A novel La-loaded magnetic hydrogel for the deep removal of low-concentration fluoride ions in industrial wastewater

Abstract

Fluoride pollution in water from industries such as photovoltaics and semiconductors has posed a growing environmental challenge, necessitating effective methods for trace fluoride (F⁻) removal. This study developed lanthanum-loaded magnetic hydrogel beads (CH-Fe-MMT-La) via a sol–gel method for deep F⁻ elimination from industrial effluents. Characterization confirmed the incorporation of La³⁺. The adsorbent achieved 96.35% removal efficiency for low-concentration F⁻ (10.0–20.0 mg L⁻¹) with 16.06 mg g⁻¹ of Langmuir capacity at 3.0 g L⁻¹ dosage and 6 h contact time. Kinetic data followed a pseudo-second order model (R² > 0.999), indicating chemisorption, and thermodynamic results revealed endothermic behavior (ΔH = +48.7 kJ mol⁻¹). The material retained >90% efficiency over a pH range of 4–9 and performed better at elevated temperatures. Field application to electroplating wastewater (F⁻: 218.7–11 604 mg L⁻¹) using a Ca(OH)₂ precipitation–adsorption hybrid process reduced the concentration of F⁻ to 1.24–1.65 mg L⁻¹, meeting EPA standards. This work demonstrates the first use of magnetic hydrogel systems for multi-stage F⁻ removal and offers a practical solution for deep treatment.