Guidance for the beneficial use of fly ash on coal mines in Virginia

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2nd International Conference on: “Advances in Mineral 1
Resources Management and Geotechnics”, Hania 2006, Greece
Z. Agioutantis and K. Komnitsas, Eds., 25-27 Sept., 2006, Hania, Crete
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Guidance for the beneficial use of fly ash on coal mines in Virginia (USA)
W.L. Daniels, M. Beck and M. Eick
Dept. of Crop and Soil Environmental Sciences, Virginia Tech, USA
ABSTRACT
Coal fly ash and flue gas desulfurization (FGD)
sludges can be returned to mine pits, fills and
revegetation zones in Virginia by regulation if
(and only if) a positive beneficial use can be
shown. Utilization of alkaline fly ash for control
of acid drainage from pyritic coal processing
waste piles, and use as a soil amendment for
revegetation, are the two dominant beneficial
uses proposed over time. Both applications must
be controlled by the basic chemical properties of
the ash proposed for utilization. Currently, pub-
lic concerns over long-term As and Se leaching
from various applications are increasingly driv-
ing regulatory options for mine site utilization.
Many fly ash materials are relatively low in in-
herent alkalinity or neutralizing ability, and cer-
tain ashes are actually acidic. Failure to add suf-
ficient total alkalinity will result in strong acidi-
fication of the ash utilization zones, stripping
heavy metals like Mn, Zn and Cu from the fly
ash matrix. Similarly, if alkaline ash is loaded
into non-acid forming coal wastes at high rates
such that leachate pH is > 9.5, significant leach-
ing of As and Se has been documented in large
scale laboratory leaching columns. Utilization
of fly ash and FGD as a mine soil amendment
for revegetation is based upon combined liming
and water holding capacity benefits, however,
levels of soluble salts (primarily sulfate and bo-
rates) limit one-time application rates to 100
Mg/ha or less.
1. INTRODUCTION AND BACKGROUND
1.1 Use of Fly Ash for Acid Drainage Control
Acid mine drainage from coal waste piles and
other acid-forming mine spoils is a major prob-
lem in the Appalachian USA coalfields in gen-
eral, and a localized problem in the Virginia
coalfields. Detailed work by our research group,
and others working in the Appalachians, has in-
dicated that coal fly ash is often alkaline, and
may be useful as an amendment for acid-
forming materials if the appropriate utilization
protocols can be developed (Stewart et al.,
1997; Daniels et al., 2002). Documented poten-
tially beneficial uses for suitable coal combus-
tion products (CCP’s) include use as a bulk-
blended additive to offset acid mine drainage
from potentially acidic coal refuse materials and
as a topical mine soil amendment at rates of up
to 20% by volume (approximately 200 Mg/ha,
incorporated). We also conducted a detailed
study of the geotechnical properties of varying
mixture ratios of fly ash and coarse coal refuse
(Albuquerque, 1994) which indicated, among
other findings, that significant reductions in
saturated hydraulic conductance are associated
with the admixture of dry fly ash into coarse
refuse. However, fly ash also contains a number
of potentially toxic trace elements (e.g. Mn, Zn
and Cu), which are leachable under certain con-
ditions, particularly if the ash is exposed to
highly acidic drainage (Stewart et al., 2001; see
Fig. 1). Thus, our overall findings from work in
the 1990’s were generally positive with respect
to the beneficial reuse potential of coal fly ash,
but they did contain significant cautionary re-
sults.
1.2 Use of Fly Ash as a Mine Soil Amendment
Utilization of fly ash and FGD as a mine soil
amendment for revegetation is based upon com-
bined liming and water holding capacity bene-

2 2nd International Conference on: “Advances in Mineral
Resources Management and Geotechnics”, Hania 2006, Greece
fits. However, most ash and FGD materials in
our region contain sufficient levels of soluble
salts (primarily sulfate and borates) that limit
one-time application rates to 100 Mg/ha or less,
assuming the materials can be physically incor-
porated. However, field plot work has shown
that higher loading rates (up to 33% v:v or 330
Mg/ah) can be utilized if the free salts are al-
lowed to leach for one winter before revegeta-
tion is attempted. Three-year response of direct
seeded vegetation to high rates (20 to 33%) ap-
plied to acid forming refuse were very positive
(Stewart and Daniels, 1995). In the short term,
however, loading rates as low as 5% v:v can
significantly reduce growth of sensitive plants
like legumes (Daniels et al., 1999), thus se-
verely affecting initial establishment of mixed
herbaceous grass/legume stands.
