Removal of ²⁰⁹Po from aquatic environment and its equilibrium and thermodynamic parameters

In this study, removal of ²⁰⁹Po from aqueous media using a natural zeolite as an adsorbent material was investigated. The adsorption experiments were performed by batch technique. The influence of specific process parameters such as initial concentration, pH of solution, contact time and temperature was studied to predict the optimum conditions for effective removing of ²¹⁰Po. Initial and equilibrium activity concentration of ²⁰⁹Po in solutions was counted by a ZnS(Ag) alpha scintillation counter. Adsorption yield of ²⁰⁹Po onto the zeolite was determined as 90 ± 2% at pH: <3 and 25 °C for 40 min of contact time. The applications of the isotherm models such as Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms were studied to evaluate adsorption characteristics of ²⁰⁹Po onto natural zeolite. Results indicated that the Dubinin-Radushkevich and Freundlich models gave a better fit to the experimental data than Langmuir isotherm models. The thermodynamic parameters such as Gibbs free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) of adsorption process were calculated. The change in entropy (ΔS^o) and enthalpy (ΔH^o) were estimated to be -0.0003 J nmol^-1 K^-1 and 0.1008 kJ nmol^-1, respectively.