Nuclear Waste Solutions Research Articles

Uptake of uranium(VI) upon a novel developed nanocomposite of bimetallic Mg/Mn bentonite lupine peels

In this work, a new green nanocomposite material was synthesized, characterized, and implemented for the removal of Uranium(VI) from nuclear waste solution. The nanocomposite material consisted of bimetallic Mg/Mn-Tartaric intercalated with bentonite and functionalized with lupine peel biochar through a refluxing process with a mixed solution of water and formaldehyde (3:1). The synthesized nanocomposite and the pristine materials were characterized using FTIR, and XRD, and the thermal stability of all the components was investigated using TGA. Finally, the morphology of the synthesized materials was investigated using SEM images. The adsorption was studied through different parameters: different pH values, sorption time, different amounts of sorbent, and different uranium concentrations. In addition to the adsorption studies, the desorption studies and the elution process were also investigated. It was found that the maximum adsorption value at pH 4.0 and 60.0 min as about 113.90 mg·g−1, the kinetics fit with pseudo second-order, and the adsorption was fitted with the Langmuir model. Finally, the desorption study was established, and the effective eluting agent was Na2CO3, with an elution efficiency of about 97.4 %.

Efficient capture of ReO4−/TcO4− on anion exchange resin from wastewater

It is still a challenge to capture TcO4− from wastewater due to its nature of non-complexing and radioactive. Herein, two types of anion exchange resins (D201 and IRA-410 resin) were selected and explored the adsorption properties for perrhenate (ReO4−, as a surrogate for TcO4−). It is found that both D201 and IRA-410 resin exhibited fast adsorption kinetic (within 120 min), and superior adsorption capacities, which could reach 671.1 mg g−1 and 561.8 mg g−1 for D201 and IRA-410 resin, respectively. In addition, D201 and IRA-410 resin showed excellent adsorption selectivity for ReO4− in the presence of a variety of 1000-fold competing anions (NO2−, Cl−, SO42−, and PO43−). Importantly, the two resins still demonstrated outstanding performance after acid/alkaline soaking, calcination procedures as well as high doses of ionizing radiation, they also could remove ReO4− from simulated Hanford and SRS wastewater by automatic separation system. Finally, the anion-exchange mechanism was revealed by characterization and DFT. This work demonstrates that D201 and IRA-410 resin are efficient adsorbents for 99Tc removal from nuclear wastewater and provides a basis for designing other novel anion exchange materials for capturing ReO4− and TcO4−.

BHOEOCC6/n-dodecane: A new solvent extraction media for Cs removal from nuclear waste without using any phase modifier

Modifier-free diluent is most advantageous in hydrometallurgical route for separation of any radioactive element from high level liquid waste (HLLW). However there is not even a single calix crown reported in the literature that is soluble in pure n-dodecane and shows very high Cs extraction from such high nitric acid condition of 4.0 M prevalent in HLLW. Herein we designed a new calix crown-6-ether with an aim to reduce polarity so as to increase solubility in n-dodecane for extraction of Cs by density functional theory (DFT). The theoretically designed calix crown has been synthesised by introducing two 2-(hexyloxy)ethoxy alkyl arms at 1, 3 position calix[4]-arene framework and abbreviated as BHOEOCC6. Characterisation of BHOEOCC6 was carried out using 1H NMR, 13C NMR, and ESI-MS etc. techniques. 0.1 M BHOEOCC6/n-dodecane mixture shows exceptionally high stability as well as high Cs extraction ability (DCs = 10.75 @ 4.0 M HNO3) from highly acidic nuclear waste solution. The mechanism and interaction of Cs with BHOEOCC6 were also probed by experimental distribution ratio studies and instrumental techniques of UV–VIS titration and NMR studies of Cs-BHOEOCC6 complex.

An Aryl-ether-linked Covalent Organic Framework Modified with Thioamide Groups for Selective Extraction of Palladium from Strong Acid Solutions.

