Method for brightening and whitening clays utilizing sodium borohydride
AssigneeAnglo-American Clays Corporation
InventorAlan J. Nott
Life of this patent
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Abstract
A method for improving the brightness and whiteness of kaolin clays or the like. An aqueous slurry of the clay is initially treated with a solution of sodium borohydride and sodium hydroxide at a pH of above 7.0 up to about 10.0. Sulphur dioxide is then bubbled through the slurry or otherwise brought into contact with same, the pH being permitted to attain a value of between 6.0 and 7.0. The pH may thereupon be adjusted to between 2.5 and 4.0 with an acid, at which pH the leach reaction may occur; or the application of gaseous sulphur dioxide may be continued to yield a pH of the indicated 2.5 to 4.0 range.
Claims5
A method for brightening and whitening a kaolin clay comprising in sequence the steps of:
- forming said clay into an aqueous slurry;
- mixing said aqueous slurry with a solution of sodium borohydride and sodium hydroxide, while maintaining a pH of above 7.0 and up to about 10.0;
- contacting said slurry with gaseous sulphur dioxide in sufficient quantities to bring said slurry to a pH of between 6.0 and 7.0;
- said sulphur dioxide reacting with said sodium borohydride and sodium hydroxide to yield sodium hydrosulfite, and the quantities of said sodium borohydride and said sodium hydroxide being sufficient to yield a reacted equivalent of between 2 and 12 lbs/ton of slurry, of sodium hydrosulfite;
- adjusting the pH of the slurry to between 2.5 and 4.0, to facilitate said leach reaction;
- the temperature of the system being maintained within the range of 25.degree. to 45.degree.C;
- and
- washing the clay free of residual leaching agents and reaction products.
Dependencies are inferred from the claim text.