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[Display omitted] • A novel Zr(IV)-based MOF with high-density free carboxylic groups was constructed. • The MOF demonstrates high stability and excellent uranium removal performance. • Dynamic sorption tests highlight its potential for treating radioactive wastewater. • The mechanism for its excellent ability to adsorb U(VI) was investigated. The extraction of uranium from aqueous environments, including the ocean and radioactive wastewater, represents a significant challenge with profound implications for energy resources and environmental remediation. This work presents the design and synthesis of a novel highly stable carboxylated metal–organic framework, BUT-12-3COOH, which achieves excellent U(VI) extraction ability from water. BUT-12-3COOH features high-density free carboxylic groups, exceptional chemical stability, fast kinetics, and high adsorption capacity for U(VI). Dynamic sorption experiments further demonstrated the potential of BUT-12-3COOH in treating real radioactive wastewater. The mechanisms for the U(VI) capture of BUT-12-3COOH are investigated through the combination of EDS, FT-IR, and XPS analysis. The results of this study underscore the promising utility of BUT-12-3COOH as an effective sorbent for extracting radionuclides from environmental specimens and liquid nuclear waste streams. [ABSTRACT FROM AUTHOR]

• New uranyl uptake strategy with combined complexation and photoreduction is shown. • An ultrahigh uranyl uptake capacity not limited by the sorption site is achieved. • Uranyl can be removed completely regardless of its initial concentration. • Uranyl extraction is not affected by the coexisting metal cations. Uranium enrichment is perhaps the most critical chemical process throughout the nuclear fuel cycle including uranium mining, uranium extraction from seawater, used fuel reprocessing and disposal, and environmental contamination remediation. New uranium extraction technology is still highly desirable at current stage, although a variety of extraction methods have been established and developed in the past several decades but all with clear demerits. Herein we present a new uranium extraction strategy with combined ligand complexation and photocatalytic reduction based on postsynthetically functionalized metal-organic frameworks (MOFs). The highly robust and photoactive MOF PCN-222 is modified with phosphono- and amino groups that can capture U(VI) from solution. Upon visible light irradiation, the photo-induced electrons from the MOF host can efficiently reduce U(VI) pre-enriched in MOF, affording neutral uranium species that evacuate the MOF structure and regenerating the active site readily for capturing additional U(VI). This auto-recycled process offers an ultrahigh uranium extraction capacity not limited by the number of adsorption sites and more importantly an extra uranium uptake selectivity over these non-redox-active competing metal cations, and can be utilized for uranium separation over extremely wide uranium concentrations and pH ranges, showing a powerful application potential. [ABSTRACT FROM AUTHOR]

In this study, the inorganic-organic hybrid of PA/TNTs was synthesized and characterized by using multiple analysis techniques. Batch experiments were conducted to investigate the removal performance of PA/TNTs towards U(VI). The sorption kinetics procedure achieved equilibrium within 6 h. The maximum sorption capacity at 293 K and pH 5.0 was calculated to be 1.16 × 10 −3 mol/g. In addition, the PA/TNTs composite showed a higher sorption selectivity towards U(VI) over many other metal ions. The ionic strength experiments, desorption results, X-ray diffraction (XRD), solid fluorescence, extended X-ray adsorption fine structure (EXAFS) and Fourier transform infrared spectroscopy (FTIR) analysis suggested the predominant sorption mechanism was inner-sphere complexation rather than ion exchange or precipitation. Overall, the synthesized PA/TNTs composite could be utilized as a cost-effective material for the removal of U(VI) from wastewater. [ABSTRACT FROM AUTHOR]

[Display omitted] • A three-step uranium oxide reduction recovery process has been developed. • The uranium recovered by this process achieved a purity of over 99.9% • The overall recovery rate of uranium reached 98.6%. • Heavy metal concentrations in wastewater meet WHO guidelines by this process. Resource utilization of uranium from the nuclear wastewater is of significance, and the facile strategy to recover high purity uranium oxide directly from wastewater is urgent to develop. Herein, a three-step uranium oxide reduction recovery process (URRP), that is integrated solid–liquid separation (SLS) and electrochemical purification (EP) together with solid-phase uranium re-recovery (SUR), is designed and applied for uranium reduction and purification. The SEM and ICP results were used to determine the carbonate system as the optimal separation system and the Ti electrode as the optimal electrochemical purification electrode. The single electron transfer process of uranyl ions in carbonate was established using cyclic voltammetry. Such three-step recovery process achieves a high-efficient recovery of uranium with a purity of over 99.9% in complex wastewater systems, and an improved return rate of uranium as high as 98.6%. Furthermore, the concentration of metal ions in wastewater is reduced to the standard set by the World Health Organization. Such a URRP offers a very promising solution for the treatment of wastewater and the recovery of high purity uranium. [ABSTRACT FROM AUTHOR]

