Quantum chemical study of inner-sphere complexes of trivalent lanthanide and actinide ions on the corundum (0001) surface

Abstract

Density functional theory / Ab initio / Sorption / Inner-sphere complex / Lanthanide / Actinide / Corundum (0001)Summary. Sorption of trivalent metal ions onto mineral surfaces is of special relevance in the safety assessment of nuclear waste disposal. In the present quantum chemical study we mainly focused on understanding the interaction of trivalent metal ions (La 3+ , Eu 3+ and Cm 3+ ) with the corundum (0001) the surface. We studied how the structure of the innersphere complex at the corundum (0001) surface depends on the deprotonation of the surface and give a prediction for the most likely structure of the inner-sphere complex (bi-, tri-or tetradentate). We approached this question using a cluster model for the surface. By deprotonating the cluster we mimicked a chemical environment at pH values above the point of zero charge. In a first step, we tested the accuracy of Density Functional Theory calculations with the BP86 functional and various basis sets by comparing them with Møller-Plesset perturbation theory of second order on a small chemically similar test system. This is followed by a series of calculations on a large and realistic cluster which is an extended model for the formation of the inner-sphere complex at the corundum (0001) surface. Our calculations predict the highest stability for a species with six water molecules remaining in the first coordination sphere of the metal ions and forming an inner-sphere surface complex attached to three surface oxygen atoms. The formation of the inner-sphere complexes is even more favoured when the coordination takes place via one or two deprotonated surface oxygen atoms.

Sorption competition and kinetics of trivalent cations (Eu, Y and Cm) on corundum (α-Al2O3): A batch sorption and TRLFS study

“…Kimura and Choppin, 1994;David and Vokhmin 2003;Skanthakumar et al 2007). This coordination is supported by quantum chemical studies by Polly et al (2010Polly et al ( , 2013 for trivalent actinides on corundum, where tri-or tetradentate surface complexes were found using density functional theory.…”

Radionuclide behaviour in the near-field of a geological repository for spent nuclear fuel

“…This latter finding fits into general observations of trivalent actinide interaction with oxide minerals (see e.g. [200]). Only weak sorption of Cs on pure magnetite is found which however can increase somewhat if silicate is adsorbed.…”

Am(III) coprecipitation with and adsorption on the smectite hectorite

“…This latter indicates slight variations in the Am\ \O distances leading to destructive interferences of EXAFS oscillations having small differences in their amplitude (Stumpf et al, 2004). For example, it can originate from the simultaneous existence of slightly different surface complex structures at the mineral surface (Polly et al, 2010). Yet, only one single shell was detected at R Am\ \O1 = 2.42 Å and can best be explained as the sum of contributions from surface oxygens (two) and from hydration water oxygens (five as usually reported e.g., (Stumpf et al, 2004)).…”