lecture 5 americium chemistry n.
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Lecture 5: Americium Chemistry

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Lecture 5: Americium Chemistry

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  1. Lecture 5: Americium Chemistry • From: Chemistry of actinides • Nuclear properties • Production of Am isotopes • Am separation and purification • Atomic properties • Metallic state • Compounds • Solution chemistry • Coordination chemistry • Analytical Chemistry

  2. Am nuclear properties • Am first produced from neutron irradiation of Pu • 239Pu to 240Pu to 241Pu, then beta decay of 241Pu • 13 Am isotopes, A from 232 to 247 • Neutron deficient isotopes 233, 235, and 236 latest found • 230,236Am by Howard Hall • Lighter isotopes decay by EC • Isomeric states observed

  3. Production of Am isotopes • 241,243Am main isotopes of interest • Long half-lives • Produced in kilogram quantity • Chemical studies • Both isotopes produced in reactor • 241Am • source for low energy gamma and alpha • Alpha energy 5.44 MeV and 5.49 MeV • Smoke detectors • Neutron sources • (a,n) on Be • Thickness gauging and density • 242Cm production from thermal neutron capture • 243Am • Irradiation of 242Pu, beta decay of 243Pu • Critical mass • 242Am in solution • 23 g at 5 g/L • Requires isotopic separation from 241Am • How to achieve this separation?

  4. Am separation and purification • Pyrochemical process • Am from Pu • O2 in molten salt, PuO2 forms and precipitates • Partitioning of Am between liquid Bi or Al and molten salts • Kd of 2 for Al system • Separation of Am from PuF4 in salt by addition of OF2 • Formation of PuF6 • Precipitation method • Formation of insoluble Am species • AmF3, K8Am2(SO4)7 , Am2(C2O4)3, K3AmO2(CO3)2 • Am(V) carbonate useful for separation from Cm • Am from lanthanides by oxalate precipitation • Slow hydrolysis of dimethyloxalate • Oxalate precipitate enriched in Am • 50 % lanthanide rejection, 4 % Am • Oxidation of Am(VI) by K2S2O8 and precipitation of Cm(III)

  5. Am solvent extraction • TBP • Am extracted from neutral or low acid solutions with high nitrate • Am(VI) • Oxidation with (NH4)10P2W17O61 to stabilize Am(VI) • 100 % TBP from 1 M HNO3 • Separation factor 50 from Nd • Am separation from lanthanides • 1 M ammonium thiocyanate aqueous phase • Dibutylbutylphosphonate (DBBP) • Phosphonate functional group • Similar to TBP, stronger extractant of Am • Trialkylphophine oxide (TRPO) • Increase in basicity of P=O functional group from TBP to DPPB to TRPO • Am and Cm extraction from 1-2 M HNO3

  6. HDEHP Am solvent extraction • Trialkylphophine oxide (TRPO) • 30 % TRPO in kerosene • Am, Cm, tetravalent Np and Pu, hexavalent U extracted • Actinides stripped with 5.5 M HNO3 (Am fraction) • TRPO with C6-C8 alkyl group • Other work with mixed alkanes • Cyanex 923 with TBP to prevent third phase formation • Bis(2-ethylhexyl)phosphoric acid (HDEHP) • Has been used to Am separation • Part of TALSPEAK • Extracts lanthanides stronger that actinides • TALSPEAK components • Bis(2-ethyl-hexyl)phosphoric acid (HDEHP) • HNO3 • DTPA • Lactic acid

  7. Am solvent extraction • Bis(2-ethylhexyl)phosphoric acid (HDEHP) • TALSPEAK • Lactic acid prevents solid precipitates • Separation of Am(VI) from Cm(III) • Musikas • Rapid reduction of Am hinders separation • Acidic phase drives Am(VI) reduction • 0.1 to 1.0 M HNO3 • HDEHP diluent has impact on extraction • Diisodecylphosphoric acid (DIDPA) • Extraction of U(VI) and tetravalent Pu and Np from 1 to 3 M HNO3 • Am and Cm extracts below 0.5 M HNO3 • Removal of Am and Cm with DTPA

