Decontamination of U(VI) from nZVI/CNF composites investigated by batch, spectroscopic and modeling techniques

Insight into the Enhanced Removal of U(VI) with Fe-Ni Bimetallic Particles Loaded on Biochar

This work develops Fe-Ni particles loaded on biochar (Fe-Ni/BC) to remove U(VI) efficiently. Fe-Ni bimetallic particles loaded on biochar (BC) can improve stability and reactivity, and the mesoporous structure of BC can effectively reduce Fe0 aggregation. The removal ability of Fe-Ni/BC is higher than that of Fe-Ni, BC, and Fe/BC. With the aid of kinetics and isotherms, the removal data were fitted by the pseudo-second-order kinetic model (R2 ≥ 0.999) and Langmuir model (R2 ≥ 0.94). Meanwhile, Fe-Ni/BC exhibited the largest removal capacity of 250.78 mg/g for U(VI) at pH 5.0 and a temperature of 303 K. Removing uranium using Fe-Ni/BC was carried out in the following steps: First, U(VI) in the solution was sorbed onto the Fe-Ni/BC surface through chemical bonds. Second, Fe(II) and Fe0 contributed to the U(VI) reduction process. At the same time, Fe-Ni formed a primary cell and underwent electron transfer. Moreover, Ni0 adsorbed H2 generated by Fe0 corrosion, forming Ni-H to prevent agglomeration and reduce U(VI). The results indicate that Fe-Ni bimetallic particles loaded on biochar enhance the removal of U(VI) by sorption-reduction synergistic effect. This work offers valuable insights into the design of bimetallic nanomaterials for environmental remediation of U(VI) contamination.

Remediation of Cr(VI) Polluted Groundwater Using Zero-Valent Iron Composites: Preparation, Modification, Mechanisms, and Environmental Implications

The extensive application of chromium (Cr) in many industries has inevitably resulted in the release of Cr(VI) into the groundwater environment, thus posing damage to the ecosystem and human health. Nano zero-valent iron (nZVI) has been widely studied and applied in the remediation of Cr(VI)-contaminated water as an ideal material with high reductive capacity, which enables the transformation of teratogenic and carcinogenic Cr(VI) into less toxic Cr(III). This review comprehensively summarizes the preparation and modification methods of nZVI Cr(VI) removal performance and mechanisms by nZVI and modified nZVI materials. The field applications of nZVI-based materials, such as combining the injection well and the permeable reactive barrier (PRB) to remove Cr(VI) in groundwater, have been reported. Subsequently, the potential toxicity of nZVI-based materials to organisms during environmental application has been highlighted in the current study. Finally, the review outlines potential improvements and explores future directions for the use of nZVI-based materials in groundwater contamination remediation.

Enhanced remediation of U(vi) ions from water resources using advanced forms of morphologically modified glauconite (nano-sheets and nano-rods): experimental and theoretical investigations

Two forms of morphologically transformed glauconite (GL) involved exfoliated nanosheets (EXG) and nanorods (GRs), which were synthesized by facile exfoliating and scrolling modification under sonication. The two advanced forms (EXG and GRs) were applied as enhanced adsorbents for U(vi) ions and compared with using raw glauconite. The developed GRs structure displays higher saturation retention properties (319.5 mg g-1) in comparison with both EXG (264.8 mg g-1) and GL (237.9 mg g-1). This enhancement is assigned to the noticeable increment in the surface area (32.6 m2 g-1 (GL), 86.4 m2 g-1 (EXG), and 123.7 m2 g-1 (GRs)) in addition to the surface reactivity and exposure of effective siloxane groups. This was supported by the steric investigation based on the isotherm basics of the monolayer model of one energy site. The steric functions declared a strong increase in the density of the existing effective uptake receptors throughout the modification stages (GRs (112.1 mg g-1) > EXG (87.7 mg g-1) > 72.5 mg g-1 (GL)). Also, each active site can be filled with 4 U(vi) ions, donating the parallel orientation of these ions and the operation of multi-ionic mechanisms. The energetic functions, either the uptake energy (<13 kJ mol-1) or Gaussian energy (<5 kJ mol-1), validate the retention of U(vi) by physical reactions. These reactions displayed spontaneous properties and exothermic behaviors based on the investigated thermodynamic functions, including entropy, enthalpy, and internal energy. The structures also showed significant recyclability, indicating potential application on a realistic and commercial scale.

