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

Drinking fluoride (F)-contaminated water (>1.5 mg L) 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 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 AlCl-modified biochar exhibited a maximum adsorption capacity of 14.07 mg g in spiked water and 13.07 mg g 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 AlCl-modified biochar by FTIR and XRD. The AlCl-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, HCO, SO, and NO). We conclude that the AlCl-modified biochar derived from pinecone could be a promising cost-effective adsorbent for the defluoridation of water.