High-level Liquid Waste Research Articles

An ultrastable luminescent covalent organic polymer for selective Pd2+ detection in strong acid

AbstractThe low natural abundance of palladium (10 ppb) in the Earth's crust highlights its considerable potential as a valuable resource, especially given that spent nuclear fuel contains approximately 1–2 kg of Pd per ton. However, the detection and separation of Pd2+ from high‐level liquid waste (HLLW) present significant challenges due to high acidity (2–5 M HNO3) and intense radiation conditions inherent in spent fuel reprocessing. We present a cyano‐olefin‐linked covalent organic polymer (COP‐TnPp) that exhibits remarkable stability in strong acidic environments and resilience to radiation. Thanks to its olefin linkage, which facilitates π‐electron conjugation, COP‐TnPp exhibits strong luminescence, whose intensity remains stable across a range of 1–5 M nitric acid solutions. Pd2+ ions can effectively quench the fluorescence of COP‐TnPp in 1 and 5 M HNO3 solutions with detection limits of 0.37 and 0.63 μM, respectively. Additionally, COP‐TnPp demonstrates exceptional selectivity for Pd2+ ions, even amidst 22 other interfering ions in a simulated HLLW solution (5 M HNO3), with the detection limit remaining at 0.697 μM. This work not only marks an advancement in the development of materials for detecting Pd2+ in extreme acidic conditions but also offers new insights into the detection of other radionuclides under similarly challenging environments.

A novel defect-rich Prussian blue analogue based on controlled doping strategy: Exceptional adsorption performance of platinum group metals and enhanced stability

The efficient separation of platinum group metals (PGMs, mainly Pd, Ru, and Rh) from high level liquid waste (HLLW) is of growing significance for resolving challenges in radioactive waste treatment and achieving sustainable development. Based on Prussian blue analogues (PBAs) with tunable compositions and morphologies, a defect-rich but also excellently stable cobalt-doped aluminum hexacyanoferrate (Co/KAlFC) was successfully synthesized for the separation of PGMs using defect engineering. Interestingly, the defects in Co/KAlFC induced an increase in active sites and vacancies, leading to a remarkable enhancement of PGM adsorption capacity compared to the undoped KAlFC. While maintaining the same excellent Pd(II) adsorption capacity, the convenient access provided by the defects led to a reduction of the Pd(II) adsorption equilibrium time to 30 min, as well as a 3-fold and 7-fold increase in the adsorption capacity for Ru(III) and Rh(III), respectively. The experimental and characterization results revealed that the adsorption mechanism of defect-rich Co/KAlFC on PGM was mainly a synergistic effect of ion-exchange and chemical complexation, and the enhanced electrostatic interaction promoted the adsorption process. The valence state of Fe shifted from divalent to trivalent during the adsorption process, which affected the strength of coordination interaction between PGMs and Fe-CN- at N-atom. Overall, this study not only demonstrated that Co/KAlFC is an excellent candidate for the removal of PGM from HLLW but also provided a new idea for the rational design and development of inorganic materials with exceptional properties and stability.

Site differentiation strategy for selective strontium uptake and elution within an all-inorganic polyoxoniobate framework

Selective uptake and elution of trace amounts of hazardous radioactive 90Sr from large-scale high-level liquid waste (HLW) is crucial for sustainable development. Here, we propose a site differentiation strategy, based on the presence of distinct selective metal capture sites (concavity site and tweezer site) within the giant polyoxoniobate (PONb) nanoclusters of an all-inorganic PONb framework (FZU-1). Through this strategy, FZU-1 can not only effectively remove 98.9% of Sr²⁺ from simulated nuclear liquid waste, performing best among the reported Sr adsorbents, but also achieve desorption of adsorbed Sr²⁺ ions by selectively loading Na⁺ ions, thus enabling the recycling of FZU-1. Based on the well-defined single-crystal structures and theoretical studies, it can be revealed that the rapid and selective uptake of Sr²⁺ is attributed to the strong binding energy between the Sr²⁺ ions and the concavity sites. The effective elution of Sr²⁺, on the other hand, stems from the preferential binding of Na⁺ ions at the tweezer sites, elevating the cluster’s electrostatic potential and indirectly facilitating the elution of Sr²⁺ ions. The exceptional stability of FZU-1, along with its rapid and selective Sr²⁺ capture and elution capabilities, positions it as a promising candidate for large-scale nuclear waste treatment and groundwater remediation applications.

The Functionalized N-Rich Covalent Organic Framework for Palladium Removal from Nuclear Wastewater.

