Sorption and direct speciation of neptunium(V) on aluminium oxide and montmorillonite [Elektronische Ressource] / Sonja Wendt

Informations

• Publié par: johannes_gutenberg-universitat_mainz
• Publié le: 01 janvier 2009
• Nombre de lectures: 11
• Langue: English
• Poids de l'ouvrage: 3 Mo

Extrait

Sorption and Direct Speciation
of Neptunium(V) on Aluminium Oxide
and Montmorillonite
Thesis submitted for
obtaining the degree of
Doktor der Naturwissenschaften
doctor rerum naturalium
in Nuclear Chemistry
at the Department of Chemistry, Pharmacy, and Geosciences
of the Johannes Gutenberg - University Mainz
Sonja Wendt
born in Langenhagen, Germany
Mainz, 2009
D77Contents
Abbreviations and Terms 3
1 Introduction and Motivation 7
2 Fundamentals 11
2.1 Neptunium – History and Current Situation . . . . . . . . . . . 11
2.1.1 Production and Global Inventory . . . . . . . . . . . . . 12
2.1.2 Industrial Usage and Application . . . . . . . . . . . . . 14
2.1.3 Releases into the Environment . . . . . . . . . . . . . . . 15
2.2 Chemical and Radiochemical Characteristics of Neptunium . . . 16
2.2.1 Aqueous Chemistry . . . . . . . . . . . . . . . . . . . . . 17
2.2.2 Radioactivity . . . . . . . . . . . . . . . . . . . . . . . . 21
2.2.3 Aspects of Toxicity – Health Effects . . . . . . . . . . . . 22
2.2.4 Neptunium in the Environment . . . . . . . . . . . . . . 24
2.3 Radioactive Waste . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.3.1 Waste Treatment . . . . . . . . . . . . . . . . . . . . . . 31
2.3.2 Disposal and Repository Safeguarding . . . . . . . . . . 33
2.3.3 Safety Assessment and Public Perception . . . . . . . . . 36
2.4 Clay – Merits for Radionuclide Retention . . . . . . . . . . . . . 36
2.4.1 Structure and Features of Montmorillonite . . . . . . . . 37
2.4.2 Aluminium Oxide as Reference Substance . . . . . . . . 43
2.5 Radionuclide Reactions with Natural Materials . . . . . . . . . . 47
2.5.1 Complexation . . . . . . . . . . . . . . . . . . . . . . . . 47
2.5.2 Sorption . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
2.5.3 Ion Exchange Processes . . . . . . . . . . . . . . . . . . 53
3 Practical Approach and Techniques 55
3.1 Laboratory System . . . . . . . . . . . . . . . . . . . . . . . . . 56
3.1.1 Neptunium Concentration . . . . . . . . . . . . . . . . . 57
3.1.2 pH-range . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
3.1.3 Ambient Air versus CO -free Conditions . . . . . . . . . 592
iiiiv Contents
3.1.4 Ionic Strength . . . . . . . . . . . . . . . . . . . . . . . . 60
3.1.5 Solid-to-liquid Ratio . . . . . . . . . . . . . . . . . . . . 61
3.1.6 Thermodynamics and Reaction Kinetics . . . . . . . . . 63
3.2 Analytical Methods . . . . . . . . . . . . . . . . . . . . . . . . . 64
3.2.1 °Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . 64
3.2.2 Liquid Scintillation Counting . . . . . . . . . . . . . . . 66
3.2.3 Direct Speciation via EXAFS . . . . . . . . . . . . . . . 66
3.3 Modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
3.3.1 The 2SPNE SC/CE Model . . . . . . . . . . . . . . . . . 81
4 Experimental 87
4.1 Radionuclides . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
237 2394.1.1 Production of the Isotopes Np and Np . . . . . . . 87
4.1.2 Separation and Purification . . . . . . . . . . . . . . . . 88
4.1.3 Assurance of the Fifth Oxidation State . . . . . . . . . . 90
4.2 Materials and Chemicals . . . . . . . . . . . . . . . . . . . . . . 90
4.2.1 Montmorillonite STx-1 . . . . . . . . . . . . . . . . . . . 90
4.2.2 Aluminium Oxide °-Al O . . . . . . . . . . . . . . . . . 912 3
4.2.3 Sodium Perchlorate NaClO and its Purification . . . . . 924
4.2.4 pH Adjustment and Buffer Solutions . . . . . . . . . . . 93
4.2.5 Carbonate and Bicarbonate . . . . . . . . . . . . . . . . 94
4.3 Procedure of Batch Experiments . . . . . . . . . . . . . . . . . . 95
4.3.1 Preparation: Conditioning of Montmorillonite . . . . . . 95
4.3.2 Assemblage, Pre-conditioning and pH-adjustment . . . . 97
4.3.3 Addition of Np(V) and Contact Time . . . . . . . . . . . 98
4.3.4 Centrifugation and ° Counting . . . . . . . . . . . . . . 100
4.3.5 Data Treatment . . . . . . . . . . . . . . . . . . . . . . . 101
4.3.6 Batch Experiments . . . . . . . . . . . . . . . . . . . . . 103
4.3.7 Sorption Isotherms . . . . . . . . . . . . . . . . . . . . . 103
4.4 EXAFS Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
4.4.1 Sample Preparation . . . . . . . . . . . . . . . . . . . . . 106
4.4.2 Beamline Setup and Measurement . . . . . . . . . . . . . 108
4.4.3 Data Processing . . . . . . . . . . . . . . . . . . . . . . . 111
4.5 Surface Complexation Modelling . . . . . . . . . . . . . . . . . . 115
