Mechanical investigation of U(VI) on pyrrhotite by batch, EXAFS and modeling techniques

An effective uranium removal using diversified synthesized cross-linked chitosan bis-aldehyde Schiff base derivatives from aqueous solutions

Three new cross-linked chitosan derivatives were yielded through intensification of chitosan with diverse types of bis-aldehydes. The prepared cross-linked chitosan was characterized by FTIR, 1H NMR, XRD, and TGA techniques. TGA indicated an improvement in thermal stability of the cross-linked chitosan compared with pure chitosan. Batch adsorption experiments showed that the three novel cross-linked chitosan bis-aldehyde derivatives possessed good adsorption capacity against U(VI) in the order of BFPA > BFB > BODB (adsorption capacity of the three adsorbents for U(VI) reaches 142, 124, and 114 mg/g respectively) and the adsorption isotherm and kinetic were well described by the Langmuir and the pseudo-second-order kinetic model, respectively. In addition, the prepared cross-linked chitosan bis-aldehyde derivatives were examined as U(VI) catcher from waste solutions.

Vanadate Bio-Detoxification Driven by Pyrrhotite with Secondary Mineral Formation

Vanadium(V) is a redox-sensitive heavy-metal contaminant whose environmental mobility is strongly influenced by pyrrhotite, a widely distributed iron sulfide mineral. However, relatively little is known about microbially mediated vanadate [V(V)] reduction characteristics driven by pyrrhotite and concomitant mineral dynamics in this process. This study demonstrated efficient V(V) bioreduction during 210 d of operation, with a lifespan about 10 times longer than abiotic control, especially in a stable period when the V(V) removal efficiency reached 44.1 ± 13.8%. Pyrrhotite oxidation coupled to V(V) reduction could be achieved by an enriched single autotroph (e.g., Thiobacillus and Thermomonas) independently. Autotrophs (e.g., Sulfurifustis) gained energy from pyrrhotite oxidation to synthesize organic intermediates, which were utilized by the heterotrophic V(V) reducing bacteria such as Anaerolinea, Bacillus, and Pseudomonas to sustain V(V) reduction. V(V) was reduced to insoluble tetravalent V, while pyrrhotite oxidation mainly produced Fe(III) and SO₄^2-. Secondary minerals including mackinawite (FeS) and greigite (Fe₃S₄) were produced synchronously, resulting from further transformations of Fe(III) and SO₄^2- by sulfate reducing bacteria (e.g., Desulfatiglans) and magnetotactic bacteria (e.g., Nitrospira). This study provides new insights into the biogeochemical behavior of V under pyrrhotite effects and reveals the previously overlooked mineralogical dynamics in V(V) reduction bioprocesses driven by Fe(II)-bearing minerals.

Constructing new Fe3O4@MnOx with 3D hollow structure for efficient recovery of uranium from simulated seawater

Enrichment of uranium from seawater is a promising method for addressing the energy crisis. Current technologies are generally not effective for enriching uranium from seawater because its concentration in seawater is low. In this study, new Fe₃O₄@MnO_x with 3D hollow structure, which is capable of enriching low concentration uranium, was prepared via a novel redox etching method. The physicochemical characteristics of Fe₃O₄@MnO_x were studied with TEM, HRTEM, SEAD, FTIR, XRD, and N₂ adsorption-desorption analysis. Dynamic kinetic studies of different initial U(VI) concentrations revealed that the pseudo-second-order model fit the sorption process better, and the sorption rates of Fe₃O₄@MnO_x in 1, 10, and 25 mg/L U(VI) solution were 0.0124, 0.00298, and 0.000867 g/mg·min, respectively. Isothermal studies showed that the maximum sorption amounts were 50.09, 56.27, and 64.62 mg/g for 1, 10, and 25 mg/L U(VI), respectively, at pH 5.0 and 313 K, suggesting that Fe₃O₄@MnO_x could effectively enrich low concentration U(VI) from water. The sorption amount of U(VI) did not significantly decrease in the presence of Na⁺, Mg²⁺, and Ca²⁺. HRTEM, FTIR, and XPS results demonstrated that Fe(II) and Mn/Fe-O-H active sites in Fe₃O₄@MnO_x were accounted for the high and specific enrichment efficiency. A column experiment was conducted to evaluate the U(VI) sorption efficiency of Fe₃O₄@MnO_x in simulated seawater. The U(VI) sorption efficiency remained above 80% in 28 days run. Our findings demonstrate that Fe₃O₄@MnO_x has extraordinary potential for the enrichment of uranium from simulated seawater.

