De‐fluoridation of Polluted Water Using Aluminium Alginate Beads Doped with Green Synthesized ‘Nano SiO2+Nano CeO2‐ZrO2’, as an Effective Adsorbent

Abstract

AbstractNanoparticles of SiO2 and ‘CeO2‐ZrO2’ are synthesized by adopting new green methods based on the classical method of homogeneous precipitation and using the extract of skins of Sapindus plant seeds as capping and/or stabilizing agent. Nano SiO2 is synthesized from red mud, a waste material obtained after extraction of aluminium from Bauxite ore. Nano SiO2, composites of ‘nSiO2+nCeO2‐ZrO2’ and Al‐alginate beads doped with ‘nSiO2+nCeO2‐ZrO2’ are investigated as adsorbents for de‐fluoridation. These three adsorbents are characterized by XRD, FTIR, FESEM and EDX. Various adsorption parameters, namely pH, adsorbent dosage, initial fluoride concentration, time of contact and temperature are optimized for maximum removal of fluoride ions. The adsorption capacities of adsorbents are 66.93 mg/g for nSiO2, 83.84 mg/g for composites of ‘nSiO2+nCeO2‐ZrO2’ and 109.4 mg/g for ‘nSiO2+nCeO2‐ZrO2/AlAL’ (beads). The cumulative affinity of fluoride towards SiO2, CeO2, ZrO2 and Al3+ has been investigated in this work in developing successful adsorbents with high adsorption capacities for de‐fluoridation. The adsorption nature is analysed with various kinetic, isotherm and thermodynamic studies. The adsorption is spontaneous and endothermic in nature. The surfaces of adsorbents are heterogeneous and Freundlich model explains well the sorption process. A sort of complex formation occurs between the adsorbents and fluoride ions. The adsorption follows pseudo‐second order kinetic model. The spent adsorbents can be regenerated and reused with marginal reduction in their adsorption capacities. The methodology developed is successfully applied to treating ground water samples of Prakasam and Guntur Districts, Andhra Pradesh, India.