De-fluoridation studies: using Lanthanum-alginate-beads impregnated with green synthesized nSiO2 and active carbon of Terminalia Ivorensis plant as an effective adsorbent.

Three effective adsorbents are developed for the de-fluoridation of water based on nano Silica and activated carbon of Terminalia Ivorensis plant (SACTI). Nano-SiO₂ particles are synthesized from the sand collected in Krishna River at Vijayawada, India, using Aloe-vera gel as a capping agent. Activated carbon (SACTI), composite of 'nSiO₂ + SACTI' and La-alginate beads doped with 'nSiO₂ + SACTI' are examined. The adsorbents are characterized. Optimum extraction conditions for the maximum defluoridation capacities are established. Effect of co-anions, thermodynamic and regeneration studies are also investigated. The results show the spontaneity and endothermic nature of sorption with high positive entropy values. Adsorption efficiency is restored even after fifth regeneration cycles. The Freundlich adsorption isotherm and pseudo 2nd order kinetic model describes well the sorption process. Adsorption capacities of adsorbents are: 2.02 mg/g for SACTI, 4.01 mg/g for nSiO₂ + SACTI, 5.13 mg/g for nSiO₂ + SACTI-La-Ali (beads). The methodologies developed are successfully applied to reduce fluoride concentration in ground water samples of Ananthapur District, Andhra Pradesh, India. [ABSTRACT FROM AUTHOR]