Efficient adsorption of palladium ions from acid nuclear waste solution is crucial for ensuring the safety of vitrification process for radioactive waste. However, the limited stability and selectivity of most current adsorbents hinder their practical applications under strong acid and intense radiation conditions. Herein, to address these limitations, we designed and synthesized an aryl-ether-linked covalent organic framework (COF-316-DM) grafted dimethylthiocarbamoyl groups on the pore walls. This unique structure endows COF-316-DM with high stability and exceptional palladium capture capacity. The robust polyarylether linkage enables COF-316-DM to withstand irradiation doses of 200 or 400 kGy of β/γ ray. Furthermore, COF-316-DM demonstrates fast adsorption kinetics, high adsorption capacity (147 mg g-1 ), and excellent reusability in 4 M nitric acid. Moreover, COF-316-DM exhibits remarkable selectivity for palladium ions in the presence of 17 interference ions, simulating high level liquid waste scenario. The superior adsorption performance can be attributed to the strong binding affinity between the thioamide groups and Pd2+ ions, as confirmed by the comprehensive analysis of FT-IR and XPS spectra. Our findings highlight the potential of COFs with robust linkers and tailored functional groups for efficient and selective capture of metal ions, even in harsh environmental conditions.

Highly efficient and selective 99TcO4 – uptake from reprocessing low-level liquid waste using a zirconium-based metal−organic framework

ABSTRACT Efficient and selective sequestration of pertechnetate ions (99TcO4 –) from nuclear low-level waste (LLW) solution is very much desirable for the safe treatment of radioactive liquid waste. However, the separation of specific radionuclides from competitors is a huge challenge in separation science. In the nuclear fuel cycle, 99TcO4 – is one of troublesome fission products due to long half-life, large inventory in spent fuel, significant radiation hazards, and high environmental mobility of 99TcO4 – ions. Recently, the metal−organic framework (MOFs) has shown significant potentials toward 99TcO4 – removal. So far, most of the studies were reported using ReO4 – ions, an inactive surrogate of 99TcO4 – ions, and very few MOF materials are applied for real-time 99TcO4 – sequestration from nuclear waste solution in the presence of extreme conditions. Herein, we report 99TcO4 – ion removal from low-level liquid nuclear waste solution using zirconium-based metal−organic framework UIO-66-NH2. The material has exhibited fast kinetics and record selectivity toward 99TcO4 – ions, making the adsorbent highly promising.

Highly efficient and selective adsorption of palladium(II) from simulated nuclear waste solution using Amberlite XAD-7 resin impregnated with a phenanthroline-derived diamide

The increasing demand and limited natural resources for rare precious metal palladium render its separation and recovery from secondary sources such as acidic nuclear liquid waste greatly interesting. Herein, a novel Et-Tol-DAPhen extraction resin was prepared by impregnating Amberlite XAD-7 resin with a phenanthroline-derived diamide extractant N,N′-diethyl-N,N′-ditolyl-2,9-diamide-1,10-phenanthroline (Et-Tol-DAPhen), and the adsorption behavior of this new extraction resin towards Pd2+ in HNO3 solution was investigated through the batch and column experiments. The Et-Tol-DAPhen extraction resin exhibited strong adsorbability, high adsorption capacity, excellent selectivity and good reusability for Pd2+ in highly acidic HNO3 solution. In addition, the pseudo-second-order and Langmuir models were applied to understand the adsorption process of Pd2+ on Et-Tol-DAPhen extraction resin, respectively. It demonstrated the characteristics of a uniform single-layer chemisorption. The maximum uptake capacity could reach as high as 74.6 mg g−1 for Pd2+ in 3.0 mol/L HNO3 solution which is much higher than most adsorbent materials of palladium reported before. Furthermore, Et-Tol-DAPhen extraction resin could selectively uptake Pd2+ from a simulated acidic nuclear waste solution containing 20 different kinds of ions with the separation factor SFPd/M values as high as 100 to 10,000. Moreover, although the adsorption efficiency had a slight decrease after 5 times of adsorption-desorption process, it still remained at a high level. This new extraction resin displayed a potential application prospect in the field of separation and recovery of Pd2+ from acidic nuclear liquid waste.

Facile Preparation of Macro-Microporous Thorium Oxide via a Colloidal Sol-Gel Route toward Safe MOX Fuel Fabrication.

