Yuanyou Yang

Pillar[5]arene-based phosphine oxides: novel ionophores for solvent extraction separation of f-block elements from acidic media

A new class of pillar[5]arene-based phosphine oxides tethered with ten chelating groups on both rims of the pillar were synthesized via two steps from macrocyclization of 1,4-bis(bromoalkoxy)benzenes with paraformaldehyde, followed by Arbusov reaction with iso-propoxydiphenylphosphine. Solvent extraction of these ligands towards selected lanthanides and actinides was investigated under acidic condition. Compared with acyclic monovalent analogs and classical extractant tri-n-octylphosphine oxide (TOPO), the remarkable efficiency and selectivity for thorium(IV) and uranyl(VI) as observed in these novel extractants bearing a varying spacer length revealed the significance of preorganization of chelating groups on pillararene platform. Log–log plot analysis indicated the 1 : 1 stoichiometry (ligand/metal) for the extracted complex formed between the ligand and thorium(IV) or uranyl(VI). The extraction efficiency was considerably improved with increasing acidity in a range of 0.1–1.5 M HNO3, a result that is distinct from the extraction behaviour of calixarene-based phosphine oxides. The extractability increased with enhancing NaNO3 concentration and high salinity assisted the preferential extraction of U(VI) over Th(IV). These ligands also showed moderate efficiency in differentiating europium(III) and americium(III) at 1 M HNO3 in the presence of a synergist (Br6-COSAN).

Behavior and analysis of Cesium adsorption on montmorillonite mineral

The adsorption of Cs by montmorillonite and the effects of experimental conditions on adsorption were investigated by using (134)Cs as a radioactive tracer. Additionally, the Cs-adsorbed and the modified montmorillonite were analyzed by X-ray Diffractometer System (XRD) and Scanning Electron Microscopy (SEM). The results showed that the adsorption of Cs by montmorillonite was efficient in the initial concentration (C(0)) of 30 microg/L Cs nitrate solution with 20 g/L montmorillonite at room temperature. In this condition, more than 98% Cs(+) ions could be adsorbed at pH approximately 8. The adsorption equilibrium was achieved within 5 min and the relationship between the concentration of Cs(+) in aqueous solutions and adsorption capacities of Cs(+) can be described by the Langmuir adsorption isotherm. The adsorption rate would decrease when temperature increase from 0 degrees C to 50 degrees C or in presence of coexistent K(+), Na(+) and Ca(2+), while modification by (NH(4))(2)SO(4), [Ag(NH(3))(2)](+), [Cu(NH(3))(4)](2+) or 450 degrees C could improve the adsorption abilities of montmorillonite for Cs(+). However, more than 89% of adsorbed Cs(+) on montmorillonite could be desorbed by 2 mol/L HNO(3) solutions. The XRD and SEM analysis further showed that the structure of the Cs-adsorbed or modified montmorillonite were different from that of the original one.

Biosorption of uranium on Bacillus sp. dwc-2: preliminary investigation on mechanism

In this paper, the biosorption mechanisms of uranium on an aerobic Bacillus sp. dwc-2, isolated from a potential disposal site for (ultra-) low uraniferous radioactive waste in Southwest China, was explored by transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis, FT-IR spectroscopy, proton induced X-ray emission (PIXE) and enhanced proton backscattering spectrometry (EPBS). The biosorption experiments for uranium were carried out at a low pH (pH 3.0), where the uranium solution speciation is dominated by highly mobile uranyl ions. The bioaccumulation was found to be the potential mechanism involved in uranium biosorption by Bacillus sp. dwc-2, and the bioaccumulated uranium was deposited in the cell interior as needle shaped particles at pH 3.0, as revealed by TEM analysis as well as EDX spectra. FTIR analysis further suggested that the absorbed uranium was bound to amino, phosphate and carboxyl groups of bacterial cells. Additionally, PIXE and EPBS results confirmed that ion-exchange also contributed to the adsorption process of uranium. All the results implied that the biosorption mechanism of uranium on Bacillus sp. is complicated and at least involves bioaccumulation, ion exchange and complexation process.

Biosorption of americium-241 by Saccharomyces cerevisiae

The biosorption of radionuclide 241Am from solution by Saccharomyces cerevisiae (S. cerevisiae), and the effects of experimental conditions on the adsorption were investigated. The preliminary results showed thatS. cerevisiae is a very efficient biosorbent. An average of more than 99% of the total 241Am could be removed by S. cerevisiae of 2.1 g/l (dry weight) from 241Am solutions of 17.54–4386.0 mg/l (2.22 MBq/l–555 MBq/l) with adsorption capacities of 7.45–1880.0 mg/g biomass (dry weight) (0.94 MBq/g–237.9 MBq/g). The adsorption equilibrium was achieved within 1 hour and the optimum pH ranged 1–3. No significant differences on 241Am adsorption were observed at 10–45 °C, or in solutions containing Au3+ or Ag+, even 2000 times above 241Am concentration. The relationship between concentrations and adsorption capacities of 241Am indicated the biosorption process should be described by the Freundlich adsorption isotherm.

Shape-persistent macrocycles: efficient extraction towards lanthanide and actinide elements

The extraction of three shape-persistent aromatic oligoamide macrocycles (cycloaramides) bearing either apolar or polar side chains at the periphery of the rings has been investigated towards some representative lanthanide and actinide ions, and alkali metal ions. The results from the liquid–liquid extraction of lanthanide and thorium ions from aqueous solutions into dichloromethane revealed remarkably high extractability of up to 99% and selectivity over alkali metal cations. The stoichiometry of the complex formed between the macrocycle and Eu3+ or Th4+ was determined to be 1:1.

