Enhancement of Uranium Extraction from Seawater using Chromic-Acid- Treated Amidoxime Fibers

Transcription

1 Technical Meeting on the Nuclear Fuel Cycle Information System 9-12 December, 2014, Vienna Enhancement of Uranium Extraction from Seawater using Chromic-Acid- Treated Amidoxime Fibers Assoc. Prof. Dr. Doonyapong Wongsawaeng Nuclear Engineering Department Faculty of Engineering Chulalongkorn University Bangkok, Thailand

2 Background Seawater contains an almost inexhaustible resource of materials. About 80 elements can be detected in seawater. Concentrations and chemical species of some metal ions dissolved in seawater Metal [mol/l] Concentration [mg/l] Main chemical species Li Li + Be Be(OH) + Na Na + Mg Mg 2+ Al [Al(OH) 4 ] - K K + Ca Ca 2+ Li Li + Ra Ra 2+ Th Th(OH) 4 Pa U [UO 2 (CO 3 ) 3 ] 4-2

3 Background Concentrations of uranium in various resources Uranium resource Concentration [ppm U] High-grade ore 20% U 200,000 Low-grade ore 0.1% U 1,000 Granite (60% of Earth s crust) 4 Sedimentary rock 2 Average in Earth s continental crust 2.8 Seawater (3 ppb) 3 The concentration of uranium in seawater is about 3 µg/m 3, and does not appear to vary significantly from oceans to oceans.

4 Background 2/3 of the earth surface is covered by oceans, so there is about 1.3 billion km 3 of seawater worldwide. Thus, there are some 4.5 billion tons of uranium in seawater. ( 700 times more than known terrestrial resources.) 4

5 Background Thailand s topography has very long coastlines. It is of interest to study the extraction of uranium from seawater --> Potential resource of nuclear fuel for Thailand s nuclear power program in the (far?) future. 5

6 Uranium in seawater Concentrations of uranium compounds dissolved in natural seawater at 25 C and at ph of 8.1 Compound Concentration [mol/l] Weight fraction [wt% of U] UO x x10-5 UO 2 (OH) x [UO 2 (CO 3 ) 2 ] x [UO 2 (OH) 3 ] x [UO 2 (CO 3 ) 3 ] x Structure of the tricarbonate uranylate anion

7 Uranium recovery from seawater Uranium adsorption mechanism by the amidoxime functional group 2R-C NOH NH 2 Amidoxime group N-O O H 2 N + [UO 2 (CO 3 ) 3 ] 4- R-C U C-R NH 2 O-N + 2H + +3CO 2-3 O Tricarbonate uranylate anion Coordination bond 7

8 Uranium recovery from seawater LDPE containing amidoxime chelating functional group Surface modification used for Enhancement of uranium extraction from seawater 8

9 Chemical surface modification Surface modification of LDPE fiber by increasing the surface roughness --> Enhance grafting efficiency Modification using chromic acid Chromic acid treatment To make it become very rough and full of crack Effectively increasing the surface area Various functional groups can be grafted onto the modified surface of LDPE 9

10 Synthesis of Amidoxime Fibers Trunk polymer Low Density Polyethylene (LDPE) fibers LDPE fibers High Density Polyethylene (HDPE) fibers Polypropylene (PP) fibers 10

11 Synthesis of Amidoxime Fibers Chromic acid solution K 2 Cr 2 O 7 7 pbw H 2 SO pbw H 2 O 12 pbw Chromic acid solution 11 Chromic acid solution composes of 150 pbw (parts by weight) sulfuric acid solution saturated with 7 pbw potassium dichromate and 12 pbw deionized water.

12 Synthesis of Amidoxime Fibers 1.Pre-treat Pre-treat the PE fibers surface by chromic acid Chromic acid sol. PE fibers Rinsed with acetone and DI water, dried in an oven for 24 hrs. Temp. 70 o C for minutes 12

13 Synthesis of Amidoxime Fibers (a) Starting LDPE fibers (b) Chromic-acid-treated LDPE fibers Modified LDPE fibers after chromic acid treatment 13

14 Synthesis of Amidoxime Fibers Monomers for grafting AN = acrylonitrile MAA = methacrylic acid DMSO = dimethyl sulfoxide 14

15 Synthesis of Amidoxime Fibers 2.AO fibers Prepare the amidoxime fibers by irradiationinduced graft copolymerization technique. -rays C(CH 3 )-COOH CH 2 CHC N CH 2 Cyano group Chromic acid-pe AN CH 2 =CH CN + MAA CH 2 =CCH 3 COOH Cografted-PE 1. Irradiation-induced graft copolymerization 2. Amidoximation 15

16 Synthesis of Amidoxime Fibers (a) Starting LDPE fibers (b) Cografted LDPE fibers Radiation grafting of LDPE fibers with AN/MAA at the total gamma ray dose of 40 kgy 16

17 Synthesis of Amidoxime Fibers 2.AO fibers Amidoximation process to convert the cyano group into the required amidoxime group. -rays Chromic acid-pe C(CH 3 )-COOH CH 2 CHC N Cyano CH 2 group Cografted-PE NH 2 OH C(CH 3 )-COOH CH 2 CHC-C=NOH CH 2 NH 2 AO-PE Amidoxime group AN CH 2 =CH CN + MAA CH 2 =CCH 3 COOH (Soaking fibers in hydroxylamine hydrochloride solution) 1. Irradiation-induced graft copolymerization 2. Amidoximation 17

18 Synthesis of Amidoxime Fibers 18 Synthesized amidoxime fibers

19 SEM analysis of fibers at various stages (a). Starting LDPE fiber (b). Cografted LDPE fiber (c). Amidoxime fiber 19

20 (f). Chromic-acid-etched LDPE fiber after the etching time of 10 minutes (g). Chromic-acid-etched LDPE fiber after the etching time of 15 minutes SEM analysis of fibers at various stages (d). Chromic-acid-etched LDPE fiber after the etching time of 2.5 minutes (e). Chromic-acid-etched LDPE fiber after the etching time of 5 minutes 20

21 (j). Chromic-acid-etched LDPE fiber after the etching time of 30 minutes (k). Chromic-acid-etched LDPE fiber after the etching time of 60 minutes SEM analysis of fibers at various stages (h). Chromic-acid-etched LDPE fiber after the etching time of 20 minutes (i). Chromic-acid-etched LDPE fiber after the etching time of 25 minutes 21

22 Uranium concentrations in Thailand's seawater at various locations and depths I Samui Island Similan Island Phuket province 50 km Map of seawater sampling points in Southern Thailand 22

23 Submersion Location Submerged plastic containers containing fibers in front of Phuket Marine Biological Center (PBMC) 23

24 Uranium elution from amidoxime fibers Eluent containing adsorbed metals 24

25 Results Saturates at ~ = 37% higher 25 Uranium uptake of chromic acid pre-treated amidoxime fibers submerged in 30 o C Phuket seawater compared to other studies

26 Uranium concentrations in Thailand's seawater Uranium concentration in Thailand's seawater is generally uniform at ~ 3 ppb regardless of location and depth. This finding is consistent with literature-report values in other parts of the world. Region Andaman Sea Gulf of Thailand Depth Coordinate (A) ' N ' E (B) ' N ' E (C) ' N ' E (D) ' N ' E (E) ' N ' E (F) ' N ' E (G) ' N ' E (H) ' N ' E (I) ' N ' E Surface 30 m 100 m 150 m Uranium concentration (ppb) = not measured

27 Thank you for your kind attention!