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School of Civil and Environmental Engineering
Ph.D. Thesis Defense Announcement
Beneficial Use and Responsible Disposal of Biomass and Coal Combustion Residuals
By
Xenia Wirth
Advisor:
Dr. Susan Burns (CEE)
Committee Members:
Dr. David Frost (CEE), Dr. Sheng Dai (CEE), Dr. Martial Taillefert (EAS), Dr. Robert Bachus (Geosyntec)
Date & Time: Monday, July 1, 9am
Location: Sustainable Education Building (SEB) 122
The work performed in this study focused on the beneficial use and responsible disposal of weathered coal and woody biomass combustion residuals. Samples were extensively characterized using mineralogical and thermal techniques, including thermogravimetry, x-ray diffraction, scanning electron microscope with electron dispersive spectroscopy, laser particle size analyzer, and x-ray fluorescence, among others. After fly ash samples were characterized, potential beneficial use alternatives were explored, including use in concrete as supplementary cementitious materials and as sorbents for Pb(II) removal from aqueous solutions. Finally, the beneficial use of weathered fly ashes requires the dewatering and mining of ash impoundment facilities, which necessitates an understanding of the fly ash saturated and unsaturated hydraulic properties. In pursuit of this understanding, a detailed study on the saturated and unsaturated characteristics of a treated high-water-retention capacity weathered coal fly ash (PY) was performed. Characterization revealed morphologies specific to weathered coal fly ashes and to biomass fly ashes. Weathered fly ashes classified as Class F coal fly ashes with variable organic carbon content. They have, on average, more hydrated mineral phases that unweathered Class F fly ashes, most likely because they were wet-disposed and exposed to precipitation. Woody biomass fly ash (PN) from a full scale, biomass only power generation facility was a high-calcium, low-organic material whose properties were consistent even when the wood fuel mixture proportions were varied. Weathered coal fly ashes had potential for use in concrete as supplementary cementitious materials. When used in concrete mortars, per ASTM C109, 9 of 13 weathered ash samples met the strength requirements per ASTM C618. However, the effectiveness of weathered coal fly ashes in sorption applications was limited. These ashes had a limited total removal capacity for Pb(II) (<6 mg/g). However, woody biomass fly ashes showed high removal capacity for aqueous Pb(II) species. The high equilibrium pH and high soluble cation concentrations of biomass fly ash indicated that a primary removal mechanism for Pb(II) was precipitation of lead carbonates and hydroxides. In terms of hydraulic properties, all PY samples had a hydraulic conductivity on the order of 10-5 or 10-6 cm/s, which was consistent with literature on silts. The as-received PY sample had unsaturated behavior consistent with fine-grained silt; its water-retention profile was characterized by a shallow drainage curve and a high residual water content. Chemical surface treatments (acid, CBD) resulted in a fly ash with higher water retention capacity than the as-received fly ash, and a calcining treatment resulted in a fly ash with reduced water retention capabilities.
