Adsorptive Removal of PFAS from Aqueous Solutions Using GAC, PAC and Ball-Milled Colloidal Activated Carbon: Characterizing Efficiency, Kinetics, and Mechanisms

Per-and polyfluoroalkyl substances (PFAS) present significant challenges for remediation due to their persistence in nature. Activated carbon is a widely used adsorbent for removing PFAS. In this study, three forms of activated carbon, granular activated carbon (GAC), powdered activated carbon (PAC), and ball-milled colloidal activated carbon (CAC_BM), are compared for their effectiveness in removing short and long-chain PFAS. Physical modification through ball-milling process enhanced the adsorptive properties of activated carbon, resulting in smaller particle size (d ₅₀ = 0.318 μm), increased surface area (968.59 m² g^-1), and improved suspension stability compared to conventional GAC and PAC. Kinetic experiments showed that CAC_BM demonstrated superior removal efficiencies of long-chain PFAS (up to 89% for perfluorooctanesulfonic acid (PFOS) and 73% for perfluorooctanoic acid (PFOA)), and moderate removal of short-chain PFAS (55% for perfluorobutanesulfonic acid (PFBS) and 30% for perfluorobutanoic acid (PFBA)). The pseudo-first-order model adequately described adsorption trends; however, the pseudo-second-order model provided a better fit, with intraparticle diffusion identified as the rate-limiting step. Isotherm studies indicated that PFAS adsorption aligned well with the Freundlich model. Competitive adsorption experiments revealed a hierarchical pattern. Overall, the study demonstrates CAC_BM as a promising adsorbent for remediation of PFAS-contaminated water systems.