Highly Efficient Recovery of Uranium from Seawater Using an

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Highly efficient recovery of uranium from seawater using an electrochemical approach Fangting Chi, Shuo Zhang, Jun Wen, Jie Xiong, and Sheng Hu Ind. Eng. Chem. Res., Just Accepted Manuscript • Publication Date (Web): 22 May 2018 Downloaded from http://pubs.acs.org on May 22, 2018

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Industrial & Engineering Chemistry Research

Highly efficient recovery of uranium from seawater using an electrochemical approach Fangting Chi†∗, Shuo Zhang†, Jun Wen‡, Jie Xiong‡, Sheng Hu‡ †

Fundamental Science on Nuclear Wastes and Environmental Safety Laboratory, Southwest University of Science and Technology, Mianyang, 621010, China

‡

Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621900, China

ABSTRACT ： Uranium recovery from seawater offers a promising route for producing scalable and sustainable nuclear energy because the world's oceans contain hundreds of times more uranium than lands. Current adsorption method presents limitations including low extraction capacity and slow extraction kinetics, making realistic implementation impractical. Here we develop an electrochemical extraction approach that demonstrates high extraction capacity and fast extraction kinetics in the uranium recovery. In the electrochemical approach, chitosan functionalized electrodes were used to offer surface specific binding to uranyl ions; voltages were then supplied to attract the ions to the electrode and induce electrodeposition of uranyl ions to form charge-neutral uranium species. The electrodeposition approach demonstrated nearly eight times higher uranium extraction capacities and three times faster extraction rates ∗ To whom correspondence should be addressed: Dr. Fangting Chi, E-mail addresses: [email protected]. 1

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than the current adsorption method in uranium spiked seawater. Because of the excellent uranium extraction performance, the electrochemical approach allows for highly efficient recovery of uranium from seawater. KEYWORDS: electrochemical approach; uranium recovery; chitosan; seawater

1. Introduction Recently, recovery of uranium from aqueous solutions has received rapidly increasing research interest, both from energy and environmental perspectives. In the energy perspective, uranium is the key fuel for nuclear energy and its reserve in terrestrial ores is estimated to be depleted within 100 years.1 Fortunately, seawater contains a vast source of uranium that is approximately 1000 times larger than the terrestrial resources.2 In the environmental perspective, uranium is the main component of nuclear wastes, which is harmful to environment, ecosystem and human health.3 Therefore, efficient recovery of uranium from aqueous solution is desirable for both the sustainable nuclear energy and the environmental protection. Recovery of uranium from seawater is of particular interest because it can contribute to the growing international nuclear industry.4-8 However, it is challenging to recover uranium from seawater due to the ultra low concentration of uranium in seawater (~ 3 ppb). Currently, adsorption based on chelating polymer adsorbents is considered to be the most promising method for the uranium recovery from seawater. The uranium adsorption capacities for the most advanced chelating polymer (e.g., amidoxime fibers) have been reported to be about 190 mg/g in simulated seawater and 2


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roughly 4 mg/g in seawater after 56 days of testing.9-11 The capacity value of 4 mg/g is still too low to be cost-effective for realistic implementation. In order to further increase the uranium extraction capacity, ongoing efforts are focused on the two elements of the adsorbents: (1) increasing the surface areas; and (2) optimizing the surface properties. Increasing the surface areas can be achieved by decreasing the size of adsorbents12, 13 or fabricating mesoporous materials14-17. Optimizing the surface properties leads to an increase in the affinity and selectivity for uranium ions and is usually accomplished via surface modification with novel functional groups, such as protein2, 1,10-phenanthroline-2,9-dicarboxylic acid18 and naphthalimidedioxime ligand19. The use of adsorption to recover uranium from seawater has had some success; however, the conventional adsorption method has several drawbacks that are difficult to overcome. First, the adsorption kinetic is slow because without driving force the diffusion rate of uranium ions to the surface of adsorbents is low. Second, a portion of the adsorption sites is inaccessible to the uranium ions because of the Coulomb repulsion resulting from existing adsorbed cations. The Coulomb repulsion increases as the amount of adsorbed cations increases. Finally, other undesirable cations present at higher concentrations in seawater compete with uranium ions for the adsorption sites, leading to a reduction in uranium uptake. Our strategy is to use an electrochemical approach in which an electric field is applied to the chelating polymers for the recovery of uranium from seawater. The electrochemical approach overcomes the drawbacks of the conventional adsorption method, which is attributed to: (1) increasing the diffusion rate of uranium ions and its 3



