Hydration and hydrolysys of Sm3+ and Eu3+ in a clay interlayer: a neutron diffraction study with isotopic substitution

The coordination of Sm and Eu in the montmorillonite interlayer was studied by neutron diffraction with isotopic substitution. It was found that the number of hydrogen atoms nearest to Sm and Eu were less (NH = 5.5 ± 2.0) than oxygen nearest atoms (NO = 7.5 ± 1.0). This means that the Sm and Eu are not surrounded only by hydration water molecules, but they are in contact with the oxygen siloxane atoms of the clay basal plane surface. It was found that the number of oxygen atoms of the clay surface giving a contribution to the total coordination number NO should be NOclay ≤ 3. Therefore, the deficit of hydrogen atoms in the first coordination shell of Sm and Eu should be explained supposing that the lanthanide cations are partially hydrolyzed. (orig.)