Application of surface complexation modeling on adsorption of uranium at water-solid interface: A review

Precise prediction of uranium adsorption at water-mineral interface is of great significance for the safe disposal of radionuclides in geologic environments. Surface complexation modeling (SCM) as a very useful tool has been extensively investigated for simulating adsorption behavior of metals/metalloids at water-mineral interface. Numerous studies concerning the fitting of uranium adsorption on various adsorbents using SCM are well documented, but the systematic and comprehensive review of uranium adsorption using various SCM is not available. In this review, we briefly summarized the rationale of SCM, including constant-capacitance-model (CCM), diffuse-layer-model (DLM), triple-layer-model (TLM); The recent progress in the application of SCM on the fitting of uranium adsorption towards metal (hydr)oxides, clay minerals and soil/sediments was reviewed in details. This review hopefully provides the beneficial guidelines for predicting the transport and fate of uranium in geologic environments beyond laboratory timescales.

Assembly of three-dimensional ultralight poly(amidoxime)/graphene oxide nanoribbons aerogel for efficient removal of uranium(VI) from water samples

Assembling graphene oxide nanoribbons (GONRs) into three-dimensional (3D) materials with controllable and desired structure is an effective way to expand their structural features and enable their practical applications. In this work, an ultralight 3D porous amidoxime functionalized graphene oxide nanoribbons aerogel (PAO/GONRs-A) was prepared via solvothermal polymerization method using acrylonitrile as monomer and GONRs as solid matrices for selective separation of uranium(VI) from water samples. The PAO/GONRs-A possessed a high nitrogen content (13.5%), low density (8.5 mg cm^-3), and large specific surface area (494.9 m² g^-1), and presented an excellent high adsorption capacity of uranium, with a maximum capacity of 2.475 mmol g^-1 at a pH of 4.5, and maximum uranium-selectivity of 65.23% at a pH of 3.0. The results of adsorption experiments showed that U(VI) adsorption on PAO/GONRs-A was a pH-dependent, spontaneous and endothermic process, which was better fitted to the pseudo-second-order kinetic model and Langmuir isotherm model. Both X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations revealed that U(VI) adsorption on PAO/GONRs-A mainly did rely on the amidoxime groups anchored on the aerogel while UO₂(PAO)₂(H₂O)₃ was dominant after interaction of uranyl with PAO/GONRs-A. Therefore, as a candidate adsorbent, PAO/GONRs-A has a high potential for the removal of uranium from aqueous solutions.

Comparative study of strontium adsorption on muscovite, biotite and phlogopite

Micaceous minerals are the natural materials that can block radioactive strontium (Sr) released in the environment, and their adsorption capacity and mechanism are highly divergent owing to the different properties of micas. In this work, we comparatively studied the adsorption of Sr(II) on three typical micas, muscovite, biotite and phlogopite. The effects of pH, contact time, ionic strength, and background electrolyte were evaluated. It was found that phlogopite and muscovite had the largest solid-liquid distribution coefficient (K_d) for a reaction time of 48 h under acidic and alkaline conditions, respectively. Under alkaline conditions, as the reaction time increased to 44 days, phlogopite and muscovite showed the highest and lowest K_d, respectively. The K_d for Sr(II) adsorption on biotite and phlogopite increased with increasing pH but decreased with increasing pH for muscovite. X-ray diffraction analysis revealed that the interlayer weathering of phlogopite (a new diffraction peak appeared at 2-theta of ~6.1°) occurred along with the adsorption of Sr(II) below pH 9.0 under 0.01 mol/L NaCl. Furthermore, the adsorption of Sr(II) was significantly inhibited in the presence of 10^-5 and 10^-2 mol/L Cs⁺, resulting in similar adsorption capacity for phlogopite and muscovite at pH ~4.1. Consequently, the difference in Sr(II) adsorption on muscovite, biotite and phlogopite mainly came from the synergistic process of adsorption and weathering, which induced the differences in availability of interlayer sites among micas over a certain time.

