Separation of Radioactive Ruthenium from Alkaline Solution: A Solvent Extraction and Detailed Mechanistic Approach.

A solvent extraction-based technique has been utilized to study the separation of ruthenium from simulated alkaline solution using Aliquat 336 as the extractant and isodecyl alcohol (IDA) as the phase modifier in n-dodecane. The effects of various experimental parameters such as solution pH, mixing time, concentration of Aliquat 336 and IDA, role of citric acid as the aqueous phase modifier/complexing agent, and stripping agents have been evaluated. It was observed that with the increase in the solution pH, the extraction efficiency increases gradually. However, when citric acid was added into the aqueous solution, an overall increase (from ∼20 to 91%) in ruthenium extraction is observed. 20 min of the mixing time was found to be sufficient to reach the extraction equilibrium. Solution composition was optimized as 50% Aliquat 336 and 10% IDA in n-dodecane (v/v) for maximum extraction. The stripping of ruthenium from the loaded organic phase has been studied using HCl and HNO3. The result indicates that in the presence of 8 M HNO3, ∼73% of ruthenium can be back extracted to the aqueous phase in a single contact. The stripping efficiency of HNO3 was found to be higher than that of HCl. Active studies with 106Ru as the radiotracer were also performed and monitored using a HPGe detector. The same method was implemented for extraction studies with real waste solution in the presence of other radionuclides such as 137Cs, 90Sr, and 125Sb. The presence of the chemical species in aqueous as well as organic phase has been identified using UV-vis spectrophotometry, Fourier transform infrared spectroscopy, and Raman spectroscopy. Density functional theory-based quantum mechanical calculations have been performed in order to unravel the extraction mechanism with the present solvent system.

Mechanistic Approach to Reveal Interaction of Uranyl Ions in Alkyltriphenylphosphonium Bromide-Based Deep Eutectic Solvent.

Speciation is known to control fundamental aspects of metal processing and electrochemical behavior such as solubility and redox potentials. Deep eutectic solvents (DESs) are an emerging class of green, low-cost and designer solvents and are being explored as alternatives for recycling nuclear fuel and critical materials. However, there is a lack of knowledge about the behavior of metals in them. Here, for the first time, we synthesized three new DESs based on alkyltriphenylphosphonium bromide (CnPPh3Br), with varied alkyl chain lengths (n), as the hydrogen-bond acceptor along with decanoic acid (DA) as the hydrogen-bond donor and explored the redox speciation of uranyl nitrate. The changes in the Fourier transform infrared and NMR spectra helped elucidate the formation of hydrogen bonds in DES. The absorption maxima of uranyl in DES was red-shifted by 10 nm compared to the free uranyl, with concomitant increase in intensity and luminescence lifetime, which suggested a strong interaction of uranyl nitrate with DES. Cyclic voltammetry was probed to understand the redox thermodynamics, transport properties, and heterogeneous electron transfer kinetics of the irreversible electron transfer of uranyl ions in the three DESs. Electrochemical and spectroscopic techniques together with density functional theory calculations unlocked microscopic insights into the solvation and speciation of UO22+ ions in three DESs and also the associated unusual trends observed in the physical properties of the DESs. The hydrogen-bonded structure of DES plays a crucial role in the redox behavior of the UO22+ ion due to its strong potent complexation with its components. The basic findings of the present work can have far-reaching consequences for the extraction, electrochemical separation, and future development of redox-based separation processes in the nuclear fuel cycle.

Colorimetric and visual determination of ultratrace uranium concentrations based on the aggregation of amidoxime functionalized gold nanoparticles.

The authors describe the synthesis and characterization of 3-mercaptopropionylamidoxime functionalized gold nanoparticles (AuNPs) for visual detection of uranium (U) by cloud point extraction. The method is capable of quantifying U at the concentration limits set by the World Health Organization in drinking water i.e., 30.0 ng mL-1. The method is based on the gradual color change from red to blue that occurs as a result of the interaction between uranyl ion and the modified AuNPs leading to particle aggregation. Such analyte-triggered aggregation results in AuNP's peak absorbance quenching as well as red shift in the wavelength range of 520 to 543 nm. The colorimetric response at 520 nm is linear in the 2-100 ng mL-1 U concentration range, and the limit of detection is 0.3 ng mL-1. No interferences by other ions are found, and the relative standard deviation is ≤4% (for n = 5). The method is validated by analyzing a certified reference material (NIST SRM 1640a; natural water), and also applied to the quantification of U in four (spiked) water samples. Graphical abstract Schematic presentation of cloud point extraction (CPE) assisted coloirmetric and visual detection of uranium (U). In CPE of gold nanoparticles (AuNPs) the color of surfactant rich phase (SRP) turns red in absence of U(VI) and blue in presence of U(VI).