HIGH-RESOLUTION TRANSMISSION ELECTRON MICROSCOPY AND TIME OF FLIGHT SECONDARY ION MASS SPECTROMETRY: AN INITIAL STUDY OF THE DISTRIBUTION OF HAZARDOUS ELEMENTS AND RARE EARTH ELEMENTS IN COAL COMBUSTION PRODUCTS

摘要

Moderately new analytical techniques can help in determining the occurrence of mineral species and the distribution of hazardous volatile elements (HVEs) and rare earth elements in coal combustion products such as minerals and amorphous phases. The continuous generation of carbonaceous matter and mixed crystalline/amorphous mineral ultrafine/nano-particles in the 1 to 100 nm size range by worldwide coal power plants represents serious environmental problems due to their potential hazards. In general the coal fly ash (CFA) that resulted from coal combustion in a thermal power plant was studied in this research. The geochemical classification of ultrafine/nano-particles present in the CFA samples and their interaction with environment are the aim of this work. The detailed methodologies applied for this work were field emission scanning electron microscopy (FE-SEM) with energy dispersive X-ray spectroscopy (EDS), high-resolution transmission electron microscopy with energy dispersive X-ray spectroscopy (HR-TEM/EDS) and time of flight secondary ion mass spectrometry (ToF-SIMS). Hazardous volatile elements, C, N, S and Hg contents were also determined in the studied sample by inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), and LECO equipment. The presented results about the CFA samples comprise carbonaceous, glassy and metallic solid spheres with some containing mixed amorphous/crystalline complex matrix. The EDS analysis coupled with the electron bean observations of the CFA particles with 100 to 0.1 nm demonstrates that these materials contain a small but significant proportion of encapsulated HVEs and rare earth elements. A wide range of organic and inorganic compounds was determined by chemical maps obtained in ToF-SIMS analysis. This work will help as a basis for further scientific research. New techniques such as spectroscopic imaging and transmission electron microscopy make it possible to check which CFA components retain HVEs and rare earth elements, thereby contributing to propose effective measures for the remediation of coal combustion products.