EPA-670/2-73-092
October 1973
Environmental Protection Technology Series
Abatement of Mine Drainage Pollution
By Underground Precipitation
Office of Research and Development
U.S. Environmental Protection Agency
Washington, D.C. 20460
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RESEARCH BEPORTING SERIES
Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were established to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL
PROTECTION TECHNOLOGY series. This series
describes research performed to develop and
demonstrate instrumentation, equipment and
methodology to repair or prevent environmental
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.
EPA REVIEW NOTICE
This report has been reviewed by the Office of Research and
Development, EPA, and approved for publication. Approval does
not signify that the contents necessarily reflect the views
and policies of the Environmental Protection Agency, nor does
mention of trade names or commercial products constitute
endorsement or recommendation for use.
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EPA-670/2-73-092
October 1973
ABATEMENT OF MIKE DRAINAGE POLLUTION
BY UNDERGROUND PRECIPITATION
By
C.K. Stoddard
Project 1U010 EFJ
Program Element 1BBOUO
Project Officer
Harold J. Snyder, Jr.
Office of Research and Development
Washington, D.C. 20^60
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20^60
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price $1.55
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ABSTRACT
Laboratory tests with synthetic acid mine water show the
sealing effect of the gelatinous precipitate that forms when
hydrated lime or powdered limestone is added in a simulated
mine entry closed by a porous barrier.
Field tests were conducted in a recently abandoned coal mine.
Hydrated lime and limestone slurries were pumped into the mine
water behind rubble barriers through 2—inch steel pipes to
test the laboratory findings. The outflow was observed at
weirs attached to the ends of two, 12—inch diameter drain
pipes. The results indicated that only temporary sealing
of the outflow was achieved and that neutralization took
place when the interior water flow conditions were favorable.
Placement of the injection outlets, dispersion of the lime
slurry, volume of water flowing, and direction of flow in
the mine interior to other outlets are important controlling
variables that greatly affect the efficiency of the sealing
and neutralization of the outfiowing acid mine water.
Further field tests are required to demonstrate the practi-
cality of the technique.
This report is submitted in fulfillment of Project l 4OlO
EFJ (CR8l. ), Contract WPRD—2 1 42—O1, under the sponsorship of
the United States Environmental Protection Agency and the
Commonwealth of Pennsylvania, by Parsons—Jurden Division,
The Ralph M. Parsons Company, 617 West Seventh Street, Los
Angeles, California 90017.
111
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CONTENTS
Section Page
I Conclusions 1
II Recommendations 3
III Introduction 5
IV Preparations at the Mine Site 7
V Tests at the Mine Site 25
VI Test Results 41
VII Acknowledgment 47
VIII References 49
IX Appendix: Laboratory Investigations 51
V
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FIGURES
Page
1 LOCATION OF DRISCOLL NO. 4 MINE 8
2 DRISCOLL NO. 4 MINE (VIEW LOOKING NORTH TOWARD
THE MINE PORTAL) 9
3 PLAN OF SURFACE AND MINE WORKINGS 10
4 PLAN OF BULKHEADS, PIPING, WEIRS AND PORTAL 12
S SECTION THROUGH NO. 1 WEST ENTRY AND MINE PORTAL 13
6 SECTIONS THROUGH BULKHEADS 15
7 SECTION THROUGH MINE PORTAL 16
8 SECTION THROUGH NO. 1 PIPE AND WEIR 17
9 SECTION THROUGH NO. 2 DRAINPIPE AND WEIR 18
10 FRONT VIEW OF NO. 1 WEIR (ENTRY TO MINE PORTAL
IS TO LEFT OF WEIR BOX) 19
11 NO. 2 WEIR WITH 90 DEGREE NOTCHED WEIR PLATE
IN PLACE 20
12 MAIN WEIR IN WATER DRAINAGE DITCH APPROXIMATELY
500 FEET FROM MINE PORTAL 21
13 SHIRLEY MIXMETER (DIAGR.AMATIC ONLY) 23
14 VIEW LOOKING NORTH SHOWING FIELD LABORATORY
BUILDING 24
15 PROFILE OF TOTAL WATER FLOW FROM PORTAL AT
MAIN WEIR 28
16 SLUDGE SETTLED IN A STAGNANT AREA OF DRAINAGE DITCH 44
vi
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TABLES
No. Page
1 Mine Water Content Prior to Bulkhead
Construction 25
2 Total Flow From the Portal as Recorded by
the Main Weir 27
3 Mialysis of Water Outflow 30
4 Data Summary - Test A, Part 1: Demonstration
of Plugging Water Flow Through the Rubble
Barrier 31
5 Data Summary - Test A, Part 2: Attempt to
Reestablish the Seal in the West Entry
No. 1 34
6 Continuous Neutralization Test Behind No. 2
Bulkhead 37
7 Dye Injection Tests 38
8 Follow-Up Weir Data 39
vii
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SECTION 1
CON CLUS IONS
PHASE I - LABORATORY PROGRAM
Laboratory investigations indicated that the underground precipita-
tion method would be feasible to abate stream pollution by acid mine
water drainage from abandoned coal mines. The laboratory investiga-
tions revealed that under proper flow conditions the precipitates
formed within the mine will settle by gravity and remain in the mine
while neutral or alkaline water will drain from the mine. The
precipitates produced in the laboratory were found to be even bulkier
than first postulated. In the tests, the precipitates that formed in
the acid mine water, which flowed to the sand barrier in a simulated
mine adit, completely sealed off or greatly reduced the water flow.
The laboratory phase confirmed the possibility of using underground
precipitation to seal drainage channels for continuous underground
neutralization, and for underground disposal of the precipitate.
PHASE II - FIELD DEMONSTRATION
Sealing
The flow of the mine water through the loose rubble barrier in the
Driscoll No. 4 mine was stopped by the precipitates formed when
hydrated lime and limestone were injected into the space upstream
of the barrier.
The flow of water was stopped for only a short time; hence, the
permanence of the plug is questionable.
Because of the tendency of the floc to settle to the entry floor at
the injection points, the floc was unable to reach the higher por-
tions of the rubble barrier as required. The No. 1 bulkhead created
a pooi of stagnant water behind the rubble pile and canceled the
pressure head that would normally hold the floc against the rubble.
Additional laboratory work is required to substantiate the hypothesis
that the gel or floc of iron hydrates and gypsum undergoes shrinkage
and structural changes with age, which weaken or impair its effec-
tiveness as a sealing agent.
1
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The actual placement of a plug in a mine depends upon conditions
developing after the outflow ceases, and provision for possible
periodic replenishment of the sealing precipitates must be made.
Maintaining the injection lines open and free is a design problem
that must be worked out.
Continuous Neutralization
Continuous neutralization of the draining mine water was achieved as
a by-product during the attempts to reestablish the seal.
During the tests, however, continuous neutralization of the out-
flowing mine water was not achieved because of the reversal of the
flow of the water away front the No. 2 drain pipe at the slurry
injection points when the outflow was reduced to a rate of 130 to
200 gpm.
The dye tests showed that the mine water in the area adjacent to the
slurry injection points did not flow to the bulkhead drain pipes
when the outflow was reduced to a rate of 130 to 200 gpm.
Point injections of the hydrated lime slurry were inefficient since
good mixing was not achieved and stratification of the slurry and
precipitates occurred on the entry floor.
Multipoint injection to achieve continuous neutralization would
require the proper correlation of the factors of the settling rate
of the floe, flow rate of the mine water to the outflow point,
location of the area of contact between the lime slurry and mine
water, and the rate of slurry injection. Changes in water inflow
and outflow and conditions in the mine would require relocation of
the injection points to obtain good results, arid this could not
readily be done in a sealed mine.
2
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SECTION II
RECOMMENDATIONS
Further work in the laboratory or the field should be guided by
information presented in this report, which shows that the physical
layout of the mine and the water flow patterns are of major impor-
tance in effecting a seal and in providing continuous underground
neutralization of the water. In most cases, continuous neutraliza-
tion would best be accomplished outside the mine with standard
chemical-processing equipment, and with adequate control of dosage
rate to changing water flow and characteristics. The precipitated
sludge could then be returned to the mine for disposal.
Plugging of mine water outflow by underground precipitation should
be used only for carefully selected cases to shift the outflow to
some other more manageable outlet.
Laboratory tests should be conducted to gather data about the effect
of aging and possible dissolution of a plug by exposure to fresh
acid water.
3
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SECTION III
INTRODUCTION
Underground precipitation as a technique for elimination of pollution
from abandoned coal mines is of interest from three standpoints:
(1) filling of mine voids; (2) sealing drainage openings; and (3)
continuous neutralization of effluent acid mine water. The use of
underground precipitation in filling mine voids is based on forming
the precipitates in the mine, thus providing an economic advantage
over the cost of their return to the mine from a surface neutralizing
installation. The use of underground precipitation in sealing
drainage openings is advantageous as the precipitation can be carried
to the outflow points and plug the openings similar to the “blinding”
of a filter cloth. Finally, underground precipitation would be a
means for continuous neutralization of effluent acid mine water
without the concurrent problem of sludge disposal.
Under a contract with the Pennsylvania Department of Mines and
Mineral Industries, Parsons-Jurden Corporation engaged in a study of
underground precipitation in abandoned mines, resulting from the
reaction of mine water with hydrated lime and limestone, to prevent
mine drainage pollution. This work, described herein, was supported
in part by a demonstration grant by the Federal Water Pollution
Control Administration to the Commonwealth of Pennsylvania, under
Title II, Section 6(a) of the Federal Water Pollution Control Act
as amended by the Clean Water Restoration Act of 1966.
The laboratory work conducted as part of this study (covered in the
Appendix) was performed by personnel at the Plymouth Meeting, Penn-
sylvania laboratories of G. W.H. Corson, Inc., under subcontract
to Parsons —Jurden.
The field tests covered in this report are summarized below, together
with the chronology of the testing activities.
