EPA-600/2-78-002
January 1978
Environmental Protection Technology Series
COMBINATION LIMESTONE-LIME
NEUTRALIZATION OF FERROUS IRON
ACID MINE DRAINAGE
Industrial Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-78-002
January 1978
COMBINATION LIMESTONE-LIME NEUTRALIZATION OF
FERROUS IRON ACID MINE DRAINAGE
Roger C. Wilmoth
Resource Extraction and Handling Division
Industrial Environmental Research Laboratory
Cincinnati, Ohio 1*5268
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 1*5268
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DISCLAIMER
This report has "been reviewed "by the Industrial Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for publication.
Mention of trade names or commercial products does not constitute endorsement
or recommendation for use.
ii
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FOREWORD
When energy and material resources are extracted, processed, converted,
and used, the related pollutional impacts on our environment and even on our
health often require that new and increasingly more efficient pollution
control methods be used. The Industrial Environmental Research Laboratory -
Cincinnati (lERL-Ci) assists in developing and demonstrating new and improved
methodologies that will meet these needs both efficiently and economically.
This report documents the investigations of the feasibility of combina-
tion limestone-lime treatment of acid mine drainage containing soluble iron
in the ferrous form. Conclusions drawn from this study indicate that in-
creases in reagent utilization efficiency and reduction in materials usage
costs can be achieved in specific situations of mine drainage treatment. In
this regard, the report will be of interest to researchers in the acid mine
drainage treatment field as well as to the coal industry and regulatory
agencies involved with treatment situations. Inquiries on this subject and
related subjects should be directed to the Resource Extraction and Handling
Division, Extraction Technology Branch.
David G. Stephan
Director
Industrial Environmental Research Laboratory
Cincinnati
iii
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ABSTRACT
Studies were conducted on ferrous-iron acid mine drainage (AMD) treatment
by a two-step neutralization process in which rock-dust limestone was mixed
with the influent AMD and then hydrated lime was added in a polishing reactor.
This combination treatment process resulted in reagent consumption cost
reductions as high as 30 percent as compared to those for single-stage hy-
drated lime treatment of the same AMD. Later data indicated that an equal
cost reduction (compared to single-stage lime treatment) could be achieved by
a two-stage hydrated lime process in which the AMD and recycled sludge were
mixed in the first reaction vessel and hydrated lime was added in the second
reactor. ''No cost advantage for the combination process over straight hydrated
lime'treatment was felt to exist in situations where sludge recycling was not
employed.
This report covers the period from November 1975, to August 1976, and
work was completed as of the latter date.
iv
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CONTENTS
Foreword iii
Abstract iv
Figures vi
Tables vii
Acknowledgments viii
1. Introduction 1
2. Conclusions and Recommendations 5
3. Procedures 6
it. Results 18
Batch-scale neutralization tests 18
Full-scale, continuous-flow studies 31
Manganese removal ^3
References 50
Glossary 51
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FIGURES
Number Page
1 Schematic flov diagram for the EPA neutralization
facility 7
2 Comparison of settling trends at pH 6.5 and pH 9.5 19
3 Settling trends for combination limestone-lime
neutralization ....... . 22
h Comparison of settling trends at pH 7 23
5 Sludge percent solids @ 1-hr settling time as a
function of pH 25
6 Supernatant turbidity @ 1-hr settling time as a
function of pH 26
7 Sludge percent solids @ 2^-hr settling time as a
function of pH 27
8 Supernatant turbidity @ 2l+-hr settling time as a
function of pH 28
9 Batch-scale combination limestone-lime feasibility
test where influent water pH was 5.0 30
10 History of the effluent manganese levels throughout
the duration of the Crown neutralization studies Ii8
vi
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TABLES
Number Page
1 Typical Detention Times ..................... 1^
2 Cro-wn Water Quality Data, 7/71* Thru 6/75 ............ 15
3 Manufacturers Chemical Analyses of Lime and Limestone ...... 16
it Spectrochemical Analysis of Germany Valley Limestone ...... 17
5 Sieve Analyses (Dry) of As-Received Lime and Limestone ..... 17
6 Results Comparison as Related to Treatment pH .......... 20
7 Results Comparison as Related to Settling Time ......... 21
8 Combination Limestone-Lime Laboratory Study ........... 29
9 Neutralization Data Summaries for Combination Treatment:
Basic Data .......................... 33
10 Data Summaries Where Process B Utilized Higher Limestone
Addition Rate than A ..................... 3^
11 Data Summaries for Combination Where Process B Utilized 2.6
Times as much First-Stage Limestone .............. 36
12 Data Summaries for Combination Vs Lime at pH 8 Using
Coagulants .......................... 38
13 Data Summaries for Combination With Reduced First-Stage
Limestone Addition Vs Lime .................. 39
lU Data Summaries for Combination With Minimal First-Stage
Limestone Addition Vs Lime .................. ^1
15 Data Summaries for Combination Where Process A Recycled Sludge
Into a First-Stage Reactor Vs Single-Stage Lime
16 Data Summaries for Combination Where Process B Recycled Sludge
Into a First-Stage Reactor Vs Single-Stage Lime
17 Chemistry Analyses for the Combination Treatment Studies . . . . U5
18 Effluent Manganese Concentrations ................ U9
vii
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ACKNOWLEDGMENTS
Thanks are extended to Ronald D. Hill, Eugene F. Harris, Robert B. Scott,
James L. Kennedy, J. Randolph Lipscomb, Harry L. Armentrout, Robert M. Michael,
Ralph S. Herron, Walter E. Grube, Jr., Loretta J. Davis, and Cathy J. Scott
for their assistance during these studies.
The cooperation of Ray Henderson, Vince Ream, Bill Light, Mike Ryan, and
Hershel Travis of Consolidation Coal Company is greatly appreciated.
viil
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SECTION 1
INTRODUCTION
The U.S. Environmental Protection Agency's (EPA's) Crown Mine Drainage
Control Field Site facility, located near Morgantown, West Virginia, was
established in 1972 to investigate the treatment requirements of predominately
ferrous iron acid mine drainage. This was a partial follow-up of earlier
studies by the same staff at Norton, West Virginia, where the iron in the
acid mine drainage (AMD) was in the ferric state.
EPA employees designed the Crown facility and performed most of the
construction work. Contracts were awarded for the plant building shell,
drying beds, lagoon, storage bins, and miscellaneous earthwork, and EPA
personnel completed the construction including wiring, plumbing, instrumenta-
tion, and fabrication.
At present, lime neutralization is the commonly accepted method for
treatment of AMD discharges. Lime treatment has several disadvantages:
- It produces a low-density, high-volume sludge.
- Its highly reactive nature provides high potential for accidental
overtreatment.
- As a refined product, it is moderately expensive and is in
increasingly short supply.
Earlier studies by EPA and others have indicated that limestone treatment
and combination limestone-lime treatment offered advantages over lime in
ferric iron situations. Most important of these advantages are:
- Production of a low-volume, high-density sludge.
- Cheaper raw-materials costs.
- Cheaper usage costs in some instances.
These processes needed to be investigated under ferrous iron conditions
before they could be fully evaluated. This report documents the results of
research conducted to evaluate combination limestone-lime treatment of ferrous
iron acid mine drainage.
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Prior to initiating the combination limestone-lime studies, investiga-
tions were completed on lime treatment and limestone treatment of the Crown
(2)
AMD. Excerpts from the conclusions from those studies are given belov for
the purpose of providing background comparisons for the current investigation
of combination treatment:
ROCK-DUST LIMESTONE TREATMENT OF FERROUS IRON AMD
- Limestone utilization efficiencies vere below 30 percent
for ferrous iron acid mine drainage neutralization to pH 6.5,
which was about the highest pH obtainable without sludge recy-
cling. Effluent quality from the thickener was terrible under
the pH 6.5 conditions.
- Recycling sludge at a rate of 20 percent of the influent
flow rate increased the utilization efficiency of limestone to
the 50-percent range. Effluent quality was still poor.
- The use of two aerators in series provided adequate de-
tention time for iron oxidation. At least U-hr detention time
was necessary to reduce the ferrous iron level from 270 to 2.1+
mg/1 at pH's near 7. The combination of increased aeration
time, better mixing, and sludge recycling enabled limestone
treatment to pH's as high as 7.U. Effluent suspended solids
(^0 mg/l) and turbidity (60 JTU) were still high. Efficiencies
ranged from 50-80 percent.
- Addition of coagulants reduced effluent iron levels
(from 20 to 1 mg/l), lowered turbidities (from 60 to 12 JTU),
and improved suspended solids (from Uo to 9 mg/l). The coag-
ulants greatly diminished pH probe fouling problems that were
generally severe below pH 7.5.
- The most satisfactory process operation involved incor-
porating a 20-percent sludge recycling rate, maintaining pH's
near 7.k, furnishing 30-min detention time with vigorous mixing
in the reactor, providing between h and 6 hr of detention time
in the aeration systems, and injecting coagulants at about a
7-ppm rate. Reagent costs for this process were approximately
1.3 cents/cu m (5 cents/1000 gal) for limestone plus approxi-
mately 2.6 cents/cu m (10 cents/1000 gal) for coagulant.
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Coagulant addition was not optimized. The thickener was most
effective in clarification around 0.05 liter/sec/sq m (0.07
2
gpm/ft ) of surface area.
LIME TREATMENT OF FERROUS IRON AMD
- Optimum overall operation of the EPA treatment system
was at pH 8. At this pH, probe fouling problems were almost
non-existent, effluent clarity was improved, and iron oxidation
was complete. Reagent cost was increased over 25 percent by
treating to pH 8 rather than pH 7; a UO-percent cost increase
was incurred by treating to pH 8.5 rather than to pH 8.
- The thickener appeared to function most satisfactorily
when the influent suspended solids were between 5»000 and
10,000 mg/1. Sludge recycling was employed to increase the
influent solids to this range and to slightly improve utili-
zation efficiency. Thickener effluents contained between k
and 10 mg/1 of suspended colloidal iron.