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collision rate onto the adsorbents due to the driving force of the electric field; (2) decreasing Coulomb repulsion via electrodeposition that neutralize the charged uranium ions; and (3) lowering the competition of the undesirable cations using a specific voltage that only reduce the uranly ions not other ions. Although electrochemical

extraction

of

uranium

has

been

reported

using

an

amidoxime-functionalized electrode as a working electrode,20 here we investigate chitosan-coated electrodes in the electrochemical extraction of uranium. With the optimized electrochemical process, we have achieved higher extraction capacity and faster extraction rate than the conventional adsorption method. The electrochemical approach demonstrated uranium extraction capacity of 1523 mg/g in uranium spiked seawater without presence of saturation. Additionally, the electrochemical approach exhibited three times faster extraction rate than the conventional adsorption method. The electrochemical approach is particularly noteworthy because it provides a highly efficient route to recover uranium from seawater.

2. Experimental section 2.1. Materials Chitosan and acetic acid were purchased from the Shanghai Chemical Reagent Company. The chemicals were analytical grade and used as received without further purification. Deionized water (14 MΩ) was used for the dissolution of chitosan. Uranyl nitrate hexahydrate (UO2(NO3)3·6H2O, B&A Quality) were used for the preparation of uranium spiked seawater. The seawater was obtained from the Bohai 4


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Gulf of China. 2.2. Fabrication of chitosan coated electrode The graphite felt was cut into 1×2 square pieces and used as electrode substrate. Chitosan, acetic acid and deionized water were mixed at a mass ratio of 2: 1: 100 and stirred until a homogenous solution was obtained. The solution was then dip coated onto the graphite felt substrate and heated at 50 °C for 3 h in air. After heating, the chitosan functionalized electrode was cooled to room temperature for use. 2.3. Characterization Voltammetric measurements were carried out using an electrochemical workstation (AUTOLAB-PGSTAT302 (Metrohm)) with a saturated calomel electrode as the reference electrode and a graphite rod as the counter electrode. The morphology of the electrodes was observed using scanning electron microscopy (SEM, Carl zeiss, Libra200) at an acceleration voltage of 200 kV, equipped with energy-dispersive spectroscopy (EDS). Fourier transform infrared spectroscopy (FTIR, Thermo, Nicolet 5700) was carried out by accumulating 60 scans over a frequency range 400-4000 cm-1 at a resolution of 1 cm-1. X-ray diffraction pattern (XRD) was recorded using a X-ray diffractometer (X’ Pert PRO). Uranium spiked solutions were prepared by dissolving uranyl nitrate hexahydrate into real seawater. The seawater used was filtered through a 0.1-µm PTFE membrane to remove any particles and microorganisms. The uranium concentrations of the spiked solutions were 5 ppm, 50 ppm, 500 ppm, and 1000 ppm, respectively. These uranium spiked solutions showed pH of 7~8. The extraction experiments were 5



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performed with 1000 ml of the uranium spiked solutions at room temperature for 24 h. The uranium concentration of the spiked solutions before and after extraction was determined by an inductively coupled plasma mass spectrometer (ICP-MS, Agilent 7700). The amount of the extracted uranium was calculated from the uranium concentration difference before and after extraction, which can be describe as q = (C0-Ce)×V/W, where C0 and Ce are the initial and the equilibrium concentrations of the uranium ions in the testing solution, V is the volume of the testing solution, and W is the weight of the electrode. In the case of electrochemical extraction, a voltage of -3 V was supplied to the electrode. In contrast, no voltage was supplied for the conventional adsorption.

