# Presentation: 476754

## 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

## Outline

**Overview of UNLV Program**
**Education**
**Research**
**Capabilities**
**Current Projects**
**Technetium Chemistry**
**US reactors produce 2 tons of ****99****Tc annually**
**Compound synthesis**
**Waste form chemistry**

## UNLV Radiochemistry Labs

## 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**

## 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**

## 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**

## 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**

## 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**

## Student opportunities in Ph.D. program

**Research intensive program**
**Graduate students perform research in the 1****st**** 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**

## 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 ZrO****2****-MgO**
**Used as basis of ****244****Pu 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**

## 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

## 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 ... )

**Synthesis and characterization of compound with a Tc-Tc bond**
****** ****Study of quadruple bonded compound. Use of Tc****2****X****8****2-**** as precursor of synthesis. ( complexation, reduction ... )**

**Fundamental Chemistry of Tc**

_**First study**_**: Tc****III****2****Br****8****2-****                   ****Br****4**** -[ Tc≣Tc ]-Br****4****  **
-  No structural ( distance Tc-Tc and Tc-Br) and speciation ( UV-Vis) data
-  Goal : structural characterization of Tc2Br82- and comparison with Tc2Cl82-
_**Second study**_**: Tc****III****2****(hpp)****4****Cl****2****   **
**    **
-  Tc-hpp compound not synthesized
-  Preliminary result with Re

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

- (n-Bu4N)TcO4

**      ****(n-Bu****4****N)TcOCl****4**

** ****(n-Bu****4****N)****2****Tc****2****Cl****8**

** ****(n-Bu****4****N)****2****Tc****2****Br****8**

**II**

**III**

**IV**

**TcO****2****/NH****4****TcO****4**

**I**

##  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, NH****4****OH / H****2****O****2**

**  ****(n-Bu****4****N)HSO****4**

**Starting material**

**(n-Bu****4****N)TcO****4**

## 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-Bu****4****N)TcO****4**

**(n-Bu****4****N)TcOCl****4**

**T = 0 ****°****C**

## 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-Bu****4****N)BH****4****, THF**

**HCl, acetone**

**(n-Bu****4****N)TcOCl****4**

**(n-Bu****4****N)****2****Tc****2****Cl****8**

## 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-Bu****4****N)****2****Tc****2****Cl****8**

**(n-Bu****4****N)****2****Tc****2****Br****8**

- Dissolution

- Crystallization

**T = 30 ****° C**

## Characterization of Tc2Br82- 

- 1- XAS  spectroscopy
- 2- UV-Vis spectroscopy**                       **

## XAS study ( Stanford synchrotron)

**XANES**   Local geometry and oxidation state
**EXAFS**   chemical and structural parameter

**- Solid compound mixed with BN**
**- XAS analysis of (n-Bu****4****N)****2****Tc****2****Br****8**
**- Reference compound : (NH****4****)TcO****4**** ,  **
**(n-Bu****4****N)TcOCl****4**** and (n-Bu****4****N)****2****Tc****2****Cl****8**

***Sample holder for active material***** **

## EXAFS

***Fig. FT of (n-Bu******4******N)******2******Tc******2******X******8****** ******EXAFS spectra.  k ******[ 3, 14 ] Å******-1***** **

## 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 Tc**_**2**_**Br**_**8**_**2-**__** = 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 Tc_2_Br_82-

## XANES: Pre – edge study 

**K****edge**** : transition 1s ******** np**
_**Orbital Mixing (np +nd) :**_
**transition permitted = pre edge**
** **
**Mixing depend of symmetry**

****** ****Pre-edge study in accordance with symmetry D****4H**

## XANES : Edge absorption study

***Fig . Position of  edge absorption /Tc(VII) in function of oxidation degree for  (n-Bu******4******N)******2******Tc******2******X******8******2-****** ( X=Cl, ******Br******) , (n-Bu******4******N)TcOCl******4******,  TcCl******6******2-****** , [TcCl******2******(PMe2Ph)******2******]******2***
**Position of Tc****2****Br****8****2-**** in agreement with oxidation degree III**
- (difference between in Tc2X82-  (X=Cl. Br) due to electronegativity of ligand)

