Uranium Adsorption Tests of Amidoxime-Based Ultrahigh Molecular

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Uranium Adsorption Tests of AO-UHMWPE fibers in Simulated Seawater and Natural Coastal Marine Seawater from Different Locations Changjian LING, Xiyan LIU, Xiaojuan Yang, Jiangtao Hu, Rong Li, Li-Juan Pang, Hongjuan Ma, Jingye Li, Guozhong Wu, Shuimiao Lu, and Deli Wang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b04181 • Publication Date (Web): 05 Jan 2017 Downloaded from http://pubs.acs.org on January 11, 2017

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Industrial & Engineering Chemistry Research

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Uranium Adsorption Tests of AO-UHMWPE fibers in Simulated Seawater and Natural Coastal Marine Seawater from Different Locations

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Changjian Ling,†XiyanLiu,†Xiaojuan Yang,†Jiangtao Hu,†Rong Li,†Lijuan Pang,†,‡Hongjuan

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Ma,*,†Jingye Li,*,†Guozhong Wu,*,†Shuimiao Lu,†‡ and Deli Wang†‡

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6 7

†

8

‡

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†‡

Shanghai Institute of Applied Physics, Chinese Academy of Sciences, No. 2019 Jialuo Road, Jiading District, Shanghai201800, P. R. China University of Chinese Academy of Sciences, Beijing 100049, P. R. China State key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361005, P.

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R. China

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ABSTRACT: Uranium recovery from seawater was investigated in simulated seawater in

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laboratory and natural seawater at the coasts of China with different amidoxime-based (AO)

13

ultrahigh-molecular-weight polyethylene (UHMWPE) fibers. The capacities of adsorbents AO-

14

UHMWPE-1 and -2 were 4.54 and 2.41 mg U/g-adsorbent, respectively, after 24 h adsorption in

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the simulated seawater with 330 ppb U. Their capacities were 2.93 and 1.95 mg U/g-adsorbent,

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respectively, after 42 days of adsorption in simulated seawater flow-through experiment with 3.3

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ppb U. While, because of sediment and marine organisms contamination, the capacities were 0.25

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and 0.04 mg U/g-adsorbent, respectively, after 68 days of adsorption in natural seawater in

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Xiamen. Capacity of AO-UHMWPE-7 was 1.41 mg U/g-adsorbent after 15 days adsorption in

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natural seawater in Daishan. The average capacity of AO-UHMWPE-7 was 1.50 mg U/g-

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adsorbent which was18 times higher than that for V after 15 days adsorption in natural seawater

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in Daishan. Results indicated that there were many factors affect adsorption capacity of uranium.

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Besides the character of adsorbent including degree of grafting, functional group density and AO

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conversion ratio, the marine hydrological conditions such as temperature, flow velocity, turbidity

25

et al. are also crucially important for uranium extraction from seawater.

26

1. INTRODUCTION

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As the rapid development of nuclear power proceeds, the demand for uranium fuel will

28

increase. The total amount of uranium in seawater is estimated at 4.5 billion tons, approximately

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1000 times that in terrestrial mines.1 Uranium extraction from seawater can provide a sustainable

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supplying fuel for nuclear power plants.2 However, the ultralow uranium concentration of 3.3

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ppb uranium in seawater make the recovery a great challenge.3

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Many approaches have been investigated in the past decades to exploit uranium from seawater,

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including flotation, ion exchange, and solvent extraction.4-8 Adsorption has received considerable

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attention since the 1960s as a highly efficient, and the most promising approach for extracting

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uranium from seawater owing to its potential advantages such as moderate operating, cost

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efficiency, and low-emission.1,

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adsorption performance in laboratory with artificial seawater. Carboni et al.14-18 investigated the

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uranium adsorption behavior of a series of functionalized mesoporous carbon materials in both

39

acidic water (pH 4) and artificial seawater (pH 8.2), and reported a maximum sorption capacity

40

of 97 mg U/g-adsorbent in acidic water and 67 mg U/g-adsorbent in artificial seawater. Liu et

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al.15 studied the adsorption behavior of the uranyl ion at low initial concentrations of 3–50 ppb

42

on polyethylene(PE)-g-polyamidoxime (PAO) nonwoven fabric in simulated seawater (pH7.5),

43

and found that the adsorption capacity increased with the increase in initial uranyl ion

44

concentration. Zeng et al.16 studied the adsorption performance of an amidoxime-based

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cationically charged fibrous adsorbent in synthetic seawater at pH 8.0 and 298.15 K. The results

46

indicated that the sorption could reach equilibrium with a capacity of 119.76 mg U/g-adsorbent,

9-13

Previous studies have been mainly devoted to improve


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which demonstrated that the cationically charged fabric was a potential promising adsorbent for

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uranium extraction from seawater.

