A novel approach for the defluorination of groundwater using trivalent-metal hydroxide/bone-char composite adsorbent

The adsorption capacity of trivalent-metal hydroxide-bone char composite (TMH/BC) for defluorination of ground water was investigated. The operating parameters for the bone char (BC) production process were optimized. The best adsorption efficiency of 88%, was recorded for the BC produced at 450 °C for 3 h of thermal treatment. The BC impregnated in hydrated aluminum sulfate and coated with the trivalent metal oxide (Al(OH) 3 ) showed higher fluoride removal efficiency of 99% compared to BC (88%) and hydroxyapatite (HAP) (87%). The SEM and EDS characterization for the modified BC confirmed the effect of thermal treatment and aluminum dispersion on the surface of the BC. The core elements determined in TMH/BC were calcium, carbon, phosphorus, oxygen, aluminum, and sodium. The fluoride was identified to be linked with the aluminum composites. The TMH/BC composite has improved specific surface area of 379 m 2 /g compared to GBC with 350.2 m 2 /g. The adsorption kinetic model of TMH/BC was fitted to the Temkin isotherm model while BC and HAP were fitted with Langmuir and Freundlich isotherms. Due to its higher adsorption ability compared to the tested adsorbents, TMH/BC was more suitable adsorbent to remove excess fluoride present in the groundwater. • Bone char (BC) production operating parameters are optimized for fluoride adsorption. • Trivalent metal oxide/bone char (TMH/BC) composite adsorbent was synthesized. • Surface modification was achieved by thermal and chemical modification of bone char. • The surface modification done on the bone char improved the adsorption efficiency. • BC and TMH/BC composite adsorbents showed better removal efficiency of fluoride ion.