Plutonium (Pu) is one of the key elements in high-level radioactive waste due to its long half-life. Understanding the sorption behavior of key radionuclides such as Pu and U is important to the safety assessment calculation for a deep geological repository for high-level radioactive waste. Europium (III) (Eu(III)), a chemical analogue of Pu, has shared similar sorption behaviors as Pu. The aim of this study is to investigate the sorption properties of europium onto MX-80 bentonite and crystalline rock (granite), a potential host rock for a deep geological repository for some countries, as a function of pH and ionic strength using batch experiment technique and surface complexation modeling. The experiments are conducted in Ca-Na-Cl solutions. For granite, the sorption coefficient Kd showed proportionate dependence on the pH. The sorption of Eu is dependent on ionic strength at near neutral to low pH region while not dependent on ionic strength at higher pH. For MX-80 bentonite, the sorption of Eu has little dependence on the ionic strength. A surface complexation modeling is also being carried out to examine the experimental results and identify the possible mechanism of the sorption. / Thesis / Master of Applied Science (MASc)