Adsorption capacity and mechanism of modified coal fly ash (CFA) for per- and polyfluoroalkyl substances (PFAS) in landfill leachate

• Published in: Journal of hazardous materials 2025-02, Vol.484, p.136763, Article 136763
• Main Authors: Patel, Harsh V., Greer, Myles, Brazil, Brian, Yu, Wenzheng, Hamoush, Sameer, Zhang, Lifeng, Zhao, Renzun
• Format: Article
• Language: English
• Subjects: And Dissolved Organic Matter (DOM); Coal Fly-Ash; Landfill leachate; Per- and Polyfluoro-Alkyl Substances (PFAS)
• ISSN: 0304-3894; 1873-3336; 1873-3336
• DOI: 10.1016/j.jhazmat.2024.136763

This study explores the potential of modified coal fly ash (CFA) as an adsorbing material for immobilizing Per- and Polyfluoroalkyl Substances (PFAS) and bulk organic matter from landfill leachate, comparing its efficacy to that of activated carbon. Physiochemical modification of CFA using hydrochloric acid (HCl) and thermal treatment significantly enhanced its adsorption properties, increasing the BET surface area by 2.5 to 3.5 times and pore volume by 2 to 3 times. Despite the high concentrations of dissolved organic matter (DOM) in landfill leachate, modified CFA achieved up to 88 % removal of total organic carbon (TOC) and 93 % decrease of UV254 at an optimal dose of 400 g/L. The PFAS adsorption capacity reached 3.5 mg/g, representing approximately 3–15 % of that of activated carbon due to its limited surface area and pore volume. CFA possesses 5 to 15 times higher surface area based adsorption capacity (in mg/m2) than activated carbon. Adsorption kinetics were best described by a pseudo-second-order model, indicating that chemisorption is the primary mechanism. Notably, longer-chain PFAS exhibited faster adsorption rates and higher adsorption capacity with CFA. The adsorption isotherm data fits better with non-linear Langmuir isotherm compared to Freundlich isotherm, indicating that the adsorption of PFAS on CFA is monolayer adsorption. Overall, CFA demonstrates exceptional performance in leachate treatment, with its low cost and energy requirements positioning it as a promising alternative to conventional carbon-based adsorbents. [Display omitted] •Coal fly ash effectively adsorbs bulk organic matter in landfill leachate.•CFA shows 3.5 mg/g PFAS adsorption, 3-15 % of activated carbon's capacity.•CFA shows higher surface area-based adsorption capacity (in mg/m2) than GAC.•Long-chain PFAS adsorbed faster and at higher capacities than short-chain variants.•PFAS adsorption on CFA is characterized by monolayer and chemisorption mechanisms.