Process for producing a kaolin clay product

Abstract

A process for producing a high solids aqueous slurry of a beneficiated kaolin. An impure crude kaolin clay is initially subjected to wet processing including a size classification step, to recover a beneficiated fine particle size kaolin fraction which is formed into a dilute aqueous slurry of deflocculated kaolin particles. The dilute slurry is filtered by flowing it 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. A gel permeation layer is thereby formed of kaolin overlying the surface of the microporous barrier. The gel permeation layer and underlaying surface are substantially impervious to the passage of clay solids while being pervious to the passage of water molecules, ions and dissolved salts; whereby water molecules, ions and dissolved salts are caused to pass through the barrier, thereby increasing the concentration of the solids in the kaolin slurry. The water having passed through the barrier as a substantially solids-free permeate is collected and, the retentate is collected as a more concentrated aqueous slurry of beneficiated kaolin particles. Additional water may be thermally evaporated from the more concentrated aqueous slurry to provide a higher solids product slurry.