Radioactive ¹⁵⁴Eu and ¹⁵⁵Eu have entered soils and sediments along with other radioactive wastes at the U.S. DOE Hanford Site, Washington. Europium can also serve as a homologue to study the geochemistry of trivalent actinides such as Am(III) and Cm(III) in the wastes. The adsorption of low concentration (10⁻¹⁴-10⁻⁶ M) europium on various minerals has been shown to be dominated by surface complexation. The reaction of higher-concentration Eu³⁺ on mineral surfaces is poorly understood. The objectives of this study are (1) to study the sorption of Eu³⁺ at relatively high concentration (millimolar) on smectite and calcite, (2) to identify and to characterize the precipitated solid phases of Eu³⁺, and (3) to investigate inhibition of the precipitation by ligands EDTA and humic acid. When twice the CEC equivalent of Eu³⁺ was added, about 50% of the added Eu³⁺ was sorbed by smectite in the pH range 3–5.5. Infrared, X-ray diffraction, and electron microscopic analyses imply that short-range ordered Eu(OH)₃ nano particles precipitated on smectite when pH was raised above 6. Sorption of Eu³⁺ in the interlayer of smectite was observed in the entire pH range (3–10) as evidenced by the expansion of the d(001) space of smectite from 1.2 nm to 1.5 nm. The EDTA ligand reduced Eu³⁺ sorption by nearly two-thirds in the pH range 4–10. This retardation effect was weakened at low pH and was insignificant at pH<3. Infrared analysis shows increasing formation of a neutral Eu-EDTA complex on smectite at lower pH. When europium reacted with calcite in open air for one year without agitation, nearly 100% of added Eu(NO₃)₃ precipitated as hydrated carbonate Eu₂(CO₃)₃·3H₂O with a trace amount of Ca²⁺ coprecipitated within this phase. When Eu³⁺-calcite suspension was agitated by shaking, another solid carbonate phase Eu₂O(CO₃)₂ ·H₂O precipitated rapidly (within one day). Presence of EDTA and humic acid completely inhibited the formation of the europium carbonate phases.