Chronology of the Field Tests
3/10/69 to 4/26/69 Mobilization and dewatering of
mine portal entries
4/27/69 to 5/10/69 Entry rehabilitation cleaning out
and timbering, pumping
5
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Chronology of the Field Tests (Contd)
5/10/69 to 6/28/69 Timbering continues, hitches cut for
No. 1 and No. 2 bulkheads; forms and
rebars installed - pumping continues
6/28/69 to 9/24/69 Work suspended except for pumping to
resolve need for No. 3 bulkhead and
arrange new construction contract
9/24/69 to 11/7/69 All bulkheads completed
9/21/70 Authorization to proceed with field
demonstration test received
10/5/70 to 11/3/70 Preparation of site, and setting up
equipment for plugging and continuous
neutralization tests
11/3/70 to 11/17/70 Plugging test in No. 1 west entry
11/18/70 to 11/22/70 Continuous neutralization test in No. 2
west and north entries
12/9/70 to 12/16/70 Replugging efforts in No. 1 west
entry
12/16/70 to 12/17/70 Site dismantling
6
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SECTION IV
PREPARATIONS AT THE MINE SITE
The workings of the Oriscoll No. 4 Mine consist of a 4-1/2-foot coal
seam that underlies an extensive hilly area. The seam dips to the
northwest from the outcropping at the base of the south side of a
hill that rises along the banks of Black Lick Creek at Vintondale,
Pennsylvania (Figure 1). The mine first opened in 1906 and was con-
sidered mined out sometime in the 1950s, but it was reactivated in
the early l960s to work a new section along the western fringe of
the older workings which are said to extend several miles from the
portal in a northerly direction. Figure 2 is a view of the area
immediately in front of the portal. A new portal was opened to the
west of the original portal. In compliance with newer regulations
covering coal mines, three entries branched out from the portal: the
No. 1 west entry, north entry, and east entry (Figure 3). A fourth
adit, the No. 2 west entry, branched off from the north entry at a
point about 25 feet from the portal and paralleled the No. 1 west
entry. The north and east entries connected with the old mine
workings. The No. 1 and No. 2 west entries comprised the active
mine.
In 1967, operation of the mine was discontinued, the pumps were
removed, and the mine began to fill with water. The east entry
was caved to prevent entry of personnel. The mine portal was also
to be backfilled with 25 feet of noncombustible material to seal the
mine against entry. However, this was not done so that the mine
could be used as the field site for demonstration purposes reported
here.
A field survey and a study of available mine maps led to the decision
to use the No. 1. west entry for the water sealing demonstration. A
rubble pile would be placed in the adit, to be sealed by the preci-
pitate formed by pumping a slurry of hydrated lime and/or ground
limestone into the mine water behind the rubble pile. Three concrete
bulkheads would be required to control the water flow. It was also
decided to use the No. 2 west entry and the north entry to test the
possibility of continuously neutralizing acid mine water, and
simultaneously eliminating the sludge disposal problem, by precipi-
tating the mineral content from the water before it drained out and
then allowing the sludge to settle into the lower portions of the
mine.
A plan of the construction undertaken at Driscoll No. 4 is shown in
Figure 4. The water level was lowered by pumping to permit repair of
the portal. Steel rails and posts were installed for maximum safety.
The north entry and the No. 2 west entry were propped up for safe
entrance. The water level was lowered further to permit cleaning and
the repair of the No. 1 west entry for a distance of 120 feet west
of the portal. After the entry had been cleaned and repaired,
emplacement of the rubble pile was started.
7
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NORTH BRANCH
BLACK LICK CREEK
CAMBRIA
COUNTY7
NE* GAS
00
PITTSBURGH
BLAC ”
Figure 1 - Location of Driscoll No.
4 Mine
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4’
..•Ir
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, 4.
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-
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4 Mine (View Looking North Toward the Mine Portal)
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Figure 2 - Driscoll No.
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N
Th 0 11 ___
W( N
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WA HER.Y
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Figure 3 - Plan of Surface and Mine Workings
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Inert material consisting of broken slate, shale, and glacial till was
placed by hand, using wheelbarrows and shovels. The entry was filled
and compacted to produce a pile 25 feet long (as measured at the roof
of the drift.) Three 2-inch steel pipes with pointed, slotted ends
were driven through the pile, terminating 3, 6, and 9 feet, respec-
tively, behind the top of the pile (Figures 4 and 5.) Following
settlement of the rubble pile, the top of the pile was refilled and
the toe reinforced with sandbags. The rubble pile was porous enough
to permit water to drain through.
Three 2-inch injection lines were installed in the No. 2 west entry,
terminating 90, 105, and 120 feet, respectively, behind the No. 2
bulkhead (described below.) Three similar injection lines were in-
stalled in the north entry, 50, 65, and 80 feet, respectively, behind
the No. 2 bulkhead. All injection lines behind the bulkheads were
Schedule 40 steel pipe, supported on wooden posts near the entry roof.
Prior to the injection tests, the steel injection pipes were connected
to plastic pipes at a point close to the outside face of the bulkheads.
Initial study of the Driscoll No. 4 Mine Layout indicated the need for
bulkhead Nos. 1 and 2, which incorporated 12-inch drainage lines with
valves. Bulkhead No. 1 was to be installed near the opening of the
No. 1 west entry. This structure, with its 12-inch drainage line and
valve, would control the water flow from the No. 1 west entry. Before
constructing the bulkhead, the 25-foot-long rubble pile was to be
placed in the entry about 10 feet behind the bulkhead. Under these
conditions, the first cross-entry to the No. 2 west entry, on the right,
would be upstream of the rubble pile and, therefore, would require no
flow control.
Later in the study it was found that the rock near the opening of the
adit was not sound enough to hold the bulkhead; hence the bulkhead
position was moved back into the adit a sufficient distance to ensure
sound rock and provide a watertight bulkhead. After moving the bulk-
head back into the mine, the cross-entry opened downstream of the
rubble pile, rather than upstream as originally conceived. Since this
would provide a bypass for water flow around the rubble pile, the No.
3 bulkhead was required in the cross-entry.
The No. 1 bulkhead was located in the No. 1 west entry and provided
with a 12-inch steel drainage pipe; and No. 3 was placed in the cross-
entry, as shown in Figure 5. The three injection lines which were
driven through the rubble pile extended through the No. 1 bulkhead.
The No. 2 bulkhead was also provided with a 12-inch steel drainage
pipe.
Six injection lines were installed, three in the No. 1 west entry and
three in the north entry. The No. 3 bulkhead in the cross-entry was
solid.
11
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NO. 1 INJECTION LINE EXTENDS 80 FT FROM NO. 2 BULKHEAD
INJECTION LINE EXTENDS 65 FT FROM NO. 2 BULK HEAD
INJECTION LINE EXTENDS 50 FT FROM NO. 2
DYL - 60 MIN.
900 GPM
t )
RUBBLE PILE SEALING
TEST AREA
‘—P40.1 BULKHEAD
Figure 4 - Plan of Bulkheads, Piping, Weirs and Portal
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IS.., IIIJICTION INI$
IrON
NJICT1ON
(#4
USI4UN TUT’ SIC TION A-A
yI
To ’
I(IW ORC(O CONCUTI
POSTAL
Ns.t SlOPS I$0 1A. DRAIN URI
Figure 5 - Section Through No. 1 West Entry and Mine Portal
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As mentioned above, the bulkheads were located where good ground con-
ditions existed in the entries. Eighteen—inch-wide slots were exca-
vated 24 inches into the side walls, floor, and roof of each entry to
lock the bulkheads in place and provide a watertight seal. Concrete
reinforcing bars were placed in the excavations, and injection lines
and drainage lines were installed. Wood forms were set in place and
concrete pumped into the form. Figure 5 shows a section in elevation
through the No. 1 bulkhead, No. 1 west entry, and mine portal. Bulk-
head details are shown in Figure 6.
Bleeder lines were placed in the back of the bulkhead excavations to
bleed off air so that the entire excavated area would accept concrete.
The 12-inch drain lines were extended front the No. 1 and No. 2 bulk-
heads out to the portal. Gate valves were installed on the ends of
these lines to permit control of the flow through the two discharge
points. The mine was then no longer accessible to personnel.
The 2—inch injection lines were capped temporarily to prevent water
flow through them. The pumping was then discontinued, and the entry
allowed to refill and drain through the two 12-inch drain lines. Some
months later, when the preparations for the tests were started, it was
found that a rock slide had occurred in the interim. To make the
portal safe once again, it was necessary to remove several large chunks
of rock from the brow of the portal and place additional timbering in
the entries. The area from the portal back to the bulkheads was pumped
out to permit access to the bulkhead faces. The 2-inch steel injection
lines were uncapped and 2-inch plastic lines were attached and extended
out to the portal. A clay core and sandbag berm was constructed at the
portal to prevent flooding this area once again and to channel the
water flow from the drainage pipes (Figure 7.) However, because of
seepage from the caved east entry, it was impossible to keep this area
from flooding.
One steel weir box containing a 30-degree V-notched plate was bolted to
No. 1 drain pipe valve (Figure 8) and a second was placed several feet
downstream of the No. 2 drain pipe valve (Figure 9.) The sandbag berm
channeled the water from the No. 2 valve to the No. 2 weir box. Because
of the large flow of water from the No. 2 drain pipe, it was necessary
to cut the front plate of the No. 2 weir to produce a 12-inch rectan-
gular weir. A 90-degree V-notched plate was inserted during periods
of low flow. Additional views of the portal and weirs are shown in
Figures 10 and 11.
Water from the No. 1 and No. 2 drainage lines discharged to an existing
drainage ditch that flowed into the south branch of Black Lick Creek
(Figure 3.) The third weir, identified as the main weir, containing a
30-degree V—notched plate (Figure 12), was placed in this ditch. A
trash-catching screen was installed about 50 feet upstream of this
weir to prevent interference by floating debris.
14
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ROOF
a., • a
4 I f, a ’ 4
. %., I . N#*c**
VIEWINS PORT 24 DRAIN LINE .]. °
I:. :i ENTRY 14t4 1/2
•.
.4 . . .. - .. . - . . . a. . . -
.* L _ ..., . ——
I.. -‘ . ‘g. • a
• • REINFORCED CONCRETE • ; ‘. ..: •. :: ‘..
-: ‘_‘ . .‘ ‘... ‘•: •‘:.
No. I BULKHEAD
SECTION B- !
ROOF
No. 2 BULKHEAD
SECTION C-C
ROOF
No. 3 BULKHEAD
SECTION 0-b
Figure 6 - Sections Through Bulkheads
č.w....’, i. .,• •.‘
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*615*4 •S ’ ’ .34 -.
ia ’4_ORAIN,..?, 6....II.j. .
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a ENTRY 1$ a 41/2 • - • • b
REINFORCED CONCRETE - . - .-. :c.. :-‘ . .-
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Ia .1 • • • — 4.. -. .1.
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‘ .‘; ‘- , .: .: - • REINFORCED CONCRETE ’ : .
. • a- - ! -.:a’, k.”
,a • . . • • --.4. ..__..
15
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INJECTION UNES
BROW OF PORTAL
-•-, EAST
ENTRY
SECTION E-E
NO. 2 DRAIN LINE
Figure 7 - Section Through Mine Portal
-------
ROOF
I
I
DAM
1
WHEEL
FLOW
FROM NO. I
WEST ENTRY
NO. I WEIR
PORTAL
-
SAND BAG
FLOW FROM WEIR 30’V NOTCH
DITCH TO BLACK LICK CREEK
— _
BOTTOM
SECTION F-F — -____
Figure 8 - Section Through No. 1 Pipe and Weir
-------
I I I
PORTAL
SAND BAG DAM
ROOF
NO.2
00
LOW
90V NOTCH
SECTION G-G
Figure 9 - Section Through No. 2 Drain Pipe and Weir
-------
.1
1
—,
ii
., -,
4
____ b.
(Entry to Mine Portal is to Left of Weir Box)
4.
