Speciation and characterization of heavy metal-contaminated soils using computer-controlled scanning electron microscopy

In the analysis of heavy metal-contaminated soils, particle-by-particle determination of elemental composition (i.e. species or mineral) as well as the characterization of particle size, external and internal morphology, can be used to assess bioavailability, remediation potential and source. The imaging capabilities of the scanning electron microscope (SEM) coupled with the elemental analysis provided by energy dispersive spectroscopy (EDS) can be used to acquire both chemical and physical information. Heavy metal particles can be analyzed automatically using computer-controlled scanning electron microscopy (CCSEM). The analysis first recognizes a particle and determines is periphery and various size measures. An EDS spectrum is obtained, the constituent elements identified and the occurrence classified into a compositional type. A TIFF microimage with spectrum is saved for later off-line review and location coordinates are saved for on-line review. Two examples illustrate the use of this technique in source identification. In one example, elevated levels of arsenic were attributed to a manufactured product rather than a fugitive source. In a second example, the lead-bearing constituents observed, as well as an association with a vuggy aluminosilicate occurrence and unburned coal, identifies coal ash as the probable source. (C) 2002 AEHS. Published by Elsevier Science Ltd. All rights reserved.