3. Results and discussion 3.1. Electrochemical approach Electrochemical approaches have been previously studied, most notably for heavy metal detection, with the advantages of rapid analysis, good selectivity, and sensitivity.21-27 Based on the previous studies, we developed an electrochemical extraction approach to recover uranium ions from seawater. For electrochemical extraction, chitosan coated graphite felt electrodes were used because graphite felt have high electric conductivity and chitosan can provide adsorption sites that preferably bind uranium ions. Then a voltage was applied to the electrodes to attract the ions to the electrode and induce electrodeposition of uranyl ions. As illustrated in Figure 1, the electrochemical extraction can be described as a two-stage process: (1) 6


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migration and (2) electrodeposition. During migration, cations and anions driven by the external electric field are delivered to the electrode and the uranyl ions can form chelation binding to the chitosan on the electrode surface. During electrodeposition, uranyl ions can be reduced as charge-neutral species (e.g., UO2) and deposited on the electrode surface. The process repeats as the voltage was continuously supplied. Therefore, further uranyl ions can be delivered to the electrode surface and reduced, allowing the deposited charge-neutral species to gradually grow into larger particles.

Figure 1. Schematic illustration of the process in electrochemical extraction. In stage 1, ions migrate to the electrode and the uranyl ions form chelation binding to the chitosan on the electrode surface. In stage 2, adsorbed uranyl ions are reduced as charge-neutral species (e.g., UO2) and deposited on the electrode surface.

In order to verify our speculation, chitosan functionalized graphite felt electrodes were prepared. The chitosan functionalized graphite felt electrode was chosen because it possesses high affinity to uranium ions, high electrical conductivity and large 7



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surface areas. For the preparation of the chitosan functionalized graphite felt electrode, graphite felt was used as substrates and coated with a layer of chitosan. The graphite felt is highly conductive, which can effectively conduct electron to the chitosan layer. The chitosan provides active sites to chealte the uranyl ions. The graphite felt electrode is about 2 cm in size (Figure 2a). The electrode surfaces were observed by scanning electron microscope (SEM) in order to see the surface microstructure. Figure 2b and c shows the SEM images of the graphite felt electrodes before and after coating of chitosan, respectively. The graphite felt electrode comprises graphite fibers with mean diameter of ~20 µm. Large amounts of voids were present among the graphite fibers, which facilitates the transport of uranium ions in the electrode and increases the utilization efficiency of chitosan active sites. Higher magnification showed that the surface of a single graphite fiber became rougher after coating of chitosan layer. The rough structure may correspond to the chitosan layer. The chemical composition of the electrode was investigated by Fourier transform infrared spectroscopy (FTIR), and the measured FTIR spectra are shown in Figure 2d. The major peaks for pure chitosan can be assigned as follows: 3452 cm-1 (O-H and N-H stretching vibrations), 1641 cm-1 (N-Hdeformation vibration), and 1397 cm-1 (C-H symmetric blending vibration).28 The IR spectrum of the chitosan coated electrode demonstrated that a layer of chitosan was formed on the surface of graphite fibers because their peaks are similar to those of pure chitosan.

8


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Figure 2. Characterization of the electrode. a, Photo of the chitosan coated graphite felt electrode. b, SEM image of the carbon felt showing the graphite felt comprises graphite fibers with mean diameter of ~20 µm. The inset represents a high-magnification image of a single graphite fiber. c, SEM image of the chitosan coated graphite felt showing that the surface of the graphite fiber became rougher after coating of chitosan layer. The inset is a high-magnification image of a single a single graphite fiber. d, Infrared spectra of the chitosan and chitosan coated electrode showing that a layer of chitosan was formed on the surface of graphite fibers. Data 9



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have been vertically offset for clarity.

