Application of Taguchi method for optimizing the process parameters for the removal of fluoride by Al-impregnated Eucalyptus bark ash

Abstract

A study on the adsorption of fluoride onto Al-impregnated Eucalyptus bark ash (Al-IEBA) was conducted and the process parameters were optimized using Taguchi L27 (ANOM) experimental design for maximizing the percentage removal of fluoride. The operating parameters including initial concentration (5–50 mg/L); pH (2–9); contact time (5–30 min); adsorbent dose (0.05–0.2 g/50 mL); and temperature (27–60 °C) were considered. Optimal experimental condition was determined by calculated signal-to-noise ratios. The best conditions for biosorption of fluoride were evaluated as initial fluoride concentration 50 mg/L; pH 2.0; adsorbent dose 0.1 g/50 mL; contact time 30 min and temperature 27 °C. Furthermore, isotherm, kinetics and thermodynamic study were performed to establish the fluoride adsorption mechanism. The experimental data fitted with the three isotherm models and it was found that Freundlich model nicely fitted (R2 = 0.996) with the equilibrium data than Langumir and D–R isotherms. Similarly, kinetics data suggests that the pseudo-first-order model is best fitted (R2 = 0.911) than pseudo-second-order and intraparticle diffusion models. On the other hand, thermodynamic data suggest that the adsorption of fluoride thermodynamically favourable at lower temperature. The active functional groups and surface morphology of the adsorbent was assessed by FTIR and SEM study. The optimization results suggest the best fluoride adsorption achieved at initial F concentration 11.11 mg/L, pH 10.69, adsorbent dose 10.21 g/L, contact time 10.89 min, and temperature 10.37 °C. The results obtained showed that sorption on the Al-IEBA could be an effective adsorbent for the removal of fluoride.