Uranium (U(VI)) pollution comes from the development and utilization of natural minerals. Based on a new concept of ecological restoration of uranium pollution into natural minerals, a new artificial mineralized process was proposed to immobilize uranium (U(VI)) for wastewater decontamination. In this work, three systems of Mg 3 (PO 4) 2 + UO 2 2+, Mg2+ + PO 4 3− + UO 2 2+ and Mg2+ + PO 4 3− + Mg 3 (PO 4) 2 + UO 2 2+ were designed. Batch experiments and theoretical calculation were conducted to study the U(VI) immobilization effectiveness and artificial mineralization mechanisms. U(VI) removal efficiencies reached up to 96% in the pH value of 5.0 in the three systems. Both precipitation and surface adsorption contributed to favorable U(VI) removal in Mg 3 (PO 4) 2 + UO 2 2+, but resulting in U desorption. Precipitation of Mg2+, PO 4 3− and UO 2 2+ into saleeite (Mg(UO 2) 2 (PO 4) 2 ·10H 2 O) crystal contributed to UO 2 2+ immobilization in the Mg2+ + PO 4 3− + UO 2 2+ and Mg2+ + PO 4 3− + Mg 3 (PO 4) 2 + UO 2 2+ systems, resulting in the negligible U desorption. It is due to the crystallization of the Mg(UO 2) 2 (PO 4) 2 ·10H 2 O through precipitation of Mg2+ and PO 4 3− with UO 2 2+ in acidic medium. PHREEQC and Visual MINTEQ fitting confirmed the favorable precipitation of Mg2+ and PO 4 3− with UO 2 2+ into saleeite in acidic medium. Thus, the U(VI) immobilization effectiveness and artificial mineralization mechanism were understood, providing a promising strategy of artificial induced mineralization of Mg(UO 2) 2 (PO 4) 2 ·10H 2 O for U(VI) decontamination in wastewater. [Display omitted] • Artificially mineralization is proposed for immobilizing uranium. • Formation of Saleéite and chernikovite is the fate of uranium immobilization. • Theorical fitting confirmed the mineralization of dissolved Mg2+ and PO 4 3− with UO 2 2+. • The leaching rate of saleéite and chernikovites is negligible. • P/U and Mg/U molar ratios determined the artificially mineralization process. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ni-Co LDO could be obtained by calcination of Ni-Co LDH. • The morphology of the Ni-Co LDO can be adjusted by the calcination temperature. • The Ni-Co LDO-500 prefer removing uranium to Ni-Co LDH. • Electrostatic attraction, surface complexation and memory effect contributed to U(VI) recovery. • Ni-Co LDO-500 showed good stability and excellent regeneration ability. The utilization and development of nuclear energy has resulted in the discharge of uranium-containing wastewater. Layer double hydroxides (LDHs) and oxides (LDOs) were reported for efficient extracting U(VI) from wastewater. In this work, nickel–cobalt layered double oxide (Ni-Co LDO-X, X represents the calcination temperature) with excellent electrostatic attraction and complexation was synthesized via calcination of nickel–cobalt layered double hydroxide (Ni-Co LDH) under air atmosphere for extracting U(VI) comparing to Ni-Co LDH. Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and zeta potential analysis were conducted to characterize the Ni-Co LDO-X. Batch adsorption experiments were carried out to investigate the U(VI) extraction properties. The U(VI) adsorption capacity on Ni-Co LDO-500 increased over 3 times compared to that of Ni-Co LDH. The process of uranium removed by Ni-Co LDO-500 conforms to the Langmuir model, the calculated maximum adsorption capacity is 707.91 mg/g. The results suggested that the excellent U(VI) adsorption ability on Ni-Co LDO-500 mainly dominated by the memory effect, electrostatic interaction, and complexation on the outer-sphere surface. Ni-Co LDO-500 has excellent regeneration ability in five adsorption/desorption experiments. The Ni-Co LDO-500 had favorable ability in removing uranium in actual wastewater with the residual concentration being lower than 0.05 mg/L. The above results highlight that the Ni-Co LDO-500 is promising to be used for the decontamination of uranium in actual uranium-containing wastewater. [ABSTRACT FROM AUTHOR]