Facile synthesis of multifunctional bone biochar composites decorated with Fe/Mn oxide micro-nanoparticles: Physicochemical properties, heavy metals sorption behavior and mechanism

The value-added utilization of waste resources to synthesize functional materials is important to achieve the environmentally sustainable development. In this work, novel micro-nano FeOx- and MnOx-modified bone biochars derived from waste bone meal were obtained at 300 °C, 450 °C and 600 °C, and applied to remove Cd(II), Cu(II) and Pb(II) from aqueous solutions. The results showed that the pyrolysis temperature greatly influenced the specific surface area (SSA), micropore creation, functional groups and heavy metal sorption capacities of FO-BCs and MO-BCs. The effects of solution pH, ionic strength, humic acid (HA), kinetics and thermodynamics on heavy metals adsorption were investigated. Langmuir and pseudo-second order kinetics models fit the adsorption data well, and the FO-BC-450 and MO-BC-600 displayed the highest sorption capacity for Cd(II) (151.3 mg/g and 163.4 mg/g), Cu(II) (219.8 mg/g and 259.0 mg/g) and Pb(II) (271.9 mg/g and 407.2 mg/g), respectively. Due to the dissolved partial hydroxyapatite (HAP), carbonate-bearing hydroxyapatite (CHAP) and the catalysis of Fe(NO₃)₃, the FO-BCs with higher SSA than the MO-BCs, whereas the sorption capacity displayed an opposite trend. The chemical complex, cation-π bonds, ion exchange and coprecipitation were the dominant mechanisms for metals adsorption. Overall, waste bone resource co-pyrolysis with Fe(NO₃)₃/KMnO₄ impregnation is a promising and high-efficient adsorbents for the remediation of heavy metals-contaminated waters.

Removal of uranium (VI) from water by the action of microwave-rapid green synthesized carbon quantum dots from starch-water system and supported onto polymeric matrix

Carbon quantum dots (CQDs) are a new class of carbon nanoparticles with superior advantages as small particle size, excellent biocompatibility and low toxicity which advance their recent applications in biotechnology, bioimaging and biosensing. The use of free CQDs in water treatment is greatly rendered by their high solubility in water. Therefore, this work is aimed to rapidly synthesize CQDs in only 10 min via microwave irradiation pyrolysis of starch-water system. The maximum fluorescence emission of CQDs was detected at 526 nm throughout the excitation wavelength (390 nm). The CQDs have been targeted to occupy the surface and pores of a polymeric material based on poly(anthranilic acid-formaldehyde-phthalic acid) (PAFP) to produce a novel CQDs@PAFP nanobiosorbent. The surface area of CQDs@PAFP was detected (28.79 m² g^-1 BET) and the nanoparticle size was confirmed (TEM). The highest removals of U(VI) by CQDs@PAFP nanobiosorbent were 95.5-98.0 % for 30-90 mg L^-1. The sorption mechanism was designated to the pseudo-second-order model and closely tailored with Freundlich model. CQDs@PAFP was emerged as an excellent nanobiosorbent for U(VI) removal from wastewater (97.3 %) and sea water (96.0 %). CQDs@PAFP confirmed its excellent reusablity for efficient multi- recovery of U(VI) from different water samples.

The removal of uranium using novel temperature sensitive urea-formaldehyde resin: adsorption and fast regeneration

A novel adsorbent of temperature sensitive urea-formaldehyde (TS-UF) resin was synthesized by base/acid two-step synthetic strategy with low formaldehyde/urea mole ratio of 0.8. The sorption kinetics of TS-UF resin obeys the pseudo-second-order model, and the adsorption is an endothermic process. The Langmuir model can well describe the sorption isotherms, through which the Q_max is calculated to be 99.2 mg/g for uranium (VI) at pH 6.0 and T = 298 K. The characterized results show that the functional groups -NH- and -CH₂OH in TS-UF resin have been involved in uranium sorption via chemical interaction. The temperature sensitive property of TS-UF resin significantly accelerates the regeneration of TS-UF resin, which can be fast regenerated within 15 min at its low critical solution temperature 333 K and exhibits high removal efficiency of uranium (VI) (>90%) over 5 cycles. Therefore, TS-UF resin can be as a promising sorbent for the uranium (VI) removal from wastewater due to its low-cost, easy-fabrication, high-efficiency and fast regeneration. This work can not only boost the exploration of novel adsorbent materials, but also promote the investigations of the regeneration and reusability of adsorbents.