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Nevertheless, adsorption performances of adsorbents in laboratory studies with simulated

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seawater are not necessarily consistent with studies in natural seawater. Capacities of adsorbents

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in simulated seawater could reach hundreds mg U/g-adsorbent as initial concentration of uranium

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was much higher than 3.3 ppb.19-23 In the early days, the Japan Atomic Energy Research Institute

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(JAERI) had carried out two types of marine experiments with amidoxime-based fibers prepared

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by radiation-induced grafting polymerization: (1) uranium collection system using amidoxime

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adsorbent stacks; (2) uranium collection system using amidoxime braid adsorbent. The stack

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adsorption system involved a floating frame stabilized with ropes and adsorption beds for

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assembling adsorbent sheets, and uranium collection experiments with adsorbent stacks were

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performed in the Aomori prefecture of Japan from 1999 to 2001. After a total submersion time of

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240 days in the ocean, approximately one kilogram of uranium in the form of yellow cake was

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collected by the stack system. Despite some achievements, researchers found that serious

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biofouling and the high collecting cost were major problems with the stack adsorption form. 24, 25

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Thus, the braid collection system was developed and adsorption test were carried out in the

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Okinawa area of Japan. The adsorption ability of the braid system was approximately two times

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higher than that of the stack form.26,27 Recently several countries have conducted marine tests

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with natural seawater. The Marine Sciences Laboratory (MSL) of the Pacific Northwest National

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Laboratory (PNNL) has been estimating the uranium adsorption performance of adsorbents with

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natural seawater from Sequim Bay. WA. Kim et al. conducted column experiments at the MSL

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using an amidoxime-based polymeric adsorbent developed at the Oak Ridge National Laboratory,

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and the maximum uranium uptake from seawater was 3.3 mg U/g-adsorbent after eight weeks


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contact with filtered seawater.24 Alexandratos et al. studied the adsorption by different fibers in

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natural seawater at PNNL for 20.8 days, and the results showed that the adsorption capacities of

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the fibers were much lower than that in simulated seawater.28 However, investigations on the

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adsorption performances of adsorbents in natural seawater are still rare.

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In this work, uranium recovery was investigated not only in simulated seawater in the lab but

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also in natural seawater at coastal marine of China. Different amidoxime-based (AO) ultrahigh-

76

molecular-weight polyethylene (UHMWPE) fibers were used to investigate the adsorption

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behavior of the uranyl ion. The adsorption performances of adsorbents in laboratory studies with

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simulated seawater and with natural coastal marine seawater were compared. The adsorption

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capacities for uranyl and other competing ions (V, Fe, Co, Ni, Cu, Zn, Pb, Mg, and Ca) were

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studied in different adsorption systems. In addition, the adsorption selectivity for uranyl ions (U)

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over vanadyl ions (V) of the materials was studied.

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2. MATERIALS AND METHODS

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2.1. Materials and Preparation of AO-UHMWPE Fibers.

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The UHMWPE fiber of 3.6 denier TYZ Safetex FT-103 provided by Beijing Tongyizhong

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Specialty Fiber Technology & Development Co., Ltd. was used as a substrate material for pre-

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irradiation-induced graft polymerization. Chemical pure grade of acrylonitrile (AN), analytical

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purity of acrylic acid (AA) and other chemical reagents were purchased from Sinopharm

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Chemical Reagent Co., Ltd. Baysalt was obtained from the salt fields in Qingdao in the

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Shandong province of China. The 1000 ppm standard solutions of uranium and other competing

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ions were purchased from SPEX Certi Prep, Inc.

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The AO functional UHMWPE fiber adsorbents (AO-UHMWPE) were prepared by pre-

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irradiation-induced copolymerization. UHMWPE fiber was pre-irradiated in air by γ-ray at room


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temperature. Then, the fibers were put into flasks filling with solution of AN, AA and DMF, and

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2.6×10−4 mol/L Mohr’s salt. The graft reaction was performed in a water bath after bubbling with

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nitrogen gas for 20 min to remove oxygen in the solution. Subsequently, the grafted fibers were

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washed with DMF to remove homopolymer and residual monomers, and were dried by a vacuum

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oven at 60 oC. The grafting conditions of different AO-UHMWPE fibers are listed in Table 1.

98

Degree of grafting (Dg) was defined as follows:

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Dg (%) =

(𝑚𝑖−𝑚0)∗100

(1)

𝑚0

100

where, m0 is the initial weight of substrate UHMWPE fiber and mi is the weight of fabricated

101

UHMWPE-g-P(AN-co-AA) fiber after graft polymerization.

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Then, 5wt% NH2OH solution was prepared using a bicomponent solvent composed of de-

103

ionized water (50vol%) and DMSO (50vol%). pH of the solution was approximately adjusted with

104

anhydrous Na2CO3. The fabricated UHMWPE-g-P(AN-co-AA) fibers were put into the NH2OH

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solution at 70 oC for converting the -CN groups into AO groups. After amidoximation, the

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UHMWPE-g-P(AO-co-AA) fibers were washed with deionized water to remove the unreacted

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NH2OH and were dried in vacuum oven at 60 °C. The amidoximation conditions of different

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AO-UHMWPE fibers are listed in Table 1.The reaction mechanism and the details of the

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preparation process were given in a previous paper.25, 29

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AO density of UHMWPE-g-P(AO-co-AA) fiber was calculated using the following equation:

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AO Density (mmol/g) =

(𝑊𝑖−𝑊0)∗1000 33𝑊𝑖

(2)

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where, W0 and Wi are the weights of fiber before and after amidoximation, 33 is the molecular

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weight of AO group (-CNH2N-OH) subtract the molecular weight of nitrile group (-CN).