1.3 Changes in CCP’s Over Time
The body of work discussed above was focused
entirely upon class F fly ash materials since they
constituted the vast majority of CCP’s generated
in the mid-Atlantic USA region in the 1990’s.
However, changes in air quality regulation and
resultant changes in air emission technologies
over the past decade have led to major changes
in the type and properties of CCP’s that are now
available for back-haul to the Virginia coal-
fields. First of all, increasing quantities of FGD
sludges are now being generated as separate
CCP’s or mixed with fly ash. The advent of low
NOx boilers has led to significant concentra-
tions of ammonia in many CCP’s. Mercury re-
moval from flue gas has recently emerged as a
federal air emission regulatory priority. Depend-
ing on which control technology is utilized,
FGD and fly ash will become more enriched in
Hg at certain plants, while other plants may util-
ize injected activated charcoal as a sorbent
which may lead to higher ash concentrations of
a range of metals in addition to Hg. One major
secondary effect of increasing ammonia and
carbon levels in CCP’s is that they have sub-
stantial negative effects on the marketability of
CCP’s for use in cement admixtures or block
manufacturing. Thus, the pressure for land ap-
plication and/or mine utilization would be ex-
pected to increase. On a positive note, however,
both of these additives could substantially im-
prove the soil amendment properties of CCP’s.
Figure 1: Effects of alkaline fly blending rate on leachate pH from acid forming coal refuse over three years as reported
by Stewart et al. (2001). The CRF ash was high alkalinity while the WVF ash was moderately alkaline. Unamended re-
fuse leachates immediately dropped to < pH 2.0, and were followed sequentially by the 5%, 10%, and 20% WVF ash
blends over extended periods of time. Pronounced leaching of Fe, Mn, Zn and Cu occurred as low alkalinity mixes acidi-
fied over time and heavy metal leaching was proportional to ash loading rate.

2nd International Conference on: “Advances in Mineral 3
Resources Management and Geotechnics”, Hania 2006, Greece
2. CURRENT PUBLIC AND REGULATORY
CONCERNS IN VIRGINIA AND USA
Our previous work on CCP’s in the 1990’s
(Daniels et al., 2002) focused primarily on the
potential water quality benefits and risks of fly
ash utilization in various mine environments,
with a principal focus upon bulk acid-base bal-
ances and heavy metal (Cu, Zn, Fe, Al, Mn,
etc.) mobility to local ground-water. However,
we did not evaluate the possibility of As, Se,
and Mo mobility in ash/refuse leachates in detail
for a variety of technical reasons combined with
a lack of focused “regulatory concern” at the
time. The current USA regulatory climate is
placing much greater focus on the potential for
As, B and Se mobility from waste disposal and
utilization environments on/in active coal
mines, along with a strong emphasis on defining
Hg levels and mobility in coal combustion
products in general. As an example, the USEPA
recently reaffirmed its 1993 position that ex-
empted CCP’s from regulation as RCRA subti-
tle C (toxic) wastes, but specifically reserved
judgment on the use of CCP’s in coal mining
environments. This delayed decision for mining
environments is due largely reports of sulfate
and borate migration to local ground-water
wells from CCP disposal fills in Midwestern
USA surface coal mines.
In April of 2006, in response to citizen and
regulatory concerns over the water quality con-
cerns discussed above, the National Academy of
Sciences released its detailed report (NRC,
2006) on potential mine site impacts of CCP
utilization. While the report did offer overall
support for the beneficial utilization of CCP’s in
mining environments, it specifically cautioned
potential permittees to: (1) Carefully character-
ize the geochemical properties of both the CCP
to be utilized and the mine site; (2) understand
and predict long-term reactions and contaminant
release patterns; and (3) fully characterize po-
tential site hydrologic impacts. Thus, the predic-
tion of the relative mobility of As, B, Se, Mo,
and other potentially water-soluble trace ions is
the current focus of our continuing research
program.
