Effective capture of aqueous uranium from saline lake with magnesium-based binary and ternary layered double hydroxides

Magnetite/β-cyclodextrin/fly ash composite as an effective and recyclable adsorbent for uranium(VI) capture from wastewater

As a novel adsorbent for the separation of uranium(VI) from wastewater, Magnetite/β-cyclodextrin/fly ash composite (Fe₃O₄/β-CD/FA) was first prepared via a chemical coprecipitation technology. The characterization results indicated that Fe₃O₄ and β-CD had been successfully loaded on FA, which had brought abundant oxygen-containing functional groups, providing numerous adsorptive sites for the removal of uranium(VI). At pH = 5.0 and T = 25 °C, the maximum uranium(VI) removal efficiency and capacity of Fe₃O₄/β-CD/FA were higher to 97.8% and 444.4 mg g^-1, respectively. Pseudo-second-order and Langmuir models fitted better with the experimental data, illustrating that chemical adsorption dominated the uranium(VI) removal process. In addition, Fe₃O₄/β-CD/FA showed good anti-interference ability and recoverability. After five cycles, the removal rate of uranium(VI) on Fe₃O₄/β-CD/FA was still higher to 90.4%. The immobilization of uranium(VI) on Fe₃O₄/β-CD/FA was mainly ascribed to the synergism of redox reaction, complex reaction, chemical reaction and electrostatic interaction. Given the above, Fe₃O₄/β-CD/FA would be regarded as an efficacious, green and promising adsorbent for uranium(VI) separation from wastewater.

Construction of dopamine supported Mg(Ca)Al layered double hydroxides with enhanced adsorption properties for uranium

A novel dopamine-supported Mg(Ca)Al layered double hydroxide composite was synthesized by co-precipitation method. The existence of Ca²⁺ and dopamine could promote the capture of uranium on the layered double hydroxides. In batch experiments, the composite exhibited good uranium removal performance, including high adsorption capacity (687.3 mg/g), strong anti-interference and good reusability (the removal percentage was still higher than 90 % after five cycles). At low initial uranium concentration, the uranium removal percentage on the composite exceeded 99.7 % and the residual concentration of uranium in the solution was <0.03 mg/L, reaching the limited standard of the World Health Organization. The studies of adsorption kinetics and isotherm indicated that the uranium adsorption behavior on the composite conformed to the pseudo-second-order kinetic and Langmuir isotherm models, suggesting that the process was a monolayer adsorption dominated by chemical adsorption. Furthermore, the high-efficiency uranium adsorption on the Mg(Ca)Al layered double hydroxide was mainly attributed to the strong complexation between the active sites (-OH and -NH₂) and uranium, the precipitation of interlayer intercalation ions (CO₃^2- and OH^-) to uranium and the ion exchange of Ca²⁺ to uranium. Due to these advantages, the dopamine-supported Mg(Ca)Al layered double hydroxide composite is expected to be used as fine adsorbent to remove uranium from wastewater.

Intercalation of salicylaldoxime into layered double hydroxide: ultrafast and highly selective uptake of uranium from different water systems via versatile binding modes

