NAOH HYDROTHERMAL SYNTHESIS OF ZEOLITES F ROM HADONG KAOLIN OF KOREA - ON INFLUENCE OF WATER-CONTENT

In the NaOH hydrothermal synthesis of zeolite using Hadong Kaolin of K orea, the structure of Hadong Kaolin changes variously depending on tr eatment conditions. The conventional research has been investigated fo r low temperature, because the synthesis of low silica zeolite was per formed at temperatures less than 100 degrees C. When Hadong Kaolin is used as raw material of high silica zeolite, the synthesis needs highe r temperatures than 100 degrees C. However, the study has been investi gated rarely. The hydrothermal synthesis of high silica zeolite was tr ied at 175 degrees C by adding amorphous silica to Hadong Kaolin. Wate r content was changed as an experimental parameter. Special attention was given to the structural change of Kaolin. The results were summari zed as follows. 1) In the case of water content 98%, sodalite, zeolite A, zeolite P-1, unknown T and mixture of those compounds were formed. Zeolite A was formed in extremely narrow range of formation. In the c ase of water content, 95%, the mixture of them was obtained. 2) In for mer case, Kaolin changed with the lapse of time as Kaolin-->amorphous phase-->sodalite-->zeolite A-->sodalite. In latter case, Kaolin change d without forming amorphous phase as Kaolin-->mixture of Kaolin and so dalite-->sodalite. 3) The dissolution of SiO2 and Al2O3 from Kaolin to NaOH aqueous solution increased with the increase of NaOH concentrati on. The concentration of Al2O3 in solution increased with the lapse of time. But the quantity of SiO2 was lower than that of Al2O3, and beca me constant after a certain reaction time. 4) The dissolution rate of Hadong Kaolin depends on concentration of NaOH solution. The dissoluti on rate coefficient, k(1), was 0.0590 min(-1) in 1.5 M (1 M = 1 mol dm (-3)), which was about 30 times as fast as that in 0.2 M (k(1)=0.0018 min(-1)).