Bone-derived biochar and magnetic biochar for effective removal of fluoride in groundwater: Effects of synthesis method and coexisting chromium.

The presence of fluoride in groundwater in excess of 1.5 mg L is a major environmental health concern, and biochar is a promising low-cost adsorbent for the treatment of such water. In the present study, pristine and magnetic biochars were synthesized by peanut hull and bovine bone for the adsorption of fluoride. The biochars were systematically characterized by SEM-EDS, BET, XRD, VSM, FT-IR, and XPS. The experiment results showed that the magnetic biochar prepared by soaking biomass in FeCl solution and then pyrolyzing ("prepyrolysis") had a higher adsorption capacity than that prepared by mixing pristine biochar with Fe /Fe solution and then treating with NaOH ("postpyrolysis"). The bone-derived biochar and magnetic biochar exhibited high adsorption capacity of fluoride (>5 mg g ) due to the presence of hydroxyapatite (HAP) and γ-Fe O . The 0.1 M NaOH solution could be optimal desorption agent, and the adsorption-desorption experiments indicated the bone biochars maintained the reasonable adsorption capacity after several cycles. Moreover, the coexisting Cr(VI) and fluoride could be removed simultaneously by bone-derived biochars. It is suggested that bovine bone-derived pristine and magnetic biochars can be used as preferential adsorbents for fluoride removal from contaminated groundwater. PRACTITIONER POINTS: Bone-derived pristine and magnetic biochars exhibit high adsorption capacity for fluoride in weakly alkaline solution. The presence of hydroxyapatite and γ-Fe O in bone-derived biochars plays an important role for fluoride adsorption. Magnetic biochars prepared by soaking biomass in FeCl solution and then pyrolyzing ("prepyrolysis") perform better. The coexisting Cr(VI) and fluoride can be simultaneously removed in groundwater by bone biochars.