- Coagulants were very effective in improving the thick-
ener effluent quality. Iron values were consistently below
2 mg/1 using coagulants at pH 8.
- Precipitating the iron without oxidation offered few
advantages over the oxidized version of the neutralization
process. For ferrous precipitation, pH's had to be elevated
to around pH 9 resulting in an increase in lime cost of 30
percent as compared to ferric treatment to pH 8. The ferrous
hydroxide sludge occupied more than 1.5 times the volume of
the ferric sludge. Thickener effluent quality was signifi-
cantly better in the ferric situation.
- Lime treatment to pH 8 required approximately 7-min
reaction time and less than 2-hr oxidation time (utilizing
a sludge recycling rate below 20 percent of the influent
rate) and required coagulant addition at a rate under 5 ppm.
Reagent costs for this process were approximately 2.9 cents/
cu m (11 cents/1000 gal) for lime plus 1.9 cents/cu m (7 cents/
1000 gal) for coagulant. Coagulant addition was not optimized.
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Sludge settling rates with coagulants were greater than .07 cm/s
(8 ft/hr) for unhindered settling.
COMPARISON OF LIMESTONE VS LIME
- Limestone (rock dust) treatment of ferrous iron acid
mine drainage involves reagent usage costs somewhat less than
those required for lime treatment. Overall costs of the lime-
stone process must include the very large reaction and oxida-
tion vessel size and increased power requirements. These and
other operational considerations render the limestone process
to be considered unfeasible for general application to acid
mine drainage waters containing over 50 mg/1 of ferrous iron.
IRON OXIDATION
- An average oxidation rate design factor of 2 mg/1 per
min is suggested for lime neutralization aeration facilities
with influent ferrous levels below 300 mg/1. On-site tests
should be made to better determine the actual rate for the
specific conditions before proceeding to final design. It is
imperative that sufficient mixing capability be incorporated
to provide sufficient top-to-bottom turbulence to prevent sol-
ids accumulation in the aeration tank.
- The stoichiometric oxygen requirement can be calculated
from the equation: Oxygen (kg/hr) = k.l6 X 10~^ X (Flow, liter/
O j-
min) X (Fe , mg/l); or, Oxygen (ib/hr) = 7.15 X lO"5 X (Flow,
gpm) X (Fe2, mg/1).
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SECTION 2
CONCLUSIONS AND RECOMMENDATIONS
Combination first-stage limestone and second-stage lime treatment of
ferrous iron acid mine drainage resulted in "better than a 30-percent reduc-
tion in reagent usage cost as compared to single-stage hydrated lime treat-
ment of the same water. Effluent quality parameters from "both processes vere
comparable.
A 30-percent reagent usage cost reduction was obtained using a two-stage
hydrated lime treatment process in which the sludge was recycled into the
first-stage reactor to mix with the influent acid mine drainage and hydrated
lime was added to the sludge/AMD mixture in the second stage. The 30-percent
reduction was relative to a single-stage hydrated lime process where the
recycled sludge, hydrated lime, and acid mine water were combined in a single
reactor.
Based upon the success of the two-stage lime process, combination
limestone-lime treatment did not appear to be a feasible alternative in
ferrous iron situations where sludge recycling capabilities existed or could
be provided. Moreover, in comparing the results of combination treatment
without sludge recycling with the results of earlier lime treatment studies
without sludge recycling, no cost advantage appeared to exist.
Because of the varying characteristics of mine drainage waters, bench-
scale feasibility studies could be made to determine the initial potential
for the applicability of combination limestone-lime treatment for each
specific situation. In general, the greater the ferrous iron content, the
less applicable any limestone .process.
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SECTION 3
PROCEDURES
DEFINITIONS
Definitions and an explanation of the calculations used in this report
are presented in the Glossary.
DESCRIPTION OF FACILITY
Acid mine water was obtained from the Stewarts Run borehole pump of
Christopher Coal Company that pumped water from the Pittsburgh Coal Seam
located approximately 85 m (280 ft) below the surface. This pump removed
water from an abandoned section of Mine 93 to prevent the drainage from
entering an active section of the mine. The borehole pump discharged approx-
imately 32 liters/sec (500 gpm) into a 3.8-cu m (1000-gal) concrete reservoir
constructed from a burial vault. The water used by the EPA facility was
pumped from the reservoir to the treatment plant--a distance of about 366 m
(1200 ft)--through a 102-mm (4-in) plastic pipe at a pressure of 480 kN/sq m
(70 psi).
The AMD flowed through the neutralization facility as illustrated in
Figure 1. Processes A and B were identical in every respect. By having a
dual system such as this, it was possible to use one side as a control and the
other side as the variable and thus expedite the research efforts. The dual
system allowed immediate evaluation of the isolated variable under study. All
AMD transfer lines were 25-mm (1-in), Schedule 40 PVC. The sludge lines were
13-mm (^-in) plastic roll piping. PVC in-line strainers removed large par-
ticulate matter from the AMD prior to its entering the pressure regulators.
Plast-0-Matic Model PR075V pressure regulators were used to maintain rela-
tively constant downstream pressures to reduce flow fluctuations. C-E Invalco
Model W3/1000 turbine flow meters with Model W315 totalizers and rate indi-
cators totalized gallonage treated and displayed instantaneous rate of flow.
Accuracy of these meters was better than 1 percent of the full-scale flow of 4
liters/sec (64 gpm).
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PROCESS A
Reactor
Sludge Recycle
Coagulant
Pressure
Regulator
Strainer Turbine
Flow
Meter
pH (control pH
*.V JM*«"***"*« ****** *i*H
THICKENER
ACID MINE
DRAINAGE
Diverter Valve
I ! I Composite
L—'Sampler
I- SLUDGE ADiver
Sludge Recycle^ j£\ W y
-—-
Limestone
Feeder
[ [Tap Water
PROCESS B
Reactor
Pressure
Regulator
Strainer Turbine
Flow
Meter
Slu_dg_e JUcycle Bi»wter Valve/
Coagulant
pH (control) pH
/TX'.".'."''.'-".""""""'*
TO DEWATERING
AND DISPOSAL
FACILITIES
Limestone
Feeder
Magnetic 1 |J(]
Flow Meter Composite
Sampler
Figure 1. Schematic flow diagram for the EPA neutralization facility.
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From the turt>ine meters, water could be channeled either:
l) Into the lime reactor, the aerator, and the thickener, or
2) Into the limestone reactor, the aerator, and the thickener, or
3) Into the limestone reactor, the lime reactor, the aerator and
the thickener.
The lime reactor tanks were type SOU stainless steel with effective capacities
of k$k liters (120 gal) and were equipped with Lightnin' Model NS-7, 3-hp,
1750-rpm mixers. High-density polyethylene tanks with 9-5-mm (3/8-in) thick
walls and effective capacities of 3785 liters (1000 gal) were used for the
limestone reactors. Lightnin1 NS-7 mixers were installed on independent mounts
for use with the polyethylene tanks. In later studies, the NS-7 mixers on the
limestone reactors were replaced by 3-hp, 350-rpm, Lightnin1 ND-UB mixers to
obtain increased turbulence. The NS-7 system provided a mixing (pumping) rate
of 93 liter/sec (lU70 gpm); the ND-HB pumped 360 liter/sec (5710 gpm). The
limestone reactors were equipped with two baffles per tank. Each baffle con-
sisted of a metal outside support frame surrounding a l68-cm by 36-cm (66-in
by lU-in), lU x lU-mesh, 30U-stainless steel screen. The screen baffles served
to improve mixing efficiency and to abrade the limestone particles in order to
remove reaction coatings.
BIF Model 25-06 helix-type volumetric dry feeders with variable-speed
drives were used to feed both hydrated lime and rock-dust limestone into the
respective reactors. The hoppers on top of the dry feeders held 0.2 cu m
(7-8 cu ft) of material. Syntron Model V-20 vibrators were bolted to the
side of each hopper to prevent bridging. The vibrators operated whenever the
dry feeders were operating. Typical observed dry feeder accuracies were
about +_ 5 percent on a weight basis. The operating time for each dry feeder
was accumulated on Eagle Model HK300A6 time totalizers reading directly in
minutes. These units were equipped with dynamic braking circuitry to prevent
the timers from coasting after the dry feeders stopped.
The lime and limestone dry feeders were refilled automatically from 36-
tonne (*tO-ton) capacity Butler bolted-steel silos equipped with Vibra-screw
bin activators to prevent bridging. Jeffrey screw conveyors with 15-cm (6-
in) screws transported the neutralizer from the silos to the top of the dry
feeders. Monitor-brand bin level indicators were mounted in the dry feeder
hoppers to activate the conveyors when the level dropped.
8
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The storage silos were periodically pneumatically filled from l8-tonne
(20-ton) supply trucks. Butler Model CS9-90 bin-vent filters were mounted on
top of the silos to prevent dust from escaping while the tanks were being
loaded.
The neutralized water was pumped from the reactors into the aerators.
The aeration tanks were 3m (10 ft) in diameter by 1.8 m (6 ft) high with a
nominal water depth of 100 cm (3.25 ft); they contained 6800 liters (l80D
gal). Four 25-cm (10-in) solid baffles were installed at equal spacing
around the periphery of the tank. The tank itself was constructed of 6.U-mm
(^-in) hot-rolled steel coated with epoxy. Lightnin' Model LAR-10, 1 hp,
fixed-mount, surface aerators were installed on top of the aeration tanks.
These aerators were designed to transfer 1.8 kg/hr (U Ib/hr) of oxygen under
standard conditions.
Although the aerators were quite satisfactory in oxygen transfer, they
lacked sufficient top-to-bottom turbulence to keep heavier particles suspended.
