Fly ASH Reactivity. Formation of hydrate phases

In this study the process of hydration of fly ash, produced by a municipal solid waste (MSW) incinerator, is examined in water and in a solution enriched with Ca(OH)2. The examined fly ash samples are characterized by a high content of alkaline chlorides and anhydrite and by remarkable amounts of heavy metals. Investigations using differential thermal analysis/thermogravimetry (DTA/TG) and X-ray diffractometry (XRD)show particular kinetics of the formation of the ettringite phase. The development of such a hydrated phase is much more intense in the presence of an excess of Ca(OH)2so as to consume the ‘free’ sulphate in the case of the more reactive fly ash. Experimental results from thermal analysis and X-ray diffractometry show the presence of different hydrated phases during the interaction between fly ash and aqueous solution. The analytical determinations, related to the aqueous solution, point out an interesting decrease in concentration of metals Pb, Zn and Cr(VI), relating to the middle period of the interaction.