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The separation and recovery of U(VI) and Th(IV) from rare earths are very important to avoid environmental pollution. A functional fibrous hierarchically bimodal mesoporous silica (F-SiO-DP) as an high efficient adsorbent for selective adsorption of uranium and thorium, which had hierarchically bimodal mesoporous structure and specific surface area of ca. 474.1 m g, was prepared by post-modification method using 2,9-diamide-1,10-phenanthroline. The synthesized adsorbent was characterized by HR-TEM, SEM, FT-IR, N adsorption-desorption, TGA techniques, XRD and NMR spectroscopy. The effects of pH, contact time, initial U(VI) and Th(IV) concentration, temperature and the presence of competitive metal ions on U(VI) and Th(IV) adsorption behavior were studied in detail. The hierarchically bimodal mesoporous structure endows F-SiO-DP with faster adsorption rate, which can reach equilibrium within 10 min, as well as higher adsorption capacities for U(VI) and Th(IV) compared with unimodal mesoporous silica like MCM-41 functionalized with 2,9-diamide-1,10-phenanthroline. The maximum adsorption capacities reach 416 mg g for U(VI) at pH 5.0 and 277 mg g for Th(IV) at pH 3.8, which are much higher than most of previously reported mesoporous silica-based adsorbents. The selectivity coefficient of U(VI) and Th(IV) over Ce(III), Nd(III), Sm(III), Eu(III), Gd(III), Y(III) and Yb(III) is all larger than 9 at pH 3.8, indicating that F-SiO-DP possesses a good simultaneously selective adsorption performance for U(VI) and Th(IV). This work demonstrates that F-SiO-DP with hierarchically bimodal mesoporous structure has promising application in adsorption and separation of actinides from lanthanides, which is crucial to the environmental protection. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Magnetic Nb-CST, which can be separated easily by an external magnetic field, is able to eliminate Sr2+ and Cs+ at ppb level. • Besides excellent selectivity towards Sr2+ and Cs+, it is able to separate them from each other by adjusting pH. • Even in real seawater, magnetic Nb-CST can remove as high as 94.19% of Cs+ at ppb level. • Its high radiation stability and acid-resistance benefit the treatment of radioactive liquid wastes. Abstract In this work, magnetic Nb-substituted crystalline silicotitanate (mag-Nb-CST), which can be used for separation of Sr2+ and Cs+ from aqueous solution, is successfully synthesized by embedding amine-functionalized Fe 3 O 4 into the Nb-substituted crystalline silicotitanate (Nb-CST), being characterized by various techniques such as XRD, SEM, EDS, XPS, and VSM. The studies on the adsorption behaviors show that the adsorption process reaches equilibrium within about 8 h, and the maximum adsorption capacity on mag-Nb-CST is 14.38 mg g−1 at pH 11.00 for Sr2+, and 11.18 mg g−1 at pH 4.00 for Cs+, respectively. Besides the excellent selectivity towards Sr2+ and Cs+ over various lanthanides and actinides, the pH dependence on the adsorption capacity suggests a possibility to separate Sr2+ and Cs+ from each other by simply adjusting pH. Mag-Nb-CST is able to remove most of the Sr2+ and Cs+ at ppb level. Even in real seawater, it is able to remove 94.19% of Cs+. Moreover, mag-Nb-CST shows good acid-resistance and radiation stability. The crystal structure and morphology remained almost the same after γ-irradiation with an adsorbed dose up to 435.8 kGy. Most importantly, only less than 0.1% of Fe is leached out from mag-Nb-CST at pH > 2, indicating that the embedded Fe 3 O 4 nanoparticles are protected from corrosion by the coated Nb-CST, which is in favor of elimination of Sr2+ and Cs+ in acidic solutions. Thus, mag-Nb-CST is a promising adsorbent in the treatment of acidic radioactive liquid wastes, and the purification of contaminated seawater. [ABSTRACT FROM AUTHOR]

The extraction and separation of uranium (U(VI)) and thorium (Th(IV)) from rare earth elements (REEs) in acidic waste solutions is very important and still challenging. In this paper, a high-efficient sorbent was successfully prepared by functionalization of graphene oxide with phenanthroline diamide (GO-PDA), which exhibited excellent selectivity towards actinides over lanthanides. The sorption behaviors of GO-PDA towards U(VI) and Th(IV) under various conditions were evaluated by batch experiment. Fast sorption kinetics and high sorption capacities were realized for both U(VI) and Th(IV), which reached equilibrium in 60 min. The sorption isotherms of both U(VI) and Th(IV) coincided with Langmuir model, while the maximum sorption capacities of U(VI) (pH = 5.5) and Th(IV) (pH = 4.0) at 298 K were calculated to be 718 and 703 mg/g respectively, which were much higher than most of the previously reported graphene oxide (GO) based sorbents. GO-PDA also possessed significantly enhanced selectivity for U(VI) and Th(IV) over Eu(III), Nd(III) and Sm(III) compared to pristine GO at ultralow low pH (0−2), with separation factors larger than 23 at pH 0. Most importantly, GO-PDA was made into membrane with porous structure, which achieved fast and efficient separation of U(VI) and Th(IV) from Eu(III), Nd(III) and Sm(III) in aqueous solution. This work demonstrates that GO-PDA is a promising sorbent for efficient selective separation of U(VI) and Th(IV) from REEs in strong acidic waste solutions, which is of great value for nuclear waste management and nuclear fuel recycling. [ABSTRACT FROM AUTHOR]