Efficiently adsorbing Pd(II) from acidic radioactive waste liquid is crucial for ensuring the safety of the radioactive waste vitrification process and significantly alleviating the scarcity of precious metals. However, the stability and selectivity of most current adsorbents are limited, hindering their practical application under acidic conditions. To address these limitations, a covalent organic framework (DHTP-TPB COF) was prepared with a high nitrogen content, leveraging the high affinity of its soft ligand N with palladium to achieve high selectivity. This work demonstrated that DHTP-TPB COF exhibits rapid adsorption kinetics, with equilibrium achieved within 10 min. The framework also boasts a high adsorption capacity of 142.8 mg/g and impressive reusability in 1.0 M nitric acid. Moreover, the DHTP-TPB COF displays excellent selectivity for Pd(II), even in the presence of 13 interfering ions. By combining FT-IR, XPS spectroscopy, and DFT theoretical calculations, the dense N sites in the framework have a strong affinity for Pd(II), resulting in exceptional adsorption performance that was confirmed. The findings of this study highlight the potential of COFs with robust linkers and customized functional groups to effectively and selectively capture Pd(II) under harsh environmental conditions of high-level liquid waste.

An acid-resistant covalent organic polymer for detection of palladium ions in high-level liquid waste

An acid-resistant covalent organic polymer for detection of palladium ions in high-level liquid waste

Conjugated Porous Organic Polymers Featuring Both Soft-Hard Combined Coordination Sites and Photoelectrochemical Properties for Palladium Capture and Subsequent Photocatalysis.

Palladium (Pd) capture from high-level liquid waste for subsequent photocatalytic applications is desirable for the development of nuclear energy and the reutilization of valuable resources. Herein, we approach our design with a unique porous organic polymer containing thiazolo[5,4-d]thiazole units (denoted as TzPOP-OH). It possesses two potential soft-hard (N-O and S-O) combined coordination sites for Pd(II) coordination and features strong donor-acceptor repeating units and high planarity of linkage enforced by hydrogen bonds for subsequent photocatalysis. Accordingly, TzPOP-OH with three hydroxyl groups on the linkage exhibits a high Pd(II) capacity of 369 mg g-1 at 3 M HNO3, considerably surpassing those of the controlled polymer TzPOP without hydroxyl groups and most other reported materials. Additionally, TzPOP-OH boasts other merits, including outstanding acid tolerance, extraordinary radiation stability, good reusability, and remarkable selectivity. After palladium adsorption, Pd@TzPOP-OH demonstrates impressive photodegradation efficiency to reduce the concentration of rhodamine B in contaminated urban water from 10 to less than 0.1 ppm. This work provides a feasible approach to designing materials with both suitable coordination microenvironments and semiconductor properties for metal separation and photocatalysis.

Crosslinking assembly of Propenyl-Calix[4]-Crown-6 interpenetrating functional mesoporous carbon Spheres: High selectivity and stability to Remove Cs(I) from high acid solution

The calix[4]-crown-6 ligand shows high selectivity for Cs(I) over other alkali and alkaline earth metal cations, making it a promising candidate for radiocesium separation. However, its high viscosity and poor adhesion limit its practical use and stability. In this study, an alkenyl-functionalized calix[4]-crown-6 (p-C[4]C6) was developed. Using a mesoporous structure and post-assembly techniques, a composite (p-C[4]C6/MMCs) was created via crosslinking within mesoporous matrix channels. The p-C[4]C6/MMCs exhibited high stability and practicality. The p-C[4]C6/MMCs demonstrated high selectivity, good reusability, and significant adsorption capacity (47.76 mg/g) for Cs(I) in 3.0 M HNO3. Kinetic, isotherm, and thermodynamic studies suggest a spontaneous chemical adsorption mechanism. This research provides insights into the design of calix[4]-crown-6 based materials and offers a viable approach for Cs(I) separation from high-level liquid waste (HLW).

Influence of temperature and flow rate on alteration layer structure and leaching properties of simulated sulfur-containing borosilicate HLW glass under multi-field coupling effects

During long-term deep geological disposal process, high-level liquid waste (HLW) glass may be exposed to “Thermodynamics-Hydrodynamics-Mechanics-Chemistry” (THMC)multi-field coupling effects. The leaching properties of sulfur-containing borosilicate HLW glass at different temperatures (40–150 °C) and different flow rates (0.01–0.10 mL/min) under THMC coupling effects were studied in this work. The alteration layer structure of waste glass surface was also characterized. The results show that honeycomb-shaped phyllosilicate alteration layer forms after leaching in simulated groundwater and white block-shaped BaSO4 crystals appear on the glass surface at 90 °C after 28 d. The amount of BaSO4 crystals increases obviously at 150 °C. The leaching rates of B, Si, Cs and U elements increase with increasing temperature and flow rate. Particularly, the leaching rates of B, Si, Cs, and U under THMC coupling effects (90 °C, 0.01 mL/min, 10 MPa, pH=8.05) after 28 d in the simulated groundwater are 1.10 × 10–1, 1.73 × 10–1, 2.91 × 10–1, 3.79 × 10–1 g·m-2·d-1, respectively.

