1. Mercury Speciation in Tank Waste at the Savannah River Site
DOE ASP Workshop, Covington, KY September 22, 2016
Mercury Speciation in Tank Waste at the Savannah River Site
Savannah River National Laboratory
Chris Bannochie, Ph.D.
William Wilmarth, Ph.D.
Brooks Applied Labs
Jamie Fox (Presenter)
Michelle Briscoe
Annie Carter
Hakan Gürleyük, Ph.D.

3. The Problem 51 Underground storage tanks exist in the SRS Tank Farms
Inventory of mercury in Tank Farms is between 60,000 and 70,000 kg
350 kg/annual influent from the Canyons
~650 kg/annually through Evaporators and Saltstone
Expected to be purged through DWPF
Safety concerns around evaporators
Formation of organic mercury species

4. The Problem
Prior to 2000, mercury believed to be mainly HgO in sludge and Hg(II) in solution
Soluble concentrations in excess of 100 mg/L
Dimethylmercury identified in evaporator vapor, and methylmercury in the evaporator condensate in late 90’s and early 2000’s
Speciation of mercury in tank waste far more complex than originally expected
Mass balance issues

5. How the Problem is Being Addressed
Many current needs at the Site
Develop protective WAC in Saltstone that is informed by the organomercury chemistry
Refine previous studies on mercury ion exchange
Improve reduction reactions in evaporators
Improve conversion of organomercury species to ionic mercury in the Saltstone feed tank (Tank 50)
Further understanding of Hg vapor chemistry at tank interfaces
Improve mercury recovery in the DWPF process…
ALL REQUIRE BETTER UNDERSTANDING OF MERCURY SPECIATION ACROSS THE TANKS

6. Approach for Recent Study
Mercury Speciation
Triplicate samples from two tanks (plus associated blanks) were collected and diluted >200,000:1 and then analyzed with traditional methodologies.
Cold vapor generation - atomic fluorescence spectroscopy (CV-AFS) based methods for:
Total Hg, Dissolved Hg, Particulate Hg
Total Volatile Hg (includes Elemental Hg & DMeHg)
MeHg and EtHg

7. Approach for Recent Study
Mercury Speciation
In addition, analyze samples for Hg speciation using ICP-MS-based methods to confirm accuracy of CV- AFS methods with tank waste matrix and identify if there are additional organic mercury forms, with the goal of 100% mass balance.
Ion pair chromatography – cold vapor generation – ICP- MS (IP-CV-ICP-MS) for Ionic Hg {Hg(I) & Hg(II)}, MeHg, EtHg, and PhHg
Reversed phase chromatography - ICP-MS for dimethylmercury (DMeHg)

8. Total Hg by CV-AFS Results (ng/L)
Sample ID
Rep 1
Rep 2
Rep 3
Mean
RSD
Tank
409
414
408
410
0.8%
Tank
425
415
419
420
1.2%
Tank
424
Tank 22 Mean
416 ± 6
Tank
1110
1090
1100
1.0%
Tank
1120
1.6%
Tank
1080
1.1%
Tank 38 Mean
1100 ± 10

9. Dissolved Hg by CV-AFS Results (ng/L)
Sample ID
Rep 1
Rep 2
Rep 3
Mean
RSD
Tank
379
401
404
395
3.5%
Tank
392
384
374
383
2.4%
Tank
369
387
380
Tank 22 Mean
386 ± 12
Tank
1010
997
0.7%
Tank
989
996
982
Tank
1020
984
1.8%
Tank 38 Mean
1000 ± 10

10. Traditional CV-AFS speciation
Hg Species Determined by CV-AFS
DMeHg* (ng/L)
TVHg (ng/L)
EtHg (ng/L)
MeHg (ng/L)
Tank 22 Mean
0.023
36.3
 < 0.10
57.0
Tank 22 Std Dev
0.004
1.6  -
3.60
Tank
0.026
35.7
< 0.10
56.3
Tank
0.024
38.2
60.9
Tank
0.018
35.1
53.8
Tank 38 Mean
0.130
186
 < 0.41
514
Tank 38 Std Dev
0.038 8 13
Tank
0.161
180
< 0.41
507
Tank
0.142
183
0.66 B
529
Tank
0.087
195
505
DMeHg – Dimethyl Hg
TVHg – Total Volatile Hg
EtHg – Ethyl Hg
MeHg – Methyl Hg
*DMeHg results possibly false positives due to elemental Hg background
B = Results is less than MRL is should be considered an estimate

11. Dimethyl Hg by CV-AFS
Instrument Blank
Low Calibration Point
Sample

12. Separation by Ion Pair Chromatography Coupled to CV-ICP-MS

13. Dimethyl Hg by RP-ICP-MS
1.07 ng/L

14. Additional Species by RP-ICP-MS
DMeHg – Dimethyl Hg
MeEtHg – Methyl Ethyl Hg
DiEtHg – Diethyl Hg

15. Mass Balance Comparison
Mass Balance (all results in ng/L)
THg
DHg
HgP
DMeHg*
TotVol Hg
EtHg
MeHg
Hg(II)
sum of species
% of THg
TK-22 (AFS)
416 ± 6
386 ± 12
31 ± 13
0.023 ± 0.004
36.3 ± 1.6
< 0.10
57 ± 4
 343¥
436
105
TK-22 (ICP)
< 0.2
 36.3¥
 < 0.6
75.7 ± 3.8
343 ± 6
455
109
TK-38 (AFS)
1099 ± 13
1000 ± 13
99 ± 11
0.130 ± 0.038
186 ± 8
< 0.41
514 ± 13
 314¥
1014 92
TK-38 (ICP)
 186¥
10 ± 0
538 ± 10
314 ± 7
1048 95
* DMeHg results by CVAFS are possibly false positives due to elemental Hg in the samples.
¥ Results were copied from a different method for mass balance calculation purposes

16. Holding Time Study For Dimethyl Hg
How stable is dimethylmercury?
Concern over use of Teflon™ bottles and storage time prior to sample shipment
Study Design:
125-mL Teflon™ bottles filled with reagent water and no headspace
1000 ng/L DMeHg spike
Stored at 4 °C in dark
Analyze aliquots at 3 time intervals ending on 77 days
To account for potential analyte loss during opening of bottles at each time interval, 3 bottles were used

17. Holding Time Study For Dimethyl Hg
Bottle 1 sampled at all 3 time intervals
Bottle 2 sampled at last 2 time intervals
Bottle 3 sampled at end of study

18. Conclusions
Excellent mass balance on both sets of tank waste samples for both CV-AFS and ICP-MS-based methods
IP-CV-ICP-MS method effectively separates and directly quantitates all target non-volatile Hg species
Provides better separation of MeHg and EtHg
RP-ICP-MS method effectively separates dimethyl Hg without elemental Hg interference
Samples for dimethyl Hg as well as other Hg samples should always be collected in glass and sent to the lab immediately following collection

19. The Team at Brooks Applied Labs
Financial Acknowledgments:
Savannah River Remediation, LLC
United States Department of Energy, Office of Environmental Management