Machine-Learning-Guided Identification of Coordination Polymer Ligands for Crystallizing Separation of Cs/Sr

Separation of Cs/Sr is one of many coordination-chemistry-centered processes in the grand scheme of spent nuclear fuel reprocessing, a critical link for a sustainable nuclear energy industry. To deploy a crystallizing Cs/Sr separation technology, we planned to systematically screen and identify candidate ligands that can efficiently and selectively bind to Sr2+ and form coordination polymers. Therefore, we mined the Cambridge Structural Database for characteristic structural information and developed a machine-learning-guided methodology for ligand evaluation. The optimized machine-learning model, correlating the molecular structures of the ligands with the predicted coordinative properties, generated a ranking list of potential compounds for Cs/Sr selective crystallization. The Sr2+ sequestration capability and selectivity over Cs+ of the promising ligands identified (squaric acid and chloranilic acid) were subsequently confirmed experimentally, with commendable performances, corroborating the artificial-intelligence-guided strategy.

Selective Separation of Radiocesium from Complex Aqueous Matrices Using Dual Solid-Phase Extraction Systems

The release of radiocesium (r-Cs) into natural aqueous systems is of concern because of its extended solubility as an alkaline metal ion and its facile incorporation into living beings. A technique for the selective separation of Cs from an aqueous matrix using dual solid-phase extraction (SPE) systems in a series is proposed in this paper. The SPEs equipped with chelates (Nobias Chelate-PA1 and Nobias Chelate-PB1), an ion-exchange resin (Nobias Ion SC-1), or macrocycles (MetaSEP AnaLig Cs-01 and MetaSEP AnaLig Cs-02) were evaluated in terms of selectivity and retention/recovery behavior toward Cs and other potentially competing ions (Li, Na, K, Rb, Ba, Ca, Mg, and Sr). The simulated solution of ¹³³Cs, a chemical analog of r-Cs, was used to optimize the separation process. Operating parameters such as pH (3-13), flow rate (0.2-5.0 mL min^-1), and elution behavior (HCl, 0.1-5.0 mol L^-1) were optimized to ensure maximum removal of Cs from the aqueous matrices. The dual SPE system comprised Nobias Chelate-PB1 that minimized the competing impact of ions, while selective Cs retention was attained with MetaSEP AnaLig Cs-02. The proposed process was verified using real r-Cs-contaminated water from Fukushima, Japan, to observe the quantitative separation and preconcentration of r-Cs from the complex matrices.

The recovery of strontium from acidic medium using novel strontium selective extractant: An experimental and DFT study

In view of the limited solvent system known for the Sr²⁺ extraction from acidic media, extraction and recovery of ⁹⁰Sr from acidic medium using novel Octabenzyloxyoctakis[[[(N,N-diethylamino)carbonyl)]methyl]oxy]calix[8]arene (BOC8A) extractant in nitro alkane medium are presented in this paper. BOC8A and nitro alkanes have been synthesized and characterized by ¹H NMR, ¹³C NMR, FTIR and GC-MS techniques. Solvent composition of 0.01 M BOC8A in nitro octane (NO) has been optimized for substantial amount of extraction of strontium from feed acidity of 3.5-4 M nitric acid, (D_{3.5-4 M HNO3} = 7.1-7.8). Poor extraction of Pu⁴⁺, Ba²⁺, Na⁺ and UO₂²⁺ and negligible extraction of Am³⁺, Cs⁺, Ru³⁺, Nd³⁺, Zr²⁺ and trivalent lanthanides are observed. Ion dissociation mechanism was found to be operative involving an extractable complex having Sr²⁺, BOC8A and HNO₃ in a ratio of 1:1:2. About 99 % of Sr²⁺ from the loaded solvent was recovered with 0.01 M HNO₃. DFT calculations were used to predict the structures of free, protonated BOC8A and its complex with Sr²⁺. DFT result showed reorientation in conformation of BOC8A due to protonation resulting in the Sr²⁺ extraction from acidic medium with significantly high interaction energy between Sr²⁺ and diprotonated form of BOC8A.

Separation of americium (III) and strontium (II) using TEHDGA and 18-crown-6

This work describes extraction of Am(III) and Sr(II) together with tetra(2-ethylhexyl) diglycolamide (TEHDGA) and selective back-extraction of strontium with a strontium complexant, 18-crown-6, leading to their separation from each other. 0.3 M TEHDGA+5% isodecyl alcohol/n-dodecane was used to extract Am(III) and Sr(II) from 4 M nitric acid into organic phase with very high D (D Am=1000, D Sr=22) and 0.1 M 18-crown-6 dissolved in 4 M nitric acid is used for selective stripping of Sr(II) from loaded extract phase. Am(III) left in the extract phase was then stripped with 0.01 M nitric acid. Stripping of Sr(II) was found to increase with increase in 18-crown-6 concentration, at 0.1 M 18-crown-6 dissolved in 4 M nitric acid, 83% of the loaded strontium (D Sr=0.20) was back-extracted in a single contact while loss of Am(III) was 0.8% (D Am=122.45). Stoichiometry limit of 1:1 was observed between strontium and 18-crown-6. Strontium was precipitated and separated from the complexant by Na2SO4 or Na2CO3. This process was tested with simulated solution of high level waste and found suitable for quantitative recovery of strontium with high purity.

Nanolayered tin phosphate: a remarkably selective Cs ion sieve for acidic waste solutions

Nanolayered tin phosphate is highly selective for Cs ions from acidic waste solutions.