Environmentally friendly product, calcium-silica-aluminum hydrate, was synthesized from oil shale fly ash, which is rendered so far partly as an industrial waste. Reaction conditions were: temperature 130 and 160 degrees C, NaOH concentrations 1, 3, 5 and 8 M and synthesis time 24 h. Optimal conditions were found to be 5 M at 130 degrees C at given parameter range. Original and activated ash samples were characterized by XRD, XRF, SEM, EFTEM, Si-29 MAS-NMR, BET and TGA. Semi-quantitative XRD and MAS-NMR showed that mainly tobermorites and katoite are formed during alkaline hydrothermal treatment. Physical adsorption of CO2 on the surface of the original and activated ash samples was measured with thermo-gravimetric analysis. TGA showed that the physical adsorption of CO2 on the oil shale fly ash sample increases from 0.06 to 3-4 mass% after alkaline hydrothermal activation with NaOH. The activated product has a potential to be used in industrial processes for physical adsorption of CO2 emissions. (C) 2011 Elsevier B.V. All rights reserved.