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Figure 10
Front View of No, 1 Weir
-------
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Figure 11 - No. 2 Weir with 90-Degree Notched Weir Plate in Place
-------
‘ A.
-
- —
r #‘
Figure 12 - Main Weir in Water Drainage Ditch Approximately 500 Feet From Mine Portal
-------
A portable gasoline-driven Shirley Mixmeter (Model 65 AP 3x4) was set
up to prepare slurries of hydrated lime and/or pulverized limestone
and inject them through the 2-inch pipes to the various flooded zones
behind the bulkheads. The charging tank had a capacity of 290 gallons.
This machine was used to deliver the slurries through the 2-inch lines
to a space behind the bulkheads (see Figure 4.) The pH meter and the
slurry metering control devices on the machine were disconnected. The
water used to prepare the slurries and carry them into the selected
spaces behind the bulkheads was taken from the ditch just downstream
of the No. 1 and No. 2 weirs by the suction line of the centrifugal
pump. A portion of the slurry stream from the centrifugal pump was
recycled back into the charging tank to maintain a constant level.
Figure 13 shows the diagrammatic hookup of the machine. The flow rate
of the recycle stream was manually controlled to keep the slurry in
the charging tank thin enough to flow properly to the pump suction
line - approximately 0.516 ground limestone or hydrated lime per gallon
(5.67 wt%.)
The Shirley Mixmeter was run for 4 hours on October 29, 1970 to check
it and other equipment, with electric power provided by a portable
gasoline generator. This was later replaced by a temporary 220-volt
power line that was run about 2200 feet across the south branch of
Black Lick Creek to the site from Vintondale. One of the field
buildings near the portal was equipped for use as a field office,
Storeroom and laboratory (Figure 14.) Preparations for testing were
completed at the mine portal by November 3, 1970.
22
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HYDRATED LIME AND/OR
PULVERIZED LIMESTONE FEED
RECYCLE
AUUL AOIJATOR
CHARGING TANK
TO
INJECTION
LINES
Figure 13 - Shirley Mixmeter
(Diagrammatic Only)
-------
-p
•$ 4’
Figure 14 - View Looking North Showing Field Laboratory Building
-------
SECTION V
TESTS AT THE MINE SITE
Operations at the mine site commenced on November 3, 1970 and continued
until December 17, 1970. However, actual injection of lime slurries
into the mine was not continuous during this period because of equipment
breakdowns, freezing weather, rain, snow, plugged injection lines, the
Thanksgiving holiday, and occasional weekend interruptions.
Tests were conducted to meet two major objectives:
Test A : The demonstration of sealing the water flow through the
rubble barrier by injecting lime slurries in the space just
upstream of it.
Test B : The neutralization of the acid mine water by injecting
lime into the space behind a bulkhead so that the resulting
precipitate of ferric and ferrous hydroxide remained in the mine,
and clear, neutralized water flowed out through the 12-inch drain
pipe.
These tests are described below.
TEST A, PART 1: SEAL OUTFLOW THROUGH THE RUBBLE BARRIER
A series of ‘water samples were obtained from the mine between March 25
and April 18, 1969, and analyzed for chemical content. The results of
the analyses are presented in Table 1.
Table 1 - Mine Water Content Prior to Bulkhead Construction
Date
Chemical Content (mg/fl
CaCO Alkalinity*
Fe
Ca
Mg
Al
Mn
P
Total
March 25
March 30
April 4
April 9
April 14
April 18
2120
2188
2266
2152
2172
2228
395
293
312
295
188
143
1046
1145
1162
1101
1126
1161
220
232
276
163
119
113
163
185
168
21
21
21
*p = Phenolphthalein; Total = Methyl Orange
25
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The No. 3 weir, the first installed, served to establish the flow charac-
teristics of the total water coming out of the portal. Daily readings
were taken, commencing October 22. These are presented in Table 2, to-
gether with conversions to gallons per minute. The data from Table 2 are
depicted graphically in Figure 15, and show that the water outflow was
slowly diminishing during the period prior to Test A. A rainstorm
between October 29 and 31 washed out the No. 3 weir, and readings were
not resumed until November 3.
As may be noted, rain water deposits did not appear at the portal until
November 3 (about five days after the rain started), they rapidly rose
to a peak of about 750 gpm, and then fell off to an average flow of
about 350 gpd.
For Test A, the slurry injection schedule into the No. 1 west entry was
4 hours of hydrated lime alternating with 4 hours of pulverized limestone.
A high-calcium hydrated lime (with a screen analysis of 98% through 325
mesh) and a pulverized high-calcium limestone (with a screen analysis of
82% through 200 mesh; 99.6% through 60 mesh) were used. This schedule
was maintained for 40 hours, during which time a total of 6500 pounds of
hydrated lime and 6050 pounds of pulverized limestone were injected.
The following 22-hour period, injection of limestone was discontinued,
and 11,000 pounds of hydrated lime was injected into the space behind the
rubble pile in the No. 1 west entry to raise the pH above 8; this event-
ually occurred.
Prior to the test, water samples were taken periodically from the No. 1
bulkhead outflow; during the test, samples were taken hourly from the
No. 1 weir. These were analyzed in the field laboratory for free acid,
total acid, total iron, ferrous iron, and total sulfate. Results of the
analyses are summarized in Table 3.
Readings of flow and pH at the No. 1 weir were taken hourly. These data
have been condensed and are summarized in Table 4.
The flow of water rapidly dropped to zero at about the 62nd hour of
slurry injection, indicating that a plug had been formed in the rubble
pile. A very small flow from the No. 1 weir started a few hours later
at about 1 gpm and varied between zero and 1-1/2 gpm thereafter. Lime-
stone mixed with hydrated lime was injected again at about the 65th hour
and continued until the 116th hour, when the injection lines plugged.
Approximately 24 hours later, one injection line was unplugged and
hydrated lime was injected alone; within 9 hours, the line plugged again.
When the injection lines became plugged the second time (after 149 hours),
the flow from the No. 1 weir was about 1/2 gpm and the valve on the
12-inch pipe from the No. 1 bulkhead was closed. Because the valve was
in a rather isolated area on the lower haulage track level of the portal,
the closure was not noticed while efforts were underway to reopen the
injection lines. As noted in Figure 5 (presented in Section 4), the
entry between the rubble pile and the No. 1 bulkhead was filled with mine
26
-------
Table 2 - Total Flow From the Portal as Recorded by the Main Weir
Flow
Date Remarks
Time Inches Gal/Mm
October 22 1600 12-1/2 325 Weir installed.
23 0800 12 300
23 1600 12 300
24 0800 11-1/2 270
25 1400 11-1/4 255
26 0800 11 245
26 1600 10-3/4 230
27 0800 10-1/4 200
27 1600 10-1/4 200
28 0800 10 195
29 9-3/4 180 Rain started.
30 9-3/4 180 Heavy rain, 24 hours.
31 9-1/2 170 Rain diminished.
November 1 Washouts and rain damage repairs
underway.
2
3 8 120 Phase A test started.
4 11-1/2 375
5 17-1/4 745 Flow stopped at No. 1 weir.
6 0600 8-3/4 135
6 1200 12-1/2 335
6 2300 14 450 Flow of 0 to 1-1/2 gpm at
No. I weir.
7 0200 13-3/4 420 Flow of 0 to 1-1/2 gpm at
No. 1 weir.
7 1800 12-3/4 350 Flow of 0 to 1-1/2 gpm at
No. 1 weir.
8 0600 11-3/4 290 Flow of 0 to 1-1/2 gpm at
No. 1 weir.
8 1200 12-1/2 335 Flow of 0 to 1-1/2 gpm at
No. 1 weir.
9 13 370 Flow of 0 to 1-1/2 gpm at
No. 1 weir.
10 Valve on No. 1 line closed.
27
-------
1000
RANGE OF RAW WATER pH 3
ZERO OR LESS
I..a
-3
THAN I GPN FLOW
NO I
PERIOD OF HEAVY RAIN STARTED
500 I I YES
OW USNEO /21
- — — —
READING
0 22 23 24 25 28 27 28 29 30 31 i 2 3 4 5 I I i I
OCT. I NOV.
Figure 15 - Profile of Total Flow of Water From Portal at Main Weir
-------
10
I
pH
8
1 O0
t—NO. 2 WEIR
.5
-4__
-3
900 GPN
C D
CD
11
12
THANKSGIVING HOLIDAY
NO OPERATIONS
NOV.
13
15
FLOW NO.1 WEIR
19
20
21
28
29
30
NOV.
Figure 15 (Contd)
-------
Table 3 - Analysis of Water Outflow
Component
Before Plugging Test
300-400 gpin
(Av mg/i)
During Plugging Test
1/2-1 gpm
(Av mg/i)
Free Acid
Total Acid
Total Fe
Total Fe 2
Total SO 4
pH
0
160
1400
1000
5000
5.1
0
0
24
5
4500
8.8
Water U to the invert of the li-inch drain pipe. Thus, since the space
behind the rubble pile was filled with water, the seal was under no
pressure head.
In an attempt to complete all field operations before impending bad
weather forced the winter shutdown, attention was then directed to the
continuous neutralization demonstration (Test B). However, while the
neutralization test was being conducted, efforts to unplug the injection
lines into the west entry continued and proved successful. Attempts
could then be made to seal off the water from the west entry. When the
No. 1 valve was reopened after being closed 168 hours, the water from
the west entry No. 1 bulkhead flowed at 20 to 45 gpm, indicating that
the seal had deteriorated.
TEST A, PART 2 - ATTEMPT TO REESTABLISH SEAL
The equipment used for the initial plugging test was also used during
the attempt to reseal the rubble pile in the No. 1 west entry. When the
No. 1 valve was reopened after having been closed for 168 hours, the
water issuing from the No. 1 weir box had dropped to the normal raw mine
water pH level of 3.8 to 4.0. The outflow of mine water, which was 20 to
45 gpm when the valve was reopened, increased to 90 to 200+ gpm by the
time the neutralization tests were completed. This led to speculation
that the great reserve of acidity in the mine water in back of the
plugged rubble pile barrier had diffused into the gel and redissolved
the ferrous and ferric hydrates) causing failure of the initial plug.
Presumably, resumption of the injection of lime slurries would reestab-
lish the seal. To verify this assumption, an attempt was made to
reestablish the seal.
30
-------
1: Demonstration of
Rubble Barrier
Table 4 - Data Summary - Test A, Part
Plugging Water Flow Through the
( 14
Period
Duration
(hr)
Addition
Water
Flow
(gpm)
Water pH
Initial Final
Total
Elapsed
Time
(hr)
Event
Hydrated
Lime
Pulverized
Limestone
.
