THE DISTRIBUTION OF RARE EARTH AND TRACE ELEMENTS IN FRACTIONS OF MARINE SHALE

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THE DISTRIBUTION OF RARE EARTH AND TRACE ELEMENTS
IN FRACTIONS OF MARINE SHALE

• Janet Frey
• D. E. Grandstaff
• Department of Geology
• Temple University
• Philadelphia, PA

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• Why Shale?
• Shales comprise 60 or more of sedimentary rocks
• Shale reactions are important as sources and
  sinks for trace elements.

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Element Groups (Families) Element Groups (Families) Element Groups (Families)
Alkali Earth Alkaline Earth Transition Metals
Rare Earth Other Metals Metalloids
Non-Metals Halogens Noble Gases
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• Why Rare Earth Elements?
• Not much is know about mobility of REE elements
  in earth surface systems.
• REE have commonly been considered conservative
  in natural waters
• water mass tracers.
• However, REE may interact with sediments.
• REE as analogs in nuclear waste disposal
• (Neptunium, Americium)
• Radioactive REE in short-term waste release

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REE concentrations in bulk shales are fairly well
known.

• However trace elements may be contained in a
  variety of phases
• Ion exchange sites on clays
• Adsorbed on hydrous ferric oxides
• Adsorbed to organic matter
• Co-precipitated in carbonates
• Bound in crystalline minerals
• The phase in which they are contained determines
  their environmental mobility.
• (pH, redox, ionic strength)

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Method of sequential extraction (Tessier
et al., 1979)
1 gram of powdered rock EXCHANGEABLE 1 m
MgCl2 CARBONATE 1 m NaOAc HFO 0.04m
NH2OHHCl - HOAc ORGANIC 0.02m HNO3
H2O2 CRYSTALLINE HF HClO4
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Shale samples Pierre Shale (K) South
Dakota Navesink (K) New Jersey Hornerstown
(K-T) New Jersey
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Replicate Analyses
Ex Car HFO ORG XTL
VA25-a VA25-b VA25-c
U
0 0.5 1 1.5 2
2.5 3 3.5 4
4.5 ppm
VA25-a VA25-b VA25c
Pb
0 2 4
6 8
10 ppm
VA25-a VA25-b VA25-c
La
0 2 4 6
8 10 12
14 ppm
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Sharon Springs
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Sum Exch Org XTL Hfo Car
1
REE / NASC
0.1
La Ce Pr Nd Sm Eu Gd Tb Dy
Ho Er Tm Yb Lu
0.01
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Verendrye
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SD-25 SD-24 VA-25 VA-24
10
30
14
Gadolinium (MREE)
EX Car Hfo
Org Xtl
SD-25 SD-24 VA-25 VA-24
ppm
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Ex
Glauconite
Carb HFO Org Xtl
ppm
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ppm
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Sharon Springs
Yb
Gd
La
Ex
XTL
Carb
car
Hfo
Org
Smectite
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Verendrye
La
Yb
Gd
car
hfo
XTL
org
Illite
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Hornerstown
Yb
La
Gd
hfo
XTL
org
Glauconite
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Yttrium
SD-25 SD-24 VA-25 VA-24
EX Car Hfo
Org XTL
0 10 20
30 40
50 ppm
JHB-2 JHA-1 JN-1
0 5
10 15
20 ppm
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SD-25 SD-24 VA-25 VA-24
0 50 100
150 200 250
300 ppm
EX Car Hfo Org
XTL
U
0 0.5 1 1.5 2
2.5 3 3.5 4
4.5 ppm
SD-25 SD-24 VA25 VA24
Th
0 5
10 15
20 25 ppm
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JN-1 JHA-1 JHB-2
U
0 1 2 3
4 5 6 7 8
9 10 ppm
JN-1 JHA-1 JHB-2
Th
0 0.5 1 1.5
2 2.5 3 3.5
4 4.5 ppm
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Conclusions

• Fractionation of REE/TE in shales is highly
  variable
• Depends on mineralogy, organic content
• In some cases lt50 of REE in refractory phases
• Carbonate, HFO, Organic and Exchangeable
  fractions may provide a source of REE and TE
  that become mobile due to environmental changes
  in redox, pH and ionic strength.
• LREE may be less conservative than HREE
• not reliable tracers.
• These reactions should be considered in waste
  disposal scenarios.

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