JRP CALL information
Supported By

European Commission

Short description of the work

The experiments carried out in HZDR-IRC were focused on determination of mechanisms of interaction of neptunium(III,IV and VI) ions with ionic species containing technetium with various oxidation states in presence of nitric acid.
The spectrophotometric titration clearly shows that neptunium bulk solutions initially contain Np(IV). These neptunium species can be electrochemically reduced in 4M H2SO4 to relatively stable Np(III) ions. Both technetium and neptunium species were electrogenerated separately in electrochemical cells equipped with gold/RVC or platinum electrodes. Such generated Tc and Np species were used for preparation of the mixed solution for Tc and Np interaction studies. UV-Vis-NIR was employed to study the interactions between both elements. The obtained results show that the interaction of technetium(III,IV) ionic species with neptunyl(VI) ions leads to formation of intermediate species characterized spectroscopically by a band with maxima at 460 nm and 760 nm also in the presence of nitric acid. Both neptunium(VI) and nitrate ions act as technetium oxidazing agents and both species are able to oxidize technetium(IV) ions in acidic media to pertechnetates. Noteworthy is the fact that in nitric acid solutions the Tc(V) intermediate species are detectable even after few minutes from its formation.

The results of the cyclic voltammetry experiments clearly show that nitrates have a great impact on the reduction of pertechnetates ions in acidic media. In contrast to pure sulfuric acid solutions, presence of nitrates leads to a significant decrease in currents due to formation of Tc(V) and TC(VI) at 0.55 V vs. Ag/AgCl. This indicates that in nitric acid solutions reduction of pertechnetates to Tc(V) and Tc(VI) species follows a different pathway as compared to sulfuric acid.
The electrochemical experiments carried out with various electrode materials (gold, platinum and glassy carbon) in the solutions of sulfuric and nitric acid reveal that presence of nitric ions changes the pathways of electroreduction and following electrooxidation of Tc species. At potentials lower than 0.5 V a broad reduction wave characteristic for nitrate ions reduction is observed.
The liquid-liquid extraction experiments performed from 4M H2SO4/HNO3 to 30% TBP in kerosene show that presence of nitrate ions leads to an increase of distribution ratio of technetium species as compared to the distribution ratio determinated for the systems without HNO3. These results confirm findings from electrochemical and spectroscopic experiments.

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: 9/7/2015
End date of the stay: 9/23/2015
Quantity of access: 10
Access Unit: Days