Nuclear Waste Streams Research Articles

Mechanistic Insights into Cs-Ion Exchange in the Zeolite Chabazite from In Situ Powder X-Ray Diffraction.

Zeolites contain extraframework cations that are exchangeable under favorable aqueous conditions; this is the fundamental feature for their application in water purification and necessary to produce cation forms for other applications such as catalysis. Optimization of the process is common, but there is little fundamental understanding based on real-time experiments of the mechanism of exchange for most zeolites. The sodium and potassium forms of zeolite chabazite selectively uptake Cs+ by ion exchange, leading to its application in removing radioactive 137Cs+ from industrial nuclear waste streams, as well as from contaminated environments in the aftermath of the Fukushima and Three Mile Island accidents. In this study, in situ synchrotron powder X-ray diffraction patterns have been collected on chabazite as it undergoes Cs-ion exchange. Applying Rietveld refinement to these patterns has revealed the time-resolved structural changes that occur in the zeolite as exchange progresses, charting the changes in the spatial distribution of the extraframework cations and water molecules in the structure during the reaction. Ultimately, a detailed mechanistic understanding of how this dynamic ion-exchange reaction occurs has been obtained.

Volumetric lattice Boltzmann method for pore-scale mass diffusion-advection process in geopolymer porous structures

Porous materials present significant advantages for absorbing radioactive isotopes in nuclear waste streams. To improve absorption efficiency in nuclear waste treatment, a thorough understanding of the diffusion-advection process within porous structures is essential for material design. In this study, we present advancements in the volumetric lattice Boltzmann method (VLBM) for modeling and simulating pore-scale diffusion-advection of radioactive isotopes within geopolymer porous structures. These structures are created using the phase field method (PFM) to precisely control pore architectures. In our VLBM approach, we introduce a concentration field of an isotope seamlessly coupled with the velocity field and solve it by the time evolution of its particle population function. To address the computational intensity inherent in the coupled lattice Boltzmann equations for velocity and concentration fields, we implement graphics processing unit (GPU) parallelization. Validation of the developed model involves examining the flow and diffusion fields in porous structures. Remarkably, good agreement is observed for both the velocity field from VLBM and multiphysics object-oriented simulation environment (MOOSE), and the concentration field from VLBM and the finite difference method (FDM). Furthermore, we investigate the effects of background flow, species diffusivity, and porosity on the diffusion-advection behavior by varying the background flow velocity, diffusion coefficient, and pore volume fraction, respectively. Notably, all three parameters exert an influence on the diffusion-advection process. Increased background flow and diffusivity markedly accelerate the process due to increased advection intensity and enhanced diffusion capability, respectively. Conversely, increasing the porosity has a less significant effect, causing a slight slowdown of the diffusion-advection process due to the expanded pore volume. This comprehensive parametric study provides valuable insights into the kinetics of isotope uptake in porous structures, facilitating the development of porous materials for nuclear waste treatment applications.

Microstructure, adsorption site energetics, and formation enthalpy control for FAU-Zeolite Cs+ exchange

Cs-137 is a radionuclide fission product that poses a significant risk to life, making it crucial to develop effective methods for its separation and sequestration from nuclear waste streams. Zeolitic structures have emerged as promising materials. This work examines the influence of structure, exchange site energetics, and formation enthalpies of nascent and cation-exchanged Faujasite-X, -Y, and -HY zeolites in terms of their Cs-exchange selectivity. Their interplay was quantified with the application of high-temperature calorimetry, adsorption isotherms, X-ray diffraction and density functional theory (DFT) calculations. Greater efficacy of Cs+ exchange was demonstrated for the Na+-substituted Fau-Y (NaY) zeolite than that of the Fau-X (NaX) and Fau-HY (Na-HY) zeolites. This is explained by a higher amount of Na+ in un-exchangeable sites in the case of NaX and a lower stability in NaY that favors the ionic exchange with Cs+. Moreover, Cs+ incorporation in the structure increases the stability of each kind of zeolite. Correspondingly, structure and DFT analyses demonstrated site-exchange thermodynamic favorability as well as the contribution from cage cell, which resulted in an energy landscape far more conducive to Cs+ incorporation for NaY than either NaX or Na-HY.