This problem was most prevalent during limestone treatment studies where a
sizable accumulation of solids occurred in the bottom of the aeration tank
and thus decreased the effective detention time. A bottom-mixing prop was
installed on the aerator shaft later in the studies to successfully decrease
the solids accumulation problem.
After aeration, the treated water was pumped into the thickener for
clarification and sludge removal. FMC Link-Belt, Type-H thickeners were
used. These thickeners were 5-7 m (18.75 ft) long, 2.1* m (8.0 ft) wide, and
2.7 m (9.0 ft) high (excluding sludge hoppers) and had an effective capacity
of 3^.8 cu m (9200 gal). Adjustable effluent weirs allowed the effective
depth to be varied from 2.7 m (9 ft) to 1.8 m (6 ft). Rakes moving at 0.005
m/sec (l fpm) pushed the sludge into a collection hopper on the influent end
of the thickener. The sludge hopper extended approximately 1.6 m (5-25 ft)
below the floor level of the thickener and held 3.^ cu m (900 gal) of sludge.
At 1 liter/sec (15.85 gpm), the surface overflow rate was 0.07 liter/sec/sq m
(0.11 gpm/sq ft).
Sludge was removed from the thickeners by timer-controlled centrifugal
pumps. Continuous removal was not possible because the lines became plugged
at low-flow rates. It was therefore necessary to pump the sludge for short
durations at high-flow rates. A Tork Model 12M8001 repeating-cycle timer
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with a 12-min full-cycle time and 60 adjustable tabs to regulate on/off time
controlled the pumping duration and frequency. Typically, in non-recycling
situations, the sludge pumps operated 10 percent of the time (on 0.6 min and
off 5.1* min). Sludge pumping rates were about 0.3 liter/sec (5.5 gpm) through
a 13-mm (*g-in) line corresponding to a linear flow velocity of 2.7 m/sec
(9 fps).
Sludge recycling was accomplished by utilizing Eagle Signal Series
HP700, adjustable-duration pulse timers to control a pneumatically operated
diverter valve in the sludge line. When the Tork timer activated the sludge
pump, it simultaneously activated the Eagle pulse timer. Sludge was recycled
into the appropriate reactor until the Eagle timer timed-out and switched the
sludge diverter valve in the waste direction.
Initially, Fischer xUoU diverter valves were used for recycling sludge.
These valves had a 3l6-stainless steel body and ball with teflon seats.
During limestone sludge recycle studies, the tiny unreacted limestone particles
wedged between the teflon seats and the ball and scored both the seat and the
ball in just a couple of weeks of operation. Later, these valves were replaced
with Model 2600 NPT Red Valves with hypalon liners and PVC end caps.
Sludge flow was measured by Brooks Model 7185FB11KA 13-mm (ig-in) magnetic
flow meters that totalized gallonage and displayed instantaneous rate-of-flow
(Model 7300B1A2C signal converters and Model 55^0BlA.iiAlAl totalizers).
Accuracy of these magnetic flow meters was 0.5 percent of the full-scale
indication of 0.63 liter/sec (10 gpm).
Since each magmeter was placed before the diverter valve, the output was
indicative of total sludge flow. To independently totalize the sludge quan-
tity being recycled and the quantity going to waste, the magmeter signal
converter output was channeled through a relay that switched (at the same
time the diverter valve switched) from one totalizer to another.
The waste sludge from both thickeners was pumped into a 1.5-cu m (1*00-
gal) reservoir located immediately adjacent to the thickeners. When the
sludge level reached the top of the reservoir, an automatic sequencer-
controlled pump transferred the sludge to disposal facilities and then flushed
the sludge lines with approximately 150 liters (1*0 gal) of tap water. Sludge
flow to the disposal facilities was initially measured by volumetrically
determining the flow rate and multiplying by pumping time. Operating time of
10
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the pump was recorded on an Eagle elapsed-time meter. Later, this flow was
totalized electronically by remote slave counters on each magmeter waste
totalizer. Typical pumping rates to the disposal facilities were 1.1
liter/sec (l? gpm) through a 25-mm (l-in) roll plastic line corresponding to
a linear flow velocity of 2.1 m/sec (6.8 fps).
Both lime and limestone feed could be controlled either manually or
automatically. Automatic control was accomplished by Universal Interloc
(Uniloc) Model 1001 pH recorder-controllers that utilized on/off type control.
The pH controllers turned the dry feeders on when the pH dropped below the set
point and off when the pH increased beyond the set point. In order to reduce
probe fouling, the pH probes (Uniloc Model 321 immersion-type) were placed in
the influent area of the thickener. Probes that were placed in the reactors
fouled within a few hours. Even in the thickener, the probes fouled severely
at pH's below 7-5. It was necessary to clean the probes with HC1 as often as
three times per day at the lower-pH conditions. It took the probes approxi-
mately 1 hr to recover from each acid cleaning. Neutralizing the probes in a
pH 10 Na?CO solution hastened the probe recovery. At pH levels above T-5»
probe fouling was not a problem and cleaning was routinely done once a day.
Effluent pH was monitored by similar Uniloc equipment with the pH
probes placed immediately in front of the thickener effluent weir.
Both influent (control) and effluent pH's for processes A and B were
recorded on Hewlett-Packard Model T100B strip chart recorders. In the normal
mode of operation, the control set-point on the influent pH meter was ad-
justed until the desired effluent pH was achieved. Generally, the entire
system could be changed from one pH to another and stabilized within 36 hr.
The pH control system worked extremely well, as the effluent pH could be
maintained within +_ 0.1 pH for extended periods of time. The design flow
rate through each process was 1 liter/sec (15-9 gpm).
All process equipment was located indoors to isolate the variable of
weather from the data evaluation.
PHYSICAL MEASUREMENTS
Flow and Reagent Usage
Water and sludge flow rates and quantities were measured by turbine
meters and magnetic flow meters, respectively, as previously described.
Reagent usage was calculated by collecting and weighing a 3-min sample from
11
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the dry feeders at the beginning and end of each data set and averaging the
values. The average rate per minute was multiplied by the number of minutes
of dry feeder operation to determine the quantity of neutralizing agent used.
These reagent data were then related to the water quantity and influent and
effluent acidity and alkalinity values to calculate the various parameters of
interest such as usage, stoichiometric addition rate, and utilization effi-
ciency. Definitions and details of these calculations are presented in the
Glossary.
Water Sampling
The water quality from the borehole pump was quite variable. Fluctua-
tions in influent acidity were as large as Uo percent in a 2U-hr period.
Initially, the beginning and ending acidities for each data set were averaged
before being used in data calculations. Later, an automatic composite sampler
was built and installed to provide more reliable influent water quality data.
Sludge Settling Rates
Sludge samples were placed in 1000-ml graduates and the sludge/super-
natant interface was recorded as a function of time. In the case of limestone,
as well as lime at low pH's, a definite interface never clearly developed
during settling. In these cases, it was possible to observe the buildup of
solids in the bottom of the graduate.
Sludge Sampling
Representative sludge samples were quite difficult to obtain from the
process. Generally, the sludge was pumped in short-duration intervals on the
timed-basis previously described. Considerable variation in sludge density
was observed from the beginning to the end of the pumping cycle. All attempts
were made to sample near the midpoint of the cycle. Later, automatic composite
samplers were built and installed in the sludge lines at the discharges of
the thickener hoppers.
The clarifier rakes moved the sludge consistently to the edge of the
3^00-liter (900-gal) sludge hopper. Movement of the sludge from the top edge
of the hopper down the steep sides to the pump intake was often erratic and
thus created difficulties in obtaining representative samples. This was not
an operational problem but merely presented difficulties in data evaluation.
12
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Detention Times of the Various Vessels
Detention time determinations were made by instantaneously injecting
either salt or acid into the inlet of the vessel and monitoring the effluent
conductivity until it returned to a base level. The mean probable detention
time was calculated from a plot on probability paper (see Glossary for explan-
ation of calculation) and represents the point in time when the centroid of
the tracer mass passed through the vessel. Results of these studies are in
Table 1. The tracer appeared almost immediately in the effluents from all
reactors and aerators because of the mixing capability of these vessels. In
the thickeners, however, the first visible trace occurred at 120 min at both
0.32-liter/sec and 0.95-liter/sec (15-gpm) flow rates with the sludge rakes
operating. The sludge rakes significantly affected mixing in the thickeners.
In a static thickener with the rakes off, it took 50 hr after tracer injection
for the tracer to diffuse sufficiently to increase the conductivity at the
discharge end of the thickener to 500 micromhos/cm; with the rakes on, the
same conductivity was attained in 14 hr.
PROCEDURES FOR CHEMICAL ANALYSES
Conductivity and pH were measured potentiometrically. Total iron,
aluminum, magnesium, manganese, and calcium were determined by atomic absorp-
tion spectrophotometry.(2) Sulfate was measured by adding barium to precipi-
tate the sulfate and analyzing for residual dissolved barium in the superna-
tant by atomic absorption.*- ' Precipitation of the barium was accelerated by
centrifuging. EPA methods(2' were used for total solids, suspended solids,
alkalinity, and turbidity determinations. Ferrous iron was determined by
colorimetrically titrating potassium dichromate against a p-Diphenylamine
sulfonic acid sodium salt indicator.^4^ A YSI Model 51 dissolved oxygen
(D.O.) meter was used for D.O. measurements. The Salotto acidity method^5-*
was used, in which hydrogen peroxide is added to oxidize the metals; a room-
temperature titration is then made to pH 7.3.
CHARACTERISTICS OF REACTANTS
Mine 93 Borehole Discharge
Table 2 presents the typical chemical quality of the AMD used for these
studies.
