Leach tests alone cannot determine the actual performance and long-term environmental impacts of solidified/ stabilized waste because they do not provide information on the physical and chemical changes between waste and additives. This research study utilized a combined approach to investigate the leaching behaviors and binding chemistry of a solidified/stabilized industrial waste. The combined approach included leach tests and microstructural analysis. The OPC system showed more satisfactory results in TCLP and DLT than the OPC/PFA system. Because no identifiable hydration products were observed, SEM/ EDS images and XRD of solidified waste suggest that the presence of zinc retards the hydration of OPC and PFA. However, a new crystalline compound, ZnO, is detected by XRD in samples A01 and B02. These are believed to be a result of the addition of cement to zinc sludge, which may cause zinc to change from its amorphous to crystalline form. In addition, a certain amount of zinc was found on the surface of solidified waste by XPS. The use of microstructural analysis has been proved to be essential in providing useful information on the physical and chemical changes within the cement matrix.

The aim of this study is to systematically quantify the physical and chemical properties of the cement based solidified/stabilised heavy metal waste with increasing replacement of cement by PFA. Bulk density and unconfined compressive strength are measured as the physical parameters. The equilibrium extraction tests, sequential chemical tests and dynamic leaching tests are reported as chemical characteristics. The results showed PFA-blended cement-based waste forms have higher porosity and lower strength than the pure cement-based waste forms at experimental curing time. The lower alkalinities of the PFA-blended cement-based waste forms, however, lead to higher leach rates of heavy metals when the waste is exposed to an acidic medium.

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