eprintid: 26789
rev_number: 19
eprint_status: archive
userid: 4539
dir: disk0/00/02/67/89
datestamp: 2019-07-19 15:39:32
lastmod: 2019-07-29 11:25:02
status_changed: 2019-07-19 15:39:32
type: doctoralThesis
metadata_visibility: show
creators_name: Maiwald, Martin Maximilian
title: Spektroskopische Speziation und thermodynamische Charakterisierung der Komplexierung des Np(V)-Ions
subjects: 540
divisions: 120300
adv_faculty: af-12
keywords: Actiniden, Komplexierung
cterms_swd: Thermodynamik
cterms_swd: Spektroskopie
cterms_swd: Actinoide
cterms_swd: Neptunium
note: Die Doktorarbeit wurde durch das BMBF unter der Fördernummer 02NUK039C gefördert.
abstract: The geochemistry of the actinides is of particular interest for the safety case of a nuclear waste repository. The present work focuses on the complexation of pentavalent actinides An(V) with different organic and inorganic ligands in aqueous solution at elevated temperatures. In the first part of the thesis the complexation of NpO2+ with different mono- and dicarboxylic ligands (formate, acetate, oxalate, malonate, succinate) and hydorxyl functionalized carboxylates (lactate, malate, tartrate) is studied. These ligands are either naturally occuring substances in the pore waters of clay rocks or serve as model ligands for macro molecular organic compounds like humic substances or polycarboxylate based cement additives. The speciation of the formed complexes and the thermodynamic functions (log b0i(T), DRH0m,i, DRS0m,i) of the corresponding complexation reactions are determined as a function of temperature and ionic strength using Vis/NIR absorption spectroscopy. Additionaly, the structures of the NpO2+ complexes with oxalate, malonate, succinate and lactate are resolved by EXAFS spectroscopy, ATR-FT infrared spectroscopy and quantum chemical calculations revealing detailed information on the coordination properties of An(V) on a molecular level. In the second part the complexation of NpO2+ with the inorganic anions fluoride, chloride, nitrate and sulfate is studied at various temperatures and ionic strengths revealing the stoichiometry of the formed complexes and the thermodynamic functions of the respective complexation reactions. These inorganic anions are integral parts of natural groundwaters. Additionaly, fluoride and chloride are available in large quantities in salt rock formations which are in discussion as host rocks of nuclear waste repositories. In the third part of this work the NpO2+ complexation up to 200 °C is studied for the first time by absorption spectroscopy. Therefor, a high-temperature spectrophotometric cell is developed at the Institute for Nuclear Waste Disposal (INE) at the Karlsruhe Institute of Technology (KIT). The applicability of this setup for speciation studies up to 200 °C is demonstrated by studies on the complexation of NpO2+ with SO42-. The obtained results contribute to an improved understanding of the (geo)chemical behaviour of pentavalent actinides in aqueous systems and provide detailed information on the complexation properties of An(V) on a molecular level. Furthermore, the implementation of a high-temperature spectrophotometric cell for speciation studies on the complexation of NpO2+ up to 200 °C opens up the possibility for thermodynamic studies at conditions that might occur in the near-field of a nuclear waste repository.
date: 2019
id_scheme: DOI
id_number: 10.11588/heidok.00026789
ppn_swb: 1669581012
own_urn: urn:nbn:de:bsz:16-heidok-267896
date_accepted: 2019-07-05
advisor: HASH(0x564e1c4b7630)
language: ger
bibsort: MAIWALDMARSPEKTROSKO2019
full_text_status: public
place_of_pub: Heidelberg
citation:   Maiwald, Martin Maximilian  (2019) Spektroskopische Speziation und thermodynamische Charakterisierung der Komplexierung des Np(V)-Ions.  [Dissertation]     
document_url: https://archiv.ub.uni-heidelberg.de/volltextserver/26789/3/Dissertation_Maiwald.pdf