6-1 Nuclear Forensics Summer School Radiochemical separations and quantification Aqueous chemical behavior of key radionuclides §Oxidation state variation §Solution phase speciation General separations §Ion exchange/column chromatography §Solvent extraction §Precipitation/carrier Quantification §Radiochemical methods §Spectroscopic §BOMARC example (at a later date) Provide basis for linking chemical behavior with separations Provide range of techniques suitable for quantification of radionuclides

6-2 Radionuclides of interest Can differentiate fissile material and neutron energetics from fission products §A near 90 (Sr, Zr), 100 (Tc) and 105 (Pd) §Mass (Pd, Ag, Cd, In, Sn, Sb) §Lanthanides (140 < A < 150) §Actinides Polonium 235 U fission yield

6-3 Fundamentals of separations Oxidation state §Elements of different oxidation states easier to separate àAnionic and cationic speciation *UO 2 2+,TcO 4 - §Variation of oxidation state àAddition of reductants/oxidants to control speciation *Method for separation of Pu from U àVaried stability of oxidation states

6-4 Fundamentals of separation Ion size §Concentration of counter anion àCan form anionic species *ThCl 4 and PuCl 5 - will behave differently àCounter anion can effect overall charge *Varied by acid concentration or addition of salt §Ionic size difference basis of lanthanide separations

6-5 Chromatography Separations Sample dissolution Adjustment of solution matrix §Based on column chemistry and other elements in solution Retention of target radionuclide on column §Removal of other elements Solution adjustment §Acid concentration, counter ion variation §Addition of redox agent Elute target radionuclide Can include addition of isotopic tracer to determine yield Chemical behavior measured by distribution

6-6 Solvent Extraction Two phase system for separation §Sample dissolved in aqueous phase àNormally acidic phase Aqueous phase contacted with organic containing ligand §Formation of neutral metal-ligand species drives solubility in organic phase Organic phase contains target radionuclide §May have other metal ions, further separation needed àVariation of redox state, contact with different aqueous phase Back extraction of target radionuclide into aqueous phase Distribution between organic and aqueous phase measured to evaluate chemical behavior

6-7 Sr separations Sr only as divalent cation §Isotopes à88 (stable), 89 (50.5 d), 90 (28.78 a) à 90 Sr/ 90 Y (3.19 h for metastable, 2.76 d) can be exploited Eichrom Sr Resin §1.0 M 4,4'(5')-di-t- butylcyclohexano 18-crown-6 (crown ether) in 1-octanol

6-8 Sr separation 8 M nitric acid, k' is approximately 90 §falls to less than 1 at 0.05 M nitric acid Tetravalent actinide sorption can be limited by addition of oxalic acid 90 Sr determined by beta counting

6-9 Technetium separation Exploit redox chemistry of Tc §TcO 4 - in aqueous phase §Separation from cations in near neutral pH solution àAnion exchange methods àInterference from other anions *Nitrate ØUse Tc redox chemistry ØRemove nitrates ØPrecipitate Tc (tetrabutylamonium) Solvent extraction §UREX (i.e., 1 M HNO 3, 0.7 M AHA) àUO 2 2+ and TcO 4 - extracted àBack extraction (pH 2 acid), separate

6-10 Mass (Pd, Ag, Cd, In, Sn, Sb) Noble metals to group 15 §Divalent Pd and Cd §Monovalent Ag §Trivalent In §Sn di- and tetravalent §Sb stable as trivalent, pentavalent Separation by changing conditions to target specific elements

6-11 Pd to Sb Extraction with HDEPH Vary aqueous phase §Basic (pH 10) §Citric acid at pH 8 §6 M HNO 3 Elements into different fractions HDEHP

6-12 In, Sn, and Sb Extraction with HCl and HI §Control of redox chemistry to enhance separations §Varied organics àIsoamyl acetate, benzene

6-13 In, Sn, and Sb The extraction behavior of In, Sn and Sb in HI and HCl examined §Extraction of Sb(V) from Sn(IV) in 7 M HCl solution with isoamylacetate. §Selective removal of Sn(IV) or In (III) from Sb(V) by extraction into benzene or isopropylether from HI