The redox behavior of uranium on Beishan granite: Effect of Fe2+ and Fe3+ content

The Beishan granitic area in Gansu Province is a site with the greatest potential for a repository of high-level radioactive waste (HLW) in China. In this study, the redox behavior of uranium on Beishan granite was investigated at pH values from ~4.4 to ~9.2. Due to the presence of Fe²⁺-containing fluorannite, results showed that U(VI) was partially reduced by the granites from boreholes 2 (486 m) and 28 (670 m) at a relatively low initial pH whether Na₂CO₃/NaCl or native groundwater was used as a background electrolyte. Partial oxidation of UO₂ was observed when UO₂ contacted Beishan granite directly. Therefore, this incomplete reduction of U(VI) was mainly attributed to minor Fe³⁺ that was either originally contained in the granite or generated during U(VI) reduction. Consequently, aliovalent oxides (e.g., U₃O₈, U₃O₇, U₄O₉, etc.) should be the thermodynamically stable phase in Beishan granite. A mechanism involving the dissolution of Fe²⁺ from the granite structure followed by interfacial adsorption/reaction was proposed for the U(VI) reduction. This study demonstrates that Beishan granite has a good reducing capacity, which is suitable for the immobilization of redox-sensitive radionuclides. However, potential oxidation of spent fuel by Fe³⁺ in the granite should also been taken into account.

Low concentration of Fe(II) to enhance the precipitation of U(VI) under neutral oxygen-rich conditions

Immobilization of U(VI) by naturally ubiquitous ferrous ions (Fe(II)) has been considered as an efficient and ecofriendly method to retard the migration of aqueous U(VI) at many nuclear sites and surface environments. In this study, we conducted Fe-U coprecipitation experiments to investigate the mechanism and stability of uranium (U) precipitation induced by a small quantity of Fe(II) under oxygen-rich conditions. The experimental results suggest that the sedimentation rates of U(VI) by Fe(II) under neutral oxygen-rich conditions are more than 96%, which are about 36% higher than those without Fe(II) and 16% higher than those under oxygen-free conditions. The Fe-U coprecipitates were observed to remain stable under slightly acidic to neutral and oxygen-rich conditions. Fe(II) primarily settles down as low-crystalline iron oxide hydroxide. U(VI) mainly precipitates as three forms: 16-20% of U forms uranyl hydroxide and metaschoepite, which is absorbed on the surface of the solids; 52-56% of U is absorbed as discrete uranyl phases at the internal pores of iron oxide hydroxide; and 27-29% of U is probably incorporated into the FeO(OH) structure as U(V) and U(VI). The U(V) generated via one-electron reduction is somewhat resistant to the oxidation of O₂ and the acid dissolution. In addition, nearly 70% of U and only about 15% of Fe could be extracted in 24 h by a hydrochloric acid solution with the H⁺ concentration ([H⁺]) of 0.01 M, revealing that U(VI) immobilization by low concentration of Fe(II) combined with O₂ has potential applications in the separation and recycling of aqueous uranium.

Efficient U(VI) adsorption on iron/carbon composites derived from the coupling of cellulose with iron oxides: Performance and mechanism

Novel iron/carbon composites were successfully prepared via coupling of cellulose with iron oxides (e.g. α-FeOOH, Fe₂O₃ and Fe(NO₃)₃·9H₂O) at different temperatures under nitrogen atmosphere. Characterization by various techniques implied that chemical interaction between cellulose and Fe₃O₄/Fe⁰ existed in the as-prepared iron/carbon composites. The site of interaction between cellulose and iron precursors was illustrated (mainly combined with COO-). The self-reduction of Fe³⁺ to Fe²⁺ or even Fe⁰ and the interaction between carbon and Fe₃O₄/Fe⁰ in the calcination process realized the strong magnetism of the composites. Batch experiments and spectroscopic techniques indicated that the maximum adsorption capacity of MHC-7 for U(VI) (105.3 mg/g) was significantly higher than that of MGC-7 (86.0 mg/g) and MFC-7 (79.0 mg/g), indicating that Fe₂O₃ can be regarded as the remarkable iron resource for the iron/carbon composites. XPS results revealed that the oxygen-containing groups were responsible for the adsorption process of U(VI) on iron/carbon composites, and the adsorption of carbon and reduction of Fe⁰/Fe₃O₄ toward U(VI) were synergistic during the reaction process. In addition, the iron/carbon composites exhibited a good recyclability, recoverability and stability for U(VI) adsorption in the regeneration experiments. These findings demonstrated that the iron/carbon composites can be considered as valuable adsorbents in environmental cleanup and the Fe₂O₃ was a promising iron resource for the preparation of iron/carbon composites.

