Extraction of uranium(VI) from sulfate solutions using a polymer inclusion membrane containing di-(2-ethylhexyl) phosphoric acid

PVDF-HFP-based polymer inclusion membrane functionalized with D2EHPA for the selective extraction of bismuth(III) from sulfate media

This study is the first application of a PVDF-HFP-based polymer inclusion membrane incorporating the poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and di(2-ethylhexyl)phosphoric acid (D2EHPA) as the base polymer and extractant for the extraction of bismuth(III), respectively. It is demonstrated that the PIM comprised of 60 wt% PVDF-HFP and 40 wt% D2EHPA is the most effective in the extraction of bismuth(III) from feed solution containing 20 mg L-1 bismuth(III) and 0.2 mol L-1 sulfate adjusted to pH 1.4. The extracted bismuth(III) ions are back-extracted quantitatively to the receiving solution containing 1 mol L-1 sulfuric acid. The stoichiometry experiments reveal that the Bi: D2EHPA ratio in the bismuth(III) extracted complex is 1:6, and D2EHPA is dimer. Moreover, it is shown that the studied PIM has high selectivity in the extraction of bismuth(III) over other interfering ions such as Mo(VI), Cr(III), Al(III), Fe(III), Ni(II), Zn(II), Cd(II), Co(II), Cu(II), and Mn(II). The interference of Fe(III) is also eliminated by masking with fluoride, leading finally to a nearly pure extraction of bismuth(III).

Optimal Synthesis of Novel Phosphonic Acid Modified Diatomite Adsorbents for Effective Removal of Uranium(VI) Ions from Aqueous Solutions

The authors synthesized a series of functionalized diatomite-based materials and assessed their U(VI) removal performance. Phosphor-derivative-modified diatomite adsorbents were synthesized by the three-route procedures: polymerisation (DIT-Vin-PAin), covalent (DIT-Vin-PAcov), and non-covalent (DIT-PA) immobilization of the functional groups. The effects of the diatomite modification have been studied using powder XRD, solid state NMR, FTIR spectroscopy, electronic microscopy, EDX, acid-base titrations, etc. The maximum adsorption capacities of DIT-Vin-PAcov, DIT-PA, and DIT-Vin-PAin samples were 294.3 mg/g, 253.8 mg/g, and 315.9 mg/g, respectively, at pH0 = 9.0. The adsorption amount of U(VI) ions using the prepared DIT-Vin-PAin was 95.63%, which is higher compared with that of the natural diatomite at the same concentration. The adsorption studies demonstrated that the phosphonic and hydroxyl groups on the surface of the diatomite played pivotal roles in the U(VI) adsorption. The U(VI) ions as a "hard" Lewis acid could easily form bonds with the "hard" donor P-containing ligands, so that the as-prepared DIT-Vin-PAin sample had excellent adsorption properties. The monolayer adsorption of the analyte on the surface of the raw diatomite and DIT-PA was observed. It was found from the thermodynamic parameters that the uptake of the U(VI) ions by the obtained adsorbents was a spontaneous process with an endothermic effect. Findings of the present work highlight the potential for using modified diatomite as effective and reusable adsorbents for the extraction of U(VI) in the waste, river, and tap waters with satisfactory results.

A poly(amidoxime)-modified MOF macroporous membrane for high-efficient uranium extraction from seawater

Although metal–organic frameworks (MOFs) own excellent uranium adsorption capacity but are still difficult to conveniently extract uranium from seawater due to the discrete powder state. In this study, a new MOF-based macroporous membrane has been explored, which can high-efficiently extract uranium through continuously filtering seawater. Through modifying the UiO-66 with poly(amidoxime) (PAO), it can disperse well in a N,N-dimethylformamide solution of graphene oxide and cotton fibers. Then, the as-prepared super-hydrophilic MOF-based macroporous membrane can be fabricated after simple suction filtration. Compared with nonmodified MOFs, this UiO-66@PAO can be dispersed uniformly in the membrane because it can stabilize well in the solution, which have largely enhanced uranium adsorbing capacity owing to the modified PAO. Last but not least, different from powder MOFs, this UiO-66@PAO membrane provides the convenient and continuously uranium adsorbing process. As a consequence, the uranium extraction capacity of this membrane can reach 579 mg·g−1 in 32 ppm U-added simulated seawater for only 24 h. Most importantly, this UiO-66@PAO membrane (100 mg) can remove 80.6% uranyl ions from 5 L seawater after 50 filtering cycles. This study provides a universal method to design and fabricate a new MOF-based adsorbent for high-efficient uranium recovery from seawater.

