JRP CALL information
Supported By

European Commission

Short description of the work

The experiments carried out in HZDR-IRC were focused on determination of the mechanisms of interaction of neptunium(IV, V and VI) ions with ionic species containing technetium with various oxidation states in aqueous acidic media.
The chemical species containing Tc and Np with required oxidation states were generated electrochemically in an electrolyte containing potassium pertechnetate or neptunyl(V) sulfate. The optimal conditions required for generation of Tc and Np with a chosen oxidation state were determined on the basis of chronoamperometric and cyclic voltammetry experiments.
Both technetium and neptunium species were electrogenerated separately in electrochemical cells equipped with gold or platinum electrodes. Such generated Tc and Np species were used in preparation of the mixed solution for Tc and Np interaction studies. UV-Vis-NIR was employed to study of the interactions between both elements. The obtained results show that the interaction of technetium(III), technetium(IV) and technetium(III,IV) ionic species with neptunyl(VI) ions leads to formation of intermediate species characterized spectroscopically by a band with the maximum at 460 nm. Neptunium(IV) acts as a technetium reducing agent and is able to reduce pertechnetates ions in acidic media to the forms characterized spectroscopically by the band at 500 nm.
The results of the cyclic voltammetry experiments clearly show that neptunyl(VI) ions have a great impact on the reduction of pertechnetates ions in acidic media. In the absence of Np(VI) the first step of TcO4- ions electroreduction leads to formation of a sharp cathodic wave at 0.55 V vs. Ag,AgCl. This wave can be attributed to the generation of unstable intermediate technetium(V and VI) species which are subsequently reduced to technetium(IV). In the presence of excess of neptunyl(VI) ions the intensity of the abovementioned cathodic wave strongly decreases which suggests that Tc(V or VI) ionic species are immediately oxidized to pertechnetate ions.
The electrochemical experiments carried out with various electrode materials (gold, platinum and glassy carbon) reveal that presence of Np changes the pathways of electroreduction and following electrooxidation of Tc species. A reasonable good separation of electrochemical signals from the noise background was obtained only for gold electrodes.
The liquid-liquid extraction experiments performed from 4M H2SO4 to 30% TBP in kerosene show that presence of Np(IV) leads to a strong decrease of distribution ratio of reduced technetium species as compared to the distribution ratio determinated for pertechnetate ions. The results of extraction experiments performed for a system containing reduced Tc and excess of Np(VI) suggest existence of a significant fraction of technetium with lower oxidation states which was not oxidized to pertechnetate ions.

Main visitor contact data
Name: Dr Maciej Chotkowski
Organisation: University of Warsaw

JRP Identification
JRP nr: TALI-C05-11
JRP title: Interaction of technetium(III, IV and III,IV) with neptunium in acidic media
JRP scope: Scope 1: Actinide separation chemistry

Visited Associated Pooled Facility
Visited APF during the stay: HZDR - IRE
Name of the APF Contact Person: Dr Andreas Scheinost

Other APF and organisation involved in the JRP
Other organisations involved:
Other APF involved in the project: HZDR - ROBL

Description of the work done at the associated pooled facility
Start date of the stay: 6/18/2015
End date of the stay: 7/7/2015
Quantity of access: 10
Access Unit: Days