Defluoridation of Aqueous Solution Using Thermally Activated Biosorbents Prepared from Adansonia digitata Fruit Pericarp

Abstract

The presence of fluoride ions in water poses a significant danger to human health. In Tanzania, where the Rift Valley passes, some people are impaired due to elevated levels of fluoride in water. The purpose of this study was to prepare thermally activated Adansonia digitata fruit pericarp biosorbents at 450, 500, 550, and 600°C for defluoridation. Using the Brunauer-Emmett-Teller analyzer, the surface area and pore diameter were measured. The scanning electron microscope and Fourier transform infrared spectrometry were used to determine morphological features and functional groups of biosorbents. To analyze the effect of pH, adsorbent dose, contact time, and initial concentration, the response surface methodology was applied. Adsorption isotherms, kinetics, and regeneration studies were also conducted. There were considerably wide surface areas of 385.44, 399.27, 445.71, and 447.70 m2/g and pore diameters of 0.3055, 3.0341, 3.0375, and 3.0471 nm for biosorbents activated at 450, 500, 550, and 600°C, respectively. FT-IR spectra indicated the oxidation of alcoholic –OH to carboxylic –OH during the activation process, which is proved by the shifting of the peak at 3500-3000 cm-1 from raw biosorbent to a very broad and strong band at 3500-2000 cm-1 from the activated biosorbent. The maximum removal efficiencies of biosorbents activated at 450, 500, 550, and 600°C were 95.55, 96.50, 97.65, and 98.36%, respectively, for all biosorbents at a pH of 2, an initial concentration of 27.50 ppm, a contact period of 75.00 minutes, and an adsorbent dose of 5.50 g, which indicates that the adsorbents were successful for fluoride removal. The isotherms and kinetics indicated that the adsorption fitted well with Freundlich ( $R^2=0.95661‐0.98445$ ) and pseudo-second-order ( $R^2=0.94230‐0.99634$ ) kinetic adsorption models, respectively. The results showed that the removal of fluoride by biosorbents prepared is effective and could be used for defluoridation of drinking water.