List of abbreviations and symbols ............................. VII
Summary ........................................................ IX
1 Introduction ................................................. 1
2 Speciation of uranium and neptunium in the environment ....... 4
2.1 Properties of uranium and neptunium ..................... 4
2.2 Reactions in aqueous solution ........................... 5
2.3 Reactions at the solid-water interface .................. 9
2.4 Migration of actinides in the environment .............. 12
3 The structural information obtained by attenuated total
reflection FT-IR spectroscopy ............................... 14
3.1 Surface analytical techniques .......................... 14
3.2 Internal reflection spectroscopy ....................... 15
3.2.1 Principles of attenuated total reflection
spectroscopy .................................... 16
3.2.2 Internal reflection element materials and cell
designs ......................................... 17
3.2.3 Infrared spectroscopy of water .................. 18
3.2.4 Reaction-induced infrared difference
spectroscopy .................................... 19
3.2.5 Interfacial spectroscopic studies of sorption
processes ....................................... 20
3.3 ATR FT-IR spectroscopy at the IRC ...................... 21
3.3.1 Instrumental set-up ............................. 21
3.3.2 In situ ATR FT-IR spectroscopic sorption
studies ......................................... 23
4 Aqueous species of U(VI), Np(VI) and Np(V) and their IR
spectroscopic characterization .............................. 27
4.1 U(VI) speciation in air ................................ 28
4.1.1 Calculation of micromolar U(VI) speciation ...... 28
4.1.2 U(VI) speciation at pH 4 ........................ 29
4.1.3 U(VI) speciation in micromolar acidic
solutions ....................................... 32
4.1.4 U(VI) speciation in micromolar neutral
solutions ....................................... 35
4.2 Np(VI) speciation in air ............................... 39
4.2.1 Calculation of Np(VI) speciation in comparison
to U(VI) ........................................ 39
4.2.2 NIR spectroscopy of Np(VI) solutions in the
acidic pH range ................................. 40
4.2.3 Isostructural complexes of Np and U ............. 41
4.2.4 Np(VI) and U(VI) speciation in aqueous
solutions in the acidic pH range ................ 43
4.2.5 Colloidal species of Np(VI) and U(VI) ........... 48
4.3 Np(VI) and U(VI) speciation in the absence of
atmospheric carbonate .................................. 50
4.3.1 Calculation of Np(VI) and U(VI) speciation at
N2 .............................................. 50
4.3.2 The species of micromolar Np(VI) and U(VI)
solutions in the acidic pH at N2 ................ 51
4.4 Np(V) speciation in the absence of atmospheric
carbonate .............................................. 54
4.4.1 Calculation of Np(V) speciation at N2 ........... 54
4.4.2 Np(V) speciation in micromolar solutions at
N2 .............................................. 55
4.5 Conclusions and Outlook ................................ 56
5 Species of U(VI) and Np(V) on mineral oxide surfaces and
their in situ spectroscopic characterization ................ 58
5.1 Introducing remarks on U(VI) sorption onto mineral
surfaces ............................................... 58
5.2 U(VI) sorption on titanium dioxide ..................... 59
5.2.1 Monitoring the U(VI) sorption process onto
ТiO2 ............................................ 60
5.2.2 Identification of different U(VI) surface
species on ТiO2 ................................. 62
5.2.3 Influence of ТiO2 crystallographic form ......... 64
5.2.4 Influence of ТiO2 ............................... 67
5.2.5 Influence of the U(VI) solution properties on
the sorption onto ТiO2 .......................... 70
5.3 Photocatalytic effects during the U(VI) sorption on
ТiO2 ................................................... 75
5.4 U(VI) sorption onto oxides of aluminium and silica ..... 78
5.4.1 Monitoring the U(VI) sorption process onto
γ-Al2O3 ......................................... 82
5.4.2 Influence of the U(VI) solution properties
on the sorption onto γ-Al2O3 .................... 84
5.4.3 Influence of the aluminate mineral phase on
U(VI) sorption .................................. 89
5.5 U(VI) sorption onto alumosilicates ..................... 92
5.6 Introducing remarks on Np(V) sorption onto mineral
surfaces ............................................... 95
5.7 Np(V) sorption on titanium dioxide ..................... 96
5.7.1 Monitoring the Np(V) sorption process onto
ТiO2 ............................................ 96
5.7.2 Influence of the Np(V) solution properties on
the sorption onto ТiO2 .......................... 99
5.8. Comparison of Np(V) sorption onto oxides of titanium,
aluminum, silicon and zinc ............................ 100
5.9 Conclusions and Outlook ............................... 103
6 Materials and methods ...................................... 104
6.1 Materials ............................................. 104
6.2 Methods ............................................... 105
6.2.1 Thermodynamic data and speciation modeling ..... 105
6.2.2 Experiments at high actinide concentrations .... 105
6.2.3 Preparation of actinide solutions .............. 105
6.2.4 Preparation of diluted solutions ............... 106
6.2.5 Check for colloids in sample solutions ......... 107
6.2.6 ATRFT-IR spectroscopic measurements ............ 107
6.2.7 NIR absorption spectroscopy .................... 107
6.2.8 Laser-induced fluorescence spectroscopy ........ 107
6.2.9 Analysis of uranium and neptunium
concentration .................................. 107
6.2.10 Measurement of pH values ....................... 108
6.2.11 ТiO2 digestion analysis ........................ 108
6.2.12 Determination of the Specific Surface Area ..... 108
6.2.13 Washing procedure of the ТiO2 samples .......... 108
6.2.14 Experiments at inert gas atmosphere ............ 109
6.2.15 AFM measurements ............................... 109
7 References ................................................. 110
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