In order to investigate the electrochemical behavior of uranium ions during electrochemical extraction, the cyclic voltammograms of uranium spiked seawater was obtained using cyclic voltammetry. Prior to measurement, the seawater was filtered through a 0.2 µm PTFE membrane and then spiked with 1000 ppm uranyl nitrate. The unspiked seawater was used as controls. Figure 3a shows the cyclic voltammograms of seawater spiked with 1000 ppm uranium, in comparison with unspiked seawater. In the case of unspiked seawater, no obvious peak was observed in the voltammogram curve. Therefore, the peaks in the curve of uranium spiked seawater can be identified as uranium redox reactions. The voltammogram curve of uranium spiked seawaters presents two pairs of redox peaks, suggesting the electrochemical reduction of U(VI) undergo two processes. The cyclic voltammogram is similar to the findings of earlier work on electrochemical behavior of uranyl in ionic liquid29 and on electrochemical behavior of uranium and thorium aqueous solutions30. The peaks at -1.41 V and -0.36 V correspond to the reduction of U (VI) to U (V) and the oxidation of U (V) to U (VI), respectively.22,

30

During the

electrodeposition process, the UO22+ was reduced to UO2+; the UO2+ is unstable and disproportionate into UO22+ and UO2 spontaneously. The two stages of the electrochemical process can be described using the following scheme: UOଶ ଶା + e → UOଶ ା , and 2UOଶ ା → UOଶ ଶା + UOଶ .The electrochemical reaction agrees well with the fact that the oxidation peak of (V) to U (VI) is much smaller than the reduction peak of U (VI) to U (V) since a portion of the U (V) is transformed into U (IV) after 10


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formation. U (IV) is insoluble in water, thereby precipitating out as immobilized UO2 onto the electrode surface. The cyclic voltammograms suggested that the UO22+ will be extracted out from the seawater and precipitated as UO2 with a reducing current. The advantages of the electrochemical extraction over conventional adsorption can be obviously demonstrated from the color of the uranium spiked seawater after extraction. Figure 3b shows an image of uranium spiked seawater after 24 h of extraction using conventional adsorption (right) and electrochemical extraction (middle), with an initial uranium concentration of 1000 ppm (left). Prior to extraction, the solution was yellow. After extraction, the solution using electrochemical extraction became clear but the solution using conventional adsorption remained yellow. In order to verify our proposed mechanism during electrochemical extraction, the electrodes after extraction were observed by SEM. The extraction experiments were performed at room temperature for 24 h with initial uranium concentration of 1000 ppm. Figure 3c and d shows SEM images of the electrodes after the electrochemical extraction and the conventional adsorption respectively. In the case of the electrochemical extraction, large amounts of micrometer-sized particles were observed on the surface of the electrode. In contrast, the surface of electrode after conventional adsorption was smooth without presence of obvious precipitate. The difference in the appearance of the electrodes after extraction between the electrochemical extraction and the conventional adsorption is a result of the different extraction mechanism. During electrochemical extraction, charge-neutral species were 11



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formed on the surface of the electrode due to electrochemical reduction and can continue to grow up into bigger particles in the progressive electrodeposition. Therefore, we can observe micrometer-sized particles on the surface of the electrode after electrochemical extraction. Higher magnification (Figure 3e) showed that the micrometer-sized particles were composed of irregular prism-shaped structures with size of about 1 µm. EDX analysis confirms that the particles include U and O elements with an atomic ratio of roughly 1:9.7. Note that H cannot be detected by the EDX due to its small mass, making us unable to calculate the amount of crystallized water through the H content. XRD characterization was performed to identify the uranium species. The diffraction peaks corresponding to UO2 (JCPDS 41-1422) and U3O8 (JCPDS 47-1439) were observed in the XRD pattern. The existence of two types of uranium species is likely due to partly transformation of UO2 into U3O8. UO2 were obtained during electrodeposition in terms of the cyclic voltammograms. However, UO2 is relatively unstable and will be gradually oxidized into the most stable uranium species, U3O8. However, the uranyl ions were just adsorbed on the surface of the electrode during conventional adsorption. The uranyl ions are very small in the macroscopic perspective, having a negligible effect on the morphology of the electrode. Hence, we cannot observe distinct change in the morphologies of the electrodes after conventional adsorption. The results of the SEM observation support our hypothesis that charge-neutral oxide species will be electrodeposited on the electrode and continue to grow up into particles during the electrochemical extraction.