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Table 1. Preparation Conditions of AO-UHMWPE Fibers Reaction Condition

AO-UHMWPE Fiber


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-1

-2

-3

-4

-5

-6

-7

Absorbed Dose (kGy)

100

100

50

50

50

50

50

AN (vol%)

48

48

48

32

64

48

48

AA (vol%)

12

12

32

48

16

12

12

DMF (vol%)

40

40

20

20

20

40

40

Grafting Tempreture (oC)

70

70

65

65

65

70

70

Grafting Time (h)

5

6

6

6

6

3

4

Dg (%)

360

450

69

127

87

131

200

Amidoximation Tempreture (oC)

70

70

70

70

70

70

70

Amidoximation Time (h)

2

2

4

4

6

3

5

Amidoximation pH

6.7

6.7

6.7

6.7

6.7

6.7

7.0

AO Density (mmol/g)

5.9

7.4

3.8

4.3

5.1

3.3

7.0

115 116

2.2. Adsorption Methods

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2.2.1. Laboratory Adsorption Experiment

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Batch adsorption experiments and flow-through adsorption experiments were carried out in the

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laboratory with simulated seawater. Batch adsorption experiments were performed in 5 L plastic

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tanks of simulated seawater, which was obtained by dissolving a certain weight of sea salt in

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deionized water to produce a salinity of 35 practical salinity units (psu). Then the standard

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solutions of uranium and competing ions were added to produce an initial concentration of 100

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times higher than that in natural seawater (Table 2). The pH value was adjusted to 8.1 by adding

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a certain amount of Na2CO3. Approximately 0.2 g of dried adsorbents was placed and freely

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suspended in the each plastic tank. Batch adsorption experiments were performed at room

126

temperature (∼25 °C) for 24 h on a rotary shaker with a shaking rate of 100 rpm.


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Flow-through adsorption experiments were conducted in a lab-scale simulated seawater

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adsorption system with a maximum volumetric flow rate of 1.5 m3/day. The simulated seawater

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was prepared as described in a previous paper.25 The concentrations of various elements are

130

listed in Table 2. It was found that the concentrations of Fe, Co, Cu, Zn, and Pb were higher than

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those in natural seawater owing to contamination of the sea salt obtained. Sample adsorption was

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conducted in the system for 1, 4, 7, 10, 15, 20, 27, 34, and 42 days at 25 ±2°C with a flow rate of

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20 ±2 mL/min.

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Table 2. Concentrations of Various Elements in the Batch, Flow-Through, and Marine Adsorption Experiments Element

Typical seawater conc. (ppb)

Conc. in simulated seawater in batch test system (ppb)

Conc. in simulated seawater in flow-through test system (ppb)

Conc. in seawater at Xiamen (ppb)

Conc. in seawater at Daishan (ppb)

Conc. in seawater at Raoping (ppb)

U

3.3

331

3.6

4.0

2.6

3.1

V

1.5–2.5

150

1.9

0.5

2.9

2.0

Fe

1.0–2.0

141

40.6

14.5

\

48.1

Co

0.05

5.3

0.3

0.02

\

0.06

Ni

1

101

1.1

0.3

\

0.5

Cu

0.6

65.4

5.4

0.1

\

1.2

Zn

4

408

8.2

0.9

\

21.6

Pb

0.03

3.5

31.6

0.07

\

0.7

Mg

1.3×106

1.2×105

1.2×105

0.6×105

\

\

Ca

0.4×106

0.6×105

0.6×105

0.2×105

\

\

136 137

2.2.2. Marine Adsorption Experiment


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Three coastal marine of China, Xiamen, Daishan and Raoping, were selected to evaluate the

139

performance of the adsorbents in this study (Figure 1).

140

Figure 1. Sites of the three adsorption experiments conducted in coastal marine of China (from

141

Google Maps).

142

The Xiamen adsorption platform was located along the Taiwan Strait (118.09°E, 24.43°N), a

143

buoy platform of the State Key Laboratory of Marine Environmental Science (Figure 2a). The

144

platform was about 500 m from the coast. Adsorbents were strapped and immersed in seawater,

145

about 3 m below the water surface (Figure 3a). The salinity of the seawater was 31 psu and the

146

flow velocity was 0.2–0.6 m/s. The pH value of the seawater was 7.5–7.9. The adsorption test in

147

this study was carried out at an average seawater temperature of 21.4 °C. All metal ion

148

concentrations in the seawater sample are listed in Table 2.

149

The Daishan adsorption platform was located in the East China Sea (122.17°E, 30.25°N) in

150

Daishan Lvyuan Desalination Co., Ltd. (Figure 2b). Adsorbents were strapped and immersed in

151

the reservoir about 1 m below the water surface for 15 days (Figure 3b). The salinity of the

152

seawater was 27 psu and the flow velocity was 0.5 m/s. The adsorption test in this study was

153

carried out at an average seawater temperature of 25.5 °C. The concentrations of uranium and

154

vanadium in the seawater sample are listed in Table 2.

155

The Raoping adsorption platform was located in South China Sea (117.08°E, 23.58°N) in

156

Guangdong Zhongkebao Biotechnology Co., Ltd. (Figure 2c). Seawater was pumped to the

157

underground impounding reservoir. The salinity of the seawater was 35 psu. The adsorption test

158

in this study was carried out at an average seawater temperature of 17.1 °C. Adsorbents were

159

strapped and immersed in the reservoir. The seawater in the reservoir was almost static with a

160

very low flow velocity of lower than 0.01 m/s. The concentrations of elements in the seawater


8

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are shown in Table 2. The analysis of trace elements in simulated seawater samples and natural

162

seawater was reported in a previous paper 25.

163

Figure 2. Photos of the three coastal marine adsorption platforms: (a) Xiamen adsorption

164

platform, (b) Daishan adsorption platform, and (c) Raoping adsorption platform.

