1. Horng-Bin Pan, Li-Jung Kuo, Jordana Wood, Jonathan Strivens,
Elution of Uranium and Transition Metals from Amidoxime-Based Polymer Sorbents for Sequestering Uranium from Seawater
Horng-Bin Pan, Li-Jung Kuo, Jordana Wood, Jonathan Strivens,
Gary Gill, Chien M. Wai
Department of Chemistry, University of Idaho,
Moscow, Idaho
Marine Sciences Lab, PNNL, Sequim, Washington
249th ACS National Meeting, Denver, CO
March 23, 2015

3. Preparation of amidoxime-based polymer Sorbents by ORNL

4. After synthesis, the polymer sorbent is treated with 2
After synthesis, the polymer sorbent is treated with 2.5% KOH solution at 80 oC
Purpose of KOH conditioning: To make the polymer sorbent hydrophilic by removing proton from the grafted carboxylic acid groups. What else does KOH conditioning do to the polymer sorbent? Not well known.

5. Kang et al. reported in 2012
Kang, S. O.; Vukovic, S.; Custelcean, R.; Hay, B. P. Ind Eng Chem Res 2012, 51, 6619.
Under highly acidic and alkaline conditions, amidoxime groups could be converted to carboxylate groups.

6. FTIR spectra of the sorbent before and after KOH conditioning (2
FTIR spectra of the sorbent before and after KOH conditioning (2.5% KOH at 80 oC)
No.
Wavenumber
(cm-1)
Mode 1
2918
as-CH2- asymmetrical stretching 2
2849
s-CH2- symmetrical stretching 3
1643
C=N stretching 4
1559
COO- stretching 5
1472
CH3 bending, or CH2 scissoring 6
1389
C-N stretching 7
928
N-O stretching

7. Effect of KOH conditioning on uranium adsorption capacity of amidoxime-based polymer sorbents
ORNL AI series sorbents -
3 hr conditioning shows slightly higher U adsorption capacity than 1 hr samples
ORNL AF1 series sorbent –
3 hr conditioning shows much lower U adsorption capacity than 1 hr samples

8. Effect of KOH conditioning duration on uranium adsorption capacity of ORNL sorbent AF1L2R1
42 day exposure for capacity determination
Average of 2-5 replicate seawater sorption experiments

9. uranium capacity (mg/g)
FT-IR spectra and signature peaks of ORNL AF1 sorbent under different KOH conditioning duration (80oC)
1643
C=N
1559
COO-
928
N-O
reaction time of KOH conditioning
IR peak ratio
of I1643/I1559
IR peak intensity of I928
uranium capacity (mg/g)
raw
0.634
20 min
1.371
0.565
3.36 ± 0.12
40 min
1.262
0.525
3.46 ± 0.07
1 hr
1.251
0.494
3.28 ± 0.12
3 hr
1.100
0.442
1.63 ± 0.49
5 hr
1.007
0.410
0.26 ± 0.09
The drops of uranium sorption capacity in 3 h and 5 h KOH-conditioned samples are not consistent with the changes in FT-IR peak intensities. Other factors may contribute to the low uranium adsorption capacity.

10. SEM images of AF1 sorbent fibers under different KOH conditioning duration: (a) original untreated, (b) 20 min, (c) 1 hr, and (d) 3 hr.

11. reaction time of KOH /NaOH conditioning uranium capacity (mg/g)
KOH conditioning vs. NaOH conditioning
(0.45 M, 80 oC)
reaction time of KOH /NaOH conditioning
uranium capacity (mg/g)
KOH coditioning
NaOH coditioning
20 min
3.36 ± 0.12
3.22 ± 0.05
40 min
3.46 ± 0.07
1 hr
3.28 ± 0.12
3.04 ± 0.05
3 hr
1.63 ± 0.49
1.13 ± 0.11
5 hr
0.26 ± 0.09
0.14 ± 0.01
0.45 M KOH = 2.5% KOH by weight; 0.45 M NaOH = 1.76% NaOH by weight.
Sorbent AF1, 42 days in seawater.

