Please use this identifier to cite or link to this item: http://hdl.handle.net/10397/25266
Title: Leaching and microstructural analysis of cement-based solidified wastes
Authors: Lo, IMC
Tang, CI
Li, XD 
Poon, CS 
Issue Date: 2000
Publisher: American Chemical Society
Source: Environmental science & technology, 2000, v. 34, no. 23, p. 5038-5042 How to cite?
Journal: Environmental science & technology 
Abstract: 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.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 toxicity characterization leaching procedure and the dynamic leach test were utilized to evaluate leaching behaviors of cement-based solidified wastes. The waste was a zinc sludge obtained from a Zn-galvanizing factory, and scanning electron microscopy/energy dispersive spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy were used to analyze the microstructure of the solidified wastes. The sludge was solidified/stabilized by Type I ordinary Portland cement, alone and combined with Grade F pulverized flyash. The data indicated that leaching was reduced more in the ordinary Portland cement product than when ordinary Portland cement was combined with pulverized flyash. Microstructural analyses indicated that the addition of cement may have caused Zn to alter from its amorphous to crystalline form.
URI: http://hdl.handle.net/10397/25266
ISSN: 0013-936X
EISSN: 1520-5851
DOI: 10.1021/es991224o
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