Quantity
(Ib)
Rate
(lb/hr)
.
Quantity
(ib)
Rate
(lb/hr)
1
40
6,500
160
6,050
151
200-500
3.9 5.4
0
Started alternate
injection of
hydrated lime and
pulverized lime-
stone.
2
22
11,000
500
0
150-700
4.6 6.8
40
Changed to injec-
tion of hydrated
lime alone. Flow
of water decreas-
ing.
3
3
2,000
0
0
-
62
Flow of water
stopped.
4
5
51
24
11,650
228
15,480
303
0-1
6.7 10.2
-
65
102
116
Changed to injec-
tion mixture of
hydrated lime and
pulverized lime-
stone.
Slight flow of
water.
Injection lines
plugged @ 116 hrs.
-------
Table 4 (Contd)
Period
Duratioj
(hr)
Addition
Water
Flow
(gpm)
Water pH
Total
Elapsed
Time
(hr)
Event
Hydrated
Lime
Pulverized
Limestone
Initial
Final
Quantity
(ib)
Rate
(lb/hr)
•
Quantity
(lb)
Rate
(lb/hr)
6
9
3,000
333
0
0-1/2
-
140
141
Unplugged one
injection line;
resumed injec-
tion of hydrated
lime alone.
No flow of water.
7
168
0
0
0
5.4
6.3
149
Injection line
plugged; closed
No. 1 valve @
149 hrs.
8
28
5,600
200
0
20-45
6.1
11.2
317
All 3 injection
lines unplugged;
opened No. 1
valve; resumed
injection of
hydrated lime
alone.
9
0
-
-
-
-
-
345
Injection lines
plugged; test
terminated.
Total
39,750
21,530
-------
During the first test period, only hydrated lime was used; 39,300 pounds
were injected continuously for 75 hours at a rate of 525 pounds per hour.
The pH of the outf lowing water rose to 10.2, but there was no significant
drop in water flow. During the second test period, which lasted 22 hours,
a mixture consisting of 4,400 pounds of hydrated lime and 5,440 pounds of
pulverized limestone was injected with no noticeable effect on the water
flow.
For the next 5 hours (the third test period), injection of hydrated lime
was continued but pulverized limestone was omitted. At the same time,
however, the production of sludge was increased by augmenting the mineral
content of the water with waste pickle liquor containing 5 to 6% H 2 S04
and 5 to 6% Fe , which was added to the hydrated lime slurry at a rate
of approximately 1 gpni as the slurry was being injected into the mine
workings. Addition of a total of 2,150 pounds of hydrated lime and 200
gallons of waste pickle liquor caused no noticeable effect on the water
flow.
Throughout the next 9 hours (the fourth test period), a mixture of 1550
pounds of hydrated lime and 1280 pounds of pulverized limestone was
injected without discernable effect on the outf lowing water at the No. 3
weir. At this point, the Mixmeter broke down and injections could not
continue until repairs were completed 29 hours later. During the repair
period (Period 5), the outf lowing water pH dropped to 4.7.
Injection of a mixture of hydrated lime and pulverized limestone was
resumed (Period 6), but 49 hours later, after 9800 pounds of hydrated
lime arid 10,560 pounds of pulverized limestone had been injected, the
injection system broke down again. Again the pH rose to the 11 to 12
range.
After repairs were completed 6 hours later, injection of a mixture of
hydrated lime and pulverized limestone was continued again for 17 hours,
during which time 3200 pounds of hydrated lime and 1680 pounds of pul-
verized limestone were injected - again without any effect on the water
outflow.
The data from these tests are summarized in Table 5. It is evident that
attempts to stop the flow of water through the rubble barrier were unsuc-
cessful even though 60,400 pounds of hydrated lime and 18,960 pounds of
pulverized limestone were injected into the entry. However, the pH of
the outflowing mine water rapidly increased to the 11 to 12 range when
the slurry was injected and rapidly fell off to the base mine water range
when the injection stopped. After the last injection period, the water
flow and pH were monitored for an additional 39 hours while arrangements
were being made to shut down for the winter.
33
-------
Period
Duratior
(hr)
Addition
—
Water
Flow
(gpm)
Water pH
Total
Elapsed
Time
(hr)
Event
Hydrated
Lime
Pulverized
Limestone
Initial
Final
.
Quantity
(ib)
Rate
(lb/hr)
Quantity
(ib)
Rate
(lb/hr)
1
75
39,300
525
0
20-90
3.8
10.2
0
Started injec-
tion of hydrated
lime alone.
2
22
4,400
200
5,440
245
20-90
12.1
12.3
75
Changed to
injection of
mixture of
hydrated lime
and pulverized
limestone.
3
5
2,150
430
0
65-90
12.1
12.3
97
Started injec-
tion of hydrated
lime and waste
pickle liquor.
4
9
1,550
175
1,280
142
65-115
12.3
11.9
102
Changed to
injection of
mixture of
hydrated lime
and pulverized
limestone.
5
29
0
0
25-115
12.0
4.7
111
Equipment Break-
down.
Table 5 - Data Summary - Test A, Part 2: Attempt to
Reestablish the Seal in the West Entry No. 1
( ‘4
-------
Table 5 (Contd)
U,
Period
Duration
(hr)
Addition
Water
Flow
(gpm)
_______
Water pH
Total
Elapsed
Time
(hr)
Event
Hydrated
Lime
Pulverized
Limestone
Initial
Final
Quantity
(ib)
Rate
(lb/hr)
Quantity
(ib)
Rate
(lb/hr)
6
49
9,800
200
10,560
216
25-55
5.0
11.7
140
Resumed injec-
tion of mixture.
7
6
0
0
35-45
10.5
8.5
189
Equipment break-
down.
8
17
3,200
188
1,680
210
35-80
8.5
11.6
195
Resumed injec-
tion of mixture.
I 9
39
0
0
55-114
5.3
4,1
212
Stopped injec-
tion of mixture.
10
0
-
-
-
-
-
251
Test terminated.
Total
60,400
18,960
-------
TEST B, PART 1: CONTINUOUS NEUTRALIZATION
Test B, Part 1, the continuous neutralization of the outfiowing water,
was conducted behind the No. 2 bulkhead (see Figure 4). The water from
this area of the mine flowed out of the No. 2 weir and was relatively
isolated from the lime injection behind the No. 1 bulkhead. Flow from
behind the No. 2 bulkhead was controlled by the No. 2 valve at the down-
stream end of the 12-inch pipeline just before it entered the No. 2 weir.
For the purposes of this test, the No. 2 valve was partially closed to
reduce the water flow to approximately 150 gpm, and, once adjusted, was
not changed for the duration of the test. However, the flow varied from
130 to 200 gpm, presumably because of changes in the head in the mine.
For this test, a slurry containing 0.5 pound of hydrated lime per gallon
was prepared using two Shirley Mixmeters. After 200 gallons of water
were pumped into the charging tank of the first Mixmeter, the mixing arm
was started and 100 pounds of hydrated lime were added. The charge was
mixed until a uniform slurry was formed. A similar charge was prepared
in the charging tank of the second Mixmeter. To provide a continuous
supply of hydrated lime slurry during the test, as each charging tank
was emptied, a new charge was prepared. The Mixmeters were used only as
slurry mixers and the batches were transferred to a 55-gallon open-end
drum which served as a feed tank for four small paddle pumps. Each pump
was connected to one of the six 2-inch injection lines that passed
through the No. 2 bulkhead into the mine. The four injection lines used
were Nos. 2 and 3 which terminated 65 and 50 feet into the north entry and
Nos. 5 and 6 which terminated 105 and 90 feet into the west entry beyond
the bulkheads. Each of these pumps had a capacity of 2 gpin of slurry;
since they were operated together, a total of 8 gpm of slurry was
injected when the tests were made.
After 39 hours, use of the paddle pumps was discontinued because the
rotors were worn out, terminating the first period of the slurry injec-
tions. Operations were stopped until replacement pumps could be obtained.
Both before and after the test the mine water had a pH of 3.8 to 4.5,
which indicated no lasting effect of the lime injection.
Theoretically, a dosage rate of 4.0 pounds of hydrated lime per minute
should raise a pH of 3.5 to 11.1. However, this did not occur; the
actual mine water readings at the No. 2 weir ranged from 3.6 to 4.6
during the 39-hour period that the hydrated lime slurry was injected.
The Period 2 test was conducted with a gasoline-driven pump, which per-
mitted the injection of the lime slurry at a higher rate than the Per-
iod 1 test; i.e., 20 gpm. The outflow of mine water was the same, and
the pH, ranging from 4.4 to 4.5 during the 10-hour period between the
tests, was essentially the same. Theoretically, the lime injection rate
in this test was sufficient to raise a pH of 3.5 to 12. Again, however
(as shown in Table 6) the outflowing water failed to respond to the
36
-------
treatment and its pH ranged from 4.4 to 4.8 during the 26 hours of
testing.
Table 6 - Continuous Neutralization Test Behind No. 2 Bulkhead
Test
Period
Dura-
tion
(hr)
Slurry
Injec-
tion
Rate
(gpm)
Hydrated
Lime
Addition
Flow of
Mine Water
Ratio of
Lime to
Mine Water
(gm/liter)
p1- I at
No. 2 Weir
lb/
mm
Total
Pounds
gpm
liters!
mm
Theoret-
ical
Actual
1
-
2
39
10
26
8
0
20
4.0
-
10.0
9,360
-
15,600
130-
200
130-
200
130-
200
492-
757
492-
757
492-
757
2.40-3.69
-
6.00-9.23
11.1
-
12.0
3.6-
4.6
4.4-
4.5
4.4-
4.8
TEST B, PART 2: DYE INJECTIONS
Failure of injection of the hydrated lime into the mine workings behind
the No. 2 bulkhead to increase the p1-I of the outflow at the No. 2 weir
raised the question of where the outflow was coming from. Therefore, a
series of dye solution injections were made to determine the flow pattern
of the water draining from the 12-inch No. 2 drain line. Both the north
entry and the No. 2 west entry were tested in this manner. The dye solu-
tion was prepared by thoroughly mixing 2 ounces of methylene blue in
50 gallons of mine water. The injections were made using the 20-gpm pump,
and took 2 minutes to complete.
North Entry
During the first dye test, the dye solution was injected through the
No. 1 injection line into the North Entry at a point 80 feet from the
No. 2 bulkhead (see Figure 4). The control valve in the 12-inch drain
line was opened completely, which gave a 900-gpm outflow of mine water.
In this test, the dye appeared at the discharge of the No. 2 drain line
30 minutes after it was injected. The outflow was allowed to continue
for approximately 2 hours to purge the dye from the north entry so that
the dye testing could be repeated with a reduced flow.