A robust Zr(IV)-based metal-organic framework featuring high-density free carboxylic groups for efficient uranium recovery

The extraction of uranium from aqueous environments, including the ocean and radioactive wastewater, represents a significant challenge with profound implications for energy resources and environmental remediation. This work presents the design and synthesis of a novel highly stable carboxylated metal–organic framework, BUT-12-3COOH, which achieves excellent U(VI) extraction ability from water. BUT-12-3COOH features high-density free carboxylic groups, exceptional chemical stability, fast kinetics, and high adsorption capacity for U(VI). Dynamic sorption experiments further demonstrated the potential of BUT-12-3COOH in treating real radioactive wastewater. The mechanisms for the U(VI) capture of BUT-12-3COOH are investigated through the combination of EDS, FT-IR, and XPS analysis. The results of this study underscore the promising utility of BUT-12-3COOH as an effective sorbent for extracting radionuclides from environmental specimens and liquid nuclear waste streams.

Creation of Cationic Polymeric Nanotrap Featuring High Anion Density and Exceptional Alkaline Stability for Highly Efficient Pertechnetate Removal from Nuclear Waste Streams.

There is an urgent need for highly efficient sorbents capable of selectively removing 99TcO4- from concentrated alkaline nuclear wastes, which has long been a significant challenge. In this study, we present the design and synthesis of a high-performance adsorbent, CPN-3 (CPN denotes cationic polymeric nanotrap), which achieves excellent 99TcO4- capture under strong alkaline conditions by incorporating branched alkyl chains on the N3 position of imidazolium units and optimizing the framework anion density within the pores of a cationic polymeric nanotrap. CPN-3 features exceptional stability in harsh alkaline and radioactive environments as well as exhibits fast kinetics, high adsorption capacity, and outstanding selectivity with full reusability and great potential for the cost-effective removal of 99TcO4-/ReO4- from contaminated water. Notably, CPN-3 marks a record-high adsorption capacity of 1052 mg/g for ReO4- after treatment with 1 M NaOH aqueous solutions for 24 h and demonstrates a rapid removal rate for 99TcO4- from simulated Hanford and Savannah River Site waste streams. The mechanisms for the superior alkaline stability and 99TcO4- capture performances of CPN-3 are investigated through combined experimental and computational studies. This work suggests an alternative perspective for designing functional materials to address nuclear waste management.

Hot corrosion behavior of the rotating kiln thermowell from a cold crucible induction melter system

A thermowell dissembled from an on-going high-temperature rotating kiln part from a cold crucible induction melter (CCIM) system was characterized, and the underlying mechanism governing its hot corrosion and degradation behavior was further studied. Results indicate that the high-temperature interaction between the thermowell and the nuclear waste stream leading to the formation of oxides with different valence states mainly composed of FeCrO2, Fe2O3, FeO and NiO, with the diffusion of the simulated radionuclides into the lattice structure The on-site corrosion and phase degradation are thermodynamically driven by the outward growth of the oxidation film.

A hydroxy containing, naphthalene-based and imine linked porous organic polymer for rapid iodine uptake

Nuclear energy is turning out to be one of the best alternatives to fossil fuels in order to meet the global electricity demand. Radioactive iodine is a volatile and hazardous component that may be present in aqueous nuclear waste and off-gas streams of a spent fuel processing plant. Iodine species are also quite mobile and their accidental leakage into the environment can adversely affect the health of animals and humans to an alarming extent. Thus, design and development of materials capable of capturing/storing iodine effectively for a long time, is of utmost importance in contemporary research. Herein, facile synthesis of a unique nitrogen rich and thermally stable porous organic polymer (POP_DH) is described that has a porous structure comprising of both micro and mesopores. The POP_DH has a specific surface area (128.3 m2 g-1), and can capture 2.855 g g−1 of iodine (vapours) at 75 °C. The POP_DH can retain the trapped iodine up to seven days without any significant release which makes it a suitable material suitable for storing iodine. The presence of O and N heteroatoms (imine linkages) also enable POP_DH to remove iodine species dissolved in water. Herein, the iodine removal is quite rapid with about 99 % of iodine captured within 2 h. POP_DH samples can be recycled up to five rounds for iodine capture with only small changes in performance as an adsorbent. Overall, POP_DH is promising material for capture of radioactive iodine from various media.