[Display omitted] • BCN was functionalized by Phenanthroline diamide with high density. • Functionalized BCN exhibited ultrahigh adsorption capacity for U(VI). • Functionalized BCN showed excellent selectivity for U(VI) from lanthanides. • Adsorption mechanism was explored by combining two-site model and DFT calculations. Separating and recovering uranium (U(VI)) efficiently from lanthanides is crucial for mitigating the radioactive hazard generated by hydrometallurgical residual solutions of lanthanide minerals and ensuring the long-term sustainability of uranium resources. The present work exploited phenanthroline diamide functionalized porous carbon doped boron nitride (BCN-DAPhen) as an adsorbent, which displayed outstanding adsorption performance for the separation of U(VI) from lanthanides. The results of batch adsorption tests indicated that BCN-DAPhen exhibited rapid adsorption kinetics and the adsorption process achieved equilibrium within 10 min. BCN-DAPhen also performed ultra-high maximum adsorption capacity that was calculated to be 2050.8 mg g−1 by fitting with the two-site Langmuir model. Theoretical calculation and experimental results of adsorption were combined to illustrate the adsorption mechanism as well, the results showed that two structures of DAPhen groups on BCN performed discrepant adsorption properties for U(VI). BCN-DAPhen retained excellent adsorption ability owing to the strong affinity of DAPhen groups with U(VI) even in the solution with high concentration of salt and acid. The selectivity coefficients of U(VI) toward various lanthanides were beyond 192.5 at a high nitric acid concentration of 5 mol L−1. This study suggested a general technique for the functionalization of porous BCN, which is expected to be useful in the treatment of residual solution in lanthanides hydrometallurgy. [ABSTRACT FROM AUTHOR]

[Display omitted] • A cationic-surfactant-assisted solvothermal exfoliation method was developed to prepare monolayer BNNSs. • Over 60% of the exfoliated BNNSs were monolayer with the assistance of CTAB. • DAPhen funtionalized BNNSs (BNNSs-DAPhen) achieved high adsorption amounts and ultrafast adsorption rate of U(VI). • BNNSs-DAPhen maintained good adsorption performance under high concentrations of acid and salts. • BNNSs-DAPhen performed excellent selectivity for U(VI) over lanthanides in strongly acidic conditions. The efficient separation and recovery of uranium(VI) (U(VI)) from lanthanides is pivotal to reduce the radioactive threat of hydrometallurgical residue solution of lanthanide minerals and benefits the sustainability of U resources. Here, we develop a cationic-surfactant-assisted solvothermal exfoliation method to prepare monolayer boron nitride nanosheets (BNNSs) for the ultrafast and selective separation of U(VI) from lanthanides. With the assistance of the strong "cation–π" interaction between cationic surfactants and BN, the monolayer BNNSs were prepared. Functionalization with diamide phenanthroline (DAPhen) groups endows the pristine BNNSs, which can hardly adsorb U(VI), with outstanding U(VI) adsorption performance. Batch adsorption experiments demonstrate that the obtained DAPhen modified BNNSs (BNNSs-DAPhen) exhibited high maximum adsorption capacity and ultrafast adsorption kinetics. The adsorption process reached equilibrium less than 1 min and the maximum adsorption capacity was estimated to be 313 mg g−1 by fitting with Langmuir model. Even under high concentrations of salts and acids, BNNSs-DAPhen still maintained excellent adsorption performance owing to the strong complexing ability of DAPhen groups with U(VI). The selectivity coefficients of U(VI) toward various lanthanides including lanthanum(III), cerium(III), europium(III), gadolinium(III), ytterbium(III), and lutetium(III) were beyond 120 at a high nitric acid concentration of 5 mol L−1. This work proposed a universal strategy for the production of monolayer BNNSs and the subsequent functionalization, which might be promising in the treatment of residual solution for lanthanides hydrometallurgy and decontamination of U(VI). [ABSTRACT FROM AUTHOR]