Examining sorption of perfluoroalkyl substances (PFAS) in biochars and other carbon-rich materials

• Published in: Chemosphere (Oxford) Vol. 302; p. 134733
• Main Authors: Fabregat-Palau, Joel, Vidal, Miquel, Rigol, Anna
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.09.2022
• Subjects: Activated carbon; biochar; Biochars; calcium; Carbon-rich materials; composts; hydrophobicity; metallurgy; Modeling; perfluorocarbons; PFAS; principal component analysis; remediation; sorbents; Sorption; surface area; Sorption; Biochars; Carbon-rich materials; PFAS; Modeling; Activated carbon
• ISSN: 0045-6535; 1879-1298; 1879-1298
• DOI: 10.1016/j.chemosphere.2022.134733

The use of carbon-rich sorbents to remove and/or immobilize perfluoroalkyl substances (PFAS) in contaminated environmental scenarios is attracting increasing interest. The identification of key sorbent properties responsible for PFAS sorption and the development of models that can predict the distribution coefficients (Kd) for PFAS sorption in these materials are crucial in the screening of candidate materials for environmental remediation. In this study, sorption kinetics, sorption isotherms, and the effects of pH, calcium concentration and dissolved organic carbon (DOC) content on PFAS sorption were evaluated in four representative carbon-rich materials: two biochars with contrasting properties, a compost, and charcoal fines rejected by the metallurgical industry. Subsequently, the sorption of seven PFAS with numbers of fluorinated carbons ranging from 4 to 11 was evaluated in a total of ten carbon-rich materials, including activated carbons, so as to build up a Kd prediction model. The sorption of PFAS increased with greater fluorinated chain length, suggesting that hydrophobic interactions play a major role in sorption and electrostatic interactions a minor one. These results were confirmed by a principal component analysis, which revealed that the CORG/O molar ratio and the specific surface area of the material were the two main sorbent properties affecting PFAS sorption. Furthermore, the DOC content in solution had a negative effect on PFAS sorption. Using this information, a simple Kd prediction model applicable to a wide range of materials and PFAS was developed, using only a few easily-derived physicochemical properties of sorbent (CORG/O molar ratio and SSA) and PFAS (number of CF2), and was externally validated with data gathered from the literature. This work aims to identify the key properties affecting PFAS sorption by carbon-rich materials and to develop a simple Kd prediction model. [Display omitted] •Sorption of PFAS was relatively fast and the sorption isotherms were linear.•The presence of Ca2+ increased PFAS sorption under alkaline conditions.•PFAS sorption was mainly driven by hydrophobic interactions.•Carbon-rich materials with lower DOC contents showed higher PFAS sorption.•A simple Kd prediction model for PFAS sorption in carbon-rich materials was developed.