Synthesis, characterization of hydroxyapatite from pomegranate fruit peel for Cr (VI) adsorption: Process modelling, kinetic and isotherm studies

The present work focuses on preparation of hydroxyapatite from pomegranate peels by precipitation method. The hydroxyapatite derived from pomegranate fruit peels (HA-PP) was characterized by XRD, FT-IR, SEM-EDS and BET techniques. The HA-PP has mesoporous in structure and had an area of 99.021 m²/g. Further HA-PP was used as adsorbent for the removal of Cr (VI) ion particles from K₂Cr₂O₇. The adsorption trials were executed and found the optimized solution using response surface methodology (RSM). The experiments included parameters like pH 2, initial chromium concentration 200 mg/L, adsorbent loading 0.8 g, and contact time 60 min, respectively. Cr (VI) removal was 89.4 % at the optimum combination of these process parameters. A mathematical and statistical optimizing technique response surface methodology (RSM) was applied to verify the interactive effects of various parameters on the adsorption capacity. The analysis of variance (ANOVA) was used to predict the adequacy of the model (F 82.16) shows developed model is valid with R² value 0.987, and p-value (>0.1). In this the Langmuir adsorption isotherm and the pseudo-second-order kinetic model are well explained for Cr (VI) adsorption onto HA-PP. This reaction is spontaneous and endothermic, as indicated by the negative change in the standard free energy (ΔG⁰ = -0.1732) and ΔH⁰ (+4.71) value at the selected temperature. The ΔS⁰ (+15.89) further confirms that the randomness increased at the solid-solution interface during adsorption.