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

Preparation of amidoxime-based polymer Sorbents by ORNL

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.

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.

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

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

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

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.

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

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.

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

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%

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

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

Elution of Uranium Using Carbonate Solutions Sodium Carbonate Elution (1 M Na2CO3 pH = 10.8) UO2A22- + 3CO32- → [UO2(CO3)3]4- + 2A2- Carbonate-H2O2 Elution UO2A22- + 3CO32- + HO2-→ [UO2(O2)(CO3)2]4- + 2A2- + HCO3-

Stability of Uranyl-Peroxo-Carbonato Complex [UO2(CO3)3]4- + HO2- → [UO2(O2)(CO3)2]4- + HCO3- K = 5 x 104 (24.4 oC) Goff et al. Inorg. Chem., 2008, 47, 1984-1990 HO2- + HCO3-

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

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

% 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 + 0.1 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

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

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

Acknowledgement U.S. Department of Energy, Nuclear Energy University Program (DOE-NEUP), Grant Number 00042246 (University of Idaho) U.S. Department of Energy, Office of Nuclear Energy, Fuel Resources – Seawater Uranium Recovery Program (PNNL)