13
-------
Table 1. TYPICAL DETENTION TIMES
Test vessel
Effective volume at
time of test
liters
Flow rate
gal liter/sec
Theoretical Mean probable Efficiency
detention time, detention time, (T/To),
gpm min min percent
Limestone reactor A 2^60
Limestone reactor B 2U60
Lime reactor B
Lime reactor B
Aerator A 6810
Aerator B 6620
Thickener B 3^820
Thickener A 3^820
650
650
120
120
1800
1750
9200
9200
0.32
0.95
0.32
0.95
0.32
0.95
0.32
0.95
5
15
5
15
5
15
5
15
130 78.6 6l
U3 28.8 67
2U 16.6 69
8.0 6.1 76
360 273 76
117 92 79
18UO (30.7 hr) lU35 (23.9 hr) 78
613 (10.2 hr) 515 (8.6 hr) 8U
-------
Table 2. CROWN WATER QUALITY DATA, 7/7** THRU 6/75
Parameter
PH
Specific conductance
Acidity as CaCO
Calcium
Magnesium
Total iron
Ferrous iron
Sodium
Aluminum
Manganese
Sulfate
Alkalinity
Total dissolved solids
Temperature
Unit
PH
ymhos/cm
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
°C
Mean
5.0l*
3760
61*0
370
110
300
270
U80
15
6
301*0
17
1*320
13.8
Maximum
5-9
1*000
1070
1*50
150
380
3UO
670
36
8
3600
100
5170
17
Minimum
1*.7
31*00
155
300
55
250
160
280
6
1*.3
2300
0
3250
9
Standard
deviation
—
260
120
1*0
20
39
31*
95
9
1
300
25
U80
2.3
-------
Lime and Limestone
The limestone and hydrated lime used in this study were obtained from
Germany Valley Limestone Company, Riverton, West Virginia. In order to
obtain the smallest particle size commercially available, the rock-dust form
of limestone was used. All tests in this study were made using the hydrated
form of lime.
Table 3 presents the manufacturer's chemical analyses and cost for lime
and limestone.
Table 3. MANUFACTURER'S CHEMICAL ANALYSES OF LIME AND LIMESTONE
Q
Hydrated lime,
Parameter minimum % composition
CaO 72.00
MgO 0.70
CaCO equivalent 130
Si02
Rock-dust limestone,
minimum % composition
53.0
0.38
98.6
0.1+9
aLime cost $38.58/tonne ($35.00/ton) or 3.86 cents/kg (1.75 cents/lb)
delivered in bulk.
^Limestone cost $12.l3/tonne ($11.00/ton) or 1.21 cents/kg (0.55 cents/lb)
delivered in bulk.
A spectrochemical analysis of the limestone was made by Bituminous Coal
Research and is reported in Table k. A dry sieve analysis of as-received lime
and limestone is presented in Table 5^
16
-------
Table U. SPECTROCHEMICAL ANALYSIS OF GERMANY VALLEY LIMESTONE
(percent)
Loss on
ignition Si02 Al^ Fe^ MgO CaO T102 Na20 K20 Mn02
1.0 O.U3 0.15 1.16 97.0 O.OU 0.02 0.1 0.03
Table 5. SIEVE ANALYSES (DRY) OF AS-RECEIVED LIME AND LIMESTONE
Screen size
50 mesh (0.297 mm)
100 mesh (0.1^9 mm)
200 mesh (0.07^ nun)
1*00 mesh (0.037 mm)
Percent not passing sieve
Hydrated lime,
percent passing
92.9
62.5
35.0
13.3
U.U
Rock-dust limestone,
percent passing
97-7
83.6
56.6
15-7
2.1
17
-------
SECTION It
RESULTS
BATCH-SCALE NEUTRALIZATION TESTS
A laboratory-scale study was performed to directly compare lime, lime-
stone, and combination limestone-lime neutralization to pH 6.5 and pH 9-5-
Limestone treatment was tested only at the 6.5 pH level. Since the tests were
almost simultaneously conducted, results can be directly compared.
Figure 2 shows the sludge settling trends. Neutralization to pH 6.5
resulted in very-low-volume sludges because of incomplete reactions at that
pH. Increasing the pH to 9-5 significantly increased sludge volumes as the
iron oxidized, hydrolyzed, and precipitated. Combination-treated sludge
settled more rapidly than lime sludge but the 2U-hr volumes were the same.
This result is not in agreement with later observations that combination
sludge settled to a lesser final volume than lime sludge.
Chemical and physical data for the tests are presented in Tables 6 and 7«
The data are the same in both tables but are presented differently to make
comparisons easier.
Very little iron oxidation occurred at pH 6.5 in 2^-hr. At pH 9.5,
complete oxidation occurred in a matter of minutes. Unexpectedly, very little
loss in calcium and sulfate was detected by the chemical analyses.
Sludge Characteristics
Bench-scale studies were made to investigate sludge characteristics as
related to the neutralizing agents used and the treatment pH.
Figure 3 presents settling trends as a function of pH for combination
limestone-lime treatment. No clear sludge/supernatant interface developed
with any of the neutralizing agents below pH 6.5. Figure U is a composite
drawing to compare the relative settling trends of lime, limestone, and
combination treatment at pH 7. Since the tests for each neutralizing agent
were made at separate times on separate AMD samples, Figure it's direct com-
parison is not strictly valid but may be useful as a guide. At the end of
18
-------
• Lime
A Limestone
• Limestone-Lime
15 min.
45 min.
30 min.
TIME
Figure 2. Comparison of settling trends at pH 6.5 and pH 9.5.
60 min. 24 hrs.
-------
Table 6. RESULTS COMPARISON AS RELATED TO TREATMENT pH
Parameter
Lime
Limestone-lime
Raw water pH b.5 pH 9-5
pH
PH 9.5
Turbidity
Ferrous iron
Total iron
Aluminum
Manganese
Magnesium
Calcium
Sodium
Sulfate
Conductivity
Acidity
Alkalinity
Sludge % solids
1-hr Settling
7
530
550
50
9.2
180
U50
620
1*050
1*800
ll*50
0
62
350
360
3.1
11
200
790
61*0
3780
5200
—
___
25
0
0.5U
0.7
0.31
150
1020
610
3690
5050
0
___
3.6
6.5
80
390
390
3.2
12
200
7l*0
620
3900
1*900
760
lt.1*
30
0
0.28
0.9
0.37
150
1010
610
3900
1*950
0
9.3
2l*-hr Settling
Turbidity
Ferrous iron
Total iron
Aluminum
Manganese
Magnesium
Calcium
Sodium
Sulfate
Conductivity
Acidity
Alkalinity
Sludge % solids
7
530
550
50
9.2
180
1*50
620
1*050
1*800
ll*50
0
314
31*0
31*0
1.1
11
180
720
600
39^0
U750
717
5
5.2
6
0
0.07
0.9
0.19
130
1010
590
3690
5000
0
79
6.5
1*2
380
380
1.2
12
180
730
590
39^0
1*950
780
5
1*.3
7
0
0.09
1.0
0.26
130
1050
590
3900
5100
0
8l
6.1
9,
All units are mg/1 except for turbidity (JTU) and sludge percent solids.
20
-------
Table 7- RESULTS COMPARISON AS RELATED TO SETTLING TIME
Parameter
Turbidity
Ferrous iron
Total iron
Aluminum
Manganese
Magnesium
Calcium
Sodium
Sulfate
Conductivity
Acidity
Alkalinity
Sludge % solids
Turbidity
Ferrous iron
Total iron
Aluminum
Manganese
Magnesium
Calcium
Sodium
Sulfate
Conductivity
Acidity
Alkalinity
Sludge % solids
Raw
water
7
530
550
50
9.2
180
1*50
620
1*050
U800
ll*50
0
7
530
550
50
9.2
180
1*50
620
1*050
1*800
ll*50
0
Lime
1-hr
62
350
360
3.1
11
200
790
61*0
3780
5200
—
—
3.6
25
0
0.5^
0.7
0.31
150
1020
610
3690
5050
0
— _
6.5
2l*-hr
31*
31*0
3l*0
1.1
11
180
720
600
391+0
^750
717
5
5.2
6
0
0.07
0.9
0.19
130
1010
590
3690
5000
0
79
6.5
Limestone
1-hr
At pH 6.5
120
1*70
1*90
3.7
12
200
710
630
39^0
5100
950
— -
1*.5
At pH 9-5
b
___
___
— — -
2l*-hr
1*9
1+50
1*50
1.3
12
190
6l*o
575
3780
1*950
91*0
8
6.7
b
_ __
___
— _
— — —
Combination
1-hr
80
390
390
3.2
12
200
7l*0
620
3900
1*900
760
__
l*.l*
30
0
0.28
0.9
0.37
150
1010
610
3900
^950
0
—
9.3
2l*-hr
1*2
380
380
1.2
12
180
730
590
39^0
1*950
780
5
1*.3
7
0
0.09
1.0
0.26
130
1050
590
3900
5100
0
81
6.1
units are mg/1 except for turbidity (JTU) and sludge percent solids,
Not applicable.
21
-------
to
NOTE: LIMESTONE WAS USED TO NEUTRALIZE (FIRST STAGE] TO pH 5.2
LIME WAS USED TO ELEVATE pH TO LEVELS SHOWN ON CURVES
NO SETTLING INTERFACE WAS OBSERVED BELOW pH 7.
15 min.
30 min.
TIME
Figure 3. Settling trends for combination limestone-lime neutralization.
-------
ro
uo
Comb.
Limestone-Lime
pH 7.2
15 min
30 miff.
TIME
Figure 4. Comparison of settling trends at pH 7
45 min.
24 krs.
-------
1 hr, the limestone sludge occupied a significantly smaller volume than the
other two sludges. The same situation was observed after 2h hr of settling.
Effluent turbidity and sludge percent-solids determinations were made on
each sample after 1 hr and after 2k hr of settling. The results are shown in
Figures 5 through 8. Limestone effluent turbidity, after 1 hr, was poor in
comparison to that of lime and to combination treatment. At pH 6.8, limestone
sludge had a percent-solids content about four times as great as the other two
sludges.
