Environmental remediation by hydroxyapatite: Solid state synthesis utilizing waste chicken eggshell and adsorption experiment with Congo red dye

This study reports the adsorption efficacy of hydroxyapatite (HAp) for removing Congo Red (CR) dye from aqueous solution. HAp was synthesized utilizing chicken eggshell as a precursor of Ca source. Solid state synthesis method was implemented which comprised calcination at 950°C (E-HAp950). XRD analysis confirmed the formation of bi-phasic HAp with 15.5% of β-TCP. Elemental composition was evaluated by XPS and EDX analysis. FESEM analysis revealed the particles are of plate and spherical shaped also confirmed by the TEM images. DLS particle size, zeta potential, BET surface area and point of zero charge were also evaluated. Adsorption efficacy of E-HAp950 for removing CR was evaluated by batch adsorption experiment. Maximum adsorption capacity (qmax) was found to be 9.64 mgg-1 which was best explained by the non-linear fitting (R2 = 0.98) of Langmuir isotherm. Adsorption kinetics profusely followed pseudo second order kinetic model (R2 = 0.999) with qe (experimental) being very much closer to qe (calculative) for this model. Thus, hydroxyapatite prepared by utilizing eggshell waste through solid state method has the potential to remove toxic dyes.