6-14 Polonium Essentially tracer chemistry due to short half-life of isotopes § 206 Po 8.8 d EC to 206 Bi; α to 202 Pb § 207 Po 5.80 h EC to 207 Bi; α to 203 Pb § 208 Po y EC to 208 Bi; α to 204 Pb § 209 Po 102 y EC to 209 Bi; α to 205 Pb § 210 Po d α to 206 Pb Range of separations from environmental samples §Sediment §seawater

6-15 Polonium extraction From aqueous α-hydroxyisobutyric acid Varied organic phase §dioctyl sulphide, Cyanex 272, Cyanex 301 or Cyanex 302 in toluene 2 mL each phase

6-16 Polonium extraction

6-17 Polonium extraction Extraction of Po from 1M α-HIBA increases §Cyanex 272 < DOS < Cyanex 302 < Cyanex 301 Extraction of Po with 1M extractants without α-HIBA aqueous phase §DOS < Cyanex 301 < Cyanex 302 < Cyanex 272.

6-18 Lanthanides Size separations Lanthanide and actinide by elution with ammonium  - hydroxyisobutyrate from Dowex 50-X4 resin columns §pH variation §Determination of peak position with pH

6-19 Lanthanides Ln separation by HPLC using Di-(2- ethylhexyl) phosphoric acid (HDEHP) coated reverse phase column   -hydroxy isobutyric acid for elution HDEHP separations

6-20 Th Solution chemistry Only one oxidation state in solution Th(III) is claimed §Th 4+ + HN 3  Th N 2 + H + àIV/III greater than 3.0 V *Unlikely based on reduction by HN 3 àClaimed by spectroscopy *460 nm, 392 nm, 190 nm, below 185 nm *Th(IV) azido chloride species Structure of Th 4+ §Around 11 coordination §Ionic radius Å §Th-O distance 2.45 Å àO from H 2 O

6-21 Solution chemistry Thermodynamic data §E º = V (Th 4+ /Th) §Δ f H º = -769 kJ/mol §Δ f G º = kJ/mol §S º = J/Kmol Hydrolysis §Largest tetravalent actinide ion àLeast hydrolyzable tetravalent àCan be examined at higher pH, up to 4 àTends to form colloids *Discrepancies in oxide and hydroxide solubility §Range of data àDifferent measurement conditions àNormalize by evaluation at zero ionic strength

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6-26 Solution chemistry Complexing media §Carbonate forms soluble species §Mixed carbonate hydroxide species can form àTh(OH) 3 CO 3 - à1,5 §Phosphate shown to form soluble species àControlled by precipitation of Th 2 (PO 4 ) 2 (HPO 4 ). H 2 O *logK sp =-66.6

6-27 Complexation Inorganic ligands §Fluoride, chloride, sulfate, nitrate §Data is lacking for complexing àRe-evaluation based pm semiemperical approach *Interligand repulsion ØDecrease from 1,4 to 1,5 ØStrong decrease from 1,5 to 1,6 Organic ligands §Oxalate, citrate, EDTA, humic substance àForm strong complexes §Determined by potentiometry and solvent extraction àChoice of data (i.e., hydrolysis constants) impacts evaluation

6-28 Th analytical methods Low concentrations §Without complexing agent Indicator dyes §Arzenazo-III ICP-MS Radiometric methods §Alpha spectroscopy §Liquid scintillation àMay require preconcentration àNeed to include daughters in evaluation

6-29 Th ore processing Main Th bearing mineral is monazite §Phosphate mineral àstrong acid for dissolution results in water soluble salts àStrong base converts phosphates to hydroxides *Dissolve hydroxides in acid Th goes with lanthanides §Separate by precipitation §Lower Th solubility based on difference in oxidation state àprecipitate at pH 1 *A number of different precipitation steps can be used ØHydroxide ØPhosphate ØPeroxide ØCarbonate (lanthanides from U and Th) ØU from Th by solvent extraction