Surprisingly, little change occurred in the sludge percent-solids between
the 1-hr 2U-hr times in all the samples. Supernatant turbidity values were
significantly lower for all samples after 24-hr of settling as compared to the
1-hr values.
In summary, limestone sludge settled fastest and compacted to the least
volume. Supernatant clarity from limestone treatment, however, was poor in
relation to lime treatment and combination treatment. Combination limestone-
lime sludge settled more rapidly than lime and settled to a final volume that
was on the order of one-half that of lime-treated sludge at pH 7. Supernatant
clarity of combination treatment after 2k hr was superior to that of lime
treatment.
Reagent Costs For Batch Neutralization
Bench-scale tests were made to determine the feasibility of combination
limestone-lime treatment of the Crown acid mine drainage. A group of one-
liter samples were neutralized to various predetermined pH's, using lime-
stone and allowing 20 min of reaction time, and then were treated with lime to
pH 7.0 and further to pH 9-5 (for ferrous oxidation or precipitation). The
quantities of limestone and lime were recorded. For comparison, samples were
treated to pH 7.0 using limestone alone. Lime was used alone to treat to pH
7.0 and pH 9-5.
The important consideration in this test was cost. Raw material costs at
Crown were: Limestone = $11.00 per ton in bulk, and lime = $35.00 per ton.
Table 8 and Figure 9 contain the data from the feasibility test. Combination
treatment using a first-stage limestone pH of 5.1 was the most economical
method of treating to pH 7.0. This combination (6.U cents/1000 gal) was 57
percent cheaper than straight limestone treatment (lh.8 cents/1000 gal) and
9 percent cheaper than straight lime treatment (7.0 cents/1000 gal).
21*
-------
ro
OO
I I
• Lime
A Limestone
• Limestone-Lime
PH
11
12
Figure 5. Sludge percent solids @ 1-hr, settling time as a function of pH.
-------
ro
ON
Lime
Limestone
Limestone-Lime
8 9 10 11
PH
Figure 6. Supernatant turbidity @ 1-hr, settling time as a function of pH.
-------
ro
—3
• Lime
ALimestone
• Limestone-Lime
10
PH
11
Figure 7. Sludge percent solids @ 24-hr, settling time as a function of pH.
-------
ro
oo
Lime
Limestone
Limestone-Lime
E 20-
9
10
PH
11
Figure 8. Supernatant turbidity @ 24-hr, settling time as a function of pH.
-------
Table 8. COMBINATION LIMESTONE-LIME LABORATORY STUDY
Treatment
Limestone
Lime
Combination
t!
It
It
tt
tt
tl
First
stage
PH
6.8
5.1
5-3
5.5
5.7
5.9
6.1
6.3
Limestone
Amount ,
g/1
3.2300
0.021*0
0.0830
0.1180
0.1500
0.1730
0.1910
0.1*020
Lime
Cost ,,
t* D
/cu m
3.195
2.681
2.570
2.319
2.81*7
2.693
2.751
2.967
Total
cost to
pH 9-5,
-------
OJ
o
_• 10
Straight lime
treatment
5.25
6.0
4.23
3.70
3.17
2.64
o
V)
CO
<=>
ej
2.11
ca
1.592
1.06
5.50 5.75
FIRST-STAGE TREATMENT pH
Figure 9. Batch-scale combination limestone-lime feasibility test where influent water pH was 5.0.
6.25
-------
Treatment to pH 9-5 was most economical using combination treatment with
a first-stage limestone pH of 5.5. In this case, combination treatment (9-3
cents/1000 gal) was 23 percent cheaper than straight lime treatment to pH 9-5
(12.1 cents/1000 gal). Limestone was incapable of treating to pH 9-5-
The raw^naterials costs greatly influence the cost advantage of combina-
tion treatment. Any consideration of combination treatment would need to
include the delivered cost of bulk lime and rock-dust for the plant site in
question.
FULL-SCALE, CONTINUOUS-FLOW STUDIES ON COMBINATION TREATMENT
Approach
The basis for these studies (i.e., pH, detention time, reagent addition
mode, reactor baffling system, etc.) was the earlier investigations by EPA on
the ferric iron AMD at Norton, West Virginia and at Crown. In these
earlier studies, it was determined that 20-30 minutes of detention time were
required in the mixing reactor, that wire-mesh reactor baffles increased both
mixing and utilization efficiencies, and that the rock-dust form of limestone
yielded utilization efficiencies in the range of 50 percent treating to pH 6.5
on ferric iron water (Norton), 30 percent on ferrous water (Crown), and 50
percent on ferrous water using sludge recycling (Crown).
The basic avenue of approach toward the continuous-flow studies was that
the first-stage limestone addition rate would be initially high for the first
comparison and would incrementally diminish to cover a full spectrum of con-
tingencies ; thus, the optimum combination parameters could be identified, with
the critical consideration being cost.
Test One
Basic data were obtained on combination treatment using a first-stage
limestone pH near 6 followed by lime addition to pH 8. The limestone addition
rate in Process B was approximately hO percent higher than Process A although
the first-stage effluent pH's were the same for both processes. The first-
stage pH of 6 was chosen because the influent pH's during the test averaged
5.6. Limestone was fed semi-continuously by incorporating cycle timers to
control the on/off frequency of the dry feeders. This was necessary because
the small quantity of limestone required was below the minimum adjustment on
the dry-feeder rate control. Typically, the limestone dry feeder ran one
31
-------
minute out of three. The AMD flow rate was I liter/sec (l6 gpm). Sludge
recycling was not used for this test. No coagulants were used.
The results of the first study (Ta"bles 9 and 17) indicated that although
more limestone was being added to Process B than to A, Process B required more
lime to reach the same end pH. Oddly, the higher level of limestone addition
in Process B is not evidenced in either the limestone reactor suspended solids
or the lime reactor suspended solids levels; both of which were lower for B
than A.
Problems had been encountered during the test with plugging of the
limestone feeders because the limestone storage bin was practically empty and
the material was somewhat damp and difficult to control. A new load of lime-
stone was obtained. In view of the unusual suspended solids results, some
question must fall on the reliability of the limestone usage figures.
Effluent chemistry values were virtually identical for both processes
with the exception that B had a slightly lower effluent suspended solids and
turbidity level.
Test Two
In the second test, the rate of limestone addition was increased in
Process B to provide a wider differential between process conditions in order
to more closely evaluate the unexplained results of Test One. The damp lime-
stone was eventually exhausted from the storage bin and more confidence could
"be placed in the limestone usage data obtained during this test.
Process B was receiving over 2.8 times the limestone quantity of Process
A as shown in Table 10. The limestone reactor suspended solids levels were
higher for B than for A in this test as contrasted with the results of Test
One. The lime reactor effluent suspended solids, however, were about equal.
As in Test One, a greater quantity of lime was required for Process B than for
A. This is an unexpected and unexplained result. Total reagent cost for
Process B was 1*6 percent greater than for A. Effluent quality parameters were
virtually identical. An unusual observation was that the sludge percent
solids from Process B averaged 10 percent as compared to 6.2 percent for
Process A. This result suggested that the gross majority of the limestone
failed to be utilized but passed directly to the sludge. Total (limestone and
lime) reagent utilization efficiency was 51 percent for Process A and 30
percent for Process B. Effluent quality parameters are shown in Table 17.
32
-------
Table 9. NEUTRALIZATION DATA SUMMARIES FOR COMBINATION TREATMENT: TEST ONE
(BASIC DATA)
First-stage effluent pH
Final effluent pH
Limestone usage, kg/cu m
Lime usage, kg/cu m
Cost, cents/1000 gal
Cost, cents/cu m
Cost, cents/10 cu m/ppm influent acidity
Utilization efficiency, percent
Stoichiometric factor (influent acidity)
Sludge to waste, % cf influent AMD
Sludge recycled , % of influent AMD
Dry solids recycled, lb/1000 gal
Dry solids to waste, lb/1000 gal
Dry solids to waste, kg/cu m
Underflow solids, percent
Effluent turbidity, JTU
Limestone reactor suspended solids, mg/1
Lime reactor suspended solids, mg/1
Effluent suspended solids , mg/1
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
Mean
6.10
6.12
7.96
7-97
0.36
0.1*9
0.1(8
0.57
8.59
9-58
2.27
2.79
1*.32
5-33
62
1*9
1.90
2.1*0
1.65
1.60
0
0
0
0
7.8
6.8
0.91*
0.82
5.7
5.1
33
28
280
2UO
1250
880
1*0
26
Std. dev.
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
1.1
1.1*
0.3
0.2
0.6
0.7
9.8
5.8
0.3
0.3
0.1
0.1
_
-
0.9
0.7
0.1
0.1
0.6
0.5
5
3
51*
37
2l*0
150
7
8
Difference in reagent usage cost between
Process A and B, percent
23
33
-------
Table 10. NEUTRALIZATION DATA SUMMARIES FOR COMBINATION TREATMENT WHERE
PROCESS B UTILIZED HIGHER LIMESTONE ADDITION RATE THAN A
First-stage effluent pH
Final effluent pH
Limestone usage, kg/cu m
Lime usage, kg/cu m
Cost, cents/1000 gal
Cost, cents/ cu m
Cost, cents/10 cu m/ppm influent acidity
Utilization efficiency, percent
Stoichiometric factor (influent acidity)
Sludge to waste, % of influent AMD
Sludge recycled, % of influent AMD
Dry solids recycled, lb/1000 gal
Dry solids to waste, lb/1000 gal
Dry solids to waste, kg/cu m
Underflow solids , percent
Effluent turbidity, JTU
Limestone reactor suspended solids, mg/1
Lime reactor suspended solids, mg/1
Effluent suspended solids, mg/1
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
Mean
6.13
6.ll*
8.01*
8.01*
0.37
1.0k
0.52
0.60
9.27
13.5
2.1*5
3.57
5.39
7.87
51
30
2.36
lt.07
1.65
1.56
0
0
0
0
8.6
13
1.01+
1.56
6.2
10
31
29
260
1*60
1060
1150
31
33
Std. dev.
