Precise recognition and efficient recovery of Pd(II) from high-level liquid waste by a novel aminothiazole-functionalized silica-based adsorbent.

Efficient recognition, separation and recovery of palladium from high-level liquid waste (HLLW) not only helps the safe, green and environmentally friendly disposal of nuclear waste, but also is an essential important supplement to overcome the growing shortage of natural palladium resources. Herein, a novel silica-based functional adsorbent named 2AT-SiAaC was prepared by a two-step method, i.e., grafting of 2-aminothiazole (2AT) via the amidated reaction after in-situ polymerization of acrylic monomers on porous silica. SEM, EDS, TG-DSC, BET and PXRD all proved the successful preparation of 2AT-SiAaC, and it exhibited ultrahigh adsorption selectivity for Pd(II) (Kd (distribution coefficient) ≥ 10,344.2 mL/g, SFPd/M (separation factor) ≥ 613.7), fast adsorption kinetics with short equilibrium time (t ≤ 1 h) and good adsorption capacity (Q ≥ 62.1 mg Pd/g). The dynamic column experiments shows that 2AT-SiAaC achieved efficiently separation of Pd(II) from simulated HLLW, and the enrichment coefficients (C/C0) of Pd(II) was as high as about 14 with the recovery rate nearly 99.9% and basically kept the same performance in three adsorption-desorption column cycle experiments. The adsorption mechanism was analyzed by FT-IR, XPS and DFT calculations, and the ultrahigh selectivity of 2AT-SiAaC was attributed to the preferred affinity of the soft N-donor atoms in 2AT for Pd(II). NO3- ions participated in the adsorption reaction to keep charge balance, and the frontier orbital electron density distribution diagram shows the charge transfer in the process of material preparation and adsorption. To sum up, 2AT-SiAaC adsorbent provided a new insight for precise recognition and efficient separation of Pd(II) from HLLW.

Synthesis of Novel Hierarchical Rod-like Mg-Al bimetallic oxides for enhanced removal of uranium (VI) from wastewater.

As one of the most frequently used nuclides for nuclear fuel and toxic heavy metal in polluted solutions, the removal and recovery of U(VI) from wastewater is significant both for nuclear energy and human health. Herein, the novel hierarchical Mg-Al bimetallic oxides (Mg/Al-BOs) were successfully synthesized by a facile hydrothermal-lyophilization-calcination method for enhanced removal of uranium (U(VI)) from wastewater. The as-synthesized Mg/Al-BOs adsorbents were characterized by a variety of techniques including SEM-EDS, XRD, high temperature in-situ XRD, TG-DSC, N2 adsorption-desorption isotherm and XPS. Batch experiments including the effects of pH, hydration species, interfering ions on U(VI) removal, adsorption kinetics, isotherms and recyclability were systematically studied. Results showed that calcined Mg/Al-BO-24 inherited the hierarchical structure from its hydrotalcite-like precursor and grew the bimetallic oxides of Al2O3/MgO into a 3D rod-like and mesoporous network with the large BET surface area (472.4 m2∙g-1), which presented abundant binding sites on the surface and contributed to preventing the aggregation of Al2O3/MgO nanoparticles, allowing the fast uptake of U(VI) for equilibrium within 180 min and the significant increase of maximum adsorption capacity to 411.5 mg∙g-1. The uptake kinetics and isotherms of U(VI) removal could be well represented by the pseudo-second-order and Langmuir models, respectively. Further, it was demonstrated that U(VI) removal by Mg/Al-BO-24 was less influenced by coexisting cations and the regeneration cycles, indicating the excellent selectivity and reusability for U(VI) by the as-prepared composites. Based on the XPS analysis results, the mechanisms for U(VI) sorption onto the Mg/Al-BO-24 were mainly ascribed to the synergistic surface complexation and electrostatic interaction. These results suggested that Mg/Al-BO-24 prepared by the method reported here was available for developing other multiple metal oxides and would be a promising material for the effective treatment of wastewater with U(VI)-contamination.

An anion exchange pretreatment method for the determination of low-level uranium in the environmental water samples.

