Document Type

Article

Abstract

Aluminosilicate bottom ash samples were examined from a thermal power plant in Talcher (sample NT-BA) and in Sambalpur (sample HR-BA), Odisha, India, to determine magnetic particle morphology, internal structure, mineralogy, mineral chemistry, ash fusion temperature, chemical composition, and leaching characteristics. The Talcher plant has adopted pulverized coal combustion, whereas the Sambalpur plant uses circulating fluidized bed combustion boiler technology. For NT-BA, most magnetic particles were ideal solid spheres (ferrospheres) with diverse morphological features (smooth, granular, dendritic and skeletal, porous, spotted, polygonal, and hollow [magnetite cenospheres]). For HR-BA, magnetic particles were subspherical, oval, and angular and showed widely varying surface morphologies, internal structures, and textures. Magnetite crystals occur as fine lacy, vermicular, granular, and anastomizing veinlets; agglomerated masses; and patches intimately admixed with an amorphous silicate mass/phase. Magnetite is considerably altered to hematite. Magnetite-rich magnetic concentrates (NT-BA) have higher ash fusion temperatures compared with hematite + magnetite mixed magnetic concentrates (HR-BA). Energy dispersive X-ray analysis identified magnetite, low- and high-Fe aluminosilicate glass, native Fe, and complex oxides and silicates. In the magnetite crystal structure, small amounts of Al, Mg, Mn, Ti, and Ca occur by isomorphous substitution of ferrous and ferric ions. The magnetic and nonmagnetic samples contained predominantly SiO2,Al2O3, and iron oxides derived from mineral matter in feed coal. The coarse dense ferrosphere and ferro-fragments containing large amounts of iron oxide minerals were probably derived from decomposition and oxidation of pyrite, siderite, and ankerite in feed coal. Iron oxide particles containing both iron oxides and glass are possibly derived from simultaneous melting of iron oxide minerals and clay minerals in feed coal. Sequential leaching experiments evaluated the elemental (Cr, Co, Ni, Mn, Cu, Zn, Pb, Na, K, Ca, and Mg) mobility from magnetic and nonmagnetic concentrates of bottom ash samples. These experiments provide information on the crystallization of magnetite from Fe-bearing melts in different coal combustion technologies and help evaluate environmental issues related to ash disposal and use.

First Page

30

Last Page

43

DOI

10.4177/CCGP-D-14-00010.1

Publication Date

1-1-2016

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