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Radiochemistry Ph.D. program at the University of Nevada, Las Vegas

¡Ken Czerwinski!

Harry Reid Center and Department of Chemistry

University of Nevada, Las Vegas

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Outline

• Overview of UNLV Program

• Education

• Research Capabilities Current Projects

• Technetium Chemistry US reactors produce 2 tons of 99Tc annually

Compound synthesis Waste form chemistry

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UNLV Radiochemistry Labs

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Ph.D. Radiochemistry Program

• Developed by Health Physics Department• Chemistry and Health Physics core Required courses in nuclear chemistry,

radiochemistry, laboratory• Initiated Fall 04 Currently 10 graduate students

• Research opportunities for undergraduates, visiting students, and visiting researchers

• Need to develop next generation of radiochemists Nuclear Waste Treatment Homeland Security Environmental Radiochemistry

• Information available at radchem.nevada.edu

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Research Program Concepts• Chemistry based analysis of actinides and radionuclides Interested in chemical species

• Program unified by investigations of chemical behavior

thermodynamics kinetics

utilization of laboratory studies, site observations, and modeling incorporation of results into codes Compare laboratory results to observations

• Research coupled with education program Provide undergraduate and graduate students with

actinide research opportunities

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Experimental Techniques• Evaluate change of actinide species under different

conditions• Spectroscopy

XAFS, UV-Visible, Laser, NMR, EELS• Radiochemical separation and detection• Thermal methods

TGA, DSC• Scattering

Powder XRD• Analytical

ICP-AES, ICP-MS• Microscopy

SEM, TEM

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Modern research facilities at UNLV

• 3 laboratories (HRC) and counting room (Health Physics) Ability to work

with actinides and fission products

Can work with macro amounts of material

• Adding three more radiochemistry laboratories at HRC

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Personnel

• Two professors in Radiochemistry Professor Ken Czerwinski, Chemistry Professor Ralf Sudowe, Health Physics

* Separations Heavy element chemistry,

environmental chemistry New radiochemistry hire in chemistry New organometallic professor

* Tc chemistry• Senior scientists in nuclear science program

Dr. Thomas Hartmann Solid phase analysis

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Student opportunities in Ph.D. program

• Research intensive program Graduate students perform research in the 1st year

• 60 credits beyond undergraduate degree 4 core courses

Nuclear, radiochemistry, detectors, laboratory Other courses based on research interests Laboratory research

• Opportunities at National Laboratories

• Program offers full support for graduate students Stipends, tuition, insurance, fees, travel

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Current Research Projects in Radiochemistry Program• Materials and solid phases

Oxide and nitride fuel research Recent NERI on actinide nitride synthesis

TRISO Fuels Repository and reprocessing chemistry

Actinides in ZrO2-MgO Used as basis of 244Pu targetry for element 114 synthesis

• Separations Fundamental chemistry of U and Pu in the tributylphosphate-nitrate-dodecane system Electrochemical separations of Am and Cm from the lanthanides

Pursuing new direction in room temperature ionic liquids Rapid and automated separations for radionuclide analysis Separation of radionuclides from drinking water

• Environmental behavior Interaction of Bacteria with Actinide Containing Mixed Waste Fate and Transport of Radionuclides at Yucca Mountain

Include impact of bacteria Identification of radionuclides in the environment Pu speciation and behavior at the Nevada Test Site and BOMARC site

• Synthesis and structure Novel Tc compounds

• Funding from DOE-NE, EMSP, DOE-Science, DOE-NSO, DARPA

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Synthesis and Characterization of Quadruple-Bonded Technetium Dimers

Frederic Poineau, Ken Czerwinski, Al Sattelberger

Harry Reid Center

University of Nevada, Las Vegas

Steve Conradson, LANL

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Development of Tc polymer chemistry:

Synthesis and characterization of compound with a Tc-Tc bond

Study of quadruple bonded compound. Use of Tc2X82- as precursor of synthesis. ( complexation,

reduction … )

Fundamental Chemistry of Tc

First study: TcIII2Br8

2- Br4 -[ Tc Tc ]-Br≣ 4

No structural ( distance Tc-Tc and Tc-Br) and speciation ( UV-Vis) data Goal : structural characterization of Tc2Br8

