Effectiveness of the engineered pinecone-derived biochar for the removal of fluoride from water

Drinking fluoride (F^-)-contaminated water (>1.5 mg L^-1) causes severe dental and skeletal disorders. In the central province of Pakistan, ∼20 times higher levels of F^- in the drinking groundwater (compared with the 1.5 mg L^-1 permissible limit of the World Health Organization) are triggering bone abnormalities in teenagers. In this study, we demonstrated the potential of pinecone-derived biochar (pristine) impregnated with Fe- and Al-salts (engineered) to defluoridate water. Batch mode adsorption experiments were carried out under variable conditions of solution pH, F^- initial concentration, adsorbent dose, and contact time. The engineered biochars resulted in greater adsorption than that of pristine biochar. Specifically, the AlCl₃-modified biochar exhibited a maximum adsorption capacity of 14.07 mg g^-1 in spiked water and 13.07 mg g^-1 in in-situ groundwater. The equilibrium isothermal and kinetic models predicted monolayer, cooperative, and chemisorption types of the adsorption process. The chemical interaction and outer-sphere complexation of F^- with Al, Na, and H elements were further confirmed by the post-adsorption analysis of the AlCl₃-modified biochar by FTIR and XRD. The AlCl₃-modified biochar resulted in 87.13% removal of F^- from the in-situ F^--contaminated groundwater, even in the presence of naturally occurring competing ions (such as Cl^-, HCO₃^-, SO₄^2-, and NO₃^-). We conclude that the AlCl₃-modified biochar derived from pinecone could be a promising cost-effective adsorbent for the defluoridation of water.