LAUSR

Abstract The interaction between Lanthanides (Ln) - ions and Ca-bentonite and the structural changes accompanying were studied. Ln -exchanged bentonites were prepared from Ca-bentonite (Istenmezeje, Hungary) by ion exchange in three consecutive washings with lanthanide solutions. Scanning Eletronmicroscopy Energy Dispersive X-ray spectroscopy (SEM-EDX) studies showed even distribution of Ln s and other components of bentonite. The natural bentonite and the lanthnide exchanged bentonites were characterized by X-ray diffraction (XRD), which revealed the same mineral composition, and the increase of the basal spacing of montmorillonite from 1.465 (Ca 2+ ) to 1.577 nm (REE 3+ ). The d 001 basal spacing of lanthanide montmorillonite increases as the ion radius of the lanthanide cation increases. The Fe 3+ , and Ln s 3+ amount on the bentonite were determined by X-ray-fluorescence spectrometry (XRF) elemental analysis. The amount of exchanged Ln s were determined by washing the Ln -bentonite with 1 M ammonium-acetate, and measuring the amount of Ln released, using inductively coupled plasma optical emission spectrometry (ICP-OES). In most Ln -bentonites, the quantity of the exchanged Ln ions was about 80–90% of the cation exchange capacity (CEC) of the bentonite. In case of some lanthanides bentonite (La 3+ , Ce 3+ , and Gd 3+ ), however, the sorbed quantity of lanthanum ions was higher than the cation exchange capacity. In case of lanthanum-bentonite, the lanthanide quantity is as high as 136% of CEC. Moreover, the iron(III) content of lanthanum bentonite is less than that of the original Ca-bentonite. Mossbauer spectra of the La-, Ce-, and Gd-exchanged samples at 78 K revealed an unexpected magnetically split component that was absent from the Ca-bentonite. This component may belong to interlayer Fe. This iron can be released from the octahedral positions crystal lattice.