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Environmental chemistry of uranyl [Elektronische Ressource] : a relativistic density functional study on complexation with humic substances and sorption on kaolinite / Alena Kremleva

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Technische Universität München Department Chemie Fachgebiet Theoretische Chemie Environmental Chemistry of Uranyl: A Relativistic Density Functional Study on Complexation with Humic Substances and Sorption on Kaolinite Alena Kremleva Vollständige Abdruck der von der Fakultät für Chemie der Technischen Universität München zur Erlangung des akademischen Grades eines Doktors der Naturwissenschaften (Dr. rer. nat.) genehmigten Dissertation. Vorsitzer: Univ.-Prof. Dr. J. P. Plank Prüfer der Dissertation: 1. Univ.-Prof. Dr. N. Rösch 2. K. Köhler Die Dissertation wurde am 18.08.2009 bei der Technischen Universität München eingereicht und durch die Fakultät für Chemie am 09.09.2009 angenommen. Acknowledgments I am deeply indebted to my supervisor Prof. Dr. N. Rösch from the Technische Universität München whose help, stimulating suggestions, and encouragement helped me in all the time of research and writing of this thesis. I am heartily thankful to Dr. Krüger, whose encouragement, guidance and support from the initial to the final level enabled me to develop an understanding of the subject. I gratefully acknowledge his extended help in academic and nonacademic issues. I offer my regards and blessings to Dr. Dassia Egorova, Dr. Ludmila Moskaleva, and Egor Vladimirov who supported me in many respects (professional and personal) during my stay in München and my work at TU München.

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Published 01 January 2009
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Technische Universität München
Department Chemie
Fachgebiet Theoretische Chemie



Environmental Chemistry of Uranyl: A Relativistic
Density Functional Study on Complexation with Humic
Substances and Sorption on Kaolinite



Alena Kremleva




Vollständige Abdruck der von der Fakultät für Chemie der Technischen Universität
München zur Erlangung des akademischen Grades eines

Doktors der Naturwissenschaften (Dr. rer. nat.)

genehmigten Dissertation.



Vorsitzer: Univ.-Prof. Dr. J. P. Plank
Prüfer der Dissertation:
1. Univ.-Prof. Dr. N. Rösch
2. K. Köhler


Die Dissertation wurde am 18.08.2009 bei der Technischen Universität München
eingereicht und durch die Fakultät für Chemie am 09.09.2009 angenommen.





Acknowledgments

I am deeply indebted to my supervisor Prof. Dr. N. Rösch from the Technische Universität
München whose help, stimulating suggestions, and encouragement helped me in all the time
of research and writing of this thesis.

I am heartily thankful to Dr. Krüger, whose encouragement, guidance and support from the
initial to the final level enabled me to develop an understanding of the subject. I gratefully
acknowledge his extended help in academic and nonacademic issues.

I offer my regards and blessings to Dr. Dassia Egorova, Dr. Ludmila Moskaleva, and Egor
Vladimirov who supported me in many respects (professional and personal) during my stay in
München and my work at TU München.

I am grateful to many of my colleagues for stimulating discussions as well as for pleasant
work and nice time which we spent together: Dr. F. Schlosser, Dr. A. Matveev, Dr. A. Genest,
Dr. R. S. Ray, Dr. S. Bosko, D. Ba şaran, S. Parker, and those not mentioned here whose
presence was helpful and memorable. It is pleasure to thank my friends Elena Medvedeva,
Eugenij Grabchak, Dr. Dominic Schupke, Dr. Claus Gruber for their friendship, support and
confidence in me, which made my way through all ups and downs much easier.

I would like to thank my parents who inspired me for study and research all my life, who
taught me never give up, and who always believed in me. Without them I would not be what I
am today.

This thesis would not have been possible without deep support of my friend Ivan Nechaev. He
deserves special mention for his love, care, and patience.

Finally, I would like to thank everybody who was important to the successful realization of
this thesis.





































to Ivan Nechaev


i






Content


Introduction 1 
Part I – Complexation of uranyl with alcoholic groups of humic substances 5 
1.  Actinides in the environment 5 
1.1  Solution chemistry of uranium 5 
1.2  Complexation by humic substances 6 
1.3  Reactive groups of humi7 
2.  Computational approach 9 
2.1  Computational details 9 
2.2  Evaluating of reaction energies 11 
2.3 Models 12 
3.  Results and Discussion 14 
3.1  Geometry parameters 14 
3.2 Energetics 20 
3.3  Alternative mechanism of complexation 21 
3.4  Uranyl complexation by catechol 25 
4. Conclusions 28 
Part II – Adsorption of uranyl on kaolinite 31 
5.  Clay minerals and their role in the environmental chemistry of actinides 31 
5.1  Clays and clay minerals 31 
5.2  Structure of clay minerals 33 
5.3  Types of surfaces 34 
5.4  Adsorption of actinides by clay minerals 37 
5.5  Adsorption of uranyl on kaolinite 40 
6  Computational treatment 41 
ii

