Low Uranium Concentrations Research Articles

Radiogenic Strontium‐ and Uranium‐Isotope Tracers of Water‐Rock Interactions and Hydrothermal Flow in the Upper Geyser Basin, Yellowstone Plateau Volcanic Field, USA

AbstractNatural radiogenic isotopes (primarily 87Sr/86Sr) from hot springs in the Upper Geyser Basin of the Yellowstone Plateau volcanic field and associated rocks were used to evaluate groundwater flow patterns, water‐rock reactions, and the extent of mixing between various groundwater sources. Thermal waters have very low uranium concentrations and 234U/238U activity ratios near 1.0, which limit their utility as tracers in this reducing setting. Thermal waters have higher Sr concentrations (<22 ng/g) and a wide range of 87Sr/86Sr values that vary both temporally at individual discharge sites and between adjacent springs, indicating that conduits tap different subsurface reservoirs to varying degrees. Sr from local rhyolites have 87Sr/86Sr compositions that bound the range of values observed in groundwater throughout the basin. Non‐boiling springs on the west flank of the basin discharge water with low 87Sr/86Sr consistent with flow through young volcanic rocks exposed at the surface. Boiling springs in the central basin have higher 87Sr/86Sr values reflecting interactions with older, more radiogenic volcanic rocks. Variability in upwelling thermal waters requires mixing with a low 87Sr/86Sr component derived from young lava or glacial sediments, or more likely, from deeper sources of hot groundwater circulating through buried Lava Creek Tuff having intermediate 87Sr/86Sr. Isotope data constrain basin‐wide output of thermal water to 110–140 kg·s−1. Results underscore the utility of radiogenic Sr isotopes as valuable tracers of hydrothermal flow patterns and improve the understanding of temperature‐dependent water‐rock reactions in one of the largest continental hydrothermal systems on Earth.

Constructing Ce–OH groups on CeO2 for enhancing removal and recovery of uranium from wastewater and seawater

Efficient recovery of uranium from wastewater and seawater provides an important guarantee for the sustainable growth of nuclear energy. Herein, we skillfully use the alkali etching method to construct CeO2 hollow spheres rich in Ce–OH groups for the removal and recovery of uranium from water matrixes. It is found that the CeO2 exhibits fast adsorption kinetics (equilibrium time within 10 min) and moderate adsorption capacity (143.1 mg/g), and the removal efficiency of low concentration uranium (0.1 g/L and 1 g/L) reaches 100% within 1 min of adsorption. Moreover, the adsorption of uranium by CeO2 is almost unaffected by common anions and cations in the environment, even if the concentration of anions is 1000 times that of uranium. More importantly, the CeO2 can enrich uranium concentration in seawater by 167.9 times and the recovery rate reaches 83.9%. Mechanistic studies reveal that the adsorption of uranium by CeO2 is mainly attributed to the rich Ce–OH groups on the surface of CeO2, resulting in the rapid adsorption of U(VI) and mainly forms a single-bridge model. The findings of this study provide a green and efficient path for the removal and recovery of uranium from wastewater and seawater.

Uranium electrolytic deposition with regenerable Se2− active sites at low cell voltage

The electrochemical extraction of uranium from wastewater represents an effective strategy for the sustainable supply of fuel and the protection of the environmental. However, the rational design of high-efficiency electrocatalysts remains a significant challenge, largely due to the lack of research on the structure–activity relationship. In this study, we developed a novel electrocatalysis based method for the extraction of uranium in solution, combining the redox of selenium (Se2-/Se4+) and uranium extraction. This method enables the high-efficiency extraction uranium in solution, even at relatively low cell voltages of 1 V. The Co3Se4-based electrocatalyst exhibits excellent UO22+ capture properties, endowing it with an electrolytic deposition capacity of 2264 mg g−1 at the concentration of 560 mg L−1 within 48 h. Even in a low concentration uranium solution (5 mg L−1), the extraction capacity can still reach 199.2 mg g−1. X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) revealed that the main active sites of Co3Se4 were renewable Se2- sites. The absorbed UO22+ can be spontaneously reduced to the unstable U(V) intermediate by reversible electron transfer, and then re-oxidized to (UO2)O2·2H2O in the presence of hydrogen peroxide (H2O2). The significant discovery provides a novel electrochemical medium, elucidates the mechanism of the uranium extraction process, and introduces a novel strategy for harvesting U from wastewater.

