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?