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.