New Greener and Sustainable Methodology for Direct Sequestering and Analysis of Uranium Using a Maline Supramolecular Scaffold and Mechanistic Understanding through Speciation and Interaction Studies

Abstract

Research, based on the development of an economical innovative green technology, is the quintessential requirement for the advancement of the nuclear fuel cycle (NFC). The present studies show that Maline, with a preorganized supramolecular scaffold, would be considered as the workhorse for its potential efficacy in diverse facets of the NFC, specifically as an elegant metal hijacker for processing of uranium (U) matrices, designer solvent for green analysis of U, and a promising U chelator for a greener alternative for the cleanup of U contamination. Seven U matrices (UO3, UN, UO2, Rb2U­(SO4)3, U metal, U3Si2, and (U, Pu)­O2) were dissolved in Maline without any external additives and cyclic voltammetry was performed to investigate the redox speciation, viz., redox thermodynamics (E p and E f) and kinetic (D 0, k 0, and αn) parameters and mechanistic electron transfer of the dissolved U species. To get an insight into the molecular speciation, the structural analysis on UO3 dissolved in Maline was conducted by extended X-ray absorption fine structure, which indicates an interesting observation of the formation of UO2 2+ kind of species with malonic acid and H2O at equatorial coordination. Molecular dynamics and density functional theory simulations were carried out to acquire diffusion, optimized structure, binding energy, and molecular orbital diagram of U species in Maline, to corroborate the experimental results and to shed light on the hydrogen-bond network in Maline with aqueous dilution. The interaction of uranyl with Maline was probed by luminescence, absorption spectroscopy, and calorimetry titration. Green analysis methodology was developed based on Maline digestion followed by voltammetric determination of U in nuclear material samples. Green chemistry metrics were evaluated to authenticate the greener aspects of the present methodology. The present developed methodology of direct sequestration and analysis of U matrices represents an appropriate replacement of the existing method, viz., hazardous acidic processing of U matrices followed by biamperometry analysis.

Biodegradable Methane Sulfonic Acid-Based Nonaqueous Dissolution, Estimation, and Recovery: Toward Development of a Simplified Scheme for Plutonium-Bearing Fuel Matrices

“…On the other hand, carbide matrices are refluxed in the nitric acid–sulfuric acid mixture to destroy any in situ generated organic acid. In the quest to develop sustainable alternative to hydrometallurgical routes for actinide dissolution, RTIL, DES, and other green solvent-based routes are being explored fervently. ,− Nevertheless, the extent of “greenness” of various RTILs remains an unanswered question. Also, low thermal stability and high viscosity of DESs pose a challenge for routine operations.…”

“…The U�O stretching frequency appeared at 950 cm −1 for UO 2 dissolved in MSA, suggesting the formation of UO 2 2+ kind of species in MSA. 26 From Figure 4a, it was observed that the absorption at 1680 and 3250 cm −1 corresponding to H−O−H bending and O−H stretching modes of water became more prominent for UO 2 dissolved in MSA than for neat MSA.…”

A Hydrophobic Deep Eutectic Solvent for Nuclear Fuel Cycle: Extraction of Actinides and Dissolution of Uranium Oxide

“…Kinetics of dissolution in this neutral DES was better that that of HDEHP in IL [21] and [DMAH][NTf 2 ]. [15] Even, dissolution time was much shorter than that of Maline [18] and PTSA/ChCl DESs. [12] To determine the solubility of UO 3 in this DES, we added higher amount (300 mg) of UO 3 into 2 mL of DES and stirred at 80 °C.…”

“…It has been reported that dissolution of UO 2 and U 3 O 8 occurs via oxidation of U 4 + to U 6 + in ILs and DESs. [18,29] In this DES due to the hydrophobic nature as well as due to the absence of oxidizing agent, the oxidation reaction is hindered. Hence, UO 3 is dissolved while UO 2 and U 3 O 8 remain insoluble.…”

“…[16] Recently, Verma et al used an acidic extractant HDEHP dissolved in C 8 mimNTf 2 ionic liquid for in situ preconcentration of uranium by dissolving UO 3 into the ionic liquid but solubility was only 8 mg/mL in ionic liquid. [17] Dissolution of uranium oxides in maline DES (composed of malic acid and choline chloride) was carried out by Srivastava et al [18] Here, also viscosity of solvent was higher due to coulombic interaction within the DES. Presence of chloride ion in DES such as in Maline may affect the speciation of uranium in the DES.…”