1991 年 99 巻 1148 号 p. 282-285
This study was undertaken to obtain kaolinite from serpentinite by treating with AlCl3 solution under various hydrothermal conditions. The serpentinite used as a starting material was from Hidaka district, Kochi Pref. Magnetite included was removed by wet magnetic separation after crushing under 280mesh. Then, 0.4g of the purified serpentinite was sealed in an ample together with AlCl3 solution and heated in an autoclave above 150°C. When this material was treated with 0.5-1.0mol/l AlCl3 solution at 200° and 245°C for 48h boehmite and/or Al24O11(OH)44Cl6 were formed together with kaolinite. Treatment with 0.5mol/l AlCl3 solution yielded only boehmite in addition to kaolinite. To prevent the formation of boehmite, mixed solutions of AlCl3 and HCl were used. When the concentrations of AlCl3 and HCl were 0.5 and 0.3mol/l, respectively, white kaolinite with low crystallinity was obtained at 245°C for 48h or 200°C for 65h. It was found that metallic elements except Si was exracted completely from the starting material into the solutions. About 98% of Si in the starting material was converted to kaolinite. The experimental results indicate that the transformation from serpentine to kaolinite proceeds at low reaction temperature in a short duration. This is presumably because the kaolinization of serpentine proceeds topotaxially as a consequence of virtually indentical crystal structure of serpentine and kaolinite.