Robert J. Pruett

Method for separating mixture of finely divided minerals

The Rio Capim Kaolin deposit contains a lower bed of soft kaolin clay that averages 10 meters thick, and an upper bed of “hard” kaolin (“RCC hard kaolin”) that may be as thick as 6 to 8 meters. Due to their high impurity content fine particle size, cementetious nature, and high degree of particle aggregation, hard kaolins are difficult to process. Disclosed herein are compositions comprising kaolin having a particle size distribution such that at least about 90% of the kaolin has a particle size of less than 1 micron and a GE brightness of at least about 91, where the kaolin may be derived from a crude kaolin having a Fe2O3 content of at least about 1.0% by weight, and optionally comprises titania in an amount of at least about 1.5% by weight. Also disclosed herein are methods of refining the hard kaolins, such as RCC hard kaolins, by dispersing the kaolin with at least one anionic organic dispersant and at least one inorganic dispersant. Also disclosed are compositions comprising an aqueous kaolin slurry comprising the hard kaolin, such as an RCC hard kaolin, at least one anionic organic dispersant, and at least one inorganic dispersant. Also disclosed are products containing the refined kaolin, such as paints, paper coatings, and plastics.