Comparative Studies of Metal Containment in Solidified Matrices by Scanning and Transmission Electron Microscopy

Abstract

Solidification/stabilization processes are widely used for the disposal of metal-containing industrial/hazardous wastes. There is little understanding of the mechanisms of metal containment in cementitious matrices. Leaching studies characterize the mechanism by which contaminants are released from the matrix, but give little information on contaminant-matrix interaction and the partitioning of contaminants within different phases of the solid structure. Recent studies have shown that different mechanisms are involved in stabilizing metals such as zinc and mercury [1,2] or cadmium and lead [3]. In this study, selected concentrations of metal salt solutions (cadmium, chromium, and lead) were stabilized using portland cement as additive. Scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and backscattered electron detection were performed on fractured and polished surfaces of specimens. Transmission electron microscopy (TEM) and X-ray microanalysis were carried out on ground particles of approximately 1 μm in size from the same specimens. The results indicate that different containment mechanisms are responsible for stabilization of the metals used and that they provide additional information on potential release of contaminants. The study shows the importance of correlating SEM and TEM analyses as well as other pertinent techniques in order to understand more fully the mechanism of waste containment.