Hydrothermal Synthesis of Clay Mineral from Anorthitic Plagioclase from Korea

Decrease of clay resource demands to synthesize clay minerals especially for fine ceramics industry. We therfore have tried to convert Ca-rich plagioclase (An 66-72) from San Chung District, Korea, to kaolin minerals by a hydrothermal reaction with HCl-solution. The plagioclase bearing rocks is known as the mother rock of halloysitic kaolin deposit in Korea. Relatively low crystalline kaolin mineral was synthesized by hydrothermal conditions such as 0.14mol/l of HCl, below 200°C and at 1.5 MPa. Addition of aluminum chloride is effective to supply aluminum to the sample of plagioclase which is deficient in aluminum component and to accelerate the conversion reaction by the aid of HCl by-product of the conversion reaction. Electron micrographs showed that kaolin minerals with the crystal size about 1.1μm could be obtained by the hydrothermal reaction for 5 days under those conditions.