Preparation of Amidoximated Ultrahigh Molecular Weight

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Preparation of Amidoximated Ultrahigh Molecular Weight Polyethylene Fiber by Radiation Grafting and Uranium Adsorption Test Jiangtao Hu,# Hongjuan Ma,# Zhe Xing,# Xiyan Liu, Lu Xu, Rong Li, Changjian Lin, Mouhua Wang, Jingye Li,* and Guozhong Wu* CAS Center for Excellence on TMSR Energy System, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, No. 2019 Jialuo Road, Jiading District, Shanghai, 201800, China ABSTRACT: An ultrahigh molecular weight polyethylene (UHMWPE) fibrous adsorbent with amidoxime (AO) groups, denoted as AO-UHMWPE, was prepared by preirradiation-induced graft copolymerization of acrylonitrile (AN) and acrylic acid (AA) on UHMWPE fibers, followed by amidoximation. The chemical structure, thermal stability, and mechanical strength were evaluated by means of Fourier transform infrared spectrometry, thermogravimetric analysis, and tensile tests, respectively. The adsorption behaviors of the AO-UHMWPE fiber were studied by batch adsorption in 331 ppb uranium solution, and flow-though adsorption experiments in simulated and natural seawater. It was found that the adsorption conditions (i.e., contact time and manner, temperature, and uranyl ion initial concentration) significantly influence the amount of uranyl ions binding to the AOUHMWPE fibers. The adsorption of uranium in the batch adsorption experiment was 4.54 g-U/kg-ad in the presence of massive amounts of interference ions.

1. INTRODUCTION Extensive research on the recovery of uranium from seawater has been conducted to replace uranium locally deposited as terrestrial ore with uranium uniformly dissolved in seawater.1,2 Presently, there are three major obstacles to using this virtually limitless reservoir as an economic source of uranium. First, the uranium is in a strongly complexed form (UO2(CO3)34−) at extreme dilution in the presence of relatively high concentrations of other ions. Second, it is very difficult to efficiently contact the extraction agent with very large volumes of seawater, which would be involved during the process of extraction. Most importantly, the extractant must work effectively at the seawater pH and ionic strength, and must be virtually insoluble.3 Third, deterioration of the extractant due to fouling in the marine environment must also be considered. There are mainly two sources of fouling: deposition of gelatinous iron oxides onto the adsorbent material surface and marine biofouling (such as shellfish and seaweed).4 Therefore, there are great challenges to make use of uranium from seawater economically. Although a number of other uranium extraction methods have been investigated,5−10 amidoxime (AO)-based adsorbents are recognized by many groups as the most promising material.11−15 Under the memorandum of understanding between the Chinese Academy of Science (CAS) and the U.S. Department of Energy (DOE), the research groups in SINAP16−21 and ORNL22−25 parallel-developed and compared several adsorbents based on AO groups. Nevertheless, real ocean adsorption experiments must still be further promoted. A recovery system for uranium in seawater using AO fibers was developed in Japan to achieve a practical cost for uranium collection. Tamada et al.26 reported a braid-type adsorbent prepared by irradiation graft polymerization, which can stand on the bottom of the sea. The ocean current easily forces © XXXX American Chemical Society

seawater through the braid-type adsorbent. The adsorption performance in marine experiments indicated 1.5 g-U/kg-ad for 30 days of soaking. To date, it is the most successful method of uranium collection from marine environments reported in the literature. Compared to chemical modification methods, radiationinduced graft polymerization is a powerful technique for preparing functional polymers because it can introduce desired functional groups to conventionally available polymers.12 In this study, UHMWPE fiber was selected as a substrate polymer for grafting since free radicals generated in the fibers after irradiation are stable and have a long half-life (26 days in vacuum, 13 days in air),27 which is favorable for preirradiation graft polymerization to obtain a high degree of grafting (DOG). For example, the DOG of γ-ray irradiated UHMWPE fibers with an absorbed dose of 50 kGy reaches 360% after 3 h of graft polymerization. Moreover, the UHMWPE fiber has high tensile strength and corrosion resistance even after radiation graft polymerization.17 In the study by Tamada et al.,26 the polyethylene fiber as a trunk polymer was irradiated with an electron beam at 200 kGy in nitrogen gas, and after 4 h of graft polymerization, the DOG reached 150%. A higher radiation dose not only leads to high-energy consumption but also impairs the mechanical properties of the fibers, which influences the lifetime and recyclability of the adsorbents. Therefore, UHMWPE fiber is at least equal to or better than Special Issue: Uranium in Seawater Received: August 28, 2015 Revised: October 25, 2015 Accepted: October 31, 2015