Engineered species-selective ion-exchange in tuneable dual-phase zeolite composites.

Controllable sorption selectivity in zeolites is crucial for their application in catalysis, gas separation and ion-exchange. Whilst existing approaches to achieving sorption selectivity with natural zeolites typically rely on screening for specific geological deposits, here we develop partial interzeolite transformation as a straightforward and highly tuneable method to achieve sorption selectivity via forming dual-phase composites with simultaneous control of both phase-ratio and morphology. The dual-cation (strontium and caesium) exchange properties of a series of granular mordenite/zeolite P composites formed from a parent natural mordenite material are demonstrated in complex, industrially relevant multi-ion environments pertinent to nuclear waste management. The relative uptake of caesium and strontium is controlled via the extent of transformation: composites exhibit significantly increased ion-exchange affinity for strontium compared to both the parent mordenite and physical mixtures of mordenite/zeolite P phases with similar phase ratios. The composite with a 40 : 60 mordenite : zeolite P ratio composite achieves higher uptake rates than the natural clinoptilolite material currently used to decontaminate nuclear waste streams at the Sellafield site, UK. In situ X-ray image-guided diffraction experiments during caesium exchange demonstrate that the mordenite core retains rapid caesium uptake likely responsible for the unique ion-exchange chemistry achievable through the partial inter-zeolite transformation. These results offer a straightforward and controllable route to optimised zeolite functionality and a strategy to engineer composites from low-grade natural sources at low cost and with formulation advantages for industrial deployment.

Functional Carbon Capsules Supporting Ruthenium Nanoclusters for Efficient Electrocatalytic 99 TcO4 - /ReO4 - Removal from Acidic and Alkaline Nuclear Wastes.

The selective removal of the β-emitting pertechnetate ion (99 TcO4 - ) from nuclear waste streams is technically challenging. Herein, a practical approach is proposed for the selective removal of 99 TcO4 - (or its surrogate ReO4 - ) under extreme conditions of high acidity, alkalinity, ionic strength, and radiation field. Hollow porous N-doped carbon capsules loaded with ruthenium clusters (Ru@HNCC) are first prepared, then modified with a cationic polymeric network (R) containing imidazolium-N+ units (Ru@HNCC-R) for selective 99 TcO4 - and ReO4 - binding. The Ru@HNCC-R capsules offer high binding affinities for 99 TcO4 - /ReO4 - under wide-ranging conditions. An electrochemical redox process then transformsadsorbed ReO4 - to bulk ReO3 , delivering record-high removal capacities, fast kinetics, and excellent long-term durability for removing ReO4 - (as a proxy for 99 TcO4 - ) in a 3m HNO3 , simulated nuclear waste-Hanford melter recycle streamand an alkaline high-level waste stream (HLW) at the U.S. Savannah River Site (SRS). In situ Raman and X-ray absorption spectroscopy (XAS) analyses showed that adsorbed Re(VII) is electrocatalytically reduced on Ru sites to a Re(IV)O2 intermediate, which can then be re-oxidized to insoluble Re(VI)O3 for facile collection. This approach overcomes many of the challenges associated with the selective separation and removal of 99 TcO4 - /ReO4 - under extreme conditions, offering new vistas for nuclear waste management and environmental remediation.

Modulating Anion Nanotraps via Halogenation for High-Efficiency 99TcO4-/ReO4- Removal under Wide-Ranging pH Conditions.

