NOTE: The following online publication is a draft
version. These pages will be updated and/or revised on an ongoing basis.
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These pages explore the geologic, environmental and economic aspects
of trace elements in West Virginia coals.
-
Environmentally significant Hazardous Air Pollutant
(HAP) trace elements are of primary interest, but all trace elements
in West Virginia coals are examined by their geologic occurrence.
Presented and interpreted are:
-
Stratigraphic distribution trends of trace elements, an
example
-
Geographic distribution trends of trace elements,
an
example
-
Statistical data on trace elements, including:
-
Histograms of trace element abundances, an
example
-
Statistical correlations between trace elements and ash yield, total
sulfur and pyritic sulfur, and correlations among the trace elements.
Introduction
Summary
Planned Enhancements
Select a page, or read on.
INTRODUCTION
What are trace elements, and why is it important to gather information
about trace elements in West Virginia coals?
Coal is made up primarily of "organic" elements (carbon, hydrogen,
oxygen and nitrogen) and "inorganic" elements (primarily silicon, aluminum,
iron, calcium, magnesium, titanium, sodium, potassium, and sulfur).
Organic elements comprise the combustible body of the coal, whereas the
inorganic elements are present in coal in minerals that largely form the
ash when the coal is burned. Inorganic elements (e.g. silicon and
aluminum) are present in most West Virginia coals in the range of several
percent or more in
ash forming minerals, but
other "inorganic" elements, such as sulfur,
present in lesser amounts, may detrimentally impact the use of West Virginia
coals.
Trace elements are defined as elements present in coal in amounts
of less than 1 percent by weight 1.
Generally, trace elements are present in coal in amounts much lower 1 percent,
and are reported in parts-per-million (ppm) by weight in the coal.
A trace element concentration of 1 ppm = 0.0001% by weight, or expressed
in another way, a 1 ppm concentration of a trace element equals one pound
in one million pounds (500 tons) of coal. Most trace elements in
West Virginia coals are present at levels of 10 to 100 ppm, or less.
Highly toxic elements (e.g. arsenic, mercury, lead, and selenium)
are present in West Virginia coals, though generally in very low concentrations.
How hazardous elements present in very low amounts adversely impact the
environment is a matter of scale. Annually, millions of tons of coal are
mined and utilized (year 2000 coal production),
potentially
liberating large amounts of various hazardous elements. For example,
a coal fired power plant with no pollution controls in place theoretically
would produce 10 tons of lead for each million tons of coal burned containing
10 ppm lead. However, modern pollution control measures provide controls
against the release of large amounts of hazardous trace elements to the
environment.
Because of the potential effects of trace element
pollutants from coal fired power plants the U.S. Environmental Protection
Agency (EPA) is currently investigating whether further regulation of trace
element emissions are necessary. Title III of the Clean Air Act Amendments
of 1990 concerns Hazardous Air Pollutants (HAP's), 11 of which are trace
elements in West Virginia coals: Arsenic (As), Beryllium (Be), Cadmium
(Cd), Cobalt (Co), Chromium (Cr), Mercury (Hg), Manganese (Mn), Nickel
(Ni), Lead (Pb), Antimony (Sb) and Selenium (Se).
The primary goal of these pages is to provide data on trace element
concentrations, statistics, stratigraphic occurrences, and geographic distributions
within West Virginia's coal beds. Economic and environmental impacts of
various trace elements are discussed, but care must be used when interpreting
the data (see Cautionary Notes page).
With pollution controls in place, significant percentages of various trace
elements, importantly HAP's, are captured, thus preventing their release
to the environment.
SUMMARY
Stratigraphic and areal distribution trends in the trace elements
in West Virginia coals as well as statistical correlations, or lack of
correlations, between various trace elements and ash yield, total sulfur,
pyritic sulfur presented in these pages revealed some interesting relationships
among the elements and ash yield.
A table of statistical correlations
of trace elements with ash yield, in decreasing order of significance,
includes Chromium (Cr), Thorium (Th), Scandium (Sc), Cesium (Cs), Rubidium
(Rb), Lithium (Li), Vanadium (V), Hafnium (Hf), Cerium (Ce), Lanthanum
(La), Zirconium (Zr), Tantalum (Ta), Niobium (Nb), Dysprosium (Dy), Holmium
(Ho), Lead (Pb), Samarium (Sm), Europium (Eu), Gallium (Ga) and Tellurium
(Te). These elements likely occur within mineral matter in coal.
Most of these elements probably occur in silicate minerals, especially
clay minerals, which make up 60-70% of the mineral matter in coals 2.
A subset of these elements and many rare earth elements cross correlate
among each other as component elements of the mineral monazite.
These include the major components Ce, La, Th, Nd and Y, and elements detected
in monazite in trace amounts, including Dy, Er, Eu, Gd, Ho, Lu, Sm, Tb
and Yb. Rubidium(Rb) and cesium (Cs) correlate well with each other
and with ash yield because these elements readily substitute for potassium
(K) in clay minerals by virtue of similarities in their atomic radii.
The zirconium (Zr) rich mineral zircon is a common
trace mineral in West Virginia coals and is known to also contain Hf, Ta,
and Nb. Zinc (Zn) is primarily present in coal as the trace mineral
sphalerite
which also contains cadmium (Cd). Lead (Pb) appears to be in coal in the
minerals galena and the selenium (Se) bearing
clausthalite,
and copper (Cu) is present in chalcopyrite.
The mineral pyrite is a significant source of sulfur (S) in West Virginia
coals and contains As, Hg and Tl, probably in solid solution. The
chalcophile elements (As, Co, Ni, Pb and Sb) correlated very poorly (except
Co and Ni) in West Virginia coals despite high mutual correlations in coals
of the Illinois Basin 3.
Elements that did not statistically correlate with ash yield are
assumed to be associated with the organic fractions of the coal.
These probably organically-bound elements in increasing order of correlation
with ash yield were Cl and Br, which negatively correlated with ash yield,
Be, Sb, Ge and Sr. Boron was found to have an organic affinity in
low rank Illinois Basin coals 3.
In West Virginia coals, B displayed a unique correlation with coal
rank, and decreased in abundance in the coal as the rank increased.
Apparently, increased metamorphism of West Virginia coals brought about
by increased temperatures, caused by depth of burial, resulted in devolatilization
of boron B from the coal. Whether the B was originally in clay minerals
or the organic fraction of the coal is unknown.
PLANNED ENHANCEMENTS
Phase I of this study reports on general aspects
of trace elements in West Virginia coals included in these pages.
As more data are acquired these pages will be updated. Phase II will
included data and trace element distribution maps on coals for which we
have a significant amount of data. Currently these include the Pocahontas
No. 3 coal (n = 30 samples), the Pocahontas No. 4 (n = 17), Sewell (n =
53), Eagle (n = 69), Powellton (n = 39), No. 2 Gas (n = 60), Peerless (n
= 18), Fire Clay (n = 19), Winifrede (n = 25), Coalburg (n = 77), Stockton
(n = 51), No. 5 Block (n = 46), Lower Kittanning (n = 17), Pittsburgh (n
= 43), Redstone (n = 42) and Sewickley (n = 16) coals. Phase III will include
data gathered on trace minerals in West Virginia coals using the SEM
mentioned throughout these pages as an "unpublished study by the WVGES".
Return to Top of Page
REFERENCES
1. Swaine,
D.J., (1990)
2. Renton,
J.J., (1982)
3. Gluskoter,
H.J., et al., (1977)
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Page last revised: December 2, 2005
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