A revisit of the cation–cation interactions between NpO2+ and UO22+ in nitric acid medium and their impact on separation processes: spectrophotometric and solvent extraction studies

Abstract

There are contradicting reports on the thermodynamics of cation-cation interactions (CCIs; inner/outer sphere) involving NpO2(+) and UO2(2+). This paper revisits CCIs of NpO2(+) (2 × 10(-4) M) under varying conditions such as reaction time, nitric acid (2 × 10(-3)-4 M HNO3)/uranium (up to 1.2 M) concentrations, and temperature (283-343 K) by spectrophotometric measurements. This study reports for the first time the appearance of a signature peak of Np(IV) (∼964 nm) in addition to NpO2(+) (980 nm) and the NpO2(+)-UO2(2+) complex (992 nm). For a pure NpO2(+) solution at 4 M HNO3, there is a gradual increase in Np(IV) peak intensity with increasing temperature and correspondingly the Np(V) peak diminishes. The CCIs are more favored at higher uranium concentrations. However, the intensity of the 992 nm peak decreases steadily with increasing temperature suggesting the exothermic nature of the complexation process. The thermodynamic data and reported structural studies indicate the formation of an inner-sphere complex under the conditions of this study. In addition, the spectral changes also suggest the formation of Np(IV) even in the presence of uranium at elevated temperatures. Solvent extraction studies using 1.1 M TBP and 1.1 M DHOA solutions in n-dodecane show that NpO2(+)-UO2(2+) complexes are extractable leaving NpO2(+) in the aqueous phase.

The Role of Residual Charges in the Interaction between NpO2+ and Th4+ Cations: Spectrophotometric and Computational Studies

“…[19] The green color of the solution suggested the presence of Np V in the nitric acid medium, which was further confirmed by the appearance of the characteristic peak of Np V at 980 nm in the absorption spectrum. [19] The green color of the solution suggested the presence of Np V in the nitric acid medium, which was further confirmed by the appearance of the characteristic peak of Np V at 980 nm in the absorption spectrum.…”

“…[19] These studies were performed considering the respective aquo complexes of the actinide cations of interest. [19] These studies were performed considering the respective aquo complexes of the actinide cations of interest.…”

“…[8,9,[11][12][13][14][15] Generally, these studies have indicated the formation of inner-sphere T-shaped solution phase geometry. [19] This study has been extended to understand the interaction between Np V O 2 + and Th IV cations under varying experimental conditions such as nitric acid (1-6 m HNO 3 ), Th IV (up to 0.86 m) concentrations, and temperature (20-70°C). [15] Experimental conditions such as ionic strength, metal concentrations, nature of acid and its concentration, and temperature show significant influence on cation-cation interactions (CCIs) in aqueous media.…”

Facilitated transport of tetravalent plutonium from nitric acid medium using a novel extractant – BenzoDODA

“…The spent 11 fuels from nuclear reactors are reprocessed for the recovery of 12 unused uranium and freshly produced plutonium by industrially 13 applied process known as PUREX [1] using 30% TBP in n-paraffin as 14 extractant. During operation of the process, depending on the 15 performance of various process parameters some amount of Pu 16 ($5-10 ppm) remains unrecovered and goes to high level waste 17 (HLW) along with other fission products, structural materials and 18 unrecovered U. Also in the operation of the PUREX plant various 19 streams of wastes are generated which contain significant quantity 20 of Pu in presence of other contaminants.…”

“…239 Np tracer was introduced in the diluted HLW 93 solution to study the transport of Np(V). The detail description of 94 Np(V) stock solution preparation is given elsewhere [18]. Other The cumulative percent transport (%T) at a given time …”