  8. CMPO Am solvent extraction • Dihexyl-N,N-diethylcarbamoylmethylphosphonate (DHDECMP) • Extraction of Am(IV,VI) • Good for trivalents • Removal of all actinides • Formation of 3rd phase, 20-30 % in diluent • Change diluent (branched, aromatic) • Addition of TBP • Removal of Am with 0.01 M HNO3 • octyl(phenyl)-N, N-dibutylcarbamoylmethyl phosphine oxide (CMPO) • Synthesized by Horwitz • Based on DHDECMP extractions • Recognized functional group, simplified ligand synthesis • Purified by cation exchange • Part of TRUEX, based on 0.2 M CMPO in 1.05 M TBP/docecane • TRUEX (fission products) • 0.01 to 7 M HNO3 • 1.4 M TBP • 0.2 M Diphenyl-N,N-dibutylcarbamoyl phosphine oxide (CMPO) • 0.5 M Oxalic acid • 1.5 M Lactic acid • 0.05 M DTPA

  9. CMPO extraction • Range of diluents studied • Aromatic, chlorinated, linear • Formation of 3rd phase • Addition of TBP inhibits 3rd phase formation • 0.2 M CMPO/1.2 M TBP • Extract Am and other actinides from 1 M HNO3 • Oxidation states 3+, 4+, and 6+ • Consistent Kd from 1-6 M HNO3 • Other metals also extracted • Zr, Tc (as HTcO4), • Trivalent actinides removed by dilute nitric acid (0.05 M HNO3) • Possible to strip all metal ions • 1,1 diphosphonic acid (VDPA) • 1-hydroxylethylene-1,1-diphosphonic acid (HEDPA) • Ferrocyanide (Fe(CN)64−) • Formic acid, hydrazine hydrate, citric acid • Hydrazine oxalate, hydrazine carbonate, and tetramethylammoniumhydroxide • Radiation resistance independent of diluent • Generates neutral and acidic organophosphorus compounds • Acidic products prevent removal of Am(III) from organic phase in dilute acid • Acidic product removed by carbonate wash of organic phase • Extractions studied in fluoroether solvent (Russian studies) • TBP not required to prevent 3rd phase formation • Issues with solvent from degradation

  10. Am solvent extraction • Tertiary amine salt • Low acid, high nitrate or chloride solution • (R3NH)2Am(NO3)5 • Quaternary ammonium salts (Aliquat 336) • Low acid, high salt solutions • Extraction sequence of Cm<Cf<Am<Es • Studies at ANL for process separation of Am • Amide extractants • (R1,R2)N-C(O)-CR3H-C(O)-N(R1R2) • Diamideextractant • Basis of DIAMEX process • N,N’-dimethyl-N,N’-dibutyl-2-tetradecyl-malonamide (DMDBTDMA) • DIAMEX with ligand in dodecane with 3-4 M HNO3 • Selective extraction over Nd

  11. Am solvent extraction • Am from lanthanides • HDEHP extract lanthanides better than actinides • Hard acid metal-ligand interaction • Preferential removal of actinides by contact with DTPA solution in aqueous phase • Reverse-TALSPEAK • Also useful with DIDPA • Selective actinide extraction with DTPA and 0.4 M NaNO3 • Ce/Am Dfof 72 • Recent efforts based on soft donor molecules • Sulfur and nitrogen containing ligands • Tripyridyltriazene (TPTZ) (C5H4N: pyridyl, (R-N:, azene) and dinonylnapthalene sulfonic acid (HDNNS) in CCl4 and dilute nitric acid • Preferential extraction of Am from trivalent lanthanides

  12. Am solvent extraction • Am from lanthanides • Initial work effected direction of further research • Focus on nitrogen and sulfur containing ligands • Thione (Phosphine SO), pyridenes, thiophosphonic acid • Research does not follow CHON principles • Efforts with Cyanex 301 achieved lanthanide/actinide separation in pH 3 solution • Bis (2,4,4-trimethylpentyl)dithiophosphinic acid

