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Uranium Separation – Challenges and Opportunities: Recovery of Uranium from Seawater with Solid Sorbents. Spiro D. Alexandratos Hunter College of the City University of New York Department of Energy Nuclear Fuels Resources Workshop October 2010. - PowerPoint PPT Presentation
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Uranium Separation – Challenges and Opportunities: Recovery of Uranium from Seawater with Solid Sorbents
Spiro D. AlexandratosHunter College of the City University of New York
Department of Energy Nuclear Fuels Resources Workshop
October 2010
U(VI) in seawater: tricarbonatouranate [UO2(CO3)3]4-
High stability constant limits choice of ligands
Problems in recovery due to very low concentrationexcess of competing ions
Approaches
Organic polymers with amidoxime ligand polymer support
physical formimmobilization method
(other) Organic polymers Inorganic oxides
Organic polymers with amidoxime ligand
high affinity for U(VI) from seawater
Challenge is to make recovery economical:high capacityhigh sorption rateplatform from which sorbent contacts seawater
Effect of particle size
Beads prepared by suspension polymerization AN + 5% DVB [chloroform as porogen]
sieve to particle diameters:0.35-0.42 // 0.42-0.50 // 0.50-0.59 // 0.59-0.71 //
0.71-0.84 // 0.84-1.19 mm
Convert each to amidoxime
Effect of particle size
No effect on uranyl uptake from nitrate solutions
But from seawater: Small particles preferable to large for rapid uptake
Further studies show:
High porosity preferable to low porosity for rapid uptake
More pronounced effect of porosity + swelling in uptake of U(VI) from seawater than from nitrate solutions
May be due to U(VI) in seawater being bulky [UO2( CO3)3]4-
Aim: Maximize surface area --- composite fibers
Beads prepared by suspension polymerization
AN + tetraethylene glycol dimethacrylate (4EGDM)
Mixture agitated in a vibromixer at high frequency; particles crushed to 14µm
Convert to amidoxime (AO)
Prepare composite fiber
Amidoxime particles (6 g) + silica (6 g) + polyethylene (6 g) + surfactant (0.2 g)
Add to hexane in autoclave having 1.5-mm nozzle
Stir suspension at 150 oC eject through nozzle to flash-evaporate solvent, produce
fine fibrils trapping particles in fiber structure
Fibrils of polyethylene contain adsorbent and silica
Silica gives hydrophilic channels; access by hydrophilic U(VI)
adsorption rate: 0.20 mg U / g Ads per day
Advantages of using fiber composite adsorbent:
Microparticles used as adsorbent (needed for high rate)
Network of fibers best for rapid flow of seawater
Aim: maximize sorption kinetics --- hydrogels
Prepare hydrogels of AO + comonomer (60:40)acrylic acid (AA)
methacrylic acid (MAA) ethylene glycol methacrylate phosphate (EGMP) 2-acrylamido-2-methyl-1-propane sulfonate (AMPS)3-(acrylamido propyl)trimethylammonium chloride (APTAC)
Crosslink: N,N -methylenebis(acrylamide)′UV initiator: α,α -dimethoxy-α-phenylacetophenone′
%U(VI)-uptake {equilibrate hydrogels with seawater spiked with 1-5 ppm of 233U}
AO
AO + AA
AO+MAA
AO+EGMP
AO+AMPS
AO+APTACAMPS
EGMP0
102030405060708090
100
AO at equilibrium in 25 min
AA and MAA did not significantly affect timeAMPS increased time slightlyEGMP and APTAC increased time significantly
EGMP alone reached equilibrium in 7 min
Advantages of EGMP hydrogels
(i) one step synthesis using one monomer
(ii) EGMP is non-volatile
(iii) EGMP is readily polymerizable
(iv) EGMP has faster kinetics than AO or AO + comonomer
(v) EGMP can be used in seawater and acidic solutions
Immobilization method - Grafting
Use when optimum bulk + surface properties not possible by a single polymer
Construct material whose bulk is made of one polymer and surface made of different polymer
Mechanical properties determined by matrix polymer, independent of adsorbent
Free radicals produced with chemical initiators or irradiation by γ-rays or electron beams
(Efficient grafting methods needed to reduce cost of radiation-grafted polymers)
U(VI) uptake dec’s with # of cycles: no uptake at 5 cycles
Elute with NaOH after HCl - 73% uptake at 5 cycles
SEM shows: surface layer comes off at 3rd HCl elution
Replace HCl with 1M tartaric acid: elute 100% U(VI) 90% uptake at 5 cyclesreduced damage on fiber surface
Amidoxime membranes
Graft polym’n of AN onto polyethylene (convert to AO)
Membrane 10-4 m thick with 70% porosityAmidoxime uniformly distributed; 1.8 mmol /g membrane
Adsorbed 0.85 mg U(VI) /g of Ads in 50 days
Adsorbent stable to repeated loading-elution cycles
Effect of crosslinker on amidoxime sorption (seawater)
U(VI) adsorption rate on polyAO crosslinked with 4EGDM is much higher than with DVB
Polymer with 4EGDM is hydrophilic: with more water uptake, U(VI) diffuses readily into polymer interior
Adsorption of U(VI): 0.20 mg/g of Ads in 10 days
Mechanism:Is the –NH2 in amidoxime active in binding U(VI)?