Preparation of double network antibacterial hydrogel modified by hydroxamic acid gelatin/polyacrylamide and high efficiency uranium extraction from seawater

Uranium extracted from seawater can solve the problem of the shortage of uranium on land and provide potential resources for the nuclear power industry. However, the high salinity and low uranium concentration in seawater, coupled with the presence of competing ions and bacteria, pose significant challenges to this technology. In this study, a hydroxyl oxime acid modified gelatin/polyacrylamide double network (Gel/PAM(DN)-HA) hydrogel developed for efficient uranium extraction from seawater. The adsorption capacity of Gel/PAM(DN)-HA hydrogel for uranium in 15 ppm uranium solution was as high as 397.04 mg-U/g-Ads, with a reuse rate of 78.46 % ± 5.84 % after 5 cycles of adsorption-desorption. Gel/PAM(DN)-HA was immersed in natural seawater for 24 days to evaluate its adsorption capacity. Gel/PAM(DN)-HA demonstrated an impressive uranium extraction capacity of 4.801 mg·g−1. Antibacterial experiments demonstrated that Gel/PAM(DN)-HA can effectively inhibit the Escherichia coli (E. coli ATCC25922) and Staphylococcus aureus (S. aureus ATCC6538). The results highlight the adsorbent's significant potential for extensive utilization in extracting uranium from seawater.

The Preparation of a Polyamidoxime-Phosphorylated Cellulose Nanofibrils Composite Aerogel for the Selective Extraction of Uranium from Seawater.

Uranium is the most important fuel for nuclear power operations, and the safe supply of its resources is the key to the development of nuclear power in China. Because of the complex seawater environment and extremely low uranium concentration, extracting uranium from natural seawater poses a significant challenge. In this study, a polyamidoxime-phosphorylated cellulose nanofibril composite aerogel was prepared as an adsorbent for uranium extraction from seawater. An adsorption kinetics test, equilibrium adsorption isotherm model fitting, an adsorption-desorption cycle test, and a selectivity test were carried out to evaluate the adsorption performance of the composite aerogel for uranium extraction. The adsorption capacities for the initial concentrations of 4 and 8 ppm in uranium-spiked pure water were 96.9 and 204.3 mg-U/g-Ads, respectively. The equilibrium uranium adsorption capacities of uranium-spiked simulated seawater were 38.9 and 51.7 mg-U/g-Ads, respectively. The distribution coefficient KD of uranium was calculated to be 2.5 × 107 mL/g. The results show that the polyamidoxime-phosphorylated cellulose nanofiber composite aerogels prepared in this study have the advantages of low cost and high uranium selectivity for uranium extraction from seawater.

Contribution of coupled ESR/U-series fossil dating to a Paleolithic-Neolithic transition site - Naminan, Southwest China

The coupled ESR and U-series (ESR/U-series) method has been increasingly utilized for dating fossil teeth from Early to Middle Pleistocene hominid sites. One significant advantage of this method is its ability to directly analyze fossil animal or human teeth. However, compared with other radiometric methods such as 14C charcoal dating, U-series carbonate dating, and OSL sediment dating, this dating method is rarely employed for Late Pleistocene or younger sites. In this study, we present an ESR/U-series dating investigation conducted at the Naminan site, a Paleolithic-Neolithic transition (P–N transition) site situated on the Sino-Myanmar border. The ESR/U-series analysis of eleven dental samples yields an age range of 18.1–13.2 ka for the fossils. These obtained ages are generally consistent with the 14C chronology of the site. When dealing with young fossil samples, it was observed that due to relatively low uranium concentration in dental tissues, internal dose rate plays a less significant role compared to external beta and gamma dose rates in the total dose rate of the fossil samples. Consequently, evaluating the dose rate of surrounding sediment becomes a primary source of uncertainty. Additionally, in this study we attempted to employ the standardized growth curve (SGC) and representative dose response curve method for determining Equivalent Dose (DE), which was then compared with values obtained using additive dose method (ADM). Although the precision of DE estimated by two methods are comparatively lower than that of ADM, it demonstrates the potential to efficiently determine a more rational Dmax for irradiation, identify samples with stratigraphic disturbances, and analyze small or valuable fossil specimens.