  13. Am solvent extraction • Lanthanide/actinide separation • Extraction reaction • Am3++2(HA)2AmA3HA+3 H+ • Release of protons upon complexation requires pH adjustment to achieve extraction • Maintain pH greater than 3 • Cyanex 301 stable in acid • HCl, H2SO4, HNO3 • Below 2 M • Irradiation produces acids and phosphorus compounds • Problematic extractions when dosed 104 to 105 gray • New dithiophosphinic acid less sensitive to acid concentration • R2PSSH; R=C6H5, ClC6H4, FC6H4, CH3C6H4 • Only synergistic extractions with, TBP, TOPO, or tributylphosphine oxide • Aqueous phase 0.1-1 M HNO3 • Increased radiation resistance

  14. Ion exchange • Cation exchange • Am3+ sorbs to cation exchange resin in dilute acid • Elution with a-hydroxylisobutyrate and aminopolycarboxylic acids • Anion exchange • Sorption to resin from thiocyanate, chloride, and to a limited degree nitrate solutions • Inorganic exchangers • Zirconium phosphate • Trivalents sorb • Oxidation of Am to AmO2+ achieves separation • TiSb (titanium antimonate) • Am3+ sorption in HNO3 • Adjustment of aqueous phase to achieve separation

  15. 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 • separation was achieved by adjusting pH and organic complexant • Separation of Cm from Am was performed with 0.01 % ethylenediamine-tetramethylphosphonic acid at pH 3.4 in 0.1 M NaNO3 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 a-hydroxylisobutyrate or diethylenetriaminepentaacetic acid as an eluting agent or a variation of the eluant composition by the addition of methanol to nitric acid • best separations were achieved under high pressure conditions • repeating the procedure separation factors greater than 400 were obtained

  16. Extraction chromatography • Mobile liquid phase and stationary liquid phase • Apply results from solvent extraction • HDEHP, Aliquat 336, CMPO • Basis for Eichrom resins • Limited use for solutions with fluoride, oxalate, or phosphate • DIPEX resin • Bis(2-ethylhexylmethanediphosphonic acid on inert support • Lipophilic molecule • Extraction of 3+, 4+, and 6+ actinides • Strongly binds metal ions • Need to remove organics from support • Variation of support • Silica for covalent bonding • Functional organics on coated ferromagnetic particles • Magnetic separation after sorption

  17. Am atomic properties • Gaseous ground state configuration • 5f77s2 • Term symbol:   8S7/2 • Gaseous Am2+; 5f7 • Radii • Metallic: 1.73 Å (CN=12) • Am3+ (CN=6): 0.984±0.003 Å • From Shannon

  18. Am atomic properties • Ionization potentials • 1st potential at 5.9738 eV • From resonance ionization mass spectroscopy • Calculated 1st: 5.66 eV, 2nd: 12.15 eV, 3rd 18.8 eV • X-ray data • K-MIII: 120.319 keV • K-LII: 102.041 keV • L x-ray energies • Lα1 Lα2 Lβ1 Lβ2 Lγ1 • 14,617.2 14,411.9 18,852.0 17,676.5 22,065.2 • Photoelectron spectroscopy • 5f electrons localized in Am metal • Mössbauer spectrum • Beta decay of 243Pu produces 83.9 keV photon • Excite 243Am to higher nuclear state, t1/2=2.34 ns • Experiment setup • 243PuO2 source, 4.2 K • 234AmF3at 55 mm/s compared to 243AmO2 • Emission spectra • Am ground state 48767 cm-1

