Development of Fluorophilic Magnetic Adsorbents with Ultrahigh Adsorption Capacity from Red Mud: Defluorination Behavior and Mechanisms
Chengjia Luo, Lang Liu, Shan Ren, Yuanpei Lan, Chunyan Xu, Jingjing Wang, Chenhong Yuan, Yanyan Li, Dongqiu Pan, Jingjing Huang, Hui Du
Abstract
High Resolution Image Download MS PowerPoint Slide To address the low fluoride (F – ) adsorption capacity of red mud (RM)-based adsorbents, a novel Mn-coated RM adsorbent (Mn-RM) was prepared by Mn loading from red mud. Mn-RM features a 3D heteropolyhedral structure, which provides abundant functional groups for F – adsorption. The maximum equilibrium adsorption capacity ( q max ) of Mn-RM for F – is 141.83 mg/g at 298 K and pH 3.0, among the highest reported for RM-based adsorbents. The adsorption kinetics and isotherms follow the pseudo-second-order and Langmuir models, respectively, suggesting monolayer adsorption involving electrostatic attraction, pore filling, ion exchange-disproportion reaction, and metal complexation. Mn-RM demonstrates excellent recyclability, maintaining an 86.69% removal rate after five reuse cycles. Competitive ion adsorption experiments reveal that PO 4 3– significantly inhibits F – adsorption, while SO 4 2–, NO 3 –, and Cl – have minimal effects. The adsorption efficiency and equilibrium capacity of Mn-RM for fluorinated wastewater from an AlF 3 industrial facility and a coal-fired power plant are 99.54% (56.26 mg/g) and 99.16% (44.38 mg/g), respectively. Moreover, F – concentrations in both wastewaters after adsorption are below 0.2 mg/L, meeting the drinking water quality guidelines of both China and the World Health Organization (WHO).