Ultra-thin iron phosphate nanosheets for high efficient U(VI) adsorption

In this study, the ultra-thin iron phosphate Fe7(PO4)6 nanosheets (FP1) with fine-controlled morphology, has been designed as a new two-dimensional (2D) material for uranium adsorption. Due to its unique high accessible 2D structure, atom-dispersed phosphate/iron anchor groups and high specific surface area (27.77 m2⋅g-1), FP1 shows an extreme-high U(VI) adsorption capacity (704.23 mg·g-1 at 298 K, pH = 5.0 ± 0.1), which is about 27 times of conventional 3D Fe7(PO4)6 (24.51 mg·g-1 -sample FP2) and higher than most 2D absorbent materials, showing a great value in the treatment of radioactive wastewater. According to the adsorption results, the sorption between U(VI) and FP1 is spontaneous and endothermic, and can be conformed to single molecular layer adsorption. Based on the analyses of FESEM, EDS, Mapping, FT-IR and XRD after adsorption, the possibile adsorption mechanism can be described as a Monolayer Surface Complexation and Stacking mode (MSCS-Mode). Additionally, the research not only provide a novel preparing method for 2D phosphate materials but also pave a new pathway to study other two-dimensional adsorption materials.

Decontamination of U(VI) on graphene oxide/Al2O3 composites investigated by XRD, FT-IR and XPS techniques

The decontamination of U(VI) on graphene oxide/nano-alumina (GO/Al₂O₃) composites were investigated by batch, XRD, FT-IR and XPS techniques. The characterization results showed that GO/Al₂O₃ composites presented a variety of oxygen-containing functional groups, which provided the more surface reactive sites. The batch experiments indicated that sorption equilibrium of U(VI) on GO/Al₂O₃ composites was achieved within 30 min, and the maximum sorption capacity derived from Langmuir model was 142.8 mg/g at pH 6.5. In addition, the slight decrease of sorption capacity was observed even after fifth recycling times. These results indicated that GO/Al₂O₃ composites displayed the fast sorption rate, high sorption capacity and good regeneration performance. No effect of ionic strength revealed the inner-sphere surface complexation of U(VI) on GO/Al₂O₃ composites. FT-IR and XPS analysis demonstrated that the high adsorption of U(VI) on GO/Al₂O₃ was attributed to the various oxygen-bearing functional groups. In addition, the nano Al₂O₃ was transferred to amorphous AlO(OH) mineral phase by XRD pattern, which provided the additional reactive sorption sites. These observations indicated that GO-based composites can be regarded as a promising adsorbent for immobilization and pre-concentration of U(VI) from aqueous solutions in the environmental remediation.

Synthesis of magnetic biochar composites for enhanced uranium(VI) adsorption

Magnetic biochar composites were successfully fabricated by pyrolysis of siderite and rice husk under N₂ condition. The results of a variety of characterization implied magnetic biochar displayed porous structures with larger specific surface area. The batch adsorption experiments showed high adsorption properties of magnetic biochar composites toward U(VI) (52.63 mg/g at pH 4.0), whereas U(VI) adsorption was significantly influenced by Na₂CO₃ and HA. U(VI) adsorbed onto magnetic biochar was reduced to U(IV) by Fe₃O₄ according to XPS and XANES analyses. In addition, no significant effect of ionic strength of NaCl and EXAFS results, illustrated the inner-sphere surface complexation of U(VI) on magnetic biochar. Owing to the simple synthesis procedure, low cost, high adsorption efficiency, easy separation and environmental friendly, magnetic biochar can be considered as a potential adsorbent for the purification of U(VI)-bearing wastewater in environmental remediation.

Nanoscale zero-valent iron/magnetite carbon composites for highly efficient immobilization of U(VI)

Nanoscale zerovalent iron/magnetic carbon (NZVI/MC) composites were successfully synthesized by simply calcining yellow pine and iron precursors. NZVI/MC pyrolyzed at 800°C (NZVI/MC800) had a higher percentage of NZVI and displayed better resistance to aggregation and oxidation of NZVI than samples prepared at other temperatures. The NZVI/MC800 material was applied for the elimination of U(VI) from aqueous solutions. The results suggested that the NZVI/MC800 displayed excellent adsorption capacity (203.94 mg/g) toward U(VI). The significant adsorption capacity and fast adsorption kinetics were attributed to the presence of well-dispersed NZVI, which could quickly reduce U(VI) into U(IV), trapping the guest U(IV) in the porous biocarbon matrix. The removal of U(VI) on the NZVI/MC samples was strongly affected by solution pH. The NZVI/MC samples also displayed outstanding reusability for U(VI) removal after multiple cycles. These findings indicate that NZVI/MC has great potential for remediation of wastewater containing U(VI).

