Solvent Extraction of Strontium and Cesium: A Review of Recent Progress

Efficient uptake of 85Sr and 60Co using fabricated inorganic sorbent for reducing radiation doses of simulated low-level waste

The present study investigated the sorption behavior of 85Sr and 60Co radionuclides from aqueous solutions onto tin molybdate (SnMo) sorbent. SnMo has been synthesized using the precipitation method and was characterized using four analytical techniques including FT-IR, XRD, SEM, and XRF. The sorption studies applied on 85Sr and 60Co include the effect of shaking time, pH, concentration, and saturation capacity. The experimental data revealed that the sorption process was carried out after equilibrium time (180 min). The saturation capacity for 85Sr and 60Co is measured to be 58.1 and 52.2 mg g-1, respectively. The sorption behavior of studied radionuclides is dependent on pH values. Sorption kinetic better fit with the pseudo-second-order model. Furthermore, the sorption isotherm is better represented by the model proposed by Langmuir. The results of the desorption investigations indicated that the most effective eluents for achieving full recovery of investigated radionuclides were identified. Finally, the recycling results demonstrate the suitability of SnMo for affected sorbing of 85Sr and 60Co from aqueous solutions. All the obtained data clarify that the SnMo sorbent is an effective means of removing 85Sr and 60Co from liquid waste.

Fabrication of polydopamine/rGO Membranes for Effective Radionuclide Removal

In this work, a novel polydopamine/reduced graphene oxide (PDA/rGO) nanofiltration membrane was prepared to efficiently and stably remove radioactive strontium ions under an alkaline environment. Through the incorporation of PDA and thermal reduction treatment, not only has the interlayer spacing of graphene oxide (GO) nanosheets been appropriately regulated but also an improved antiswelling property has been achieved. The dosage of GO, reaction time with PDA, mass ratio of PDA to GO, and thermal treatment temperature have been optimized to achieve a high-performance PDA/rGO membrane. The resultant PDA/rGO composite membrane has exhibited excellent long-term stability at pH 11 and maintains a steady strontium rejection of over 90%. Moreover, the separation mechanism of the PDA/rGO membrane has been systematically investigated and determined to be a synergistic effect of charge repulsion and size exclusion. Results have indicated that PDA/rGO could be considered as a promising candidate for the separation of Sr2+ ions from nuclear industry wastewater.

Infrared Ion Spectroscopic Characterization of the Gaseous [Co(15-crown-5)(H2O)]2+ Complex

We report fingerprint infrared multiple-photon dissociation spectra of the gaseous monohydrated coordination complex of cobalt(II) and the macrocycle 1,4,7,10,13-pentaoxacyclopentadecane (or 15-crown-5), [Co(15-crown-5)(H2O)]2+. The metal-ligand complexes are generated using electrospray ionization, and their IR action spectra are recorded in a quadrupole ion trap mass spectrometer using the free-electron laser FELIX. The electronic structure and chelation motif are derived from spectral comparison with computed vibrational spectra obtained at the density functional theory level. We focus here on the gas-phase structure, addressing the question of doublet versus quartet spin multiplicity and the chelation geometry. We conclude that the gas-phase complex adopts a quartet spin state, excluding contributions of doublet species, and that the chelation geometry is pseudo-octahedral with the six oxygen centers of 15-crown-5 and H2O coordinated to the metal ion. We also address the possible presence of higher-energy conformers based on the IR spectral evidence and calculated thermodynamics.

Machine-Learning-Enabled Ligand Screening for Cs/Sr Crystallizing Separation

The reprocessing of spent nuclear fuel is critical for the sustainability of the nuclear energy industry. However, several key separation processes present challenges in this regard, calling for continuous research into next-generation separation materials. Herein, we propose a high-throughput screening framework to improve efficiency in identifying potential ligands that selectively coordinate metal cations of interest in liquid wastes that considers multiple key chemical characteristics, including aqueous solubility, pKa, and coordination bond length. Machine-learning models were designed for the fast and accurate prediction of these characteristics by using graph convolution and transfer-learning techniques. Suitable ligands for Cs/Sr crystallizing separation were identified through the "computational funnel", and several top-ranking, nontoxic, low-cost ligands were selected for experimental verification.