2- and comparison with Tc2Cl82-

Second study: TcIII2(hpp)4Cl2

Tc-hpp compound not synthesized Preliminary result with Re

Cl -[ Tc ≣Tc ]-Cl

4

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Synthetic Route To (n-Bu4N)2Tc2Br8 [Pre-94]

(n-Bu4N)TcO4 (n-Bu4N)TcOCl4

(n-Bu4N)2Tc2Cl8 (n-Bu4N)2Tc2Br8

II

III

IV

TcO2/NH4TcO4

I

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I - Synthesis of (n-Bu4N)TcO4

Starting material not pure ( Mix TcO2/NH4TcO4):

1- Evaporation of mix in NH4OH/H2O2 at 80 ° C

2 - Precipitation in H2O with (n-Bu4N)HSO4

T = 80 ° C, NH4OH / H2O2

(n-Bu4N)HSO4

Starting material (n-Bu4N)TcO4

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II - (n-Bu4N)TcO4 (n-Bu4N)TcOCl4

Reduction of Tc(VII) to Tc(V) by 12 M HCl

(n-Bu4N)TcO4 + 6 HCl (n-Bu4N)TcOCl4 + Cl2 + 3H2O

12 M HCl

(n-Bu4N)TcO4 (n-Bu4N)TcOCl4

T = 0 °C

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III - (n-Bu4N)TcOCl4 (n-Bu4N)2Tc2Cl8

Reduction (1) Tc(V) Tc(III) by (n-Bu4N)BH4 in THF and acidification (2) by 12 M HCl in acetone

1- (n-Bu4N)TcOCl4 + 4 (n-Bu4N)BH4 Brown intermediate

2- Brown intermediate + HCl (n-Bu4N)2Tc2Cl8

(n-Bu4N)BH4, THF

HCl, acetone

(n-Bu4N)TcOCl4(n-Bu4N)2Tc2Cl8

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IV- (n-Bu4N)2Tc2Cl8 (n-Bu4N)2Tc2Br8

Ligand exchange reaction in dichloromethane using HBr gas

(n-Bu4N)2Tc2Cl8 + 8 HBr (Bu4N)2Tc2Br8 + 8 HCl

HBr gas

(n-Bu4N)2Tc2Cl8 (n-Bu4N)2Tc2Br8

Dissolution

Crystallization

T = 30 ° C

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Characterization of Tc2Br82-

1- XAS spectroscopy

2- UV-Vis spectroscopy

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XAS study ( Stanford synchrotron)

XANES Local geometry and oxidation stateEXAFS chemical and structural parameter

- Solid compound mixed with BN

- XAS analysis of (n-Bu4N)2Tc2Br8

- Reference compound : (NH4)TcO4 , (n-Bu4N)TcOCl4 and (n-Bu4N)2Tc2Cl8Sample holder for active material

0

0.5

1

21.01 21.11 21.21 21.31 21.41

Energy (keV)

A.U

XAS spectra of (n-Bu 4 N) 2 Tc2 Br 8

EXAFSXANES

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EXAFS

0

0.01

0.02

0.03

0.04

0.05

0 1 2 3 4 5

R + D (Å)

FT

Ma

g.

____ Exp. Data------- Fit

(n-Bu4N)2Tc2Br8

(n-Bu4N)2Tc2Cl8 Tc-C1l

Tc-Br1

Tc-Tc

Tc-Tc

Tc-Cl2

Tc-Br2

Fig. FT of (n-Bu4N)2Tc2X8 EXAFS spectra. k [ 3, 14 ] Å-1

Tc1Tc0

X1

X1

X1

X1

X2

X2

X2

X2

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Results

(n-Bu4N)2Tc2Br8 Structural parameter

Scattering C.N R (Å) 2 Eo ( eV)

Tc0-Tc1 1.07 2.168 0.0025 5.59

Tc0-Br1 3.71 2.486 0.0021 5.59

Tc0-Br2 3.71 3.701 0.0073 5.59

d (Å) [Tc2Cl8]2- [Tc2Br8]