Efficient and sustainable methods for 99TcO4- removal from acidic nuclear waste streams, contaminated water, and highly alkaline tank wastes are highly sought after. Herein, we demonstrate that ionic covalent organic polymers (iCOPs) possessing imidazolium-N+ nanotraps allow the selective adsorption of 99TcO4- under wide-ranging pH conditions. In particular, we show that the binding affinity of the cationic nanotraps toward 99TcO4- can be modulated by tuning the local environment around the nanotraps through a halogenation strategy, thereby enabling universal pH 99TcO4- removal. A parent iCOP-1 possessing imidazolium-N+ nanotraps showed fast kinetics (reaching adsorption equilibrium in 1 min), a high adsorption capacity (up to 1434.1 ± 24.6 mg/g), and exceptional selectivity for 99TcO4- and ReO4- (nonradioactive analogue of 99TcO4-) removal in contaminated water. By introducing F groups near the imidazolium-N+ nanotrap sites (iCOP-2), a ReO4- removal efficiency over 58% was achieved in 60 min in 3 M HNO3 solution. Further, introduction of larger Br groups near the imidazolium-N+ binding sites (iCOP-3) imparted a pronounced steric effect, resulting in exceptional adsorption performance for 99TcO4- under super alkaline conditions and from low-activity waste streams at US legacy Hanford nuclear sites. The halogenation strategy reported herein guides the task-specific design of functional adsorbents for 99TcO4- removal and other applications.

Design and Application of Materials for Sequestration and Immobilization of 99Tc.

99Technetium (99Tc) is a hazardous radionuclide that poses a serious environmental threat. The wide variation and complex chemistries of liquid nuclear waste streams containing 99Tc often create unique, site specific challenges when sequestering and immobilizing the waste in a matrix suitable for long-term storage and disposal. Therefore, an effective management plan for 99Tc containing liquid radioactive wastes (such as storage (tanks) and decommissioned wastes) will likely require a variety of suitable materials/matrixes capable of adapting to and addressing these challenges. In this review, we discuss and highlight the key developments for effective removal and immobilization of 99Tc liquid waste in inorganic waste forms. Specifically, we review the synthesis, characterization, and application of materials for the targeted removal of 99Tc from (simulated) waste solutions under various experimental conditions. These materials include (i) layered double hydroxides (LDHs), (ii) metal-organic frameworks (MOFs), (iii) ion-exchange resins (IERs) as well as cationic organic polymers (COPs), (iv) surface modified natural clay materials (SMCMs), and (v) graphene-based materials (GBMs). Second, we discuss some of the major and recent developments toward 99Tc immobilization in (i) glass, (ii) cement, and (iii) iron mineral waste forms. Finally, we present future challenges that need to be addressed for the design, synthesis, and selection of suitable matrixes for the efficient sequestration and immobilization of 99Tc from targeted wastes. The purpose of this review is to inspire research on the design and application of various suitable materials/matrixes for selective removal of 99Tc present globally in different radioactive wastes and its immobilization in stable/durable waste forms.

Iodine Removal from Carbonate-Containing Alkaline Liquids Using Strong Base Resins, Hybrid Resins, and Silver Precipitation

The ability of several material types to remove aqueous iodine from a mildly alkaline, carbonate-rich nuclear waste stream was evaluated: strong base anion exchange resins (SBARs), hybrid resins, Ag-containing materials, and Bi-containing hybrid resins. A combination of batch testing and flow-through column testing was used in the evaluation. In batch testing, hybrid resins CHM-20, SIR-110-CE, and RTBI were shown to have high efficiency for the removal of both iodide and iodate simultaneously, while Ag-containing materials and SBAR demonstrated high capacity for iodide removal. One example of each material type (CHM-20, A532E, and Ionex 400) was further evaluated for their sorption isotherms and column performance. The Langmuir isotherm, or a Langmuir–Freundlich hybrid isotherm, best described the sorption of iodide to the CHM-20 hybrid resin and Purolite A532E. The Freundlich isotherm best described the uptake of iodate to CHM-20 and A532E and for both iodide and iodate to Ag-containing Ionex 400. In column testing, Purolite A532E had exceptional performance for overall iodide removal. However, with the capacity demonstrated, the A532E resin would exceed class C waste classification before breakthrough initiated, and column change-outs in processing would be dictated by eventual waste classification, not breakthrough. Ionex 400, a Ag-zeolite, was observed to degrade over time under mild alkaline column conditions, whereas the hybrid CHM-20 was limited in the single pass through design and would be best suited for applications where iodide and iodate are present and recirculation of the column effluent is feasible. This work highlights the feasibility of commercially available materials to separate radioiodine from liquid environments.

