Method for improving the brightness of gray sedimentary kaolin clay

Claim 1

A method for improving the brightness of crude gray sedimentary kaolin clay containing a colored titania impurity and also containing calciferous and organic impurities which comprises agitating said kaolin crude in water in the presence of sufficient alkali metal carbonate salt to provide a fluid alkaline pulp, removing grit from said pulp, bubbling ozone into the pulp in amount sufficient to increase the brightness of the clay, incorporating an alkaline reagent capable of increasing the pH and decreasing the calcium ion concentration of the pulp, deflocculating the pulp by addition of sodium silicate, subjecting said pulp to flotation in the presence of an anionic carboxylic collector for the titania impurity in the clay, producing a slip of brightened clay having a reduced titania content and a concentrate of titania, and recovering said slip of brightened clay.

Claim 7

A method for improving the brightness of gray kaolin clay containing as impurities discrete colored titania and small amounts of calcium carbonate and organic matter which comprises agitating said clay in water in the presence of soda ash to produce a pulp having a pH of about 9, degritting the pulp, bubbling ozone gas into the pulp in amount sufficient to brighten the clay, thereby reducing pH below 9, incorporating an alkaline compound capable of decreasing calcium ion concentration in amount sufficient to increase pH to about 9, deflocculating the pulp by addition of sodium silicate, conditioning the deflocculated pulp for the selective flotation of colored titania with hydrogen peroxide and shortly thereafter with an anionic carboxylic reagent, subjecting the conditioned pulp to flotation, producing a float product which is a concentrate of titania impurity and a deflocculated slip of purified clay, and recovering said slip of purified clay.