Facile method to synthesize efficient adsorbent from alumina by nitric acid activation: Batch scale defluoridation, kinetics, isotherm studies and implementation on industrial wastewater treatment

The excess amount of fluoride contamination in the groundwater or industrial effluents fosters various health problems. Considering the advantages of adsorption, the current research reports the synthesis of a novel adsorbent (HNAA) by simple and convenient process of nitric acid activation of alumina. The physiochemical characterization (SEM, EDX, XRF, FTIR, BET, and pH_ZPC) results exhibited successful activation of alumina and adsorption of fluoride ions. The effect of process parameters (contact time, initial pH, adsorbent dose, initial fluoride concentration and presence of coexisting ions) on adsorption of fluoride ions on HNAA were investigated in batch scale. The adsorption of fluoride ion on HNAA followed the Freundlich isotherm and pseudo second order kinetic model. The Q_max of HNAA adsorbent was 45.75 mg/g at 45 °C. The fluoride ion adsorption was revealed to be endothermic and spontaneous. The experimentation of the HNAA adsorbent on industrial wastewater, with fluoride concentration of 17.5 mg/L, inferred the significant defluoridation potential at the optimized adsorbent dose and pH. The nitric acid activation of alumina resulted in improvement of defluoridation efficiency from 74.18% to 97.43%. The HNAA also exhibited the better regeneration and reusability features which distinguish it as a promising adsorbent to be applied for real field wastewater.