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Speciation, Characterization, And Mobility Of As, Se and Hg In Flue Gas Desulphurization Residues
Citation:
AL-ABED, S. R., G. JEGADEESAN, K. G. SCHECKEL, AND T. M. TOLAYMAT. Speciation, Characterization, And Mobility Of As, Se and Hg In Flue Gas Desulphurization Residues. DOI: 10.1021/es70247, J. Schnoor (ed.), ENVIRONMENTAL SCIENCE AND TECHNOLOGY. American Chemical Society, Washington, DC, 42(5):1693-1698, (2008).
Impact/Purpose:
In this study, we examine the speciation and mobility of As, Se, and Hg in FGD residues using sequential chemical extraction (SCE) and synchrotron based spectroscopy techniques. X-ray absorption spectroscopy (XAS) and X-ray fluorescence spectroscopy (XRF) are frequently used to glean information on metal bonding and coordination in solid samples. XAS and XRF studies would help provide molecular structure information that would help evaluate appropriate disposal and reuse scenarios of the FGD residue. Also, we determine the release of the trace metals as a function of pH to examine the behavior of these metals under reuse or disposal scenarios.
Description:
Flue gas from coal combustion contains significant amounts of volatile toxic trace elements such as arsenic (As), selenium (Se) and mercury (Hg). The capture of these elements in the flue gas desulphurization (FGD) scrubber unit has resulted in generation of a metal-laden residue. With increasing reuse of the FGD residues in beneficial applications, it is important to determine metal speciation and mobility to understand the environmental impact of its reuse. In this paper, we report the solid phase speciation of As, Se and Hg in FGD residues using X-ray absorption spectroscopy (XAS), X-ray fluorescence spectroscopy (XRF), and sequential chemical extraction (SCE) techniques. The SCE results combined with XRF data indicated a strong possibility of As association with iron oxides, while Se was distributed among all geochemical phases. Hg appeared to be mainly distributed in the strong-complexed phase. XRF images also suggested a strong association of Hg with Fe oxide materials within FGD residues. XAS analysis indicated that As existed in its oxidized state (As (V)) while Se and Hg was observed in primarily reduced states as selenite (Se (IV)) and Hg (I), respectively. The results from the SCE and variable pH leaching tests indicated that the labile fractions of As, Se and Hg were fairly low and thus suggestive of their stability in the FGD residues. However, the presence of a fine fraction enriched in metal content in the FGD residue suggested that size fractionation is important in assessing the environmental risks associated with their reuse.
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Speciation, Characterization, And Mobility Of As, Se and Hg In Flue Gas Desulphurization Residues