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
9-1
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
9-2
Production of Am isotopes
•
241,243Am




•
241Am





•
•
main isotopes of interest
Long half-lives
Produced in kilogram quantity
Chemical studies
Both isotopes produced in reactor
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?
9-3
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)
9-4
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
• Dibutyl butylphosphonate (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
9-5
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
HDEHP
* Bis(2-ethyl-hexyl)phosphoric acid (HDEHP)
* HNO3
* DTPA
* Lactic acid
9-6
Am solvent extraction
• Bis(2-ethylhexyl)phosphoric acid (HDEHP)
 TALSPEAK
 Lactic acid prevents solid precipitates
 Separation of Am(VI) from Cm(III)
* 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
9-7
Am solvent extraction
•
•
Dihexyl-N,N-diethylcarbamoylmethyl phosphonate (DHDECMP)

Extraction of Am(IV,VI)

Good for trivalents
 Removal of all actinides

Formation of 3rd phase, 20-30 % in diluent
CMPO
 Change diluent (branched, aromatic)
 Addition of TBP

Removal of Am with 0.01 M HNO3
octyl(phenyl)-N, N-dibutyl carbamoylmethyl 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
9-8
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 tetramethylammonium hydroxide
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
9-9

Issues with solvent from degradation
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)
 Diamide extractant
 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
9-10
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 Df of 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
9-11
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 (2,4,4trimethylpentyl)dithiophosphinic acid
9-12
•
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
9-13
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
9-14
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
9-15
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
9-16
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
(10.1107/S0567739476001551)
•
•
Ion
CN
IR (Å)
•
Am2+
6
1.21
•
Am2+
8
1.26
Am3+
6
0.975
Am3+
8
1.09
Am4+
6
0.85
Am4+
8
0.95
•
Ionization potentials

1st potential at 5.9738 eV
 From resonance ionization mass
spectroscopy
* Calculated rd1st: 5.66 eV, 2nd:
12.15 eV, 3 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
* 234AmF
3 at 55 mm/s compared
to 243AmO
2
Emission spectra

Am ground state 48767 cm-1
9-17
9-18
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 10-6 torr

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
9-19
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
9-20
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 20.2 M NaOH with NaOCl or 7 M KOH
with peroxydisulfate (S2O8 )

Suggested precipitation of AmO2OH in slightly basic concentrated NaCl

Stable LiAmO2(OH)2 formed
Am hydrides

AmH2+x isostructural with Np and Pu hydrides

Fcc phase
9-21

From hydrogen and metal
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 Rb salt
Am(V) halides

KAmO2F2 and RbAmO2F2

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)
9-22
 Reaction of AmF3 with KrF2 in anhydrous HF
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-Am2S3 forms 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
9-23
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
9-24
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
9-25
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
9-26
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
molybdate observed
9-27
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
9-28
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)
 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, AmO2 dissolution)
 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
9-29
 Measurement of fluorescence lifetime in H2O and
D2O
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
9-30
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
9-31
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)
9-32
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
9-33
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
9-34
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
9-35
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 ClComplexation 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
9-36
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
9-37
Am hydrolysis: 1mM Am3+
1 mM Am, 1 mM carbonate
1 mM Am, 0.1 mM carbonate
1 mM Am, 10 mM carbonate
9-38
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(2pyridylmethyl)ethyleneamine)

0.1 M NaClO4, complexation
constant for Am 2 orders
greater than Sm
9-39
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
9-40
Am(IV) solution chemistry
• Am(IV) can be stabilized by heteropolyanions

P2W17O61 anion; 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
9-41
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
9-42
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
9-43
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 AmSi3 pyramids
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 AmO8 dodecahedron
9-44
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
9-45
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
9-46
Am coordination chemistry
•
•
•
EXAFS of Am(NO3)3TEMA2

TEMA= N,N,N,N’-tetraethylmalonamide

Similar to Nd coordination
 10 coordinate, 2.52 Å bond distance
Gas phase organics

