Synthesis of calcium-alumino-silicate hydrates from oil shale ash in different alkaline media

Abstract

Synthesis of Ca-Al-Si-hydrates from oil shale ash using NaOH, KOH and OH-substituted alkaline ionic liquid was carried out. The material from ionothermal activation was used in carbon dioxide fixation experiments. The influence of the alkaline medium on the activation of oil shale fly ash was studied using physisorption (BETN2), SEM/EDX, FESEM, XRD, and 29Si high-resolution MAS-NMR measurement techniques. In the presence of strong alkali (8 M NaOH) the silicon in the original fly ash was completely converted into Ca-Al-Si-hydrates, mainly into tobermorite and katoite structure during 24-hour treatment at 160 °C. In similar reaction conditions, the hydrothermal activation with KOH converted fly ash into tobermorites only partially. The silicon was not converted into Ca-Al-Si-hydrates by ionothermal activation with OH-substituted alkaline ionic liquid, tricaprylylmethylammonium hydroxide, either with conventional or microwave heating. It was found that both the original material and ionothermally activated oil shale ash displayed similar CO2-adsorption capacity. © 2010 Estonian Academy Publishers.