Process for producing a kaolin clay product

A process for increasing the solids content of an aqueous slurry of a dispersed kaolin, which has an initial solids level of 40% or less, and a kaolin particle size distribution such that at least 90% by weight of said particles are of less than 2 .mu.m E.S.D.;

• comprising:
• flowing the surry generally parallel to and in contact with the surface of a microporous barrier while maintaining a pressure drop across the barrier in a direction transverse to the slurry flow, thereby forming a gel permeation layer of kaolin overlying the said surface of the microporous barrier;
• said layer and underlying surface being substantially impervious to the passage of clay solids therethrough while being pervious to the passage therethrough of water molecules, ions and dissolved salts;
• whereby water molecules, ions and dissolved salts are caused to pass through said barrier as a substantially solids-free permeate, thereby increasing the concentration of the solids in said kaolin slurry;
• and collecting as the retentate the more concentrated aqueous slurry of kaolin particles from which said permeate has been separated.

A process for producing a high brightness kaolin clay product consisting essentially of beneficiated kaolin clay particles in a high solids aqueous slurry, said process comprising:

• a. subjecting an impure crude kaolin clay to wet processing including a size classification step, as to provide a dilute aqueous slurry of beneficiated kaolin particles which are dispersed in water and having a particle size distribution such that at least 90% by weight of said particles are of less than 2 .mu.m E.S.D.
• b. subjecting said dilute aqueous slurry of beneficiated dispersed kaolin particles to membrane filtration by flowing said dilute aqueous slurry parallel to the surface of a semi-permeable membrane, while imposing a pressure differential across the membrane surface;
• said semi-permeable membrane being substantially impervious to the passage of clay solids therethrough and pervious to the passage therethrough of water molecules, ions and dissolved salts, whereby water molecules, ions and dissolved salts are caused to pass through said semi-permeable membrane, thereby increasing the concentration of the solids in said kaolin slurry;
• c. collecting the water having passed through said membrane as a substantially solids-free filtrate and, separately therefrom, collecting said aqueous kaolin slurry as a more concentrated aqueous slurry of beneficiated kaolin particles;
• and
• d. thermally evaporating additional water from the more concentrated aqueous slurry of beneficiated kaolin particles to provide a high solids product slurry.

A process for producing a high brightness kaolin clay product consisting essentially of fine-particle size beneficiated kaolin clay particles in a high solids aqueous slurry, said process comprising:

• a. subjecting impure crude kaolin clay to wet processing in such a manner as to provide a dilute aqueous slurry of fine-particle size beneficiated kaolin particles dispersed in water at a solids content of from about 15% to 40% solids by weight and having a particle size distribution of at least about 90% by weight less than 2 .mu.m in equivalent spherical diameter;
• b. subjecting said dilute aqueous slurry of beneficiated kaolin particles to membrane filtration to provide a substantially solids-free filterate and a more concentrated aqueous slurry of beneficiated kaolin particles having a solids content of from about 45% to about 60% solids by weight;
• and
• c. thermally evaporating additional water from the more concentrated aqueous slurry of beneficiated kaolin particles to provide a higher solids product slurry.