Performance and mechanism of fluoride adsorption from groundwater by lanthanum-modified pomelo peel biochar.

To obtain an economical and effective adsorbent for fluoride removal, lanthanum-loaded pomelo peel biochar (PPBC-La) was synthesized using a facile approach. The batch adsorption experiments were investigated to determine adsorbent performance. The PPBC-La and its pristine biochar (PPBC) were characterized by scanning electronic microscopy (SEM), zeta potential, Brunauer-Emmett-Teller (BET), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) methods. Experimental results showed that the adsorption data were described well by the pseudo-second-order kinetic and Freundlich isotherm models. The maximum fluoride adsorption capacity for PPBC-La was found to be 19.86 mg/g at 25 °C and pH 6.5. The PPBC-La worked well at pH 2.4-9.6 and carried positive charge at pH < 5.8. The presence of SO42-, Cl-, and NO3- had a slight effect on fluoride uptake except HCO3- and PO43-. The real groundwater study testified that 9.8 mg/L of fluoride was removed effectively at 1.0 g/L of dosage and pH 5.2. The regeneration results revealed that the PPBC-La had a good reusability. According to FTIR, XPS analysis and the anion exchange experiment, anions (NO3- and OH-) exchange with fluoride ions was mainly responsible for fluoride adsorption.