Phosphonation of Alginate-Polyethyleneimine Beads for the Enhanced Removal of Cs(I) and Sr(II) from Aqueous Solutions

Although Cs(I) and Sr(II) are not strategic and hazardous metal ions, their recovery from aqueous solutions is of great concern for the nuclear industry. The objective of this work consists of designing a new sorbent for the simultaneous recovery of these metals with selectivity against other metals. The strategy is based on the functionalization of algal/polyethyleneimine hydrogel beads by phosphonation. The materials are characterized by textural, thermo-degradation, FTIR, elemental, titration, and SEM-EDX analyses to confirm the chemical modification. To evaluate the validity of this modification, the sorption of Cs(I) and Sr(II) is compared with pristine support under different operating conditions: the pH effect, kinetics, and isotherms are investigated in mono-component and binary solutions, before investigating the selectivity (against competitor metals) and the possibility to reuse the sorbent. The functionalized sorbent shows a preference for Sr(II), enhanced sorption capacities, a higher stability at recycling, and greater selectivity against alkali, alkaline-earth, and heavy metal ions. Finally, the sorption properties are compared for Cs(I) and Sr(II) removal in a complex solution (seawater sample). The combination of these results confirms the superiority of phosphonated sorbent over pristine support with promising performances to be further evaluated with effluents containing radionuclides.

Facial vs. meridional coordination in gaseous Ni(II)-hexacyclen complexes revealed with infrared ion spectroscopy

We report fingerprint infrared multiple-photon dissociation (IRMPD) spectra of the isolated gaseous hexa-coordinated complex of the macrocycle hexa-aza-18-crown-6 (hexacyclen, 1,4,7,10,13,16-hexaazacyclooctadecane, 18-azacrown-6) with Ni2+. The metal-ligand complexes are generated using electrospray ionization (ESI) and IR action spectra are recorded in a Fourier transform ion cyclotron resonance mass spectrometer (FTICR) MS coupled to the infrared free-electron laser FELIX. We investigate geometric structure of the complexes and in particular the chelation motif, by comparison with computed vibrational spectra, obtained using density functional theory (DFT) at the B3LYP/6-31++G(d,p) level. The quasi-octahedral chelation motif of the complex has been well documented in condensed-phase studies, and we focus here on the gas-phase structure, addressing in particular the question of a facial (fac) versus a meridional (mer) octahedral chelation geometry. Based on the good agreement between calculated linear IR spectra and experimental IRMPD spectra, we conclude that the gas-phase complex adopts a mer chelation geometry and we exclude significant contribution of the fac isomer, which is computed to lie about 10 kJ mol-1 higher in energy. We also address the possible presence of both meridional diastereomers and of higher energy conformers of meridional isomers. Finally, as expected for the d8 Ni2+-ion in an octahedral ligand environment, the IR spectrum also shows that the complexes are in a high-spin electron configuration.

Isotherm, Kinetic, and Selectivity Studies for the Removal of 133Ba and 137Cs from Aqueous Solution Using Turkish Perlite

The efficiency of 133Ba and 137Cs removal from aqueous solution is vital to mitigate ecological concerns over spreading these radionuclides in the environment. The present work focused on the use of Turkish perlite for the sorptive removal of 133Ba and 137Cs from aqueous solution by the radioindicator method. Perlite was characterized by XRF, XRD, FTIR, SEM−EDX, and BET analyses. The maximum percentage removals of 88.2% and 78.7% were obtained for 133Ba and 137Cs at pH 6 and pH 9, respectively. For both ions, the sorption equilibrium was attained relatively rapidly. Experimental kinetic data were well described with pseudo-second-order and intraparticle diffusion models. The uptake of both ions increased with the increase in metal concentration (1 × 10−5 to 5 × 10−2 mol/L) in solution. The maximum uptake capacities of 133Ba and 137Cs were found to be 1.96 and 2.11 mmol/g, respectively. The effect of competing ions decreased in the order of Ca2+>K+>Ni2+>Na+ for 133Ba sorption, whereas for 137Cs sorption, the order was determined as Ca2+>Ni2+>K+>Na+. Selectivity studies pointed out that sorption of 133Ba onto perlite is preferable to 137Cs. Therefore, Turkish perlite is a promising, cost-effective, and efficient natural material for the removal of 133Ba and 137Cs from relatively diluted aqueous solution.