The identification of new colloidal sol-gel routes for the preparation of actinide oxides, which have a homogeneous and accessible porosity that can easily be impregnated by any concentrated actinide solution, opens new perspectives for the preparation of homogeneous nuclear fuel for minor actinide transmutation. This homogeneity allows us to avoid "hot spot" formation due to the local accumulation of more fissile elements. Here, we report the preparation of macro-microporous ThO2 materials by a colloidal sol-gel route. Using a thorium salt with 6-aminocaproic acid as a complexing agent at a controlled pH, we were able to pilot the condensation of thorium hydroxo species forming colloids of tuned nanometric size and thus the sol stability. After a freeze-drying process to concentrate colloids and a thermal treatment allowing complexing agent removal and macroporosity formation by a brutal gas release during combustion, a loose packing of ThO2 nanoparticles with an ordered distribution of interparticular porosity and a fraction of nanometric crystallites, whose size depends on the initial colloidal size, were obtained. The sols, pastes, and final materials were characterized by small- and wide-angle X-ray scattering to determine the colloidal size and the final structure of the materials, which was also confirmed by transmission electron microscopy. The most promising material was finally successfully impregnated by a simulating minor actinide solution and thermally treated to prepare a mixed actinide oxide material. This safe technology, relying on the colloidal sol-gel process and the formulation of complex fluids forming tunable precursors, opens new perspectives for the reuse of nuclear waste solutions as new fuel.

Understanding the coordination behavior of quaternary ammonium and phosphonium nitrate ionic liquids under gamma irradiation: A combined spectroscopic investigation

In the process of spent nuclear fuel reprocessing, it is very essential to investigate the radiation stability of the extracting phase.From the ionic liquid (IL) family, quaternary ammonium or phosphonium based ILs: methyltrioctylammonium nitrate ([N1888][NO3]) or trihexyl(tetradecyl)phosphonium nitrate ([P66614][NO3]) have many commendable features while being used as the solvent for the extraction and separation of the target metal ions from nuclear waste solution. In this context, a comparative investigation on the irradiation effect on the stability of [N1888][NO3] and [P66614][NO3] and their coordination ability towards acid and metal ion was furnished systematically. A marginal change in the extraction ability was acquired upon irradiation. The spectroscopictechniques such as UV–Visible, ATR-FTIR and fluorescence spectroscopy were employed to deduce the intrinsic role of the applied dose. The peak at ∼ 260 nm in UV–Visible spectra is broadened and red shifted upon irradiation for both ILs with substantial shift in [P66614][NO3]. FTIR spectra suggests the appearance of new peaks at 752 cm−1 upon radiation exposure for both ILs indicating the formation of degraded products of NO3– ion (bending vibration of NO2. radical) and - CH2 group (cleavage of - H. radical). A remarkable difference in the peak intensity and shape for [P66614][NO3] as compared to [N1888][NO3] confirms the radiation tolerance level of two ILs. For both irradiated and unirradiated ILs, the presence of water coordination was confirmed due to the peak at (bending mode of H2O), which later showed blue shift upon metal (or acid) loading.Luminescence patterns of Eu(III) in the irradiated ILs realizes an adequate quenching of Eu(III) emission in [P66614][NO3] in comparison to [N1888][NO3] which was less affected by the radiation. In all the spectroscopic evidences specify the vital role of NO3– anion in altering the radiation stability of ILs.

Chromium enriched peraluminous glasses: Incorporation limit, crystalline phase equilibrium and impact of chromium on the rheological properties of the glass