0.1
0.1
0.1
0.1
0.03
0.2
0.01
0.02
0.2
0.7
0.06
0.2
0.9
1.1*
8.1
5.8
0.1*
0.8
0.1
0.03
-
-
0.7
1.6
0.1
0.2
0.1*
1.3
1*
3
30
61*
260
21*0
8.9
11
Difference in reagent usage cost between
Process A and B, percent
1*6
-------
(2)
Earlier studies at Crown on straight lime neutralization to pH 8
without sludge recycling resulted in reagent usage costs around 2.k cents/cu m
(9.1 cents/1000 gal). The 2.U5 cents/cu m cost observed in Process A in this
study indicates similar costs for combination treatment and straight lime
treatment in situations without sludge recycling.
Test Three
The third study involving combination limestone-lime treatment investi-
gated the relative effectiveness of adding 2.6 times as much limestone in the
first step (Process B) as was added in Process A while incorporating sludge
recycling in both processes. Results of this study are presented in Tables 11
and 17. A slight improvement was noted in utilization efficiencies by em-
ploying sludge recycling as compared to the previous study. Even though
considerably more limestone was added to B than to A, the effluent pH's from
the first stage were approximately equal. Also, Process B required more lime
than Process A to reach pH 8. As would be expected, total utilization effi-
ciency for Process B was considerably lower than that for A (33 vs 57 percent).
The excessive limestone consumption of Process B was similarly reflected in
underflow solids levels significantly higher than those of Process A (7-1 vs
U.5 percent) because of the unused limestone. Effluent quality of Process B
(Table 17) was slightly better than that of Process A. Coagulants were in-
jected into both processes during this study at 6-ppm rates (Dowell Ml^H
anionic flocculant). Reagent cost (excluding coagulants) for Process B was
1.5 times that of Process A.
Several operational problems were noted during this study. First, pH
probe fouling was much more severe (without coagulants) than had been observed
in earlier lime studies at pH 8. The use of coagulants was necessary, there-
fore, to improve pH probe performance as well as to improve clarity and set-
tling characteristics. Secondly, erroneous reactor suspended solids values
were obtained in the earliest phases of the test because the suspension set-
tled so rapidly that representative aliquots were not being obtained for
suspended solid analyses. This was corrected by modifying the lab technique
in obtaining the aliquot. It was necessary during the course of these studies
to enlarge the coagulant reservoirs from two separate l*50-liter (120-gal)
tanks to a single 1900-liter (500-gal) tank equipped with a Lightnin' variable
35
-------
Table 11. NEUTRALIZATION DATA SUMMARIES FOR COMBINATION LIMESTONE AND LIME
WHERE PROCESS B UTILIZED 2.6 TIMES AS MUCH FIRST-STAGE LIMESTONE
First-stage effluent pH
Final effluent pH
Limestone usage, kg/cu m
Lime usage, kg/cu m
Cost, cents/1000 gal
Cost, cents/cu m
Cost, cents/10 cu m/ppm influent acidity
Utilization efficiency, percent
Stoichiometric factor (influent acidity)
Sludge to waste, % of influent AMD
Sludge recycled, % of influent AMD
Dry solids recycled, lb/1000 gal
Dry solids to waste, lb/1000 gal
Dry solids to waste, kg/cu m
Underflow solids, percent
Effluent turbidity, JTU
Limestone reactor suspended solids, mg/1
Lime reactor suspended solids, mg/1
Effluent suspended solids, mg/1
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
Mean
6.68
6.70
7.95
7.99
.1*1
1.07
0.53
0.66
9.67
ll*.5l*
2.56
3.81*
1*.77
7.27
57
33
2.12
3.71
1.1*1
1.1*0
19.9
17.3
78
100
5.1*
8.1
0.61*
0.96
l*.5l*
7.10
17
6
15000
18000
31*000
1*1000
ll*
9.0
Std. dev.
0.1
0.1
0.1
0.06
0.05
O.ll*
0.06
0.07
0.9
1.6
0.3
O.U
0.6
1.7
6.6
6.2
0.3
0.9
0.1
0.2
1.1*
0.9
1*2
60
2.3
U.5
0.3
0.5
2.1
1*.3
2
1.1*
3300
2800
-
3.0
3.5
Difference in reagent usage cost between
Process A and B, percent
50
36
-------
speed mixer. This change eliminated virtually all the coagulant pumping,
mixing, and service time problems that had been experienced earlier.
Test Four
The operating parameters for Process A were unchanged from the last test;
i.e., combination treatment to pH 8, 0.9-liter/sec (l^-gpm) flow rates, 20-
percent (of the influent) sludge recycle rate, coagulant addition at approxi-
mately a 6-ppm rate, and a 2-percent sludge-to-waste rate. Process B utilized
straight lime treatment with identical operating parameters to Process A. An
extra mixing chamber (a 2-gal bucket) was installed in the Process A thickener
to provide better mixing of the coagulant with the treated AMD. The coagulant
was injected into the line to the thickener at a point approximately 3 meters
(10 ft) from the thickener inlet. Process B's coagulant injection point was
located approximately 12 meters (1*0. ft) from the B-thickener inlet and provided
better contact between the coagulant and the AMD than was provided in Process
A. The bucket was suspended beneath the Process A influent pipe so that all
flow would first enter the bucket, mix, and then enter the thickener. This
modification was quite effective as the effluent turbidities were reduced from
as high as 30 JTU prior to use of the bucket to an average of 5 JTU. The
combination treatment results (Table 12 and IT) indicated that a reduction in
lime requirement was achieved by utilizing first-stage limestone addition
followed by lime, in contrast to lime treatment alone. More importantly, the
reagent cost for lime treatment (excluding coagulants) was 28 percent higher
than for combination treatment (3.21 vs 2.51 cents/cu m or 12.13 vs 9.51
cents/1000 gal). Effluents from both processes were of comparable quality.
Test Five
All operating parameters were the same as those for Test Four except that
the first-stage limestone addition rate was cut in half. The decrease in
limestone usage resulted in an overall increase in the cost advantage of
combination treatment over lime treatment (Table 13) as compared to Test Four
(Table 12). Test Four used twice as much limestone as Test Five and exhibited
a 28-percent cost advantage over lime, whereas Test Five's cost advantage was
3k percent. No appreciable difference was noted in the underflow solids
concentrations (2.6 vs 3.5 percent).
Effluent quality parameters from all processes were comparable (Table IT).
3T
-------
Table 12. NEUTRALIZATION DATA SUMMARIES FOR COMBINATION TREATMENT (PROCESS A)
VS LIME (PROCESS B) AT pH 8 USING COAGULANTS
First-stage effluent pH
Final effluent pH
Limestone usage, kg/cu m
Lime usage, kg/cu m
Cost, cents/1000 gal
Cost, cents/cu m
•3
Cost, cents/10 cu m/ppm influent acidity
Utilization efficiency, percent
Stoichiometric factor (influent acidity)
Sludge to waste, % of influent AMD
Sludge recycled, % of influent AMD
Dry solids recycled, lb/1000 gal
Dry solids to waste, lb/1000 gal
Dry solids to waste, kg/cu m
Underflow solids, percent
Effluent turbidity, JTU
Limestone reactor suspended solids, mg/1
Lime reactor suspended solids, mg/1
Effluent suspended solids, mg/1
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
Mean
6.72
-
8.00
8.00
.1.1
0
• 52
.83
9.51
12.13
2.51
3.21
U.70
5.91
59
58
2.09
2.15
1.92
1.88
21.2
17.8
65
67
6.0
7.1
0.71
0.85
3.8
It. 5
5
5
13600
—
21200
17200
7.2
6.9
Std. dev.
0.2
-
0.01
0.00
0.08
-
o.oU
0.12
0.5
1.8
0.1
0.5
0.8
0.7
10
6.6
O.I*
0.1*
0.2
0.1
2.1*
0.9
33
19
3.0
1.9
0.3
0.2
2.1
1.3
1.8
1.1
1500
—
5000
3000
2.7
2.1*
Difference in reagent usage cost between
Process A and B, percent
28
38
-------
Table 13. NEUTRALIZATION DATA SUMMARIES FOR COMBINATION TREATMENT WITH
REDUCED FIRST-STAGE LIMESTONE ADDITION (PROCESS A) VS LIME
(PROCESS B) USING COAGULANTS
First-stage effluent pH
Final effluent pH
Limestone usage, kg/cu m
Lime usage, kg/cu m
Cost, cents/1000 gal
Cost, cents/cu m
Cost, cents/10 cu n/ppm influent acidity
Utilization efficiency, percent
Stoichiometric factor (influent acidity)
Sludge to waste, % of influent AMD
Sludge recycled, % of influent AMD
Dry solids recycled, lb/1000 gal
Dry solids to waste, lb/1000 gal
Dry solids to waste, kg/cu m
Underflow solids , percent
Effluent turbidity, JTU
Limestone reactor suspended solids, mg/1
Lime reactor suspended solids , mg/1
Effluent suspended solids, mg/1
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
Mean
6.8
8.0
8.0
0.21
0
0.53
0.79
8.6?
11.60
2.29
3.06
1*.15
5.57
71
63
1.69
1.95
1.98
1.88
21.7
17.6
1*3
51
3.9
5.5
0.51
0.66
2.6
3.5
I*
!*
13600
21700
161*00
5.5
5.U
Std. dev.
