isotherms, kinetics, equilibrium, and thermodynamic studies on the uptake of hexavalent chromium ions from aqueous solution using synthetic hydroxyapatite

The effective and economic removal of heavy metals from industrial effluents is one of the important issues globally. in this study, hydroxyapatite (hap) was synthesized using the wet chemical precipitation method and was characterized using fourier transform infrared (ftir) spectroscopy, uv-visible spectrometry, scanning electron microscopy (sem) and x-ray diffraction (xrd) methods. different physico-chemical parameters of the hap such as color, bulk density, and ph were determined. removal efficiency of cr(vi) was investigated by different parameters such as initial concentration, contact time, ph, adsorbent dosage and temperature. results showed that the adsorption of cr (vi) was favorable in acidic medium. adsorption kinetics using pseudo-first order and pseudo-second order kinetic models were tested on the experimental data. the kinetics of the adsorption followed a pseudo-second order kinetics model as we obtained a higher correlation coefficient value of r2 = 0.978. the equilibrium data were evaluated using two adsorption isotherms: langmuir and freundlich adsorption isotherms. the equilibrium data fitted well with langmuir adsorption isotherm model, showing monolayer coverage of cr(vi) ions over the surface of hap and this fact is supported by the langmuir isotherm plot and the correlation coefficient value of r² = 0.9639.