On the Potential of a Poly(vinylidenefluoride-co-hexafluoropropylene) Polymer Inclusion Membrane Containing Aliquat® 336 and Dibutyl Phthalate for V(V) Extraction from Sulfate Solutions

A polymer inclusion membrane (PIM) composed of 50 wt% base polymer poly(vinylidenefluoride-co-hexafluoropropylene), 40 wt% extractant Aliquat^® 336, and 10 wt% dibutyl phthalate as plasticizer/modifier provided the efficient extraction of vanadium(V) (initial concentration 50 mg L⁻¹) from 0.1 M sulfate solutions (pH 2.5). The average mass and thickness of the PIMs (diameter 3.5 cm) were 0.057 g and 46 μm, respectively. It was suggested that V(V) was extracted as VO₂SO₄⁻ via an anion exchange mechanism. The maximum PIM capacity was estimated to be ~56 mg of V(V)/g for the PIM. Quantitative back-extraction was achieved with a 50 mL solution of 6 M H₂SO₄/1 v/v% of H₂O₂. It was assumed that the back-extraction process involved the oxidation of VO₂⁺ to VO(O₂)⁺ by H₂O₂. The newly developed PIM, with the optimized composition mentioned above, exhibited an excellent selectivity for V(V) in the presence of metallic species present in digests of spent alumina hydrodesulfurization catalysts. Co-extraction of Mo(VI) with V(V) was eliminated by its selective extraction at pH 1.1. Characterization of the optimized PIM was performed by contact angle measurements, atomic-force microscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis/derivatives thermogravimetric analysis and stress–strain measurements. Replacement of dibutyl phthalate with 2-nitrophenyloctyl ether improved the stability of the studied PIMs.

FUNCTIONALIZED ELECTROSPUN POLYMER NANOFIBERS FOR TREATMENT OF WATER CONTAMINATED WITH URANIUM

Uranium (U) contamination of drinking water often affects communities with limited resources, presenting unique technology challenges for U⁶⁺ treatment. Here, we develop a suite of chemically functionalized polymer (polyacrylonitrile; PAN) nanofibers for low pressure reactive filtration applications for U⁶⁺ removal. Binding agents with either nitrogen-containing or phosphorous-based (e.g., phosphonic acid) functionalities were blended (at 1-3 wt.%) into PAN sol gels used for electrospinning, yielding functionalized nanofiber mats. For comparison, we also functionalized PAN nanofibers with amidoxime (AO) moieties, a group well-recognized for its specificity in U⁶⁺ uptake. For optimal N-based (Aliquat® 336 or Aq) and P-containing [hexadecylphosphonic acid (HPDA) and bis(2-ethylhexyl)phosphate (HDEHP)] binding agents, we then explored their use for U⁶⁺ removal across a range of pH values (pH 2-7), U⁶⁺ concentrations (up to 10 μM), and in flow through systems simulating point of use (POU) water treatment. As expected from the use of quaternary ammonium groups in ion exchange, Aq-containing materials appear to sequester U⁶⁺ by electrostatic interactions; while uptake by these materials is limited, it is greatest at circumneutral pH where positively charged N groups bind negatively charged U⁶⁺ complexes. In contrast, HDPA and HDEHP perform best at acidic pH representative of mine drainage, where surface complexation of the uranyl cation likely drives uptake. Complexation by AO exhibited the best performance across all pH values, although U⁶⁺ uptake via surface precipitation may also occur near circumneutral pH value and at high (10 μM) dissolved U⁶⁺ concentrations. In simulated POU treatment studies using a dead-end filtration system, we observed U removal in AO-PAN systems that is insensitive to common co-solutes in groundwater (e.g., hardness and alkalinity). While more research is needed, our results suggest that only 80 g (about 0.2 lbs.) of AO-PAN filter material would be needed to treat an individual's water supply (contaminated at ten-times the U.S. EPA Maximum Contaminant Level for U) for one year.

Separation and Recovery of Scandium from Sulfate Media by Solvent Extraction and Polymer Inclusion Membranes with Amic Acid Extractants

