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

U(VI) removal by zerovalent manganese modified corn straw biochar in acidic wastewater: Efficiency, characteristics and mechanism

The chemical and radiological toxicity of uranium can present a significant risk to both human health and environmental safety. Thus, ZVMn-BC was synthesized through borohydride reduction aimed at investigating its performance in removing U(VI) in acidic environment (pH = 3). Several batch experiments were conducted to assess the sorption capability under various operational conditions and the relevant experimental data were investigated by kinetics, isotherms and thermodynamic equations. ZVMn-BC exhibited excellent resistance to interference and showed a superiority on U(VI) removal over zerovalent manganese (ZVMn) and corn straw biochar (BC). Under condition of pH 3, and ambient temperature of 303 K with 0.4 g/L of adsorbent, ZVMn-BC exhibited a theoretical sorption quantity of 274.78 mg/g. The sorption process was spontaneous and endothermic, primarily relying on chemical adsorption. The interaction mechanism involved electrostatic interaction, hydrolysis precipitation, complexation, and redox reactions. This study verified that ZVMn-BC exhibits effective performance for U(VI) eliminating in acidic wastewater.

A review of remediation technologies for uranium-contaminated water

Uranium is a naturally existing radioactive element present in the Earth's crust. It exhibits lithophilic characteristics, indicating its tendency to be located near the surface of the Earth and tightly bound to oxygen. It is ecotoxic, hence the need for its removal from the aqueous environment. This paper focuses on the variety of water treatment processes for the removal of uranium from water and this includes physical (membrane separation, adsorption and electrocoagulation), chemical (ion exchange, photocatalysis and persulfate reduction), and biological (bio-reduction and biosorption) approaches. It was observed that membrane filtration and ion exchange are the most popular and promising processes for this application. Membrane processes have high throughput but with the challenge of high power requirements and fouling. Besides high pH sensitivity, ion exchange does not have any major challenges related to its application. Several other unique observations were derived from this review. Chitosan/Chlorella pyrenoidosa composite adsorbent bearing phosphate ligand, hydroxyapatite aerogel and MXene/graphene oxide composite has shown super-adsorbent performance (>1000 mg/g uptake capacity) for uranium. Ultrafiltration (UF) membranes, reverse osmosis (RO) membranes and electrocoagulation have been observed not to go below 97% uranium removal/conversion efficiency for most cases reported in the literature. Heat persulfate reduction has been explored quite recently and shown to achieve as high as 86% uranium reduction efficiency. We anticipate that future studies would explore hybrid processes (which are any combinations of multiple conventional techniques) to solve various aspects of the process design and performance challenges.

Elucidating uranium interactions with synthetic Na-P1 zeolite/Ca2+-substituted alginate composite granules through batch and spectroscopic studies: Emphasizing the significance of ion exchange and complexation

Uranium, a key member of the actinides series, is radioactive and may cause severe environmental hazards once discharged into the water due to high toxicity. Removal of uranium via adsorption by applying tailored, functional adsorbents is at the forefront of tackling such pollution. Here, we report the optimized functionalization of the powder coal fly-ash (CFA) derived Na-P1 synthetic zeolite to the form of granules by employing the biodegradable polymer-calcium alginate (CA) and their application to remove aqueous U. The optimized synthesis showed that granules are formed at the CA concentration equals to 0.5 % wt., and that application of 1% wt. solution renders the most effective U scavengers. The maximum U adsorption capacity (qmax) increases significantly after CA modification from 44.48 mgU/g for native, powder Na-P1 zeolite to 62.53 mg U/g and 76.70 mg U/g for 0.5 % wt. and 1 % wt. CA respectively. The U adsorption follows the Radlich-Peterson isotherm model, being the highest at acidic pH (pHeq∼4). The U adsorption kinetics reveals swift U uptake, reaching equilibrium after 2h for 1 % ZACB and 3 h for 0.5 % wt. ZACB following the pseudo-second-order (PSO) kinetic model. SEM-EDXS investigation elucidates that adsorbed U occurs onto materials as an inhomogenous, well-dispersed, and micrometer-scale aggregate. Further, XPS and μ-XRF spectroscopies complementarily confirmed the hexavalent oxidation state of adsorbed U and its altered distribution on ZACBs with varying CA concentrations. U distribution was probed "in-situ" onto materials while correlations between the major elements (Al, Si, Ca, U) contributing to U scavenging were calculated and compared. Finally, a real-life coal mine wastewater (CMW) polluted by 238U and 228,226Ra was successfully purified, satisfying WHO guidelines after treatment using ZACBs. These findings offer new insights on successful yet optimized Na-P1 zeolite modification using biodegradable polymer (Ca2+-exchanged alginate) aimed at efficient U removal, displaying a near-zero environmental impact.