We report the first example of MgAl layered double hydroxide intercalated with salicylaldoxime (SA-LDH) which exhibits excellent uranium (U(VI)) capture performance. In U(VI) aqueous solutions, the SA-LDH shows a tremendous maximum U(VI) sorption capacity (q_m^U) of 502 mg·g^-1, surpassing most known sorbents. For the aqueous solution with an initial U(VI) concentration (C₀^U) of ∼ 10 ppm, ≥99.99 % uptake is achieved in a wide pH range of 3-10. At C₀^U ∼ 20 ppm, >99 % uptake is reached within only 5 min, and pseudo-second-order kinetics rate constant (k₂) of 44.9 g·mg^-1·min^-1 reaches the record value, placing the SA-LDH amongst the fastest U adsorbing materials reported to date. In contaminated seawater with 35 ppm of U while highly concentrated metal ions of Na⁺, Mg²⁺, Ca²⁺, and K⁺, the SA-LDH still displays exceptionally high selectivity and ultrafast extraction for UO₂²⁺, giving >95 % uptake of U(VI) within 5 min, and the k₂ value of 0.308 g·mg^-1·min^-1 for seawater surpasses most reported values for aqueous solutions. Versatile binding modes toward U by SA-LDH, including complexation (UO₂²⁺ with SA^- and/or CO₃^2-), ion exchange and precipitation, contribute to the preferable uptake of U at different concentrations. X-ray absorption fine structure (XAFS) analyses demonstrate that one uranyl ion (UO₂²⁺) binds to two SA^- anions and two H₂O molecules forming 8-coordinated configuration. The U coordinates with O atom of the phenolic hydroxyl group and N atom of the -CN-O^- group of SA^-, forming a stable six-membered ring motif, which endows the fast and robust capture of U. The wonderful uranium trapping ability makes the SA-LDH among the best adsorbent used for uranium extraction from various solution systems including seawater.

Design anion regulated layered double hydroxide and explore its theoretical mechanism of immobilizing uranium

It is momentous to comprehensively understand the anion's effect during the formation of Mg-Al layered double hydroxide (LDH), especially relating to the long-term disposal of uranium-containing (UO₂²⁺) residue. In this research, the CO₃^2-, PO₄^3- and SO₄^2- anions were inserted into the LDH's interlayer driven by its reconstructive memory effect. The UO₂²⁺ removal capacity increased in order (typically SO₄^2- < PO₄^3- < CO₃^2-). This was further confirmed by the bond length of U-S, U-P and U-C data acquired by theoretical calculation. The SEM-EDS showed anion-regulated LDH materials got fleecy and facilitated the insertion of anions. The increased average pore size and volume of calcined LDH provided convenient access for anions to easily enter interlayer. XRD results showed inserted interlayer anions could increase the interlayer spacing and expose more active sites, which was conducive to the removal of UO₂²⁺. The FTIR combined with theoretical calculation results certified anions could grasp UO₂²⁺. XPS results gave a compelling evidence that the amount of anion insertion was proportional to UO₂²⁺ removal capacity. In short, the anions could significantly improve LDH to the removal of UO₂²⁺ by the mechanism of surface and interlayer complexation. What was discovered can better evaluate the environmental behavior of UO₂²⁺ influenced by anion factors.

Layered double hydroxide intercalated with dimethylglyoxime for highly selective and ultrafast uptake of uranium from seawater

In this study, we demonstrate the first example of a MgAl layered double hydroxide intercalated by a ketoxime compound (dimethylglyoxime, DMG), that is, MgAl-DMG-LDH (abbr. DMG-LDH), which exhibits excellent capture of uranium (U(VI)) both at high (ppm) and low (ppb) concentrations. The as-formed DMG-LDH shows an enormous maximum U(VI) sorption capacity (qUm) of 380 mg g^-1 and an exceptionally rapid sorption rate (k₂ = 2.97 g mg^-1 min^-1), reaching a high uptake of 99.14% within 5 min. For natural and contaminated seawater with high concentrations of Na⁺, Ca²⁺, Mg²⁺ and K⁺ concomitant cations, the DMG-LDH still can trap ∼85% U, displaying highly effective sorption toward U. The interaction mechanism between UO₂²⁺ and DMG^2- provides an important reference for the development of highly effective capture of U(VI) by ketoxime materials. The DMG-LDH is currently the best ketoxime material for uranium extraction from nuclear waste and seawater.

