Adsorption Behaviour of La(III) and Eu(III) Ions from Aqueous Solutions by Hydroxyapatite: Kinetic, Isotherm, and Thermodynamic Studies

The hydroxyapatite was successfully synthesized, characterized, and used as an alternative low-cost adsorbent material to study the adsorption behaviour of La(III) and Eu(III) ions from nitrate aqueous solutions as a function of contact time, initial metal ion concentration, pH, and temperature by using a bath technique. The kinetic data correspond very well to the pseudo-second-order equation, and in both cases the uptake was affected by intraparticle diffusion. Isotherm adsorption data were well fitted by the Freundlich model equation with 1/n > 1, indicating a multilayer and cooperative-type adsorption. Thermodynamic parameters for the adsorption systems were determined at 293, 303, 313, and 323 K. These parameters show that adsorptions of La(III) and Eu(III) ions on hydroxyapatite are endothermic and spontaneous processes. The adsorption was found to follow the order Eu(III) > La(III) and is dependent on ion concentration, pH, and temperature.