Interaction between uranium and humic acid (I): Adsorption behaviors of U(VI) in soil humic acids

Abstract The adsorption behaviors of uranium on three soil humic acids (HAs), which were extracted from soils of different depths at the same site, were investigated under various experimental conditions. The adsorption results showed that U(VI) in solutions can be adsorbed by the three soil HAs, with the order of FHA (HA from 5 m depth of soil) >SHA (HA from the surface) >THA (HA from 10m depth of soil) for adsorption efficiency in each desirable condition, and the adsorption reached equilibrium in about 240 min. Although the maximum adsorption efficiency was achieved at a suitable uranium concentration (10 mg•L −1 U(VI) for SHA and THA, 20 mg•L −1 U(VI) for FHA), the adsorption could be described with Langmiur isotherm or Freundlich isotherm equation. The L/S (liquid/solid, mL/g) ratio and pH were important factors influencing the adsorption in our adsorption system besides uranium concentration. The adsorption efficiency decreased with the increase of the L/S ratio and pH at the pH range of 2.0–3.0 for SHA and THA or 2.5 – 6.0 for FHA. However, no significant difference in adsorption of U(VI) was observed at the experimental temperature. All the results implied that humic substances have different characteristics in samples even collected at the same site.

Removal of radioactive cesium from solutions by zinc ferrocyanide

Abstract Adsorption of 134Cs from aqueous solution by zinc ferrocyanide, and the effect of experimental conditions on the adsorption were investigated. Preliminary results showed that zinc ferrocyanide was very efficient as an absorbent. Over 98% of 134Cs could be removed by zinc ferrocyanide of 0.33 g·L−1 from 134Cs solution (Co) of 3.2∼160.0 kBq·L−1, with adsorption capacities (Q) of 9.6∼463.0 kBq·g−1. The adsorption equilibrium time was within one hour and the suitable pH ranged 1∼10. No significant differences on 134Cs adsorption were obsrved at 0∼50°C, or in solutions containing Ca2+, Fe3+, Mg2+, HCO3−, CO32- Cl− and SO42-, even though they are 1000 times higher than the anions or cations in groundwater. However, the adsorption rates decreased when solutions contained K+ or Na+. The adsorption process could be described by Freundlich and Langmuir adsorption equations.

The removal of uranium(VI) from aqueous solution by graphene oxide–carbon nanotubes hybrid aerogels

Novel graphene oxide–carbon nanotubes (GO–CNTs) hybrid aerogels were fabricated via a freeze-drying method using aqueous solutions of GO and CNTs. The resulting aerogels were characterized by scanning electron microscopy, X-ray diffraction, Fourier transformed infrared spectroscopy and thermal gravity analysis. The three-dimensional GO–CNTs aerogels were used to remove uranium(VI) from aqueous solutions. The results showed that GO–CNTs aerogels had high removal ability to uranium(VI) and could be a promising sorbent for many environment applications.

Adsorption and desorption of uranium (VI) in aerated zone soil

In this paper, the adsorption and desorption behavior of uranium (VI) in aerated zone soil (from Southwest China) was systematically investigated using a static experimental method in order to provide useful information for safety assessment of the disposal of (ultra-)low uraniferous radioactive waste, as well as a potential remediation method for uranium-contaminated soils. The adsorption behavior of uranium (VI) was firstly studied by batch experiments as functions of contact time, pH, liquid/solid ratio, temperature, colloids, minerals and coexistent ions. The results indicated that the adsorption of uranium (VI) by natural soil was efficient at an initial concentration of 10 mg/L uranium (VI) nitrate solution with 100 mg natural soil at room temperature when pH is about 7.0. The adsorption was strongly influenced by the solution pH, contact time, initial concentration and colloids. The adsorption equilibrium for uranium (VI) in soil was obtained within 24 h and the process could be described by the Langmuir adsorption equation. For uranium (VI) desorption, EDTA, citric acid and HNO(3) were evaluated under different conditions of temperature, concentration and proportion of liquid to solid. The adsorbed uranium (VI) on natural soil could be easily extracted by all these agents, especially by HNO(3), implying that the uranium-contaminated soils can be remedied by these reagents.

Synthesis of amidoximated graphene oxide nanoribbons from unzipping of multiwalled carbon nanotubes for selective separation of uranium(VI)

A kind of uranium-selective sorbent has been studied using graphene oxide nanoribbons (GONRs) from the unzipping of multiwalled carbon nanotubes as a solid matrix and amidoxime (AO) as a functional group. Amidoxime-functionalized GONRs (AOGONRs) were successfully prepared by chemical grafting technology and characterized by scanning electron microscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, elemental analysis, thermogravimetric analysis and X-ray photoelectron spectroscopy. The as-prepared AOGONRs were applied to adsorb U(VI) from aqueous solutions and exhibited a high sorption capacity towards U(VI) due to the strong chelation of AO to U(VI). It can be noted that the uranium sorption on the AOGONRs was pH-dependent, ionic strength-independent, fast, endothermic, spontaneous and a pseudo-second order process. The U(VI) sorption amount reached up to 2.112 mmol g−1 (502.6 mg g−1) at pH = 4.5 and T = 298 K. The sorption study performed in a simulated nuclear industry effluent demonstrated that the new sorbent had a desirable selectivity towards U(VI) ions over a range of competing metal ions. The results suggest that AOGONRs may be a potential and suitable candidate for the separation of U(VI) from various uranium-containing water samples.