12. Can we mitigate the impact of KOH conditioning at a lower temperature?

13. Metal Adsorption Capacities of ORNL AF1 Adsorbent (42 days in a seawater flow-through column at 250 mL/min)
Element
Adsorption Capacity (g/kg adsorbent)
% of Total (by mass) Mg
24.3
27% Ca
23.7
26% Na
16.3
18% V
14.9
17% U
3.95
4.4% Fe
1.95
2.2% Zn
1.59
1.8% Cu
1.04
1.2% K
0.80
0.89% Ni
0.49
0.55% Sr
0.20
0.22% Ti
0.12
0.13% Cr
0.03
0.037% Co
0.034% Mn
0.02
0.026% Mo
0.01
0.013%
Sum
89.4
100%
Element
Adsorption Capacity (mol/kg adsorbent)
% of Total (by mol%) Mg
1.000
37% Ca
0.590
22% Na
0.708
26% V
0.293
11% Fe
0.035
1.3% Zn
0.024
0.89% K
0.021
0.75% U
0.017
0.61% Cu
0.016
0.60% Ni
0.008
0.31% Sr
0.002
0.083% Ti
0.090% Cr
0.001
0.023% Co
0.019% Mn
0.0004
0.016% Mo
0.0001
0.004%
Sum
2.718
100%

14. Acid leaching – KOH conditioning is required for reuse of sorbent.
Elution Methods Tested for Recovering Uranium and Transition Metals from Amidoxime-based Polymer Sorbents
Acid leaching – KOH conditioning is required for reuse of sorbent.
Carbonate leaching – KOH conditioning is not required for reuse of sorbent.
Chelating agent leaching
Supercritical CO2 leaching

15. Elution of Uranium and Transition Metals from ORNL 38H6 Adsorbent Using Hydrochloric Acid

16. Elution of Uranium Using Carbonate Solutions
Sodium Carbonate Elution (1 M Na2CO3 pH = 10.8)
UO2A CO32- → [UO2(CO3)3]4- + 2A2-
Carbonate-H2O2 Elution
UO2A CO32- + HO2-→ [UO2(O2)(CO3)2]4- + 2A2- + HCO3-

17. Stability of Uranyl-Peroxo-Carbonato Complex
[UO2(CO3)3]4- + HO2- → [UO2(O2)(CO3)2]4- + HCO3-
K = 5 x (24.4 oC)
Goff et al. Inorg. Chem., 2008, 47,
HO2-
+ HCO3-

18. Uranium Elution with Na2CO3+H2O2 at Room Temperature (21 oC)

19. Uranium Loading Capacity of Recycled Polymer Fiber – Leaching with 1 M Na2CO3 + Different Amount of H2O2 or 0.5 M HCl

20. % iron removed from adsorbent % vanadium removed from adsorbent
Elution of transition metals (Fe, V) from amidoxime-based sorbents by different ligands
Ligand pH
% iron removed from adsorbent
% vanadium removed from adsorbent
0.5 M Tiron
12.59
83.44%
6.12%
7.17
94.00%
6.96%
3.36
36.61%
0.30%
1 M TSCIT
7.98
29.57%
0.02%
1 M TSCIT M Tiron
6.42
84.90%
4.28%
1 M TRIS
4.41
61.15%
1.47%
1 M TRIS +
0.1 M Tiron
4.50
68.99%
0.99%
Leaching condition: at 40 oC for 24 hr.
Tiron = 4,5-Dihydroxy-1,3-benzenedisulfonic acid disodium salt
TSCIT = Trisodium citrate dihydrate
TRIS = Nitrilotris(methylene)triphosphonic acid

21. Tiron elution I1643/I1559 ratio 928 (N-O) Before 1.320 0.515 After
FTIR Spectra of ORNL Sorbent (AF1 ) Before and After Tiron Elution
Tiron elution
I1643/I1559
ratio
928
(N-O)
Before
1.320
0.515
After
1.391
0.513
no change

22. Supercritical Fluid Extraction of Uranium
UV-Vis spectrum of UO2(NO3)2(TBP)2 dissolved in sc-CO2

23. Acknowledgement
U.S. Department of Energy, Nuclear Energy University Program (DOE-NEUP), Grant Number (University of Idaho)
U.S. Department of Energy, Office of Nuclear Energy, Fuel Resources – Seawater Uranium Recovery Program (PNNL)