Navigating the complexity of detrital rutile provenance: methodological insights from the Neotethys Orogen in Anatolia

Abstract. Sedimentary provenance is a powerful tool for reconstructing convergent margin evolution. However, single mineral approaches, like detrital zircon, have struggled to track sediment input from mafic and metamorphic sources. Detrital rutile complements detrital zircon datasets by offering a path forward in sedimentary provenance reconstructions where metamorphic terranes are potential source regions. However, U–Pb geochronology in rutile can be difficult due to low uranium concentrations and incorporation of common Pb, and multiple workflows are currently in use. Here, we investigate U–Pb and trace element data reduction, processing, and common Pb correction workflows using new detrital rutile U–Pb geochronology and trace element geochemistry results from the Late Cretaceous to Eocene Central Sakarya and Sarıcakaya basins in Anatolia. A significant number of analyses were rejected (54 %) due to signal intensity limitations, namely low U, low Pb, anomalous signal, and inclusions. We identify this as a universal limitation of large-n detrital rutile studies and recommend the systematic reporting of the amount of discarded analysis and the processes for rejection in all studies using detrital rutile U–Pb geochronology. Additionally, we show that (1) the 208Pb and 207Pb common Pb reduction schemes produce similar age distributions and can be used interchangeably, while (2) the Stacey–Kramers distance is a suitable metric for quantifying U–Pb discordance, but a discordance filter is not recommended. (3) Instead, filtering U–Pb data by a power law function based on the corrected date uncertainty is appropriate. (4) The exclusion of low uranium concentration rutile biases date distributions and favors pelitic-derived, higher Zr-in-rutile temperature, and higher U–Pb concordance grains. (5) Paired U–Pb and trace elements can be used to evaluate potential bias in U–Pb data rejection, which reveals that data rejection does not bias the provenance interpretations. Finally, (6) The signature of sediment recycling can be identified through U–Pb dates and Zr-in-rutile temperatures. To better navigate the complexity of detrital rutile datasets and to facilitate the standardization of data reporting approaches, we provide open-access code as Jupyter notebooks for data processing and analysis steps, including common Pb corrections, uncertainty filters, discordance calculations, and trace element analysis.

Highly acid-stable polyvinyl alcohol/chitosan/phytic acid aerogel for selective separation of uranium from actual wastewater

Conventional adsorption materials encounter difficulties in achieving optimal selectivity in uranium-containing wastewater (UCW) because of the low uranium concentration and the presence of diverse coexisting ions. Aerogel, renowned for its abundance of adsorption sites and remarkable structural flexibility, is widely regarded as an innovative material. Nonetheless, its stability in solution hinders its utility in the separation of uranium during wastewater treatment. To counter this limitation, a polyvinyl alcohol/chitosan/phytic acid aerogel (PCPA) was synthesized by employing several polymerization agents. An exceptional degree of selectivity, speed, and stability was achieved in the separation of low concentration uranium from UCW. The results indicated that polyvinyl alcohol (PVA) proved to be the most effective in generating stable aerogels, even when immersed in 0.1 M HCl or acidic UCW. PCPA displayed the highest efficacy in isolating U(VI) in UCW at a pH of 6.0. The novel aerogel exhibited remarkable resistance to ion interference during adsorption, leading to an impressive 96.3 % efficiency in the separation of U(VI) from actual low-concentration UCW. Even after five desorption, PCAC could still achieve U(VI) separation efficiencies of more than 80 %. The adsorption of U(VI) in this aerogel is characterized by chemisorption. PVA plays a crucial role in the condensation process of the aerogel, resulting in an increase in the presence of easily dissociable -OH groups. This, in turn, effectively improves the selectivity of the aerogel. PCPA has demonstrated successful capability in the efficient recovery of uranium from UCW.

