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Selenium Distributions in Kanawha Formation Rocks from Boone County, West Virginia
Dr. Dorothy Vesper
West Virginia UniversityDepartment of Geology & GeographyWV WRI Hydrogeology Research CenterDOE-NETL Research Fellow
Hydrogeology Research Center WV Water Research Institute
WEST VIRGINIA MINE DRAINAGE TASK FORCE SYMPOSIUMApril 22-23, 2008
Vesper DJ, M Roy and CL Rhoads (2008) International Journal of Coal Geology 73: 237-249.
Selenium distribution and mode of occurrence in the Kanawha Formation, southern West Virginia, USA
Two topics
1. Distribution in rock cores - stratigraphy
2. Mode of occurrence in rocks
Se in rock core
Overall Purpose• Better understand the chemistry of Se in coals and
related strata• Help predict where Se is most likely to be found
2004 – 1 core, mostly mode of occurrence
WVGES
Location of cores
WVGES, 2002
(coals only)
Stratigraphy Coal Se (ppm dry wt)
Selenium by coal bed
Pittsburgh
Kittanning
Coalburg &Winifrede
Distribution in rock core
5 rock cores• Coal, shale, mudstone, sandstone,
carbolith • Kanawha Formation (Coalburg –
Winifrede coal beds)
Bull Creek Mine (Coal River watershed)
Distribution in rock core
287 Samples• 191 had Se > 0.2 mg/kg• Max 11.9 mg/kg in a mudstone
Sample prep by Research Environmental & Industrial Consultants
• Lithology described
• Ground/composited to <60 mesh by lithology
• Total digestion using nitric acid and hydrogen peroxide (EPA Method 3050B)
• Analysis for total Se using Graphite Furnace Atomic Absorption Spectroscopy (GFAA) (EPA Method 270.2)
Bull Creek Mine
Bull Creek
Lick Creek
Coal River
1 km
Coalburg
Winifrede2004
Coalburg (upper line)Winifrede (lower line)
Distribution in rock core
• Stratigraphy– Rock type– Formation– Location relative to coal bed
• Other chemical parameters – Sulfur (S)– Total organic carbon (TOC)
How is the Se distributed?
Distribution in rock core
Do Se concentrations change with rock type?
0
2
4
6
8
10
12
Se
(mg/
kg)
Carbolith (9)
Coal (44)
M udstone (54)
Shale (85)
Sandstone (74)
Distribution in rock core
Do Se concentrations change by core?
C 1(43)
C 2(44)
C 3(25)
C 4(31)
C 5(32)
C 6 c7
0
2
4
6
8
10
12S
e (m
g/kg
)
Distribution in rock core
For non-coal units – distance to the coal matters
• Proximate distance – shortest distance from bed to coal
• 0 distance = adjacent to coal
• Trends agree with Mullenex (2005) for a similar section in WV
0 2 4 6 8 10Proxim ate d istance to coal (m )
0
2
4
6
8
10
12
Se
(mg
/kg
)
Distribution in rock core
What is the relationship between Se & sulfur?
All data (R2 = 0.21)
-2 -1 0 1Log tota l S (% )
-0.8
-0.4
0.0
0.4
0.8
1.2
log
Se
(mg
/kg)
-2 -1 0 1Log tota l S (% )
-0.8
-0.4
0.0
0.4
0.8
1.2
-2 -1 0 1Log tota l S (% )
-0.8
-0.4
0.0
0.4
0.8
1.2
Coal only Shale
Agrees with Coleman et al. (1993), Mullenex (2005), Neuzil et al. (2005) – FOR THIS REGION. Only Mullenex looked at multiple rock types
Distribution in rock core
What is the relationship between Se & total organic carbon (TOC)?