2-

(Tc-Tc) 2.16 2.17

(Tc-X) 2.34 2.49

Distance Tc-Tc in Tc2Br82- = 2.16 ± 0.02 Å

- No influence of X on d Tc-Tc in Tc2X82-

- Presence of quadruple bond

EXAFS in accordance with the stochiometry Tc2Br82-

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XANES: Pre – edge study

Compound symmetry Orbital mixing Pre edge (NH4)TcO4 Td 4p+4d 21049 eV (n-Bu4N)TcOCl4 C4V 4pz+4d 21047 eV (n-Bu4N)2Tc2Cl8 D4H - - (n-Bu4N)2Tc2Br8 D4H - -

Kedge : transition 1s np

Orbital Mixing (np +nd) :transition permitted = pre edge Mixing depend of symmetry

Pre-edge study in accordance with symmetry D4H

0

0.5

1

1.5

2

2.5

21.01 21.025 21.04 21.055 21.07 21.085 21.1

Energy (keV)

A.U

(n-Bu4N)2Tc2Br8

(n-Bu4N)2Tc2Cl8

(n-Bu4N)TcOCl4

(NH4)TcO4

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-14

-12

-10

-8

-6

-4

-2

0

1 2 3 4 5

Oxidation degree

A) [TcCl2(PMe2Ph)2]2 [Alm-95]

B) (n-Bu4N)2[Tc2Cl8]

C) (n-Bu4N)2[Tc2Br8]

D) TcCl62- [Poi-06 ]

E) (n-Bu4N)[TcOCl4]

A)

B)

C)

D)

E)

D E (

eV

) /

NH

4 [T

cO 4]

Fig . Position of edge absorption /Tc(VII) in function of oxidation degree for (n-Bu4N)2Tc2X8

2- ( X=Cl, Br) , (n-Bu4N)TcOCl4, TcCl62- , [TcCl2(PMe2Ph)2]2

Position of Tc2Br82- in agreement with oxidation degree III

(difference between in Tc2X82- (X=Cl. Br) due to electronegativity of ligand)

XANES : Edge absorption study

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UV-Vis study

Speciation of Tc2Br82- in CH2Cl2

Interpretation of spectra

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0

0.3

0.6

0.9

300 400 500 600 700 800 900

l (nm)

Abs

orba

nce

[Tc2Cl8]2-

[Tc2Br8]2-

Tc2X82- X = Cl X = Br

l (nm) ε (mol-1.l.cm-1) l (nm) ε (mol-1.l.cm-1)

679 1391 729 1147

390 8674 509 4019

487 5007

Fig. UV-Vis Spectra of Tc2X82- ( X = Cl, Br) in CH2Cl2

[Tc2Cl82-] = 0.826. 10-4 M, [Tc2Br8

2-] = 0.678.10-4 M

UV-Vis spectra of Tc2Cl82- in agreement with [Cot-81]

UV-Vis spectra of Tc2Br82- present a band around 730 nm.

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Quadruple bonded compound :- Metal–Metal bond involves : one , two and one orbital.- Presence of : Transition * ( Ex : Re2X8

2-, X = Cl, Br)

- * transition at low energy

Interpretation of the 730 nm Band

OM involved in quadruple bond

Tc2Br82- is quadruple bonded must present the *

Band at 730 nm assigned to *

0

0.3

0.6

0.9

250 350 450 550 650 750 850

l (nm)

Ab

s.

[Re2Cl8]2-

[Re2Br8]2-

*

UV-Vis of Re2X82- ( X=Cl, Br) in CH2Cl2

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Results

New structural and speciation data on Tc2Br82-:

- EXAFS : Tc-Tc = 2.16 Å and Tc-Br = 2.49 Å .

- XANES : position of the edge absorption in accordance with an oxidation degree III

- UV-Vis : Band 730 nm assigned to the d d* transition.

Use of (n-Bu4N)2Tc2X8 for synthesis of new Tc compound

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M2(hpp)4Cl2 ( M = Re,Tc)

42Mo

43Tc ?