Unconventional extraction of uranium from seawater through microenvironment-specific conjugated microporous poly(aniline)s

The sustainability of uranium-based nuclear energy relies on the development of quick and effective uranium adsorbents. Herein, we propose a facile post-synthetic technique by grafting amino-functional groups onto the fluorenone-functionalized conjugated microporous poly(aniline)s (CMPs) network to acquire a novel class of N decorated polymers for uranium capture. By leveraging the abundant N sites and microenvironment-containing molecular structure, CMPA-F-BDA showcases excellent UO22+ adsorption performance with fast adsorption kinetic with initial adsorption rate up to 43.78 mg g−1 min−1, Langmuir adsorption capacity of 443 mg g−1 and exceptional adsorption selectivity of Kd = 1.3 × 107 mL g−1 even in the serious presence of competitive cations. Additionally, CMPA-F-BDA could treat up to 18.5 L g−1 of low-concentration uranium solution (1 mg L−1) and actual seawater, removing 87.9% of uranium from 10 L of seawater, and has excellent reusability. This study demonstrates the bright future of CMPs for the extraction of low-concentration uranium.

Enhanced capture of uranyl in simulated seawater by supramolecular PSA@PAO hydrogel through carboxyl synergistic effect

Efficient capture of uranium from seawater is of great significance for promoting the sustainable development of nuclear energy and environmental protection. The preparation of highly efficient adsorbent materials plays a key role in this process. In this study, a composite gel PSA@PAO with ultra-high uranium adsorption capacity and excellent desorption efficiency was successfully designed through the supramolecular crosslinking and synergistic effect of glutaraldehyde, hydrazine oxime, sodium alginate, and polyvinyl alcohol. The gel achieved a uranium adsorption capacity of 348 mg·g−1 in a solution with an extremely low uranium concentration (8 ppm) and exhibited ultra-high adsorption selectivity for uranium oxyanions in simulated seawater containing various metal ions. XPS analysis showed that the acylhydrazone groups and carboxylic acid ligands in the PSA@PAO gel could form more stable synergistic uranium complexes. In the desorption solution, the recovery rate of uranium by the PSA@PAO gel reached 98 %, providing a certain strategy for designing efficient adsorbent materials with multi-functional group synergistic effect.

Open-Framework Vanadate as Efficient Ion Exchanger for Uranyl Removal.

The elimination of uranium from radioactive wastewater is crucial for the safe management and operation of environmental remediation. Here, we present a layered vanadate with high acid/base stability, [Me2NH2]V3O7, as an excellent ion exchanger capturing uranyl from highly complex aqueous solutions. The material possesses an indirect band gap, ferromagnetic characteristic and a flower-like morphology comprising parallel nanosheets. The layered structure of [Me2NH2]V3O7 is predominantly upheld by the H-bond interaction between anionic framework [V3O7]nn- and intercalated [Me2NH2]+. The [Me2NH2]+ within [Me2NH2]V3O7 can be readily exchanged with UO22+. [Me2NH2]V3O7 exhibits high exchange capacity (qm = 176.19 mg/g), fast kinetics (within 15 min), high removal efficiencies (>99%), and good selectivity against an excess of interfering ions. It also displays activity for UO22+ ion exchange over a wide pH range (2.00-7.12). More importantly, [Me2NH2]V3O7 has the capability to effectively remove low-concentration uranium, yielding a residual U concentration of 13 ppb, which falls below the EPA-defined acceptable limit of 30 ppb in typical drinking water. [Me2NH2]V3O7 can also efficiently separate UO22+ from Cs+ or Sr2+ achieving the highest separation factors (SFU/Cs of 589 and SFU/Sr of 227) to date. The BOMD and DFT calculations reveal that the driving force of ion exchange is dominated by the interaction between UO22+ and [V3O7]nn-, whereas the ion exchange rate is influenced by the mobility of UO22+ and [Me2NH2]+. Our experimental findings indicate that [Me2NH2]V3O7 can be considered as a promising uranium scavenger for environmental remediation. Additionally, the simulation results provide valuable mechanistic interpretations for ion exchange and serve as a reference for designing novel ion exchangers.