Synergetic and advanced isotherm investigation for the enhancement influence of zeolitization and β-cyclodextrin hybridization on the retention efficiency of U(vi) ions by diatomite

In synergetic investigations, the adsorption effectiveness of diatomite-based zeolitic structure (ZD) as well as its β-cyclodextrin (CD) hybrids (CD/ZD) towards uranium ions (U(vi)) was evaluated to examine the influence of the transformation procedures. The retention behaviors and mechanistic processes have been demonstrated through analyzing the steric and energetic factors employing the modern equilibrium approach (a monolayer model with a single energy level). After the saturation phase, the uptake characteristics of U(vi) were dramatically improved to 297.5 mg g-1 after the CD blending procedure versus ZD (262.3 mg g-1) or 127.8 mg g-1. The steric analysis indicated a notable increase in binding site levels after the zeolitization steps (Nm = 85.7 mg g-1) as well as CD implementation (Nm = 91.2 mg g-1). This finding clarifies the reported improvement in the ability of CD/ZD to effectively retain the U(vi) ions. Furthermore, every single active site of the CD/ZD material has the capacity to adsorb around four ions, which are aligned according to a vertical pattern. The energetic aspects, specifically Gaussian energy (<8 kJ mol-1) along with retention energy (<40 kJ mol-1), validate the regulated influences of the physical mechanistic processes. The physical adsorption of U(vi) seems to depend on various intermolecular forces, such as van der Waals forces, in conjunction with zeolitic ion exchanging pathways (0.6-25 kJ mol-1). The thermodynamic assets have been evaluated to confirm the exothermic together with spontaneous adsorption U(vi) by ZD and its blend with CD (CD/ZD).

Biosorption and biomineralization of U(VI) by Kocuria rosea: Involvement of phosphorus and formation of U-P minerals

The biosorption and biomineralization behavior of U(VI) by Kocuria rosea with uranium resistance higher than other general microorganisms was investigated in this study. The results showed the obvious effects of initial U(VI) concentration, biomass, time, and especially pH, and presented that U(VI) was immobilized to K. rosea by physical and chemical action. The characterization results for the precipitation proved that U-P minerals with U(VI) (H₃OUO₂PO₄·3H₂O, H₂(UO₂)₂(PO₄)₂·8H₂O) or U(IV) (CaU(PO₄)₂) were dominant, and the crystallization level increased with time. In the process, the phosphorous containing groups, amino, hydroxyl and carboxyl groups played important roles in adsorption of U(VI), and the phosphate groups were crucial in immobilization of uranium, showing the importance of groups containing phosphorus in both biosorption and biomineralization processes. Our findings focus on the biosorption and biomineralization mechanism of U(VI) by K. rosea, emphasize the synergy of physical adsorption and chemical immobilization in the process and formation of U(VI)-P and U(IV)-P minerals, and highlight the significance of phosphorus involvement in the reaction.

Insight into chitosan/mesoporous silica nanocomposites as eco-friendly adsorbent for enhanced retention of U (VI) and Sr (II) from aqueous solutions and real water

The chitosan chains were integrated with MCM-48 mesoporous silica in an eco-friendly composite (CH/MCM-48) of enhanced adsorption capacity. The prepared CH/MCM-48 composite was applied in systematic retention of U (VI) as well as Sr (II) ions from water as the commonly detected radioactive pollutants. It displayed promising retention capacities of 261.3 mg/g and 328.6 mg/g for U (VI) and Sr (II) considering the equilibrium time interval that was identified after 420 min. The composite showed the kinetic behavior of the Pseudo-First order model and the isotherm properties of the Langmuir assumption. The thermodynamic assessment of the reactions validated the retention of both U (VI) and Sr (II) ions by spontaneous, favorable, and exothermic reactions. Based on the theoretical values of entropy (-5.94 kJ mol^-1 (U (VI)) and -2.93 kJ mol^-1 (Sr (II))), Gibbs free energy (less than 20 kJ mol^-1), and Gaussian energy (5.77 kJ mol^-1 (U (VI)) and 4.56 kJ mol^-1 (Sr (II))) the uptake processes are related to physical adsorption reactions. The CH/MCM-48 composite is of significant recyclability and showed considerable affinities for the studied radioactive ions even in the presence of other metal ions (Cd (II), Pb (II), Zn (II), and Co (II)).

