Hydrothermal synthesis of magadiite and kenyaite

Abstract

In order to synthesize well-crystallized magadiite and kenyaite as a single phase in a short reaction time, amorphous silica was hydrothermally reacted with alkaline solutions in the temperature range from 150°C to 200°C. From a suspension containing SiO2 and NaOH with molar ratios of H2O/SiO2 = 18.5 and NaOH/SiO2 = 0.23, magadiite was formed after a reaction time of 48 h at 150°C or after 18 h at 170°C. The formation of Na-kenyaite, however, required 6 h at 200°C. Then, KOH and K2CO2 were used to lower the formation temperature of kenyaite. K-kenyaite was synthesized after 16 h at 185°C from a suspension with molar ratios of H2 O/SiO2 = 18.5 and KOH/SiO2 = 0.23. Furthermore, (Na, K)-kenyaite was formed after 48 h at 150°C or after 24 h at 170°C from suspensions with molar ratios of H2O/ SiO2 = 18.5, NaOH/SiO2 = 0.23 and NaOH/K2CO2 = 0.95-23. Magadiite and kenyaite were formed through a difinite induction period after dissolution of amorphous silica.