Enhancement strategies for efficient activation of persulfate by heterogeneous cobalt-containing catalysts: A review

As a clean and efficient technology for the degradation of organic contaminants, sulfate radical based advanced oxidation processes (SR-AOPs) have attracted more and more attention in the past decades. Cobalt is regarded as the most reactive and efficient non-noble metal catalyst for the activation of persulfate including peroxymonosulfate (PMS) and peroxydisulfate (PDS) to produce sulfate radicals. Due to the limitations of homogeneous catalytic systems, the heterogeneous cobalt-containing catalysts have been emerged and rapidly developed. Various strategies have been schemed to further enhance the activation ability of persulfate by heterogeneous cobalt-containing catalysts. This paper provides an overview on the recent progress in enhancement strategies for the highly efficient activation of persulfate by heterogeneous cobalt-containing catalysts. With a brief introduction on the chemistry and feature of sulfate radical reactions catalyzed by homogeneous Co²⁺/Co³⁺ species, the main strategies for enhancing persulfate activation by heterogeneous cobalt-containing catalysts are summarized, such as surface and morphology design, multiple reactive centers design, organic-inorganic hybrids and heterostructure composites. Future perspectives of heterogeneous SR-AOPs systems catalyzed by cobalt-containing catalysts are outlined.

Hydrotalcite Colloidal Stability and Interactions with Uranium(VI) at Neutral to Alkaline pH

In the United Kingdom, decommissioning of legacy spent fuel storage facilities involves the retrieval of radioactive sludges that have formed as a result of corrosion of Magnox nuclear fuel. Retrieval of sludges may re-suspend a colloidal fraction of the sludge, thereby potentially enhancing the mobility of radionuclides including uranium. The colloidal properties of the layered double hydroxide (LDH) phase hydrotalcite, a key product of Magnox fuel corrosion, and its interactions with U(VI) are of interest. This is because colloidal hydrotalcite is a potential transport vector for U(VI) under the neutral-to-alkaline conditions characteristic of the legacy storage facilities and other nuclear decommissioning scenarios. Here, a multi-technique approach was used to investigate the colloidal stability of hydrotalcite and the U(VI) sorption mechanism(s) across pH 7-11.5 and with variable U(VI) surface loadings (0.01-1 wt %). Overall, hydrotalcite was found to form stable colloidal suspensions between pH 7 and 11.5, with some evidence for Mg²⁺ leaching from hydrotalcite colloids at pH ≤ 9. For systems with U present, >98% of U(VI) was removed from the solution in the presence of hydrotalcite, regardless of pH and U loading, although the sorption mode was affected by both pH and U concentrations. Under alkaline conditions, U(VI) surface precipitates formed on the colloidal hydrotalcite nanoparticle surface. Under more circumneutral conditions, Mg²⁺ leaching from hydrotalcite and more facile exchange of interlayer carbonate with the surrounding solution led to the formation of uranyl carbonate species (e.g., Mg(UO₂(CO₃)₃)^2-_(aq)). Both X-ray absorption spectroscopy (XAS) and luminescence analysis confirmed that these negatively charged species sorbed as both outer- and inner-sphere tertiary complexes on the hydrotalcite surface. These results demonstrate that hydrotalcite can form pseudo-colloids with U(VI) under a wide range of pH conditions and have clear implications for understanding the uranium behavior in environments where hydrotalcite and other LDHs may be present.

Confinement effect of layered double hydroxide on intercalated pyromellitic acidic anions and highly selective uranium extraction from simulated seawater

The oxygen-rich pyromellitic acidic anions (PMA4-) have been intercalated into MgAl-layered double hydroxide to fabricate the MgAl-PMA-LDH (abbr. PMA-LDH) composite, exhibiting excellent adsorption performance toward uranium (U(VI)). Benefiting from the...

