Synthesis of Pumice Modified with Lanthanum Oxycarbonate Nanoparticles and Its Fluoride Ion Adsorption Properties

The immobilization of lanthanum oxycarbonate nanoparticles on pumice [lanthanum oxycarbonate-modified pumice (LOCP)] was explored as a novel approach for enhancing fluoride removal in water treatment. Fluoride contamination in water is a significant environmental issue, and developing efficient adsorbents is crucial for sustainable remediation. Synthesized through a combined hydrothermal and annealing approach, LOCP demonstrated exceptional fluoride adsorption characteristics. Kinetic studies revealed optimal fitting with the Elovich model (R2=0.98), while adsorption isotherms followed the Langmuir model with a theoretical maximum capacity of 25.15 mg/g. The material maintained stable fluoride removal efficiency (exceeding 80%) across a broad pH range (2–10), with phosphate showing the strongest interference among coexisting anions (inhibitory order: NO3−<SO42−<Cl−<HCO3−<CO32−<PO43−). Spectroscopic analysis indicated that the adsorption mechanism primarily involves ligand exchange between fluoride ions and protonated La─ O bonds, forming stable La–F complexes. After four regeneration cycles, LOCP retained 53.9% of its initial capacity, while column tests demonstrated continuous operation for 35 h with effluent fluoride concentrations below 1 mg/L.