**XANES : Edge absorption study**

## UV-Vis study

- Speciation of Tc2Br82- in CH2Cl2
- Interpretation of spectra

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

| Tc2X82- | X = Cl |  | X = Br |  |
| --- | --- | --- | --- | --- |
|  |  (nm) | ε (mol-1.l.cm-1) |  (nm) | ε (mol-1.l.cm-1) |
|  | 679 | 1391 | 729 | 1147 |
|  | 390 | 8674 | 509 | 4019 |
|  |  |  | 487 | 5007 |

***Fig. UV-Vis Spectra of Tc******2******X******8******2- ******( X = Cl, ******Br******) in CH******2******Cl******2***
***[Tc******2******Cl******8******2-******] = 0.826. 10******-4****** M, [Tc******2******Br******8******2-******] = 0.678.10******-4****** M***

****** ****UV-Vis spectra of Tc****2****Cl****8****2-**** in agreement  with ****[Cot-81]**
****** ****UV-Vis spectra of Tc****2****Br****8****2-**** present a band around 730 nm.**

## Interpretation of the 730 nm Band

**Quadruple bonded compound :**
- - Metal–Metal bond involves  : one , two  and one  orbital.
-  Presence of  :  Transition  * ( Ex : Re2X82-, X = Cl, Br)
- -  * transition at low energy

**Interpretation of the 730 nm Band**

***OM  involved in quadruple bond***

**Tc****2****Br****8****2-**** is quadruple bonded must present the ******** ******** ***********
-    Band  at 730 nm assigned to   *

***UV-Vis of Re******2******X******8******2-******  ( X=Cl, Br) in CH******2******Cl******2***

## Results

- _New  structural and speciation data on Tc_2_Br_82-**:**
**- ****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-Bu****4****N)****2****Tc****2****X****8** **for synthesis of new Tc compound**

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

| 42
Mo | 43
Tc ? | 44
Ru |
| --- | --- | --- |
| 74
W | 75
Re | 76
Os |

*Re**2**(hpp)**4**Cl**2 ****[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-**H**exahydro
- -2***H***-**P**yrimido[1,2-*a*]**P**yrimidine

## 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**

**(Bu****4****N)****2****Re****2****Cl****8**

**Re****2****(hpp)****4****Cl****2**

## UV-Vis spectroscopy

|  (nm) | ε (mol-1.l.cm-1) |
| --- | --- |
| 361 | 16 695 |
| 558 | 900 |

****** ****Spectra of Re****2****(hpp)****4****Cl****2**** exhibits the ******** ******** ********* transition**

***Fig. UV-Vis Spectra of  [Re******2******(hpp)******4******Cl******2*** ***]***** *****= 5.2.10******-5******M*** ***in CH******2******Cl******2***

## Electrochemical study

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

****** ****System exhibits 3 electro-active species :**
**     ****Re****2****(hpp)****4****Cl****2****, Re****2****(hpp)****4****Cl****2****+**** and Re****2****(hpp)****4****Cl****2****2+ [Cot-99]**

***Fig. CV of [Re******2******(hpp)******4******Cl******2 ******]****** ******=****** ******0.005M in CH******2******Cl******2******. Scan 300 mV.s******-1******. (Ref = Ag) ***

## Tc waste form

**In UREX+1A**
**Tc and U extracted into organic phase**
**UO****2****TcO****7****NO****3****.****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 TcO****4****-**** from UO****2****2+**
**Zr-Tc waste form**
**Need to form metallic Tc**
**Pyrolysis/steam reforming of Tc loaded resin**

## 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 HNO****3 **
**100 mg resin**

## Tc sorption

- 8E-6 M TcO4-, 0.01 M HNO3, 100 mg resin, 10 mL

## Sorption results

**TcO****4****-**** 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**
**H****2****O + C ******** CO + H****2**
**Formed metallic Tc**

## Tc metal

## Tc Metal

## 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**

## 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**