In the next part of this test, the control valve was partially closed to
restrict the discharge flow to 150 gpm, and a second injection of dye
solution was made under the same pumping conditions. This time the dye
solution did not appear at the discharge point after 4 hours, which was
long eough to drain a volume of water from a mine one-third greater
than that necessary to show the dye at the higher rate of outflow.
37
-------
No. 2 West Engry
For the second dye test, the dye solution was injected through injection
line No. 4 into the No. 2 west entry at a point 120 feet from the No. 2
bulkhead (see Figure 4).
As in the first dye test, the valve controlling the 12-inch drain line
was left completely open and discharged mine water at a rate of 900 gpm.
This time the dye appeared at the discharge 60 minutes after it was
injected into the imine entries.
With the valve again partially closed to restrict the discharge flow to
150 gpm, a second injection of dye solution was made. Observation of the
outflow for approximately 8 hours revealed no dye at the discharge outlet.
As before, the volume of water drained from the mine at the low outflow
rate exceeded the volume that showed the dye at the high outflow rate by
one-third. Results of the dye tests are summarized in Table 7.
Table 7 - Dye Injection Tests
Test Condition
Results
injection
Point
No. 2
Valve Position
No. 2 Line
(180 ft in
north entry)
Fully open
(Approx 900 gpm)
Partially open
(Approx 150 gpm)
Dye appeared within
30 minutes
No dye appeared
after 4 hours
No. 4 Line
(120 ft in
No. 2 west
entry)
Fully open
(Approx 900 gpni)
Partially open
(Approx 150 gpm)
Dye appeared within
60 minutes
No dye appeared
after 8 hours
The dye tests indicated that the flow pattern of the water adjacent to
the ends of the injection lines in the north entry and the No. 2 west
entry changes when the outflow from behind the No. 2 bulkhead is changed.
Obviously, when the valve is wide open, the flow at the end of the injec-
tion line is sufficient to carry the dye into the 12-inch pipe at the
No. 2 bulkhead. When the valve was partly closed, the outflow was insuf-
ficient to bring the dye to the inlet of the 12-inch pipe. Presumably,
this same effect was occurring when the slurry was being injected. Thus,
any effect of acid water neutralization by the hydrated lime would not
be observed at the weir box for the flow rate of 150 gpm. Injection of
the slurry at flow rates substantially greater than 20 gpni, to be
38
-------
compatible with the 900-gpm outflow rate, was not possible with the
existing equipment.
FOLLOWIJP INSPECTION OF MINESTIE, SPRING 1971
A field inspection of the minesite was made on May 3, 1971, after the
relatively mild winter. The weirs were still in place and no subsidence
or othe/damage was observed at the portal. Weir and pH measurements
made at the site are summarized in Table 8.
Table 8 - Followup Weir Data
Time
(hrs)
No. 1 Weir
No. 2 Weir
Main Weir
Flow
(gpm)
pH
Flow
(gpm)
pH
Flow
(gpm)
pH
800
830
900
930
1000
1030
1100
1130
1200
15
16
15
15
15
16
16
16
16
4.2
4.3
4.1
4.3
4.2
4.2
4.2
4.2
4.2
454
530
545
545
545
545
545
545
545
3.8
3.7
3.7
3.8
3.9
3.9
3.8
3.8
3.8
560
545
560
560
560
560
560
560
560
3.9
3.9
3.9
3.8
3.8
3.9
3.8
3.8
3.8
Elevations were measured on the bottoms of the 12-inch discharge pipes,
and showed that the No. 2 pipe is 0.62 foot lower than the No. 1 pipe.
The valves on both pipes were wide open and No. 2 pipe was blowing full.
The higher pH at the No. 1 weir indicates that the lime slurry injected
into the No. 1 west entry is still causing some neutralizing effect.
The No. 2 and main weirs were badly corroded by the acid water.
39
-------
SECTION VI
TEST RESULTS
SEALING
After hydrated lime and ground limestone had been injected into the
acid mine water behind the rubble pile for 65 hours (Table 4), the
flow through the emplaced rubble pile was reduced from approximately
500 gpm to zero. Thus, the initial sealing was successful.
Although the flow had been reduced to zero when the seal was first
accomplished, some water began to seep at the rate of about 1-1/2 gpm,
as observed at the No. 1 weir during the test period, until the 149th
hour, at which time the valve was closed. Continued injections of
lime and/or limestone had no effect in reducing these seepages to zero.
An attempt was made to reestablish the seal when the No. 2 valve was
reopened, but it failed. Even adding waste sulfate pickle liquor to
augment the minerals in the water and produce a higher volume of
precipitate failed.
As the pH of acid mine water is raised by the reaction of neutralizing
agents with the acid water, dissolved ferrous and ferric ions precipi-
tate as a sludge consisting of hydroxides or hydrated oxides. The
calcium from the lime forms calcium sulfate, most probably gypsum,
which is crystalline and only slightly soluble. The form and charac-
teristics of this sludge can vary extensively, depending on such
variants as water constituents, neutralizing agents, and the rate of
addition of neutralizing agents. While the sludge varies from a light,
fluffy floc to a dense particulate precipitate, it is always in a
nonfilterable form that would blind a filtering medium. Its non-
filterability is the basis for using the sludge to seal drainage
openings, using the water flow to carry the sludge into the voids to
plug them.
However, for the precipitated sludge to be effective, the size of the
voids or channels that the sludge is to seal must not exceed some
unknown maximum. It is certain that the precipitate, when relatively
freshly formed, did indeed stop the flow of water through the channels
of the rubble pile. Flows of 1/2 to 1 gpm are not regarded as signi-
ficant indications of seal failure; hence, it was during the time that
the No. 1 valve was closed (after 149 hours) that the seal failed, and
flows of 20 to 45 gpm could be observed when the valve was reopened.
Two factors may have contributed to this: (1) the well-known shrink-
age of gels as they age may have loosened the plugs, and (2) diffusion
of acid mine water into the gelatinous plugging material may have
caused re-solution of the iron hydrate gel. It is entirely possible
that the neutralization of the acid mine water at the face of the
41
-------
rubble harrier was badly impaired by the stratification of the lime
slurry precipitate and its flow downslope into the mine depths. This
could have occurred when the slurry fell from the ends of the injecting
pipes to the floor of the entry. Since the water at the face of the
rubble barriers was stagnant, once the seal was established there was
no flowing force to carry or hold the injected slurry and precipitates
into the channels and maintain the seals. When the seal failed later
and water flows upward of 100 gpm set in, the efforts to reestablish
the seal could have failed because the sandbag seal at the top of the
barrier had failed and the resulting channels were too large for the
gel to close. The sandbags had been in position for approximately a
year and protected only the last 18 to 24 inches of the 25-foot crown
of the rubble pile that had settled a few inches beneath the entry
roof.
During the tests to reestablish the seal, the outfiowing mine water
was highly alkaline and slightly murky because of blue-green iron
hydrates. This led to the hypothesis that one or more of the injection
lines had been ruptured between the No. I bulkhead and the rubble pile,
and that slurry was issuing in that zone. The rupture of the injection
line could have been caused by the efforts to clear the pluggages and
possibly from corrosion by the acid mine water during the 13 months
or so between their placement behind the No. 1 bulkhead and the com-
mencement of the tests. However, it is postulated that the bulk of
the gel rapidly sank to the floor of the entry and was unable to act
as a sealing agent near the roof at the top of the rubble barrier,
even though approximately 40 tons of material had been pumped into
the mine.
The laboratory tests revealed that the sludge does, in fact, stop the
flow of water through a porous sand barrier. Seals were formed within
minutes, remained watertight for weeks, and withstood calculated
hydrostatic heads up to 2 0 feet. Laboratory tests were performed
using 2-inch tubes to simulate a coal mine adit that measured 4.5 by
14 feet at Driscoll No. 4. Under laboratory conditions, such problems
as the settling of particles in the porous barrier and movement of
surrounding rock do not affect the long-term stability of the seal.
In the field, however, these problems could become serious. The
breakdown of the seal in the field was disappointing, especially since
the cause of the breakdown could not be determined.. iile many explan-
ations could be postulated, the sole cause cannot be determined with
iy degree of certainty. A combination of factors was probably to
hi are.
It is possible that, In trying to reopen the plugged injectien lines,
the compressed air that was forced into the injection lines stirred
up the exposed layer of sludge that formed part of the seal. If this
was the cause of the breakdown, then a fast development of the seal is
undesirable because the sludge does not have the opportunity to pene-
trate very deeply into the rubble pile and can easily be disturbed.
42
-------
It would also indicate that a lower dosage level would be desirable so
as to form the sludge at a slower rate. The increased water flow for a
longer period of time would then carry the sludge farther into the
rubble pile. Although it would take longer to develop a seal, the
seal might be more durable.
Another possibility is that the initial composition of the ferrous
hydroxide sludge gradually converts to a hydrated ferric oxide, which
has a higher density than the ferrous hydroxide. This would result in
shrinkage cracks similar to the mud cracks that develop as a lake
bottom dries up. If this was the cause of the breakdown, the need
for the development of the seal at a slower rate is again indicated.
The conversion of lightweight, green, fluffy floc to a reddish granu-
lar form characteristic of precipitating ferric ion, as hydrated
ferric oxide, was observed in the laboratory. With the seal forming
at a slower rate, more time would be available for the oxidation of
the ferrous hydroxide to the hydrated ferric oxide, and additional
sludge could fill the cracks as they develop. The seal, once achieved,
would not be subject to the crack formation from subsequent shrinkage.
This shrinkage phenomenon was observed in the sludge settling in the
bed of the drainage ditch immediately upstream of the main weir, but
downstream of the screen across the ditch. Although the sludge was
always submerged and never subjected to drying, cracks developed in
the sludge that was deposited in the relatively quiescent pond.
Figure 16 shows one of the quiet spots where the cracks were observed.
It is also possible that during the injection of limestone some of the
limestone does not react with the acid water, perhaps due to poor dis-
persion in forming a slurry, and is carried with sludge into the
rubble pile to react subsequently with acid water. Carbon dioxide
would be liberated and, if formed in a large pocket, could suddenly
erupt, breaking the seal.
CONTINUOUS NEUTRALIZATION
During the first 39-hour period of the continuous neutraliz ation
trials, the dosage level of the lime addition should have resulted
in a rise in pH to 11.1. However,, the pH never rose above 4.6. During
the next 10-hour period, when no lime was added, the pH did not drop
significantly. During the last 26-hour period, the dosage level of
lime addition should have resulted in a pH rise to 12. However, during
this period the pH did not rise above 4.8.
The dye tests showed that when the No. 1 valve was only partially open,
and the outflow of mine water was low, the flow from the end of the
injection pipe to the inlet of the 12-inch drain pipe was essentially
nonexistent. Conversely, with the valve fully open, the high rate of
outflow from the drain pipe created a rapid flow from the injection
points to the drain pipe inlet. This shows that when the lime slurry
was injected, there was essentially no flow toward the drain pipe;
hence, there was no increase in pH, as anticipated.