Flexible self-supporting Na3MnTi(PO4)3@C fibers for uranium extraction from seawater by electro sorption

As an eco-friendly technique with the superior adsorption performance, electroadsorption has shown great potential for application in uranium (U(VI)) recovery in recent years. However, the electrodes used in the electrosorption generally suffer the adsorbent to be loaded on the conductors, which greatly limited the adsorption performance of the electrodes for uranyl ions. In present study, a flexible self-supporting Na3MnTi(PO4)3@C fibers (NMTP@C fibers) electrode material was rationally designed and prepared by electrostatic spinning method and annealing technique, and its ability to capture U(VI) efficiently was preliminarily demonstrated by batch adsorption and electro sorption. The plentiful phosphate groups provide sufficient active sites for adsorption, while the axially continuous electron conduction and radially short-range ion transport give NMTP@C fibers fast charge/ion transport capability. The NMTP@C fiber can remove 99% of 5 ppm U(VI) in seawater by electro absorption within 1 h. After several cycles of adsorption under seawater conditions, the adsorbent can still maintain a stable adsorption capacity. The adsorption mechanism of NMTP@C nanofibers for U(VI) was investigated by XPS, FT-IR, Raman, SEM-EDS, and XRD, which was electrostatic interactions and surface complexation. These results suggest that NMTP@C fibers are promising high-capacity adsorbents for efficient and selective capture of U(VI) from seawater.

Nonthermal plasma-irradiated polyvalent ferromanganese binary hydro(oxide) for the removal of uranyl ions from wastewater

Nonthermal plasma (NTP) irradiation was employed to adjust the morphological structures and valence distribution of ferromanganese (Fe-Mn)-based binary hydro (oxide) to enhance the heterogeneous adsorption of uranyl ions. The output voltage and the liquid-plate distance played a more vital role among the NTP factors in the irradiation system in influencing the polyvalent Fe-Mn binary hydro (oxide) (poly-Fe-Mn). The formation of plates, flakes, and nanoscale nodules was specifically observed, which caused more pores and fractures in the poly-Fe-Mn binary hydro (oxide). The poly-Fe-Mn performed explicitly better in the adsorption of uranium ions in comparison with the counterpart of the Fe-Mn, which was appropriately fitted by the pseudofirst-order kinetic and Elovich models. Maximum equilibrium adsorption capacities of 663.92 and 923.45 mg/g were obtained for the Fe-Mn and poly-Fe-Mn binary hydro (oxides) toward U ions in the orthogonal design, respectively. The maximum monolayer adsorption capacity achieved by the fitting of the Langmuir model was 1091.10 mg/g. Both physisorption and chemisorption contributed to the heterogeneous process of the poly-Fe-Mn toward uranium ions. The employment of NTP irradiation changed the monolayer adsorption of the traditional Fe-Mn materials and diversified the reaction mechanisms between the interface of the Fe-Mn materials and uranium ions. The elements, including O, N, and U exhibited higher compatibility and overlapped in the samples. The highly effective capture of uranium ions from the solution by the poly-Fe-Mn binary hydro (oxide) was mainly related to the chemical deposition of O and N radicals.