Laser In Situ U–Pb Isotope Dating of Carbonate Rocks in Weijia Guyot in the Western Pacific Ocean and Its Geological Significance

Shallow-water carbonate rocks constitute a crucial component of large guyots, arising in distinct environments and harboring valuable insights into the evolutionary stages of seamount islands as well as the tectonic conditions of the underlying oceanic plate. Laser Ablation Multi-Collector Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICP-MS) was used to conduct in situ U–Pb isotope dating of carbonate minerals with low uranium content collected from Weijia Guyot. This dating approach yielded crucial evidence for the vertical development of the seamount. Our study indicates that shallow-water carbonate rocks in Weijia Guyot had a temporal range between 91 My and 137 My. The carbonate rocks underwent two growth phases, Hauterivian to Barremian and Cenomanian to Turonian, with a hiatus of approximately 20 My. Since the Hauterivian age, the shield volcano of Weijia Guyot is essentially complete, with its seamount top exposed at or near sea level and receiving its first stage of shallow-water carbonate sedimentation. Based on the dating of both shallow-water carbonate rocks and hawaiite within the Weijia Guyot, it is inferred that approximately 10 My elapsed from shield-building volcanism to late alkalic volcanism. During the Turonian age, the main reason for the second phase of shallow-water carbonate rocks in the seamounts was the regional tectonic uplift triggered by the drift of the Weijia Guyot along with the Pacific Plate toward the Society hotspot.

Magnetic alginate supported potassium manganese ferrocyanide for the recovery of uranium from acidic wastewater

Abstract With the rapid development of the atomic energy industry, the demand for nuclear fuel has risen, while the limited resources of uranium mines make it difficult to meet the needs of the future development of nuclear energy. Expanding sources of uranium acquisition is necessary, and the enrichment and recovery of precious uranium from uranium-containing wastewater is invaluable. By synthesizing alginate supported potassium manganese ferrocyanide nanocomposites with magnetic response (KMnFC/MA/Fe3O4), the high efficiency adsorption and separation of uranium in acidic uranium-containing wastewater can be realized conveniently and quickly. The magnetic composite was characterized by a variety of technical means, and the adsorption behavior of the magnetic material on uranium was studied by static adsorption experiments under different environmental conditions. The adsorption kinetics and isotherm of uranium by KMnFC/MA/Fe3O4 were studied by using some common linear adsorption models. The results show that the adsorption rate of KMnFC/MA/Fe3O4 on uranium is fast, and the adsorption equilibrium can be reached within 90 min. The adsorption process conforms to a pseudo-secondary kinetic model and is dominated by chemisorption. The adsorption of uranium by KMnFC/MA/Fe3O4 magnetic material is single molecular layer adsorption, and the maximum adsorption capacity is 425.5 mg g−1 at 35 °C. KMnFC/MA/Fe3O4 is a promising adsorbent in the field of acidic low-concentration uranium wastewater treatment because of its good effect on the treatment of low concentration uranium wastewater, the concentration of uranium in the wastewater reaches the emission standard after treatment and it is easy to be separated magnetically after adsorption.

Adsorbents for the Uranium Capture from Seawater for a Clean Energy Source and Environmental Safety: A Review.

On the global level, uranium is considered the main nuclear energy source, and its removal from terrestrial ores is enough to last until the end of the current century. Therefore, a major focus is attracted toward the capture of uranium from a sustainable source (seawater). Uranium recovery from seawater has been reported over the last few decades, and recently many efforts have been devoted to the preparation of such adsorbents with higher selectivity and adsorption capacity. The purpose of this review is to report the advancement in adsorbent preparation and modification of porous materials. It also discusses challenges such as adsorbent selectivity, low uranium concentration in seawater, contact time, biofouling, and the solution to the problems necessary to ensure a better adsorption performance of the adsorbent.