12


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Figure 3. Electrochemical extraction. a, Cyclic voltammograms of 1000 ppm uranyl-nitrate-spiked seawater in comparison with unspiked seawater. b, photos of initial 1000 ppm uranium spiked seawater and the seawater after 24 h of extraction using the electrochemical and adsorption methods. c. SEM image of the electrode after 24 of electrodepositon showing that the electrode was covered with particles. d. SEM image of the electrode after 24 h of adsorption showing that no particle was observed. e. Higher magnification of the particles showing they were composed of irregular prism-shaped structures with size of about 1 µm. f. XRD pattern of the particles.

3.2 Uranium extraction performance As described in the introduction, the driving force for developing the electrochemical approach was to develop a novel extraction method that has higher uranium extraction capacity and faster extraction kinetics than the conventional adsorption method. To illustrate the enhanced extraction performance of the 13



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electrochemical approach, a series of electrochemical extraction experiments was performed in uranium spiked seawater in comparison with conventional adsorption. The electrochemical extraction experiments were performed at room temperature for 24 h using the chitosan functionalized graphite felt electrode as the working electrode and graphite rod as the counter electrode. The graphite rod is graphite in the form of rod, which has high electrical conductivity. A voltage of -3 V was applied to the electrodes. The initial uranium concentrations were 5 ppm, 50 ppm, 500 ppm and 1000 ppm in the four cases of uranium spiked seawater. The conventional adsorption was conducted in the same manner as the electrochemical extraction except that no voltage was supplied. As shown in Figure 4, the electrochemical method exhibited higher extraction amount than the adsorption method in all four cases, and the difference became larger with increasing the initial uranium concentration. Furthermore, the electrochemical extraction seems to show no saturation. However, the adsorption method was limited by a saturation extraction capacity. For example, the saturation extraction capacity for the adsorption method is 180 mg/g, beyond which, the extraction capacity did not increase with increasing the initial uranium concentration. This result is similar to previous reports.9,

10, 12

One possible

explanation for the existence of saturation adsorption is that the adsorption sites on the adsorbents are limited. The adsorbents cannot absorb more uranyl ions after the adsorption sites were fully occupied. In contrast, the electrochemical extraction exhibited no saturation even at extraction capacity of 1533 mg/g. The high uranium extraction capacity for the electrochemical method was approximately eight times 14


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larger than that of the conventional adsorption. The high uranium extraction capacity without saturation is likely due to the fact that UO22- can be progressively reduced to charge-neutral species under the electric effect.

Figure 4. Uranium extraction performance of the electrochemical extraction in comparison to adsorption with initial uranium concentration of 5 ppm (a), 50 ppm (b), 500 ppm (c), and 1000 ppm (d).

In addition to a much higher uranium extraction capacity, the electrochemical approach also demonstrated a faster extraction rate. The extraction kinetics was investigated under room temperature with initial uranium concentration of 50 ppm for the electrochemical extraction compared with the conventional adsorption. Figure 5 15



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shows the uranium extraction amounts as a function of the extraction time. The rapid increase in the uranium extraction amount during the electrochemical extraction indicates fast kinetics. The rate of the uranium extraction process was analyzed by a pseudo-first-order kinetic model and a pseudo-second-order kinetic model. The best fit of the experimental data is the pseudo-second-order kinetic model, and therefore we can conclude that the electrochemical extraction follows the pseudo-second-order kinetic model. Based on the fitting of the pseudo-second-order kinetic model, the electrochemical extraction is estimated to have three times faster extraction kinetics than the conventional adsorption. The fast extraction rates of the electrochemical approach can be explained by the accelerated diffusion rate of ions under electric field. Because the extraction of uranyl into the adsorbent is diffusion controlled

31

, the

accelerated diffusion rate of uranyl ions under electric field can increase the extraction rate. The results of the extraction experiments indicate that the electrochemical method demonstrated not only higher uranium extraction capacity but also faster extraction

kinetics

than

the

conventional

adsorption

method.