Adsorption-photocatalysis processes: The performance and mechanism of a bifunctional covalent organic framework for removing uranium ions from water

Photocatalytic reaction could become an effective way to solve the energy crisis and environmental restoration and governance. Herein, we reported a covalent organic framework (COF-TpBpy) was connected by polyhydroxy-containing unit (Tp) and bipyridine unit (Bpy), which was utilized as photocatalytic semiconductor for photocatalytic detoxification of U(VI). Firstly, TpBpy was comprehensively characterized by physical chemistry (PXRD, SEM, TEM, FT-IR, BET, EA) and photoelectrochemistry (Vis-DRS, M-S plots, photocurrent-time, EIS, PL). Hereafter, the adsorption capacity of TpBpy for U(VI) was investigated by batch adsorption experiment, reaching 455 mg/g within 60 min. The adsorption experimental data conformed to the second-order kinetics, suggesting the chemisorption or surface complexation mechanism. Following that, TpBpy exhibited the narrower optical band gap (Eg = 2.2 V, ECB = -0.95 and EVB = 1.25 V vs. NHE) due to its extended π-conjugation system and electron-rich units of the skeleton (N-14.56%, O-27.73%). After visible light irradiation for 420 min, the photoreduction removal rate of U(VI) by TpBpy was about 55.4%. ESR spectra corroborated that O2– radicals and photoelectrons were the main active species involved in the photoreduction process. XPS analysis revealed the formation of NU bond and UO bond, whether in the process of adsorption or photoreduction. In short, the structure of TpBpy possessed strong coordination ability with U(VI) ions, and promoted the transfer of electrons from electron-rich groups to U(VI), thereby reducing to U(IV). As a multifunctional material, TpBpy possess the advantage in eliminating nuclear waste streams.

Efficient separation of strontium ions from aqueous solution by dibenzo-18-crown-6 functionalized resin: Static and dynamic adsorption studies with computational DFT insights

The separation and utilization of radiotoxic 90Sr from liquid nuclear waste streams generated in the nuclear fuel reprocessing is highly desirable and challenging. Herein, we studied dibenzo-18-cown-6 functionalized chloromethyl-polystyrene (CMPS-DB18C6) resin which displays an excellent affinity toward Sr2+ion adsorption from aqueous solution. Adsorption behaviors were investigated as a function of solution pH, contact time, Sr2+ion concentration, temperature and presence of other metal ions. The prepared grafted resin exhibits high adsorption capacity of 141.37 mg/g at pH 6 with good selectivity in the presence of interfering coexisting ions such as Li+, Na+, Mg2+and Ca2+ions.The adsorption kinetics and isotherm were well fitted by the pseudo second order and Langmuir model, respectively. The adsorption efficiency was seen to be reduced with temperature. The regeneration of the used CMPS-DB18C6 resin was accomplished by 0.5 M HNO3acid and regenerated resin was reused up to four cycles with modest change in the adsorption capacity. The breakthrough curve analysis using a fixed-bed column showed 99.6% adsorber performance with bed capacity of 147.56 mg/g and 1.38 mbar pressure drop across the adsorber bed. The adsorbent showed good radiation stability as seen from the almost constant strontium distribution coefficient up to 500 kGy radiation dose. Further, the high adsorption and selectivity of Sr2+ ion was complimented using complexation Gibbs free energy by performing density functional theoretical calculations. The present work might provide an easy and efficient adsorptive removal process for the separation Sr2+ ions from radioactive waste stream for environmental remediation.