A

DOI: 10.1021/acs.iecr.5b03175 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research

Scheme 1. Preparation of AO-UHMWPE Adsorbents by Preirradiation-Induced Graft Copolymerization of AA/AN and Subsequent Amidoximation

polyethylene fiber as a trunk polymer used for uranium adsorption. It is the objective of the present paper to summarize the work performed at SINAP-CAS on the development of more suitable adsorbent materials for the recovery of uranium from seawater. This work is based on amidoximed UHMWPE fibers, which meet the criteria of high physical and chemical stability against seawater and show fast and selective uptake of uranium, as well as a sufficient loading capacity.

The hydrophilic comonomer, AA, not only promoted the grafting of AN on the UHMWPE fiber but also improved the adsorption performance of the adsorbent in seawater. The AN-UHMWPE fiber was reacted with hydroxylamine hydrochloride in a MeOH/H2O (v/v = 1:1) solution with pH 7.0 at 70 °C for 2 h. The mole ratio of the cyano group to hydroxylamine was 0.5. Subsequently, the sample was removed from the solution and washed repeatedly with distilled water. The resultant was coded as AO-UHMWPE. 2.3. Characterizations. Attenuated total reflection infrared spectrometry (ATR-IR) was recorded using a Bruker Tensor 207 FT-IR spectrometer attached to an attenuated total reflection (ATR) apparatus; the resolution of the wavenumber was 4 cm−1, and the average result of 32 automatic scans from 600 to 4000 cm−1 was output as the test result. X-ray diffraction (XRD) analysis was performed on a RIGAKU D/Max2200 XRD instrument equipped with Cu− Kα radiation (λ = 1.54 Å). Thermogravimetry analysis (TGA) was performed on a TG 209 F3 Tarsus (NETZSCH, Germany) instrument. The samples were heated from 50 to 800 °C at a heating rate of 10 °C/min under nitrogen atmosphere. The initial decomposition temperature (Tdi) was defined as the temperature at which the weight loss was 5 wt %. Scanning electron microscopy (SEM) analysis was performed on a JEOL JSM-6700F SEM instrument. The pristine UHMWPE fiber and AO-UHMWPE fiber were deposited of gold by sputtering. The SEM voltage was set at 10 and 13 kV. All digital photographs were recorded by Nikon camera D3200 AF-S DX 18-55 mm f/3.5−5.6G VR II. 2.4. Adsorption Tests. 2.4.1. Batch Adsorption Experiment. Batch adsorption experiments were performed using 5 L plastic tanks of simulated seawater. First, 175 g of sea salt was dissolved in 5 L of deionized water to produce a salinity of 35 practical salinity units (psu). The concentrations of uranium and coexisting ions were quantitatively monitored by adding standard solution to the sea salt solution to create an initial concentration 100 times higher than that of natural seawater (Table 1). Then solution pH values were adjusted to 8.1 by the addition of 0.2 g of Na2CO3. Then, 0.2 g of adsorbents was added and freely suspended in the 5 L simulated seawater solution. Batch adsorption experiments were performed at room temperature (∼25 °C) on a rotary shaker at a rate of 100 rpm for 24 h. 2.4.2. Flow-through Adsorption Experiment. Flow-through experiments were carried out using a lab-scale simulated seawater adsorption system with a volumetric flow rate of 1.5 m3/day. The simulated seawater was prepared by adjusting the salinity, metallic ion concentration, and pH value of the deionized water solution. The adsorption process was quantitatively monitored for temperature and flow rate.