43
-------
I
.p.
p
p
/
.
I -
rn.
• -: .
‘I
Figure 16 - Sludge Settled in a Stagnant Area of Drainage Ditch
-------
Calculations indicate that the 24,960 pounds of hydrated lime added
during the 65 hours of slurry injection were sufficient to react with
gradually rose to 11, then 12 during the lime injection and remained
liter of Fe and 700 milligrams per liter of The volume of the
entries behind the No. 2 bulkhead to 10 feet beyond the ends of the in-
jection lines is estimated to be on the order of 90,000 gallons. Thus,
about 3.4 times more hydrated lime was added than was necessary to
neutralize the iron content of this mine water. The flow rate from the
No. 2 lines was 130 to 200 gpm; hence, 585,000 to 900,000 gallons.
Thus, water outfiowed during the 75-hour test period (including the
10 hours between Test 1 and Test 2 when no slurry was injected.) Con-
sequently, there were between 8.2 to 12.7 theoretical water changes in
the entries during the test period, which would be a change every 5.9
to 9.1 hours. Since the dye tests did not show any flow to the drain
from the injection point at this level of outflow, there must have
been a significant flow away from the injection points into the depths
of the mine.
During some rough bench tests in the field laboratory, it was also
observed that the floc formed by the reaction of the lime slurry
and the mine water rapidly settled to the bottom of the vessel in
large clumps or curds. This probably took place at the end of the
injection pipes located at the roof of the entries. The inlet to the
12-inch drain pipe is also at the roof where it comes through the
No. 2 bulkhead. Any stratification of the lime precipitates at the
bottom of the entry, back to the inlet of the drain pipe, would have
approximately 2 to 3 feet before its level reaches the inlet to the
12-inch drain pipe. Thus, the flow away from the drain inlet and the
rapid settling of the lime-mine water floc to the entry floors com-
bined to migrate the lime slurry reaction products away from the drain.
This would explain the negative result of the continuous neutraliza-
tion tests.
The probability that this method of treatment can be successfully
applied is indicated by the results obtained while attempting to
reestablish the seal in the rubble pile. The pH of the discharging
water, which was 3 to 4 prior to resumption of the lime injection,
gradually rose to 11, then 12 during the lime injection and remained
at 12 during the lime and limestone injection. When the injection
was stopped, the pH dropped back into the 3 or 4 range. When the
injection of a lime and limestone slurry was resumed the pH again rose
to approximately 11, then gradually dropped back to approximately 4
after the injection was stopped for the last time in preparation for
shutting down the test site.
Thus, while a seal was not reestablished, continuous neutralization of
the acid mine water (without the iron oxidation step) was taking place
and, presumably, the sludge being formed was settling back into the
mine.
45
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SECTION VII
ACKNOWLEDGEMENT
The support and assistance of the Department of Mines and Mineral
Industries of the Commonwealth of Pennsylvania, through the loan of
a Shirley Mixmeter for use during the field test program, is
acknowledged with sincere thanks.
This report was prepared by the Parsons—Jurden Division, The Ralph
M. Parsons Company, 617 West Seventh Street, Los Angeles, California
90017 for the Commonwealth of Pennsylvania, Department of Environ—
mental Resources, Harrisburg, Pennsylvania.
-------
SECTION VIII
REFERENCES
1. Jones J.B., and Ruggeri, S., “Abatement of Pollution from
Abandoned Coal Mines by Means of In-Situ Precipitation Techniques,”
Preprint of paper presented at Minneapolis, Minnesota, American
Chemical Society Division of Fuel Chemistry Symposium on Pollution
Control in Fuel Combustion, Processing and Mining, 116-9
(April 1969).
2. Jones, J.B., and Ruggeri, S., “Use of In-Situ Precipitation
Techniques - Pollution Control Survey,” Investment Dealer’s
Digest , 24-6 (May 27, 1969).
3. Handy, J.O., “Mine Water Purification,” Mining Congs. J. ,
12, 421-3 (1926).
4. Braley, S.A., Brady, G.A., and Levy, R.S. “A Pilot Plant Study of
the Neutralization of Acid Drainage from Bituminous Coal Mines,”
Sanitary Water Board, Commonwealth of Pennsylvania Department of
Health, Harrisburg, Pa. (April 1951).
5. Charmbury, H.B. and Maneval, D.R., “Operation Yellowboy, Design
and Economics of a Lime Neutralization Mine Drainage Treatment
Plant,” Preprint No. 67P35, Society of Mining Engineers of AIME
(February 1967).
49
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SECTION IX
ALPPENDIX: LABORATORY INVESTIGATIONS
SUMMARY
The laboratory investigations were conducted to assist in a study of
underground precipitation in acid mine water so as to select materials
and formulate a program for the field demonstration phase at the test
mine. The program had three objectives: filling mine voids, plugging
drainage openings, and continuous neutralization of mine effluent.
Individual studies of each concept were made. Within budgetary limits,
these studies were made in sufficient depth to determine their applica-
bility or, if this could not be done, to determine whether additional
work would be recommended.
It was necessay to develop several basic test procedures for use in the
various evaluations. Bulking ratios resulting from the addition of
various materials were determined, and plugging capabilities of pre-
cipitates obtained with various materials were evaluated. Effects of
size and composition of feed materials, of air agitation, and of static
head on plugging properties were studies. A wide range of acid mine
waters was tested to determine the effects of various pH ratios on pre-
cipitation of metal ions and to determine the composition of acid mine
water which could be treated effectively. Other studies included:
gelling of acid mine water with synthetic gelling agents, coating of
mine surfaces by precipitates formed in situ, augmentation of mineral
content of acid mine water by addition of waste pickle liquor, and
continuous neutralization of acid mine water.
The use of fly ash in connection with coal mine pollution abatement was
investigated separately by G. E W.H. Corson, Inc., and results made
available for use in this study are included in this report.
Except for the fly ash investigation, all of the laboratory work de-
scribed in this volume was performed by personnel of G. W.H. Corson,
Inc. at their laboratory facilities in Plymouth Meeting, Pa., under the
supervision of the cognizant Project Engineer.
The individual tests and results are summarized below.
EFFECT OF pH ON PRECIPITATION OF METAL IONS IN ACID MINE WATER
Titration of individual aqueous solutions of Fe , and as
sulfate salts with sodium hydroxide solutions indicate that:
precipitates in the pH range of 1.5 to 3.5; Fe precipitates in the pH
range of 3 to 8.5; and Al precipitates in the pH range of 2.5 to 5.
Precipitated Al 4 redissolves at pH of 10 or over.
51
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BULKING RATIOS OBTAINED DURING PRECIPITATION
A simple test was used to determine bulking ratios of various candidate
materials. Bulking ratio is defined as the volume of precipitate formed
in acid mine water by a weighed quantity of material divided by the vol-
ume occupied by the same weight of the additive material in deionized
water. High-calcium and dolomitic limestones and lime products were
evaluated. The highest hulking ratios were achieved using dolomitic
monohydrated lime. In general, both the doloniitic monohydrated and
dolomitic dihydrated limes gave higher bulking ratios than did high-
calcium hydrated limes; pulverized limestones yielded -lower bulking
ratios than did hydrated limes; and high-calcium limestone gave higher
bulking ratios than did dolomitic limestone.
Bulking ratio depends partly on the type of material, and partly on the
dosage (quantity of additive relative to amount of mine water, i.e.,
grams additive per liter of mine water). As the dosage is increased
the bulking ratio at first remains constant (or may apparently increase)
up to a point, and then decreases, showing that after all the mineral
content as precipitated, further additions of reactants increase the
total volume of precipitate but only at a bulking ratio of one, thus
lowering the overall bulking ratio.
Nine limestones and five hydrated limes locally available near Vintondale
were evaluated to form a basis for selection of specific limestones and
hydrated limes to be used during the field demonstration phase. The
limestone yielding the highest bulking ratio was Gold Bond #10 pulverized
limestone. The hydrated limes yielding the highest bulking ratio were
New Enterprise Hydrated Lime and Chemical Hydrated Lime (Standard Lime).
PLUGGING CHARACTERISTICS OF PRECIPITATES FORNED UNDERGROUND
Three test procedures were considered for evaluating plugging by pre-
cipitates. The simplest procedure, the static plugging test, is most
expedient for screening candidate materials. The vertical dynamic plug-
ging test is somewhat more complicated, but more closely approximates
mine conditions where constant flow of mine water exists. The horizon-
tal dynamic plugging test substitutes a horizontal tube for the vertical
tube that represents the main adit. Except for scale, this is more
realistic in approximating actual mine conditions, but the additional
time and apparatus were not considered justified for this refinement.
Therefore, the vertical dynamic plugging test was selected. Results
of plugging tests made with all three methods indicate that, although
bulky, precipitates formed underground in acid mine water are capable
of plugging the voids in a porous obstruction through which the water
must pass.
52
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STUDIES TO OPTIMIZE SIZING OF FEED MATERIALS AND COMPOSITIONS VERSUS
PRECIPITATE BULKING
Three variables in the composition of the slurry injected into the mine
adit were of interest in their possible effect on the neutralization and
precipitation in the mine water: the particle size of the additive
material, the solids content of the slurry, and the quality of the water
in the slurry. The studies performed show that: (1) specification of
particle size is importa it for pulverized limestone but not for hydrated
lime, providing a good quality, correctly calcined and slaked material is
specified; (2) slurry concentration is not critical if a good dispersion
is obtained; and (3) the quality of the water used to make up the slurry
is not critical.
EFFECT OF AIR AGITATION ON BULKING RATIOS AND PLUGGING CHARACTERISTICS
The purpose of introducing air into acid mine water is to convert fer-
rous iron to the ferric state, since ferric iron precipitates at a lower
pH than does ferrous iron. However, the conversion proceeds very slowly
at the lower pHs (approximately pH 3) and somewhat more rapidly at
slightly higher pHs (pH 5 or 6). Therefore, introducing air at the
lower pH would not be as effective as at the higher pH. Also, ferrous
iron precipitates are much bulkier than ferric iron precipitates (which
tend to be more particulate) so that even though more iron would be pre-
cipitated, the total volume of precipitate might be lower than if pre-
cipitated at the higher pH. Therefore, air agitation appears to be
either useless or even detrimental in creating as high a bulking ratio
as possible.
On the other hand, air agitation might be beneficial from a pH stand-
point because a precipitate having a somewhat particulate structure is
presumably more favorable to plugging. However, the results of the
tests in this area are not conclusive.
