Abstract
The cristobalite rocks, which are mainly composed of opal-CT, are abundant at Higashidorimura, Aomori Prefecture, Japan. The SiO2 content is about 90 wt%. The cristobalite rocks have been expected to be a ceramic raw material as a source of silica. In this study, type A zeolite was synthesized from the cristobalite rocks in the presence of sodium aluminate, sodium hydroxide and water at the low temperature of 40°C and atmospheric pressure. The rate of the formation of the type A zeolite was governed by the concentration of sodium hydroxide, and the SiO2/Al2O3 molar ratio.
When the SiO2/Al2O3 molar ratio was 2, the Na2O/SiO2 molar ratio 2, water 50 ml per 1 g of the cristobalite rock, the type A zeolite with high crystallinity was obtained at 40°C for 216 hours and at 50°C for 72 hours. The synthesized type A zeolite showed cubic crystal habit with a maximum crystal size of 1 μm, and the chemical formula is almost the same as the theoretical one (Na2O·Al2O3·2SiO2·4.5H2O). Present results make the cristobalite rock attractive candidates for the preparation of zeolite.