2. EXPERIMENTS 2.1. Raw Materials. UHMWPE fiber (TYZ Safetex FT-103, size of 3.6 denier), purchased from Beijing Tongyizhong Advanced Material Company, was used as a substrate material for preirradiation graft polymerization. Acrylonitrile (AN, CP), acrylic acid (AA, AR), dimethylformamide (DMF, AR), methanol (MeOH, AR), Mohr’s salt [(NH4)2Fe(SO4)2·6H2O, AR], hydroxylamine hydrochloride (NH2OH·HCl) and sodium carbonate (AR) were purchased from Sinopharm Chemical Reagent Company and used without further purification. Baysalt was obtained from the salt fields in Qingdao city of Shandong province China, and used without any refining. All standard solutions with 1000 ppm concentration were offered by SPEX CertiPrep Company. Deionized water was used for all experiments unless otherwise stated. 2.2. Preparation of the Amidoxime Adsorbents. UHMWPE fiber adsorbents with the AO groups were prepared by preirradiation-induced copolymerization of acrylonitrile and acrylic acid, with subsequent amidoximation of the PAN grafting chains. The reaction process is outlined in Scheme 1. The UHMWPE fiber was irradiated with 60Co in air at room temperature at a dose rate of 2.2 kGy/h. The absorbed dose was 50 kGy, and all samples were stored at −10 °C after irradiation. The irradiated UHMWPE fiber samples were placed in flasks containing monomer solution and then purged with nitrogen to remove the oxygen. The monomer solution was composed of 64 vol % AN, 16 vol % AA, 20 vol % DMF, and 2.6 × 10−4 mol/L Mohr’s salt. Graft polymerization was performed in a water bath for 3 h at 60 °C. The samples were then washed with DMF and deionized water at room temperature for complete removal of the homopolymer and remaining monomer. The modified UHMWPE fibers were dried in a vacuum oven at 60 °C and coded as AN-UHMWPE. The DOG of the grafted UHMWPE fiber was determined as the weight increase of the sample, according to eq 1: DOG (%) = (W1 − W0)/W0 × 100

(1)

where W1 and W0 are the sample weights after and before grafting, respectively. B

DOI: 10.1021/acs.iecr.5b03175 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research Table 1. Concentrations of Various Elements in a Batch, Flow-through and Marine Adsorption Tests

element

typical seawater (ppb)

total valence ions

simulated seawater concn in batch test system (ppb)

U V Fe Co Ni Cu Zn Pb Mg Ca Na

3.3 1.5−2.5 1.0−2.0 0.05 1.0 0.6 4.0 0.03 1.3 × 106 0.4 × 106 1.08 × 107

UO22+ VO3− Fe3+ Co2+ Ni2+ Cu2+ Zn2+ Pb2+ Mg2+ Ca2+ Na+

331 150 141 5.3 101 65.4 408 34.6 1.2 × 105 0.6 × 105 1.53 × 107

simulated seawater concn in flow-through test system (ppb)

seawater concn of Xiamen Island (ppb)

3.6 1.9 40.6 0.3 1.1 5.4 8.2 31.6 1.2 × 105 0.6 × 105 1.53 × 107

4.4 8.5 173.9 4.9 1.4 2.0

Figure 1. System of flow-through adsorption. (a) the main structure of the adsorption apparatus, (b) adsorption bed, and (c) user interface.

To characterize the adsorption of uranyl ions from simulated seawater, the experiment was conducted using the adsorption systems, and the adsorption result was illustrated in Figure 8 (No.2). Adjustments were made automatically when the temperature fluctuation was more than 2 °C, and the flow rate was more than 10% above or below the target. 2.4.3. Marine Adsorption Experiment. Figure 2 shows the uranium recovery process from natural seawater. The AO-

