The desulphurizing ability of ettringite formed during the hydration/reactivation of FBC coal fly ash

A hydrated FBC waste as well as synthetic preparations of calcium hydroxide and ettringite were investigated in a laboratory-scale fluidized bed reactor operating at 850°C under simulated desulphurization conditions. X-ray diffraction analysis, simultaneous differential thermal/thermogravimetric analyses and mercury intrusion porosimetry were the main experimental techniques employed for the materials characterization. The hydration/reactivation of FBC residue was carried out at 70°C for 48 hours with a water/solid ratio equal to 100, giving a hydration product mainly containing ettringite. The hydrated FBC waste showed a good desulphurizing ability due to calcium oxide generated during thermal decomposition of ettringite. When compared to synthetic ettringite, the hydrated FBC waste shows a lower desulphurization efficiency, a greater degree of calcium conversion and a higher attrition propensity. From a comparative evaluation between ettringite and calcium hydroxide it can be drawn that sulphation mainly involves different pore sizes ranges of the two sorbents