Investigations to the Complexation in the An(III)/Ln(III)-Borate System
Investigations to the migration of radionuclides are essential in the risk assessment of radionuclides in the environment and the safety assessment of nuclear waste repositories. The mobilization of radionuclides takes place for instance by the formation of water soluble complexes. Concerning the required risk and safety assessments a wide knowledge about the chemical and physical behavior of radionuclides, particularly actinides, is needed. Thus, interaction studies of radionuclides are carried out, e.g. complexation studies with components of the environmental compartments (inorganic ligands, bioligands, humic acids, bacteria, …).
Borates are ubiquitous compounds in the environment (rocks, soils, natural waters) and are used in many applications (glass, ceramic and metal production, detergents and bleaches, agriculture, nuclear technology, …). Thus, there are many sources for the release of borates in the environment. Another aspect is the occurrence of borates in salt formations, which is important concerning the search of a proper nuclear waste repository.
The aqueous chemistry of borates depends strongly on the pH and the borate species concentration. For instance in dilute aqueous solutions of boric acid monomeric B(OH)3 and B(OH)4- species exists. In more concentrated boric acid solutions a polymerization of the boric acid molecules occur with the formation of polyborate species like B3O3(OH)4- or B4O5(OH)42-.
But although there is a relevance of borates in the environment and, perhaps, in nuclear waste repositories, the Ln(III)/An(III)-borate system is investigated insufficiently.
The aims of this work are to determine borate and An(III)/Ln(III)-borate species in aqueous solution using different analytical methods (UV/vis, TRLFS, titration methods, solvent extraction, Raman and IR spectroscopy, NMR, …), to study the complex formation in this system and to investigate the influence of different parameters like temperature (> 25 °C) and ionic strength (> 0.1 M).
Part of the Joint Research Project "Rückhaltung endlagerrelevanter Radionuklide im natürlichen Tongestein und in salinaren Systemen" (members: Johannes-Gutenberg-Universität Mainz, Karlsruher Institut für Technologie, TU Dresden, TU München, Universität Heidelberg, Universität Potsdam, Universität des Saarlandes)