First, 100 kg of sea salt was dissolved in 450 L of deionized water to produce a highly concentrated sea salt solution. After the salt solution was filtered by 100 and 10 μm polypropylene membranes and successively sterilized by ultraviolet radiation, it was transferred to a 2 m3 storage tank by a fluorine plastic centrifugal pump. Deionized water was then pumped into the tank to adjust the salinity of the simulated seawater, which was controlled by a 3−8850 SIGNET conductivity meter. The salinity of the simulated seawater was 35 when the conductivity value reached 49000 ± 2000 μS·cm−1. After the salinity of the simulated seawater was adjusted accurately, a standard solution of uranyl and other coexisting ions were added into the salt solution. The pH value of the solution was controlled to 8.0 ± 0.3 by adding a specific amount of saturated Na2CO3 solution. The concentrations of elements U and V from UO22+ and VO3− were 3.6, and 1.9, respectively, and Ni2+ was 1.1 ppb, which are equal to their concentrations in natural seawater. The Co2+, Cu2+, and Zn2+ concentrations were slightly higher than the natural seawater values but the same ppb level was maintained. The Fe3+ and Pb2+ concentrations were 10 and 1000 times, respectively, higher than those of natural seawater, due to contamination of the sea salt obtained. All metal ion concentrations are shown in Table 1. The adsorption bed was prepared using a 10 mm internal diameter organic glass column with a filter holder. AOUHMWPE fibers (0.2 g) were freely dispersed and packed in the column where they were held in place by polyethylene terephthalate (PET) fiber, which was used to fill the empty space in the column. Schematic diagrams of the physical layout used for adsorption exposure experiments are presented in Figure 1. For this parallel configuration, a 12-port, all polypropylene-homo (PPH) manifold system was used. The simulated seawater was drawn from a reservoir and forced through the manifold using a pump with all-fluorine plastic components in the pump head and PPH tubing feed lines. Prior to initial use, the adsorbent exposed cartridges and columns, feed lines, and fittings were cleaned with a weakly acidic (5% HCl) solution and deionized water to minimize contamination. Simulated seawater adsorption testing was performed at a temperature of 25 ± 2 °C, which was controlled with a thermostatic water tank before the simulated water flowed through the adsorption column, and at a flow rate of 20 ± 2 mL·min−1 using actively pumping systems.

Figure 2. Recovery of uranium from natural seawater. (a) AOUHMWPE fiber adsorbent, (b) AO-UHMWPE fiber adsorbent floating in the seawater.

UHMWPE fiber was immersed in the East China Sea of Xiamen Island, which is located about 100 m from the Chinese coast. The adsorbent floats in a sea stream ∼3 m below the sea surface by a combination of floating buoys and an anchor. The AO-UHMWPE fibers were immersed in seawater for 60 days. 2.4.4. Sample Handling and Analytical Procedures. After a fixed period, the AO-UHMWPE fiber adsorbent was collected from adsorbent columns, washed with deionized water to remove salts, and dried in a vacuum oven at 60 °C. The dried fibers (100 mg) were then digested with 10 mL of high-purity concentrated nitric acid at a programmed temperature (25 min heating from 25 to 190 °C, hold 25 min, and then natural cooling) by a MARS6Microwave Digestion System (CEM, USA). High-purity deionized water (PALL, Cascada BIO) was then added to produce a 50 mL dilute acid solution and obtain a desired concentration range of uranium for the analysis. Inductively coupled plasma atomic emission spectrometry (ICP-AES, PerkinElmer Optima 8000) was used for quantitative analysis. The average of two replicate measurements per sample was used to quantify uranium and other coexisting ions against a four-point calibration curve. C

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UHMWPE fibers was mainly ascribed to the irradiation damage. Grafting polymerization and amidoximation had no evident influence on the tensile strength.17 The tensile strength of AO-UHMWPE fibers with a DOG of 360% is 88.69 cN, which is slightly higher than that of UHMWPE fiber with an adsorbed dose of 50 kGy. Figure 3 shows the dependence of

The amount of adsorbed ions in AO-UHMWPE fiber was calculated using eq 2: q=

CV w

(2)

where q (mg/g) is the amount of adsorbed ions, C (mg/L) is the ion concentration, V (L) is the digested solution volume, and w (g) is the amount of AO-UHMWPE fibers used. Determination of uranium in simulated seawater samples was conducted using an inductively coupled plasma mass spectrometer (ICP-MS, PerkinElmer NexION 300 D) and the method of standard addition calibrations. Instrumental calibration curves were prepared in simulated seawater that was diluted 20-fold with a 2% nitric acid solution and then spiked at concentrations of 0, 0.1, and 0.5 μg/L, along with a 2% nitric acid blank in diluted seawater. The seawater samples were analyzed at a 20-fold dilution with high-purity deionized water and were then quantified using the matrix matched additions calibration curve. The analysis of trace elements in simulated seawater samples was also conducted using solid-phase extraction at pH 4.5 with Chelex-100 resin (100 meshes, Bio-Rad). Before loading, the resin was immersed in 2 M nitric acid for 12 h to convert the resin from the Na+ to H+ form. The resin (2 g) was packed in a 7 mm diameter column by the wet packing method. Then the column was activated to the H+ form again by rinsing three times with Milli-Q water, twice with 1.5 M ammonium hydroxide, three times with Milli-Q water, three times with 1 M nitric acid, and three times with Milli-Q water. The pH of a 100 mL seawater sample was adjusted to 4.5 with nitric acid. After the pH adjustment, 10 mL of the water sample was immediately loaded at a rate of 1 mL/min, onto a poly prep column with H+ form Chelex 100 resin using a peristaltic pump with Teflon tubing extending from the head of the column to the water sample. After the system was rinsed with 20 mL of Milli-Q water, metals were eluted with 5 mL of 2 M nitric acid, and then the column was rinsed with 5 mL of Milli-Q water. Metals in both eluted solutions were measured by ICP−MS, and the total concentrations of trace metals were evaluated.