6-30

6-31 Pa Solution chemistry Both tetravalent and pentavalent states in solution §No conclusive results on the formation of Pa(III) §Solution states tend to hydrolyze Hydrolysis of Pa(V) §Usually examined in perchlorate media §1 st hydrolyzed species is PaOOH 2+ §PaO(OH) 2 + dominates around pH 3 §Neutral Pa(OH) 5 form at higher pH §Pa polymers form at higher concentrations Constants obtained from TTA extractions §Evaluated at various TTA and proton concentrations and varied ionic strength §Fit with specific ion interaction theory Absorption due to Pa=O

6-32

6-33 Solution chemistry Pa(V) in mineral acid §Normally present as mixed species §Characterized by solvent extraction or anion exchange §Relative complexing tendencies àF - >OH - >SO 4 2- >Cl - >Br - >I - >NO 3 - ≥ClO 4 - Nitric acid §Pa(V) stabilized in [HNO 3 ]M>1 §Transition to anionic at 4 M HNO 3 HCl §Precipitation starts when Pa is above 1E-3 M §Pa(V) stable between 1 and 3 M àPaOOHCl + above 3 M HCl HF §High solubility of Pa(V) with increasing HF concentration §Up to 200 g/L in 20 M HF §Range of species form, including anionic

6-34

6-35 Solution chemistry Sulfuric acid §Pa(V) hydroxide soluble in H 2 SO 4 §At low acid (less than 1 M) formation of hydrated oxides or colloids §At high acid formation of H 3 PaO(SO 4 ) 3

6-36

6-37 Solution chemistry Redox behavior §Reduction in Zn amalgam §Electrochemistry methods àPt-H 2 electrode àAcidic solution àPolarographic methods *One wave ØV to IV §Calculation of divalent redox Pa(IV) solution §Oxidized by air §Rate decreases in absence of O 2 and complexing ions

6-38 Solution chemistry Pa(IV) §Precipitates in acidic solutions ài.e., HF Spectroscopy §6d 1  5f 1 àPeak at 460 nm

6-39 Pa Analytical methods Radiochemical §Alpha and gamma spectroscopy for 231 Pa §Beta spectroscopy for 234 Pa àOverlap with 234 Th Activation analysis  231 Pa(n,  ) 232 Pa, 211 barns Spectral methods §263 lines from 264 nm to 437 nm §Microgram levels Electrochemical methods §Potentiometric oxidation of Pa(V) Absorbance §Requires high concentrations §Arsenazo-III Gravimetric methods §Hydroxide from precipitation with ammonium hydroxide

6-40 Pa Preparation and purification Pa is primarily pentavalent Pa has been separated in weighable amounts during U purification §Diethylether separation of U §Precipitation as carbonate àUse of Ta as carrier Sulfate precipitation of Ra at pH 2 §Inclusion of H 2 O 2 removes U and 80 % of Pa §Isolated and redissolved in nitric acid àPa remains in siliceous sludge Ability to separate Pa from Th and lanthanides by fluoride precipitation §Pa forms anionic species that remain in solution §Addition of Al 3+ forms precipitate that carriers Pa

6-41 Pa purification Difficult to separate from Zr, Ta, and Nb with macro amounts of Pa Precipitation §Addition of KF àK 2 PaF 7 *Separates Pa from Zr, Nb, Ti, and Ta àNH 4 + double salt *Pa crystallizes before Zr but after Ti and Ta §Reduction in presence of fluorides àZn amalgam in 2 M HF àPaF 4 precipitates *Redissolve with H 2 O 2 or air current §H 2 O 2 precipitation àNo Nb, Ta, and Ti precipitates §Silicates àK, Na silicates with alumina

6-42 Pa purification Ion exchange §Anion exchange with HCl àAdhere to column in 9-10 M HCl *Fe(III), Ta, Nb, Zr, U(IV/VI) also sorbs àElute with mixture of HCl/HF §HF àSorbs to column àElute with the addition of acid *Suppresses dissociation of HF *Lowers K d àAddition of NH 4 SCN *Numerous species formed, including mixed oxide and fluoride thiocyanates

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6-44 Pa purification Solvent extraction §At trace levels (<1E-4 M) extraction effective from aqueous phase into a range of organics àDi-isobutylketone *Pa extracted into organic from 4.5 M H 2 SO 4 and 6 M HCl *Removal from organic by 9 M H 2 SO 4 and H 2 O 2 àDi-isopropylketone *Used to examine Pa, Nb, Db ØConcentrated HBr ØPa>Nb>Db àDimethyl sulfoxide

