Metal(loid) liberation from Alaskan coal combustion products as a function of time in various aqueous media

Thesis (M.S.) University of Alaska Fairbanks, 2018Little is known about the fate and potential toxicity of metal(loid)s that could be leached from coal combustion products by a (sub- )Arctic environment. Several potentially toxic elements are enriched in coal combustion products relative to the average crustal abundance including As, Cu, Se, and Sb. The overarching goal of this project is to examine the release of these and other metal(loid)s from early stage coal ash and fly ash from the University of Alaska Fairbanks (UAF) power plant and identify transformations in the presence of aqueous environmental media. Bioaccessibility experiments performed indicate that early stage coal ash and fly ash contain bioaccessible Cr, As, Se, Sb, and Pb. Bioaccessible concentrations of these commonly known toxic metal(loid)s were found to exceed EPA drinking water and freshwater regulations. Early stage coal ash and fly ash was reacted with 18 MΩ H₂O (control) or simulated rainwater to quantify metal(loid) liberation as a function of time. Leachate pH increased to ca. 12.5 within the first hour. Some metal(loid)s quickly reached the maximum measured concentration and consistently decreased in concentration with time such as Ba, Pb, and Zn, while other metal(loid)s increased in concentration with increased reaction time (e.g., Al, V, and Cr). Leaching behavior of between early stage coal ash and fly ash may be controlled by total initial concentrations present in the two ashes, differences in particle size, dissolution and precipitation reactions, and heterogeneity of metal(loid) distribution within the particles. Early stage coal ash and fly ash were also reacted with reconstituted dissolved organic matter solutions to simulate possible environmental interactions. It was found that for some elements (e.g., Ca), dissolved organic matter did not affect the mobility. Other metal(loid) mobilities were affected by the presence of dissolved organic matter, such as that of Sb, As, Zn, Se, Mo, and V. Some metal(loid) concentrations decreased while others increased with increasing dissolved organic carbon concentrations. Through these experiments, we have obtained a quantitative understanding of the kinetic controls of metal(loid) release from coal ash leaching with various aqueous media. Results from these experiments can help to improve storage and remediation processes for coal combustion products in an effort to protect human and the ecosystem health.UAF Undergraduate Research and Scholarly Activity, Biomedical Learning and Student Training, The IDeA Network of Biomedical Research ExcellenceChapter 1: Introduction -- 1.1 Coal combustion products -- 1.2 Environmental impacts of accidental coal combustion product releases -- 1.3 Toxicity characteristic leaching procedure and synthetic precipitation leaching procedure -- 1.4 Previous coal combustion product leaching studies -- 1.5 Metal(loid)-organic matter interactions -- 1.6 This study. Chapter 2: Site description -- 2.1 Travelling grate combustion. Chapter 3: Methods -- 3.1 Sample collection, preparation, and preservation -- 3.1.1 Dissolved organic matter collection, isolation, and storage -- 3.2 Chemicals and reagents -- 3.3 Wavelength dispersive X-ray fluorescence and multi-acid digestion -- 3.4 Brunauer-Emmett-Teller surface area analysis -- 3.5 Environmental scanning electron microscopy -- 3.6 Solid-state 13C nuclear magnetic resonance -- 3.7 Fly ash and early stage coal ash leaching -- 3.8 Synthetic precipitation leaching procedure -- 3.9 Physiological based extraction tests -- 3.10 Elemental analysis of aqueous samples -- 3.11 Statistical analysis -- 3.12 Coal combustion product-dissolved organic matter interactions -- 3.13 Geochemical modeling. Chapter 4: Results -- 4.1 Physiochemical properties -- 4.1.1 Elemental composition -- 4.1.2 Particle morphology -- 4.1.3 Organic composition -- 4.2 Synthetic precipitation leaching procedure -- 4.3 Leaching experiments -- 4.3.1 pH trends with time -- 4.3.2 Calcium leaching trends -- 4.3.3 Barium leaching trends -- 4.3.4 Aluminum leaching trends -- 4.3.5 Iron leaching trends -- 4.3.6 Lead leaching trends -- 4.3.7 Vanadium leaching trends -- 4.3.8 Molybdenum leaching trends -- 4.3.9 Chromium leaching trends -- 4.3.10 Copper leaching trends -- 4.3.11 Zinc leaching trends -- 4.3.12 Selenium leaching trends -- 4.3.13 Manganese leaching trends -- 4.3.14 Antimony leaching trends -- 4.3.15 Cobalt leaching trends -- 4.3.16 Arsenic leaching trends -- 4.3.17 Tellurium leaching trends -- 4.3.18 Bismuth leaching trends -- 4.4 Initial coal combustion product-dissolved organic matter leaching observations -- 4.4.1 Calcium-dissolved organic matter leaching -- 4.4.2 Iron-dissolved organic matter leaching -- 4.4.3 Vanadium-dissolved organic matter leaching -- 4.4.4 Molybdenum-dissolved organic matter leaching -- 4.4.5 Cobalt-dissolved organic matter leaching -- 4.4.6 Zinc-dissolved organic matter leaching -- 4.4.7 Selenium-dissolved organic matter leaching -- 4.4.8 Manganese-dissolved organic matter leaching -- 4.4.9 Antimony-dissolved organic matter leaching -- 4.4.10 Arsenic-dissolved organic matter leaching -- 4.4.11 Tellurium-dissolved organic matter leaching -- 4.5 Coal combustion product metal(loid) bioaccessibility -- 4.5.1 Chromium bioaccessibility -- 4.5.2 Arsenic bioaccessibility -- 4.5.3 Selenium bioaccessibility -- 4.5.4 Antimony bioaccessibility -- 4.5.5 Lead bioaccessibility. Chapter 5: Discussion -- 5.1 Physical and chemical characteristics of fly ash and early stage coal ash -- 5.1.1 Carbon -- 5.1.2 Major elements -- 5.1.3 Solid phase equilibrium modeling of major elements -- 5.1.4 Minor and trace elements -- 5.1.5 Solid phase equilibrium modeling of minor and trace elements -- 5.2 Competing controlling processes -- 5.2.1 pH controls -- 5.2.2 Total initial concentration -- 5.2.3 Dissolution reactions -- 5.2.4 Higher early stage coal ash leached concentrations -- 5.2.5 Particle size -- 5.2.6 Possible equilibrium -- 5.2.7 Other metal(loid) trends -- 5.3 Synthetic precipitation leaching procedure and other leaching comparisons -- 5.4 Dissolved organic matter leaching trends -- 5.4.1 Dissolved organic carbon independent metal(loid) mobility -- 5.4.2 Dissolved organic carbon dependent metal(loid) mobility -- 5.5 Unreacted coal combustion product metal(loid) bioaccessibility -- 5.5.1 Reacted early stage coal ash metal(loid) bioaccessibility. Chapter 6: Conclusions -- References