Investigation of Fluoride Adsorption from Aaqueous Solutions by Modified Eucalyptus Leaves: Isotherm and Kinetic and Thermodynamic Studies

Background and purpose: The World Health Organization (WHO) has specified the tolerance limit of fluoride content of drinking water to be 1.5 mg/L, since excessive intake of fluoride leads to various detrimental diseases. The present study assessed the adsorption effectiveness of HCl-modified eucalyptus leaves in fluoride removal from synthetic solutions. Materials and Methods: In this experimental study, pseudo-first and pseudo-second order kinetics, Langmuir and Freundlich isotherm models, as well as pH (2-12), initial concentration (5-30 mg/L), adsorbent dose (0.1-1 g/L), and temperature (25-45 0C) were investigated on defluoridation. Results: The results with the maximum removal efficiency of 90% was obtained in pH = 10, initial concentration = 5 mg/L, and adsorbent dose = 0.1 g/L. In the investigation of the effect of temperature on removal rates, the maximum removal of fluoride was observed to be in 45 0C. The removal efficiency also decreased while the adsorbent dose increased, the initial concentration of fluoride increased, and the temperature in the studied ranges decreased. It was also found that the adsorption equilibrium and kinetic data were in good agreement with Langmuir Model (R2=0.994) with qmax= 61.35 mg/g and pseudo-second order reaction (R2=0.999). Conclusion: On the basis of the obtained results, HCl-modified eucalyptus leaves were found to be able to remove fluoride from aqueous environments with good removal efficiency and adsorption capacity.