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Figure 3. Placement of adsorbents in the seawater atthe different marine locations: (a)Xiamen

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adsorption platform, (b) Daishan adsorption platform, and (c) Raoping adsorption platform.

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2.3. Sample Analysis

168

Adsorbents were washed with deionized water to remove contaminants and dried in a vacuum

169

oven at 60 °C for 12 h. Analyses of uranium and other competing elements were performed

170

using a digestion method. Additional details of the analysis process for the trace elements were

171

reported in a previous paper.25

172 173

The amount of uranium and other competing ions adsorbed in adsorbents was calculated using the following equation:

174

Q=

𝐶𝑉

(3)

𝑊

175

where, Q (mg/g) is the amount of uranyl and other competing ions adsorbed in adsorbents, C

176

(mg/L) is ion concentration in digestion solution , V (L) is the volume of digestion solution, and

177

W (g) is the weight of the dried AO-UHMWPE fiber used in the digestion process.

178 179 180

The adsorption rate of uranium in the flow-through adsorption test was calculated using the following equation: R (%) =

𝑄𝑚 𝐶𝑉

(4)


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181

where, C (mg/L) is the uranium concentration in flow-through simulated seawater, V (L) is the

182

flow-through simulated seawater volume, Q (mg/g) is the amount of U adsorbed onto the AO-

183

UHMWPE fibers, and m(g) is the weight of the dried AO-UHMWPE fiber packed in the column.

184 185

3. RESULTS AND DISCUSSION

186

3.1. Adsorption Capacity and Adsorption Kinetics from Laboratory Studies

187

3.1.1. Batch Adsorption Experiment

188

The fiber samples (AO-UHMWPE-1–5) were tested in simulated seawater in the batch test

189

system. The adsorption capacities for uranium and other competing ions, which were calculated

190

using eq 3 are shown in Table 3.

191

Table 3. Adsorption Capacities for Uranium and Other Elements in Batch Test System Sample

Adsorption capacity (mg/g-adsorbent) U

V

Fe

Co

Ni

Cu

Zn

Pb

Mg

Ca

AO-UHMWPE-1

4.54

2.14

0.54

0.10

1.71

0.78

28.4

0.39

6.51

4.50

AO-UHMWPE-2

2.41

1.44

0.57

0.08

1.52

0.59

27.19

0.33

8.04

6.37

AO-UHMWPE-3

8.14

3.67

3.03

0.15

2.58

1.37

10.05

0.99

11.62

11.50

AO-UHMWPE-4

7.10

3.22

2.40

0.10

1.53

0.96

6.92

0.82

12.38

11.38

AO-UHMWPE-5

3.69

1.97

3.33

0.07

0.94

0.73

3.76

0.48

13.59

14.98

192 193

As it was shown in Table 3 that the uranium adsorption capacities of all five fiber samples

194

could reach relatively high values from 2.41 to 8.14 mg/g-adsorbent in 24 h. Because

195

concentrations of U and other seven metal ions (V, Fe, Co, Ni, Cu, Zn and Pb) in the simulated

196

seawater were 100 times higher than that in natural seawater. The capacities for uranium were


10

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197

lower than zinc, magnesium, and cadmium ions in this simulated seawater. A possible reason

198

was that the concentrations of zinc, magnesium, and cadmium ions were higher than that of

199

uranyl ions in simulated seawater, while the concentrations of other competing ions (V, Fe, Co,

200

Ni, Cu, and Pb) were lower. Vanadium was considered the most important competing ion during

201

the extraction of uranium, as the elution of vanadium required a very high concentration of acid,

202

which would damage the adsorbents. Results from the five adsorbents in Table 3 showed that the

203

capacities for uranium were all higher than those for vanadium. The adsorbents in order of

204

descending Quranium were AO-UHMWPE-3 > AO-UHMWPE-4 > AO-UHMWPE-1 > AO-

205

UHMWPE-5 > AO-UHMWPE-2, and this was in good agreement with the order for Qvanadium.

206

3.1.2. Flow-Through Adsorption Experiment

207

Flow-through adsorption test of AO-UHMWPE-1 and AO-UHMWPE-2 were conducted in

208

simulated seawater for different exposure times. The adsorption capacities for uranium and other

209

competing ions obtained using flow-through column testing after 42 days of adsorption are listed

210

in Table 4. Results for the two samples at other exposure times are shown in Table S1 and Table

211

S2, respectively. The adsorption capacities of uranium and adsorption kinetics are given in

212

Figure 4.

213

Table 4. Adsorption Capacities in Flow-Through Test System after 42 Days of Adsorption Sample

Adsorption capacity (mg/g-adsorbent) U

V

Fe

Co

Ni

Cu

Zn

Pb

Mg

Ca

AO-UHMWPE-1

2.93

1.32

0.77

0.02

0.22

0.81

0.52

31.1

6.14

7.32

AO-UHMWPE-2

1.95

0.84

0.56

0.01

0.2

0.55

0.65

34.7

5.63

6.52

214


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215

Figure 4. Time-series measurements of the (a) adsorption capacities and (b) adsorption rates of

216

AO-UHMWPE-1 and AO-UHMWPE-2.