EFFECT OF STATIC HEAD ON PLUGGING CHARACTERISTICS
Tests on a “fresh t ’ seal formed by the precipitate formed in the mine
water flowing into and plugging the voids in the drainage channel indi-
cate that the seal can withstand a pressure of 100 feet of water backed
up behind it with no appreciable increase in permeability. It is assumed
that additional precipitate formed as the injection of the slurry con-
tinues, together with “aging” of the seal, will result in a seal which
can withstand even higher pressures. (Gels are known to have aging
characteristics, generally observed as shrinking and the appearance of
liquid drops on the surfaces. Presumably they gain in strength with
age.)
53
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COMPOSITION OF ACID MINE WATER WHICH CAN BE TREATED EFFECTIVELY
Within the wide range of acid mine waters tested, all could be success-
fully treated to result in high bulking precipitates with good plugging
properties. Where high acidity was present, a large amount of additive
slurry was required to raise the pH sufficiently to precipitate all of
the mineral content in the water. At higher acidities, however, the
precipitates do not bulk as much as at lower acidities.
GELLING OF ACID MINE WATER WITH SYNTHETIC GELLING AGENTS
Cellulose gum is capable of gelling water containing heavy metal ions
since the heavy metal ions react with the cellulose gum to cross-link
and result in gel structures of varying degrees of rigidity, depending
on concentrates of reactants. Under favorable conditions, the reac-
tion proceeds slowly enough to allow the cellulose gum to be mixed with
the acid mine water and to be pumped back into the mine adit before the
reaction proceeds far enough to produce the gel. In this way the gel
structure is produced underground in the mine adit. Good dispersion of
the cellulose gum in the acid mine water is essential.
COATING OF MINE SURFACES BY PRECIPITATES FORMED UNDERGROUND
Precipitates formed underground in the acid mine water do not appear to
have any value for selectively coating and sealing pyrites contained in
the coal.
AUGMENTATION OF MINERAL CONTENT BY ADDITION OF WASTE PICKLE LIQUOR
Augmentation of mineral content of acid mine water, when necessary be-
cause of reduced mine water flow, can be done with waste pickle liquor
(sulfate) from the steel industry. Addition of such waste pickle liquor
raises theacidity as well as the mineral content, thereby requiring
additional slurry.
CONTINUOUS NEUTRALIZATION OF ACID MINE WATER
The laboratory tests indicate the feasibility of continuous neutraliza-
tion of acid mine drainage by injection of the slurry into the adit, and
allowing the precipitate to flow back down the adit to lower portions of
the mine. However, because of the difficulty of correlating laboratory
work with field conditions, it appeared to be more productive to plan a
field demonstration as the next step.
USE OF FLY ASH
The usefulness of fly ash depends on its composition and its ability to
augment defici-ent constituents in the mine water. Fly ash is capable of
entering into a reaction to produce ettringite (6CaO A1 2 0 3 • 3S0 4
331 -120), with accompanying expansive forces. Ettringite contains calcium,
54
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aluminum, and sulfate ions. Replacement of part of the calcium with
magnesium appears to be beneficial. Replacement of some of the
aluminum with iron is possible, thus allowing the utilization of iron
in acid mine water in the formation of the ettringite structure. When
all the ingredients are present, either within the fly ash itself or
through augmentation, good results are obtained, both from the stand-
point of filling mine voids and plugging effluent drainage flows.
Fly ash of the proper composition is capable of hardening when placed
in contact with acid mine water. However, while some slight expansion
does take place, the bulking ratio is insignificant. The resultant
solid structure is very hard, making it useful even though the bulking
ratio is very low.
When the fly ash is added to flowing acid mine water to seal an effluent
drainage channel, the fly ash (together with whatever augmentation mate-
rails may be required) tends to flow into and plug the interstices of a
rubble barrier present in the drainage channel. From this standpoint
the use of the proper fly ash, or properly augmented fly ash, gives
excellent results.
Since fly ash of the proper composition was not readily available near
the demonstration site, augmentation would be required which would be
costly at this site. Therefore, fly ash should be evaluated at a later
date at a more suitable mine site.
55
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TEST 1
EFFECT OF pH ON PRECIPITATION OF METAL IONS
PRESENT IN ACID MINE WATER
The metal ions present in acid mine waters consist mainly of iron
(ferrous, ferric, or a mixture of both) and aluminum. Therefore, a know-
ledge of the effect of pH on the precipitation of these ions is of basic
interest in the underground precipitation concept for abatement of pollu-
tion due to acid mine water.
In individual tests, aqueous solutions of Fe , Fe +, and Al ’ were
prepared by dissolving the sulfate salt of each metal in deionized water.
These individual solutions were then titrated, using a sodium hydroxide
solution, to determine the pH at which each hydroxide precipitate first
appears, and the p11 at which precipitation is complete. In the case of
titration was continued to the point at which the precipitate
starts to redissolve. Sodium hydroxide was used for these titrations
because the sodium sulfate formed during the neutralization, being water
soluble, would not interfere with the visual observation of the resultant
precipitation.
LABORATORY PROCEDURE
Ferrous Iron
For the ferrous iron test, 0.5 g of FeSO 4 was dissolved in a minimum
quantity (9.17 ml) of 0.3042N H 2 S0 4 , and diluted to 100 ml with dis-
tilled water. The H 2 S0 4 is required to lower the pH to below the precip-
itation point. This solution was then titrated with 0.5046N NaOH. The
pH at which precipitation started and at which precipitation was complete
was determined.
Ferric Iron
To test ferric iron, 0.5 g of Fe 2 (S0 4 ) 3 was dissolved in a minimum quant-
ity (26.88 ml) of 03042N H 2 S0 4 , and diluted to 100 ml with distilled
water. The H 2 S0 4 was required to lower the pH to below the precipitation
point. This solution was then titrated with 0.5046N NaOH. The pH at
which precipitation started and at which precipitation was complete was
determined.
Aluminum
For testing aluminum, 0.5 g of A1 2 (S0 4 ) 3 was dissolved in a minimum
quantity (8.42 ml) of 0.3042N H 2 S0 4 , and diluted to 100 ml with distilled
water. The H 2 S0 4 was required to lower the pH to below the precipitation
57
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point. This solution was then titrated with O.5046N NaOH. The pH at
which precipitation started and at which precipitation was complete was
determined. In addition, the titration was continued until the precipi-
tate began to redissolve.
RESULTS
Results of these tests indicate that ferric iron precipitates in the pH
range of 1.5 to 3.5., ferrous iron in the p1-I range of 3 to 8.5, and alumi-
nuin in the pH range of 2.5 to 5. Precipitated alwninum redissolves at a
pH of 10 and over. The experimental data are shown in Table 1-1 and
Figure 1-1.
58
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Table 1-1 - Continuous Titration of Fe, and Al” With NaOH
Time
NaOH
Fe
(mm)
(ml)
pH
pH
pH
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
2.2
2.2
2.3
1 . 80
1.80
1.89
2.02
2.24
2.59 *
3.45
3.77
3.92
4.02
4.13
4.26
4.71 **
8.00
9.20
> 10 ***
0
1.39
1.32
1.08
1.40
1.38
2.16
1.47
1.38
3.24
1.51
1.38
4.32
1.60
1.38
5.42
1.65
1.40
6.48
1.70
1.41
7.56
1.80
1.50
*
8.67
1.90
1.52
9.72
2.02
1.60
10.80
2.26
1.67
11.88
2.36
1.76
12.96
2.63
1.81
14.04
3.15
*
1.95
15.12
4.06
2.03
16.20
5.78
2.18
17.28
6.60
2.37
18.36
7.23
2.58
19.44
7.58
2.74
20.52
7.80
3.03
21.60
8.10
**
3.32
**
22.68
9.96
5.98
23.76
7.71
24.84
9.74
* First precipitate.
** Precipitation complete.
Precipitate redissolves.
59
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12
I NIN 10.8mI NaOH
11
10
9
8
1
C’
0
5
4
3
2
0
TIME (mm )
2.4
++ +++
Figure 1-1 - Titration of Fe , Fe and with NaOH
-------
TEST 2
BULKING RATIOS
One of the main objectives in considering the precipitation concept for
abatement of pollution from acid mine water is to achieve as high a
bulking ratio as practical during the neutralization. The hulking
ratio, in this context, is defined as the ratio of the volume of pre-
cipitate formed when a given quantity of reactant is added to mine
water, to the volume occupied by the same quantity of reactant when
added to distilled water. Therefore, the bulking ratio gives an
indication of the economic leverage gained by the use of reactants
rather than unreactive additives such as sand, gravel, and concrete
(which would have bulking ratios of one).
LABORATORY PROCEDURE
Synthetic mine water was prepared in accordance with a recommendation
by Dr. Harold L. Lovell of The Pennsylvania State University. This
consisted of deionized water to which was added 300 mg/i of Fe
(as FeSO 4 ) and 75 mg/i of [ as Al 2 (SO 4 ) 3 ], with the pH adjusted
to 3.0 by addition of H 2 SOa. There is no typical acid mine water, but
this synthetic water included a moderate concentration of the two
predominant metal ions found in acid mine waters. The pH of 3 was
an average figure most likely to be encountered at an actual mine
site.
A slurry was prepared by adding a given quantity of additive to 50 ml
of distilled water. This slurry was then added to a liter of syn-
thetic mine water contained in a graduated cylinder. The cylinder was
allowed to stand undisturbed for 18 hours, and the volume of the
precipitate (which usually settled to the bottom of the graduate) was
noted. The pH of the water was also noted to determine what degree of
neutralization had been achieved.
In conducting bulking tests following this test method, it must be
recognized that: (1) reading the volume of precipitate is subject to
a large experimental error; and (2) the volume of precipitate produced
varies considerably when tests are repeated under supposedly similar
conditions. Difficulty in reading the precipitate volume is due to
the nature of the apparatus; the variation in the volume of precipitate
is due to the complexity of the hydrated iron oxides produced. Because
of these two inherent sources of variation, differences in volume of
precipitate must be evaluated on the basis of order-of-magnitude
differences rather than on an absolute difference basis.
61
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EVALUATION OF TYPICAL LIMESTONES AND LIMES
The prime candidates for neutralizing materials are the limestones and
lime products, which have high neutralization values, are readily
available, and low in cost.
Limestones fall into two basic types: high-calcium limestone and
dolomitic limestone. High-calcium limestone consists of CaCO3, plus
impurities such as Si0 2 , and has a minimum of 98% CaCo 3 . Dolomitic
limestone consists of CaCO 3 and MgCO 3 , plus impurities such as Si0 2 .
High-calcium limestone occurs throughout the Commonwealth of
Pennsylvania. However, dolomitic limestone is found mainly in East-
ern Pennsylvania, thus limiting its use to the eastern portions of the
state, unless its performance is superior enough to offset the cost
of transportation.
The hydrated limes fall into three basic types: high-calcium hydrated
lime, monohydrated dolomitic lime, and dihydrated dolomitic lime. High-
calcium hydrated lime conists of Ca(OH) 2 , and is made by hydrating
calcined high-calcium quickline. It will have 92% to 95% Ca(OH) 2 .