5 Results and Discussion 119
5.1 Np(V) Sorption on Montmorillonite and Aluminium Oxide . . . 119
5.1.1 pH-Dependency: Edge and Maximum . . . . . . . . . . . 119
5.1.2 Effect of Variations in Ionic Strength . . . . . . . . . . . 124
5.1.3 Isotherms . . . . . . . . . . . . . . . . . . . . . . . . . . 127
5.1.4 Neptunium Complexation by Carbonates . . . . . . . . . 132v
5.1.5 Distribution Coefficients . . . . . . . . . . . . . . . . . . 134
5.2 Speciation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
5.2.1 Theoretical Implications . . . . . . . . . . . . . . . . . . 141
5.2.2 Indications from the Sorption Behaviour . . . . . . . . . 142
5.2.3 EXAFS-data and Curve-fitting . . . . . . . . . . . . . . 142
5.2.4 Structure of the Neptunium Carbonate Surface Complexes 149
5.2.5 Insights into the Sorption Mechanism . . . . . . . . . . . 151
5.2.6 EXAFS on °-Al O – Reliability Test of the Results . . . 1512 3
5.2.7 Compilation of Speciation Results . . . . . . . . . . . . . 157
5.3 Modelling Np(V) Sorption on Montmorillonite and °-Al O . . . 1582 3
5.3.1 Fixed Programme Parameters . . . . . . . . . . . . . . . 158
5.3.2 Adjusted Constants . . . . . . . . . . . . . . . . . . . . . 159
5.4 Consolidation of Results . . . . . . . . . . . . . . . . . . . . . . 165
6 Conclusion and Outlook 169
6.1 Summary of the Experiments . . . . . . . . . . . . . . . . . . . 170
6.1.1 Sorption Processes . . . . . . . . . . . . . . . . . . . . . 170
6.1.2 Surface Species . . . . . . . . . . . . . . . . . . . . . . . 171
6.2 Evaluation and Usability of the Results . . . . . . . . . . . . . . 172
6.3 Future Progression . . . . . . . . . . . . . . . . . . . . . . . . . 173
Bibliography 175
ooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo189
APPENDIXooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo189
A Chronology of Nuclear Research and Development 191
B Nuclear Properties of Np 199
B.1 Electronic Configuration of Np . . . . . . . . . . . . . . . . . . 19993
B.2 Isotopes and Decay Modes . . . . . . . . . . . . . . . . . . . . . 200
B.3 Colour of Np-Ions in Aqueous Solution . . . . . . . . . . . . . . 201
C Radioactivity 203
C.1 Types of Radioactive Decay . . . . . . . . . . . . . . . . . . . . 203
C.2 Nuclear Data Sources . . . . . . . . . . . . . . . . . . . . . . . . 204
C.3 Decay Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
D Disposal of Radioactive Material 207
D.1 Treatment of Nuclear Waste . . . . . . . . . . . . . . . . . . . . 207vi Contents
E Definition and Classification of Clay Minerals 209
E.1 Definition by Particle Size . . . . . . . . . . . . . . . . . . . . . 209
E.2 Classification According to Mineral Composition and Structure . 210
F Instructions for Experimentation 211
237F.1 The Np(V) Stock Solution . . . . . . . . . . . . . . . . . . . . 211
239F.2 The Stock . . . . . . . . . . . . . . . . . . . . 213
F.3 Conditioning of Montmorillonite . . . . . . . . . . . . . . . . . . 215
F.3.1 Adjustment of Ionic Strength from 0.1 to 0.01M NaClO 2184
G Experimental Overview 219
H Periodic Table of the Elements 221
ooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo221
I Curriculum Vitae 225
J Declaration 227List of Tables
3.1 2SPNE SC/CE model – fixed parameters . . . . . . . . . . . . . 84
4.1 Characteristics of the montmorillonite STx-1 . . . . . . . . . . . 91
4.2 Buffer substances . . . . . . . . . . . . . . . . . . . . . . . . . . 93
4.3 Volumes of NaHCO and Na CO . . . . . . . . . . . . . . . . . 943 2 3
4.4 Experimental conditions for the EXAFS samples . . . . . . . . . 107
4.5 Specifications of the beamlines at ANKA and ESRF . . . . . . . 109
5.1 Bond distances determined for montmorillonite . . . . . . . . . 146
5.2 Literature data on bond distances . . . . . . . . . . . . . . . . . 147
5.3 Reproducibility of EXAFS analysis – example °-Al O . . . . . 1532 3
5.4 Bond distances determined for °-Al O . . . . . . . . . . . . . . 1542 3
5.5 Fit parameter for the soddyite model . . . . . . . . . . . . . . . 154
5.6 Model parameters for Np(V) sorption on STx-1 and °-Al O . . 1622 3
G.1 Batch experiments of this study . . . . . . . . . . . . . . . . . . 219
G.2 pH and Np(V) concentration range of the sorption isotherms . . 220
G.3 Summary of the EXAFS samples prepared . . . . . . . . . . . . 220
viiList of Figures
2.1 Edwin Mattison McMillan and Philip Hauge Abelson . . . . . . 13
2.2 Solubility of Np(V) . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.3 Radiotoxicity based on ingestion . . . . . . . . . . . . . . . . . . 23
2.4 Redox diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.5 Eh/pH-diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.6 Activity of nuclear waste . . . . . . .