Hydrothermal Syntheses of Na-Magadiite and Na-Kenyaite in the Presence of Carbonate

摘要

In order to synthesize well-crystallized Na-magadiite and Na-kenyaite as a single phase in a short reaction time, the amorphous silica was hydrothermally reacted with the alkali solution of NaOH-Na2CO3 in the temperature range of 150 to 180 ∩. From a suspension containing SiO2 and NaOH-Na2CO3 with the molar ratios of SiO2/(NaOH+Na2CO3)=5 and H2O/(NaOH+Na2CO3)=100, magadiite was formed after 24 hours of reaction at 150 ∩. On the other hand, kenyaite was formed with magadiite or quartz simultaneously in 48-96 hours of reaction at 160 or 170 ∩. In the molar ratios of SiO2/(NaOH+Na2CO3)=5-10, H2O/(NaOH+Na2CO3)=100, and SiO2/(NaOH+Na2CO3)=3, H2O/(NaOH+Na2CO3)=150-200, well-crystallized kenyaites were purely synthesized. In the higher molar ratios of Si/Na [SiO2/(NaOH+Na2CO3)=20 and H2O/(NaOH+Na2CO3)=200], kenyaite can be directly synthesized from amorphous silica without the formation of magadiite as an intermediate. These results indicate that the composition of reactant is one of the important factors in the formation of kenyaite. In spite of the similarity of XRD pattern, the morphology of kenyaite represents diverse shapes.