3. PROPERTIES OF POST 2000 CCP’S
Over the past two years, we have collected over
40 CCP’s from major consumers of Virginia
coal. The chemical properties of a representative
subset of those materials are presented in Ta-
ble 1. While the majority of CCP’s are net alka-
line, their calcium carbonate equivalence (CCE)
and saturated extract conductivities (EC) vary
widely, as do levels of the potentially mobile
elements discussed above. Approximately 10 to
15% of the materials sampled are net acidic in
reaction, but this is a lower proportion than we
observed in our earlier regional CCP characteri-
Table 1: Selected chemical properties of coal combustion products (CCP’s) in 2003-2004 from Virginia coals.
Type of
CCP pH1 EC1 CCE Extr. B2 B As Se Cr Mo
dS m-1 % mg kg-1 Total Elemental Concentrations (mg kg-1)
Fly ash 3.57 11.7 0.0 91.6 220 184.3 82.7 153.3 32.1
Fly ash 5.83 4.4 3.2 28.6 61 42.0 15.9 101.8 72.0
Fly ash 7.18 11.8 1.0 43.7 55 69.8 9.0 37.6 6.4
Fly ash 8.85 3.2 0.3 123.4 383 119.1 10.1 86.6 33.3
Fly ash 8.90 8.0 2.5 14.2 50 94.4 13.7 63.9 9.5
Fly ash 9.32 26.8 22.5 16.6 183 20.7 23.7 28.8 4.1
Fly ash 9.36 3.6 1.3 23.3 70 160.7 3.6 57.1 15.3
Fly ash 10.69 4.1 13.2 118.6 1022 17.0 10.9 63.1 56.1
Fly ash3 11.54 3.1 7.7 3.6 82 63.2 12.6 80.4 17.1
Fly ash 12.11 5.1 28.3 24.2 677 8.7 11 61.2 15.2
Fly ash 12.15 11.2 29.8 0.3 22 32.2 3.6 67.2 2.3
FGD 8.17 19.72 0.0 3.4 53 0.8 1.2 0.7 11.4
FGD 9.14 5.25 41.0 29.2 282 24.2 4.1 44.8 10.4
1 By saturated paste method.
2 By hot CaCl2 extraction.
3 Ash utilized for analyses depicted in Figs. 2, 3 and 4.

4 2nd International Conference on: “Advances in Mineral
Resources Management and Geotechnics”, Hania 2006, Greece
zation study (Daniels et al., 2002). The wide
range of CCP chemical properties portrayed in
Table 1 reconfirms our earlier findings that de-
tailed characterization of these materials must
occur prior to mine site utilization to properly
match CCP properties to utilization site geo-
chemical conditions. This also reaffirms the
NRC (2006) findings discussed above.
One method for assessing the relative
bioavailability of elements such as As and Se is
sequential fractionation (Tessier et al., 1979),
and the results of a modified Tessier type ex-
traction on a representative strongly alkaline
CCP from Virginia are given in Figure 2. For
this particular product, this differential extrac-
tion analysis reveals that large proportions of
total Mo and Se are held in readily soluble ex-
changeable forms while the majority of total As
is associated with amorphous Fe and Mn phases
which would presumably be less soluble or
“leachable” over time.
4. POTENTIAL FOR CONTAMINANT
MOVEMENT UNDER NET ALKALINE
CONDITIONS
4.1 Background on Alkaline Leaching Issues
To date, the vast majority of CCP’s disposed of
or utilized in Appalachian coal mining envi-
ronments have been placed into large controlled
fills on surface mines and in coal refuse disposal
fills. The general presumption in many in-
stances, particularly coal refuse fills, is that the
geochemical environment will be strongly acid
forming and the alkaline loadings from the
CCP’s will be beneficial. However, CCP’s are
seldom bulk-blended with acid forming materi-
als. More typically, they are placed into large
CCP disposal cells or thick layers within spoil
or coal waste fills and will therefore generate
leachates that are strongly alkaline when high
pH CCP’s are utilized. Additionally, many mine
1.2
18.6
58.0
12.9
9.3
Fraction 1: Exchangeable
Fraction 2: Carbonates
Fraction 3: Amorph. Fe & Mn
Fraction 4: Crystaline Fe & Mn
Fraction 5: Residual
As
33.0
20.0 19.0
19.0
9.0
Mo
3.7
8.8
11.7
11.3 64.4
Cr
61.4
24.3
14.3
Se
Figure 2: Distribution of arsenic, selenium, molybdenum, and chromium (VI) of the fly ash utilized in alkaline column
study. Sequential fractionation according to Tessier et al. 1979.

