

Studies at ANL for process separation of Am Amide extractants



(R

 

1 ,R 2 )N-C(O)-CR 3 H-C(O)-N(R Diamide extractant Basis of DIAMEX process 1 R 2 )



N,N’-dimethyl-N,N’-dibutyl-2-tetradecyl-malonamide (DMDBTDMA)



DIAMEX with ligand in dodecane with 3-4 M HNO

*

Selective extraction over Nd 3

15-13

• • • •

Am/Ln solvent extraction

Extraction reaction



Am H +



3+ +2(HA) 2



AmA Cyanex 301 stable in acid



HCl, H 2 SO 4 , HNO 3 3 HA+3 Release of protons upon complexation requires pH adjustment to achieve extraction

*

Maintain pH greater than 3



Below 2 M Irradiation produces acids and phosphorus compounds



Problematic extractions when dosed 10 4 to 10 5 gray New dithiophosphinic acid less sensitive to acid concentration



R 2 PSSH; R=C 6 H 4 , CH 3 C 6 6 H H 4 5 , ClC 6 H 4 ,

  

Only synergistic extractions with, TBP, TOPO, or tributylphosphine oxide Aqueous phase 0.1-1 M HNO 3 Increased radiation resistance

Distribution ratios of Am(III ) and Ln(III ) in 1.0 M Cyanex 301‐heptane (16 mol% of Cyanex 301 neutralized before extraction contacts) 15-14

• • • •

Ion exchange separation Am from Cm

LiCl with ion exchange achieves separation from lanthanide Separation of tracer level Am and Cm has been performed with displacement complexing chromatography



DTPA and nitrilotriacetic acid in presence of Cd and Zn as competing cations



displacement complexing chromatography method is not suitable for large scale Ion exchange has been used to separate trace levels of Cm from Am



Am, Cm, and lanthanides sorbed to a cation exchange resin at pH 2



Separation of Cm from Am was performed with 0.01 % ethylenediamine tetramethylphosphonic acid at pH 3.4 in 0.1 M NaNO 3



separation factor of 1.4

Separation of gram scale quantities of Am and Cm by cation and anion exchange



use of acid

 a *

-hydroxylisobutyrate or diethylenetriaminepentaacetic acid as an eluting agent or a variation of eluant composition by addition of methanol to nitric best separations were achieved under high pressure conditions separation factors greater than 400

Distribution coefficients of actinides and lanthanides into Dowex 1 8 resin from 10 M LiCl 15-15

•

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 (Eichrom)

* *

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

15-16

• •

Am separation and purification

Precipitation method



Formation of insoluble Am species



AmF 3 , K 8 Am 2 (SO 4 ) 7 , Am 2 (C 2 O 4 ) 3 , K 3 AmO 2 (CO 3 ) 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 K 2 S 2 O 8 Pyrochemical process



Am from Pu



O 2 in molten salt, PuO 2 and precipitation of Cm(III) forms and precipitates

 

Partitioning of Am between liquid Bi or Al and molten salts

*

K d of 2 for Al system Separation of Am from PuF 4

*

Formation of PuF 6 in salt by addition of OF , volatility separation 2

15-17

• • • • • • •

CHEM 312: Lecture 15 Americium and Curium Chemistry

• •

Readings: Am and Cm chemistry chapters



Link on web page Combined due to similar chemical properties of elements



Cover Am then Cm Nuclear properties Production of isotopes Separation and purification Metallic state Compounds Solution chemistry Coordination chemistry

15-18

• • • • • • •

CHEM 312: Lecture 15 Americium and Curium Chemistry Part 2

• •

Readings: Am and Cm chemistry chapters



Link on web page Combined due to similar chemical properties of elements



Cover Am then Cm Nuclear properties Production of isotopes Separation and purification Metallic state Compounds Solution chemistry Coordination chemistry

15-19

Am metal and alloys

• • •

Preparation of Am metal

   

Reduction of AmF 3 Reduction of AmO 2 with Ba or Li with La Bomb reduction of AmF 3 with Ca Decomposition of Pt 5 Am



1550 °C at 10 -6 torr La or Th reduction of AmO 2 with



distillation of Am Metal properties



Ductile, non-magnetic

 

(dhcp) and fcc temperature and melting point at 1170

 

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 Alloys investigated with 23 different elements



Phase diagrams available for Np, Pu, and U alloys

15-20

• • • • • •

Am compounds: Oxides and Hydroxides

AmO, Am 2 O 3 , AmO 2



Non-stoichiometric phases between Am 2 O 3 and AmO 2 AmO lattice parameters varied in experiments