6-45 Pa purification TTA §10 M HCl àPaOCl 6 3- §With TBP, Tri-n-octylphosphine oxide (TOPO), or triphenylphosphine oxide (TPPO) Triisooctylamine §Mixture of HCl and HF à0.5 M HCl and 0.01 M HF *Used to examine the column extraction ØSorbed with 12 M HCl and 0.02 M HF ØElute with 10 M HCl and M HF, 4 M HCl and 0.02 M HF, and 0.5 M HCl and 0.01 M HF ØExtraction sequence Ta>Nb>Db>Pa

6-46 Pa purification Aliquat 336 §Methyl- trioctylammonium chloride §Extraction from HF, HCl, and HBr

6-47 Uranyl chemical bonding Bonding molecular orbitals   g 2  u 2  g 4  u 4 àOrder of HOMO is unclear *  g <  u <  g <<  u proposed  Gap for  based on 6p orbitals interactions  5f  and 5f  LUMO §Bonding orbitals O 2p characteristics §Non bonding, antibonding 5f and 6d §Isoelectronic with UN 2 Pentavalent has electron in non-bonding orbital

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6-50 f orbitals From LANL Pu chemistry

6-51 Uranyl chemical bonding Linear yl oxygens from 5f characteristic §6d promotes cis geometry yl oxygens force formal charge on U below 6 §Net charge 2.43 for UO 2 (H 2 O) 5 2+, 3.2 for fluoride systems àNet negative 0.43 on oxygens àLewis bases *Can vary with ligand in equatorial plane *Responsible for cation-cation interaction *O=U=O- - -M *Pentavalent U yl oxygens more basic Small changes in U=O bond distance with variation in equatorial ligand Small changes in IR and Raman frequencies §Lower frequency for pentavalent U §Weaker bond

6-52 Uranium aqueous solution complexes Strong Lewis acid Hard electron acceptor §F - >>Cl - >Br -  I - §Same trend for O and N group à based on electrostatic force as dominant factor Hydrolysis behavior §U(IV)>U(VI)>>>U(III)>U(V) Uranium coordination with ligand can change protonation behavior §HOCH 2 COO - pKa=17, 3.6 upon complexation of UO 2 àInductive effect *Electron redistribution of coordinated ligand *Exploited in synthetic chemistry U(III) and U(V) §No data in solution àBase information on lanthanide or pentavalent actinides

6-53 Np chemistry Basic solutions §Difficulty in understanding data àChemical forms of species Determine ratios of each redox species from XANES §Use Nernst equation to determine potentials

6-54 Np solution chemistry Disproportionation §NpO 2 + forms Np 4+ and NpO 2 2+ àFavored in high acidity and Np concentration §2NpO H +  Np 4+ + NpO H 2 O §K for reaction increased by addition of complexing reagents àK=4E-7 in 1 M HClO 4 and 2.4E-2 in H 2 SO 4 *Suggested reaction rate Ø-d[NpO 2 + ]/dt=k[NpO 2 + ][H + ] 2 Control of redox species §Important consideration for experiments §LANL write on methods

6-55 Np solution chemistry Oxidation state control §Redox reagents àAdjustment from one redox state to another àBest for reversible couples *No change in oxo group *If oxo group change occurs need to know kinetics àEffort in PUREX process for controlled separation of Np focused on organics *HAN and derivates for Np(VI) reduction *Rate 1 st order for Np in excess reductant à1,1 dimethylhydrazine and tert-butylhydrazine selective of Np(VI) reduction over Pu(IV)

6-56 Np solution chemistry Applied to Np(III) to Np(VII) and coordination complexes §Applied to Np(V) spin-orbit coupling for 5f 2 Absorption in HNO 3 §Np(IV): 715 nm §Np(V): weak band at 617 nm §Np(VI): below 400 nm àNo effect from 1 to 6 M nitric Np(VII) only in basic media §NpO 6 5- à2 long (2.2 Å) and 4 short (1.85 Å) àAbsorbance at 412 nm and 620 nm *O pi  5f *Number of vibrational states ØBetween 681 cm -1 and 2338 cm -1 Np(VI) §Studies in Cs 2 UO 2 Cl 4 lattice §Electronic levels identified at following wavenumbers (cm -1 ) à6880, 13277, 15426, 17478, and *6880 cm -1 belongs to 5f 1 configuration

