Kaolin and Other Kaolinic Clays (Calcined or Not)

Water-washed kaolin is beneficiated by hydraulic processing to remove impurities and achieve a specific particle-size distribution; it retains its hydrated aluminosilicate chemistry. Calcined kaolin is thermally treated to dehydroxylate the clay, increasing brightness and abrasion resistance. Both forms fall within the same SITC heading, but the processing state should be clearly described on invoices because it affects duty treatment under some tariff schedules and is a key commercial specification for buyers.

Paper coating and filling applications demand the tightest particle-size distribution, brightness (ISO whiteness), and viscosity specifications, as off-spec material can disrupt coating machinery and affect print quality. Ceramic and refractory applications are somewhat more tolerant of particle-size variation but are sensitive to iron and titanium impurity levels that cause discoloration during firing.