Prepare acrylamide analogue
No affinity for U(VI)
Braid adsorbents
Beads need container for effective contact with seawater
National Institute of Advanced Science & Technology (Japan) developed AO fibers from AN
Fibrous adsorbents use ocean current when moored to seabed
But mechanical strength was insufficient for mooring
Intrinsic mechanical strength lost after amidoximation
To increase strength, graft polym’n applied to prepare fibrous amidoxime
Graft AN onto polyethylene non-woven fabric
Graft copolym’n of AN with hydrophilic methacrylic acid improved adsorption rate ; mechanically strong
Seawater circulated upward through column containing bis(amidoxime) particles; flow rate 6 mL/min
Adsorption capacity1 h 13.08 mg U / g adsorbent1 day 28.1
Time to equilibrium: 3 h
Vary acrylamide-crosslinker mole ratios
0.95/0.05, 0.85/0.15, 0.75/0.25
0.95/0.05 gave highest uptake capacities
Place 1 g in glass column - 50 L seawater at 3mL/min
Recovery of metals from seawater
seawater(µg/L) uptake(µg/g)
Ti 1 0.18U 3.3 18.2V 1.9 6.0 Co 0.4 5.6Mo 10 1.1
Other polymers: Uranyl ion-imprinted polymers (IIP)
Two-step synthesis of IIP resins:(i) complex formation(ii) copolymerize complex with monomers
UO22+ + 5,7-dichloroquinoline-8-ol + 4-vinylpyridine
Copolymerize with [2-hydroxyethyl methacrylate] and [ethylene glycol dimethacrylate]
After polymer formation
Remove UO22+ with 5 M HCl
Contact seawater; remove 83% of the uranyl present
Stability constant of U–DCQ (1.29×1021) is greater than U-carbonate (1.67×1016)
Application of microbial biomass
R. arrhizus and P. chrysogenum are effective U(VI) sequestering agents
From seawater: Amount of U(VI) sorbed by R. arrhizus is much less than that sorbed from U(VI) solutions
P. chrysogenum has negligible uptake
Carbonates in seawater inhibit biomass from sorbing U(VI)
Inorganic oxides
First pilot plant for uranium recovery from seawater with hydrous TiO2: Ministry of International Trade & Industry (Japan), 1981 – 1988
Adsorption capacity: 0.1 mg U / g adsorbentMust increase > 10 X to decrease recovery cost
Adsorbent attrition resistance is low
Inorganic adsorbents: slow adsorption rates; low mechanical stability
Hydrous zirconium oxide (13 µg/g)Hydrous tin oxide (17 µg/g)Hydrous lanthanum oxide (38 µg/g)Hydrous iron(III) oxide (60 µg/g)Hydrous aluminum oxide (61 µg/g)Hydrous titanium oxide
freshly precipitated (1550 µg/g)after >60 days storage (200 µg/g)
Silica titania gel (27 µg/g)
Matrix (Cell-Ti)
Prepare cellulose xanthate viscose (cellulose + CS2 / NaOH)Add TiO2 to viscose (1.5 : 10 weight ratio)
Disperse in solution of chlorobenzene + oilAgitate suspension at 90 ◦C for 1 h
Filter, wash particlesDecompose xanthate in HOAc + EtOH
Graft PMAA onto Cell-Ti
TiO2 embedded in cellulose to form composite
TiO2 particles increase density of the composite
Adsorbent stable in mineral acids and alkalies
Apply to removal of U(VI) from simulated nuclear industry wastewater
2.5 g adsorbent/L sample: ≈100% U(VI) removal
Can preparation of Cell-Ti be modified to give synergism between Ti and ligands grafted onto cellulose for removal of U(VI) from seawater?
Future Directions:
Broad study of immobilized ligands:Amidoxime (long-term stability, regenerant scheme)Mechanistic studyPhosphates, phenolics, …Immobilization method:Homopolym’n, graft polym’n, blends, IPNs,…Physical form: nanobeads on membranes, fiber,…Support polymer: PPE, PE, rayon, Lucite,…
Organic / inorganic oxide composites
References
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Sep. Sci. Tech. 2005, 39, 3753Rad. Phys. Chem. 2000, 57, 187Erice seminar 2009Can. J.Chem. Eng. 1984, 62, 559Bull. Chem. Soc. Jpn. 1980, 53, 1BARC Newsletter, December 2003Ind. Eng. Chem. Res. 1987, 26, 1977Ind. Eng. Chem. Res. 1987, 26, 1970Macromolecules 1985, 18, 2357Adsorption 2004, 10, 309Sep. Sci. Tech. 1987, 22, 1609