Defluoridation studies using active carbon derived from the barks of Ficus racemosa plant

An adsorbent prepared by activating the carbon powder derived from the barks of Ficus racemosa plant with HNO3 (ACBFR) has been used for defluoridation studies. Extraction conditions have been optimized for the maximum removal of fluoride; 88% removal is observed at pH: 7, sorbent dosage: 4 gm/L, time of agitation: 60 min, initial concentration of the fluoride ions: 5 mg/L and temperature: 30 °C. On analyzing the nature of adsorption using Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin isotherm models, Langmuir model has provided a best correlation (R2 value: 0.9936) for the adsorption of fluoride ions. Adsorption kinetics is found to follow the pseudo second ordered model with correlation coefficient value of R2 = 0.998. Surface morphological studies are made using SEM, EDX and FTIR. Thermodynamic parameters are studied and found that the adsorption process is endothermic and spontaneous in nature. The influence of co-anions on the% of extraction of fluoride ions is in the order of: PO43− > HCO3− > SO42− > NO3− > Cl−. The removal of fluoride is found to be 1.65 mg/g. The methodology developed in this work has been applied to real fluoride-polluted waters and found to be successful.