INFLUENCE OF THE CALCIUM CONTENT ON THE COAL FLY-ASH FEATURES IN SOMEINNOVATIVE APPLICATIONS

Despite a low chemical reactivity, recent trends in the innovative use s of coal fly ash based on the chemical properties have been successfu l. Lots of fly ash showing sharply alkaline reaction (water pH rising to 11-12 upon contact) usually are high-calcium (> 3-4%), most of whic h is present as CaO. These lots are suitable to be used as remotion ag ents of heavy metals in wastewater or retentive agents of them in poll uted solids. Lots giving substantially neutral reaction are usually lo w-calcium (0-3%). They are suitable for conversion by hydrothermal tre atments into zeolitic products, where higher calcium contents interfer e. A reverse destination is destitute of good results. Causes are disc ussed. (C) 1997 Elsevier Science B.V.