Effectiveness and mechanism of uranium adsorption on size-graded red mud

As a type of useful solid waste, red mud (RM) should be reused to achieve waste-to-resource strategies. Additionally, the fast development of nuclear industry requires effective and reliable materials for treating uranium (U)-containing wastewater. This study attempted to remove uranyl ions [U(VI)] from mimic radioactive wastewater by various RM particles with different size fractions (e.g., >75, 45-75, 20-45, 10-20, 5-10, and <5-μm). Sorption data confirmed that the RM with a size fraction of <5-μm exhibited the largest adsorption capacity. The U removal behavior was favorably described by the pseudo-second-order model and Langmuir model. The mineral phases in the RM remarkably influenced U(VI) removal. Cancrinite, katoite, grossular, calcite, and calcium aluminum silicate phases made contributions to U(VI) adsorption. In addition, redox precipitation with iron-bearing minerals on RM surface also led to U(VI) adsorption. The findings of this work offer fundamental knowledge on the potential application of RM for clean-up of U(VI) from contaminated sites.

Facile synthesis of low-cost MnPO4 with hollow grape-like clusters for rapid removal uranium from wastewater

In order to deal with the environmental resource problems caused by nuclear pollution and uranium mine wastewater, it is particularly important to develop uranium removal adsorbent materials with low cost, high efficiency and controllable rapid preparation. In this work, the hollow grape-like manganese phosphate clusters (h-MnPO₄) were synthesized in 4 h by in-situ etching without template at room temperature, which can quickly and effectively remove uranium ions from wastewater. Due to the reasonable hollow structure, more effective adsorption sites are exposed. The obtained sample h-MnPO₄-200 reaches adsorption equilibrium in 1 h and can remove 97.20% uranyl ions (initial concentration is 100 mg L^-1). Under the condition of 25 ℃ and pH= 4, the maximum adsorption capacity of h-MnPO₄-200 for uranium was 751.88 mg g^-1. The FT-IR, XPS and XRD analysis showed that -OH and PO₄^3- groups played a key role in the adsorption process. Thanks to the synergistic adsorption mechanism of surface complexation and dissolution-precipitation, h-MnPO₄-200 maintained a high removal rate in the presence of competitive anions and cations. In a word, h-MnPO₄-200 can be rapidly synthesized through a facile and low-cost method and has a great application prospect in the practical emergency treatment of uranium-containing wastewater.

Indole-functionalized cross-linked chitosan for effective uptake of uranium(VI) from aqueous solution

Herein, a novel indole-modified cross-linked chitosan aerogel (IAA-CTSA) was fabricated by grafting 3-indoleacetic acid onto chitosan and adding glutaraldehyde as crosslinking agent through a facile two-step one pot method. The...

Preparation of novel porous Al2O3-SiO2nanocomposites via solution-freeze-drying-calcination method for the efficient removal of uranium in solution

In this work, the efficient extraction of uranium in solution using Al₂O₃-SiO₂-T was reported. Kinetics and isotherm models indicated that the removal process of uranium on Al₂O₃-SiO₂-T accorded with pseudo-second-order kinetic model and Langmuir isotherm model, which showed that the adsorption process was a uniform mono-layer chemical behavior. The maximum adsorption capacity of Al₂O₃-SiO₂-T reached 738.7 mg g^-1, which was higher than AlNaO₆Si₂(349.8 mg g^-1) and Al₂O₃-SiO₂-NT (453.1 mg g^-1), indicating that the addition of template could effectively improve the adsorption performance of Al₂O₃-SiO₂to uranium. Even after five cycles of adsorption-desorption, the removal percentage of uranium on Al₂O₃-SiO₂-T remained 96%. Besides, the extraction efficiency of uranium on Al₂O₃-SiO₂-T was 72.5% in simulated seawater, which suggested that the Al₂O₃-SiO₂-T was expected to be used for uranium extraction from seawater. Further, the interaction mechanism between Al₂O₃-SiO₂-T and uranium species was studied. The results showed that the electrostatic interaction and complexation played key roles in the adsorption process of Al₂O₃-SiO₂-T to uranium.