2nd International Conference on: “Advances in Mineral 5
Resources Management and Geotechnics”, Hania 2006, Greece
spoils, and approximately 10 to 15% of coarse
coal refuse materials in the central Appalachian
region are also neutral to alkaline in reaction.
Therefore, it is realistic to expect that moderate
to strongly alkaline leaching conditions will oc-
cur at least locally in a field setting where alka-
line CCP’s are utilized or disposed of. Such
conditions are of concern to the potential for
enhanced solubility and mobility of oxyanions
of As, B, Se and Mo.
As discussed earlier, the vast majority of our
work in the 1990’s evaluated the potential to
offset acid drainage production via alkaline
CCP additions to acid forming materials, and
we generally endorsed that concept just as long
as net-acid base balances could be maintained
over time. To assess net contaminant leaching
under strongly alkaline conditions, and to focus
our attention on potentially mobile oxyanions of
As, B, Mo, and Se, we developed a new column
leaching experiment in 2004 as described be-
low.
4.2 Column leaching methods
To simulate the potential leaching of oxyanions,
metals, and other potential contaminants in a
strongly alkaline field setting, we utilized a
moderately alkaline (pH 8.5) coarse coal refuse
matrix mixed with varying rates of a strongly
alkaline (pH 11; CCE = 5%) coal fly ash. The
chemical properties of this particular ash are
given in Table 1 and Figure 2. Simulated rain-
fall (pH 4.8) was used for periodic leaching of
the coal refuse and fly ash mixture treatments.
We utilized (with minor modifications) the
leaching column design developed by and
Stewart et al. (2001) to equilibrate and subse-
quently obtain the leachates. The columns were
20cm diameter, 75cm long, ABS plastic drain-
age pipes with a flexible PVC endcap to hold
the material. A 15 cm layer of glass beads
(mean diameter is 3 mm) provided a drainage
layer (below the treatment refuse/ash mix) that
served as a leachate reservoir to ensure that the
bottom section of the fly ash/refuse treatment
mixture remained unsaturated in the unsaturated
treatment columns. The overall experiment con-
sisted of three ash-mixing rates (0, 10 and 20%
by volume) and two leaching environments
(saturated vs. unsaturated). We simulated bulk
blending fly ash/refuse mixture ratio and appro-
priate field density conditions. Three replica-
tions of each treatment (ash/refuse at 10:90 and
20:80 (v:v) and refuse alone) were run under
unsaturated conditions and three replications of
each treatment were run under saturated condi-
tions for a total period of six months. Leachates
were collected every three to five days and ana-
lyzed for pH, EC, and total As, B, Cr, Se, Mo
and other parameters of environmental concern.
4.3 Results of alkaline leaching
As expected, the leachate pH from the una-
mended columns remained between 8.0 and 8.5
for the duration of the experiment while the
leachate pH of the ash amended columns ranged
from 9.6 to 11.5 initially, and then declined over
time (Fig. 3). Leachate levels of As in both of
the ash treatments (Fig. 4) were significantly
elevated above those in the refuse control col-
umns and greater than an order of magnitude
above current (10 μg/L) USEPA primary drink-
ing water standards. Interestingly, the highest
leachate As levels were seen in the 10% ash
blended treatment, rather than the 20% treat-
ment, and the As elution was time-lagged. The
higher elution from the 10% blending rate
seems to indicate some sort of refuse:ash inter-
action affecting solid:liquid phase flow dynam-
ics, diffusion differences, or other packing/flow
phenomena. The time lag effect may also be re-
lated to the level of As associated with amor-
phous solid phases as discussed earlier, or some
other undetermined factor. Selenium levels in
all leachates were also much higher (Fig. 5) than
the primary drinking water limit of 0.05 mg/L
and were directly related to ash loading rate.
Over time, the Se levels in the ash blended
leachates dropped quickly, but remained at or
above 0.1 mg/L. Interestingly, the 10% blended
treatment also appears to support higher solu-
tion Se levels after the initial flush than the 20%
treatment, again indicating the possibility of an
ash:refuse interaction as noted above for As.
However, Se release after six months was actu-
ally higher for the 20% unsaturated columns
than immediately after onset of leaching, indi-
cating a potential for prolonged Se release.