5 5.5 6
Log TO C (m g/kg)
-1.2
-0.8
-0.4
0.0
0.4
0.8
1.2
3 4 5 6
Log TO C (m g/kg)
-1.2
-0.8
-0.4
0.0
0.4
0.8
1.2
3 4 5 6
Log TO C (m g/kg)
-1.2
-0.8
-0.4
0.0
0.4
0.8
1.2
log
Se
(mg/
kg)
n=49
R 2=0.39
n=9
R 2=0.25n=37
R2=0.28
All data Coal Mudstone &Shale
(only core 2)
Principle component analysis (PCA) • Multivariate• Looks for commonalities between variables• Identifies “factors” which are groups of
variables
Multivariate analysis
PCA Results
Variables included: PC1 PC2
Log Total S (%) 0.575 0.043
Log Potential acidity 0.475 0.452
Log Neutralization potential
-0.334 0.608
Paste pH -0.440 -0.372
Log Total Se (mg/kg) 0.373 -0.535
Eigenvalues 2.63 1.25
% variance explained 52.6 25
169 samples; acidity and neutralization potential as calcium carbonate equivalent tons per 1000 tons
• PC1– Sulfur, acidic, non-carbonate, strongly related to sulfur concentration
• PC2 –Carbonate, some acid, limited S
• Se loads onto both the sulfur and non-sulfur PCs
• Similar results obtained for PCA of coals in WV, based on WVGES database (2003)
PCA Results
Map Se and S concentrations for each sample against
PC1 and PC2 scores for each sample
-0 .8 -0.4 0 0.4 0.8 1.2
log S e (m g/kg)
-4
-2
0
2
4
6
PC
1 S
core
-4
-2
0
2
4
PC
2 S
core
-2 -1 0 1
log S (% )
R 2=0.87
R 2 <0.01
R 2=0.36
R 2=0.36
PC1Scores (Sulfur-rich)
PC2Scores (more neutral)
Selenium Sulfur
R2 = 0.36 R2 = 0.87
R2 = 0.36 R2 = 0.01
Scores provide the weighting of that sample on that principle component
-4 -2 0 2 4 6PC 1 S core
-4
-2
0
2
4
PC
2 S
core
Mudstone, shale, sandstone
Coal
Carboliths
Sulfur more controlling
Neutral. potential more controlling
PCA Results
Distribution of total Se: • Se highest in coals; rocks adjacent to coals
• Not all units close to coal are high in Se; but the layers that are high in Se are typically found with two feet of the coals
• Se probably present in more than 1 modeNo strong correlations with S, TOCExtraction data indicates both organic & sulfidePCA analysis shows no single trend for Se
Sulfide more important for coals & organic-bound for shales (?)
Conclusions of rock core study
Why these patterns in the rock record?
Possible Interpretation
Steps to preservation:
1.Changing source through time
2.Immobile – during/after rock formation
(Se less mobile at low pH)
Depositional environment for Kanawha Formation
Domed swamp(Rain water fed,Typically acidic,Low in nutrients)
Possible Interpretation
Planar swamp (Ground water fed, neutral pH)
Modified from USGS Circular 1143 (2003), Coal—A Complex Natural Resource
Why these patterns in the rock record?
1. Less S-associated Se• Deposition in domed peat swamp, more oxidizing• Less total S in system (no source vs. loss)• Se reduction vs. S reduction
Possible Interpretation
2. Possible redistribution after deposition• Se conc. above & below coal have similar trends• From compaction or later fluids
Possible Interpretation
0 2 4 6 8 10Proxim ate d istance to coal (m )
0
2
4
6
8
10
12
Se
(mg
/kg
)
A final thought Depositional environments
Acknowledgements
U.S. Department of Interior Office of Surface Mining (OSM)
West Virginia Water Research Institute
REIC (Tim Keeney)
Decota Consulting
Pritchard Mining
Selected References
Cecil, CB, RW Stanton, SG Neuzil, FT Dulong, LF Ruppert and BS Pierce (1985). "Paleoclimate controls on the late Paleozoic sedimentation and peat formation in the central Appalachian Basin (U.S.A.)." International Journal of Coal Geology 5: 195-230.
Coleman, L, LJ Bragg and RB Finkelman (1993). "Distribution and mode of occurrence of selenium in US coals." Environmental Geochemistry and Health 15(4): 215-227.
Mullennex R (2005) Stratigraphic Distribution of Selenium in Upper Kanawha-Lower Allegheny Formation Strata at a Location in Southern West Virginia. The 23rd Annual Intern Pitt Coal Conf
Neuzil, SG, FT Dulong and CB Cecil (2005). Spatial trends in ash yield, sulfur, selenium, and other selected trace element concentrations in coal beds of the Appalachian Plateau Region, U.S.A. (preliminary report). Reston, VA, U.S. Geological Survey.
USGS (2005). Coal—A Complex Natural Resource, An overview of factors affecting coal quality and use in the United States with a contribution on coal quality and public health. Circular 1143.
WVGES (2003) Trace Elements in West Virginia Coals. Selenium. Online graphs and data
Questions?