The adsorption behavior of Cs+ and Ba2+ cations on magnesite has been studied as a function of time, cation concentration and temperature, utilizing both the radiotracer method and X-ray photoelectron spectroscopy (XPS). Saturation was approached in about I day for both cations. The sorption data were found to follow Freundlich type isotherms. Sorption of both Cs+ and Ba2+ cations were found to be exothermic in nature with ΔH0 (kJ/mol) of -37, -13 and ΔS0 (kJ/mol·K) of -0.09, -0.009, respectively. Negative ΔG0 values were obtained for both cations, indicating the spontaneity of their sorption on magnesite. The magnitude of ΔG0 suggest that ion exchange is the dominating sorption mechanism. The adsorption behavior of Cs+ and Ba2+ cations on magnesite has been studied as a function of time, cation concentration and temperature, utilizing both the radiotracer method and X-ray photoelectron spectroscopy (XPS). Saturation was approached in about 1 day for both cations. The sorption data were found to follow Freundlich type isotherms. Sorption of both Cs+ and Ba2+ cations were found to be exothermic in nature with ΔH0 (kJ/mol) of -37, -13 and ΔS0 (kJ/mol·K) of -0.09, -0.009, respectively. Negative ΔG0 values were obtained for both cations, indicating the spontaneity of their sorption on magnesite. The magnitude of ΔG0 suggest that ion exchange is the dominating sorption mechanism.