Green Preparation of Nanoporous Pyrrhotite by Thermal Treatment of Pyrite as an Effective Hg(Ⅱ) Adsorbent: Performance and Mechanism

The removal of Hg(II) from aqueous solutions by pyrrhotite derived from the thermal activation of natural pyrite was explored by batch experiments. The adsorption isotherms demonstrated that the sorption of Hg(II) by modified pyrite (MPy) can be fitted well by the Langmuir model. The removal capacity of Hg(II) on MPy derived from the Langmuir model was determined to 166.67 mg/g. The adsorption process of Hg(II) on MPy was well fitted by a pseudo-second-order model. The sorption of Hg(II) on MPy was a spontaneous and endothermic process. The removal of Hg(II) by MPy was mainly attributed to a chemical reaction resulting in cinnabar formation and the electrostatic attraction between the negative charges in MPy and positive charges of Hg(II). The results of our work suggest that the thermal activation of natural pyrite is greatly important for the effective utilization of ore resources for the removal of Hg(II).

Sorption of uranyl ions on TiO2: Effects of pH, contact time, ionic strength, temperature and HA

Sorption of U(VI) onto TiO₂ as functions of pH, ionic strength, contact time, soil humic acid (SHA), solid-to-liquid ratio and temperature was studied under ambient conditions using batch and spectroscopic approaches. The sorption of U(VI) on TiO₂ was significantly dependent on pH and ionic strength. The presence of SHA slightly enhanced the sorption of U(VI) on TiO₂ below pH4.0, while it inhibited U(VI) sorption in the higher pH range. U(VI) sorption on TiO₂ was favored at high temperatures, and the sorption process was estimated to be endothermic and spontaneous. Reduction of U(VI) to lower valent species was confirmed by X-ray photo-electron spectroscopy analysis. It is very interesting to find that U(VI) sorption on TiO₂ was promoted in solutions with higher back-ground electrolyte concentrations. In the presence of U(VI), higher back-ground electrolyte made more TiO₂ particles aggregate through (001) facets, leading more (101) facets to be exposed. Therefore, the reduction of U(VI) was enhanced by the exposed (101) facets and more U(VI) removal was observed.

In Situ Anchoring of Pyrrhotite on Graphitic Carbon Nitride Nanosheet for Efficient Immobilization of Uranium

Enrichment of U^VI is an urgent project for nuclear energy development. Herein, magnetic graphitic carbon nitride nanosheets were successfully prepared by in situ anchoring of pyrrhotite (Fe₇ S₈ ) on the graphitic carbon nitride nanosheet (CNNS), which were used for capturing U^VI . The structural characterizations of Fe₇ S₈ /CNNS-1 indicated that the CNNS could prevent the aggregation of Fe₇ S₈ and the saturation magnetization was 4.69 emu g^-1 , which meant that it was easy to separate the adsorbent from the solution. Adsorption experiments were performed to investigate the sorption properties. The results disclosed that the sorption data conformed to the Langmuir isotherm model with the maximum adsorption capacity of 572.78 mg g^-1 at 298 K. The results of X-ray photoelectron spectroscopy (XPS) demonstrated that the main adsorption mechanism are as follows: U^VI is adsorbed on the surface of Fe₇ S₈ /CNNS-1 through surface complexation initially, then it was reduced to insoluble U^IV . Thereby, this work provided an efficient and easy to handle sorbent material for extraction of U^VI .

Highly efficient carbonaceous nanofiber/layered double hydroxide nanocomposites for removal of U(VI) from aqueous solutions

The three-dimensional (3D) carbonaceous nanofiber and Ni-Al layered double hydroxide (CNF/LDH) nanocomposite was successfully prepared by a facile one-step hydrothermal methodology. Characterization of scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), XRD, and Fourier transformed infrared spectroscopy (FTIR) provided a demonstration that the modified CNF/LDH nanocomposite possessed abundant functional groups, for instance, metal-oxygen surface bonding sites (Ni–O as well as Al–O) and free-metal surface bonding sites (C–O, C–O–C, as well as O–C=O). The elimination of representative radionuclide (i.e. U(VI)) on the CNF/LDH nanocomposite from aqueous solutions was explored as a key function of pH, ionic strength, contact time, reaction temperature as well as radionuclide preliminary concentrations with the use of the batch methodology. As revealed by the findings, the sorption of radionuclides on CNF/LDH nanocomposite adhered to the pseudo-second-order kinetic model as well as Langmuir model. The maximum elimination capacity of U(VI) amounted to be 0.7 mmol/g. The independent of ionic strength shed light on the fact that inner-sphere surface complexation mainly overpowered radionuclide uptake by the CNF/LDH nanocomposite, which was further verified through the combination of FTIR and XPS spectral analyses. The abovementioned analyses shed light on the fact that the CNF/LDH nanocomposite can be regarded as a latent material to preconcentration radionuclides for environmental remediation.