  19. Am metal and alloys • Preparation of Am metal • Reduction of AmF3 with Ba or Li • Reduction of AmO2 with La • Bomb reduction of AmF3 with Ca • Decomposition of Pt5Am • 1550 °C at 10-6torr • La or Th reduction of AmO2 with distillation of Am • Metal properties • Ductile, non-magnetic • Double hexagonal closed packed (dhcp) and fcc • Evidence of three phase between room temperature and melting point at 1170 °C • Alpha phase up to 658 °C • Beta phase from 793 °C to 1004 °C • Gamma above 1050 °C • Some debate in literature • Evidence of dhcp to fcc at 771 °C • Interests in metal properties due to 5f electron behavior • Delocalization under pressure • Different crystal structures • Conversion of dhcp to fcc • Discrepancies between different experiments and theory

  20. Am metal, alloys, and compounds • Alloys investigated with 23 different elements • Phase diagrams available for Np, Pu, and U alloys • Am compounds • Oxides and hydroxides • AmO, Am2O3, AmO2 • Non-stoichiometric phases between Am2O3 and AmO2 • AmO lattice parameters varied in experiments • 4.95 Å and 5.045 Å • Difficulty in stabilizing divalent Am • Am2O3 • Prepared in H2 at 600 °C • Oxidizes in air • Phase transitions with temperature • bcc to monoclinic between 460 °C and 650 °C • Monoclinic to hexagonal between 800 °C and 900 °C

  21. Am compounds • Am oxides and hydroxides • AmO2 • Heating Am hydroxides, carbonates, oxalates, or nitrates in air or O2 from 600 °C to 800 °C • fcc lattice • Expands due to radiation damage • Higher oxidation states can be stabilized • Cs2AmO4 and Ba3AmO6 • Am hydroxide • Isostructural with Nd hydroxides • Cystalline Am(OH)3 can be formed, but becomes amorphous due to radiation damage • Complete degradation in 5 months for 241Am hydroxide • Am(OH)3+3H+,Am3++3H2O • logK=15.2 for crystalline • Log K=17.0 for amorphous • Am hydroxides • Am(OH)4 • Heat Am(OH)3 to 90 °C in 0.2 M NaOH with NaOCl or 7 M KOH with peroxydisulfate • Suggested precipitation of AmO2OH in slightly basic concentrated NaCl • Stable LiAmO2(OH)2 formed • Am hydrides • AmH2+xisostructural with Np and Pu hydrides • Fcc phase • From hydrogen and metal

  22. Am halides • Compounds formed with Am(II) to Am(VI) • Am(II) • AmCl2 (orthrorhombic), AmBr2 (tetragonal), and AmI2 (monoclinic) • From Am metal and Hg halides • Sm, Eu, and Yb from H2 reduction of trivalent halides • Does not work with Am • Am(III) • Binary adducts: AmCl3MCl • M=Li, Cs • Ternary compounds • MAmX4, M2AmX5, KAm2F7, MsAmX6 • Am(IV) • Rb2AmO2F2 (orthorhombic) • From concentration HF with RbAmO2F2 or Am(OH)4 with Rbsalt • Am(V) halides • KAmO2F2 andRbAmO2F2 • Precipitated from concentrated HF solutions of Am(V) • Cs3AmO2Cl4 precipitates in EtOH from 6 M HCl containing Am(V) hydroxide and CsCl • Am(VI) halides • AmO2F2 prepared from solid Am(VI) acetate with HF containing F2 at -196 °C • Cs2AmO2Cl4 from oxidation of Cs3AmO2Cl4 in concentrated HCl • Conflict surrounds AmF6 • Inability to repeat experiments • Based on volatility and IR spectrum (604 cm-1) • Reaction of AmF3 with KrF2 in anhydrous HF

  23. Am chalcogenides • AmX, Am3X4, AmX3, Am2X3 (X=S, Se, Te) • AmX2-n (X=S, Se) • AmTe2 • Vapor phase reaction of AmH3 with Te at 350 °C for 120 hours forms AmTe3 • In high vacuum at 400 °C forms AmTe2 • AmX from AmH3 and elements at 800 °C in vacuum • a-Am2S3forms at 500 °C • Further heating to 1100 °C forms Am3X4 • Am3Se4 and Am3Te4 (bcc) are isostructural with Am3P4 • Heating Am with elements at 950 °C for 24 hours