Figure 5. Kinetics fitting of both adsorption and electrochemical extraction. The rate 16


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constants for conventional adsorption case are 1.43 × 10-3 s-1 (pseudo-first-order) and 4.46 × 10-6 M-1s-1 (pseudo-second-order). The rate constants for electrochemical extraction case are 6.88 × 10-2 s-1 (pseudo-first-order) and 1.67 × 10-5 M-1s-1 (pseudo-second-order).

4. Conclusions Highly efficient recovery of uranium from seawater has been achieved by an electrochemical extraction approach where chitosan functionalized electrodes were used as working electrodes and supplied with -3 voltage. The electrochemical approach demonstrated nearly eight times higher uranium extraction capacities and three times faster extraction rates than the current adsorption approach. In spiked seawater with uranium concentration of 1000 ppm, the electrochemical approach exhibited uranium extraction capacity as high as 1000 mg/g, compared with 200 mg/g for the conventional adsorption approach. The high extraction capacity and fast extraction rates of the electrochemical approach may be due to the fact that the electric field can accelerate the migration of uranyl ions to the electrodes and induce the electrodeposition of uranium compounds, forming charge-neutral species. SEM observation confirmed the formation and deposition of charge-neutral particles on the electrode surface after electrochemical extraction. The electrochemical extraction provides an efficient approach to recover uranium from seawater.

Acknowledgments 17



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This work was sponsored by the National Natural Science Foundation of China (Grant No. 21401152).

References (1) Chen, L.; Bai, Z.; Zhu, L.; Zhang, L.; Cai, Y.; Li, Y.; Liu, W.; Wang, Y.; Chen, L.; Diwu, J.; Wang, J.; Chai, Z.; Wang, S. Ultrafast and Efficient Extraction of Uranium from Seawater Using an Amidoxime Appended Metal-Organic Framework. ACS Appl. Mater. Interfaces 2017, 9, 32446. (2) Zhou, L.; Bosscher, M.; Zhang, C.; Özçubukçu, S.; Zhang, L.; Zhang, W.; Li, C. J.; Liu, J.; Jensen, M. P.; Lai, L.; He, C. A protein engineered to bind uranyl selectively and with femtomolar affinity. Nat. Chem. 2014, 6, 236. (3) Barrett, C. A.; Chouyyok, W.; Speakman, R. J.; Olsen, K. B.; Addleman, R. S. Rapid extraction and assay of uranium from environmental surface samples. Talanta 2017, 173, 69. (4) Yue, Y.; Mayes, R. T.; Kim, J.; Fulvio, P. F.; Sun, X.-G.; Tsouris, C.; Chen, J.; Brown, S.; Dai, S. Seawater Uranium Sorbents: Preparation from a Mesoporous Copolymer Initiator by Atom-Transfer Radical Polymerization. Angew. Chem. Int. Ed. 2013, 52, 13458. (5) Endrizzi, F.; Leggett, C. J.; Rao, L. Scientific Basis for Efficient Extraction of Uranium from Seawater. I: Understanding the Chemical Speciation of Uranium under Seawater Conditions. Ind. Eng. Chem. Res. 2016, 55, 4249. (6) Shao, D.; Li, Y.; Wang, X.; Hu, S.; Wen, J.; Xiong, J.; Asiri, A. M.; Marwani, H. 18


Page 19 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


M. Phosphate-Functionalized Polyethylene with High Adsorption of Uranium(VI). ACS Omega 2017, 2, 3267. (7) Xiong, J.; Hu, S.; Liu, Y.; Yu, J.; Yu, H.; Xie, L.; Wen, J.; Wang, X. Polypropylene

