Hydration and hydrolysis of samarium (III) in montmorillonite clay: a neutron diffraction study

Abstract : Neutron diffraction with isotopic substitution was carried out at room temperature on hydrated samples of Sm montmorillonite, prepared at pH = 4 and 8, in order to find out whether Sm is present as aqueous Sm(OH)3o, Sm3+, or intermediate hydrolyzed species, and how it is linked to the clay surface. It was found that the number of hydrogen atoms (5.5 ± 2.0) nearest to Sm3+ at pH = 4 is equal to or even slightly smaller than that of oxygen atoms (7.5 ± 1.0). This means that Sm3+ is bound to the clay surface and it is probably partially hydrolyzed. This result is very close to those obtained earlier for Yb3+ and Nd3+, despite the different methods of sample preparation and the different mineralogy of the samples.