Chromium is a multivalent element with very low solubility in silica-based glasses. It is incorporated into glass via the solubilisation of Cr2O3 as Cr3+ through an acido-basic reaction, and is in redox equilibrium with Cr6+ and Cr2+ oxidation states depending on the surrounding atmosphere. The least soluble form of chromium is Cr3+, which is also the most common form of chromium in glass elaborated in air. This study investigated the behavior of chromium in peraluminous glasses, which are potential matrices for nuclear waste containment. Chromium is often present in nuclear waste solutions as a corrosion product coming from the waste reprocessing steps. Consequently, it is important to understand the effect of chromium addition to peraluminous glasses, both in terms of the microstructure and the processing ability of the glass melt. The study investigated the effect of chromium added as a Cr2O3 chromium (+III) oxide on the homogeneity, the viscosity, and the glass transition temperature (Tg) of peraluminous glasses. The chromium redox state and its effect on the incorporation limit of chromium was determined. Peraluminous glasses have an incorporation limit of between 0.50 and 0.55 wt% Cr2O3 in air, and between 1.25 and 1.50 wt% Cr2O3 in a reducing environment. Chromium (+III) oxide was found to have a limited effect on the viscosity of peraluminous glasses up to 2 wt% of Cr2O3, despite the presence of crystals above 0.5 wt%. The addition of chromium oxide had no significant effect on the Tg of the glass, except after a slow cooling of the sample containing the highest content of 2.0 wt% Cr2O3. Two forms of chromium were identified under UV-visible spectroscopy for the glasses elaborated in air: Cr3+ (6-fold) and Cr6+ (4-fold).

Efficient enrichment of U(VI) by two-dimensional layered transition metal carbide composite

Abstract With the rapid development of nuclear energy, how to safely and efficiently dispose of radioactive waste solution has become an urgent environmental problem of public concern. It is of great significance to construct a new type of high-efficiency adsorbent material to recover uranium from nuclear waste solution. In this work, the Ti3C2Tx material (an emerging two-dimensional inorganic layered material) with a stable layered structure was used as the matrix, and the amidoxime functionalized MXene composite material (PAO/Ti3C2Tx) was synthesized by in-situ polymerization. The amidoxime-functionalized Ti3C2Tx showed excellent capacity to capture U(VI), with a maximum adsorption capacity of 98.04 mg/g at 25 °C, which was significantly better than that of Ti3C2Tx, and the adsorption selectivity for U(VI) was greatly improved. The adsorption was conformed to Langmuir isotherm model and pseudo-second-order kinetic model. In addition, the adsorbed UO22+ could be effectively desorbed by 0.1 M HNO3, and the adsorption performance of PAO/Ti3C2Tx did not decrease significantly after 5 adsorption/desorption cycles. The results of ionic strength experiment, FT-IR, SEM, and XPS jointly indicated that adsorption mechanism of U(VI) on PAO/Ti3C2Tx was the combined effect of the amidoxime group and -O and -OH active groups on the surface of Ti3C2Tx, mainly inner complexation. These advantages make PAO/Ti3C2Tx composite a highly potential U(VI) adsorbent with great application prospects.

Precise recognition of palladium through interlaminar chelation in a covalent organic framework

<h2>Summary</h2> Palladium isotopes as fission products in used nuclear fuel represent precious alternative resources besides its natural reserves and therefore have a high extraction value. The practical use of currently proposed solvent extraction is challenging, originating from the limited stability and separation selectivity of the extractants under harsh reprocessing conditions. Herein, we present an interlayer synergistic binding strategy, a metal-recognition manner deviating from chelation within a single ligand molecule in solvent extraction, for selective palladium chelation in a covalent organic framework. The experimental, structural, and theoretical analyses corroborate that the enol-to-keto tautomerization leads to selective synergistic chelation of Pd²⁺ instead of other undesired metal ions, where two oxygen donors from adjacent layers and two free nitrate ions work together in a planar tetracoordination model. Fast adsorption kinetics, high adsorption capacity, and one-round enrichment of Pd²⁺ from the simulated high-level nuclear waste solution are unprecedentedly achieved in the dynamic breakthrough experiment.

Direct single-step synthesis of phase pure zeolite Na–P1, hydroxy sodalite and analcime from coal fly ash and assessment of their Cs+ and Sr2+ removal efficiencies