Modified

with

Amidoxime/Carboxyl

Groups

in

Separating

Uranium(VI) from Thorium(IV) in Aqueous Solutions. ACS Sustainable Chem. Eng. 2017, 5, 1924. (8) Ma, S.; Huang, L.; Ma, L.; Shim, Y.; Islam, S. M.; Wang, P.; Zhao, L.-D.; Wang, S.; Sun, G.; Yang, X.; Kanatzidis, M. G. Efficient Uranium Capture by Polysulfide/Layered Double Hydroxide Composites. J. Am. Chem. Soc. 2015, 137, 3670. (9) Das, S.; Oyola, Y.; Mayes, R. T.; Janke, C. J.; Kuo, L. J.; Gill, G.; Wood, J. R.; Dai, S. Extracting Uranium from Seawater: Promising AF Series Adsorbents. Ind. Eng. Chem. Res. 2016, 55, 4110. (10) Das, S.; Oyola, Y.; Mayes, R. T.; Janke, C. J.; Kuo, L. J.; Gill, G.; Wood, J. R.; Dai, S. Extracting Uranium from Seawater: Promising AI Series Adsorbents. Ind. Eng. Chem. Res. 2016, 55, 4103. (11) Brown, S.; Yue, Y.; Kuo, L.-J.; Mehio, N.; Li, M.; Gill, G.; Tsouris, C.; Mayes, R. T.; Saito, T.; Dai, S. Uranium Adsorbent Fibers Prepared by Atom-Transfer Radical Polymerization (ATRP) from Poly(vinyl chloride)-co-chlorinated Poly(vinyl chloride) (PVC-co-CPVC) Fiber. Ind. Eng. Chem. Res. 2016, 55, 4139. (12) Saito, T.; Brown, S.; Chatterjee, S.; Kim, J.; Tsouris, C.; Mayes, R. T.; Kuo, L.-J.; Gill, G.; Oyola, Y.; Janke, C. J.; Dai, S. Uranium recovery from seawater: 19



Page 20 of 24

development of fiber adsorbents prepared via atom-transfer radical polymerization. J. Mater. Chem. A 2014, 2, 14674. (13)Neti, V. S.; Das, S.; Brown, S.; Janke, C. J.; Kuo, L.-J.; Gill, G. A.; Dai, S.; Mayes, R. T. Efficient Functionalization of Polyethylene Fibers for the Uranium Extraction from Seawater through Atom Transfer Radical Polymerization. Ind. Eng. Chem. Res. 2017, 56, 10826. (14) Xue, G.; Yurun, F.; Li, M.; Dezhi, G.; Jie, J.; Jincheng, Y.; Haibin, S.; Hongyu, G.; Yujun, Z. Phosphoryl functionalized mesoporous silica for uranium adsorption. Appl. Surf. Sci. 2017, 402, 53. (15) Yang, S.; Qian, J.; Kuang, L.; Hua, D. Ion-Imprinted Mesoporous Silica for Selective Removal of Uranium from Highly Acidic and Radioactive Effluent. ACS Appl. Mater. Interfaces 2017, 9, 29337. (16) Liu, W.; Dai, X.; Bai, Z.; Wang, Y.; Yang, Z.; Zhang, L.; Xu, L.; Chen, L.; Li, Y.; Gui, D.; Diwu, J.; Wang, J.; Zhou, R.; Chai, Z.; Wang, S. Highly Sensitive and Selective Uranium Detection in Natural Water Systems Using a Luminescent Mesoporous Metal–Organic Framework Equipped with Abundant Lewis Basic Sites: A Combined Batch, X-ray Absorption Spectroscopy, and First Principles Simulation Investigation. Environ. Sci. Technol. 2017, 51, 3911. (17) Zheng, T.; Yang, Z.; Gui, D.; Liu, Z.; Wang, X.; Dai, X.; Liu, S.; Zhang, L.; Gao, Y.; Chen, L.; Sheng, D.; Wang, Y.; Diwu, J.; Wang, J.; Zhou, R.; Chai, Z.; Albrecht-Schmitt, T. E.; Wang, S. Overcoming the crystallization and designability issues in the ultrastable zirconium phosphonate framework system. Nat. Commun. 20


Page 21 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2017, 8, 15369. (18) Lashley, M. A.; Ivanov, A. S.; Bryantsev, V. S.; Dai, S.; Hancock, R. D. Highly Preorganized Ligand 1,10-Phenanthroline-2,9-dicarboxylic Acid for the Selective Recovery of Uranium from Seawater in the Presence of Competing Vanadium Species. Inorg. Chem. 2016, 55, 10818. (19)Chatterjee, S.; Bryantsev, V. S.; Brown, S.; Johnson, J. C.; Grant, C. D.; Mayes, R. T.;

Hay,

B.