6-57 Np solution chemistry Np(IV) §Absorbance from 300 nm to 1800 nm permitted assignment at 17 excited state transitions §IR identified Np-O vibrational bands à825 cm -1 §Absorbance in nitrate àVariation seen for nitrate due to coordination sphere

6-58 Np(III) Np(IV) Np(V) Np(VI)

6-59 Np solution chemistry

6-60 Np solution chemistry Np hydrolysis §Np(IV)>Np(VI)>Np(III)>Np(V) §For actinides trends with ionic radius Np(III) §below pH 4 §Stable in acidic solution, oxidizes in air §Potentiometric analysis for determining K §No K sp data Np(IV) §hydrolyzes above pH 1 àTetrahydroxide main solution species in equilibrium with solid based on pH independence of solution species concentration Np(V) §not hydrolyzed below pH 7 Np(VI) §below pH 3-4 Np(VII) §No data available

6-61 Np separation chemistry Most methods exploit redox chemistry of Np Solvent extraction §2-thenoyltrifluoroacetone àReduction to Np(IV) *Extraction in 0.5 M HNO 3 *Back extract in 8 M HNO 3 ØOxidation to Np(V), extraction into 1 M HNO 3 §Pyrazolone derivatives àNp(IV) extracted from 1 to 4 M HNO 3 àPrevents Np(IV) hydrolysis àNo extraction of Np(V) or Np(VI) §Pyrazolone derivatives synergistic extraction with tri-n- octylphosphine oxide (TOPO) àSeparate Np(V) from Am, Cm, U(VI), Pu(IV) and lanthanides §1:2 Np:ligand ratio as extracted species

6-62

6-63 Np solvent extraction Tributylphosphate §NpO 2 (NO 3 ) 2 (TBP) 2 and Np(NO 3 ) 4 (TBP) 2 are extracted species àExtraction increases with increase concentration of TBP and nitric acid *1-10 M HNO 3 àSeparation from other actinides achieved by controlling Np oxidation state CMPO (Diphenyl-N,N-dibutylcarbamoyl phosphine oxide) §Usually used with TBP §Nitric acid solutions §Separation achieved with oxidation state adjustment àReduction of Pu and Np by Fe(II) sulfamate àNp(IV) extracted into organic, then removed with carbonate, oxalate, or EDTA

6-64 Np solvent extraction HDEHP §In 1 M HNO 3 with addition of NaNO 2 àU, Pu, Np, Am in most stable oxidation states àNp(V) is not extracted àOxidized to Np(VI) then extracted àReduced to Np(V) and back extracted into 0.1 M HNO 3 Tri-n-octylamine §Used for separation of Np from environmental samples àExtracted from 10 M HCl àBack extracted with 1 M HCl+0.1 M HF

6-65 Chromatography with Chelating Resins Resin loaded with Aliquat 336 §TEVA resin àNp controlled by redox state *Reduction with Fe(II) sulfamate and ascorbic acid Ascorbic acid

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6-67

6-68 Pu solution chemistry Originally driven by the need to separate and purify Pu Species data in thermodynamic database Complicated solution chemistry §Five oxidation states (III to VII) àSmall energy separations between oxidation states àAll states can be prepared *Pu(III) and (IV) more stable in acidic solutions *Pu(V) in near neutral solutions ØDilute Pu solutions favored *Pu(VI) and (VII) favored in basic solutions ØPu(VII) stable only in highly basic solutions and strong oxidizing conditions §Some evidence of Pu(VIII)

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6-71 Pu solution chemistry Other spectroscopic methods employed in Pu analysis §Photoacoustic spectroscopy §Thermal lensing Vibrational spectroscopy §Oxo species àAsymmetric stretch cm -1 *962 cm -1 in perchloric acid àLinear arrangement of oxygen §Raman shifts observed àSensitive to complexation *Changes by 40 cm -1