Effect of EDTA Complexation on the Kinetics and Thermodynamics of Uranium Redox Reactions Catalyzed by Pyrite: A Combined Electrochemical and Quantum-Mechanical Approach

Ethylenediaminetetraacetic acid (EDTA), a strong complexing agent, is a common constituent of liquid nuclear waste streams. The interaction of EDTA or other organic or inorganic ligands with uranyl enhances the mobilization of uranium and therefore significantly influences the disposal and remediation of uranium waste. Although numerous studies have focused on the effect of EDTA on the mobilization of environmental uranium, including the adsorption and redox reactions of uranium on mineral surfaces, few studies have differentiated the reaction-controlling steps (diffusion, adsorption, and chemical reaction/electron transfer) occurring at heterogeneous interfaces to assess the effect of EDTA complexation on each of these processes. Here, a combination of in situ electrochemical methods and quantum-mechanical calculations was used to study the effect of EDTA complexation on the kinetics and thermodynamics of redox reactions of uranium at the pyrite-solution interface. Experiments indicate a potential shift of U(VI)/U(V) on the pyrite surface of ∼0.04 V due to surface adsorption and −0.21 V due to EDTA complexation, with similar results from the calculations. The oxidation of the U(IV) reaction is more sensitive to EDTA complexation in solution than that of U(V). Disproportionation, affecting 2/3 of the intermediate pentavalent state, is the rate-limiting step of the overall redox cycle of uranyl. The charge transfer was controlled by diffusion and adsorption processes. EDTA can promote the delivery of free uranyl from the bulk solution to the pyrite–water interface where the reaction takes place, making the electron-transfer process less diffusion-limited. Adsorption of uranyl onto pyrite surfaces in the gradient electric field is multimolecular layer adsorption, through which electron transfer can occur.

Leveraging Multiple Raman Excitation Wavelength Systems for Process Monitoring of Nuclear Waste Streams

Leveraging Multiple Raman Excitation Wavelength Systems for Process Monitoring of Nuclear Waste Streams

Incorporation of Europium into (Ba,Ca)2[formula omitted

Synchrotron-based powder diffraction measurements in combination with inductively coupled plasma optical emission spectrometry, Raman and fluorescence spectroscopy show that (Ba,Ca)2(CO3)2 can incorporate significant amounts (up to 6 ​mol%) of europium. This solid solution is therefore of potential interest for the solidification of nuclear waste streams involving aqueous nitrate solutions of lanthanides. Europium replaces Ba/Ca on lattice sites and is not incorporated as an interstitial defect. Charge compensation is likely due to the presence of OH−-groups as we could exclude a coupled substitution involving Na+. The Eu-containing compound is stable to at least 723 ​K. We show that the one-phase-field of (Bax,Ca(1−x))CO3 solid solutions at ambient conditions is larger (0.36 <x< 0.51) than previously thought. The synthesis routes employed here lead to compounds which have similar molar volumes than those of the naturally occurring (Ba,Ca)-double carbonates, in noted contrast to another synthetic phase, “balcite”.

An exploration of benchtop X‐ray emission spectroscopy for precise characterization of the sulfur redox state in cementitious materials

