Acid and alkali treatment of kaolins

Two kaolins containing kaolinites of different crystallinity, as confirmed by the Aparicio-Galan-Ferrell index. were treated in HCl and KOH solutions at 95 degrees and 80 degrees C, respectively, for periods up to 36 h. Changes resulting from the treatments have been characterized by several methods. Fe occurs in the octahedral sheets of both kaolinites and dissolves similarly to At. Lower structural ordering, more structural defects and particles of smaller average size and less regular shape are responsible for faster dissolution of KGa-2 in comparison to well ordered Gold Field (Tanzania) kaolinite. More Si than Al is dissolved in KOH from both kaolins after any dissolution time. An aluminosilicate (feldspathoid) phase is thought to Occur in the material prepared from KGa-2 in KOH. Near-IR spectra provide very useful information on changes in the mineral structure upon the treatment, oil the solid reaction products and oil the adsorbed water molecules.