Co-Removal of Cadmium and F-53B from Aqueous Solutions Using Montmorillonite-Supported Sulfidated nZVI: Performance and Mechanistic Insights

The co-contamination of cadmium (Cd) and per- and polyfluoroalkyl substances (PFASs) in water, particularly from electroplating industries, poses a significant environmental threat. This study presents the first investigation into the simultaneous removal performance and mechanisms of Cd(II) and chlorinated polyfluoroalkyl ether sulfonate (F-53B, a prevalent PFAS alternative) using montmorillonite-supported sulfidated nano-zero-valent iron (MMT/S-nZVI). The composite exhibited high performance, with maximum sorption capacities of 157.5 mg/g for Cd(II) and 22.3 mg/g for F-53B at 25 °C, following pseudo-second-order kinetics. In cocontaminated solutions, MMT/S-nZVI effectively removed simultaneously Cd(II) (50.0 mg/L) and F-53B (1.0 mg/L) under neutral to alkaline conditions, achieving 95.0% Cd(II) and 75.0% F-53B removal at a dosage of 1.0 g/L. A key finding was the asymmetric interaction between contaminants. Cd(II) slightly inhibited F-53B removal, whereas F-53B had a minimal effect on Cd(II) removal. Furthermore, MMT/S-nZVI effectively remediated Cd(II) and a mixture of 11 PFASs at environmentally relevant concentrations (μg/L), although removal was more challenging for short-chain compounds. Mechanistic studies revealed that Cd(II) was removed primarily through electrostatic attraction, ion exchange, and precipitation, while F-53B was adsorbed via electrostatic and hydrophobic interactions. These findings provide key insights into the mechanistic interactions for sorbent development to tackle the critical challenge of heavy metal and PFASs co-contamination in water.