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Systematic characterization of selenium speciation in coal fly ash.
Estefania Garcia1, Pan Liu1, Sharon E Bone2
1School of Earth and Atmospheric Sciences, Georgia Institute of Technology, 311 Ferst Dr, Atlanta, Georgia 30332, USA. yuanzhi.tang@eas.gatech.edu.
Environmental Science. Processes & Impacts
|November 5, 2024
Summary
Coal fly ash contains toxic selenium (Se). Selective catalytic reduction (SCR) during combustion leads to reduced Se oxidation states, impacting environmental health risks.
Area of Science:
- Environmental Science
- Geochemistry
- Materials Science
Background:
- Coal fly ash (CFA) is a major byproduct of coal combustion, posing environmental challenges due to heavy metal content.
- Selenium (Se) in CFA is a toxic heavy metal, and its environmental impact is strongly dependent on its chemical form (speciation).
- Understanding Se speciation in CFA is crucial for assessing risks associated with its disposal and beneficial reuse in concrete.
Purpose of the Study:
- To investigate selenium speciation in coal fly ash.
- To determine the influence of coal source and combustion conditions, particularly selective catalytic reduction (SCR), on Se speciation.
- To correlate Se speciation with CFA characteristics.
Main Methods:
- Characterization of Se speciation using synchrotron X-ray absorption spectroscopy (XAS).
- Micro-X-ray fluorescence spectromicroscopy (μ-XRF/XAS) for spatially resolved analysis of Se-containing particles.
- Principal component analysis to link Se speciation with sample characteristics (e.g., Al2O3, SiO2, CaO, FeO, LOI, particle size, Se concentration).
Main Results:
- Se-containing particles in CFA are heterogeneous, with individual particles exhibiting multiple oxidation states: Se(0), Se(IV), and Se(VI).
- Selective catalytic reduction (SCR) is strongly associated with the prevalence of reduced Se oxidation states, with up to 90% Se(0) observed in SCR-treated samples.
- Iron oxide (FeO) content may also play a role in influencing Se speciation in CFA.
Conclusions:
- Combustion conditions, especially SCR, significantly alter Se speciation in coal fly ash, favoring reduced forms.
- The heterogeneous nature of Se distribution and oxidation states within CFA particles necessitates advanced analytical techniques for accurate assessment.
- Findings provide critical insights into the environmental behavior and potential risks of selenium in coal fly ash, informing safe disposal and reuse strategies.
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