Combustion by-products of coal from thermal power plants cause environmental pollution; efforts are made to develop techniques and green processes that could reduce the waste volume and convert the waste to useful materials. Synthesis of phase pure zeolites from coal fly ash and its use as adsorbent and ion exchangers to remove Cs+ and Sr2+ from simulated nuclear waste solutions is the focus of the current study. Zeolite Na–P1, hydroxy sodalite and analcime were synthesized from fly ash obtained from an Indian thermal power plant by using hydrothermal method. Zeolite synthesis conditions were optimized by studying the effect of concentration of NaOH solution, homogenization time, hydrothermal temperature and time. The zeolite phase formation, surface morphology, thermal stability studies were carried out by XRD, SEM, TG-DTA techniques; specific surface area was determined by BET analysis. Crystalline pristine zeolite Na–P1 was prepared from fly ash on reaction with 1 M NaOH at 150 °C. Similarly, hydroxy sodalite and analcime were also synthesized from the fly ash by hydrothermal reaction with 3 M NaOH at 150 °C and 5 M NaOH at 200 °C respectively. The removal efficiencies of synthesized zeolites were investigated with aqueous simulated nuclear waste solutions containing Cs+ and Sr2+. The adsorption capacities and cation exchange capacity (CEC) of zeolite Na–P1, hydroxy sodalite and analcime for Cs+ and Sr2+ ions were demonstrated. The results show the adsorption capacity of Na–P1 for Cs+ is 39.3 mg/g and for Sr2+ is 92.48 mg/g respectively and is a better adsorbent than analcime and hydroxy sodalite.

Technetium(I) Carbonyl Chemistry with Small Inorganic Ligands.

[Tc(OH2)(CO)3(PPh3)2](BF4) has been used as a synthon for reactions with small inorganic ligands with relevance for the treatment of nuclear waste solutions such as nitrate, nitrite, pseudohalides, permetalates (M = Mn, Tc, Re), and BH4-. The formation of bond isomers and/or a distinct reactivity has been observed for most of the products. [Tc(NCO)(CO)3(PPh3)2], [Tc(NCS)(CO)3(PPh3)2], [Tc(CN)(CO)3(PPh3)2], [Tc(N3)(CO)3(PPh3)2], [Tc(NCO)(OH2)(CO)2(PPh3)2], [Tc(η2-OON)(CO)2(PPh3)2], [Tc(η1-NO2)(CO)3(PPh3)2], [Tc(η2-OONO)(CO)2(PPh3)2], [Tc(η1-ONO2)(CO)3(PPh3)2], [Tc(η2-OO(CCH3))(CO)2(PPh3)2], [Tc(η2-SSC(SCH3))(CO)2(PPh3)2], [Tc(η2-SSC(OCH3))(CO)2(PPh3)2], [Tc(η2-SSC(CH3))(CO)2(PPh3)2], [Tc(η2-SS(CH))(CO)2(PPh3)2], [Tc(OTcO3)(acetone)(CO)2(PPh3)2], [Tc(OTcO3)(CO)3(PPh3)2], and [Tc(η2-HHBH2)(CO)2(PPh3)2] have been isolated in crystalline form and studied by X-ray crystallography. Additionally, the typical reactivity patterns (isomerization, thermal decomposition, hydrolysis, or decarbonylation) of the products have been studied by spectroscopic methods. 99Tc NMR spectroscopy has proved to be a particularly useful tool for the evaluation of such reactions of the diamagnetic technetium(I) compounds in solution.

Polyphosphate‐Grafted Fe3O4 Nanomagnets for the Removal of Trivalent Radionuclides from Acidic Nuclear Waste Solution

AbstractThe removal of radionuclides from nuclear waste solution is one of the biggest environmental challenges in today's world. In this aspect, polyphosphate grafted Fe3O4 nanomagnets (PPNMs) were investigated for its efficiency in removal of trivalent radionuclides from acidic nuclear waste solution. Various characterization techniques like XRD, FTIR, TEM and DLS were used to characterize these PPNMs, which showed successful formation of single phase, polyphosphate functionalized aqueous stable Fe3O4 nanostructure with average size ∼10 nm. The kinetics of sorption for Am(III) and Eu(III) by the PPNMs was found to be very fast with equilibrium being attained within ∼5 min. The sorption of both the radionuclides was following pseudo second order kinetic model. With increasing pH of the solution, the sorption efficiency of PPNMs for both the radionuclides was found to increase, whereas it decreased with increasing ionic strength of the medium. These observations clearly suggested that the sorption process proceeds through electrostatic interaction between the nanomagnets and trivalent radionuclides. Moreover, the PPNMs retained their sorption efficiency for at least 10 successive cycles when desorbed with 0.2 M HNO3. Thus, these magnetic nanosorbents can be used as highly effective, separable and reusable materials for removal of trivalent radionuclides from acidic nuclear waste solution.