Ni-Al layered double hydroxides modified sponge skeleton with polydopamine coating for enhanced U(VI) extraction from aqueous solution

Uranium (VI) (U(VI)) is a major fuel for nuclear power, and the mass of it in seawater is about 4.5 billion tons. However, many current U(VI) adsorbents exist in the form of powder, which hinders the smooth recovery of U(VI) from aqueous solutions and its application in actual environments. Herein, the MP@LDH as an easy-to-recover and 3D macroscopic adsorbent for U(VI) extraction from aqueous solution was successfully prepared. The adsorbent was obtained via anchoring of LDH on the surface of melamine sponge (MS) coated with polydopamine (PDA). The maximum experimental adsorption capacity of MP@LDH sponge for U(VI) was as high as 559.8 mg g^-1 (at pH = 8.0, T = 298 K). In the competitive sorption experiments against the competitions of Ba(II), Sr(II), Zn(II) and others ions, MP@LDH still exhibited a particularly excellent selectivity for U(VI) (almost 90% removal rate). Furthermore, the removal rate of MP@LDH towards U(VI) reached 88.18% under simulated seawater (C₀ = 3.47 μg L^-1). We believe that the MP@LDH with easy retrieval, excellent selectivity and uptake amount provides a convenient way for U(VI) extraction from seawater.

Uranium uptake from wastewater by the novel MnxTi1-xOy composite materials: Performance and mechanism

The novel Mn_xTi_1-xO_y composite materials with different mole ratios (Mn to Ti = 3:7, 5:5 and 7:3) were prepared to remove uranium species from wastewater. These composite materials were characterized by various techniques, such as thermogravimetric analysis (TG), X-ray diffraction (XRD), Fourier transformed infrared (FT-IR) and scanning electron microscopy (SEM). It was found that the chitosan in Mn_xTi_1-x-Chi were completely removed after calcination at 650 °C and Mn_xTi_1-xO_y composites possessed uniform distribution of the porous structure as well as plentiful hydroxyl-containing groups. Moreover, the as-prepared Mn_xTi_1-xO_y composite materials were applied to remove uranium from solution to evaluate the adsorption performance. It was found that the Mn_0.5Ti_0.5O_y possessed relatively excellent uptake performance for uranium comparing with the Mn_0.3Ti_0.7O_y and Mn_0.7Ti_0.3O_y and its maximum uptake capacity and efficiency reach 695.2 mg/g and 98.6% (pH = 4, m/V = 0.1 g/L, T = 298 K), respectively, which were much superior than most of reported materials based on titanium oxide or manganese oxide. Besides, the uranium uptake on Mn_0.5Ti_0.5O_y was independent on ionic strength and it had considerable reusability, which might be the necessary condition for Mn_0.5Ti_0.5O_y to be applied in uranium uptake from uranium-containing wastewater. As a candidate adsorbent, Mn_0.5Ti_0.5O_y possessed a high potentiality to remove uranium from wastewater.

The synthesis of a novel titanium oxide aerogel with highly enhanced removal of uranium and evaluation of the adsorption mechanism

A TiO2 aerogel with a high removal percentage and adsorption capacity was manufactured via template synthesis. Subsequently, the as-prepared TiO2 aerogel was characterized by various techniques and applied as an adsorbent for the removal of U(vi). The results revealed that the U(vi) adsorption was very rapid and reached apparent equilibrium within 100 min. The maximum removal percentage was 97.1%, which was calculated using the pseudo-second-order kinetic model (T = 298 K, t = 180 min, pH = 5, m/V = 0.1 g L-1 and C0 = 10 mg g-1). The Langmuir isotherm model was used to determine the maximum adsorption capacity and it achieved 638.0 mg g-1 (T = 298 K, pH = 5 and m/V = 0.1 g L-1). In addition, the removal of U(vi) on the TiO2 aerogel was relatively good in acidic solution and the removal behavior was independent of the influence of ionic strength. The removal percentage of the as-prepared TiO2 aerogel was higher than 90% after five cycles. Due to these excellent properties such as easy recovery, fast adsorption kinetics, high adsorption capacity and high removal percentage, the TiO2 aerogel might become an extremely employable adsorbent for the extraction of U(vi) in seawater.