Uranium (U) immobilization from wastewater by zero valent iron (ZVI) was widely concerned through reduction and surface adsorption. Releasing of U due to re-oxidation of U(IV) into U(VI) limited the application of ZVI in U decontamination. In this work, a kind of biochar supported nano zero valent iron (Fe/BC(900)) was obtained by carbothermal reduction of starch mixed with ferric nitrate at 900 °C. U immobilization behavior by Fe/BC(900) in the presence of phosphate (P) was investigated. The U immobilization reaction was adjusted by controlling the sequence of U, Fe/BC(900) and P. U immobilization efficiency was enhanced to 99.9% in the presence of P. Reaction sequence of U, Fe/BC(900) and P influenced the U immobilization efficiency, which followed the order of (U-P)+Fe/BC(900)>(U- Fe/BC(900))+P>U+Fe/BC(900)>(P-Fe/BC(900))+U. P and nZVI both contributed to enhancing U immobilization through precipitation of uranyl-P and reductive co-precipitate (U(IV)) in a wide pH range. The released Fe ions could precipitate with uranyl and phosphate. Consumption of P and nZVI in the (P-Fe/BC(900))+U system limited U immobilization ability. The precipitate is highly dependent on U, P and Fe elements. U desorption in (U-P)+Fe/BC(900) system was not observed with stability. [Display omitted] • Enhanced immobilization of uranium by Fe/BC(900) in the presence of phosphate. • Reaction sequence of uranium, phosphate and Fe/BC(900) determined the uranium immobilization. • Consumption of nZVI by phosphate limited uranium immobilization. • Co-immobilization of uranium and phosphate on Fe/BC(900). • Uranium immobilization with neglected desorption in the presence of phosphate. [ABSTRACT FROM AUTHOR]

Uranium (U) immobilization from wastewater by zero valent iron (ZVI) was widely concerned through reduction and surface adsorption. Releasing of U due to re-oxidation of U(IV) into U(VI) limited the application of ZVI in U decontamination. In this work, a kind of biochar supported nano zero valent iron (Fe/BC(900)) was obtained by carbothermal reduction of starch mixed with ferric nitrate at 900 °C. U immobilization behavior by Fe/BC(900) in the presence of phosphate (P) was investigated. The U immobilization reaction was adjusted by controlling the sequence of U, Fe/BC(900) and P. U immobilization efficiency was enhanced to 99.9% in the presence of P. Reaction sequence of U, Fe/BC(900) and P influenced the U immobilization efficiency, which followed the order of (U-P)+Fe/BC(900)>(U- Fe/BC(900))+P>U+Fe/BC(900)>(P-Fe/BC(900))+U. P and nZVI both contributed to enhancing U immobilization through precipitation of uranyl-P and reductive co-precipitate (U(IV)) in a wide pH range. The released Fe ions could precipitate with uranyl and phosphate. Consumption of P and nZVI in the (P-Fe/BC(900))+U system limited U immobilization ability. The precipitate is highly dependent on U, P and Fe elements. U desorption in (U-P)+Fe/BC(900) system was not observed with stability. [Display omitted] • Enhanced immobilization of uranium by Fe/BC(900) in the presence of phosphate. • Reaction sequence of uranium, phosphate and Fe/BC(900) determined the uranium immobilization. • Consumption of nZVI by phosphate limited uranium immobilization. • Co-immobilization of uranium and phosphate on Fe/BC(900). • Uranium immobilization with neglected desorption in the presence of phosphate. [ABSTRACT FROM AUTHOR]

With the wide application of nuclear energy and the rapid development of mining, a great quantity of uranium (U(VI)) containing wastewater is inevitably generated. In this work, a facile environmental-friendly coprecipitation method was proposed for the green synthesis of binary layered double hydroxides (Ni–Co LDH W -7), which could be used to efficiently adsorb U(VI) from wastewater. Pseudo-second-order kinetic model and Dubinin-Radushkevich model fitted well with the adsorption of U(VI) on Ni–Co LDH W -7, the maximum adsorption capacity of U(VI) on Ni–Co LDH W -7 was 201.09 mg/g calculated by the Langmuir model. Adsorption equilibrium reached after 30 min, which is a spontaneous and endothermic process. Fourier Transform Infrared Spectrometer (FTIR) and X-ray Photoelectron Spectroscopy (XPS) measurements manifested that the favorable U(VI) extraction on Ni–Co LDH W -7 is mainly ascribed to inner-layer surface electrostatic interaction and complexation, which is dominated by abundant oxygen-containing M-OH and interlayer OH− ions. Briefly, this work provides a facial and environmental-friendly Ni–Co LDH W -7 for removing U(VI) in actual uranium-containing wastewater. [Display omitted] • A facile environmental-friendly coprecipitation method was proposed for green synthesis of Ni–Co LDH W -7. • Adsorption capacity of uranium reached 201.09 mg/g calculated by Langmuir model at pH = 6 and 298 K. • Metal hydroxyl group configuration and the hydroxyl groups contributed to U(VI) binding on Ni–Co LDH W -7. • Ni–Co LDH W -7 showed good stability. [ABSTRACT FROM AUTHOR]