Highly efficient removal of strontium from contaminated wastewater by a porous zirconium phosphate material

Effective and efficient disposal of radioactive pollution has been crucial for responding to unexpected nuclear accidents and guaranteeing the sustainable development of nuclear energy. In this study, a kind of porous zirconium phosphate was synthesized with a sol-gel process followed by a post-synthesis modification to remove the radioactive Sr²⁺ from wastewater. The prepared materials were characterized by different technologies including FT-IR, SEM-EDS, XRD and XPS, and then the adsorption performance was evaluated in batch and column modes. Experimental results suggested that the porous zirconium phosphate adsorbent was successfully prepared with Na⁺ dispersed in the channels for exchange. It inherited the excellent properties of zirconium dioxide aerogel and exhibited mesoporous structure and large specific surface area. Compared with traditional zirconium phosphate, the adsorption kinetics and the adsorption capacity were improved simultaneously. Especially, it showed excellent selectivity towards Sr²⁺ among different cations, and even could remove the low-level Sr²⁺ from natural seawater efficiently, which powerfully demonstrated that the prepared material could be applied in the treatment of practical wastewater. Spectra studies uncovered that the adsorption activities were dominated by the ion exchange mechanism between external Sr²⁺ and interlaminar Na⁺ or H⁺. In conclusion, this paper not only reports a novel synthesis strategy for the acquisition of porous zirconium phosphate, but also presents a promising adsorbent for the Sr²⁺ removal.

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.

Current status and future prospects of membrane separation processes for value recovery from wastewater

Resource constraints and deteriorating environment have made it necessary to look for intensification of the industrial processes, to recover value from spent streams for reuse. The development of reverse osmosis has already established that water can be recovered from aqueous streams in a cost-effective and beneficial manner to the industries. With the development of several membrane processes and membrane materials, the possibility of recovering value from the effluents looks like a workable proposition. In this context, the potentialities of the different membrane processes in value recovery are presented. Among the pressure-driven processes, reverse osmosis can be used for the recovery of water as value. Nanofiltration has been used for the recovery of several dyes including crystal violet, congo red, methyl blue, etc., while ultrafiltration has been used in the fractionation of different solute species using membranes of different pore-size characteristics. Diffusion dialysis is found useful in the separation of acids from its salt solutions. Bipolar membrane electrodialysis has the potential to regenerate acid and base from salt solutions. Thermally driven membrane distillation can provide desalinated water, besides reducing the temperature of hot discharge streams. Passive membrane processes such as supported liquid membranes and membrane-assisted solvent extraction have been found useful in separating minor components from the wastewater streams. The details are discussed to drive home that membrane processes can be useful to achieve the objectives of value recovery, in a cost-effective manner through process intensification, as they are more compact and individual streams can be treated and value used seamlessly.