Silica-Reinforced AMP-Calcium Alginate Beads for Efficient and Selective Removal of Cesium from a Strong Acidic Medium.

Due to the significant selectivity for Cs+, ammonium molybdophosphate (AMP) possesses potential to uptake radiocesium from high-level liquid waste (HLLW), whereas its micro-crystalline structure and fine powder morphology limit its industrial application. Although the granulation method with alginate is prospective for the preparation of an AMP exchanger, the mechanical strength of obtained beads may be insufficient for application. In this context, we prepared silica-reinforced AMP-calcium alginate (ACS) beads and evaluated their performance for Cs+ removal from strong acidic solutions. It was found that the addition of silica in the fabrication significantly improved the mechanical strength of the beads in comparison to those without silica. Notably, the beads with an AMP/silica mass ratio of 1.0 exhibited an exceptional mechanical strength, surpassing that of ACS beads composed of other components. The batch experiment results indicated that the Cs+ adsorption follows a non-linear pseudo-second-order rate equation. The distribution coefficient of Cs+ was high even in extreme acidic conditions (∼1.6 × 102 mL/g in 8.0 mol/L HNO3 solution). The Cs+ adsorption can be well fitted with the Langmuir model, and the estimated maximum exchange capacity in 3.0 mol/L HNO3 could reach 23.9 mg/g. More importantly, ACS beads showed excellent selectivity toward Cs+ uptake over eight co-existing metal ions in simulated HLLW, with separation factor values all above 145. The column experiment exhibited that the beads can serve as the stationary phase in columns to effectively remove Cs+. The findings of this study are significant as they provide insights into the development of efficient materials for radiocesium removal from high-level liquid waste. The results demonstrate the potential of silica-reinforced ACS beads for Cs+ adsorption, with promising applications in industrial settings.

Process development studies on the recovery of caesium specific calix-crown-6 extractant from actual spent calix solution for efficient spent solvent management

Abstract This paper reports the studies carried out on the development of a process for the recovery of 1,3-dioctyloxycalix[4]arene-18-crown-6 (CC-6) from the spent solvent generated during industrial scale separation of 137Cs from High Level Liquid Waste (HLLW). Initial works involved the validation of a conceptual process design and optimization of the process parameters with a simulated solvent. The optimized process was then tested with actual spent solvent to recover calix-crown-6. Such a process to recover undegraded and potentially re-usable calix-crown-6 from the spent solvent has been attempted for the first time with the aim of value recovery and reduced spent solvent management burden.

Precise separation and efficient recovery of Pd(II) from high-level liquid waste by XAD-based adsorbents

Precise separation and efficient recovery of Pd(II) from high-level liquid waste by XAD-based adsorbents

Research on calcination thermal decomposition process of simulated high-level liquid waste based on two-step vitrification

The two-step vitrification process involves converting high-level waste from a liquid to a solid state through calcination, followed by melting the calcines with glass matrix material to form glassy wasteforms. The calcination process is a critical stage in the vitrification process. This study investigated the thermal decomposition performance and phase evolution of power reactor simulated high-level waste during the calcination process. As the calcination temperature increased from 100 to 900 °C, the resultant waste calcines showed increasingly darker color and smaller general particle sizes. Below 600 °C, the waste experienced thermal decomposition of nitrate and formate compounds, leading to an approximate 40 wt% weight reduction. At 600 °C, the waste's weight remained constant, and crystalline phases such as ZrxM1-xO2 (M = Ce, Pr, Nd), BaMoO4, CeO2, and GdxCe1-xO2 were observed.