Highly efficient capture of uranium from seawater by layered double hydroxide composite with benzamidoxime

Through swelling/restoration reaction, benzamidoxime (BAO) is introduced into MgAl-LDH interlayers to assemble a new composite of MgAl-BAO-LDH (abbr. BAO-LDH). Wet samples of the BAO-LDH obtained by washing with diverse solvents are present in colloidal state, which facilitates the fabrication of thin film adsorbents convenient for actual application. After drying, the assembled sample exhibits floral morphology composed of thin nanosheets, much different from hexagonal morphology of NO₃^- intercalated MgAl-LDH precursor (NO₃-LDH), demonstrating a phenomenon rarely found in swelling/restoration. The BAO-LDH depicts an extremely large maximum sorption capacity (q_m^U) of 327 mg·g^-1 and ultra-high selectivity for U. At low U concentrations (5-10 ppm), nearly complete capture (~100%) is achieved in a wide pH range of 3-11, while at high U concentrations (110 ppm), quite high U removals (≥93.0%) are obtained at pH = 6-8, meaning perfect suitability for trapping U from seawater. For natural seawater containing trace amounts of U (3.93 ppb) coexisting with high concentration of competitive ions, the BAO-LDH displays significantly high U removal (87%). Complexation between interlayer BAO (N and O as ligands) with UO₂²⁺ and synergistic interactions of LDH layer hydroxyls with UO₂²⁺ contribute to the highly effective uranium capture. All results demonstrate the BAO-LDH is a promising adsorbent applied in seawater uranium extraction and nuclear wastewater disposal.

Immobilized Co2+ and Cu2+ induced structural change of layered double hydroxide for efficient heterogeneous degradation of antibiotic

In this study, MgMn-layered double hydroxide (MgMnLDH) exhibited excellent remediation functionality for heavy metals-antibiotics combined pollution. On the one hand, Co²⁺ and Cu²⁺ was efficiently immobilized on MgMnLDH with maximum quantity of 4.30 and 10.65 mmol g^-1, respectively. A series of characterizations reflected the changes in structure and physicochemical properties of MgMnLDH after the immobilization. Density functional theory calculations (DFT) confirmed that the binding modes were lattice substitution for Co²⁺ and surface precipitation for Cu²⁺. On the other hand, the immobilized heavy metals enhanced the heterogeneous degradation for sulfamethoxazole (SMX) by peroxymonosulfate (PMS) activation. Complete degradation was achieved within 10 min in MgMnLDH-Co-4/PMS system and 60 min in MgMnLDH-Cu/PMS system, while only 20% in MgMnLDH/PMS system. The pH adaptability, reusability, stability and activation mechanism of two systems were systematically compared. The superior degradation performance of MgMnLDH-Co-4 benefited from the intense Co/Mn synergism and abundant oxygen vacancies, which could accelerate electron transfer during PMS activation process. The applicability of two catalysis system was confirmed in purifying other antibiotics and actual wastewater. The results highlight the importance of structural control in heterogeneous catalysis and provide new idea for environmental remediation.

Memory effect induced the enhancement of uranium (VI) immobilization on low-cost MgAl-double oxide: Mechanism insight and resources recovery

