clay by leaching with acid which has been purified by subjecting an aqueous pulp of the clay to froth flotation in a mildly alkaline circuit in the presence of a fatty acid flotation reagent selective to the flotation of colored titaniferous impurity particles in said clay, producing a froth which is a concentrate of said impurity and a machine discharge which is a dilute, mildly alkaline dispersion of purified, gray-colored clay, said method for improving the brightness of said clay consisting essentially of continuously incorporating ozone in the form of finely divided bubbles below the surface of said dilute slip of purified gray-colored clay at a pH within the range of 7 to 9 until the clay is brightened substantially, flocculating said slip by adding an acid thereto, thickening the slip by decanting water therefrom, and filtering and washing the thickened slip.

Claim 7

A method for brightening sedimentory gray domestic kaolin clay containing an organic impurity and a ferruginous impurity which is not removable from the clay be leaching with acid which comprises providing a fluid aqueous slip of said clay in the form of a body of substantial depth, while agitating said slip with an impeller agitator located near the bottom of said slip, incorporating pressurized ozone gas into said slip below the impeller agitator, whereby said gas is dispersed into minute bubbles at a point substantially below the surface of said slip, and continuing to incorporate said gas into said slip in this manner until said clay is brightened to a desired value.

Claim 8

A method for improving the brightness of sedimentary gray-colored domestic kaolin clay containing an organic impurity and a ferruginous impurity which is not removable from the clay by leaching with acid which has been purified by subjecting an aqueous pulp of the clay to froth flotation in an alkaline circuit in the presence of a fatty acid flotation reagent selective to the flotation of particles of a colored titaniferous impurity in said clay, producing a froth which is a concentrate of said impurity and a machine discharge which is an alkaline aqueous dispersion of purified, gray-colored clay, said method for improving the brightness of said clay comprising continuously incorporating ozone in the form of finely divided bubbles below the surface of said aqueous dispersion of purified gray-colored clay at a pH within the range of 7 to 9 until the clay is brightened substantially, flocculating said dispersion of clay by adding an acid thereto, further bleaching the clay with a reducing agent, and filtering and washing the bleached clay.

Claim 9

A method for improving the brightness of sedimentary gray-colored domestic kaolin clay containing an organic impurity and a ferruginous impurity which is not removable from the clay be leaching with acid which has been purified by subjecting an aqueous pulp of the clay to froth flotation in a mildly alkaline circuit in the presence of a fatty acid flotation reagent selective to the flotation of colored titaniferous impurity particles in said clay, producing a froth which is a concentrate of said impurity and a machine discharge which is a dilute, mildly alkaline dispersion of purified, gray-colored clay, said method for improving the brightness of said clay consisting essentially of continuously incorporating ozone in amount within the range of 1 to 10 pounds per ton of clay in the form of finely divided bubbles below the surface of said dilute slip of purified gray-colored clay at a pH within the range of 7 to 9 until the clay is brightened substantially, flocculating said slip by adding an acid thereto, thickening the slip by decanting water therefrom, and filtering and washing the thickened slip, said gray kaolin clay analyzing at least 0.8 percent Fe203 before and after said ozone treatment and said flocculation, and said ozone being the sole bleach reagent.