The synthesis and evaluation of new extractants for spent nuclear fuel reprocessing are described. New bitopic ligands constituted of phenanthroline and 1,3,5-triazine cores functionalized by picolinamide groups were designed. Synthetic routes were investigated and optimized to obtain twelve new polyaza-heterocyclic ligands. In particular, an efficient and versatile methodology was developed to access non-symmetric 2-substituted-4,6-di(6-picolin-2-yl)-1,3,5-triazines from the 1,3,5-triazapentadiene precursor in the presence of anhydride reagents. Extraction studies showed the ability of both ligand series to extract and separate actinides selectively at different oxidation states (U(VI), Np(V,VI), Am(III), Cm(III), and Pu(IV)) from an acidic solution (3 M HNO3). Phenanthroline-based ligands show the most promising efficiency for use in the group actinide extraction (GANEX) process due to a higher number of donor nitrogen atoms and a suitable pre-organization of the dipicolinamide-1,10-phenanthroline architecture.
In the TALSPEAK liquid–liquid
distribution process, dissolved
lanthanides can be separated from actinides using a complexing agent
such as N-(2-hydroxyethyl)ethylenediamine-N,N′,N′-triacetic
acid (HEDTA, CAS Reg. No. 150-39-0) in a low pH buffered aqueous phase
in contact with an organic phase containing a suitable extractant.
This study focuses on the chemical speciation of HEDTA, citrate pH
buffer, and Eu3+ in aqueous solutions of 1:1 Na+ salts (mainly NaNO3) as a function of ionic strength
and pH. New measurements of stoichiometric protonation constants of
HEDTA, and the HEDTA complex of Eu3+, in aqueous NaNO3 are reported for ionic strengths from 0.5 to 4.0 M at 25
°C. A Pitzer activity coefficient model of the aqueous mixture
has been developed based upon these measurements, available osmotic
and activity coefficient data, and stoichiometric equilibrium constants
in different 1:1 electrolyte media over a range of ionic strengths.
This enables the HEDTA and buffer speciation, and complexation of
Eu3+ by both HEDTA and citrate, to be calculated for different
solution compositions and pH values. The model of the citrate buffer,
which is based on an extensive range of data for NaCl and NaNO3 media, should also be useful in other practical applications.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.