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6-74 Pu solution chemistry Preparation of pure oxidation states §Pu(III) àGenerally below pH 4  Dissolve  -Pu metal in 6 M HCl àReduction of higher oxidation state with Hg or Pt cathode *0.75 V vs NHE àHydroxylamine or hydrazine as reductant §Pu(IV) àElectrochemical oxidation of Pu(III) at 1.2 V *Thermodynamically favors Pu(VI), but slow kinetics due to oxo formation §Pu(V) àElectrochemical reduction of Pu(VI) at pH 3 at 0.54 V (vs SCE) *Near neutral in 1 micromole/L Pu(V) §Pu(VI) àTreatment of lower oxidation states with hot HClO 4 àOzone treatment §Pu(VII) àOxidation in alkaline solutions *Hexavalent Pu with ozone, anodic oxidation

6-75 Pu solution chemistry Pu(VI) oxo oxygen exchange with water § 18 O enriched water exchange àneed to maintain hexavalent oxidation state *Exchange rate increases with lower oxidation state §Exchange half life = 4.55E4 hr at 23 °C àTwo reaction paths *Reaction of water with Pu(VI) *Breaking of P=O bonds by alpha decay ØFaster exchange rate measured with 238 Pu Pu redox by actinides §Similar to diproportionation §Rates can be assessed against redox potentials àPu 4+ reduction by different actinides shows different rates *Accompanied by oxidation of An 4+ with yl bond formation §Reduction of Pu(VI) by tetravalent actinides proceeds over pentavalent state §Reactions show hydrogen ion dependency

6-76 Pu solution chemistry Pu reduction by other metal ions and ligands §Rates are generally dependent upon proton and ligand concentration àHumic acid, oxalic acid, ascorbic acid §Poor inorganic complexants can oxidize Pu àBromate, iodate, dichromate §Reactions with single electron reductants tend to be rapid àReduction by Fe 2+ §Complexation with ligands in solution impacts redox àDifferent rates in carbonate media compared to perchlorate àMono or dinitrate formation can effect redox *Pu(IV) formation or reaction with pentavalent metal ions proceeds faster in nitrate than perchlorate *Oxidation of Pu(IV) by Ce(IV) or Np(VI) slower in nitrate §Pu(VI) reduction can be complicated by disproportionation §Hydroxylamine (NH 2 OH), nitrous acid, and hydrazine (N 2 H 4 ) àUsed in PUREX for Pu redox control àPu(III) oxidized *2Pu 3+ +3H + +NO 3 -  2Pu 4+ +HNO 2 +H 2 O *Re-oxidation adds nitrous acid to the system which can initiate an autocatalytic reaction

6-77 Pu anion exchange

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6-80 Pu cation exchange General cation exchange trends for Pu § HN0 3, H 2 S0 4, and HC10 4 show stronger influence than HC1 §Strong increase in distribution coefficient in HClO 4 at high acidities exhibited for Pu(III) and Pu(VI)

6-81 Pu separations Alkaline solutions §Need strong ligands that can compete with hydroxide to form different species àF -, CO 3 2-, H 2 O 2 *High solubility, based on oxidation state *Stabilize Pu(VII) Room temperature ionic liquids §Quaternary ammonium with anions àAlCl 4 -, PF 6 - §Liquid-liquid extraction §Electrochemical disposition N S S O O O O CF 3 F 3 C

6-82 Am solution chemistry Oxidation states III-VI in solution §Am(III,V) stable in dilute acid §Am(V, VI) form dioxo cations Am(II) §Unstable, unlike some lanthanides (Yb, Eu, Sm) àFormed from pulse radiolysis *Absorbance at 313 nm *T 1/2 of oxidation state 5E-6 seconds Am(III) §Easy to prepare (metal dissolved in acid, AmO 2 dissolution) àPink in mineral acids, yellow in HClO 4 when Am is 0.1 M Am(IV) §Requires complexation to stabilize àdissolving Am(OH) 4 in NH 4 F àPhosphoric or pyrophosphate (P 2 O 7 4- ) solution with anodic oxidation àAg 3 PO 4 and (NH 4 ) 4 S 2 O 8 àCarbonate solution with electrolytic oxidation