0.2
0
0
o.ok
0
0.07
0.1
0.9
1.5
0.3
O.U
0.5
0.9
8.0
9-1
0.2
0.3
0.1
0.1
1.0
1.0
22
17
2.1
1.8
0.2
0.2
0.9
1.1
1.2
1.1*
1200
2600
2800
2.1*
1.3
Difference in reagent usage cost between
Process A and B, percent
31*
39
-------
Test Six
The limestone addition rate was again reduced by a factor of 2 from Test
Five values while all other operating parameters were unchanged. Coagulant
addition rates for both processes were approximately 10 ppm. No improvement
in the cost advantage of combination treatment was gained by the lower first-
stage limestone addition rate of this study as compared to that of Test Five
(33- vs 3^-percent cost reduction, respectively). Operating parameters for
this test are presented in Table lit and chemical data are given in Table IT.
As expected, the effluent quality parameters were comparable to the earlier
studies. It was surprising that no change one way or the other was noted in
the reagent usage cost advantage.
Test Seven
It was deduced that the cost advantage previously noted in the combination
treatment studies may have been more strongly related to the sludge having been
recycled into the first-stage reactor than to the effect of limestone addition.
To test this, no limestone was added in the first-stage reactor. The recycled
sludge contacted the raw AMD in this first step and then the lime was added in
the second reactor (Process A). Process B remained the same; i.e., lime treat-
ment and sludge recycling in a single reactor. Both processes used coagulant
addition at approximately a 5-ppm rate. AMD flow rates remained at 0.9 liter/
sec (lit gpm). Results of the study (Tables 15 and IT) indicated a 5it-percent
cost difference was obtained by recycling the sludge into a separate reactor
for contact with the AMD in this two-stage process. Utilization efficiency
averaged 99 percent for the two-stage process as opposed to 65 percent for the
single-stage process. It was felt that a portion of the 99 percent figure
might have been attributable to utilization of residual alkalinity present in
the sludge from previous studies. To insure validity of the results, all pro-
cess tanks were drained and cleaned and the test was repeated (Test Eight) re-
versing Processes A and B so that the two-stage process would be Process B
rather than A.
Test Eight
As previously described, the process flow schemes were reversed from
those of Test Seven. Sludge was recycled into the B limestone reactor (but no
limestone was added) where it contacted the raw AMD. The sludge-AMD solution
-------
Table lU. NEUTRALIZATION DATA SUMMARIES FOR COMBINATION TREATMENT WITH
MINIMAL LIMESTONE ADDITION VS LIME TREATMENT USING COAGULANTS
First-stage effluent pH
Final effluent pH
Limestone usage , kg/cu m
Lime usage , kg/cu m
Cost, cents/1000 gal
Cost, cents/cu m
Cost, cents/10 cu m/ppm influent acidity
Utilization efficiency, percent
Stoichiometric factor (influent acidity)
Sludge to waste, % of influent AMD
Sludge recycled, % of influent AMD
Dry solids recycled, lb/1000 gal
Dry solids to waste, lb/1000 gal
Dry solids to waste, kg/cu m
Underflow solids, percent
Effluent turbidity, JTU
Limestone reactor suspended solids, mg/1
Lime reactor suspended solids, mg/1
Effluent suspended solids, mg/1
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
Mean
6.8
8.0
8.0
0.130
0
0.51
O.Tit
8.06
10. 7k
2.13
2.81*
3.91*
5. 2?
79
65
1.52
1.85
1.98
1.97
21.5
18.2
68
58
6.3
6.3
0.8
0.8
3.8
3.8
5
5
12000
19200
15700
5.6
5.7
Std. dev.
0.2
0.1
0.1
0.01
0.05
0.05
0.8
0.7
0.2
0.2
0.1*
0.7
6
6
0.2
0.2
0.2
0.1
2.7
1.2
21
28
1.9
3.0
0.2
0.1*
1.1
1.8
1.5
0.6
2100
21*00
1800
2.1
2.2
Difference in reagent usage cost between
Process A and B, percent
33
-------
Table 15. NEUTRALIZATION DATA SUMMARIES FOR LIME WHERE PROCESS A RECYCLED
SLUDGE INTO A FIRST-STAGE REACTOR VS SINGLE-STAGE LIME
First-stage effluent pH
Final effluent pH
Lime usage , kg/cu m
Cost, cents/1000 gal
Cost , cents/cu m
Cost, cents/10 cu m/ppm influent acidity
Utilization efficiency, percent
Stoichiometric factor (influent acidity)
Sludge to waste, % of influent AMD
Sludge recycled, % of influent AMD
Dry solids recycled, lb/1000 gal
Dry solids to waste, lb/1000 gal
Dry solids to waste, kg/cu m
Underflow solids , percent
Effluent turbidity, JTU
Limestone reactor suspended solids, mg/1
Lime reactor suspended solids, mg/1
Effluent suspended solids, mg/1
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
Mean
6.63
8.01
8.01
O.U6
0.71
6.71
10.31
1.77
2.72
3.U2
5.25
99
65
1.20
1.8U
1.96
2.23
19.9
18.2
1*9
66
M
8.0
0.6
1.0
3.3
M
5
9
10300
16200
11000
6.0
10.5
Std. dev.
0.1
0.02
0.03
o.oi*
0.06
0.6
0.9
0.2
0.2
0.1*
0.6
8.1*
5.8
0.1
0.2
0.2
0.2
2.3
O.lt
12
19
1.2
2.1
0.1
0.2
1.2
1.8
1.1*
2.5
2700
5200
3200
1-7
l*.l
Difference in reagent usage cost betveen
Process A and B, percent
-------
was then pumped to the lime reactor for lime addition. Recycled sludge and
lime were added to the AMD in the same vessel in Process A.
Results of the study (Tables l6 and IT) generally verified the findings
of Test Seven. The cost difference between the two-stage process and single-
stage process was 30 percent; a slightly lower figure than the 5U percent of
Test Seven. The difference between the results was felt to be that Test
Seven's sludge bed contained some residual alkalinity from earlier studies as
previously discussed. The single-stage process utilization efficiency aver-
aged 6l percent during this test, which compares favorably with the 65 percent
observed during the previous test. The two-stage efficiency averaged 8l per-
cent for this study as opposed to 99 percent for Test Seven.
MANGANESE REMOVAL
The Effluent Guidelines Division of EPA was preparing the recommended
discharge standards for mine drainage at approximately the same time as the
Crown tests were underway. The interim effluent guidelines that were devel-
oped by that Division and incorporated in the Federal Register (May 13, 1976)
included limits for manganese of 2.0 mg/1 on a 30-day continuous average and
k.O mg/1 for a daily maximum.
These manganese restrictions immediately prompted considerable contro-
versy. All the data taken over the two years of neutralization studies at
Crown were reviewed to collate the manganese levels of the effluents from a
wide variety of test conditions.
Over 320 separate manganese analyses were performed on unfiltered efflu-
ents during the study period. Approximately 180 of these were on samples with
a pH of 7 or above. An equal number of analyses were performed on filtered
samples. The filtered sample data are not presented here but were consist-
ently lower in manganese concentration than the unfiltered samples.
The Crown influent manganese concentration from 106 analyses averaged 5-2
mg/1 with a standard deviation of 1.0 mg/1. A plot of the effluent manganese
concentrations as a function of treatment pH is presented in Figure 10. The
values were grouped in 0.5 pH intervals and are presented in Table l8.
Manganese was very effectively removed whenever the effluent pH was above 8.0.
Below pH 8, the systems had difficulty meeting the guidelines criteria.
-------
Table 16. NEUTRALIZATION DATA SUMMARIES FOR LIME WHERE PROCESS B RECYCLED
SLUDGE INTO A FIRST-STAGE REACTOR VS SINGLE-STAGE LIME
First-stage effluent pH
Final effluent pH
Limestone usage, kg/cu m
Lime usage , kg/cu m
Cost, cents/1000 gal
Cost, cents/cu m
Cost, cents/10 cu m/ppm influent acidity
Utilization efficiency, percent
Stoichiometric factor (influent acidity)
Sludge to waste, % of influent AMD
Sludge recycled, % of influent AMD
Dry solids recycled, lb/1000 gal
Dry solids to waste, lb/1000 gal
Dry solids to waste, kg/cu m
Underflow solids , percent
Effluent turbidity, JTU
Limestone reactor suspended solids , mg/1
Lime reactor suspended solids , mg/1
Effluent suspended solids, mg/1
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
Mean
6.5
8.0
8.0
0
0
o.Jk
0.57
10.8
8.3
2.85
2.19
5-52
U.23
61
81
1.93
1.U8
2.U
2.3
17.3
16.9
5k
39
7.2
5.3
0.9
0.6
3.7
2.8
k
5
5500
8000
7200
5.1
5.2
Std. dev.
0.2
0.11
0.05
-
0.07
0.07
1.0
1.0
0.3
0.3
0.9
0.7
9
12
0.3
0.2
0.5
0.1
0.2
0.5
20
11
2.6
1.1*
0.3
0.2
1.1*
0.8
1.2
1.6
1300
1600
ll*00
2.6
2. It
Difference in reagent usage cost between
Process A and B, percent
30
-------
Table IT. CHEMISTRY ANALYSES FOR THE COMBINATION TREATMENT STUDIES
Ui
Sample
Raw feed
Effluent A
Effluent B
Filtered A
Filtered B
Rav feed
Effluent A
Effluent B
Filtered A
Filtered B
Cond
3700
3800
3800
3800
3700
3700
Acid
570
0
0
TEST
l*6o
0
0
TEST THREE
Raw feed
Effluent A
Effluent B
3700
3700
3700
1*80
0
0
PH
5.6
8.0
7.9
TWO -
5.8
8.0
8.0
Ca
TEST
UUo
6UO
630
61*0
580
INCREASED
390
600
570
600
570
- B UTILIZED 2.