  24. Am pnictides • Compounds with N, P, As, Sb, and Bi prepared • AmN of fuel interest • known difficulties with carbothermic reduction • AmH3 or Am metal with N2 above 750 °C • Also in 99.9 % N2, 0.1 % H2 • AmP • Red phosphorus with AmH3 in sealed quartz tube at 580 °C • AmAs from AmH3 with excess As • For up to 7 days at 400 °C with initial heating up to 675 °C • Evaluated by XRD, AmO observed • AmSb from metals at 630 °C under vacuum • AmBi from Bi vapor and Am metal or hydride • Sealed tubes at 975 °C for 48 hours • Magnetic susceptibilities of compounds measured • Antiferromagnetic transition for AmSb at 13 K

  25. Am carbides and carbonates • Am2C3 • Only known carbide • Arc melting Am metal with graphite • Carbonates of Am(III) • No observed carbonates of Am(IV) or Am(VI) • Am2(CO3)3 from CO2 saturated solution of NaHCO3 • Can also form NaAm(CO3)2 and hydrated carbonates • Am(V) carbonates from precipitation in bicarbonate solutions • MAmO2CO3 • M=K, Ma, Rb, Cs, NH4 • K3AmO2(CO3)2 and K5AmO2(CO3)3 • With large excess K2CO3

  26. Am phosphates and sulfates • AmPO4 precipitates from dilute H3PO4 • Hydrates, dehydrates with heat • Anhydrous at 1000 °C • Am(VI) phosphates • Prepared from pH 3.5 to 4.0 • MAmPO4.xH2O • M=NH4, K, Rb, Cs • Sulfate compounds • Am(III, V, and VI) compounds • Double salts for Am(III) • Am(III) • Evaporation in SO42- solutions forms Am2(SO4)3.8H2O • Variations in hydration • Precipitation in ethanol solution (5 H2O) • Anhydrous when heated 500-600 °C in air • MAm(SO4)2 hydrate, K3Am(SO4)3 hydrate, and M8Am2(SO4)7 hydrate • From metal sulfate to Am solution in 0.5 M H2SO4 • No XRD data • Hydrate of (AmO2)2SO4 from evaporation of Am(V) in H2SO4 • Ozone treatment of Am(III) after addition of H2SO4 • Double salts from H2SO4 with Cs2SO4

  27. Other inorganic Am compounds • Am(III) Keggin-type PW12O403+ • Si from AmF3 and Si up to 950 °C • Am5Si3, AmSi, Am2Si3, and AmSi2 • AmB4 and AmB6 • AmSiO4 from Am(OH4) and excess SiO2 in 1 M NaHCO3 at 230 °C • Other compounds of chromate, tungstate, and molybate observed

  28. Am organic compounds • From precipitation (oxalates) or solution evaporation • Includes non-aqueous chemistry • AmI3 with K2C8H8 in THF • Yields KAm(C8H8)2 • Am halides with molten Be(C5H5) forms Am(C5H5)3 • Purified by fractional sublimation • Characterized by IR and absorption spectra

  29. Am solution chemistry • Oxidation states III-VI in solution • Am(III,V) stable in dilute acid • Am(V, VI) form dioxocations • Am(II) • Unstable, unlike some lanthanides (Yb, Eu, Sm) • Formed from pulse radiolysis • Absorbance at 313 nm • T1/2 of oxidation state 5E-6 seconds • Am(III) • Easy to prepare (metal dissolved in acid, AmO2dissolution) • Pink in mineral acids, yellow in HClO4 when Am is 0.1 M • Am(III) has 9 inner sphere waters • Others have calculated 11 and 10 (XAFS) • Based on fluorescence spectroscopy • Lifetime related to coordination • nH2O=(x/t)-y • x=2.56E-7 s, y=1.43 • Measurement of fluorescence lifetime in H2Oand D2O

