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 is a poly–hydroxocarboxylic acid, HGLU 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 Ca2+has been shown to facilitate complexation through the formation of ternary species, i.e., that comprise of An(III), Ca2+ and GLU−. Despite the relevance of Mg2+ in several repository concepts for radioactive waste disposal, no studies assessing the role of Mg2+ 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, Mg2+–An(III)–gluconate is thus required to properly assess the impact of this ligand on the mobilization of An(III) under repository-relevant conditions.

During the first stay within this TALISMAN project, TRLFS investigations were conducted on the Mg2+–Cm(III)–GLU− system. A glovebox and technical set-up for the Am(III) solubility experiments were prepared at the pooled facility. The experiments are ready to be initiated in the second stay of the project, and will take advantage of the on-going Mg2+–Nd(III)–GLU− solubility experiments (complementary to this TALISMAN project). All experiments were carried out in Ar-gloveboxes(O2< 1 ppm) at T = 22 ± 2 °C.

Cm(III)–TRLFS single spectra and lifetime measurements were performed with two series of solutions with 0.25 M and 4.5 M MgCl2 at pHc 8 and 9.[GLU−] was varied from 10-5 to 0.1 M by step-wise additions of gluconate stock solutions.The total concentration of Cm(III) was ~10-7 M. The obtained TRLFS data show distinct Cm(III) spectra in the presence of GLU−, clearly hinting towards the formation of some complexes built up of Cm(III) and GLU−. Cm(III) spectra collected in 0.25 M MgCl2 and pHc = 9 show a single isobestic point, indicating the formation of a single Cm(III)–GLU−species. Based on previous TRLFS studies with the Ca2+−Cm(III)–GLU− system, it is hypothesized that in analogous solutions containing magnesium ions, ternary Mg2+–Cm(III)–GLU− species are formed. Data collection and evaluation is on-going.

A lead-block with inserts specially adapted for centrifuge tubes has been designed and built at KIT-INE. These will be used for Am(III) solubility experiments under Ar-atmosphere. A total of 4 samples are planned, containing 0.5 mg Am-241 each. The experimental conditions will be carefully chosen based on a systematic on-going solubility study with Nd(III) in diluted to concentrated MgCl2 solutions, with pHc = 8–9 and [GLU] between 10-4 and 0.10 M.

Main visitor contact data
Name: Ágost Gyula Tasi
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: 7/12/2014
End date of the stay: 8/30/2014
Quantity of access: 30
Access Unit: Days