Uncovering nano-bonechar for attenuating fluoride in naturally contaminated soil

Fluoride ion (F^-) is one of the major geogenic contaminants in water and soil. Excessive consumption of these geogenic contaminants poses serious health impacts on humans and plants. In this study, a novel carbonaceous material, nano-bonechar, was synthesized from cow bones and applied as a soil amendment at rates of 0, 0.5, 1, and 2% to remediate and revitalize naturally F^--contaminated soil. The results revealed that the nano-bonechar significantly reduced the mobility and bioavailability of F^- by 90% in the contaminated soil, and improved the soil quality by increasing the soil water holding capacity, soil organic matter, and the bioavailable contents of PO₄^3-, Ca²⁺, and Na⁺. Subsequently, the pot experiment results showed a significant reduction in the uptake of F^- by 93% in Zea mays plants. Moreover, the nano-bonechar application improved the plant's growth, as indicated by the higher fresh and dry weights, root and shoot lengths, and total content of PO₄^3-, Ca²⁺, and K⁺ than those of un-amended soil. The F-immobilization in soil was mainly due to the presence of the hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂] mineral in the nano-bonechar. Ion exchange between OH^- (of nano-bonechar) and F^- (of soil), and the formation of insoluble fluorite (CaF₂) contributed to the attenuation of F^- mobility in the soil. It is concluded that nano-bonechar, due to its size and enrichment in hydroxyapatite, could successfully be utilized for the rapid remediation and revitalization of F^--contaminated agricultural soil.