Demonstration of Mixer-Settlers Runs for Separation of Uranium and Neptunium by TBP Vis-a-Vis DHOA Under a Legacy Waste Condition

ABSTRACT Separation of neptunium from an acidic feed containing 0.063 mol/L uranium in 3 mol/L HNO3 was demonstrated in counter-current extraction in mixer-settlers with TBP (tri-n-butyl phosphate) and DHOA (N,N’-dihexyl octanamide) as the organic extractants. With a feed solution of 0.063 mol/L uranium (in the absence of neptunium) and at an organic to aqueous phase ratio (O/A) = 1, >99.9% uranium could be extracted into the organic phase in 6 stages with the raffinate containing <10−5 mol/L of uranium. The extraction results with TBP and DHOA were comparable. However, stripping of uranium with 0.01 mol/L HNO3 from the loaded organic phase was better with DHOA vis-a-vis TBP phase. From the DHOA phase, loaded with 0.063 mol/L uranium, the entire metal ion could be stripped in 6 stages at an O/A = 1. However, ca. 17% uranium remained in the TBP phase even after 6 stages of stripping. With these preliminary results, the extraction of neptunium was systematically studied in mixer-settlers from feed containing uranium, and from simulated high level liquid waste. Our results of neptunium extraction in the presence of 0.021 mol/L uranium yielded excellent result. Similarly, the extraction of neptunium from simulated high level liquid waste was also demonstrated with good extraction efficiency.

Release Behavior of Gaseous Ruthenium Tetroxide During Heating of High-Level Liquid Waste Simulant During Simulated Accident Conditions

A malfunction of the cooling system of high-level liquid waste (HLLW) and the failure of countermeasures may lead to the evaporation to dryness due to the loss of cooling functions (EDLCF) of the HLLW. In the EDLCF, ruthenium (Ru) can be released at a greater fraction to the initial amount than the other elements in HLLW by forming gaseous Ru. It is important to identify the chemical form of the released gaseous Ru to achieve a comprehensive understanding of the events impacting the source term assessment of Ru in this accident, such as particle formation, gas absorption, and deposition on migration pathways. In this study, we observed the ultraviolet/visible spectroscopy of the off-gas generated during the heating of a HLLW simulant. Employing a program that allows for the separation and quantification of known components within the spectrum [ruthenium tetroxide (RuO4), nitrogen dioxide, and nitric acid], we attempted to analyze the composition of gaseous Ru within the generated off-gas. Our findings revealed RuO4 as the main component of the gaseous Ru in the off-gas after comparing the total amount of released Ru and the RuO4 released amount obtained via spectroscopic analysis.

Efficient and Selective Removal of Palladium from Simulated High-Level Liquid Waste Using a Silica-Based Adsorbent NTAamide(C8)/SiO2-P.

In order to realize the effective separation of palladium from high-level liquid waste (HLLW), a ligand-supported adsorbent (NTAamide(C8)/SiO2-P) was prepared by the impregnation method in a vacuum. The SiO2-P carrier was synthesized by in situ polymerization of divinylbenzene and styrene monomers on a macroporous silica skeleton. The NTAamide(C8)/SiO2-P adsorbent was fabricated by impregnating an NTAamide(C8) ligand into the pore of a SiO2-P carrier under a vacuum condition. The adsorption performance of NTAamide(C8)/SiO2-P in nitric acid medium has been systematically studied. In a solution of 0.2 M HNO3, the distribution coefficient of Pd on NTAamide(C8)/SiO2-P was 1848 mL/g with an adsorption percentage of 90.24%. With the concentration of nitric acid increasing, the adsorption capacity of NTAamide(C8)/SiO2-P decreases. Compared to the other 10 potential interfering ions in fission products, NTAamide(C8)/SiO2-P exhibited excellent adsorption selectivity for Pd(II). The separation factor (SFPd/other metals > 77.8) is significantly higher than that of similar materials. The interference of NaNO3 had a negligible effect on the adsorption performance of NTAamide(C8)/SiO2-P, which maintained above 90%. The adsorption kinetics of Pd(II) adsorption on NTAamide(C8)/SiO2-P fits well with the pseudo-second order model. The Sips model is more suitable than the Langmuir and Freundlich model for describing the adsorption behavior. Thermodynamic analysis showed that the adsorption of Pd(II) on NTAamide(C8)/SiO2-P was a spontaneous, endothermic, and rapid process. NTAamide(C8)/SiO2-P also demonstrated good reusability and economic feasibility.

Adsorption and Desorption Behavior and Mechanism of Ruthenium in Nitrite-Nitric Acid System.

