Applications of Extraction Chromatography in Marine Geochemistry
Bill BurnettDepartment of OceanographyFlorida State University
Acknowledgments
FSU: Mike Schultz, Reide Corbett, Peter Cable, Jaye Cable, Mike Lambert, Jamie Christoff, Guebuem Kim, Christine Andre
GEL: James Westmoreland, Richard Kinney, Barry Stewart
IAEA (MEL): Pavel Povinic, Jerry LaRosa
Eichrom: Mike Fern, Larry Jassin, Anil Thakkar, Michaela Langer
PG Research Foundation: Phil Horwitz
U-Series Disequilibrium in the Sea
238U ~ 3.2 g/L
230Th
226Ra
Seawater
Sediments
238U 234U
237 271
230Th 226Ra
<1 ~10dpm/100L:
(231Pa, 210Pb, etc.)
~50
222Rn 210Pb222Rn 222Rn
Example Applications
U-series (230Th/234U, etc.) dating of fossil corals: sea level, uplift studies, etc.
U-series dating of biogenic materials and sea-floor minerals: ages, growth rates & directions
Sediment accumulation rates (230Th, 210Pb, etc.)
Tracing groundwater flow into the ocean via natural Ra isotopes (226Ra, 228Ra, etc.)
Analytical Challenges for Environmental SamplesComplex and variable matrices, e.g.,
seawater, sediment, fish, Mn nodules, etc. — methods must be versatile
Very low abundance of certain nuclides — yields must be high
Many U/Th-series nuclides are characterized by similar alpha decay energies — separations must be complete
Eichrom Technologies, Inc.
Eichrom
AnilPhil Larry Mike
Development of an idea at Eichrom Technologies, Inc...
PHIL...“Phil Has Ideas that Last”
Phil Bill
“Bill…you need to use extraction chromatography
to make your life easier”
Distribution of Ocean-Floor Phosphorites
MODERN
AREA OF UPWELLING
RELICT
UNDIFFERENTIATEDX
XX
fsu
U-Series Dating
0.0
0.2
0.4
0.6
0.8
1.0
0 50 100 150 200 250
Age (103 yrs)
230Th/234U
231Pa/235U
231Pa235U
=1−e−λ 231t
230Th234U
= 1−e−λ230t( )+ λ230
λ230 −λ234
234U238U
⏐
⏐ ⏐
⏐
↵ √
o
−1⏐
⏐ ⏐ ⏐
⏐
⏐ ⏐ ⏐
e−λ234t −e−λ230t( )
“Phil, how can we do this separation…”
“Bill, when is FSU going to play a real football team?”
Phil Bill
U/Th/Pa Method
1/2
34
5
6
56 Th
U/Pa
.
1-4 (discard)
2M HNO3
9M HCl4M HCl
1M HCl
0.1M HCl - 0.1M HF
(~90-95%)
Resin
TRURecent results have shown that Pa may be
effectively isolated from U and Th on
TRU.Resin alone.
Burnett and Yeh, 1995cation exchange
Pa-231 Alpha Spectrum
Pa-231 is determined via low-level alpha-particle spectrometry after separation by extraction chromatographic resins.
0
20
40
60
80
4 5 6 7
Energy (MeV)
231Pa
Groundwater Discharge into the Coastal Zone
Naturally-occurring radium isotopes are useful for tracing groundwater flow into the coastal ocean.
224Ra, 228Ra, 226Ra, 222Rn
226Ra224Ra, 228Ra
226Ra
224Ra 228Ra
Naturally-Occurring Radium Isotopes
Isotope t1/2 DecayChain
DecayMode
EnergyMeV
Ra-223 11.4 d U-235 α 5.615.72
Ra-224 3.66 d Th-232 α 5.69
Ra-226 1600 y U-238 α 4.78
Ra-228 5.75 y Th-232 β- 0.046
Flow Chart - Ln•Resin Method
1 2
Load sample in 0.09M HNO3
Rinse 0.09M HNO3
1
2
3 0.35M HNO3
3
3
Ln•
Resin
1
20.5-2 L acidified sample
Ba-133
BaSO4 ppt
Conversion to BaCO3
{hold for ~30 hrs.}
0.09M HNO3
-ray measurement Ba-133
228Ra via 228Ac
{proportional or HPGe counter}
226Ra via Rn emanation
223,224Ra via α-spectrometry
Ra concentrated by ppt with BaSO4. Ac separated from other radioactive species via Ln.Resin (Burnett et al., 1995)
Elution Curve — Ln•Resin
The Ac fraction is collected and a CeF3 precipitate prepared for low-level gas-flow proportional counting
(Burnett et al., 1995).
The “Double-Pass” Approach
1 2
Actinide•
Resin#2
1
2
226Ra via Rn emanation
223,224Ra via-spectrometry
1 2
Rinse 2M HCl1
2
Actinide
•
Resin#1
1
2
Load sample in 2M HCl
•Collect•Ba-133 yield•Hold >30 hrs.
Process Actinide Elements
First Pass:
Rinse 2M HCl
1
2
Load sample in 2M HCl
Extrude resin into plastic vial; add
cocktail, count via LSC
Second Pass:
2nd column options: TRU.Resin — load 2.5M HNO3; elute Ac 1M HCl, ppt CeF3, count
Diphonix — load 2M HCl; elute Ac 0.5M HEDPA, evap., count
Water Samples: MnO2 ppt• Seawater, 100-400 liters• Acidify to pH 2, add Pu/Am tracers, stir/hold• For 100L sample, add 35 mL sat KMnO4 (~2.1g);
Pu-->Pu(VI), org oxid, purple color• Adjust pH to 8-9 with NaOH• Add 0.5M MnCl2 (2x vol of KMnO4); --> MnO2 ppt,
dark brown
2MnO4- + 3Mn2+ + 2H2O = 5MnO2 + 4H+
•Re-adjust pH to 8-9 as necessary•Stir occasionally to keep MnO2 suspended for few hours•Allow Mn02(Pu, Am) ppt to settle overnight•Pump supernatant into clean tank for Cs, Sr processing•Drain MnO2 slurry from bottom tap
Seawater
MnO2
Suspension
MnO2 ppt(Pu, Am, Ra, Ba)
supernatantCs, Sr,...
centrifuge/filter
(Povinic et al., 2000)
Large Volume Seawater Samples
Supernatant seawater transferred from one plastic tank to another via pumping — this
will be used for 90Sr and 137Cs.
MnO2 suspension withdrawn from bottom of conical-shaped plastic
tanks — processed for Am and Pu.
Smaller-Scale MnO2 ppt
MnO4 (purple) is reduced by added MnCl2 to precipitate MnO2 (brown). MnO2 precipitate settles
relatively quickly.
Summary
U/Th decay-series disequilibrium in nature may be exploited to measure environmental processes
Known source and fixed rate of decay provides information stable elements cannot provide
Extraction chromatographic methods have greatly simplified processing of environmental samples.