Effects of progressive carbonation on heavy metal leaching from cement-bound waste

Contradictory leaching results from carbonated cement-bound wastes have been reported in various investigations. However, the degree of carbonation of the examined samples is rarely considered as an important parameter in leaching results. This article focuses on the effect of progressive carbonation on leaching properties of cement-bound waste (bottom ash or flue gas cleaning residue), including uncarbonated, partially carbonated, and almost completely carbonated samples. Leaching is investigated after carbonation by means of semi-dynamic leaching of monoliths, supported by batch solubility and release measurements on particle-size reduced material. For partially carbonated samples, leaching of metals is in most cases less than observed from uncarbonated samples, resulting from the conversion of hydroxides to carbonates. For completely carbonated samples, increased leaching of most metals was observed in comparison to partially carbonated samples, resulting from leachate induced transformation of carbonate into more soluble bicarbonate speciation.