Kaolin clay processing

Claim 1

In a process for producing white fine-particle size calcined kaolin pigment particles which comprises subjecting impure crude hydrated kaolin to wet processing in a manner such as to provide a dilute deflocculated fluid suspension in water of a fine particle size fraction of kaolin clay, dewatering said suspension by spray drying or by filtration followed by spray drying and provide dry pulverulent hydrated kaolin clay in the form of beads, pulverizing said beads and calcining the pulverized beads to remove water of hydration from the pulverized beads, thereby providing the desired calcined kaolin clay pigment particles; the improvement to improve the energy efficiency of said process which comprises: removing a part of the water from said dilute fluid deflocculated suspension of fine particle size hydrated clay by charging said dilute deflocculated fluid suspension at a pH in the range of 6 to 9.5 to an electrofilter operated to remove sufficient water and to produce a deflocculated partially dewatered suspension at a predetermined controlled solids content suitable for spray drying and thereafter spray drying said deflocculated partially dewatered suspension to remove the remainder of the water and form spray dried beads before pulverizing and calcining the clay, said deflocculated suspension having been charged to said electrofilter without addition of a flocculating agent thereto and without prior partial dewatering by conventional filtration, said electrofilter being an electrically augmented vacuum filter operated with alkaline bath overflow and producing an acidic filter cake as an anodic deposit which is mixed with bath overflow and additional deflocculating agent, if necessary, to produce said deflocculated partially dewatered suspension.