217

It was shown that the adsorption capacities of AO-UHMWPE-1 and AO-UHMWPE-2

218

increased almost linearly with the extension of adsorption time, and maximal adsorption

219

capacities of 2.93 and 1.95 mg/g-adsorbent, respectively, were obtained within 42 days. The

220

results showed that the adsorption capacities did not reach adsorption saturation. The adsorption

221

capacities for lead, magnesium, and cadmium ions were higher than that for uranium ions in

222

simulated seawater, while the capacities for other ions were lower. Moreover, the adsorption

223

capacity for lead was not expected to be so much higher than those for other ions, because the

224

concentration of lead in the flow-through system was far higher than typical seawater

225

concentrations (Table 2). Results from Figure 4 show that the capacity for uranium of AO-

226

UHMWPE-1 was higher than that of AO-UHMWPE-2, which was in good agreement with the

227

results in Table 3 from the batch adsorption experiment.

228

Flow-through adsorption experiments were conducted in a sustaining uranium solution with a

229

concentration of 3.3 ppb. The adsorption rates were calculated from eq. 4 and the results are

230

shown in Figure 4. For AO-UHMWPE-1, the adsorption rate was 35.0% at the beginning of

231

adsorption and decreased sharply to 26.6% after four days. The adsorption rate was only 15.6%

232

after 42 days. AO-UHMWPE-2 was less efficient than AO-UHMWPE-1. The adsorption rate

233

was 26.5% at the beginning of adsorption and decreased sharply to 19.7% after four days. The

234

adsorption rate was only 10.7% after 42 days.

235

3.2. Adsorbent Testing at Different Coastal Marine

236

Marine testing was conducted at three coastal: Xiamen, Daishan, and Raoping adsorption

237

platforms. These efforts were undertaken to compare the adsorption performances of adsorbents


12

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238

in laboratory studies with simulated seawater and with natural seawater, and to examine the

239

differences among the three coastal marine locations. The adsorption capacities for uranium and

240

other competing ions at the three marine locations are shown in Table 5.

241 242

Table 5. Adsorption Capacities of Different AO-UHMWPE Adsorbents at Three Marine Locations Sample Marine Time Adsorption capacity (mg/g-adsorbent) location (days) U V Fe Co Ni Cu Zn Pb Mg Ca -1

Xiamen

68

0.25

0.88 3.31

0.07 0.64

0.14

0.25 0.04 14.67 11.43

-2

Xiamen

68

0.04

0.39 1.69

0.04 0.34

0.19

0.21 0.04 14.32 13.45

-3

Xiamen

110

0.50

2.45 8.14

0.23 0.36

0.27

0.54 0.09 18.76 24.50

-4

Xiamen

110

0.77

3.26 9.16

0.24 0.08

0.34

0.17 0.06 27.59 23.33

-5

Xiamen

73

0.33

2.02 7.05

0.06 0.01

0.22

0.06 0.01 20.23 33.27

-6

Daishan

15

0.05

0.04 2.04

0.01 0.22

0.35

0.73 0.02 8.34

11.94

-7

Daishan

15

1.41

0.05 11.35 0.09 0.95

0.73

0.61 0.03 2.95

18.62

-5

Raoping 101

0.44

0.51 1.95

0.00 0.00

0.06

0.14 0.00 37.67 28.74

-7

Raoping 72

0.18

0.30 1.34

0.00 0.06

0.07

0.19 0.00 31.27 24.09

243 244

Table 5 shows that the uranium adsorption capacities of the five fiber samples (AO-

245

UHMWPE-1–5) were 0.04–0.77 mg U/g-adsorbent, which were considerably lower than those

246

from the laboratory studies with simulated seawater as shown in Tables 3 and 4. The most

247

important reason for this adsorption difference might be that simulated seawater contains no

248

sediment and marine life. All marine adsorption tests in this study were carried out in the open

249

sea. Adsorbents were seriously contaminated by sediment and microorganisms once immersed in

250

seawater. The results of biofouling are shown in section 3.4. The adsorption performances for the

251

competing ions in the marine adsorption experiments and the laboratory adsorption experiments

252

were also significantly different. The adsorption capacities for zinc and lead from marine testing


13


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Page 14 of 31

253

with natural seawater were much lower than those in simulated seawater, especially in the batch

254

test system for zinc ions and in the flow-through test system for lead ions. The adsorption

255

capacities for magnesium and cadmium in natural seawater were higher than those in laboratory

256

simulated seawater. The adsorption capacities for iron were unexpectedly higher than those

257

obtained from the other two testing systems, likely because of offshore iron contamination. The

258

adsorption capacities for vanadium, copper, cobalt, and nickel ions from marine testing with

259

natural seawater were similar to those from laboratory studies with simulated seawater.

260

The adsorbents in descending order of Quranium were AO-UHMWPE-4 > AO-UHMWPE-3 >

261

AO-UHMWPE-5 > AO-UHMWPE-1 > AO-UHMWPE-2. This was in good agreement with the

262

orders for Qvanadium and Qiron. Although the order was different from that in the batch adsorption

263

experiment, AO-UHMWPE-3 and AO-UHMWPE-4 showed the highest capacities and AO-

264

UHMWPE-2 showed the lowest in both the batch adsorption experiment and natural seawater

265

adsorption experiment. The results indicated that laboratory simulated seawater adsorption

266

testing was only suitable for primary screening of large numbers of adsorbents. The capacities

267

obtained using laboratory simulated seawater were not the true capacities of the adsorbents, and

268

the real natural seawater adsorption experiment must be carried out to estimate the adsorption

269

performances of adsorbents.

