Box-Behnken optimization of glyphosate adsorption on to biofabricated calcium hydroxyapatite: kinetic, isotherm, thermodynamic studies

Calcium hydroxyapatatite (CHAP) has been fabricated from waste material as an egg shell towards the applicability of glyphosate (GLY) removal from aqueous phase via biosorption method. However, regarding parameters, which have been obtained to influence adsorption capability to perform the optimization study by Box-Behnken design (BBD). The materials were characterized by BET surface, field-emission scanning electron microscope (FESEM) equipped with an energy-dispersive X-ray spectrometer (FESEM-EDX), Fourier transformed infrared spectroscopy (FT-IR study), zero-point charge (ZPC), X-ray patterns (XRD), etc. The highest optimization was recorded as 99.9532% adsorption, regarding adsorption dose of 0.05 g, GLY concentration of 49.99 mg/L and pH of 4.22, respectively. The adsorption kinetics study was demonstrated with pseudo-first order, pseudo-second order and intraparticle diffusion modelling, as compared to maximum fitted with pseudo-second order. The study of equilibrium was employed through Langmuir, Freudlich, Dubinin-Radushkevitch (D-R), Tempkin isotherms, leads maximum with Freundlich (K-F = 177.47 Lmg(-1)) and Temkin to derive the mechanism as usually engaged chemisorption. The thermodynamic parameters revealed that Delta H-o (5E-13 kJ/mol) has positive showed with negative on Delta S-o (- 0.0572 kJ/mol) to conform endothermic reaction facilitated with spontaneous response. The regeneration study was examined by three types of eluting agents, the NaOH: NaCl medium is the best recommended in stage of six cycles with 80% efficiency. This adsorbent utility could be beneficial to GLY adsorption in sustainable ways.