Enhanced Adsorption of Zn(II) onto Graphene Oxides Investigated Using Batch and Modeling Techniques

Graphene oxide (GO) was synthesized and employed as an adsorbent for Zn(II) removal from an aqueous solution. The adsorption isotherms showed that Zn(II) adsorption can be better described using the Freundlich model than the Langmuir model. The maximum adsorption capacity of Zn(II) on GO determined using the Langmuir model at pH 7.0 and 293 K was 208.33 mg/g. The calculation of thermodynamic parameters revealed that the process of Zn(II) adsorption on GO was chemisorptions, endothermic, and spontaneous. Kinetic studies indicated that the pseudo-second-order kinetic model showed a better simulation of Zn(II) adsorption than the pseudo-first-order kinetic model. On the basis of surface complexation modeling, the double layer model provided a satisfactory prediction of Zn(II) by inner-sphere surface complexes (for example, SOZn⁺ and SOZnOH species), indicating that the interaction mechanism between Zn(II) and GO was mainly inner-sphere complexation. In terms of reusability, GO could maintain 92.23% of its initial capability after six cycles. These findings indicated that GO was a promising candidate for the immobilization and preconcentration of Zn(II) from aqueous solutions.

N, P, and S Codoped Graphene-Like Carbon Nanosheets for Ultrafast Uranium (VI) Capture with High Capacity

The development of functional materials for the highly efficient capture of radionuclides, such as uranium from nuclear waste solutions, is an important and challenging topic. Here, few-layered N, P, and S codoped graphene-like carbon nanosheets (NPS-GLCs) that are fabricated in the 2D confined spacing of silicate RUB-15 and applied as sorbents to remove U(VI)ions from aqueous solutions are presented. The NPS-GLCs exhibit a large capacity, wide pH suitability, an ultrafast removal rate, stability at high ionic strengths, and excellent selectivity for U(VI) as compared to multiple competing metal ions. The 2D ultrathin structure of NPS-GLCs with large spacing of 1 nm not only assures the rapid mass diffusion, but also exposes a sufficient active site for the adsorption. Strong covalent bonds such as P-O-U and S-O-U are generated between the heteroatom (N, P, S) with UO2 2+ according to X-ray photoelectron spectroscopy analysis and density functional theory theoretical calculations. This work highlights the interaction mechanism of low oxidation state heteroatoms with UO2 2+, thereby shedding light on the material design of uranium immobilization in the pollution cleanup of radionuclides.

Novel Ion-Imprinted Carbon Material Induced by Hyperaccumulation Pathway for the Selective Capture of Uranium

The development of nuclear energy is significant for resource sustainability. Uranium is the main nuclear fuel, and its effective absorption has captured the attention of researchers. In this study, the green technologies hyperaccumulation effect of the plant and ion-imprinted technology were used to prepare the uranium ion-imprinted hierarchically porous carbon material (II-HPC). At the same time, a nonimprinted hierarchically porous carbon (HPC) was prepared for comparison. The adsorption isotherm was fitted to the Langmuir model and maximum sorption capacity of II-HPC was 503.64 mg g^-1 at 298 K. The kinetic data followed the pseudo-second-order model, indicating a dominant role of chemisorption. Initial studies were performed on a lab-scale simulated continuous-flow system for the adsorption kinetics testing of II-HPC in simulated seawater. The results showed that the amount of uranium adsorbed after 35 days was 0.379 mg g^-1, which determined that II-HPC adsorbent is a potential material for enrichment of U(VI) from the seawater.

Mechanistic insights into sequestration of U(VI) toward magnetic biochar: Batch, XPS and EXAFS techniques

The magnetic iron oxide (Fe₃O₄) nanoparticles stabilized on the biochar were synthesized by fast pyrolysis of Fe(II)-loaded hydrophyte biomass under N₂ conditions. The batch experiments showed that magnetic biochar presented a large removal capacity (54.35mg/g) at pH3.0 and 293K. The reductive co-precipitation of U(VI) to U(IV) by magnetic biochar was demonstrated according to X-ray diffraction, X-ray photoelectron spectroscopy and X-ray absorption near edge structure analysis. According to extended X-ray absorption fine structure analysis, the occurrence of U-Fe and U-U shells indicated that high effective removal of uranium was primarily inner-sphere coordination and then reductive co-precipitation at low pH. These observations provided the further understanding of uranium removal by magnetic materials in environmental remediation.