270

AO-UHMWPE-5 was tested in Xiamen for 73 days and in Raoping for 101 days. The

271

capacities for uranium were 0.33 and 0.44 mg U/g-adsorbent, respectively. However, the

272

capacities for vanadium were 2.02 and 0.51 mg V/g-adsorbent, respectively. Capacity of

273

vanadium was higher than that of uranium. Difference from Xiaman and Raoping was

274

considerable and was in conflict with the contact time. The average seawater temperature during

275

our adsorption test in Xiaman was 21.4 °C, which was higher than that of Raoping (17.1°C).


14

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276

Flow velocity of seawater in Xiaman was 0.2-0.6 m/s more than 10 times higher than that in

277

Raoping. These suggest temperature and flow velocity had great effect on the adsorption of

278

vanadium rather than uranium for AO-UHMWPE-5.

279

AO-UHMWPE-7 was tested in Daishan for 15 days and in Raoping for 72 days. The capacities

280

for uranium were 1.41 and 0.18 mg U/g-adsorbent, respectively. And the capacities for vanadium

281

were 0.05 and 0.30mg V/g-adsorbent, respectively. It was noteworthy that the adsorption

282

capacity of 1.41 mg U/g-adsorbent of the AO-UHMWPE-7 fiber was the highest in this study.

283

There is no essential difference between these adsorbents as all our adsorbents were prepared by

284

radiation induced graft polymerization and followed by amidoximation. However, there are

285

many factors affect the adsorption capacity such as Dg, function group density and AN

286

conversion ratio et al. From our precious study we found Dg was an important factor as generally

287

high Dg would result in high function group density. However, too much Dg (Dg >200%) is not

288

always good for adsorption. From our previous study we learned that amidoximation resulted in

289

gelatinization of the fibers. Gelatinization might hinder the diffusion of uranyl ions into the

290

interior of the fibers.

291

AO density of 7.0 mmol/g and an adequate Dg of 200%. This might be one of the reasons why it

292

exhibited higher adsorption capacity. However, there were still many parameters affect on the

293

adsorption capacity of uranium. Besides the material itself the marine hydrological condition

294

such as temperature, flow velocity, turbidity et al. also affect much on the adsorption capacity.

295

The average seawater temperature during adsorption test was 25.5 °C, which was higher than in

296

Xiaman and Raoping. What’s more Daishan Desalination Company could provide a steady and

297

high flow velocity of 0.5 m/s. Two other parallel experiments at the Daishan adsorption platform

298

were carried out for UHMWPE-7 fiber, and the results are shown in Figure 5. The capacities

11

Compared with other AO-UHMWPE fiber, AO-UHMWPE-7 has high


15


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Page 16 of 31

299

were 1.01 and 2.07 mg U/g-adsorbent after 15 days of adsorption. The average capacity for U

300

was 1.50 mg U/g-adsorbent. A huge difference from 1.01 and 2.07 mg U/g-adsorbent of the

301

same AO-UHMWPE-7 fiber indicated that the uniformity and stability of the materials should be

302

improved. After adsorption, the top three metal ions in AO-UHMWPE-7 were magnesium,

303

cadmium, and iron, for which the capacities were approximately 2–10 times higher than that for

304

uranium. The concentrations of magnesium and cadmium in natural seawater were 106 times

305

higher than that of uranium, which resulted in their inevitable adsorption. The iron concentration

306

in the natural seawater at this location is also approximately 100 times higher than that of

307

uranium because of human activities, which was the reason why capacities for iron were higher

308

than those for uranium. Apart from these three metal ions, the capacity for uranium was the

309

highest. The short contact time of 15 days resulted in a relatively high capacity for uranium and

310

very low capacity for vanadium, which suggested that the Daishan adsorption platform was very

311

appropriate for uranium extraction by such adsorbents as AO-UHMWPE-7.

312

Figure 5. Adsorption capacities for uranium and other competing ions of AO-UHMWPE-7

313

obtained at Daishan adsorption platform.

314

3.3. Adsorption Selectivity

315

For the adsorption performances for uranium and other competing ions of the AO-UHMWPE

316

fibers in simulated and natural seawater, it was important to investigate the adsorption selectivity

317

for uranium over the other competing ions. Vanadium was selected as the representative

318

competing ion because it could strongly bond on amidoxime fibers and could be eluted with high

319

concentration of 0.5 mol/L hydrochloric acid.30


16

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320

The adsorption selectivities of the AO-UHMWPE fibers in natural seawater were obtained

321

from the adsorption capacities for uranyl ions (U) and vanadyl ions (V) using the following

322

equation:

323

α=

𝑄𝑢𝑟𝑎𝑛𝑖𝑢𝑚 𝑄𝑣𝑎𝑛𝑎𝑑𝑖𝑢𝑚

(5)

324

where, α is the adsorption selectivity for uranyl ions over vanadyl ions, and Quranium and Qvanadium

325

(mg/g) are the adsorption capacities for uranyl ions and vanadyl ions, respectively.

326

Generally, the adsorption selectivity for uranyl ions over vanadyl ions is high when the value

327

of α is higher than 1; a higher value of α indicates higher adsorption selectivity and a lower value

328

of α indicates lower adsorption selectivity.