4.95 Å and 5.045 Å



Am 2 O 3

  

Difficulty in stabilizing divalent Am Prepared in H Oxidizes in air Phase transitions with temperature

 

2 at 600 °C bcc to monoclinic between 460 °C and 650 °C Monoclinic to hexagonal between 800 °C and 900 °C AmO 2

  

°C to 800 °C Crystalline Am(OH) 3 2 from 600 fcc lattice



Expands due to radiation damage Higher oxidation states can be stabilized



Cs 2 AmO 4 and Ba 3 AmO 6 Am hydroxide



Isostructural with Nd hydroxides can be formed, but



damage



Complete degradation in 5 months Am(OH) 3 +3H + ,



Am 3+ +3H 2 O

 

logK=15.2 for crystalline Log K=17.0 for amorphous

15-21

• •

Am organic compounds

From precipitation (oxalates) or solution evaporation Includes non-aqueous chemistry



AmI 3 with K 2 C 8 H 8 in THF

 

Yields KAm(C 8 H 8 ) 2 Am halides with molten Be(C 5 H 5 ) forms Am(C 5 H 5 ) 3



Purified by fractional sublimation



Characterized by IR and absorption spectra

15-22

• •

Am coordination chemistry

Little known about Am coordination chemistry



46 compounds examined

 

Halides



Coordination numbers 7-9, 11



XRD and compared to isostructural lanthanide compounds Structural differences due to presence of oxo groups in oxidized Am Coordination include water



AmCl

*

2 (H 2 O) 6 + Outer sphere Cl may be present

15-23

Am coordination chemistry

•

Oxides



Isostructural with Pu oxides



AmO may not be correct

 

Am(V)=O bond distance of 1.935 Å Am 2 O 3 has distorted O h symmetry with Am-O bond distances of 2.774 Å, 2.678 Å, and 1.984

15-24

• •

Am coordination chemistry

Cyclopentadienyl (CP) ligands



Am(C 5 H 5 ) 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(C 8 H 8 ) 2



In THF with 2 coordinating solvent ligands

 

Decomposes in water, burns in air XRD shows 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

15-25

• • • •

Curium: Nuclear properties

Isotopes from mass 237 to 251 242 Cm, t 1/2 =163 d



122 W/g



Grams of oxide glows



Low flux of of 242 241 Am target decrease fission Am, increase yield of 242 Cm 244 Cm, t 1/2 =18.1 a



2.8 W/g 248 Cm, t 1/2 = 3.48E5 a



8.39% SF yield

 

Limits quantities to 10 20 mg Target for production of transactinide elements

15-26

• • • •

Cm Production

From successive neutron capture of higher Pu isotopes



242 Pu+n



243 Pu (

b

, 4.95 h)



243 Am+n



244 Am (

b

, 10.1 h)



244 Cm



Favors production of



Isotopes above 244 244,246,248 Cm to Cm 247 Cm are not isotopically pure



Pure 248 Cm available from alpha decay of 252 Cf Large campaign to product Cm from kilos of Pu 244 Cm separation

 

Dissolve target in HNO 3 and remove Pu by solvent extraction Am/Cm chlorides extracted with tertiary amines from 11 M LiCl in weak acid

 

Back extracted into 7 M HCl Am oxidation and precipitation of Am(V) carbonate Other methods for Cm purification included NaOH, HDEHP, and EDTA



Discussed for Am

15-27

• • • • •

Cm aqueous chemistry

Trivalent Cm 242 Cm at 1g/L will boil 9 coordinating H 2 O from fluorescence

  

Decreases above 5 M HCl 7 waters at 11 M HCl In HNO



3 steady decrease from 0 to 13 M 5 waters at 13 M



Stronger complexation with NO 3 Inorganic complexes similar to data for Am



Many constants determined by TRLFS Hydrolysis constants (Cm 3+ +H 2 O



CmOH 2+ +H + )

 

K 11 =1.2E-6 Evaluated under different ionic strength

15-28

• • •

Cm atomic and spectroscopic data

Cm(III) absorbance



Weak absorption in near-violet region



Solution absorbance shifted 20-30 Å compared to solid



Reduction of intensity in solid due to high symmetry

*

f-f transitions are symmetry forbidden



Spin-orbit coupling acts to reduce transition energies when compared to lanthanides Cm(IV) absorbance



Prepared from dissolution of CmF 4



CmF 3 under strong fluorination conditions 5f 7



has enhanced stability Half filled orbital

 

Large oxidation potential for III



IV Cm(IV) is metastable

15-29

Absorption and fluorescence process of Cm

3 + Optical Spectra 30 Fluorescence Process 20 H G F Emissionless Relaxation A 7/2 10 Excitation Fluorescence Emission 15-30 0 Z 7/2