44Ru

74W

75Re

76Os

Re2(hpp)4Cl2 [Cot-99]

Preliminary study with Re

Compound with a multiple bond: M26+

Complexation of L-[M-M]-L with hpp ligand.

hpp anion : stabilize the M26+ bond

- compound resistant to chemical attack

Already synthesized for:

Hhpp: 1,3,4,6,7,8-Hexahydro

-2H-Pyrimido[1,2-a]Pyrimidine

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SYNTHESIS [Cot-99]

Ligand exchange reaction in Hhpp melted under Ar

(Bu4N)2Re2Cl8 + 4 Hhpp Re2hpp4Cl2 + 4HCl + 2 (Bu4N)Cl

145 ° C

Hhpp

Air stable and Low solubility(Bu4N)2Re2Cl8

Re2(hpp)4Cl2

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UV-Vis spectroscopy

0

0.25

0.5

0.75

1

240 340 440 540 640 740

l (nm)

Ab

s.

l (nm) ε (mol-1.l.cm-1)

361 16 695

558 900

Spectra of Re2(hpp)4Cl2 exhibits the * transition

Fig. UV-Vis Spectra of [Re2(hpp)4Cl2 ] = 5.2.10-5M in CH2Cl2

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Electrochemical study

Cyclic voltammetry :electro activity domain of Re-hpp system.

-60

-30

0

30

60

90

-400-200020040060080010001200

cu

rren

t (

µ A)

E (mV)

Re(IV)-Re(III) + e- Re(III)-Re(III)

Re(IV)-Re(IV) + e- Re(III) -Re(IV)

System exhibits 3 electro-active species : Re2(hpp)4Cl2, Re2(hpp)4Cl2

+ and Re2(hpp)4Cl22+ [Cot-99]

Fig. CV of [Re2(hpp)4Cl2 ] = 0.005M in CH2Cl2. Scan 300 mV.s-1. (Ref = Ag)

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Tc waste form

• In UREX+1A Tc and U extracted into organic phase UO2TcO7NO3

.2TBP• Treatment of organic stream to produce pure U waste

Ease waste disposal• Need to separate Tc from U and create suitable waste

form Anion exchange

Separation of TcO4- from UO2

2+

Zr-Tc waste form Need to form metallic Tc Pyrolysis/steam reforming of Tc loaded resin

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Anion exchange of Tc

• Dowex Marathon, Reillex TGA under Ar to

evaluate resin properties

Mass loss above 400º C

• Evaluate Tc sorption in batch test 10 mL of 0.01 M HNO3

100 mg resin

0.00

20.00

40.00

60.00

80.00

100.00

0 200 400 600 800 1000

Dowex MarathonReillex

% M

as

s

T (oC)

11 mg Doxew Marathon15 mg ReillexUnder Ar

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Tc sorption

0.00

1.00 10-6

2.00 10-6

3.00 10-6

4.00 10-6

5.00 10-6

6.00 10-6

7.00 10-6

8.00 10-6

0 100 200 300 400 500

tc kin res data

Dowex [Tc] MReillex [Tc] M

[Tc]

M in

sol

utio

n

time (min)

8E-6 M TcO4-, 0.01 M HNO3,

100 mg resin, 10 mL

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Sorption results

• TcO4- sorbs to resins at different rates

Both suitable• Form metal

Heating under Ar 450 ºC, then 750 ºC

* Reduction in mass, but could not determine if metal formed by XRD

Steam reforming Increase to 900 ºC with water in Ar gas stream

* H2O + C CO + H2

Formed metallic Tc

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Tc metalDowEx 6 h 900°C HR 07-21-06.raw:1

2Th Degrees11511010510095908580757065605550454035302520

Sq

rt(C

ou

nts

)

400

380

360

340

320

300

280

260

240

220

200

180

160

140

120

100

80

60

40

20

0

-20

-40

Silicon SRM 640c 42.59 %Technetium Metal SG P63/mmc 57.41 %

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Tc Metal

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Results

• Sorption of Tc to resin• Able to synthesize metal• Next step

Perform on column with U in solution Synthesize metal Make Zr-Tc solid

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Program overview

• Variety of projects involving actinide chemistry and radiochemistry Solid phase Solution phase Environmental Synthesis and characterization

• Educational program centered on radiochemistry

• Opportunity to learn a variety of techniques

• Interaction with DOE and international laboratories