Figure 3. Tensile strength of UHMWPE fibers with an absorbed dose of 50 kGy and immersed in simulated seawater for a definite time. S1 was soaked in sulfuric acid for 30 min prior to immersion in simulated seawater.

the tensile strength of the UHMWPE fiber with an absorbed dose of 50 kGy on the immersion time in simulated seawater. After immersion in seawater for 13 months, the tensile strength decreases by about 14%, even when soaked in sulfuric acid for 30 min prior to immersion in seawater. 3.2. Characterization of the AO-UHMWPE Fiber. 3.2.1. Surface Appearance and Chemical Structure. Figure 4 presents the FT-IR spectra of the pristine UHMWPE, AN-

3. RESULTS AND DISCUSSION 3.1. Merits of UHMWPE Fiber as a Trunk Polymer. In our previous paper, the decay rate of the trapped radicals in the UHMWPE fiber irradiated by γ-rays was determined by measuring ESR spectra of the samples with various storage times. The results indicated that the decay rate of alkyl radicals trapped in UHMWPE fiber was very small, that is, the alkyl radicals can survive for a long time at room temperature, even in air. The decay rate was about 1/30 (in vacuum) and 1/100 (in air) of that of HDPE.27 This means that the radical lifetime of UHMWPE fiber can be 100 times longer than that of HDPE irradiated in air, which is favorable for preirradiation graft polymerization to obtain a higher DOG at a lower absorbed dose. The adsorbent material needs to withstand shock waves, solar irradiation, and acid elution; therefore, excellent mechanical properties, higher radiation resistance, and good acid−base stability are other important reasons to choose UHMWPE fiber as a trunk polymer. The tensile strength of the pristine UHMWPE fiber at the breaking point is more than 128.6 cN. However, after γ-irradiation at an absorbed dose of 50 kGy, the tensile strength decreases dramatically to 61.7 cN. In our previous paper, the tensile strength deterioration of

Figure 4. FT-IR spectra of (a) pristine UHMWPE fiber, (b) ANUHMWPE fiber, and (c) AO-UHMWPE fiber.

UHMWPE, and AO-UHMWPE fibers. The adsorption bands of −CH2− antisymmetric stretching (2919 cm−1) and symmetric stretching (2851 cm−1)16 are observed in the spectra of all three samples. In Figure 4b, a sharp peak at 2243 cm−1 is observed because of the adsorption of nitrile groups, which almost disappear in Figure 4c. The appearance of such a peak shows the successful grafting of AN, while the disappearance of this peak indicates the conversion of the nitrile groups to AO groups after reaction with NH2OH. In Figure 4c, the new characteristic adsorption bands at 3200− 3500, 1650, and 920 cm−1 are attributed to the adsorption of −OH, −CN−, and −N−O− of the AO groups, respectively.28 These results suggest that PAN is grafted onto D

DOI: 10.1021/acs.iecr.5b03175 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research the pristine UHMWPE fiber and the grafted nitrile groups are converted to the AO groups, which means the AO-UHMWPE adsorbent was prepared successfully. SEM and digital photographs of pristine UHMWPE fibers and AO-UHMWPE fibers with a DOG value of 332% are shown in Figure 5. The pristine UHMWPE fiber has a smooth