Highly Efficient Uptake of Cs+ by Robust Layered Metal-Organic Frameworks with a Distinctive Ion Exchange Mechanism

¹³⁷Cs with strong radioactivity and a long half-life is highly hazardous to human health and the environment. The efficient removal of ¹³⁷Cs from complex solutions is still challenging because of its high solubility and easy mobility and the influence of interfering ions. It is highly desirable to develop effective scavengers for radiocesium remediation. Here, the highly efficient uptake of Cs⁺ has been realized by two robust layered metal-organic frameworks (MOFs), namely [(CH₃)₂NH₂]In(L)₂·DMF·H₂O (DMF = N,N'-dimethylformamide, H₂L= H₂aip (5-aminoisophthalic acid) for 1 and H₂hip (5-hydroxyisophthalic acid) for 2). Remarkably, 1 and 2 hold excellent acid and alkali resistance and radiation stabilities. They exhibit fast kinetics, high capacities (q _m ^Cs = 270.86 and 297.67 mg/g for 1 and 2, respectively), excellent selectivity for Cs⁺ uptake, and facile elution for the regeneration of materials. Particularly, 1 and 2 can achieve efficient Cs⁺/Sr²⁺ separation in a wide range of Sr/Cs molar ratios. For example, the separation factor (SF _Cs/Sr) is up to ∼320 for 1. Moreover, the Cs⁺ uptake and elution mechanisms have been directly elucidated at the molecular level by an unprecedented single-crystal to single-crystal (SC-SC) structural transformation, which is attributed to the strong interactions between COO^- functional groups and Cs⁺ ions, easily exchangeable [(CH₃)₂NH₂]⁺, and flexible and robust anionic layer frameworks with open windows as "pockets". This work highlights layered MOFs for the highly efficient uptake of Cs⁺ ions in the field of radionuclide remediation.

A low-cost photo-evaporation inorganic membrane preparation and treatment of the simulated high salinity radioactive waste water

Solar-driven desalination is an energy-saving and environmentally benign wastewater treatment technology. A method of in situ self-reduction of graphene oxide (rGO) by cheap geopolymer was introduced, and a photo evaporation membrane device (rGOPGC) for treatment of the simulated high salt liquid radioactive waste (HSLRW) was prepared in the present study. Compared with other rGO based photo evaporation membrane materials, geopolymer matrix has the advantages of low cost, reductant free, simple preparation process and mild conditions. After desalination of simulated seawater, the concentrations of Na⁺, K⁺, Ca²⁺ and Mg²⁺ ions reached the WHO standard, and the removal rates of radioactive I^-, Cs⁺ and Sr²⁺ in the simulated high salinity wastewater reached 99.62%, 99.71% and 99.99% respectively; The evaporation rate of rGOPGC remained stable at 1.5 kg/m²/h after 16 cycles in high salinity environment. There was no obvious salt accumulation on the upper surface of the device, indicating its high stability. Furthermore, the evaporation performance at high temperature near the nuclear power plant (NPP) waste water was simulated and tested. Under one solar intensity and 35 °C ambient temperature, the evaporation rate of 1.75 kg/m²/h and the evaporation efficiency of 98.51% were achieved. The results indicated that the rGOPGC device is potential in the concentration evaluation of HSLRW.

Sr(ii) extraction by crown ether in HFC: entropy driven mechanism through H2PFTOUD

The solvent extraction of Sr(ii) was carried out using dicyclohexano-18-crown-6 (DCH18C6) and two HFC mixed solvents MS1 and MS2, where MS1 was composed of 30/60 (w/w)% trans-1,2-dichloroethylene/HFC-43 (HFC-43: 1,1,1,2,2,3,4,5,5,5-decafluoropentane) and MS2 was 5/95 (w/w)% heptane/HFC-43. Nitric acid and perfuruoro-3-6-9-trioxaundecane-1,11-dioic acid (H₂PFTOUD) were used to study the effect of acid on the extraction. The maximum distribution ratio of Sr(ii) (D_Sr) observed for H₂PFTOUD conditions was ∼180, and >10 times larger than aqueous nitric acid conditions. The D_Sr value was influenced by concentrations of the DCH18C6, Sr(ii), and acid, and by temperature. The composition of extracted complexes was estimated using slope analysis as an Sr(ii)–anion–DCH18C6 ratio of ∼1 : 2 : 1. From the extended X-ray absorption fine structure (EXAFS) measurements of Sr(ii) in the aqueous and organic phases, it is inferred that regardless of the acid used, DCH18C6 coordinates to the first coordination sphere of the Sr(ii) extracted complexes and Sr(ii) is hydrated (complexation with H₂PFTOUD cannot be distinguished) in the aqueous phase. Thermodynamic data were significantly changed by choice of acid, i.e., both enthalpy and entropy values were negative for nitric acid conditions, on the other hand, entropy values were large and positive for H₂PFTOUD conditions. These results have demonstrated that the combination of HFC solvent and crown ether is applicable for metal extraction.

