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The reaction products formed in a series of fully "equilibrated," roomtemperature-hydrated, fumed colloidal silica plus lime water mixtures were examined using 29Si magic angle spinning nuclear magnetic resonance. The data suggest that two structurally d i s t in c t ca 1 c i u m s i I i c a t e hydrate (C-S-H) phases exist in the system CaO-SiO,-H,O. The more silica-rich C-S-H (Ca/Si=O.65 to 1 .O) consists predominantly of long chains of silica tetrahedra (Q2 middle units) similar to those found in 1.4-nm tobermorite. The studied more lime-rich C-S-H ( C a / S i = l . l t o 1.3) consists of a mixture of dimer ( Q ' ) and shorter chains (Q' end units and Q' middle units) similar to that reported for synthetic jennite. No monomer units (Q') were detected. [

Zeolites X, Y, and Na-P1 (90 °C) and analcime and sodalite (150 °C) were synthesized from Class F fly ash using 3 M sodium hydroxide solutions and autogenous pressures. The partially zeolitized fly ashes were dried overnight in air at room temperature and then characterized using X-ray diffraction and SEM. On occasion, a few samples were dried to constant weight for an additional 8−10 min in a microwave oven to remove bound water as well. The dried samples were evaluated for their ability to adsorb sulfur dioxide (SO2) from a simulated stack gas containing ∼2000 ppm SO2. Determinations were made in real time using a UV/vis spectrophotometer followed by a total sulfur analysis of the “loaded” samples once testing was complete. Breakthrough curves indicate that the zeolites in the samples are able to remove all of the SO2 in the simulated flue gas (zero SO2 emission) for varying periods of time, and that the actual amount of SO2 removed by the zeolite depended on the type and degree of “dryness” of the zeolite or zeolite-like material present. For example, a 7 day 150 °C cured sample containing analcime and sodalite was able to adsorb 6−7 mg of SO2 per gram of sample regardless of the source of the fly ash, whereas a 90 °C cured sample containing X, Y, and Na-P1 was significantly less efficient.