on the orthorhombic crystalline phase but that they cause disorder in the monoclinic crystalline and intermediate phases. 3.2.2. Thermal Properties. Thermal analysis techniques are often used for characterizing the thermal resistance of polymeric materials. Figure 7 shows the TGA and DTG curves of pristine UHMWPE and AO-UHMWPE fibers. The thermogram of the pristine UHMWPE fibers shows a clean, single-step degradation with an initial decomposition temperature of 446 °C, which is in accordance with the reported results.31 For the AO-UHMWPE fibers, four degradation platforms appear with maximum decomposition temperatures of around 150, 261, 385, and 479 °C, which are due to the decarboxylation of AA groups,32 degradation and carbonization of the PAO molecular chains, and the degradation of the UHMWPE molecular chains, respectively. 3.3. Uranyl Ion Adsorption Performance. To assess and characterize the adsorption performance of AO-UHMWPE adsorbents, seawater adsorption tests were performed in batch adsorption, flow-through adsorption, and marine adsorption modes. The loading of uranium in the AO-UHMWPE fibers from different concentrations of simulated seawater and natural seawater are given in Figure 8. No.1 and No.2 were conducted by batch and flow-through adsorption experiments, respectively. The adsorption conditions are described in sections 2.4.1 and 2.4.2. Natural seawater was used in No.3 and No.4 but the adsorption conditions were different. No.3 was conducted at the Marine Sciences Laboratory (MSL) of the Pacific Northwest National Laboratory (PNNL) in Sequim, WA. During the period, the average salinity, seawater flow rate, seawater temperature, and absorption cycle were 31.4, 250− 300 mL/min, 20 °C, and 42 days, respectively. No.4 was immersed in the East China Sea of Xiamen Island, and the adsorption conditions are described in section 2.4.3. All AOUHMWPE fibers used during the adsorption process had the same DOG of 360%. The amounts of uranium adsorbed by No.1, No.2, No.3, and No.4 AO-UHMWPE fibers are 4.54, 2.97, 0.48, and 0.25 mg-U/g-ad, respectively. No.1 has the highest adsorption capacity and adsorption rate, which is due to the high ion concentrations. The simulated seawater used in No.2 and natural seawater in No.3 and No. 4 have similar uranyl ion concentrations, but No.2 has a higher adsorption capacity than No.3 and No. 4. The reasons behind this phenomenon require more experiments to verify the above results; the investigation of the detailed mechanism is now underway. No.4, which was placed in the marine environment of the East China Sea of Xiamen Island, has the lowest uranium adsorption amount, even lower than that of No.3. No.3 was filtered (0.45 μm) and was relatively clean. In the marine test in the East China Sea of Xiamen Island, the fibers were freely placed in the seawater. In addition to the impact of competitive ions, biofouling is another important factor influencing the amount of uranyl ions binding to the AO-UHMWPE adsorbent. From Figure 9, it can be seen that sediment and marine life (i.e., seaweed and shellfish) adhere to the surface of the AO-UHMWPE fibers, which highly affects the diffusion of uranyl ions to the adsorbents.

Figure 5. SEM and digital photographs of pristine UHMWPE fibers (a, a′), AO-UHMWPE fibers with a DOG of 332% (b, b′). (a, b) SEM images with a magnification of 1000; (a′, b′) in water.

surface with microgrooves along the axial orientation of the fiber. For the AO-UHMWPE fiber, the microgrooves are covered by the grafted layer, and the surface becomes rough. When immersed in water, the pristine UHMWPE fibers float and show very strong hydrophobicity. However, the AOUHMWPE fibers loosely soaked in water are strongly hydrophilic. Good hydrophilicity is very important for improving the adsorption rate of uranium in seawater. XRD patterns of the pristine UHMWPE, AN-UHMWPE, and AO-UHMWPE fibers are shown in Figure 6. Two distinct

Figure 6. Normalized XRD spectra of the UHMWPE, AN-UHMWPE, and AO-UHMWPE fibers with a DOG of 360%.

diffraction peaks (21.6° and 24.1°), due to diffraction planes (110) and (200) of the orthorhombic crystal of polyethylene,29 are observed for the UHMWPE fiber and modified UHMWPE fibers. These two peaks show no change after graft polymerization and amidoximation. Minor diffraction peaks at 19.7, corresponding to the diffraction planes (010) of the monoclinic crystal,30 disappear in the patterns of the modified UHMWPE fibers. This indicates that the grafting chains have no influence

4. CONCLUSIONS AO-UHMWPE fibrous adsorbents for the extraction of uranium from seawater were prepared by radiation-induced graft copolymerization of AN and AA on UHMWPE fiber and subsequent amidoximation. The DOG can be higher than E

DOI: 10.1021/acs.iecr.5b03175 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Figure 7. TGA and DTG curves of the pristine UHMWPE and AO-UHMWPE fibers with a DOG of 360%. Ordinates of AO-UHMWPE in DTG curves were enlarged 10-fold.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We greatly appreciate support from the “Strategic Priority Research Program” of the Chinese Academy of Sciences (Grant XDA02030200), the National Natural Science Foundation of China (11305243, 11305241, 11275252, 11405249, 21306220) and the “Knowledge Innovation Program” of Chinese Academy of Sciences (Grant KJCX2-YW-N49).

