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Spiro D. Alexandratos Hunter College of the City University of New York Department of Energy

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.

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Spiro D. Alexandratos Hunter College of the City University of New York Department of Energy

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  1. 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

  2. U(VI) in seawater: tricarbonatouranate [UO2(CO3)3]4- • High stability constant limits choice of ligands • Problems in recovery due to • very low concentration • excess of competing ions

  3. Approaches • Organic polymers with amidoxime ligand • polymer support • physical form • immobilization method • (other) Organic polymers • Inorganic oxides

  4. Organic polymers with amidoxime ligand • high affinity for U(VI) from seawater • Challenge is to make recovery economical: • high capacity • high sorption rate • platform from which sorbent contacts seawater

  5. Immobilization method – Polymerization of acrylonitrile

  6. 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

  7. Effect of particle size • No effect on uranyl uptake from nitrate solutions • But from seawater: • Small particles preferable to large for rapid uptake

  8. 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-

  9. 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)

  10. 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

  11. 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

  12. Advantages of using fiber composite adsorbent: • Microparticles used as adsorbent (needed for high rate) • Network of fibers best for rapid flow of seawater

  13. Aim: maximize sorption kinetics --- hydrogels • Prepare hydrogelsof AO + comonomer (60:40) • acrylic acid (AA) • methacrylic acid (MAA) • ethylene glycol methacrylate phosphate (EGMP) • 2-acrylamido-2-methyl-1-propane sulfonate (AMPS) • 3-(acrylamidopropyl)trimethylammonium chloride (APTAC) • Crosslink: N,N′-methylenebis(acrylamide) • UV initiator: α,α′-dimethoxy-α-phenylacetophenone

  14. AO hydrogels: AO AO+AA AO+MAA AO+EGMP AO+AMPS AO+APTAC

  15. %U(VI)-uptake {equilibrate hydrogels with seawater spiked with 1-5 ppm of 233U}

  16. AO at equilibrium in 25 min • AA and MAA did not significantly affect time • AMPS increased time slightly • EGMP and APTAC increased time significantly • EGMP alone reached equilibrium in 7 min

  17. Advantages of EGMP hydrogels • one step synthesis using one monomer • EGMP is non-volatile • EGMP is readily polymerizable • EGMP has faster kinetics than AO or AO + comonomer • EGMP can be used in seawater and acidic solutions

  18. 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

  19. 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)

  20. Graft Polymerization

  21. Prepare amidoxime grafted onto polyethylene(AN:MAA ratio --- 70:30)

  22. 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 cycles • reduced damage on fiber surface

  23. Amidoxime membranes • Graft polym’n of AN onto polyethylene (convert to AO) • Membrane 10-4 m thick with 70% porosity • Amidoxime 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

  24. Effect of crosslinker on amidoxime sorption (seawater) • U(VI) adsorption rate on polyAOcrosslinked 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

  25. Mechanism:Is the –NH2 in amidoxime active in binding U(VI)?

  26. Mechanism:Is the –NH2 in amidoxime active in binding U(VI)? Prepare acrylamide analogue

  27. Mechanism:Is the –NH2 in amidoxime active in binding U(VI)? Prepare acrylamide analogue No affinity for U(VI)

  28. 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

  29. But mechanical strength was insufficient for mooring • Intrinsic mechanical strength lost after amidoximation • To increase strength, graft polym’n applied to prepare fibrous amidoxime

  30. Graft AN onto polyethylene non-woven fabric

  31. Graft AN onto polyethylene non-woven fabric Graft copolym’n of AN with hydrophilic methacrylic acid improved adsorption rate ; mechanically strong

  32. Collection system for braid adsorbent: Anchor to seabed

  33. Modified ligand: Bis(amidoxime)

  34. Seawater circulated upward through column containing bis(amidoxime) particles; flow rate 6 mL/min • Adsorption capacity • 1 h 13.08 mg U / g adsorbent • 1 day 28.1 • Time to equilibrium: 3 h

  35. Modified ligand: Polyhydroxamic acid

  36. 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

  37. Recovery of metals from seawater • seawater(µg/L) uptake(µg/g) • Ti 1 0.18 • U 3.3 18.2 • V 1.9 6.0 • Co 0.4 5.6 • Mo 10 1.1

  38. Other polymers: polyallylamine Uranium removal from seawater , 24 h contact 23% 35% 78%

  39. 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]

  40. 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)

  41. Other polymers: immobilized tannin Adsorption capacity: 2.35 mg U / g adsorbent (22 h)

  42. 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)

  43. 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 adsorbent • Must increase > 10 X to decrease recovery cost • Adsorbent attrition resistance is low

  44. U(VI) from seawater using hydrous TiO2: effect of particle size

  45. U(VI) from seawater using hydrous TiO2: effect of pH

  46. 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)

  47. Composites • Hydrous TiO2 on activated carbon • Zinc carbonate on activated carbon

  48. Composite: carboxylate-functionalized graft copolymer of PMAA on TiO2-densified cellulose

  49. Matrix (Cell-Ti) • Prepare cellulose xanthate viscose (cellulose + CS2 / NaOH) • Add TiO2 to viscose (1.5 : 10 weight ratio) • Disperse in solution of chlorobenzene + oil • Agitate suspension at 90 ◦C for 1 h • Filter, wash particles • Decompose xanthate in HOAc + EtOH

  50. 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

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