4th EucheMs chemistry congress

Monday, 27-Aug 2012
s639
chem. Listy 106, s587–s1425 (2012)
Environment and Green Chemistry
Environmental Radiochemistry – speciation of actinides in
the environment
o - 0 2 8
ACtinide And LAnthAnide SPeCiAtion with
x-rAy SPeCtroSCoPy: MiCro- to nAno- And
other diMenSionS
M. A. deneCKe 1
1 Karlsruhe Institute of Technology - Campus North, Institut fuer
Nukleare Entsorgung, Karlsruhe, Germany
One of the key safety issues associated with high level
nuclear waste disposal is the potential release of radionuclides
following water intrusion into a repository, followed by corrosion
and leaching of waste forms, subsequent breach of the
multi-barrier system and radionuclide transport into the
surrounding environment. Predicting, ultimately controlling or
prohibiting transport of released radionuclides requires detailed
understanding of the physical and chemical factors and processes
determinant in their transport. Of central importance is the
radionuclide speciation, or its chemical and physical form.
Synchrotron-based X-ray techniques are extremely useful
speciation methods for such investigations related to the safe
disposal of high level nuclear waste. Growing sophistication of
these techniques and increased brilliance of modern synchrotron
sources is helping surmount challenges in speciation
investigations of systems with inherent high chemical and
physical heterogeneity including waste forms, containers, backfill,
hostrock and ground water, to name a few. In my presentation
I will show results from X-ray spectroscopy studies combined
with imaging techniques for actinide speciation in spent fuel
models, granite, sediment and colloids. Each example is selected
to both illustrate several processes affecting radionuclide
mobilization or immobilization and to demonstrate the utility of
different state-of-the-art techniques on varying length scales.
Keywords: XANES/EXAFS; actinide; speciation; X-ray
techniques;
4 th EucheMs chemistry congress
Environmental Radiochemistry – speciation of actinides in
the environment
o - 0 2 9
urAniuM CheMiStry in CitriC ACid SoLution
r. Steudtner 1 , K. MüLLer 1 , e. JäCKeL 1 ,
r. Meyer 1 , K. SChMeide 1 , A. Günther 1
1 Helmholtz-Zentrum Dresden-Rossendorf, Institute of Resource
Ecology, Dresden, Germany
For the long-term safety assessment of radioactive waste
disposal sites, detailed knowledge of the actinides’s migration
behavior as a function of pH, temperature, redox potential of the
solution and concentration of complex partners is mandatory. The
majority of the studies on the uranium chemistry in the presence
of carboxylic acids was performed in the acidic pH range and at
room temperature. Thermodynamic data of the complexation of
U(IV) and U(VI) by citric acid was given by Hummel. [1] The
complexation was comprehensively studied by Bonin [2] and
Guenther [3] and the photoreduction by Ohyoshi. [4] However, the
mechanistic understanding of the basic interaction processes is
very fragmentary.
This study is focused on the mechanism and kinetics of the
uranium complexation and redox reactions as a function of
carbonate and visible light in citric acid solution. To evaluate the
impact of these reaction parameters on the uranium – citric acid
– system we used UV-Vis, ATR FT-IR and TRLF spectroscopy.
In all systems the uranium citrate complexes were detected as
solved species. The variation of reaction parameters strongly
influence the complexation and redox reactions. The highest
reduction rate could be determinate between pH ~3.5 at anaerobic
conditions. Especially the presence of carbonate strongly
influenced the mechanism of the redox processes. The uranium is
stabilized as U(VI) carbonate complex in the U(VI) – as well as
in the U(IV) – citric acid – system. The determination and
verification of thermodynamic and kinetic parameters of
complexation and redox processes will improve the safety
assessment of nuclear waste disposal sites.
references:
1. Hummel et al. (2005), Chemical Thermodynamics Vol. 9.,
OECD Nuclear Energy Agency.
2. Bonin et al. (2008), Radiochimica Acta 96, 145–152.
3. Günther et al. (2011), Radiochimica Acta 99, 535–541.
5. Ohyoshi & Ueno (1974), Journal of Inorganic & Nuclear
Chemistry 36, 379–384.
Keywords: Complexation; Redox processes; Uv-vis;
ATR FT-IR;
AUGUst 26–30, 2012, PrAGUE, cZEcH rEPUbLIc