Ruthenium is required to separate from high-level liquid waste (HLLW) because Ru is a valuable resource and is negatively influential on the vitrification process of HLLW. However, the separation of Ru is very challenging due to its complicated complexation properties. In this study, the adsorption and desorption characteristics of ruthenium on a synthesized SiPyR-N3 (weak-base anion exchange resin with pyridine functional groups) composite were investigated in nitric acid and nitrite-nitric acid systems, respectively, and the adsorption mechanism was explored. The experimental results showed that SiPyR-N3 has a significantly better adsorption effect on Ru in the nitrite-nitric acid system than in the nitric acid system, with an increase in the adsorption capacity of approximately three times. The maximum adsorption capacity of Ru is 45.6 mg/g in the nitrite-nitric acid system. The SiPyR-N3 possesses good adsorption selectivity (SFRu/other metal ions is around 100) in 0.1 M NO2--0.1 M HNO3 solution. The adsorption processes of Ru in the two different systems are fitted with the pseudo-second-order kinetic model and Langmuir model for uptake kinetics and adsorption isotherms, respectively. The results obtained from the FT-IR, XPS, and UV absorption spectrometry indicate that NO2- was involved in the adsorption process either as a complexing species with the metal ions or as free NO2- from the solution. A 0.1 M HNO3 + 1 M thiourea mixed solution shows effective desorption performance, and the desorption efficiency can reach 92% at 328 K.

Optimisation of synthesis procedures and structural investigation of monazite-cheralite solid solutions

The monazite-cheralite solid solutions LnPO4-Ca0.5Th0.5PO4 with Ln = La, Gd were prepared via a co-precipitation route, showcasing an optimised, scalable synthesis procedure for a possible waste form accommodating high level liquid waste streams. A distortion of the cheralite structure with respect to the monazite structure was observed throughout both solid solutions as evidenced by a deviation of the lattice parameters from the linear behaviour known from other monazite solid solutions. Using a high temperature flux method, cheralite single crystals were grown for the first time for in-depth structural investigations. Both thorium and calcium were found to deviate from the central position of the LnO9 polyhedron, supporting previous neutron diffraction investigations of identical cheralite samples.Graphical

Boiling and Drying Accident of High-Level Liquid Waste in a Reprocessing Plant: Examination of the Time-Dependent Temperature Increase of the Waste and of the Generation Rates of the Individual Components Released into the Gas Phase

Using the amount, composition, and decay power density of high-level liquid waste in a storage tank, the temperature change of the waste up to 600°C and the corresponding vapor and gas release rates of H2O, HNO3, NO2, NO, and O2 as a function of time after the loss of cooling function were obtained by the following method. The heat balance equations in and around the tank were derived, and the solution of the waste temperature change was numerically obtained using the vaporization rates of H2O and HNO3 and the generation rate of NOx, which were both obtained from the experiments using the simulated liquid waste. Utilizing the temperature versus time curve obtained from the equation, the release rates of the components described above were obtained as a function of time. This information on the progress of the accident can be used to study the Leak Path Factor of radioactive materials, especially of volatilized Ru, and further, it becomes basic information when considering accident management and suppressing the impact of a disaster.

Understanding the extraction behavior of Eu(III) from acidic medium and the feasibility of separation of simulated high level liquid waste compositions using a phosphonium ionic liquid containing diglycolamide extractant

Liquid-Liquid extraction behavior of trivalent lanthanides (by taking Eu(III) as a representative) in a strongly hydrophobic phosphonium based ionic liquid (IL) in conjunction with a diglycolamide (DGA) based extractant was perused in detail to emphasize the extraction pathway and coordination behavior. Trihexyl(tetradecyl)phosphonium nitrate (Cyphos nitrate: [P66614][NO3]) was chosen as IL solvent phase containing N,N,N’,N’-tetra-(2-ethylhexyl)diglycolamide (T2EHDGA) (a well-known DGA ligand) as the extractant.The extraction behavior of Eu(III) was furnished at different experimental parameters such as the concentration of initial nitric acid, concentration of ligand, equilibration time and experimental temperature to explore the extractability of the proposed IL system. The extraction showed an increasing trend with an increase in the feed acidity followed by attaining a plateau region at higher acid concentration inferring the occurrence of a neutral solvation type coordination mechanism. The mixture of T2EHDGA/[P66614][NO3] was implemented on the extraction of Fast Reactor Simulated High Level Liquid Waste (FR-SHLLW) solution spiked with Am(III) and the results were promising with respect to efficacy of the proposed IL phase. All the trivalent Ln(III) and Am(III) were selectively separated from some of the co-extracting fission products using a suitable holding agent in the feed phase. IL composition chosen for the study was radiation stable exhibiting comparable extraction behavior for SHLLW metal ions. The present study uses only dilute nitric acid as the stripping agent without adding any aqueous phase complexing agent which is a major underscore as far as the economic and environmental benefits are concerned.

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.