Cm fluorescence

•

Fluoresce from 595-613 nm



6 Attributed to D 7/2



8 S 7/2 transition



Energy dependent upon coordination environment



Speciation



Hydration



complexation constants

15-31

• • •

Cm separation and purification: Similar to Am

Solvent extraction



Organic phosphates



Function of ligand structure

*

Mixed with 6 to 8 carbon chain better than TBP

 

HDEHP



From HNO 3 and LiCl CMPO



Oxidation state based removal with different stripping agent



Extraction of Cm from carbonate and hydroxide solutions, need to keep metal ions in solution



Organics with quaternary ammonium bases, primary amines, alkylpyrocatechols, -diketones, phenols Ion exchange



Anion exchange with HCl, LiCl, and HNO 3

 

Precipitation



Separation from higher valent Am



10 g/L solution in base

 

Includes aqueous/alcohol mixtures Formation of CmCl

*

4 at 14 M LiCl From fluorescence spectroscopy Precipitation of K 5 AmO 2 (CO 3 ) 3 at 85 °C Precipitation of Cm with hydroxide, oxalate, or fluoride

15-32

• • •

Cm metallic state

Preparation of Cm metal



CmF 3 reduction with Ba or Li

 

Dry, O 2 free, and above 1600 K Reduction of CmO in MgF 2 /MgCl 2 2 with Mg-Zn alloy Melting point 1345 °C



Higher than lighter actinides Np-Am



Similar to Gd (1312 °C) Two states



Double hexagonal close-packed (dhcp)



Neutron diffraction down to 5 K

 

No structure change fcc at higher temperature

• • • •

XRD studies on 248 Cm Magnetic susceptibility studies



Antiferrimagnetic transition near 65 K



200 K for fcc phase Metal susceptible to corrosion due to self heating



Formation of oxide on surface Alloys

 

Cm-Pu phase diagram studied Noble metal compounds



CmO 2 and H 2 heated to 1500 K in Pt, Ir, or Rh

*

Pt Rh 5 3 Cm, Pt Cm 2 Cm, Ir 2 Cm, Pd 3 Cm,

15-33

• • •

Cm oxide compounds

Cm 2 O 3

 

Thermal decomposition of CmO Mn



2 O 3 type cubic lattice damage Monoclinic at 800 °C 2 at 600 °C and 10 -4 torr Transforms to hexagonal structure due to radiation

 

CmO 2



Heating in air, thermal treatment of Cm loaded resin, heating Cm 2 O 3 at 600 °C under O 2 , heating of Cm oxalate Shown to form in O 2 as low as 400 °C at lower temperature

   

Evidence of CmO 1.95

fcc structure Magnetic data indicates paramagnetic moment attributed to Cm(III)



Need to re-evaluate electronic ground state in oxides Oxides



Similar to oxides of Pu, Pr, and Tb



Basis of phase diagram BaCmO

 

3 and Cm 2 CuO 4 Based on high T superconductors Cm compounds do not conduct

15-34

• • • •

Cm compounds

Cm(OH) 3

 

Cm 2 (C 2 O 4 ) 3 .

10H 2 O

 

From aqueous solution, crystallized by aging in water Same structure as La(OH) 3 ; hexagonal From aqueous solution Stepwise dehydration when heated under He



Anhydrous at 280 °C



Converts to carbonate above 360 °C

*

TGA analysis showed release of water (starting at 145 °C) Converts to Cm 2 O 3 around 500 °C



Cm(NO 3 ) 3

 

Evaporation of Cm in nitric acid From TGA, decomposition same under O 2 and He Dehydration up 180 °C, melting at 400 °C

  

Final product CmO 2 Oxidation of Cm during decomposition Organometallics



Studies hampered by radiolytic properties of Cm



Some compounds similar to Am

 

Cm(C 5 H 5 ) 3 form CmCl 3 and Be(C Weak covalency of compound 5 H 5 ) 2



Strong fluorescence

15-35

Review

• • • • •

Production and purification of Am and Cm isotopes



Suitable reactions



Basis of separations from other actinides Formation of Am and Cm 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

15-36

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?

15-37

Questions

• • • • •

Which Cm isotopes are available for chemical studies?

Describe the fluorescence process for Cm



What is a good excitation wavelength?

What methods can be use to separate Cm from Am?

How many states does Cm metal have? What is its melting point?

What are the binary oxides of Cm? Which will form upon heating in normal atmosphere?

15-38

Questions

• •

Comment on blog Provide response to PDF Quiz 15

15-39