Adsorption Kinetics, Isotherms, and Thermodynamics of Cr(III), Pb(II), and Cu(II) on Porous Hydroxyapatite Nanoparticles.

Porous hydroxyapatite (HAP) nanoparticles with the specific surface area of 76.1 m2 g-1 were facilely prepared using calcium nitrate and phosphoric acid as the starting materials and ammonia aqueous solution as the pH regulator by a hybrid precipitation and hydrothermal method at lower reaction temperatures of 35 and 110 °C. The adsorption of Cr(III), Pb(II), and Cu(II) ions on HAP nanoparticles was well simulated by the pseudo-second-order adsorption kinetics and Langmuir adsorption isotherm. The maximum adsorption capacities of HAP nanoparticles for Cr(III), Pb(II), and Cu(II) ions were 96.9, 440.5, and 69.9 mg g-1, respectively, at 20 °C based on the Langmuir adsorption isotherms. The thermodynamic analysis revealed that the adsorption processes of Cr(III), Pb(II), and Cu(II) ions on HAP nanoparticles were spontaneous and endothermic.