Uranium in environmental water is usually at trace or ultra-trace levels with high concentrations of background ions so that the detection of uranium often couples with pretreatment processes to lower the detection limit, and improve the selectivity and accuracy of instruments. A simple, green, effective and efficient anion exchange pretreatment method was proposed to favor the determination of low-level uranium in natural environmental water samples. To determine the applicability and obtain the optimum operating parameters, the effects of coprecipitation, pH, contact time, uranium concentration, background ions, eluent and the flow speed on the uranium recovery were investigated. The experimental results showed that the proper addition of saturated Na2CO3 solution for pH adjustment did not lead to uranium loss in natural water samples, and the optimum pH value for adsorption was determined from 6 to 8. The adsorption speed was improved a lot with the employment of a novel silica-supported anion exchange resin, which also showed good linear dependence in the concentration range from <0.5 µg/L to 1000 µg/L with high tolerance limits towards common background ions. The optimum eluent was determined as 1 M HNO3, and the optimum flow speeds for adsorption and desorption were about 4.0 and 1.0 mL/min, respectively. Based on these results, a pretreatment process was finally established, which realized the quantitative recovery of uranium from six different natural water samples with the chemical yields exceeding 95% and the enrichment factors about 100 times.

Phosphorylation of Guar Gum/Magnetite/Chitosan Nanocomposites for Uranium (VI) Sorption and Antibacterial Applications.

The development of new materials is needed to address the environmental challenges of wastewater treatment. The phosphorylation of guar gum combined with its association to chitosan allows preparing an efficient sorbent for the removal of U(VI) from slightly acidic solutions. The incorporation of magnetite nanoparticles enhances solid/liquid. Functional groups are characterized by FTIR spectroscopy while textural properties are qualified by N2 adsorption. The optimum pH is close to 4 (deprotonation of amine and phosphonate groups). Uptake kinetics are fast (60 min of contact), fitted by a pseudo-first order rate equation. Maximum sorption capacities are close to 1.28 and 1.16 mmol U g-1 (non-magnetic and magnetic, respectively), while the sorption isotherms are fitted by Langmuir equation. Uranyl desorption (using 0.2 M HCl solutions) is achieved within 20-30 min; the sorbents can be recycled for at least five cycles (5-6% loss in sorption performance, complete desorption). In multi-component solutions, the sorbents show marked preference for U(VI) and Nd(III) over alkali-earth metals and Si(IV). The zone of exclusion method shows that magnetic sorbent has antibacterial effects against both Gram+ and Gram- bacteria, contrary to non-magnetic material (only Gram+ bacteria). The magnetic composite is highly promising as antimicrobial support and for recovery of valuable metals.

Separation of thorium and uranium in nitric acid solution using silica based anion exchange resin.

To separate thorium and uranium in nitric acid solution using anion exchange process, a strong base silica-based anion exchange resin (SiPyR-N4) was synthesized. Batch experiments were conducted and the separation factor of thorium and uranium in 9M nitric acid was about 10. Ion exchange chromatography was applied to separate thorium and uranium in different ratios. Uranium could be eluted by 9M nitric acid and thorium was eluted by 0.1M nitric acid. It was proved that thorium and uranium can be separated and recovered successfully by this method.

Understanding the bonding nature of uranyl ion and functionalized graphene: a theoretical study.

Studying the bonding nature of uranyl ion and graphene oxide (GO) is very important for understanding the mechanism of the removal of uranium from radioactive wastewater with GO-based materials. We have optimized 22 complexes between uranyl ion and GO applying density functional theory (DFT) combined with quasi-relativistic small-core pseudopotentials. The studied oxygen-containing functional groups include hydroxyl, carboxyl, amido, and dimethylformamide. It is observed that the distances between uranium atoms and oxygen atoms of GO (U-OG) are shorter in the anionic GO complexes (uranyl/GO(-/2-)) compared to the neutral GO ones (uranyl/GO). The formation of hydrogen bonds in the uranyl/GO(-/2-) complexes can enhance the binding ability of anionic GO toward uranyl ions. Furthermore, the thermodynamic calculations show that the changes of the Gibbs free energies in solution are relatively more negative for complexation reactions concerning the hydroxyl and carboxyl functionalized anionic GO complexes. Therefore, both the geometries and thermodynamic energies indicate that the binding abilities of uranyl ions toward GO modified by hydroxyl and carboxyl groups are much stronger compared to those by amido and dimethylformamide groups. This study can provide insights for designing new nanomaterials that can efficiently remove radionuclides from radioactive wastewater.