JRP CALL information
Supported By

European Commission

Short description of the work
Title of the proposed JRP: “Thermodynamic study on the complexation of gluconate with An(III) in diluted to concentrated MgCl2 solutions”

Gluconic acid (HGLU) is a poly–hydroxocarboxylic acid expected in repositories for low and intermediate–level radioactive waste as component of cementitious materials. Radionuclide solubility and sorption in cementitious and saline systems can be affected by the presence of this organic ligand. Formation of stable An(III)-GLU complexes has been reported in the literature. The presence of Ca has been shown to facilitate complexation through the formation of ternary Ca-An(III)-GLU species. Despite the relevance of Mg in several repository concepts for radioactive waste disposal, no studies assessing the role of Mg in An(III)-GLU complexation have been conducted so far. The development of complete and correct chemical, thermodynamic and activity models for the ternary system, Mg–An(III)–GLU is thus required to properly assess the impact of this ligand on the mobilization of An(III) under repository-relevant conditions.

The main goal of the second stay of this TALISMAN project was to complete the TRLFS measurements of the Mg-Cm(III)-GLU system initiated during the first stay of the project. Hence, the speciation of Cm(III) in the Cm(III)-GLU system was studied in series containing 0.25 M MgCl2 and 0.01 M NaGLU at pHm = 5–8.7 (pHm = –log mH+). The effect of GLU concentration on the speciation of Cm(III) was investigated in 0.25/4.5 M MgCl2 solutions with pH = 6 and 8.7, and 10–4 M £ [GLU]tot £ 10–1 M). In order to assess the possible formation of ternary Mg–Cm(III)–GLU species, analogous experiments in the absence of MgCl2 were conducted in 0.1/4.5 M NaCl solutions.
In agreement with previous results obtained within this project, the formation of a new Cm(III)-GLU complex is confirmed in both MgCl2 and NaCl systems. The complex shows a wavelength corresponding to the maximum intensity (λmax) of ~ 606.2 nm. This species becomes dominant with increasing ligand concentration except for 4.5 M MgCl2, where the complex formation is less pronounced. This observation is probably due to the formation of the binary complex MgGLU+, and the corresponding competition with Cm(III)-GLU complexes. In contrast to the investigations in CaCl2 solutions, no unequivocal evidence on the formation of ternary Mg(II)-Cm(III)-GLU species has been obtained in the present study. This is probably due to the limitations in pH posed by the precipitation of Mg(OH)2(s) or Mg–OH–Cl(s) phases, which buffer the maximum pHm to » 9. Based on the generated spectroscopic results and in combination with the solubility data gained for the Mg-Nd(III)-GLU system (outside this TALISMAN project), chemical, thermodynamic and activity models for the system Mg-An(III)-GLU will be derived.

Main visitor contact data
Name: Bence Kutus
Organisation: University of Szeged

JRP Identification
JRP nr: TALI-C03-11
JRP title: Thermodynamic study on the complexation of gluconate with An(III) in diluted to concentrated MgCl2 solutions
JRP scope: Scope 2: Actinide in the geological environment

Visited Associated Pooled Facility
Visited APF during the stay: KIT-INE - Laboratories
Name of the APF Contact Person: Thorsten Schäfer

Other APF and organisation involved in the JRP
Other organisations involved:
Other APF involved in the project:

Description of the work done at the associated pooled facility
Start date of the stay: 7/6/2015
End date of the stay: 8/27/2015
Quantity of access: 39
Access Unit: Days