  30. Am solution chemistry • Am(IV) • Requires complexation to stabilize • dissolving Am(OH)4 in NH4F • Phosphoric or pyrophosphate (P2O74-) solution with anodic oxidation • Ag3PO4 and (NH4)4S2O8 • Carbonate solution with electrolytic oxidation • Am(V) • Oxidation of Am(III) in near neutral solution • Ozone, hypochlorate (ClO-), peroxydisulfate • Reduction of Am(VI) with bromide • Am(VI) • Oxidation of Am(III) with S2O82- or Ag2+ 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 N2O or S2O82- saturated solution

  31. Am solution chemistry • Thermodynamic data available (NEA data) • Systematic differences at Am • Thermodynamic changes with atomic number • Deviation at Am due to positive entropy of vaporization

  32. Am solution chemistry: Autoreduction • Formation of H2O2 and HO2 radicals from radiation reduces Am to trivalent states • Difference between 241Am and 243Am • Rate decreases with increase acid for perchloric and sulfuric • Some disagreement role of Am concentration • Concentration of Am total or oxidation state • Rates of reduction dependent upon • Acid, acid concentration, • mechanism • Am(VI) to Am(III) can go stepwise • starting ion • Am(V) slower than Am(VI)

  33. Am solution chemistry • Disproportionation • Am(IV) • In nitric and perchloric acid • Second order with Am(IV) • 2 Am(IV)Am(III) + Am(V) • Am(IV) + Am(V)Am(III) + Am(VI) • Am(VI) increases with sulfate • Am(V) • 3-8 M HClO4 and HCl • 3 Am(V) + 4 H+Am(III)+2Am(VI)+2 H2O • Solution can impact oxidation state stability

  34. Am solution chemistry • Redox kinetics • Am(III) oxidation by peroxydisulfate • Oxidation due to thermal decomposition products • SO4.-, HS2O8- • Oxidation to Am(VI) • 0.1 M to 10 nM Am(III) • Acid above 0.3 M limits oxidation • Decomposition of S2O82- • Induction period followed by reduction • Rates dependent upon temperature, [HNO3], [S2O82-], and [Ag+2] • 3/2 S2O82- + Am3++2 H2O3 SO42- +AmO22++4H+ • Evaluation of rate constants can yield 4 due to peroxydisulfate decomposition • In carbonate proceeds through Am(V) • Rate to Am(V) is proportional to oxidant • Am(V) to Am(VI) • Proportional to total Am and oxidant • Inversely proportional to K2CO3

  35. Am solution chemistry: Redox kinetics • Am(VI) reduction • H2O2 in perchlorate is 1st order for peroxide and Am • 2 AmO22++H2O22 AmO2+ + 2 H++ O2 • NpO2+ • 1st order with Am(VI) and Np(V) • k=2.45E4 L / mol s • Oxalic acid reduces to equal molar Am(III) and Am(V) • Am(V) reduction • Reduced to Am(III) in NaOH solutions • Slow reduction with dithionite (Na2S2O4), sulfite (SO32-), or thiourea dioxide ((NH2)2CSO2) • Np(IV) and Np(V) • In both acidic and carbonate conditions • For Np(IV) reaction products either Np(V) or Np(VI) • Depends upon initial relative concentration of Am and Np • U(IV) examined in carbonate

  36. Am solution chemistry • Radiolysis • From alpha decay • 1 mg 241Am release 7E14 eV/s • Reduction of higher valent Am related to dose and electrolyte concentration • In nitric acid need to include role of HNO2 • In perchlorate numerous species produced • Cl2, ClO2, or Cl- • Complexation chemistry • Primarily for Am(III) • F->H2PO4->SCN->NO3->Cl->ClO4- • Hard acid reactions • Electrostatic interactions • Inner sphere and outer sphere • Outer sphere for weaker ligands • Stabilities similar to trivalent lanthanides • Some enhanced stability due to participation of 5f electron in bonding

