Characterization of novel polysulfide polymer coated fly ash and its application in mitigating diffusion of contaminants

Authors: ZHAO, L - University Of Illinois; ZABOROWSKI, E - University Of Illinois; BORDOLOI, SANANDAM - Aalto University; RAJAGOPALAN, NANDAKISHORE - University Of Illinois; Sharma, Brajendra - Bk; BAROI, CHINMOY - University Of Illinois; XING, W - New Jersey Institute Of Technology; ZHANG, L - New Jersey Institute Of Technology

Submitted to: Environmental Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2024
Publication Date: 3/15/2023
Citation: Zhao, L., Zaborowski, E., Bordoloi, S., Rajagopalan, N., Sharma, B.K., Baroi, C., Xing, W., Zhang, L. 2023. Characterization of novel polysulfide polymer coated fly ash and its application in mitigating diffusion of contaminants. Environmental Pollution. 347:123706. https://doi.org/10.1016/j.envpol.2024.123706.
DOI: https://doi.org/10.1016/j.envpol.2024.123706

Interpretive Summary: The fly ash generated in coal power plants consists of hazardous elements with high mobility and even proper landfill disposal poses environmental hazards due to the high leaching potential. This hinders their efficient reuse in the construction and/or material industry. To enhance its utilization as filler material for polymers, a novel coating of fly ash has been developed, which consists of a polymer made from vegetable oils and sulfur. On structural and surface characterization, it was found that the coated fly ash particles maintained their spherical shape, and exhibited increased surface roughness, robust hydrophobicity, and high thermal stability. These were then subjected to a series of leaching experiments under practical environmental conditions (varying pH conditions) based on the Environmental Protection Agency methodology. The results suggest a substantial reduction in leachate concentration from fly ash for multiple concerning elements and prevented mercury volatilization. The study highlights the use of modified vegetable oils as a suitable coating of fly ash to mitigate the diffusion of hazardous elements and their potential use as a filler in polymers. This work will improve the economic value of waste cooking oil, and increase the utilization of vegetable oils, thereby increasing the demand for farm products.

Technical Abstract: Fly ash consists of hazardous elements with high mobility, that poses substantial environmental hazards during storage in surface impoundments and landfills. This hinders its efficient reuse in construction or material industries. To enhance the versatility of fly ash applications, a novel surface modification technique, termed SuMo, has been developed to create a hydrophobic polysulfide polymer coating on the surface of fly ash particles. The physicochemical properties of SuMo-coated fly ash samples were examined using atomic force microscopy (AFM), environmental scanning electron microscopy (ESEM), thermal gravimetric analysis (TGA), Fourier Transform Infrared spectroscopy (FTIR), and subjected to a series of leaching experiments under practical environmental conditions (pH 4-12) based on the EPA's leaching environmental assessment framework (LEAF). The successful SuMo coating on the surface of fly ash was verified through an increased percentage of C, S, and O in elemental mapping, coupled with the identification of S-O, C=O, and C-H functional groups consistent with the chemical structure of polysulfide polymer. While the SuMo-coated fly ash particles maintained their spherical shape, they exhibited increased surface roughness, robust hydrophobicity, and thermal stability up to 250 °C. Notably, owing to the coating's resilience against water leaching, the SuMo-coated fly ash demonstrated a substantial reduction (up to 60-fold) in leachate concentration for multiple concerning elements, including B, Be, Ba, Mn, Zn, As, Cr, Hg, etc., across various pH levels compared to the original samples. Furthermore, the SuMo coating effectively prevented Hg volatilization from fly ash at heating temperatures below 163 °C. This study highlights the efficacy of the developed SuMo coating in mitigating the diffusion of hazardous elements from fly ash, thereby enhancing its potential reutilization in material, construction, and agriculture industries.