Demonstration of Iodine Removal Efficiency of Mof-74 and Uio-66 from Nuclear Waste Solutions in the Presence of Interfering Ions

Demonstration of Iodine Removal Efficiency of Mof-74 and Uio-66 from Nuclear Waste Solutions in the Presence of Interfering Ions

Synthesis of nano-crystalline zeolite-A and zeolite-X from Indian coal fly ash, its characterization and performance evaluation for the removal of Cs+ and Sr2+ from simulated nuclear waste

Phase pure zeolite-A and zeolite-X were synthesized using coal fly ash (CFA) obtained from Indian thermal power plants by employing alkali fusion method followed by hydrothermal technique. The fusion of fly ash with Na2CO3 was accomplished by heating at 800 °C/2 h by maintaining fly ash to Na2CO3 ratio at 1.2. The fused mass was found to be nepheline (Na4Al4Si4O16); and on subsequent treatment of the fused mass with 3 M NaOH under hydrothermal condition transformed to zeolite-A (Na12Al12Si12O48.27H2O) and zeolite-X (Na88Al88Si104O384.194H2O). The effluent solution from zeolite-A synthesis was utilized to prepare cancrinite. The zeolites were characterized by XRD, FTIR, TG-DTA, SEM and surface area of the powders were measured by BET technique. The specific surface area of the zeolite-A and zeolite-X were found to be 58.29 ± 0.20 and 164.34 ± 5.4 m2g−1 respectively. The TG-DTA studies showed the conversion of nano-crystalline to micro-crystalline zeolites with loss of adsorbed water. The ion exchange capacities of these nano-crystalline zeolites were evaluated by using simulated nuclear waste solutions containing Cs+or Sr2+ ions. The adsorption capacity of zeolite-A was found to be 95.74 mg/g and 54.12 mg/g respectively for Sr2+ and Cs+ions. Similarly, zeolite-X shows the adsorption capacity of 93.14 mg/g and 53.14 mg/g respectively for Sr2+ and Cs+ ions.

Efficient Removal of Cs+ and Sr2+ Ions by Granulous (Me2NH2)4/3(Me3NH)2/3Sn3S7·1.25H2O/Polyacrylonitrile Composite

The need to effectively and selectively remove radioactive 137Cs and 90Sr from nuclear waste solutions persists to mitigate their environmental mobility and high radiotoxicity. Because it is difficult to effectively remove them from acidic environments that degrade most sorbents, new sorbent materials are highly desirable. Here, efficient removal of Cs+ and Sr2+ is achieved by the composite of layered tin sulfide (Me2NH2)4/3(Me3NH)2/3Sn3S7·1.25H2O (FJSM-SnS) and polyacrylonitrile (PAN) (FJSM-SnS/PAN). The granulous composite possesses regular particle morphology and good mechanical strength as an engineered form. It shows excellent acid-base and γ-irradiation resistance, high maximum adsorption capacities (qm) of 296.12 and 62.88 mg/g for Cs+ and Sr2+ ions, respectively, and high selectivity even in the presence of excess Na+ ions or using lake water. Impressively, qmCs of FJSM-SnS/PAN reaches 89.29 mg/g under even acidic conditions (pH = 2.5). The column loaded with FJSM-SnS/PAN granules exhibits high removal rates (R) toward low-concentration Cs+ and Sr2+ ions under both neutral and acidic conditions. Moreover, the composite can be recycled and reused with high RCs and RSr. This work highlights the great potential of metal sulfide ion-exchangers in engineered form for the efficient removal of Cs+ or Sr2+ ions, especially under acidic conditions, for radionuclide remediation.