Promising porous materials for uranium extraction from seawater

Uranium extraction from seawater is a promising approach for ensuring continued uranium fuel supply to the nuclear power industry. However, extracting uranium by this route is challenging due to the low concentration of uranium, high ionic strength, and marine micro-organisms in seawater. Recently, a range of novel porous adsorbent materials have been developed for uranium extraction from ocean water. These adsorbents rely on specific pore characteristics and functional groups (hydroxyl, carboxyl, amidoxime, phosphate, etc.) to achieve a high affinity and selectivity for uranyl ions (UO22+) relative to other ions. Relying strongly on coordination principles, specific binding sites for uranium are assembled in these porous materials, with cooperative actions of several functional groups often used to achieve strong uranium capture and adsorption selectivity. In addition to traditional adsorbents, adsorption-photocatalytic and adsorption-electrocatalytic materials are also being pursued, which include both specific adsorption sites and photocatalytic or electrocatalytic moieties in their frameworks. These innovative strategies allow the conversion of uranyl ions into harvestable solid products (such as UO2 or Na2O(UO3·H2O)x) and result in high extraction efficiencies together with good biofouling resistance. This perspective aims to capture some of the recent breakthroughs in the design of porous materials for selective uranium extraction from seawater.

Emerging Nanomaterials toward Uranium Extraction from Seawater: Recent Advances and Perspectives.

Nuclear energy holds great potential to facilitate the global energy transition and alleviate the increasing environmental issues due to its high energy density, stable energy output, and carbon-free emission merits. Despite being limited by the insufficient terrestrial uranium reserves, uranium extraction from seawater (UES) can offset the gap. However, the low uranium concentration, the complicated uranium speciation, the competitive metal ions, and the inevitable marine interference remarkably affect the kinetics, capacity, selectivity, and sustainability of UES materials. To date, massive efforts have been made with varying degrees of success to pursue a desirable UES performance on various nanomaterials. Nevertheless, comprehensive and systematic coverage and discussion on the emerging UES materials presenting the fast-growing progress of this field is still lacking. This review thus challenges this position and emphatically focuses on this topic covering the current mainstream UES technologies with the emerging UES materials. Specifically, this review elucidates the causality between the physiochemical properties of UES materials induced by the intellectual design strategies and the UES performances and further dissects the relationships of materials-properties-activities and the corresponding mechanisms in depth. This review is envisaged to inspire innovative ideas and bring technical solutions for developing technically and economically viable UES materials.

An integrated study of constraining the initial 230Th of a stalagmite and its implications

High-precision U–Th age is the key to promoting speleothem as an important archive for paleoclimate study. Notably, obtaining reliable U–Th age primarily relies on the accurate initial 230Th correction. However, correcting the U–Th age of stalagmite with the average 232Th/238U value in the crust is sometimes not enough to eliminate the effect of the initial 230Th, using other dating methods (e.g., 14C) and referring to the characteristics of speleothem δ18O values are useful to guide its age correction and establish the chronology. This paper presents a comprehensive study of the chronology and isotopic record of a stalagmite XBL-5 from Xiaobailong Cave, Yunnan, China, using a combination of stalagmite U–Th dating, 14C dating, and δ18O wiggle match dating. The low uranium content of this stalagmite and the apparent inversion of U–Th dating prevent us from establishing the proxy profiles with reliable chronology. We determined the actual age range based on 14C ages assuming various dead carbon proportion (DCP) and uncorrected U–Th ages, along with the characteristic of stalagmite δ18O variations, and then established a credible chronology of this stalagmite through wiggle match of δ18O records. Taking the tuned ages as a reference, the initial 230Th/232Th values were reciprocally calculated. The initial 230Th/232Th atomic ratio of the studied samples was back-calculated to be 75.7 ± 11.4 × 10−6, an order of magnitude higher than the commonly used correction value. The reconstructed XBL-5 δ18O record spans the Younger Dryas (YD) period, indicating that the precipitation δ18O generally increased within the YD chronozone with significant centennial scale oscillations in regions affected by the Indian summer monsoon, in contrast to the speleothem records from East Asian summer monsoon domains which show no or even weakly decreased long-term trend in precipitation δ18O. This study highlights the importance of initial thorium correction in stalagmite chronology study and provides a paradigm for sequence reconstruction of similar samples.

Design of amidoximized hydroxyapatite for extracting uranium from seawater

Extracting uranium from natural seawater is a huge challenge because of the complex environment of seawater and extremely low uranium concentration. In this work, amidoximized hydroxyapatite (AO-HAP) was prepared to capture uranium from seawater. The introduction of amidoxime group greatly improved the recognition ability of AO-HAP for uranium in neutral and weakly alkaline environment (pH = 7–8). The uptake process of AO-HAP for uranium was fitted by Langmuir and pseudo-second-order models, suggesting that the capture behavior of AO-HAP for uranium was a homogeneous chemisorption. The saturated uranium uptake capacity of AO-HAP was 865.3 mg g−1 from aqueous solution, which was better than most of other reported uranium extractants. More importantly, AO-HAP had good regeneration ability and excellent adsorption performance in natural seawater (6.25 mg g−1 in 30 days). In sum, AO-HAP is a highly potential candidate as adsorbent material for the efficient extraction of uranium from seawater.