We report on the separation and recovery of scandium(III) from sulfate solutions using solvent extraction and a membrane transport system utilizing newly synthesized amic acid extractants. Scandium(III) was quantitatively extracted with 50 mmol dm-3 N-[N,N-di(2-ethylhexyl)aminocarbonylmethyl]glycine (D2EHAG) or N-[N,N-di(2-ethylhexyl)aminocarbonylmethyl]phenylalanine (D2EHAF) in n-dodecane at pH 2 and easily stripped using a 0.5 mol dm-3 sulfuric acid solution. The extraction mechanisms of scandium(III) extraction with D2EHAG and D2EHAF were examined, and it was established that scandium(III) formed a 1:3 complex with both extractants (HR), that is, Sc(SO4)2 - aq + 1.5(HR)2org ⇄ Sc(SO4)R(HR)2org + H+ aq + SO4 2- aq. The equilibrium constants of extraction were evaluated to be 4.87 and 9.99 (mol dm-3)0.5 for D2EHAG and D2EHAF, respectively. D2EHAG and D2EHAF preferentially extracted scandium(III) with a high selectivity compared to common transition metal ions under high acidic conditions (0 < pH ≤ 3). In addition, scandium(III) was quantitatively transported from a feed solution into a 0.5 mol dm-3 sulfuric acid receiving solution through a polymer inclusion membrane (PIM) containing D2EHAF as a carrier. Scandium(III) was completely separated thermodynamically from nickel(II), aluminum(III), cobalt(II), manganese(II), chromium(III), calcium(II), and magnesium(II), and partially separated from iron(III) kinetically using a PIM containing D2EHAF as a carrier. The initial flux value for scandium(III) (J 0,Sc = 1.9 × 10-7 mol m-2 s-1) was two times higher than that of iron(III) (J 0,Fe = 9.3 × 10-8 mol m-2 s-1).

Fast and Selective Removal of Aqueous Uranium by a K+-Activated Robust Zeolitic Sulfide with Wide pH Resistance

For the nuclear industry, uranium is not only an important strategic resource but also a serious global contaminant with radiotoxicity and high chemotoxicity. It is very important to efficiently capture uranium from complex aqueous solutions for further treatment and disposal of nuclear wastes. Herein, we first demonstrate the suitability of a three-dimensional (3D) water-stable K⁺-exchanged zeolitic sulfide, namely K@GaSnS-1, for the remediation of radioactive and toxic uranium by ion exchange. In comparison to the pristine compound GaSnS-1, the K⁺-activated porous sulfide K@GaSnS-1 exhibits faster [UO₂]²⁺ ion uptake kinetics, following the pseudo-second-order adsorption model. Further studies indicate that K@GaSnS-1 shows high exchange capacity (q_m^U = 147.6 mg/g) and wide pH resistance (pH 2.75-10.87). In particular, it can efficiently capture [UO₂]²⁺ ion even when excessive amounts of Na⁺, K⁺, Mg²⁺, and Ca²⁺ ions are present. The highest distribution coefficient value K_d, signifying the affinity and selectivity for [UO₂]²⁺ ion, reaches as high as 1.24 × 10⁴ mL/g. More importantly, the uranium in corresponding exchanged samples can be facilely and effectively eluted by a low-cost and eco-friendly method. These merits of K@GaSnS-1 make it promising for the effective and selective removal of uranium from complex contaminated water.

Photocatalytic reduction of Uranium(VI) under visible light with Sn-doped In2S3 microspheres

Visible light-driven conversion of soluble U(VI) to slightly soluble U(IV) has been regarded as a efficient and environmentally friendly technology to deal with uranium containing wastewater. In this paper, we attempted to use photocatalytic technology to reduction U(VI) from aqueous solution by constructing a highly efficient photocatalysts. The novel Sn-doped In₂S₃ microspheres photocatalyst were synthesized for the first time by a simple hydrothermal method, and characterized with various analytical and spectroscopic techniques to determine their structural, morphological, compositional, optical and photocatalytic properties. In determination of photocatalytic activity, the results showed that all Sn-doped In₂S₃ samples exhibited greater photocatalytic performance in reduction of U(VI) under visible light than the pure In₂S₃. The optimum SnIn₂S₃ photocatalyst with Sn:In molar ratio of 1:4.8 (SnIn₂S₃) had the highest photocatalytic performance (95% reduction efficiency within 40 min irradiation time), which was approximately 15.60 times faster than that of pure In₂S₃. The enhanced photocatalytic activity of the optimum SnIn₂S₃ was largely ascribed to the higher specific surface area, red-shift in the absorption band, the efficient separation of photogenerated electron-hole pairs (e^-/h⁺) and the narrowed band gap with an up shifting of valence band, conduction band potentials. In addition the optimum SnIn₂S₃ photocatalyst exhibited a good recyclability and stability during the repetitive experiments. Finally, the possible active species and the possible mechanism on basis of the experimental results were discussed in detail.