P.; Dai,

S.; Saito,

T.

Synthesis

of

Naphthalimidedioxime

Ligand-Containing Fibers for Uranium Adsorption from Seawater. Ind. Eng. Chem. Res. 2016, 55, 4161. (20) Liu, C.; Hsu, P.-C.; Xie, J.; Zhao, J.; Wu, T.; Wang, H.; Liu, W.; Zhang, J.; Chu, S.; Cui, Y. A half-wave rectified alternating current electrochemical method for uranium extraction from seawater. Nat. Energy 2017, 2, 17007. (21) Ziółkowski, R.; Górski, Ł.; Malinowska, E. Carboxylated graphene as a sensing material for electrochemical uranyl ion detection. Sens. Actuators, B 2017, 238, 540. (22) Guin, S. K.; Ambolikar, A. S.; Kamat, J. V. Electrochemistry of actinides on reduced graphene oxide: craving for the simultaneous voltammetric determination of uranium and plutonium in nuclear fuel. RSC Adv. 2015, 5, 59437. (23) Güney, S.; Güney, O. A novel electrochemical sensor for selective determination of uranyl ion based on imprinted polymer sol–gel modified carbon paste electrode. Sens. Actuators, B 2016, 231, 45. (24) Wang, Y.; Wang, L.; Huang, W.; Zhang, T.; Hu, X.; Perman, J. A.; Ma, S. A metal-organic framework and conducting polymer based electrochemical sensor for 21



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high performance cadmium ion detection. J. Mater. Chem. A 2017, 5, 8385. (25) Bagheri, H.; Hajian, A.; Rezaei, M.; Shirzadmehr, A. Composite of Cu metal nanoparticles-multiwall carbon nanotubes-reduced graphene oxide as a novel and high performance platform of the electrochemical sensor for simultaneous determination of nitrite and nitrate. J. Hazard. Mater. 2017, 324, 762. (26) Özcan, A.; Đlkbaş, S.; Atılır Özcan, A. Development of a disposable and low-cost electrochemical sensor for dopamine detection based on poly(pyrrole-3-carboxylic acid)-modified electrochemically over-oxidized pencil graphite electrode. Talanta 2017, 165, 489. (27) Xie, S.; Yuan, S.; Liao, P.; Tong, M.; Gan, Y.; Wang, Y. Iron-Anode Enhanced Sand Filter for Arsenic Removal from Tube Well Water. Environ. Sci. Technol. 2017, 51, 889. (28) Liu, X.; Hu, Q.; Fang, Z.; Zhang, X.; Zhang, B. Magnetic Chitosan Nanocomposites: A Useful Recyclable Tool for Heavy Metal Ion Removal. Langmuir 2009, 25, 3. (29) Tan, X.-F.; Yuan, L.-Y.; Nie, C.-M.; Lui, K.; Chai, Z.-F.; Shi, W.-Q. Electrochemical behavior of uranyl in ionic liquid 1-butyl-3-methylimidazolium chloride mixture with water. J. Radioanal. Nucl. Chem. 2014, 302, 281. (30) Dash, A.; Agarwal, R.; Mukerjee, S. K. Electrochemical behaviour of uranium and thorium aqueous solutions at different temperatures. J. Radioanal. Nucl. Chem. 2017, 311, 733. (31) Ladshaw, A. P.; Das, S.; Liao, W. P.; Yiacoumi, S.; Janke, C. J.; Mayes, R. T.; Dai, 22


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S.; Tsouris, C. Experiments and Modeling of Uranium Uptake by Amidoxime-Based Adsorbent in the Presence of Other Ions in Simulated Seawater. Ind. Eng. Chem. Res. 2016, 55, 4241.

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TOC

An electrochemical extraction approach was developed to recover uranium from seawater. The electrochemical extraction demonstrated nearly eight times higher uranium extraction capacities and three times faster extraction rates than the current adsorption method in uranium spiked seawater.

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Highly Efficient Recovery of Uranium from Seawater Using an

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