Micro- and nanochemistry of fly ash from a coal-fired power plant

Abstract

Fly ash from a coal-fired power plant was investigated to obtain detailed information on its physical and chemical properties, and to gain an understanding of potential environmental and health impacts associated with its disposal in landfills. The studied material was produced through combustion of Illinois Basin coal and trapped within the power plant by an electrostatic precipitator. It is a finegrained, low-Ca fly ash containing primarily SiO 2 , Al 2 O 3 , and Fe 2 O 3 , and is enriched in many toxic elements (e.g., Be, Zn, As, Cd, Tl, Pb, and U) by a factor of up to 30 relative to coal. The ash consists of mainly hematite, magnetite, mullite, quartz, and amorphous material. These constituents occur mostly as spherical particles with diameters of less than 13 mm. We examined the physical, chemical, and structural characteristics of individual fly ash particles by scanning and transmission electron microscopy and electron probe microanalysis. The results demonstrate that, with the exception of complex plerospheres, individual particles are chemically fairly homogeneous, but a pronounced compositional variation exists among particles with similar physical and structural attributes. Electron microprobe data document that several trace elements, including U, are partitioned into the Ferich particles. Transmission electron microscopy revealed that various types of small (<1 mm) crystalline Ca-rich phases, including lime, are attached to the glass spheres, particularly the nonmagnetic glass. These crystals may contain substantial amounts of S. Even though only a few of these crystals were analyzed quantitatively, our data indicate that the Ca-rich and S-rich phases may be important hosts for trace elements such as V and Zn. The observed element partitioning and the existence of surface-attached crystals enriched in certain trace elements suggest that fly ash from coal-fired power plants might have a more deleterious environmental impact than is inferred from bulk analytical data.

Geochemical investigations of metals release from submerged coal fly ash using extended elutriate tests

“…Although the major constituents of fly ash are similar to those of natural soils and rocks, fly ash tends to be enriched in many trace metals (Guthrie et al, 1982;Eary et al, 1990;Mattigold et al, 1990;Gieré et al, 2003;Chaudhary and Banerjee, 2007). Furthermore, the pH dependent leaching of metal ions (e.g., arsenic, cadmium, chromium, zinc, lead, mercury, selenium) (Baba et al, 2008) raises concern regarding potential for toxic effects if contacted by aquatic receptors (Roy et al, 1981;Carlson and Adriano, 1993;Rowe et al, 2002;Kuzmick et al, 2007).…”

Analysis of Coal Ash for Trace Elements and their Geo-environmental Implications

“…Coal utilization in thermal power plants for electrical power generation has increased significantly and accumulating coal ash poses disposal challenges and a threat to the geoenvironment (Adriano 1986). Apart from being a continuing disposal problem their uses in soil treatment, as conditioners or filler material for low lying waste lands, in refuse dumps reclamation and construction or geotechnical secondary raw materials (Cabrera and Woolley 1994;Eymael and Cornelissen 1996;Barnes 2001;Adriano et al 2002;Giere et al 2003) increases their potential geoenvironmental impact. Trace elements in coal and coal ash have been discussed extensively (Adriano 1986;Eary et al 1990;Mattigold et al 1990;Swaine 1990;Finkelman 1994) and their presence is an environmental concern (Hansen et al 2002, Reijnders 2005.…”

Specific features of adsorption of azo dyes on fly ash

“…The mineral composition is characteristic of the high calcium FA obtained from lignite coal combustion. 23 The X ray diffraction pattern also shows a pronounced broad peak at 2θ = 17-48°, which can be attributed to diffuse scattering of X rays by amorphous silica. Similar features were reported in other works.…”