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Figure 8. The amount of uranyl ions binding to AO-UHMWPE fibers under different adsorption conditions. No.1, batch adsorption of simulated seawater; No.2, flow-through adsorption of simulated seawater; No.3, natural seawater adsorption in MSL-PNNL; No.4, natural seawater adsorption in Xiamen Island.

(1) Manos, M. J.; Kanatzidis, M. G. Layered Metal Sulfides Capture Uranium from Seawater. J. Am. Chem. Soc. 2012, 134, 16441−16446. (2) Wang, C. Z.; Lan, J. H.; Wu, Q. Y.; Luo, Q.; Zhao, Y. L.; Wang, X. K.; Chai, Z. F.; Shi, W. Q. Theoretical Insights on the Interaction of Uranium with Amidoxime and Carboxyl Groups. Inorg. Chem. 2014, 53, 9466−9476. (3) Rao, L. Recent International R&D Activities in the Extraction of Uranium from Seawater; LBNL Paper LBNL-4034E; Lawrence Berkeley National Laboratory; 2011. (4) Sekiguchi, K.; Saito, K.; Konishi, S.; Furusaki, S.; Sugo, T.; Nobukawa, H. Effect of seawater temperature on uranium recovery from seawater using amidoxime adsorbents. Ind. Eng. Chem. Res. 1994, 33, 662−666. (5) Schenk, H. J.; Astheimer, L.; Witte, E. G.; Schwochau, K. Development of Sorbers for the Recovery of Uranium from Seawater. 1. Assessment of Key Parameters and Screening Studies of Sorber Materials. Sep. Sci. Technol. 1982, 17, 1293−1308. (6) Kim, Y. K.; Lee, S.; Ryu, J.; Park, H. Solar conversion of seawater uranium (VI) using TiO2 electrodes. Appl. Catal., B 2015, 163, 584− 590. (7) Leggett, C. J.; Rao, L. Complexation of calcium and magnesium with glutarimidedioxime: Implications for the extraction of uranium from seawater. Polyhedron 2015, 95, 54−59. (8) Tan, L.; Liu, Q.; Jing, X.; Liu, J.; Song, D.; Hu, S.; Liu, L.; Wang, J. Removal of uranium(VI) ions from aqueous solution by magnetic cobalt ferrite/multiwalled carbon nanotubes composites. Chem. Eng. J. 2015, 273, 307−315. (9) Tan, L.; Wang, J.; Liu, Q.; Sun, Y.; Zhang, H.; Wang, Y.; Jing, X.; Liu, J.; Song, D. Facile preparation of oxine functionalized magnetic Fe3O4 particles for enhanced uranium (VI) adsorption. Colloids Surf., A 2015, 466, 85−91. (10) Yamazaki, Y.; Tachibana, Y.; Kaneshiki, T.; Nomura, M.; Suzuki, T. Adsorption behavior of uranium ion using novel phenol-type resins in contaminated water containing seawater. Prog. Nucl. Energy 2015, 82, 74−79.

Figure 9. AO-UHMWPE adsorbent (a) after uranyl ion adsorption and (b) contaminated by marine organisms.

300%. UHMWPE fibers can form stable radicals and have a long lifetime, which contributes to the preirradiation graft polymerization to obtain a higher DOG at a lower absorbed dose. The tensile strength of the AO-UHMWPE adsorbents is primarily influenced by the absorbed dose. The amount of uranyl ions binding to the AO-UHMWPE fibers is highly affected by changes in the adsorption conditions.

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Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Author Contributions #

J.H., H.M., and Z.X. contributed equally to this work. F

DOI: 10.1021/acs.iecr.5b03175 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.iecr.5b03175 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX