v>EPA
United States
Environmental Protection
Agency
Industrial environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600(ff7-81-033 June 1981
Project Summary
Limestone - Lime Treatment
of Acid Mine Drainage -
Full Scale
David G. McDonald and Alten F. Grandt
Utilizing a full scale neutralization
plant, the effect of detention time,
sludge recirculation, flow pattern, and
treatment pH have been observed
using limestone and lime separately
and in combination. Data have been
accumulated on highly acidic ferric
iron acid mine drainage to determine
the most economical method of treat-
ment.
Plant operation indicates that com-
bination limestone-lime treatment
with sludge recirculation on both
treatment lines is the most economical
scheme of treatment.
Sludge studies indicate limestone
treatment to high pH levels yielded
sludges with the highest solids con-
tent. Sludges of slightly lower solids
content were acquired during series
flow treatment of similar AMD with
lime and sludge recirculation.
This Project Summary was developed
by EPA's Industrial Environmental
Research Laboratory, Cincinnati, OH,
to announce key findings of the re-
search project that is fully documented
in a separate report of the same title
(see Project Report ordering informa-
tion at back).
Introduction
The nationwide problems related to
acidic discharges from coal mining
operations are well documented in the
popular and technical literature. Neu-
tralization continues to be a necessary
short-term measure in numerous in-
stances, while long-range programs are
being developed to abate acid production
at the source.
Considerable effort has been expended
in investigating the neutralization of
acid mine drainage (AMD) with lime-
stone, lime, and soda ash. Acombination
limestone-lime process has been shown
to have cost advantages with improved
effluent quality and sludge settling
characteristics. Peatoody Coal Company,
in cooperation with the U.S. Environ-
mental Protection Agency, designed,
constructed, and operated a full scale
treatment plant to study the process.
.Objectives of the study were:
1. To determine the most economical
method of treatment of highly acidic
mine drainage in large volumes.
2. To observe and report effectiveness
of acid mine drainage treatment,
with special emphasis on metal ion
removal.
3. To characterize sludges from treat-
ment processes as to settling behav-
ior and solids content.
Background
The Will Scarlet Mine is an active
coal-producing mine located approxi-
mately 3 miles southwest of Carrier
Mills, Illinois, in Saline and Williamson
Counties. Mining operations were started
at Will Scarlet by the Stonefort Coal
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Company in 1953. Peabody Coal Com-
pany purchased the mine in 1967.
Before construction and operation of
the full scale treatment plant, acid mine
runoff from old surface works was
diverted into inactive surface mine pits.
Even with construction of extensive dike
systems and relocation of the South
Fork of the Saline River, the major
waterway, incidental pollution occurred
during periods of river overflow, as well
as seepage and surface runoff, and thus
some acidic water entered the river.
Water quality of the plant influent
varied with the amount of rainfall. With
increasing amounts of precipitation,
dilution of the plant influent was ob-
served but was preceded by a flushing of
more acidic influent water. The range of
water quality observed in the plant
influent is shown in Table 1. Small
concentrations of ferrous iron were
observed during the research period,
usually associated with periods of heavy
rainfall and seepage from the slurry
lagoon next to the plant influent channel.
A neutralization process for coal mine
drainage entails a series of individual
units of operation. This design, however,
is limited to one straight-line treatment
system. Thus, to incorporate series
treatment (with the potential for in-
creased detention time) and combination
treatment, the design of the Will Scarlet
Water Treatment Plant consists of two
identical systems of individual units
with recirculation capabilities (Figure
1).
Limestone vs. Lime
Two parallel continuous-flow studies
were made using limestone on Line No.
1 and lime on Line No. 2 to treatment
levels of pH 5.0 and 6.0, respectively.
Parallel flow treatment with no sludge
Line 1
Rapid Mix Aeration
Sludge
Separation
Recirculatiom
Pump
Drainage
Collection
Channel
Pump
Station
Line 2
Rapid Mix
\
Chemical Storage
& Feeder
Sludge
Separation
Figure 1. Flow diagram of Will Scarlet treatment plant.
recirculation allowed for simultaneous
treatment of the same plant influent in
order to observe differences in opera-
tional data and effluent water quality.