  37. Am solution chemistry • Hydrolysis • Mono-, di-, and trihydroxide species • Am(V) appears to have 2 species, mono- and dihydroxide • Am hydrolysis (from CHESS database) • Am3++H2OAmOH2++H+: log K =-6.402 • Am3++2H2OAm(OH)2++2H+: log K =-14.11 • Am3++3H2OAm(OH)3+3H+: log K =-25.72 • Carbonate • Evaluated by spectroscopy • Includes mixed species • Am hydroxide carbonate species • Based on solid phase analysis • Am(IV) • Pentacarbonate studied (log b=39.3) • Am(V) solubility examined

  38. Am hydrolysis: 1mM Am3+; pH

  39. 1 mM Am, 0.1 mM carbonate

  40. 1 mM Am, 1 mM carbonate

  41. 1 mM Am, 10 mM carbonate

  42. 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 NaClO4, complexation constant for Am 2 orders greater than Sm

  43. Am solution chemistry • Fluorides • Inner sphere complexes, complexation constants much higher than other halides • 1,1 and 1,2 Am:F complexes identified • Only 1,1 for Cl • Sulfates • 1,1 and 1,2 constants known • No evidence of AmHSO42+ species • Thiocyanate (SCN-) • Useful ligand for Ln/Ac separations • 1,1 to 1,3 complex forms • Examined 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 • AmHPO4+ • Complexation with H2PO4; 1,1 to 1,4 species • From cation exchange, spectroscopic and solvent extraction data

  44. Am(IV) solution chemistry • Am(IV) can be stabilized by heteropolyanions • P2W17O61anion; formation of 1,1 and 1,2 complex • Examined by absorbance at 789 nm and 560 nm • Autoradiolytic reduction • Independent of complex formation • Displacement by addition of Th(IV) • Disproportionation of Am(IV) to Am(III) and Am(VI) • EXAFS used with AmP5W30O11012- • Cation-cation interaction • Am(V)-U(VI) interaction in perchlorate • Am(V) spectroscopic shift from 716-733 nm to 765 nm

  45. Am coordination chemistry • Little known about Am coordination chemistry • 46 compounds examined • XRD and compared to isostructural lanthanide compounds • Structural differences due to presence of oxo groups • Halides • Coordination numbers 7-9, 11 • Coordination include water • AmCl2(H2O)6+ • Outer sphere Cl may be present

  46. Am coordination chemistry • Oxides • Isostructural with Pu oxides • AmO may not be correct • Am(V)=O bond distance of 1.935 Å • Am2O3 has distorted Oh symmetry with Am-O bond distances of 2.774 Å, 2.678 Å, and 1.984

  47. Am coordination chemistry • Am S, Se, and Te species (1,1) • NaCl type structure • Lattice parameter increases with increasing Z • Am N, P, Sb, As (1,1) • Same trends as chalcongenide series • AmSi • Bridging Si atoms and corner sharing AmSi3pyramids • Oxygen donor ligands • Mono- and bidentate bonding with carboxylic acids • Bidentate with carboxylic acid and phenolic group • Am(VI) acetate characterized • Double salt with hexafluoro-acetylacetone (HFA) • EXAFS of one Am nitrate with organic examined • 8-coordinate Am2(SO4)3.8H2O • Similar to anions of MoO4 and IO3 • Distorted AmO8dodecahedron

  48. Am coordination chemistry • Oxygen-donor ligands • Carboxylic acid based ligands • Only single crystal from hydrated salicylicate (1,3 with 1 water) • 9 coordinate • 6 ligands and 1 water • Ligands show different bonding • 4 with monodentate over carboxylic group • 1 bidentate carboxylic • 1 salicylate (1 carboxylic and 1 phenolic) • Am(VI) Na acetate complex: NaAmO2(CH3CO2)3 • Am(V) analogous Cs species (CsAmO2(CH3CO2)3) • Structure based on Np(V) • Bidentate equatorial coordination for ligand

  49. Am coordination chemistry • Single crystals of CsAm(hfa)4 • Recrystallized in butanol • Am(hfa) chains that interact with Cs+ • Am coordinated bidentate to hfa • Am-O bond distance 2.36 Å and 2.45 Å • Degrades to AmF3 within a week