In this work, the structure of lanthanide-bentonites was analyzed for nuclear waste
and environmental protection purpose by several analytical methods. The main mineral
the bentonite is the montmorillonite, which has a permanent negative charge. The negative
charge is neutralized by cations attracted to the interlayer space where cation exchange
place and sometimes modifies the properties of the bentonite. The natural interlayer
may be exchanged by Lns. The importance of lanthanide ions is that they are model
interactions between soil and transuranium ions, also, lanthanide cations are produced
fission of 235U in nuclear power plants.
Ln-exchanged bentonites were prepared from Ca-bentonite by ion exchange procedure
from Ln-perchlorate solution. To prove the successful modification Scanning Eletron
Microscopy, Energy Dispersive X-ray analysis (SEM-EDX) was used showing distribution
Ln’s and other components of bentonite. The natural bentonite and the lanthanide exchanged
bentonites were characterized by X-ray diffraction (XRD), which revealed the same
composition, and the increase of the basal spacing of montmorillonite. The Ca2+, Fe3+,
Ln’s3+ amount on the bentonite were determined by X-ray-fluorescence spectrometry
In most Ln-bentonites, the quantity of the exchanged Ln ions was about 80-90% of the
cation exchange capacity (CEC) of the bentonite. For some lanthanide bentonite (Y3+,
Ce3+, and Gd3+), however, the sorbed quantity of lanthanide ions was higher that the
exchange capacity. Moreover, the iron(III) content of lanthanide bentonite was less
of the original Ca-bentonite.
The observation is that lanthanide ions can somehow supersede iron from the octahedral
positions of crystal lattice. We assume that the departure of positively charged iron
the lattice increases the negative layer charge and the cation exchange capacity.
motivate the enhance sorption of lanthanides.
To prove our previous statement, we examined how the pH and the concentration influences
the bentonite structure without and with Lns. Ca-H, Ca-Y and Ca-La cation exchange
were carried out. The results revealed that the pH has high influence during the Ca-H
exchange procedure. The more acidic solution the more calcium was exchanged. In this
iron loss was not observed. In the case of Ca-Y, La cation exchange procedure, the
low influence, meanwhile the concentration has higher influence to high amount of
during divalent- trivalent cation exchange. Thus, high amount of trivalent lanthanides
the structural iron release.