Development of a rare earth modified residue of leaching aluminium from gangue for fluoride ion adsorption from mine water

Abstract

The increasing anthropogenic and industrial activities have led to widespread contamination of water resources. Among the various pollutants, excess fluoride in water poses a global environmental and public health challenge due to its toxicity and persistence. To address this challenge, Ce and La loaded the residue of leaching aluminium from gangue were synthesized as adsorbents (Ce-La@LR) for the removal of fluoride ion (F⁻) from water. The as-prepared samples were characterized using scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), X-ray diffractometry (XRD), and Fourier transformed infrared spectroscopy (FT-IR). Batch adsorption experiments were conducted to examine the effects of Ce-La loading, adsorbent dosage, initial solution pH, and the presence of coexisting ions on fluoride adsorption. The results indicated that fluoride removal efficiency exceeded 95 % at a 15 % Ce-La loading, pH value of 5, and an adsorbent dosage of 0.1 g/L. The adsorption kinetics of fluoride ion (F⁻) on Ce-La@LR were best described by the proposed second-order kinetics, with a correlation coefficient (R²) of 0.9997, suggesting that chemical adsorption plays a significant role in the fluoride removal process. The isotherm data were fitted to the Langmuir model, revealing a maximum adsorption capacity of 56.81 mg/g. Except for carbonate (CO₃²⁻) and phosphate (PO₄³⁻) ions, the influence of other ions was negligible for the adsorption of F⁻ on the Ce-La@LR. The possible adsorption mechanism of fluoride ion removal on the Ce-La@LR involves electrostatic attraction and ion exchange. This research not only offers an effective solution for treating mine water but also presents a novel approach for resource recovery from coal mine waste.