Structural curiosities of lanthanide (Ln)-modified bentonites analyzed by radioanalytical methods

Kovács, Eszter Mária [Kovács, Eszter Mária (Kémia), szerző]; Kónya, József [Kónya, József (Radiokémia), szerző]; Nagy, Noémi [M. Nagy, Noémi (Környezettudomány), szerző]

Angol nyelvű Tudományos Absztrakt / Kivonat (Egyéb konferenciaközlemény)
    • MTMT: 30672805
    In this work, the structure of lanthanide-bentonites was analyzed for nuclear waste treatment, and environmental protection purpose by several analytical methods. The main mineral of 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 takes place and sometimes modifies the properties of the bentonite. The natural interlayer cations 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 during the 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 of 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 mineral composition, and the increase of the basal spacing of montmorillonite. The Ca2+, Fe3+, and Ln’s3+ amount on the bentonite were determined by X-ray-fluorescence spectrometry (XRF). 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+, La3+, Ce3+, and Gd3+), however, the sorbed quantity of lanthanide ions was higher that the cation exchange capacity. Moreover, the iron(III) content of lanthanide bentonite was less than that 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 ions from the lattice increases the negative layer charge and the cation exchange capacity. This can 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 cation exchange procedure. The more acidic solution the more calcium was exchanged. In this case, iron loss was not observed. In the case of Ca-Y, La cation exchange procedure, the pH has low influence, meanwhile the concentration has higher influence to high amount of iron loss during divalent- trivalent cation exchange. Thus, high amount of trivalent lanthanides cause the structural iron release.
    Hivatkozás stílusok: IEEEACMAPAChicagoHarvardCSLMásolásNyomtatás
    2021-10-26 16:00