While not shown here, significant leaching of B,
Cr and Mo was also observed as will be re-
ported in a major journal article in the near fu-
ture.

6 2nd International Conference on: “Advances in Mineral
Resources Management and Geotechnics”, Hania 2006, Greece
4.4 Implications for field leaching behavior
Column leaching trials such as these certainly
create “worst case” scenarios with respect to
expected field leaching conditions, and one of
the major current challenges faced today is the
development of appropriate scaling factors to
relate laboratory data such as these to actual
0 50 100 150
7
8
9
10
11
Leachate pH
Days of leaching
Unsaturated 0%
Unsaturated 10%
Unsaturated 20%
Satura ted 0%
Saturated 10%
Saturated 20%
Figure 3: Leachate pH from saturated and unsaturated columns of alkaline coal refuse amended with 0, 10, and 20% alka-
line fly ash. Ash properties given in Table 1 and Figure 2.
0 50 100 150
0.0
0.2
0.4
0.6
0.8
1.0
Leachate As (mg L
-1
)
Days of leaching
Unsaturated 0%
Unsaturated 10%
Unsaturated 20%
Saturat ed 0%
Saturated 10%
Saturated 20%
Figure 4: Arsenic (As) leaching from saturated and unsaturated columns of coal alkaline coal refuse amended with 0, 10,
and 20% alkaline fly ash. Ash properties given in Table 1 and Figure 2.

2nd International Conference on: “Advances in Mineral 7
Resources Management and Geotechnics”, Hania 2006, Greece
field impacts (NRC, 2006). Considerable at-
tenuation and dilution of any such contaminant
plume would be expected in a field setting, and
we are currently not capable of predicting the
actual concentration of these contaminants that
would actually reach local ground or surface
water. However, these data do clearly indicate
that significant localized leaching and move-
ment of arsenate, selenate, and molybdate are
likely under alkaline conditions. This possibility
must be considered when the overall geochemi-
cal CCP utilization environment is assessed and
modeled for permit approval. Similarly, appro-
priate water quality monitoring designs should
be implemented at all sites receiving CCP’s to
assess potential mobility of these constituents.
5. SUMMARY AND CONCLUSIONS
After 15 years of study, we remain convinced
that a wide range of CCP’s can be beneficially
utilized in Virginia coal mining environments.
However, the chemical properties of CCP’s,
particularly levels of soluble salts, CCE, and
potentially soluble oxyanions continue to vary
widely and must be carefully assessed and
matched to utilization site geochemical and hy-
drologic conditions. Alkaline CCP’s can be
safely and beneficially utilized to offset acid
drainage potential in sulfidic mine wastes if
provisions are made to ensure sufficient net al-
kalinity is present to meet long-term acid-base
balance demands. Similarly, if the CCP utiliza-
tion/disposal environment is allowed to become
strongly alkaline, CCP fills or layers should be
expected to be internal sources of high pH solu-
ble oxyanions such as arsenate, borate and sele-
nate if those constituents are elevated in the in-
bound CCP materials. While not currently a
common practice, utilization of CCP’s as a topi-
cal amendment to mine soils and coal waste for
soil improvement and revegetation purposes is
viable, but application rates will be limited to
less than 10% (100 Mg/ha) for most CCP’s due
to deleterious effects of soluble salts on initial
plant growth.
Federal and state regulatory authorities will
necessarily need to respond to a mixture of
technical issues such as those raised in this pa-
per and the recent NRC (2006) report to ade-
quately address growing public concerns over
the actual long-term water and soil quality ef-
fects of utilization of CCP’s on active mine
sites.
ACKNOWLEDGMENTS
The support of the Powell River Project and the
0 50 100 150
0.5
1.5
2.5
Leachate Se (mg L
-1
)
Days of leaching
Unsaturated 0%
Unsaturated 10%
Unsaturated 20%
Saturated 0%
Saturated 10%
Saturated 20%
Figure 5: Selenium (Se) leaching from saturated and unsaturated columns of alkaline coal refuse amended with 0, 10, and
20% alkaline fly ash. Ash properties given in Table 1 and Figure 2.

8 2nd International Conference on: “Advances in Mineral
Resources Management and Geotechnics”, Hania 2006, Greece
southwest Virginia coal industry over time is
gratefully acknowledged.
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