6-83 Am solution chemistry Am(V) §Oxidation of Am(III) in near neutral solution àOzone, hypochlorate (ClO - ), peroxydisulfate àReduction of Am(VI) with bromide Am(VI) §Oxidation of Am(III) with S 2 O 8 2- or Ag 2+ in dilute non- reducing acid (i.e., sulfuric) §Ce(IV) oxidizes IV to VI, but not III to VI completely §2 M carbonate and ozone or oxidation at 1.3 V Am(VII) §3-4 M NaOH, mM Am(VI) near 0 °C §Gamma irradiation 3 M NaOH with N 2 O or S 2 O 8 2- saturated solution

6-84 Am solution chemistry Am(III) has 9 inner sphere waters §Others have calculated 11 and 10 (XAFS) §Based on fluorescence spectroscopy àLifetime related to coordination *n H2O =(x/  )-y Øx=2.56E-7 s, y=1.43 ØMeasurement of fluorescence lifetime in H 2 O and D 2 O

6-85 Am solution chemistry Autoreduction §Formation of H 2 O 2 and HO 2 radicals from radiation reduces Am to trivalent states àDifference between 241 Am and 243 Am §Rate decreases with increase acid for perchloric and sulfuric §Some disagreement role of Am concentration àConcentration of Am total or oxidation state §Rates of reduction dependent upon àAcid, acid concentration, àmechanism * Am(VI) to Am(III) can go stepwise àstarting ion *Am(V) slower than Am(VI)

6-86 Am solution chemistry Disproportionation §Am(IV) àIn nitric and perchloric acid àSecond order with Am(IV) *2 Am(IV)  Am(III) + Am(V) *Am(IV) + Am(V)  Am(III) + Am(VI) ØAm(VI) increases with sulfate §Am(V) à3-8 M HClO 4 and HCl *3 Am(V) + 4 H +  Am(III)+2Am(VI)+2 H 2 O àSolution can impact oxidation state stability

6-87 Am solution chemistry Redox kinetics §Am(III) oxidation by peroxydisulfate àOxidation due to thermal decomposition products *SO 4.-, HS 2 O 8 - àOxidation to Am(VI) *0.1 M to 10 nM Am(III) àAcid above 0.3 M limits oxidation *Decomposition of S 2 O 8 2- àInduction period followed by reduction àRates dependent upon temperature, [HNO 3 ], [S 2 O 8 2- ], and [Ag +2 ] à3/2 S 2 O Am H 2 O  3 SO AmO H + *Evaluation of rate constants can yield 4 due to peroxydisulfate decomposition àIn carbonate proceeds through Am(V) *Rate to Am(V) is proportional to oxidant *Am(V) to Am(VI) ØProportional to total Am and oxidant ØInversely proportional to K 2 CO 3

6-88

6-89 Am solution chemistry Hydrolysis §Mono-, di-, and trihydroxide species §Am(V) appears to have 2 species, mono- and dihydroxide Carbonate §Evaluated by spectroscopy §Includes mixed species àAm hydroxide carbonate species àBased on solid phase analysis §Am(IV)  Pentacarbonate studied (log  =39.3) §Am(V) solubility examined

6-90 Am solution chemistry: Organics Number of complexes examined §Mainly for Am(III) Stability of complex decreases with increasing number of carbon atoms With aminopolycarboxylic acids, complexation constant increases with ligand coordination Natural organic acid §Number of measurements conducted §Measured by spectroscopy and ion exchange TPEN (N,N,N’,N’-tetrakis(2- pyridylmethyl)ethyleneamine) §0.1 M NaClO 4, complexation constant for Am 2 orders greater than Sm

6-91 Am solution chemistry Fluorides §Inner sphere complexes, complexation constants much higher than other halides à1,1 and 1,2 Am:F complexes identified àOnly 1,1 for Cl Sulfates §1,1 and 1,2 constants known §No evidence of AmHSO 4 2+ species Thiocyanate (SCN - ) §Useful ligand for Ln/Ac separations §1,1 to 1,3 complex forms àExamined by solvent extraction and spectroscopy Nitrate §1,1 and 1,2 for interpreting solvent extraction data §Constant for 1,1 species Phosphate §Interpretation of data complicated due to degree of phosphate protonation §AmHPO 4 + §Complexation with H 2 PO 4 ; 1,1 to 1,4 species àFrom cation exchange, spectroscopic and solvent extraction data