Limestone treatment exhibits several
advantages over lime treatment: (1)
lower sludge volumes; (2) higher solids
content in the sludges; (3) lower chemi-
cal treatment costs; and (4) greater ease
of materials handling. However, lime-
stone's inefficient reactivity at higher
pH waives results in inability to attain
pH levels greater than 6.5 and in the
deposition of large quantities of lime-
stone "fines" in aeration tanks and
effluent structures and channels. The
lower efficiency of limestone treatment
can only indicate that much of this
Table 1. Range of Water Quality of Plant Influent
Parameter
Range
pH
Acidity', b.p. to pH 8.3
Acidity', cold with H20a to pH 7.3
Alkalinity', to pH 4.5
Specific conductivity0
Iron, total, ppm
Iron, ferrous, ppm
Iron, ferric, ppm
Sulfate, ppm
2.4 - 3.1
1700-9200
1500 - 8500
0-93
2800 - 7900
145 - 1130
0-65
145 - 1070
2200 - 6600
'ppm as CaCOs.
ti(jmhos/cm at 25C.
chemical is unreacted at the plant
outfall and, in essence, wasted into the
sludge settling basin. 4
Combination Limestone-Lime "
Treatment
In an effort to combine theadvantages
of limestone and lime treatment, a
series of combination (two-stage) lime-
stone-lime treatment processes were
performed. Limestone's high reactivity
and efficiency with low treatment costs
at lower pH ranges (pH 3.4 to 4.1) were
utilized in the first stage of treatment
with recirculation of resultant sludges.
Lime, though more expensive, proved to
be highly reactive, efficient, and capable
of effecting desirable results in the pH
range 6.0 to 7.0. Second stage lime
treatment was utilized to achieve neu-
tralization of the final treated effluent at
pH 7.0, "polishing" the intermediate
limestone effluent.
Investigations of combination lime-
stone-lime treatment involved operation
of the treatment plant in series (two-
stage) flow with the effluent from Line
No. 1 being recirculated as influent to
Line No. 2.
Conclusions
Acid mine drainage from the Will I
Scarlet Mine area can be neutralized to^
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pH 7.0 with a combination of limestone
and hydrated lime, or with hydrated lime
alone.
Variations in treatment schemes
indicated that the most economical
mode of treatment in terms of operating
cost (0/1000 gals/1000 ppm acidity as
CaCOs), was achieved through combi-
nation treatment by utilizing limestone
on Line No. 1 with effluent pH 3.7 and
lime on Line No. 2 with final effluent pH
7.0. Sludge was recirculated on both
treatment lines at an approximate rate
of 200GPM(757 l/min.)toeach respec-
tive rapid mix vessel, representing 12-
18% of.the volume of plant influent.
Sludge recirculation had the overall
effect of reducing cost of treatment
when limestone was used as the neu-
tralizing agent. In combination treat-
ment, sludge recirculation was effective
due to the recirculation of limestone,
rather than lime sludge.
Detention time of treatment processes
in excess of the theoretical minimum
required contributed little in reducing
the cost of treatment regardless of the
treatment agent used.
5. A detailed study should be conducted
to determine the feasibility and
economics of removal of purported
trace toxic pollutants (i.e., Cd and Hg)
in acid mine drainage.
6. A separate report should be prepared
on operational aspects of treatment
of high volume delivery of acid mine
drainage.
Sludge Characteristics
Favorable settling behavior was ex-
hibited by limestone-lime and lime
treatment processes with the majority
of resultant sludges settling in one hour.
Higher solids content and more dense
sludges resulted from limestone treat-
ment of acid mine drainage at pH levels
in excess of pH 4.5, than with lime
treatment.
Recommendations
1. Further studies should be conducted
to determine adequate mixing of
limestone in high volume delivery
treatment of acid mine drainage. A
tremendous solids buildup occurred
in the aeration tanks at the Will
Scarlet Water Treatment Plant when
limestone was used as the neutral-
izing agent.
2. Highly alkaline industrial wastes
should be considered as potential
treatment agents in a search for
more economical treatment costs.
3. Detailed study should be conducted
to determine the effects of settling
basin (Pit #10) effluent on the South
Fork of the Saline River.
4. The settling basin (Pit # 10) should be
studied for possible industrial and
recreational uses.
David G. McDonald and Alien F. Grand! are with Peabody Coal Company, St.
Louis. MO 63102.
John F. Martin is the EPA_P[oj^t~QtticsLjsee below).
The complete report, entitled "Limestone^ui^pe^reatment of Acid Mine Drain-
age - Full Scale," (Orider No. PB 81-172 645; Copt: $ 17.OO, subject to change)
will be available only^om: ' S
National Technicannfofmation Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
ft US GOVERNMENT PRINTINGOFFICE 1W1-757-01Z/7152
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Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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