It remains challenging to develop high-performance technologies for uranium (U(VI)) removal/recovery from wastewater/seawater. In this study, MgAl-double oxide (MgAl-LDO-500) was fabricated by calcining MgAl-layered double hydroxide (MgAl-LDH) at 500 ℃ in air. It showed excellent performance in U(VI) removal with an equilibrium time of 15 min and the maximal adsorption capacity of 1098.90 mg g^-1. MgAl-LDO-500 also showed good adaptability in a wide range of pH (from 3 to 10), coexisting ions and different water matrices for U(VI) immobilization. It was found that the anion form of U(VI) intercalated into the layer of MgAl-LDO-500 and caused recombination of layered structures. A series of characterizations (XRD, SEM, FTIR, XPS) proved that memory effect and surface complexation were the key mechanism for the enhancement of U(VI) immobilization on MgAl-LDO-500. Due to the remarkable memory effect, the performance of MgAl-LDO-500 for U(VI) immobilization was superior to MgAl-LDH and other high-cost materials. Besides, the fixed-bed column experiments illustrated that the removal rate achieved 99 % before 1500 BV at initial U(VI) concentration of 20 μg L^-1, and the breakthrough volumes (BVs) were 4500 BVs. These results confirm that MgAl-LDO-500 is a promising material for extracting U(VI) from seawater and wastewater.

Facile modification of graphene oxide and its application for the aqueous uranyl ion sequestration: Insights on the mechanism

Graphene oxide (GO) has been proved with favorable affinity to U(VI), while some drawbacks such as poor dispersity and low adsorption performance limit its application. Herein, cetyltrimethylammonium bromide (CTAB) modified graphene oxide (MGO) composites were successfully fabricated, characterized and compared with graphene oxide (GO) in the sequestration of U(VI) in aqueous solutions. The results showed that maximum adsorption rate of MGO (99.21%) was obviously higher than that of GO (66.51%) under the same initial condition. Simultaneous introduction of C-H and NO coupled with the enhanced dispersity of GO after modification were mainly responsible for the updated performance verified with multiple characterization techniques. Based on the results of kinetics and isotherms investigations, the experimental data were best described by Pseudo-first-order kinetic model and Redlich-Peterson isotherm model. The results of ΔH, ΔS and ΔG show that adsorptive behaviors of uranyl ion on MGO are endothermic and spontaneous. The study provides a feasible alternative to the chemical modification of GO and enhancing the performance towards uranyl ion removal from solution.

Fabrication and Optimization of the Thermo-Sensitive Hydrogel Carboxymethyl Cellulose/Poly(N-isopropylacrylamide-co-acrylic acid) for U(VI) Removal from Aqueous Solution

In this work, the thermo-sensitive materials N-isopropylacrylamide (NIPAM) and acrylic acid (AA) were crosslinked with carboxymethyl cellulose (CMC) (CMC/P (NIPAM-co-AA)) via a free radical polymerization method for the removal of U(VI) from aqueous solution. The L16 (45) orthogonal experiments were designed for the optimization of the synthesis condition. The chemical structures of the crosslinking hydrogel were confirmed by FTIR spectroscopy. The microstructural analyses were conducted though scanning electron microscopy (SEM) to show the pore structure of the hydrogel. The adsorption performance of the CMC/P (NIPAM-co-AA) hydrogel for the uptake of U(VI) from simulated wastewater was also investigated. The adsorption reached equilibrium within 1 h. Under the reaction of pH = 6 and a temperature of 298 K, an initial concentration of U(VI) of 5 mg·L-1, and 10 mg of the CMC/P(NIPAM-co-AA) hydrogel, the maximum adsorption capacity was 14.69 mg g-1. The kinetics fitted perfectly with the pseudo-second-order model, and the isotherms for the composite hydrogel adsorption of U(VI) was in accordance with the Langmuir model. The chemical modification confirmed that the acylamino group played an important role in uranium adsorption. The desorption and reusability study revealed that the resolution rate was still available at approximately 77.74% after five alternate heating cycles at 20 and 50 °C of adsorption-desorption.

Effective removal of uranium from aqueous solution by using novel sustainable porous Al2O3 materials derived from different precursors of aluminum

Novel porous Al₂O₃ materials with high adsorption capacity for U(vi) were prepared via solution-freeze-drying-calcination technology.

Hollow cobalt sulfide for highly efficient uranium adsorption from aqueous solutions

The preparation of hollow Co₃S₄nanostructures by ZIF-67 guarantees high uranium adsorption performance in aqueous solutions.