The evolution of sulfur chemistry in cements is best known in the bailiwick of failure mechanisms via sulfate attack, but is equally important for its contributions to the reduction capacity of cementitious materials often used for immobilizing nuclear waste streams destined for long‐term storage, for example, cementitious waste forms (CWF). The total reduction capacity of CWFs, encompassing contributions from both S and Fe reductants, and its implications toward radionuclide immobilization is most often studied by destructive wet chemistry methods requiring acid digestion in the presence of Ce(IV) and subsequent titration and colorimetric interpretation. Here, we investigate a similarly analytical but nondestructive alternative, benchtop high resolution wavelength‐dispersive X‐ray fluorescence spectroscopy, most commonly known as X‐ray emission spectroscopy (XES), for probing the bulk sulfur oxidation state distribution. We present here an initial investigation of S XES, including an improved experimental protocol for lab XES of inhomogeneous samples, both as a complement to the Ce(IV) test and for new scientific opportunities that it enables for observing changes in sulfur chemistry. We discuss future improvements and opportunities, including: (1) the practical challenges associated with coordinating XES and Ce(IV) liquid extraction for a more comprehensive perspective on reduction capacity and for a high‐precision evaluation of uncertainties in the Ce(IV) test; and (2) new opportunities, due to the nondestructive nature of XES, for controlled evolution studies aimed at elucidating specific chemical responses of CWFs exposed to invasive gas or liquid species or to accelerated aging by radiative dose or thermal treatment.

Thermodynamic Probability Analysis of the Effects of Rb on the Corrosion Susceptibility of Cr-Containing Steels for Nuclear Materials Canisters

Rubidium (Rb) generated from the β-decay of Kr-85 has been theorized to be corrosive toward steel, specifically in the storage of Kr-85 nuclear waste streams. In the present study, the phase equilibria of RbxCryOz with Rb in dry oxygen and water are investigated to understand a possible pathway to unusual deterioration of the corrosion resistance of canister steels in the presence of Rb. It was found that, in dry oxygen environments, the accumulation of Rb (more than 0.01 mol) can completely consume the Cr in 1 mol of AISI 4130 steel by forming α-Rb2CrO4 and Rb3CrO4 and prevent the formation of protective Cr2O3 scale. In aqueous environments, RbxCryOz are metastable species. In order to investigate their role, the probability of forming various oxides is invoked in order to avoid the all-or-nothing approach to oxide formation typical of E-pH diagram, which only predicts the most stable species dissolved, ionized, or solid ionized. Thus, the probability of forming RbxCryOz was considered and reported herein. It was found RbxCryOz can possess a larger than 7% probability of forming over Cr2O3 in the Rb-rich case and 15% in the Cr-rich case, indicating that it is expected to find a small amount of RbxCryOz in the thermodynamically formed reaction products. Even though Cr2O3 is more stable than RbxCryOz, the protective Cr2O3 scale is likely to have some vulnerability to Rb, leading to one possible route for the decline in the corrosion resistance of steel canisters in aqueous environments. Therefore, from a thermodynamic perspective, the current study supports the hypothesis that Rb can thermodynamically react with Cr in steels and can lead to the formation of RbxCryOz at certain potentials and pH levels, showing the Rb influence of steel corrosion cannot be discounted. The paper considers experimental mixed potential and pH levels observed and their relationship to thermodynamic probability. From this relative corrosion resistance can be assessed in a preliminary way in aqueous environments.

Reversible iodine vapor capture using bipyridine-based covalent triazine framework: Experimental and computational investigations

To address the environmental issues arising from the emission of radiotoxic iodine from nuclear waste streams, developing high-capacity and recyclable adsorbents is urgently demanded. In this study, a nitrogen-rich covalent-triazine framework (CTF-bpy) was synthesized through the ionothermal synthetic method and was used as a reusable adsorbent to capture iodine vapor for sequential cycles. The obtained CTF-bpy adsorbent showed ultrahigh iodine vapor capture capacity of 4.52 g.g−1 at 90 °C and atmospheric pressure, which ranks among the highest values reported to date. CTF-bpy could be simply recycled by washing and heating while preserving above 89.6% of its initial iodine capture capacity after five consecutive cycles, demonstrating its excellent structural stability. Assessment of the adsorption kinetics of the iodine vapor through the fractal-like pseudo-first-order (FL-PFO) kinetic model revealed that the diffusion through micropores was the rate-controlling mechanism. Moreover, the density functional theory (DFT) calculations further demonstrated the significance of the surface's basicity and aromaticity of the structure in efficiently capturing the iodine species. This study may shed light on designing and developing novel adsorbents suitable for solving one of the main environmental issues.