Chemical treated laterite as promising fluoride adsorbent for aqueous system and kinetic modeling

Efficiency of acid–base treated raw laterite (RL) is investigated for removal of fluoride. FTIR, SEM-EDX, and surface area analyzer are used to characterize the treated laterite (TL). The batch adsorption of fluoride is explored using TL under varying process conditions like adsorbent dose, pH of solution, temperature, particle size and contact time. The adsorption isotherm data of fluoride ions on TL are fitted well to both Langmuir and Freundlich models. The temperature dependent maximum Langmuir adsorption capacities of fluoride ion on TL are found to be 36.3, 37.9, and 39.1 mg/g at 288, 305, and 315 K, respectively. A simple shrinking core model is applied to predict the batch adsorption kinetics of fluoride ions onto treated laterite (TL). In the proposed two-resistance model, external mass transfer (Kf) and pore diffusion coefficient (De) are estimated by comparing the simulated concentration profile with the experimental data using a non-linear optimization technique. Estimated values of De and Kf are found to be 4.8 × 10−10 m2/s and 8.5 × 10−4 m/s at 305 K, respectively. The fluoride adsorption in presence of other competitive ions as well as desorption of fluoride ions from spent adsorbent are studied in detail.