A convenient functionalization strategy of polyimide covalent organic frameworks for uranium-containing wastewater treatment and uranium recovery

The purpose of this research was to design and synthesize an adsorbent based on polyimide covalent organic frameworks (PICOFs) for uranium-containing wastewater treatment and uranium recovery. A modified solvothermal method was innovatively proposed to synthesize PICOFs with high specific surface area (1998.5 m2 g−1) and regular pore structure. Additionally, a convenient functionalization strategy of PICOFs was designed through polydopamine (PDA) and a well-dispersed polymer (MPC-co-AO) containing multiple functional groups, forming stable composite (PMCA-TPPICOFs) in which the hydrogen bonding and cation-π interactions between PDA and MPC-co-AO played a key role. The obtained PMCA-TPPICOFs as an adsorbent exhibited strong selectivity for uranyl ions (maximum adsorption capacity was 538 mg g−1). In simulated wastewater with low uranium concentrations, the removal rate reached 98.3%, and the concentration of treated simulated wastewater met discharge standards. Moreover, PMCA-TPPICOFs was suitable for fixed-bed column adsorption because of its favorable structure. According to the research about adsorption mechanism, the adsorption primarily relied on electrostatic interaction and complexation. In summary, PMCA-TPPICOFs exhibited good potential for uranium-containing wastewater treatment, expanding the application of PICOFs. And the proposed functionalization strategy and modified solvothermal method may promote research in the fields of material functionalization and COFs synthesis. Environmental ImplicationUranium is a raw material for nuclear energy applications, which is toxic and radioactive. If uranium is discharged with wastewater, it would not only pose a threat to the environmental protection and life safety, but also cause the loss of precious nuclear raw materials. Although adsorption was considered to be an effective way to remove uranium, many of the developed adsorbents were difficult to apply due to the harsh wastewater environment and complex preparation processes. This study reported a novel adsorbent and a new functionalization strategy, which was expected to solve the problem of uranium recovery in wastewater.

High-strength ionic hydrogel constructed by metal-free physical crosslinking strategy for enhanced uranium extraction from seawater

Uranium is one of the most important elements in the nuclear industry, and efficient extraction of uranium from the ocean is conducive to the sustainable development of nuclear energy. In this work, rigid perylene tetracarboxylate anion (PTC4−) was introduced by physical (non-covalent) crosslinking strategy to obtain metal-free ionic hydrogel PAOIB-PTC. PTC4− not only increased the rigid structure content of ionic hydrogel, but also formed dynamic macrocycle AO-PTC with amidoxime (AO) through hydrogen bonds. Unlike reported heterogeneous additives, PTC4− did not undergo inhomogeneity or shedding. Therefore, PAOIB-PTC exhibited high strength (7.34 MPa), excellent solvent resistance and salinity tolerance. A large number of hydrophilic groups and multistage pore structure endowed PAOIB-PTC with high hydrophilicity, which facilitated U(VI) mass transfer and led to rapid adsorption rates (88.6 mg g−1 h−1, c0 = 250 ppm). Since the metal-free component enabled more adsorption sites to be utilized, the maximum adsorption capacity of PAOIB-PTC was as high as 1008.03 mg g−1, which exceeded most reported hydrogel-based uranium adsorbents. Experiments and DFT calculations proved that PAOIB-PTC possessed high adsorption selectivity through uranyl recognition via hydrogen bonding and synergistic coordination by supramolecular structure AO-PTC. The low-concentration uranium capture capability and excellent recycling performance demonstrated the practical application potential of PAOIB-PTC. This work provides an idea for the design of metal-free ionic hydrogels with high-strength, and the established PAOIB-PTC is expected to be a candidate material for enhanced uranium extraction from seawater.