Tetrad effect in the distribution constants of the lanthanides in their adsorption on the zeolite A

In this study, the changes of the distribution constants Kd of the lanthanide nitrates in the system: zeolite A (solid phase)–sodium nitrate (aqueous phase) were investigated. The convex and concave tetrad effect in the run of the Kd values of the lanthanides was found. The explanation of the tetrad effect through the covalency in Ln–O lanthanide bond (where Ln is lanthanide, O– oxygen) is included. It is evident from the supplementary data of diffusive reflectance spectra of the zeolites and lanthanide oxides in the VIS and infrared region, that the Nd3þ ion forms more covalent complex with the negatively charged oxygen atoms of the zeolite framework than the rest of the lanthanide ions and that La3þ, Nd3þ, Sm3þ ions strongly hydrolyze in the zeolite phase, which results in the shift of T–O–T band (asymmetric stretching vibration band of –Si–O–Al-subunits) toward lower wavelengths. q 2004 Elsevier B.V. All rights reserved