Cubical-Shaped Rods of Pectin–Hydroxyapatite Composite for Adsorption Studies of Fluoride by Statistical Method and Adsorption Experiments

This research details the synthesis and application of a novel pectin–hydroxyapatite (PHAp) composite for fluoride (F–) adsorption from aqueous solutions. To determine the efficiency of the adsorption process parameters, i.e., adsorbent dose (0.1–0.4 g), initial fluoride concentration (10–30 mg/L), and temperature (298–313 K), the Box–Behnken design with three levels and three factors have been utilized. The quadratic model was established on 27 batch runs by regression analysis of the experimental data of these runs. The efficacy of adsorption was observed using the Langmuir and Freundlich models. The adsorption rate was found at 3.17 mg g−1min–1, and adsorption kinetics followed pseudo-second order (PSO) for PHAp. The significant novelty of this work is the synthesis of unique cubical-shaped rods biopolymer composite from hydroxyapatite. Additionally, this composite showed high adsorption capacity for F– compared to other hydroxyapatite adsorbents, and the improved adsorption capacity is attributed to its unique shape which provides a larger surface area. It can be reused for up to six cycles, which makes this method environment-friendly. The economic viability of the synthesized PHAp composite, in comparison to other adsorbents, is evident from the cost–benefit analysis.