6-92 Am(IV) solution chemistry Am(IV) can be stabilized by heteropolyanions §P 2 W 17 O 61 anion; formation of 1,1 and 1,2 complex àExamined by absorbance at 789 nm and 560 nm àAutoradiolytic reduction *Independent of complex formation àDisplacement by addition of Th(IV) *Disproportionation of Am(IV) to Am(III) and Am(VI) §EXAFS used with AmP 5 W 30 O Cation-cation interaction §Am(V)-U(VI) interaction in perchlorate àAm(V) spectroscopic shift from nm to 765 nm

6-93 Am solvent extraction Lanthanide/actinide separation §Extraction reaction àAm 3+ +2(HA) 2  AmA 3 HA+3 H + *Release of protons upon complexation requires pH adjustment to achieve extraction ØMaintain pH greater than 3 §Cyanex 301 stable in acid àHCl, H 2 SO 4, HNO 3 *Below 2 M §Irradiation produces acids and phosphorus compounds àProblematic extractions when dosed 10 4 to 10 5 gray §New dithiophosphinic acid less sensitive to acid concentration àR 2 PSSH; R=C 6 H 5, ClC 6 H 4, FC 6 H 4, CH 3 C 6 H 4 *Only synergistic extractions with, TBP, TOPO, or tributylphosphine oxide *Aqueous phase M HNO 3 *Increased radiation resistance

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6-95 Ion exchange Cation exchange §Am 3+ sorbs to cation exchange resin in dilute acid  Elution with  -hydroxyisobutyrate and aminopolycarboxylic acids Anion exchange §Sorption to resin from thiocyanate, chloride, and to a limited degree nitrate solutions Inorganic exchangers §Zirconium phosphate àTrivalents sorb *Oxidation of Am to AmO 2 + achieves separation §TiSb (titanium antimonate) àAm 3+ sorption in HNO 3 àAdjustment of aqueous phase to achieve separation

6-96 Ion exchange separation Am from Cm Separation of tracer level Am and Cm has been performed with displacement complexing chromatography §separations were examined with DTPA and nitrilotriacetic acid in the presence of Cd and Zn as competing cations § use of Cd and nitrilotriacetic acid separated trace levels of Am from Cm §displacement complexing chromatography method is too cumbersome to use on a large scale Ion exchange has been used to separate trace levels of Cm from Am §Am, Cm, and lanthanides were sorbed to a cation exchange resin at pH 2 àseparation was achieved by adjusting pH and organic complexant àSeparation of Cm from Am was performed with 0.01 % ethylenediamine-tetramethylphosphonic acid at pH 3.4 in 0.1 M NaNO 3 with a separation factor of 1.4 Separation of gram scale quantities of Am and Cm has been achieved by cation and anion exchange  methods rely upon use of  -hydroxylisobutyrate or diethylenetriaminepentaacetic acid as an eluting agent or a variation of the eluant composition by the addition of methanol to nitric acid àbest separations were achieved under high pressure conditions àrepeating the procedure separation factors greater than 400 were obtained

6-97 Extraction chromatography Mobile liquid phase and stationary liquid phase §Apply results from solvent extraction àHDEHP, Aliquat 336, CMPO *Basis for Eichrom resins *Limited use for solutions with fluoride, oxalate, or phosphate àDIPEX resin *Bis(2-ethylhexylmethanediphosphonic acid on inert support *Lipophilic molecule ØExtraction of 3+, 4+, and 6+ actinides *Strongly binds metal ions ØNeed to remove organics from support §Variation of support àSilica for covalent bonding àFunctional organics on coated ferromagnetic particles *Magnetic separation after sorption

6-98 Questions 1.What are some key fission products for nuclear forensics? Why? 2.Describe a method for the separation of Sr 3.What methods are suitable for the separation of Pd and In? How would these be quantified? When would it necessary to investigate these isotopes? 4.What is the fundamental chemistry that control lanthanide separation? 5.Describe two methods for the separation of U from Pu. Under which conditions would it be preferable to separate Pu from U for forensics applications?