Environmental application of emerging zero-valent iron-based materials on removal of radionuclides from the wastewater: A review

Owing to high surface energy, strong chemical reactivity and large surface area, nanoscale zero-valent iron (nZVI) as a novel emerging material has been extensively utilized in environmental cleanup. Although a lot of reviews regarding the removal of organic contaminants and heavy metals on nZVI are summarized in recent years, the advanced progress concerning the removal of radionuclides on nZVI is still scarce. In this review, we summarized the removal of technetium (Tc), uranium (U), selenium (Se) and other radionuclides on nZVI and nZVI-based composites, then their interaction mechanisms were reviewed in details. This review is crucial for the environmental chemist and material engineer to exploit the actual application of nZVI-based composites as the emerging materials of permeable reactive barrier on the removal of radionuclides from aqueous solutions.

Effective decontamination of As(V), Hg(II), and U(VI) toxic ions from water using novel muscovite/zeolite aluminosilicate composite: adsorption behavior and mechanism

Muscovite/phillipsitic zeolite was introduced as a novel inorganic composite of stunning adsorption properties. The composite was investigated in the uptake reactions of Hg(II), As(V), and U(VI) as highly toxic water contaminants considering different adsorption factors. The adsorption properties of muscovite/phillipsitic zeolite are highly dependent on the pH values and the best decontamination percentages can be obtained at pH 4, pH 5, and pH 5 for Hg(II), As(V), and U(VI), respectively. The kinetic studies demonstrated adsorption equilibrium for Hg(II), As(V), and U(VI) after 360 min, 300 min, and 360 min, respectively. The equilibrium modeling suggested monolayer uptake for all the metals and represented mainly by the Langmuir model considering both the values of determination coefficient and chi-squared (χ²). The estimated maximum capacities are 117 mg/g (Hg(II)), 122.5 mg/g (As(V)), and 138.5 mg/g (U(VI)) which are higher values than several studied adsorbents. The Dubinin-Radushkevich adsorption energies of Hg(II) (19.4 kJ/mol), As(V) (25.6 kJ/mol), and U(VI) (26.47 kJ/mol) signify chemical adsorption mechanisms and close to the obtained values for the ion-exchange process. Additionally, the composite is of high reusability properties and was applied effectively for five decontamination cycles. Graphical abstract.

Synthesis of rod-like metal-organic framework (MOF-5) nanomaterial for efficient removal of U(VI): batch experiments and spectroscopy study

With the widespread application of radionuclide ²³⁵U(VI), it is inevitable that part of U(VI) is released into the natural environment. The potential toxicity and irreversibility impact on the natural environment has become one of the most forefront pollution problems in nuclear energy utilization. In this work, rod-like metal-organic framework (MOF-5) nanomaterial was synthesized by a solvothermal method and applied to efficiently adsorb U(VI) from aqueous solutions. The batch experimental results showed that the sorption of U(VI) on MOF-5 was strongly dependent on pH and independent of ionic strength, indicating that the dominant interaction mechanism was inner-sphere surface complexation and electrostatic interaction. The maximum sorption capacity of U(VI) on MOF-5 was 237.0 mg/g at pH 5.0 and T = 298 K, and the sorption equilibrium reached within 5 min. The thermodynamic parameters indicated that the removal of U(VI) on MOF-5 was a spontaneous and endothermic process. Additionally, the FT-IR and XPS analyses implied that the high sorption capacity of U(VI) on MOF-5 was mainly attributed to the abundant oxygen-containing functional groups (i.e., CO and CO). Such a facile preparation method and efficient removal performance highlighted the application of MOF-5 as a candidate for rapid and efficient radionuclide contamination's elimination in practical applications.

Molecule adsorption and corrosion mechanism of steel under protection of inhibitor in a simulated concrete solution with 3.5% NaCl

Herein, the protective performance of a new triazole inhibitor for carbon steel was studied by electrochemical methods. Potentiodynamic polarization curves showed that the anti-corrosion efficiency improved with increasing concentrations of the inhibitor and the results show that it is 22 times corrosion resistance efficiency for inhibitor compared to bare aggressive solution. X-ray photoelectron spectroscopy showed that the film adsorbed well on the carbon steel surface. The scanning vibrating electrode technique demonstrated the corrosion process of carbon steel with and without the protection of inhibitor. Thus, a mechanism for the corrosion process was proposed and the behavior of carbon steel under the protection of the inhibitor was discussed.

Herein, the protective performance of a new triazole inhibitor for carbon steel was studied by electrochemical methods.