No structural information, information on organometallic reactions

Laser ablated Am with alcohols
 Formation RO- species as mono- or divalent cationic species
 Other laser ablation studies
* Polyimides, nitriles (RCN), butylamines
* Am forms Am2+
 Not observed with other actinides

Reaction with dimethylether
 Am(OCH3)+
Few complexes with Nitrogen and Sulfur donors

XAFS studies used to examine bond distances and coordination
9-47
Am coordination chemistry
•
•
CP ligands

Am(C5H5)3
 Isostructural with Pu(III) species
* Not pyrophoric
 Absorbance on films examined
* Evaluated 2.8 % relative bond covalency
* Indicates highly ionic bonding for species
* Data used for calculations and discussion of 5f and 6d orbitals
in interactions
Bis-cyclooctatetraenyl Am(III) KAm(C8H8)2

In THF with 2 coordinating solvent ligands

Decomposes in water, burns in air

XRD show the compound to be isostructural with Pu and Np
compounds
 From laser ablation mass spectra studies, examination of
molecular products
 Differences observed when compared to Pu and Np compounds
 Am 5f electrons too inert to form sigma bonds with organic, do not
participate
9-48
Solution absorption spectroscopy
• Am(III)
 7F05L6 at 503.2-1nm
(e=410 L mol cm )
 Shifts in band position
and molar absorbance
indicates changes in
water or ligand
coordination
 Solution spectroscopy
compared to Am
doped in crystals
 Absorbance measured
in acids and carbonate
• Am(IV)
 In acidic media, broad
absorption bands
 13 M HF, 12 M
KF, 12 M H3PO4
 Resembles solid AmF4
spectrum

See:
http://dx.doi.org/10.1063/1.1698619
9-49
Solution absorption spectroscopy
• Am(V)
 5I43G5; 513.7 nm; 45 L
mol cm-1
 5I43I7; 716.7 nm; 60 L
mol cm-1
 Collected in acid,
NaCl, and carbonate
• Am(VI)
 996 nm; 100 L mol cm-1
 Smaller absorbance at
666 nm
 Comparable to
position in Am(V)
 Based on comparison
with uranyl, permits
analysis based on
uranyl core with
addition of electrons
9-50
Solution absorption spectroscopy
•
•
Am(VII)

Broad absorbance at 740 nm
Am(III) luminescence
7F 5L at 503 nm

0
6
 Then conversion to other excited state

Emission to 7FJ
5D 7F at 685 nm

1
1
5D 7F at 836 nm

1
2

Lifetime for aquo ion is 20 ns
 155 ns in D2O

Emission and lifetime changes with speciation
 Am triscarbonate lifetime = 34.5 ns, emission at 693 nm
9-51
Am spectroscopy
• Vibrational
 AmO2+
 Antisymmetric vibration in solids at 802 cm-1
 Raman of Am(III) phosphate
 Symmetric stretch of PO43- at 973 cm-1
 PO3- groups at 1195 cm-1
• X-ray absorption
 Absorption edge at 18504 eV
 4 eV difference between Am(IV) and Am(III)
9-52
Review
• Production and purification of Am isotopes
 Suitable reactions
 Basis of separations from other actinides
• Formation of Am metallic state and properties
 Number of phases, melting points
• Compounds
 Range of compounds, limitations on data
• Solution chemistry
 Oxidation states
• Coordination chemistry
 Organic chemistry reactions
• Analytical Chemistry
 Radiochemical and other techniques
9-53
Questions
• What is the longest lived isotope of Am?
• Which Am isotope has the highest neutron induced
fission cross section?
• What are 3 ligands used in the separation of Am?
 What are the solution conditions?
• What column methods are useful for separating Am
from the lanthanides?
• Which compounds can be made by elemental reactions
with Am?
• What Am coordination compounds have been
produced?
• What is the absorbance spectra of Am for the different
oxidation states?
• How can Am be detected?
9-54
Pop Quiz
• How can high valent oxidation states of Am be
formed?
9-55