6.1  Challenges and different approaches of computational treatment 41 
6.2  Computational details 42 
7.  Kaolinite bulk and surfaces structures 44 
7.1  Bulk structure of kaolinite 44 
7.2  Models of (001) basal kaolinite surfaces 45 
7.3  Models of adsorption complexes at (001) kaolinite surfaces 49 
7.4  Models of the bare (010) edge surface of kaolinite 50 
7.5  Models of adsorption complexes on (010) kaolinite 57 
8.  Adsorption of uranyl on bare surfaces of kaolinite 59 
8.1  A simple model of uranyl adsorption on the Al(o) surface 59 
8.2  Improved neutralization model 62 
8.3  Energy cycle 66 
8.4  Improved models of uranyl adsorption at Al(o) kaolinite 70 
8.5  Adsorption on Si(t) kaolinite 78 
8.6  Adsorption of uranyl on bare (010) kaolinite surfaces 80 
8.7  Comparison of gas phase results to experiment 84 
9.  Adsorption at solvated surfaces 85 
9.1  Comparison LDA versus GGA 87 
9.2  Solvation of basal (001) kaolinite surfaces 92 
9.3  edge (010) kaolinite surfaces 94 
9.4  Adsorption on solvated Al(o) kaolinite 97 
9.5  Adsorption on solvated (010) edge surfaces 101 
9.6  Comparison with experiment 109 
Summary 125 
Appendix A – Basis sets 131 
Appendix B – Data for bulk kaolinite 135 
Bibliography 137 

Introduction





Introduction


The migration and the transport of actinides, released from various sources to the
1environment, nowadays are of great concern. The strong ability of actinides to from
complexes with different natural organic macromolecules (humic substances) as well as
organic and inorganic colloids allows the fast distribution of radioactive pollutants in an
2aquatic environment. Contamination of aquatic natural systems, e. g. groundwaters, can lead
to poisoning of drinking water, accumulation of radionuclides in plants, animals, and humans,
etc. Preventing the contamination of groundwater and terrain from the results of
anthropogenic actions will help to avoid numerous problems. In turn, understanding the
environmental chemistry and the transport of actinide can help to avoid and solve these
issues.
Long-living radioactive elements in nature derive from various sources. First, there is
natural accumulation. Natural actinide isotopes are present in rocks and minerals, e.g.
phosphates containing uranium or thorium. These places are known and most of them are
used as mining sites for some naturally occurring radionuclides. There are natural deposits of
uranium, for example, in Saskatchewan in Canada, in South Australia, in Kazakhstan.
Uranium mining itself is more dangerous than other underground mining due to radon gas
emitted by uranium ore and the elevated level of radiation. Besides, any mining site has an
increased risk for contamination, not only for workers, but for people living nearby.
Another source is anthropogenic: actinides have been artificially produced starting from
the middle of the last century. Actually, the use of several naturally occurring actinide
isotopes has increased as well. In general, this happened due to the production and use of
nuclear weapons and the nuclear power industry. Artificial or anthropogenic actinides are U-
3 4236, Pu-238, Np-239, etc. About 2000 tons of Pu have been produced until now. The
amount of artificially produced actinides is larger than that occurring naturally, and they have
occasionally been released into the environment.

1 Introduction
Currently, the most pressing international problem of the nuclear industry with regard to
5,6establishing a long-term energy production plan is the disposal of nuclear waste, which
represents a possible source of permanent contamination. The composition of nuclear waste
varies depending on the source of the waste and how it was treated. Nevertheless, uranium is
the main component of spent fuel, ~ 94%, plutonium takes about 1 %, the rest are minor
7actinides (Np, Am, Cm) and fission products. Therefore, uranium interaction in aqueous
solution, with organic matter, mineral surfaces, etc. are intensely investigated. To protect our
biosphere we need a long-term management strategy including storage, disposal and/or
transformation of the waste into a non-toxic and faster decaying form. The radioactive waste
has to be converted in such a form which will not react or degrade for a long time period.
Also, it needs to be isolated from the biosphere. The timeframe needed for the isolation of
4 6waste repositories ranges from 10 to 10 years. For the moment only deep geological
formations are seriously considered for such long periods. Many countries try to find an
appropriate solution for a final rather deep and safe repository for high-level waste and spent
5,6fuel. In the meantime storing high-level nuclear waste above ground for a century is
considered appropriate as well, since it allows the material to be observed easily and any
problems to be detected and managed.
The German Federal Ministry for the Environment, Nature Conservation and Nuclear
8Safety (BMU) has developed safety requirements for the final disposal of radioactive waste
and established criteria and procedures to be used in the site selection procedure. A long-term
geological repository should fulfill the following requirements: (i) the integrity of the
isolating rock zone must be ensured for a period of 1 million years; (ii) the pore water present
in the geological rock zone must not in any case mix with groundwater; (iii) there should be
no advective transport within the rock zone; (iv) secondary pathways leading to ingress of
8aqueous pollutant solutions from the isolation rock host must be excluded. Based on these
criteria, the BMU would like to compare one of the controversially discussed possible
repositories in Germany, the Gorleben site, with other potential sites. Among those, clay is
one option beside salt formations or granite for disposing radioactive waste. One of the
5possibilities of host rocks considered in Europe is the opalinus clay formation in Switzerland.
The sedimentary rock known as opalinus clay takes the form of a homogeneous layer, around
110 meters thick in the region of interest. It formed in a marine environment by deposition of
fine silts that altered over geological timescales to a clay rock. opalinus clay layers can be
found in Northern Switzerland, in various areas of Southern Germany and in France. This
clay has very good sealing and isolation capacity, which is provided by microscopically small
2