Adsorption behavior of radionuclides, 137Cs and 140Ba, onto solid humic acid

Abstract

In this research, the adsorption behaviors of two important fission product radionuclides (137Cs and 133Ba) onto sodium form of insolubilized humic acid (INaA) were investigated as a function of time, cation concentration and temperature, utilizing radiotracer method. The resulting data was fitted well to the Freundlich and Dubinin-Radushkevich (D-R) isotherms. Thermodynamic constants such as; free energy (ΔGads), enthalpy (ΔHads), entropy (ΔSads) of adsorption were determined. Temperature change didn't effect sorption processes significantly. Best fitting kinetic models were found for a better understanding of adsorption mechanisms. It was found that Ba2+ was adsorbed five times more than Cs+ onto structurally modified humic acid and kinetic studies indicated that adsorption behaviors of both ions obey the pseudo second order rate law. The effect of pH changes on adsorption was also examined and optimum pH range was found in the range of pH 6-8. FTIR and solid state carbon nmr (13CNMR) spectroscopic techniques were used to understand the structural changes during insolubilization process. Quantitative determination of adsorption sites was carried out using potentiometric titration method and the resulting data was treated by using appropriate Gran functions.