Facile synthesis of hierarchical nickel (III) oxide nanostructure: A synergistic remediating action towards water contaminants

Heavy metal ion removal from consumable water is an indispensable need to maintain healthy life. Therefore cost effective and highly efficient sorbents are strongly needed to pose threat to real water pollution. Nanomaterials are widely used to maintain clean aqueous system in a very cost effective way with high removal efficiency. In this present work, pure coral like Ni₂O₃ nanostructures were prescribed for Cr(VI) remediation which were prepared by two step synthesis procedure at room temperature. The single hierarchical morphology as confirmed from HRTEM (size∼200 nm) were subjected to toxic Cr(VI) ion removal experiments. They were found to remove ∼65% Cr(VI) ions that was higher than that of pure Ni₂O₃ nanoparticles of comparable size. The enhanced properties were explained on the basis of the defect states present within the nanostructure, investigated by positron annihilation lifetime spectroscopy (PALS). It was found that the hierarchical nanostructure had more number of di-vacancies and vacancy-clusters as compared to the particles. On performing isotherm fitting, it was found that the coral like morphology had a high heterogeneity factor that aided to a high adsorption rate when compared to the pure Ni₂O₃ nanoparticles (which had a homogenous surface). The synthesized nanostructure was severely toxic to bacterial community having minimum inhibitory concentration (MIC) of ∼300 μg/L. Also the nanostructure exhibited dual functionality towards Cr(VI) and bacteria contaminated water at 200 μg/ml. The maximum Cr(VI) removal efficiency for this dual system is found to be 39% whereas antibacterial activity was turned out to be 30% which was extensively higher than that of toxic Cr(VI) ions. A plausible mechanism for the dual functionality was also predicted.

Extraction of Gold(III) from Hydrochloric Acid Solutions with a PVC-based Polymer Inclusion Membrane (PIM) Containing Cyphos(®) IL 104

Abstract: Poly(vinyl chloride) (PVC) based polymer inclusion membranes (PIMs), with different concentrations of Cyphos® IL 104 as the membrane extractant/carrier, were studied for their ability to extract Au(III) from hydrochloric acid solutions. Some of the PIMs also contained one of the following plasticizers or modifiers: 2-nitrophenyloctyl ether, dioctylphthalate, 1-dodecanol, 1-tetradecanol, or tri(2-ethylhexyl) phosphate. The best performance, in terms of extraction rate and amount of Au(III) extracted, was exhibited by a PIM consisting of 25 wt% Cyphos^® IL 104, 5 wt% 1-dodecanol, and 70 wt% PVC. An almost complete back-extraction of the Au(III) extracted from this membrane was achieved by using a 0.10 mol L⁻¹ Na₂SO₃ receiver solution at pH 8. The stoichiometry of the extracted Au(III)/Cyphos® IL 104 adduct was determined as [P]⁺ [AuCl₄]⁻ H⁺ [PO₂]⁻ where [P]⁺ and [PO₂]⁻ represent trihexyl(tetradecyl) phosphonium and bis(2,4,4-trimethylpentyl) phosphinate ions, respectively. Back-extraction of Au(III) is suggested to occur by reduction of Au(III) to Au(I), with the formation of the species [Au(SO₃)₂]³⁻ in the aqueous receiver solution. Loss of 1-dodecanol from the newly developed PIM to the aqueous solutions in contact with it was observed, which indicated that this membrane was suitable for single use in the efficient recovery of Au(III) from hydrochloric acid solutions of electronic scrap or recycled jewelry.

The synthesis of a manganese dioxide–iron oxide–graphene magnetic nanocomposite for enhanced uranium(vi) removal

A MnO₂–Fe₃O₄–rGO composite was prepared and exhibited fast and efficient sorption for uranium(vi).

Liquid-liquid extraction of uranium(VI) in the system with a membrane contactor

Raising role of the nuclear power industry, including governmental plans for the construction of first nuclear power plant in Poland, creates increasing demand for the uranium-based nuclear fuels. The project implemented by Institute of Nuclear Chemistry and Technology concerns the development of effective methods for uranium extraction from low-grade ores and phosphorites for production of yellow cake—U₃O₈. The Liqui-Cel^® Extra-Flow 2.5 × 8 Membrane Contactor produced by CELGARD LLC (Charlotte, NC) company is the main component of the installation for liquid–liquid extraction applied for processing of post leaching liquors. In the process of membrane extraction the uranyl ions from aqueous phase are transported through the membrane into organic phase. The flow of two phases in the system was arranged in co-current mode. The very important element of the work was a selection of extracting agents appropriate for the membrane process. After preliminary experiments comprising tests of membrane resistivity and determination of extraction efficiency, di(2-ethylhexyl)phosphoric acid was found to be most favourable. An important aspect of the work was the adjustment of hydrodynamic conditions in the capillary module. To avoid the membrane wettability by organic solvent and mixing two phases equal pressure drops along the membrane module to minimize the transmembrane pressure, were assumed. Determination of pressure drop along the module was conducted using Bernoulli equation. The integrated process of extraction/re-extraction conducted in continuous mode with application of two contactors was designed.

Hydrothermal growth of large-size UO2 nanoparticles mediated by biomass and environmental implications

We reveal the hydrothermal conversion rule for amorphous U(vi) to large-size UO₂.