329

The adsorption selectivities of the fibers at the three different marine locations are shown in

330

Figure 6. The values of α obtained at Xiamen were all lower than 1 for AO-UHMWPE-1–5. For

331

AO-UHMWPE-5, the α value obtained at Raoping was higher than that obtained at Xiamen. For

332

AO-UHMWPE-6 and AO-UHMWPE-7, the α value obtained at Daishan was higher than 1. It

333

was noteworthy that the value of α for AO-UHMWPE-7 obtained at Daishan reached 28.2, 10.0,

334

and 14.8 in the three parallel experiments, which were the highest among the adsorbents tested at

335

the three coastal marine locations. The results indicated that the AO-UHMWPE-7 fiber had the

336

great advantage of improving selectivity for uranium over vanadium. Compared with other

337

adsorbents in this manuscript, AO-UHMWPE-7 was prepared with the amidoximation solution

338

pH ≥7.0. This might be one of the reasons. As is well-known, during the amidoximation process

339

not only amidoxime group was obtained but also some cyclic imide dioxime group was obtained.

340

Some researchers believe the stronger complexing ability and higher instability of the cyclic

341

imide dioxime are probably the reason for the deteriorating performance of the

342

poly(acrylamidoximes).31 We believe there must be some factors affect the structure of


17


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Page 18 of 31

343

functional group when amidoximation. However, it is still a puzzling problem and we should

344

continue to find them out.

345

Figure 6. Adsorption selectivity of fiber materials at three different marine test locations.

346

3.4. Biofouling

347

The adsorption behavior of uranium and other competing ions on the AO-UHMWPE fibers in

348

simulated and natural seawater was extremely complex.32,

33

349

factors such as temperature, pH value, ion concentrations, and water quality which includes

350

turbidity, microbial contamination, e al.34, 35 Effects from water quality was examined intuitively

351

by comparing the changes of the adsorbents after adsorption with simulated seawater and natural

352

seawater.

It could be affected by various

353

Pictures of the adsorbents after adsorption in the flow-through test system in lab and the

354

marine adsorption test are shown in Figure 7. It is obvious that the color of the fiber after

355

adsorption in the flow-through test system deepened gradually with the increase of contact time,

356

and the surface of the sample was relatively clean. The simulated seawater was filtered with

357

polypropylene membranes (10 and 100 μm) and sterilized with ultraviolet radiation before

358

flowing through the adsorption column. Accordingly, almost no microorganism contamination

359

was found in the adsorbents. Figure 7b and c shows that sediment and marine life adhered to the

360

surface of the sample after submersion in natural seawater. The results indicated that the effect of

361

biofouling was serious, and had a great effect on the diffusion of uranyl ions to the adsorbents.

362 363

Figure 7. Photos of (a) adsorbents after adsorption in flow-through test system with simulated

364

seawater and (b, c) marine adsorption test system.

365

4. CONCLUSIONS


18

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366

Recovery of uranium from seawater was investigated in simulated seawater in the laboratory

367

and natural seawater at coastal marine of China. Results showed that the adsorption capacities

368

obtained from the marine adsorption test and laboratory adsorption test were quite different. The

369

AO-UHMWPE adsorbents showed good adsorption performances in simulated seawater but

370

relatively poor adsorption performances in coastal marine seawater. Results showed that

371

simulated seawater adsorption test in lab was only suitable for screening adsorbents and was not

372

a precise method to evaluate the adsorption performance in natural seawater. Regarding uranium

373

uptake performance, experimental data indicated that an AO-UHMWPE-7 adsorbent showed a

374

maximum capacity of 2.07 mg U/g-adsorbent after 15 days in natural seawater and the average

375

capacity for U was 1.50 mg U/g-adsorbent. The variance of capacity indicated that the

376

uniformity and stability of the materials should be improved. The average capacity for U was 18

377

times higher than that for V, which represented the highest selectivity for U in seawater thus far.

378

The pH of amidoximation solution might be one of factors affect the selectivity. In the marine

379

adsorption test, the effect of biofouling was serious, and might have a great effect on the

380

diffusion of uranyl ions to the adsorbents. Results indicated that there were many factors effect

381

on adsorption capacity of uranium. Besides the character of adsorbent including degree of

382

grafting and functional group density, the marine hydrological condition such as temperature,

383

flow velocity, turbidity et al. is also crucially important. Antifouling must be considered in the

384

application to extraction of uranium from seawater.

385

ASSOCIATED CONTENT

386

Supporting Information

387

AUTHOR INFORMATION

388

Corresponding Author


19


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389

*E-mail: [email protected].

390


391


392

Author Contributions

393

The manuscript was written through contributions of all authors. All authors have given

394

approval to the final version of the manuscript.

395

Notes

396

The authors declare no competing financial interest.

397

ACKNOWLEDGMENT

Page 20 of 31

398

We appreciate supports from the “Strategic Priority Research Program” of the Chinese

399

Academy of Sciences (Grant XDA02030200), the National Natural Science Foundation of China

400

(11305241, 11305243, 11275252, 11405249, 21306220, 21676291, 11605275) and the

401

“Knowledge Innovation Program” of Chinese Academy of Sciences (Grant KJCX2-YW-N49).

402

We appreciate the help from Daishan Lvyuan Desalination Co., Ltd., Institute of Process

403

Engineering, Chinese Academy of Sciences and Guangdong Zhongkebao Biotechnology Co.,

404

Ltd in the marine adsorption.

405

Supporting Information

406

Figure S1. ATR-FTIR spectra of UHMWPE fiber, UHMWPE-g-P(AN-co-AA) fiber, and

407

UHMWPE-g-P(AO-co-AA) fiber.

408

Table S1. Adsorption Capacities of Uranium and Other Competing Ions for Different Exposure

409

Time in AO-UHMWPE-1 Fiber Sample. Experimental Condition: 25 ± 2°C, Flow rate of 20 ± 2

410

mL/min.