Effect of carbonate on U(VI) sorption by nano-crystalline α-MnO2

U(VI) sorption on nano-crystalline α-MnO2was studied in NaClO4medium as a function of pH by batch sorption method in presence and absence of carbonate and subsequently employing surface complexation modeling (SCM) to predict species responsible for U(VI) sorption. The kinetic study of U(VI) sorption on nano-crystalline α-MnO2was carried out to fix the time of equilibration. In presence of carbonate, U(VI) sorption on nano-crystalline α-MnO2increases with pH of the suspension, leveling off in the pH range 5–8.5 thereafter decreasing at higher pH. However, in absence of carbonate, U(VI) sorption on nano-crystalline α-MnO2remains close to 100% at pH>5. The difference in sorption behavior of uranium in the presence and absence of carbonate can be explained in terms of uranium speciation in the two systems. The dissolution of nano-crystalline α-MnO2was studied in presence and absence of carbonate to ascertain its role in sorption. Surface complexation modeling was satisfactorily able to explain the sorption phenomena in all the systems. In addition, U(VI) sorption on nano-crystalline α-MnO2was compared with literature data on U(VI) sorption by δ-MnO2.

Plasma-Facilitated Synthesis of Amidoxime/Carbon Nanofiber Hybrids for Effective Enrichment of 238U(VI) and 241Am(III)

Plasma- and chemical-grafted amidoxime/carbon nanofiber hybrids (p-AO/CNFs and c-AO/CNFs) were utilized to remove ²³⁸U(VI) and ²⁴¹Am(III) from aqueous solutions, seawater, and groundwater. Characteristic results indicated more nitrogen-containing groups in p-AO/CNFs compared to c-AO/CNFs. The maximum adsorption capacities of p-AO/CNFs at pH 3.5 and T = 293 K (588.24 mg of ²³⁸U(VI)/g and 40.79 mg of ²⁴¹Am(III)/g from aqueous solutions, respectively) were significantly higher than those of c-AO/CNFs (263.18 and 22.77 mg/g for ²³⁸U(VI) and ²⁴¹Am(III), respectively), which indicated that plasma-grafting was a highly effective, low-cost, and environmentally friendly method. Adsorption of ²³⁸U(VI) on AO/CNFs from aqueous solutions was significantly higher than that of ²³⁸U(VI) from seawater and groundwater; moreover, AO/CNFs displayed the highest effective selectivity for ²³⁸U(VI) compared to the other radionuclides. Adsorption of ²³⁸U(VI) onto AO/CNFs created inner-sphere complexes (e.g., U-C shells) as shown by X-ray absorption fine structure analysis, which was supported by surface complexation modeling. Three inner-sphere complexes gave excellent fits to pH-edge and isothermal adsorption of ²³⁸U(VI) on the AO/CNFs. These observations are crucial for the utilization of plasma-grafted, AO-based composites in the preconcentration and immobilization of lanthanides and actinides in environmental remediation.

New Synthesis of nZVI/C Composites as an Efficient Adsorbent for the Uptake of U(VI) from Aqueous Solutions

New nanoscale zerovalent iron/carbon (nZVI/C) composites were successfully prepared via heating natural hematite and pine sawdust at 800 °C under nitrogen conditions. Characterization by SEM, XRD, FTIR, and XPS analyses indicated that the as-prepared nZVI/C composites contained a large number of reactive sites. The lack of influence of the ionic strength revealed inner-sphere complexation dominated U(VI) uptake by the nZVI/C composites. Simultaneous adsorption and reduction were involved in the uptake process of U(VI) according to the results of XPS and XANES analyses. The presence of U-C/U-U shells demonstrated that innersphere complexation and surface coprecipitation dominated the U(VI) uptake at low and high pH conditions, respectively. The uptake behaviors of U(VI) by the nZVI/C composites were fitted well by surface complexation modeling with two weak and two strong sites. The maximum uptake capacity of U(VI) by the nZVI/C composites was 186.92 mg/g at pH 4.0 and 328 K. Additionally, the nZVI/C composites presented good recyclability and recoverability for U(VI) uptake in regeneration experiments. These observations indicated that the nZVI/C composites can be considered as potential adsorbents to remove radionuclides for environmental remediation.