INVESTIGATION ON MSW FLY-ASH TREATMENT BY REACTIVE CALCIUM ALUMINATESAND PHASES FORMED

In this study hydration reactions of MSW fly ash with an experimental C(12)A(7) / C(3)A - cement are investigated. The fly ash has high cont ents of soluble calcium sulphates, alkali chlorides and heavy metals. During the first hours the calcium aluminates react with the calcium s ulphate to form ettringite. On condition that the amount of added ceme nt is sufficient, after complete consumption of calcium sulphates furt her hydration leads to additional crystallization of Friedel's salt. T he same course of hydration Is found for synthetic model mixtures of c alcium aluminate + gypsum + alkali chlorides. TEM/EDX-analysis indicat es that ettringite is able to incorporate the heavy metals Pb and Zn b y substitution, but no contents of Cl- are detected. Treatment by reac tive calcium aluminates could be a suitable method for the immobilizat ion process of a wide range of toxic wastes.