5-3
7-9
8.0
390
550
1*80
Mg
ONE -
120
110
100
110
100
Total Fe2+ Na
iron
BASIC DATA
290 250 1*88
9.2 0 510
8.7 0 1*1*0
1.3 0 500
0.1 0 1*30
DIFFERENCE IN LIMESTONE
120
110
100
110
100
230 210 500
10 0 500
7.8 0 1*60
0.08 0 1*90
0.07 0 1*50
Al
15
0.8
0.9
0.1
0.1
RATES
11
0-9
0.8
0.2
0.1
Mn
6.3
2.1
1-9
2.0
1.9
1*.3
1.6
1.5
1.5
1.5
sou
3300
3100
2900
3000
3000
2800
Alk
30
110
110
37
120
120
TDS
1*600
1*1*00
1*100
1*200
1*200
3900
6 TIMES AS MUCH FIRST-STAGE LIMESTONE
100
100
90
2l*0 210 1*60
U.o o 1*50
1.0 0 1*30
8
0.1
0.1
1*
2.1
1.3
2900
2700
21*00
62
150
130
UlOO
3800
31*00
(cont'd)
-------
Table 17. CHEMISTRY ANALYSES FOR THE COMBINATION TREATMENT STUDIES (cont'd)
Sample
Raw feed
Effluent
Effluent
Filtered
Filtered
A
B
A
B
TEST FIVE
Raw feed
Effluent
Effluent
Filtered
Filtered
A
B
A
B
Cond
3700
3500
31*00
Acid
550
0
0
- COMBINATION
3600
3500
3500
TEST SIX -
Raw feed
Effluent
Effluent
Filtered
Filtered
A
B
A
B
1*100
3900
3900
630
0
0
pH Ca
TEST FOUR -
5.6 1*00
8.0 610
8.0 580
560
550
Mg
Total
iron
Fe2+
Na Al
Mn
SO^ Alk
TDS
COMBINATION VS LIME TREATMENT
120
110
110
100
110
260
1.3
1.1*
0.3
0.2
250
0
0
0
0
TREATMENT WITH REDUCED FIRST-STAGE
5.2 31*0
8.0 560
8.0 560
550
5^0
COMBINATION TREATMENT
600
0
0
5-3 350
8.0 600
8.0 550
600
550
100
83
95
83
90
290
2.3
1.1*
0.1
0.1
270
0
0
0
0
WITH MINIMAL LIMESTONE
110
100
100
95
100
270
o.i*
0.6
0.1
0.1
250
0
0
1*70 8.1*
1*60 0.7
1*50 0.3
1*50 0.3
1*50 0.2
LIMESTONE
380 15
370 0.5
360 0.2
360 0.3
360 0.2
6.3
2.7
1.5
2.7
l.l*
VS LIME
5.1*
2.2
1.2
2.1
1.2
3000 13
2900 no
2900 110
TREATMENT
2700 1*.U
2500 100
2500 110
1*200
1*100
1*000
3800
3500
3500
VS LIME USING COAGULANTS
370 10
350 0.3
350 0.1*
350 0.1
350 0.1
6.0
2.5
1.1
2.1*
1.1
2700 6.1*
2500 110
2500 110
3750
3600
3500
(cont'd)
-------
Table 17- CHEMISTRY ANALYSES FOR THE COMBINATION TREATMENT STUDIES (cont'd)
Sample
Cond Acid
pH Ca Mg Total Fe2+ Na
iron
Al
Mn
SO,
Alk
TDS
Raw feed
Effluent A
Effluent B
Filtered A
Filtered B
Raw feed
Effluent A
Effluent B
Filtered A
Filtered B
TEST
3300
3300
3300
TEST
3500
3500
3UOO
SEVEN
510
0
0
EIGHT
630
0
0
- LIME TREATMENT
5.1
8.0
8.0
3Uo
500
U80
1+60
480
- LIME TREATMENT
U.T
8.0
8.0
1*00
650
600
650
570
USING
100
90
93
85
93
USING
120
100
110
100
110
TWO STAGES
2UO
1.2
1.2
0.1
0.1
TWO STAGES
280
0.7
0.6
0.1
0.1
(A)
230
0
0
(B)
260
0
0
VS SINGLE
Uio
390
380
360
380
9.2
O.U
0.2
0.2
0.2
VS SINGLE
Uio
Uoo
390
1+00
380
19
O.U
0.1
0.2
0.1
STAGE (B)
5-5
2.7
l.U
2.6
1.3
STAGE (A)
7
l.U
3.0
l.U
3.0
2700
2UOO
2UOO
3000
2900
2800
17
110
95
U
8l
97
3800
3300
3300
U200
Uooo
3900
NOTE: All units are mg/1 except for conductivity (micromhos/cm) and pH. Alkalinity and acidity are
expressed as CaCO
3'
-------
... _.
MAXIMUM DAILY LIMIT
2 3
CJ
LU
A
A
to
« _ 30-DAY AVERAGE LIMIT
A
I
•I
• ft
*?t
•
* '
•
78 D 10
EFFLUENT pH
Figure 10. History of the manganese levels throughout the duration
of the Crown neutralization studies.
-------
Table 18. EFFLUENT MANGANESE CONCENTRATIONS
Samples meeting limit, percent
pH range <_ 2.0 mg/1 <_ k.O mg/1
Below 6.5 0 8
6.5 to 6.99 0 26
7.0 to 7.^9 39 83
7.5 to 7.99 81 97
8.0 to 8.k9 87 100
8.5 to 8.99 100 100
9.0 to 9.^9 100 100
9.5 to 9.99 100 100
49
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REFERENCES
1. Wilmoth, Roger C., Lime and Limestone-Lime Neutralization of Acid Mine
Drainage, U.S. Environmental Protection Agency Report 670/2-7^-051,
Cincinnati, Ohio. 197U.
2. Wilmoth, Roger C. , Limestone and Lime Neutralization of Ferrous Iron Acid
Mine Drainage, U.S. Environmental Protection Agency (not released yet for
publication), Cincinnati, Ohio. January 1976.
3. U.S. Environmental Protection Agency, Methods for Chemical Analysis of
Water and Wastes, 1971-
k. Dunk, R., M. A. Mostyn, and H. C. Hoare, General Procedure for Indirect
Determination of Sulfate, Analytical Methods for Atomic Absorption
Spectrophotometry, Perkin-Elmer Corporation, Norwalk, Connecticut.
March 1971.
5. U.S. Steel Corporation, Sampling and Analyses of Coal and Coke and By-
products, Third Edition. 1929.
6. Salotto, B. V., et al., Procedure for Determination of Mine Waste
Acidity, paper given at the 15Uth National Meeting of the American
Chemical Society, Chicago, Illinois. 1966.
50
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GLOSSARY
CALCULATIONS AND DEFINITIONS
Mean Probable Detention Time
A mathematical approximation of the average actual time a flowing liquid
is detained in a vessel. The value is determined by tracer studies in which
the tracer concentration exiting from the tank is monitored in respect to
time. Two values are plotted on probability paper for each measurement point;
i.e., cumulative tracer quantities to each point + total cumulative tracer
quantity measured (percent passing) and the ratio of elapsed time of each
measurement + theoretical detention time of the vessel. The theoretical time
equals the tank volume divided by the flow rate. The resulting probability
plot is interpolated to derive the time for 50-percent passing.
Detention Efficiency
The ratio of mean probable detention time to theoretical detention time
expressed as a percentage.
Utilization Efficiency
A measure of the proportion of a neutralizer that reacts with the acid
water as compared to the amount originally added. Since alkalinity imparted
to the water is considered a benefit, the formula for utilization efficiency
13: Alkalinity Used
Utilization Efficiency = Alkalinity Added
therefore, Influent Acidity - Effluent Acidity +
Effluent Alkalinity (all as CaCO ) X 100
Utilization Efficiency = Alkalinity Added (as CaCO )d
Stoichiometric Factor
The ratio of amount of neutralizer required to treat original amount of
acid present: Alkalinity Added (as CaCO )
Stoichiometric Factor = Influent Acidity (as CaCO::)
51
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TECHNICAL REPORT DATA
' (Please read IttOructions on the reverse before completing)
1. REPORT NO. 2.
EPA 600/2-78-002
4. TITLE AND SUBTITLE
COMBINATION LIMESTONE-LIME NEUTRALIZATION OF FERROUS
IRON ACID MINE DRAINAGE
7. AUTHOR(S)
Roger C- Wilmoth
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Resource Extraction and Handling Division
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
CMnpinnati T Ohio 145268
12. SPONSORING AGENCY NAME AND ADDRESS
Industrial Environmental Research Lab. - Cin,, OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati f Ohio ^526$
3. RECIPIENT'S ACCESSION-NO.
5. REPORT DATE
January 1 Q7T issuing' r)n.t.p
6. PERFORMING ORGANIZATION CODE
600/12
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
1BB610
11. CONTRACT/GRANT NO.
In-house
13. TYPE OF REPORT AND PERIOD COVERED
'Pin^l 1 1 /7S R/7fi
14^iNioArWG(A)GENC?/ CC?DE
EPA/ 600/1 2
15, SUPPLEMENTARY NOTES
16. ABSTRACT
two-step neutralization process in which rock-dust limestone was mixed with the
influent AMD and then hydrated lime was added in a polishing reactor. This combi-
nation treatment process resulted in reagent consumption cost reductions as high as
30 percent as compared to single-stage hydrated lime treatment of the same AMD.
Later data indicated that an equal cost reduction (compared to single-stage lime
treatment) could be achieved by a two-stage hydrated lime process in which the AMD
and recycled sludge were mixed in the first reaction vessel and hydrated lime was
added in the second reactor. No cost advantage for the combination process over
straight hydrated lime treatment was felt to exist in situations where sludge
recycling was not employed.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
*Limestone
*Calcium hydroxides
Neutralizing
*Drainage
Acid Mine Drainage
Coal Mine Drainage
Ferrous Iron
West Virginia
Cost comparison
Mine (excavations)
68 0
'18. DISTRIBUTION STATEMENT
EPA Form 2220-1 (9-73)
19. SECURITY CLASS
Unclassified
60
20. SECURITY CLASS (TMspage)
22. PRICE
52
»II.S.<»VBBIIilO«mi«™GOmC[:l97«— 757-140/6685
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