Precise Recognition of Palladium Through Interlaminar Chelation in a Covalent Organic Framework

Palladium isotopes as fission products in used nuclear fuel (UNF) represent precious alternative resources of this noble metal besides its natural reserves and therefore has a high extraction value. However, although solvent extraction of Pd from UNF has been considered for several decades, its practical use is still challenging mostly originating from the harsh fuel reprocessing conditions that lead to the extractant decomposition and the vast co-existing metal ions that depress the extraction efficiency. Herein, we present an interlayer synergistic binding strategy, a metal-recognition manner markedly deviating from chelation within a single ligand molecule in solvent extraction, for selective palladium chelation by a radiation-resistant and acid-stable salicylaldimine-based covalent organic framework (COF-TzDa), where the binding sites are pre-organized and spatially separated for the preference of Pd coordination between adjacent COF layers. COF-TzDa, as expected, shows ultrahigh extraction selectivity towards Pd ions both in static and dynamic conditions, primarily due to that the preorganized Pd-specific binding sites are less prone to match other undesired metal ions. Fast adsorption kinetics, high adsorption capacity (265.4 mg g-1), and more importantly one-round enrichment and purification of Pd from the simulated high level nuclear waste solution are unprecedentedly achieved. The powder X-ray diffraction analysis, X-ray photoelectron spectroscopy results, and in-depth density functional theory corroborate the interlayer synergistic binding to be the result of enol-to-keto tautomerization where oxygen donors from two adjacent layers work together in a cooperative fashion. This work demonstrates the feasibility of structure-engineering of framework materials in designing upgraded adsorbent for targeted guests.

Highly selective uranium adsorption on 2-phosphonobutane-1,2,4-tricarboxylic acid-decorated chitosan-coated magnetic silica nanoparticles

The separation and recovery of uranium resources from nuclear waste solutions is important for achieving uranium reuse and environmental protection. In this study, a novel adsorbent, 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA)-decorated chitosan-coated magnetic silica nanoparticles, was fabricated and applied to the highly selective adsorption of uranium from aqueous solution. Selective sorption in a multi-ion solution (pH 4.0) containing 14 coexisting cations resulted in CoFe2O4@SiO2@CS-PBTCA showing an excellent uranium adsorption capacity of up to 83.16 mg g−1, which was much higher than that of ungrafted CoFe2O4@SiO2@CS (29.99 mg g−1). The adsorbent also exhibited higher acid resistance than uncoated silica adsorbent under pH 1.0 conditions, with CoFe2O4@SiO2@CS-PBTCA showing barely any iron and cobalt leaching, while CoFe2O4@CS-PBTCA showed iron and cobalt leaching amounts of 2.97 and 0.93 mg L−1, respectively. The desorption experiment used 0.2 M PBTCA (pH 1.0) as eluent, with the results showing that uranium ions were readily and rapidly desorbed. Furthermore, CoFe2O4@SiO2@CS-PBTCA maintained outstanding stability and adsorption performance after five reuse cycles. The mechanism for U(VI) removal was investigated by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy, with the results suggesting that the adsorbent binds to uranium mainly though oxygen atoms of carboxyl groups and phosphonic groups in PBTCA. This strategy shows strong potential for developing a variety of novel, highly active, acid resistance, and reusable immobilized functional magnetic materials for effective separation of uranium from a multi-ion solution.

Quaternary Phosphonium-Grafted Porous Aromatic Framework for Preferential Uranium Adsorption in Alkaline Solution

Uranium, as an energy source and radioactive waste, is very important in the nuclear fuel cycle. Recovery of uranium from nuclear waste solution is essential for further treatment and disposal. Herein, an ionic liquid-functionalized porous aromatic framework material P–C4 (PPN-6-CH2P+(C4H9)3Cl–) for uranium adsorption from alkaline solution was synthesized by grafting PPN-6 with the quaternary phosphonium for the first time. The U-exchange kinetics perfectly conforms to the pseudo-second-order dynamic model, which reveals the chemical adsorption process. P–C4 exhibits a record high uranium exchange capacity of over 670 mg/g and can efficiently capture [UO2(CO3)3]4– ions in the presence of the high concentrations of HCO3–, CO32–, F–, SO42–, Cl–, and NO3–. In addition, the uranyl tricarbonate in the loaded material could be easily eluted with a diluted hydrochloric acid. These advantages make P–C4 a new potential material for separating uranium from alkaline solution.