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Abstract
The effect of quantity and classifications of the hydration products, strength and alkalinity of the cement-municipal solid wastes incineration (MSWI) fly ash solidified body on the leaching concentration of Pb and Cd was investigated. The results revealed that the alkalinity of the solidified body is the key factor for the stabilisation/solidification of heavy metals Pb and Cd by cement. Taken the stabilisation/solidification of Pb and Cd ions into consideration, the optimised pH value of leachate shall be 9·5–10·5. The quantity and classifications of hydration products also play a role in the stabilisation/solidification of Pb and Cd by cement and the effect of calcium monosulphate aluminate hydrate (3CaO·Al2O3·CaSO4·12H2O, abbreviated as AFm), C3S2H3, C5S6H5 is better than that of ettringite (3CaO·Al2O3·3CaSO4·32H2O, abbreviated as AFt), C3S2H8, C-S-H in terms of stabilisation/solidification. As for the stabilisation/solidification mechanism, the metathetical precipitation effect, which is dominated by the alkalinity of the solidified body, is proved to be the main mechanism in the stabilisation/solidification by cement; the effects of physical adsorption, encapsulation and isomorphous substitution are not comparable with that of the metathetical precipitation.