The solvent extraction of Sr(ii) was carried out using DCH18C6, and two HFC mixed solvents composed of organic solvents and HFC-43 (HFC-43: 1,1,1,2,2,3,4,5,5,5-decafluoropentane), and two acids (nitric acid and H₂PFTOUD).

Kilo-scale synthesis and purification of 4,4′-[di-t-butyldibenzo]-18-crown-6 and its catalytic reduction to 4,4′-[di-t-butyldicyclohexano]-18-crown-6

This article reports the large scale synthesis, scale up chromatographic purification and Rh catalyzed hydrogenation of DTBDB18C6. Confirmation of molecular structure was done by SCXRD and complete hydrogenation was achieved with the use of K+ ions.

High-Efficiency Separation of Mg2+/Sr2+ through a NF Membrane under Electric Field

The efficient separation of Sr²⁺/Mg²⁺ through nanofiltration (NF) technology is a great challenge because Sr²⁺ and Mg²⁺ ions are congeners with the same valence and chemical properties. In this work, an NF membrane under an electric field (EF) was successfully employed to separate Mg²⁺ and Sr²⁺ ions for the first time. The effects of current densities, Mg²⁺/Sr²⁺ mass ratios, pH of the feed, and coexisting cations on separation performance were investigated. Dehydration of Sr²⁺ or Mg²⁺ ions under EF was proved by molecular dynamics simulation. The results showed that a high-efficient separation of Mg²⁺/Sr²⁺ was achieved: Mg²⁺ removal of above 99% and increase in Sr²⁺ permeation with increasing EF. A separation factor reached 928 under optimal conditions, far higher than that without EF. The efficient separation of Mg²⁺/Sr²⁺ ions was mainly due to rejection of most Mg²⁺ ions by NF membrane and in situ precipitation of partly permeated Mg²⁺ ions by OH⁻ generated on the cathode under EF. Meanwhile, preferential dehydration of Sr²⁺ ions under EF due to lower hydration energy of Sr²⁺ compared with Mg²⁺ resulted in an increase of permeation of Sr²⁺ ions. This work provided a new idea for separation of congener ions with similar valence and chemical properties.

Sorbent extraction behavior of cesium and strontium from nitric acid solutions using a new high thermal stability material

In this study a new low-cost carbonaceous material was prepared from husks of opuntia-ficus-indica as a starting material (precursor) which was accomplished by chemical activation route using H₃PO₄ impregnation. The material has been identified by different analytical tools. The sorption performance of Cs(I) and Sr(II) from HNO₃ solutions was examined through batch system. Variations of the distribution coefficients (K_d) as a function of HNO₃ concentration in the range 0.001-5.0 M were presented. Some of separation probabilities were suggested. The results attained signals that the Sr(II) selectivity is higher than that of Cs(I) at high molarities. The retention capacity (q_e) of Cs(I) and Sr(II) ions increased with growing temperature. The capacities at 0.001 M HNO₃ are 34 and 108 mg/g for Cs(I) and Sr(II), respectively. Whereas, at 2.0 M HNO₃ capacities were about 4 and 37 mg/g for each of Cs(I) and Sr (II), respectively. This studies demonstrates that the prepared carbonaceous sorbent is an economically effective sorbent for retention of Cs(I) and Sr(II) species from HNO₃ solutions. Cs(I) and Sr(II) removal potential was tested from simulated low- and intermediate-level radioactive waste samples.

Application of response surface method in the separation of radioactive material: a review

Response Surface Method (RSM) is one of the most popular and powerful tools for experimental design and optimization. This paper first reviewed the research progress of RSM in the separation and recovery of various radioactive materials, and verified the application of RSM in adsorption isotherm analysis and thermodynamic calculation. The main advantage of RSM in radioactive material separation is the reduction in the number of experiments required, resulting in considerably less radioactive material consumption, secondary waste generation, workload and radiation dose, which is valuable for the research of radioactive material separation.

Achieving highly efficient and selective cesium extraction using 1,3-di-octyloxycalix[4]arene-crown-6 in n-octanol based solvent system: experimental and DFT investigation

Due to the long half-life of ¹³⁷Cs (t_1/2 ∼ 30 years), the selective extraction of cesium (Cs) from high level liquid waste is of paramount importance in the back end of the nuclear fuel cycle to avoid long term surveillance of high radiotoxic waste. As 1,3-di-octyloxycalix[4]arene-crown-6 (CC6) is suggested to be a promising candidate for selective Cs extraction, the improvement in the Cs extraction efficiency by CC6 has been investigated through the optimization of the effect of dielectric media on the extraction process. The effects of the feed acid (HNO₃, HCl, and HClO₄) and the composition of the diluents for the ligand in the organic phase on the extraction efficiency of Cs have been investigated systematically. In 100% n-octanol medium, Cs is found to form a 1 : 1 ion-pair complex with CC6 (0.03 M) providing a very high distribution ratio of D_Cs ∼ 22, suggesting n-octanol as the most suitable diluent for Cs extraction. No significant interference of other relevant cations such as Na, Mg and Sr was observed on the D_Cs value in the optimized solvent system. Density functional theory (DFT) based calculations have been carried out to elucidate the reason of ionic selectivity and enhanced Cs extraction efficiency of CC6 in the studied diluent systems. In addition to the ionic size-based selectivity of the crown-6 cavity, the polarity of the organic solvent system, the hydration energy of the ion, and the relative reorganization of CC6 upon complexation with Cs are understood to have roles in achieving the enhanced efficiency for the extraction of Cs by the CC6 extractant in nitrobenzene medium.

Separation scheme was developed for selective extraction of long-lived fission product ¹³⁷Cs using substituted calix crown 6 ether from aqueous acidic solution.

An asymmetric pulsed current-assisted electrochemical method for Sr(Ⅱ) extraction using supramolecular composites

The development of effective, economical, and sustainable seawater extraction strontium techniques is of great significance to the environment and industrial needs. In this paper, an asymmetric pulsed current-assisted electrochemical (AP-CE) method was used to extract Sr(Ⅱ) from seawater using a carbon electrode modified by dibenzo-18-crown-6-ether and cellulose acetate. An asymmetric pulsed current was used to prevent unwanted cations from blocking adsorption sites to prevent water splitting. It also prevented the cellulose acetate membrane from sealing the crown ether. Compared with traditional physicochemical adsorption of Sr(Ⅱ), the AP-CE method achieved a higher removal efficiency and adsorption capacity. When the concentrations of Sr(Ⅱ) were 10, 20, 50, and 100 mg L^-1, the removal efficiencies of Sr(Ⅱ) were 99.3%, 97.6%, 97.3%, and 96.1%, and the adsorption capacities of Sr(Ⅱ) were 14.9, 29.3, 73.0, and 144.2 mg g^-1, respectively. This method exhibited excellent selectivity for Sr(Ⅱ) adsorption from simulated seawater, suggesting that the asymmetric pulse electrochemical method is promising for extracting strontium ions from seawater.

Synergistic effect of carboxyl and sulfate groups for effective removal of radioactive strontium ion in a Zr-metal-organic framework

Rapid removal of radioactive strontium from nuclear wastewater is of great significance for environmental safety and human health. This work reports the effective adsorption of strontium ion in a stable dual-group metal-organic framework, Zr₆(OH)₁₄(BDC-(COOH)₂)₄(SO₄)_0.75 (Zr-BDC-COOH-SO₄), which contains strontium-chelating groups (-COOH and SO₄) and a strongly ionizable group (-COOH). Zr-BDC-COOH-SO₄ exhibits very rapid adsorption kinetics (<5 min) and a maximum adsorption capacity of 67.5 mg g^-1. The adsorption behaviors can be well fitted to the pseudo-second-order model and the Langmuir isotherm model. Further investigations indicate that the adsorption of Sr²⁺ onto Zr-BDC-COOH-SO₄ would not be obviously affected by solution pH and adsorption temperature. The feasible regeneration of the adsorbent was also demonstrated using a simple elution method. Mechanism investigation suggests that free -COOH contributes to the rapid adsorption based on electrostatic interaction, while the introduction of -SO₄ significantly enhanced the adsorption capacity. Thus, these results suggest that Zr-BDC-COOH-SO₄ is a potential candidate for Sr²⁺ removal. They also introduce dual groups as an effective strategy for designing high-efficiency adsorbents.

Macrocyclic Pyridone Pentamers for Highly Selective High-Capacity Removal of Caesium Ions from Radioactive High-Salinity Waste

We report here that macrocyclic H-bonded pyridone pentamers, containing five properly and convergently spaced electron-rich O-atoms that decorate a rigid cavity of 2.85 Å across, exhibit an extraordinarily high yet pH-independent capacity and selectivity in Cs⁺ removal. In particular, with [host]=240 μM and [Cs⁺ ]=15 μM, a single extraction efficiently removes more than 91% of Cs⁺ ions from artificial sea water, containing various competitive metal ions at a total concentration of 0.68 M ([total Mⁿ⁺ ]/[Cs⁺ ]=4.5×10⁴ ]). To our best knowledge, these pyridone pentamers represent the best small organic molecule-based extractants that target Cs⁺ ions.

Rapid solidification of Portland cement/polyacrylamide hydrogel (PC/PAM) composites for diverse wastewater treatments

Cementitious solidification is an effective but time-consuming method for waste disposal, and the incorporation of polyacrylamide hydrogel in Portland cement paste is a simple way to enhance the time-efficiency of cementitious solidification. In this study, a series of Portland cement/polyacrylamide hydrogel (PC/PAM) composites suitable for the wastewater treatment were prepared by a one-pot method and their time-dependent reaction processes, mechanical properties and microstructures were tested. Based on the gelation time method, PC/PAM composites showed great solidification efficiency when treating simulated radioactive liquids, organic dye waste and solutions with strong alkalinity and acidity. At temperatures ranging from 5 °C to 40 °C, it took only a few minutes for these composites to solidify wastes. Also, PC/PAM composites containing wastes had a compressive strength that is more than 2 MPa after reacting for 3 days and were suitable for landfill or secondary treatments. The rapid gelation and sufficient strength development demonstrated that PC/PAM composites have great potential for application in solidifying multi-component wastes, especially in some emergency circumstances.

Novel and stable PC/PAM composites were designed and could serve as a matrix for rapid solidification of various wastewaters, greatly facilitating the applicability of the cementitious solidification method in emergency circumstances.

Synthesis of Metal-Organic Framework ZnO x -MOF@MnO2 Composites for Selective Removal of Strontium Ions from Aqueous Solutions

A Zn(II)-based metal-organic framework (MOF) compound and MnO2 were used to prepare ZnO x -MOF@MnO2 composites for selective Sr2+ removal in aqueous solutions. The ZnO x -MOF@MnO2 composites were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and Brunauer-Emmett-Teller surface area analysis. The functional groups, morphologies, thermal stabilities, and specific surface areas of the composites were suitable for Sr2+ adsorption. A maximum adsorption capacity of 147.094 mg g-1 was observed in batch adsorption experiments, and the sorption isotherms were fit well by the Freundlich model of multilayer adsorption. Adsorption reached equilibrium rapidly in kinetic experiments and followed the pseudo-second-order kinetic model. The adsorption capacity of the ZnO x -MOF@MnO2 composite with the highest MnO2 content was high over a wide pH range, and the composite was highly selective toward Sr2+ in solutions containing coexisting competing ions. Also, it has a good reusability for removing Sr2+.

Prussian blue-embedded carboxymethyl cellulose nanofibril membranes for removing radioactive cesium from aqueous solution

In this study, we synthesized a Prussian blue (PB)-embedded macroporous carboxymethyl cellulose nanofibril (CMCNF) membrane for facile cesium (Cs) removal. The PB was formed in situ at Fe³⁺ sites on a CMCNF framework cross-linked using FeCl₃ as a cross-linking agent. Cubic PB particles of size 5-20 nm were observed on the macroporous CMCNF membrane surface. The PB-CMCNF membrane showed 2.5-fold greater Cs adsorption capacity (130 mg/g_PB-CMCNF) than commercial PB nanoparticles, even though the PB loading of the PB-CMCNF membrane was less than 100 mg/g_PB-CMCNF. The macroporous structure of the CMCNF membrane led to improved diffusion in the solution, thereby increasing the Cs adsorption capacity. The Cs adsorption behavior was systematically investigated in different solution chemistry. Finally, ¹³⁷Cs removal using a semicontinuous adsorption module was demonstrated in real seawater. The results showed that the PB-CMCNF membrane is a highly effective, practical material for the removal of ¹³⁷Cs from aqueous environments.

Selective Cesium Adsorptive Removal on Using Crosslinked Tea Leaves

To remove the radioactive cesium from the polluted environment, tea leaves were chosen as cheap, and abundantly available environment-friendly bio-adsorbents to investigate the alkali metals adsorption. Fresh and used tea leaves (FT and UT) were found to have high efficiency and selectivity for cesium adsorption, after the crosslinking with concentrated sulfuric acid. Calculation of the proton-exchanged amount suggested adsorption mechanism of three alkali metals on crosslinked tea leaves involve a cationic exchange with a proton from the hydroxyl groups of the crosslinked tea leaves, as well as coordination with ethereal oxygen atoms to form the chelation. Further, considering the practical application of the polluted water treatment, the competitive adsorption of Cs+ and Na+ ions was investigated by the batch-wise method and column chromatography separation. Unlike the conventional ion exchange and chelate resins with less selectivity for Cs+ coexisting cations, both crosslinked fresh tea leaves (CFT) and crosslinked used tea leaves (CUT) exhibited Cs selectivity over Na. In addition, batch adsorption studies revealed that the cesium adsorptions were driven by the Langmuir isotherm model; the capacity of both crosslinked tea leaves for cesium adsorption was determined to be around 2.5 mmol g−1. The adsorption capacities are sufficiently higher in comparison with those of synthetic polymers, inorganic ion-exchangers, and other bio-adsorbents.

Studies on purification of 89Sr from irradiated yttria target by multi-column extraction chromatography using DtBuCH18-C-6/XAD-7 resin

89Sr is being produced using yttria target via the nuclear reaction 89Y(n,p)89Sr in Fast Breeder Test Reactor (FBTR), Kalpakkam. The isotope 89Sr is a pure beta emitter with a half-life of 50.53 days which is useful mainly for bone pain palliation in patients with bone metastases. The existing method for processing the irradiated yttria target to obtain the pure 89Sr source involves separation of the bulk yttrium target by solvent extraction using TBP-HNO3 followed by purification of 89Sr source by cation exchange chromatography technique using Dowex resin. The study described here involves the selective extraction and purification of 89Sr by multi-column extraction chromatography technique using the Sr-specific crown ether, DtBuCH18C6 (CE) coated onto an XAD-7 resin matrix for superior separation and increased yield compared to single column technique. The 89Sr source thus purified from the irradiated yttria target is free from other radionuclidic impurities produced during the target irradiation i.e. 88Y, 65Zn, 139,141Ce, 154Eu and 160Tb.