411

Table S2. Adsorption Rates of Uranium at Different Exposure Time from AO-UHMWPE-1

412

Fiber Sample. Experimental Condition: 25 ±2°C, Flow rate of 20 ±2 mL/min.

413

Table S3. Adsorption Capacities of Uranium and Other Competing Ions for Different Exposure

414

Time in AO-UHMWPE-2 Fiber Sample. Experimental Condition: 25 ± 2°C, Flow rate of 20±2

415

mL/min.


20

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416

Table S4. Adsorption Rates of Uranium at Different Exposure Time from AO-UHMWPE-1

417

Fiber Sample. Experimental Condition: 25 ±2°C, Flowrate of 20 ±2 mL/min.

418

ABBREVIATIONS

419

AA, acrylic acid; AN, acrylonitrile; AO, amidoxime; JAERI, Japan Atomic Energy Research

420

Institute; MSL, Marine Sciences Laboratory; PAO, polyamidoxime; PE, polyethylene; PNNL,

421

Pacific Northwest National Laboratory; psu, practical salinity units; UHMWPE, ultrahigh-

422

molecular-weight polyethylene

423

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424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453

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(26) Seko, N.; Katakai, A.; Hasegawa, S.; Tamada, M.; Kasai, N.; Takeda, H.; Sugo, T.; Saito, K., Aquaculture of uranium in seawater by a fabric-adsorbent submerged system. Nucl. Technol. 2003, 144, 274-278. (27) Seko, N.; Tamada, M.; Yoshii, F., Current status of adsorbent for metal ions with radiation grafting and crosslinking techniques. Nucl. Instrum. Meth. B. 2005, 236, 21-29. (28) Alexandratos, S. D.; Zhu, X. P.; Florent, M.; Sellin, R., Polymer-Supported Bifunctional Amidoximes for the Sorption of Uranium from Seawater. Ind. Eng. Chem. Res. 2016, 55, 42084216. (29) Li, R.; Pang, L.J.; Ma, H.J.; Liu, X.Y.; Zhang, M.X.; Gao, Q.H.; Wang, H.L.; Xing Z.; Wang M.H.; Wu, G.Z., Optimization of molar content of amidoxime and acrylic acid in UHMWPE fibers for improvement of seawater uranium adsorption capacity. J. Radioanal. Nucl. Chem.2016，doi:10.1007/s10967-016-5117-6. (30) Suzuki, T.; Saito, K.; Sugo, T.; Ogura, H.; Oguma, K., Fractional elution and determination of uranium and vanadium adsorbed on amidoxime fiber from seawater. Anal. Sci. 2000, 16, 429432. (31) Astheimer, L.; Schenk, H.J.; Witte, E.G.; Schwochau, K., Development of adsorbers for the recovery of uranium from seawater. Part 2. Sep. Sci. Technol., 1983, 18, 307-339. (32) Gittens, J. E.; Smith, T. J.; Suleiman, R.; Akid, R., Current and emerging environmentallyfriendly systems for fouling control in the marine environment. Biotechnol. Adv. 2013, 31, 17381753. (33) Almeida, J. R.; Vasconcelos, V., Natural antifouling compounds: Effectiveness in preventing invertebrate settlement and adhesion. Biotechnol. Adv. 2015, 33, 343-357. (34) Park, J.; Jeters, R. T.; Kuo, L. J.; Strivens, J. E.; Gill, G. A.; Schlafer, N. J.; Bonheyo, G. T., Potential Impact of Seawater Uranium Extraction on Marine Life. Ind. Eng. Chem. Res. 2016, 55, 4278-4284. (35) Park, J.; Gill, G. A.; Strivens, J. E.; Kuo, L. J.; Jeters, R. T.; Avila, A.; Wood, J. R.; Schlafer, N. J.; Janke, C. J.; Miller, E. A.; Thomas, M.; Addleman, R. S.; Bonheyo, G. T., Effect of Biofouling on the Performance of Amidoxime-Based Polymeric Uranium Adsorbents. Ind. Eng. Chem. Res. 2016, 55, 4328-4338.

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Figure 1.Sites of the three adsorption experiments conducted in coastal marine areas of China (from Google Maps). 338x190mm (96 x 96 DPI)


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Figure 2. Actual conditions of the three coastal marine locations: (a) Xiamen adsorption platform, (b) Daishan adsorption platform, and (c) Raoping adsorption platform. 338x190mm (96 x 96 DPI)



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Figure 3. Placement of AO-UHMWPE fiber samples in the seawater at the different marine locations: (a) Xiamen adsorption platform, (b) Daishan adsorption platform, and (c) Raoping adsorption platform. 338x190mm (96 x 96 DPI)


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Figure 4. Time-series measurements of the (a) adsorption capacities and (b) adsorption rates of AOUHMWPE-1 and AO-UHMWPE-2. 338x190mm (96 x 96 DPI)



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Figure 5. Adsorption capacities for uranium and other competing ions of AO-UHMWPE-7 obtained at the Daishan adsorption platform. 338x190mm (96 x 96 DPI)


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Figure 6. Adsorption selectivity of fiber materials at three different marine test locations. 338x190mm (96 x 96 DPI)



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Figure 7. Photos of (a) adsorbents after adsorption in flow-through test system with simulated seawater and (b, c) marine adsorption test system. 338x190mm (96 x 96 DPI)


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305x133mm (96 x 96 DPI)


Uranium Adsorption Tests of Amidoxime-Based Ultrahigh Molecular

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