Beneficial use of biomass and coal combustion residuals
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Wirth, Xenia
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Abstract
The work performed in this dissertation focused on the beneficial use of coal and biomass combustion residuals. They were extensively characterized using mineralogical and thermal techniques. Additionally, a detailed study on the saturated and unsaturated characteristics of a treated high-water-retention capacity weathered coal fly ash (PY) was performed. Finally, potential beneficial use alternatives were explored, including use in concrete as supplementary cementitious materials and as sorbents for Pb(II) removal from aqueous solutions. Characterization revealed that weathered fly ashes classified as Class F coal fly ashes with variable organic carbon content. They had, on average, more hydrated mineral phases than unweathered Class F fly ashes. Woody biomass fly ash from a full scale, biomass only power generation facility (PN) was a high-calcium, low-organic material whose properties were consistent across multiple combustion cycles. 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. Its high water-retention capacity was due to both kaolinite and diatom frustules present in the ash. Weathered coal fly ashes met ASTM C618 requirements for chemical, physical, and mechanical properties for Class F fly ashes, though some of these ashes had LOI values that exceeded 6%. These ashes had the potential for use in concrete as supplementary cementitious materials. 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. Geochemical modeling analysis using PHREEQC confirmed that the high equilibrium pH and high soluble cation concentrations of biomass fly ash contributed to Pb(II) precipitation. Wastewater treatment applications may be a beneficial use sector for woody biomass fly ash if metal removal is the primary objective for the treatment.
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2020-08-31
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Dissertation