Monohydrated dolomitic lime consists of Ca(OH)2, MgO, and is made by
hydrating calcined dolomitic limestone under atmospheric pressure
conditions. Dihydrated dolomitic lime consists of Ca(OH) 2 , Mg(OH) 2 ,
and is made by hydrating calcined dolomitic limestone at pressures
above atmospheric.
Nine materials typical of this group of products were selected for the
initial evaluation. The characteristics of these materials are shown
in Table 2-1.
The highest bulking ratios were achieved using monohydrated dolomitic
lime. In general, the hydrated dolomitic limes gave higher bulking
ratios than did high-calcium hydrated lime; pulverized limestones
yielded lower bulking ratios than hydrated limes; and high-calcium
limestone gave higher bulking ratios than dolomitic limestone.
From the standpoint of neutralization, the high-calcium hydrated lime
yielded a higher pH than the hydrated dolomitic lime; hydrated lime
yielded a higher pH than the pulverized limestone; and dolomitic
limestone yielded a higher pH than the high-calcium limestone.
A study of the bulking ratios achieved (Table 2-2) shows that as the
additive level (g/l of mine water) is increased, the bulking ratio at
first remains constant (or may apparently increase - “apparently”
because at very low levels of addition it is difficult to read the
volume of precipitate accurately) up to a point, then decreases.
This is explained by the fact that after all the mineral content has
precipitated (and assuming no redissolving of minerals), further
62
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Table 2 -1 - Characteristics of Typical Limestone and Dolomitic Lime Products
C’
Type
Product
Screen
Analysis
Specific
Gravity
Loose
Bulk
Densit
(lb/ft )
Volume
Occupied By
100 gm
in H 2 0
(ml)
Approximate
Price
(fob Quarry)
($/ton)
High-
Calcium
Pulverized Limestone
Quicklime
Hydrated Lime
95% thru 200 mesh
100% thru 10 mesh
90% thru 325 mesh
2.72
3.34 - 3.40
2.30
100 - 120
50 - 60
35 - 45
78
268
5.00
15.50
16.00
Dolomitic
Pulverized Dolomite
Selectively Calcined
Dolomite
Quicklime (Soft
Burned)
Monohydrated
Dolomitic Lime
Milled Dihydrated
Dolomitic Lime
Unmilled Dihydrated
Dolomitic Lime
95% thru 200 mesh
100% thru 10 mesh
100% thru 10 mesh
90-95% thru 325 mesh
90-95% thru 325 mesh
85-90% thru 325 mesh
2.84 - 2.88
2.90 - 3.00
3.40 - 3.45
2.60 - 2.65
2.40 - 2.50
2.40 - 2.50
100 - 200
75 - 80
45 - 50
35 - 45
35 - 40
35 - 40
72
78
150
224
206
5.00
14.00
15.50
14.50
19.00
18.50
*Assumed to
be same as for corresponding hydrated lime.
-------
C’
Table 2-2 - Comparison of Volume of Precipitate and Bulking Ratio Achieved
(Produced by Different Types of Lijnestones and Hydrated Limes
When Added as a Water Slurry to Synthetic Acid Mine Water- SAMW)
Gram.
R i Ifl
per Liter
Of S .614J
High-Calcime Lim.atone
Dolomitic Limeitona
Pulverized
Stone
Quicklime
Hydrated Lime
Pulverized
Stone
Selectively
Calcined
Stone
Soft Surned
Quicklime
Monohydrated
Lime
Hilled
Dihydrated
DoIoiiiltic Lime
Unmilled
Dihydrated
Dolomitic Lime
Vol
(ml)
Sulking
Ratio
Vol
(ml)
Sulking
Ratio
Vol
(ml)
8 lking
Ratio
Vol
(ml)
Bulking
Ratio
Vol
(ml)
Sulking
Ratio
PPT
Vol
(ml)
Sulking
Ratio
Vol
(ml)
Sulking
Ratio
•1•
¶fol
(ml)
Sulking
Ratio
rr
Vol
(ml)
Sulking
Ratio
0.2
0.5
1.0
1.5
2.0
3.0
4.0
5.0
*
**
10
15
20
20
20
20
—-
—.
12.8
12.8
12.8
8.6
6.4
5.1
25
25
50
70
100
75
75
60
46.6
16.7
18.7
17.6
18.7
9.3
7.0
4.5
50
90
85
75
70
75
75
80
93.3
67.2
31.7
18.6
• 13.1
9.3
7.0
6.0
*
**
**
5
5
5
5
5
--
--
4.6
3.5
2.3
1.7
1.4
*
5
5
5
10
15
25
25
--
12.8
6.4
4.3
6.4
6.4
8.0
6.4
7
65
100
110
100
80
80
95
23.3
86.7
66.7
48.8
33.3
17.8
16.7
12.7
45
80
115
120
115
100
80
95
150.0
106.7
76.7
43.6
38.3
22.2
1).)
12.7
10
35
70
75
80
75
60
70
22.3
31.2
31.2
22.3
17.6
11.1
6.7
6.2
10
25
65
70
75
70
55
50
24.2
24.3
31.6
22.7
18.2
11.3
6.7
4.6
* 6 ieee than 5 ml.
**Le,i than 5 ml.
-------
additions of reactants increase the total volume of the “precipitate,”
but only at a bulking ratio of 1, since there is no further chemical
reaction. Therefore, the additional volume lowers the overall bulking
ratio.
A study of the pHs achieved (Table 2-3) shows that pulverized stone
can raise the pH of the water only to 4.5 to 5.0, while the hydrated
limes can raise it higher. No leveling off of the pH was noted within
the addition level of S g/l of hydrated lime used in these tests.
However, the pHs achieved, being 8 or over, were high enough to
precipitate all the iron present (ferrous as well as ferric).
EVALUATION OF LOCALLY AVAILABLE MATERIALS
A survey of specific commercially available products from sources
located near the demonstration mine site revealed no dolomite deposits
within a reasonable distance. Therefore, only high-calcium limestone
and hydrated lime made from high-calcium limestone were considered for
use in the demonstration phase. Fourteen lime products (nine lime-
stones and five hydrated limes) from five local producers, were se-
lected as candidate materials. Characteristics of these 14 products
are shown in Tables 2-4 and 2-5.
Results of the tests with the commercial lime products are shown in
Tables 2-6 and 2-7, which list volume of precipitate and bulking
ratio, and the pH of solution after 18 hours, respectively.
The highest bulking ratio achieved by the limestones was 30 for the
addition of 1 gram of Gold Bond #10 pulverized limestone to 1 liter
of acid mine water. The pH of the solution was raised to 4.3. The
Bell Mine #90 pulverized limestone raised the solution pH to 4.35
(for the same addition level); however, the bulking ratio was only 10.
The highest bulking ratio achieved by the hydrated limes was 67 for
the addition of 1/2 gram of New Enterprise Hydrated Lime to 1 liter
of acid mine water. However, the pH of the solution was raised to
only 4.1, indicating much mineral content still remaining in the
solution. Since the limes are capable of precipitating all the
mineral content (even redissolving some such as aluminum at higher
pHO, a more meaningful criterion for rating effectiveness if the
weight of material required to raise the solution pH to the range of
10 to 11. On this basis, the most effective lime was Standard’s
Chemical Hydrated Lime, which required 2 g/l to reach a pH of 11;
next was National’s Chemical Hydrated Lime #26, which required 3 g/l;
next was Bell Mine Chemical Hydrated Lime, which required S g/l; next
was New Enterprise’s Hydrated Lime, which at S g/l raised the pH to
10.8. Nittany Hydrate performed more like a limestone than a lime.
At the 2 g/l addition level, the bulking ratio varied from 6.1 to
65
-------
0 ’
0’
Table 2-3 - Comparison of pH Resulting From Addition of Different
Types of Limestones and Hydrated Lime (Injected as a Water
Slurry to Synthetic Acid Mine Water)
Grams of
Reactant
per Liter
of SAMW
High-Calcium Limestone
Dolomitic Limestone
Pulverized
Stone
Quick-
lime
Hydrated
Lime
Pulverized
Stone
Selectively
Calcined
Stone
Soft
Burned
Quick-
lime
Mono-
hydrated
Lime
Milled
Dihydrated
Lime
linmilled
Dihydrated
Lime
0.2
0.5
1.0
1.5
2.0
3.0
4.0
5.0
4.5
4.5
4.5
4.5
4.5
4.5
4.5
4.5
5
5
5
-
6
9
-
10
4.5
5.0
5.5
5.5
6.0
-
8.5
11.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
4.5
4.5
4.5
4.5
4.5
5.0
5.0
5.0
4,5
4.5
4.5
5.0
6.0
7.0
8.5
9.5
4.5
4.5
5.0
5.5
5.5
8.5
9.0
9.5
5.0
5.0
5.0
5.0
5.0
5.0
8.0
8.0
4.5
4.5
5.0
5.0
5.5
7.0
8.5
9.0
-------
Table 2-4 - Characteristics of Locally Available
Pulverized Limestones
Trade Name
Supplier
Screen Analysis
Loose
Bulk
Density
(lb/cu ft)
Delivered
Price, Bulk
(Jtme 1969)
($/ton)
Code 55
Limestone
Standard Lime
Refr. Co.
100% -3/8 in.
110-115
4.65
Dry CAL-AG
Standard Lime
f Refr. Co.
70-90% -20
80-90
5.15
Gold Bond
Screenings
#20
National
Gypsum Co.
100% -1/8 in.
90-100
4.75
Gold Bond
#10 PLS
National
Gypsum Co.
81.5% -200
99.6% —60
55—70
(loose)
95-100
(packed)
9.60
Wet Kiln
Sludge
Warner
Company
87% -325
100% —4
39
(dry basis)
11.00
(dry basis)
Bell Mine
#90 PLS
Warner
Company
60% -325
100% -30
60
(loose)
95
(packed)
9.95
Pennsylvania
No. 1 Stone
New Enterprise
Stone Lime
Co.
100% -1/4 in.
NA
4.65
Asphalt
Filler
New Enterprise
Stone F Lime
Co.
85% -200
100% -20
NA
7.00
Agricultural
Limestone
Sproul Lime
Stone Co.
60% -100
ioot -20
105
6.50
67
-------
Table 2-5 - Characteristics of Locally Available Hydrated Limes
Trade Name
Supplier
Screen
Analysis
Loose
Bulk
Density
(lb/cu ft)
Delivered
Price, Bulk
(June 1969)
($/ton)
Washington
chemical
Hydrate
Standard Lime
Refr. Co.
98% -325
25
21.10
Chemical
Hydrated
Lime #26
National
Gypsum Co.
95.3% -325
99.8% -100
20
(loose)
43
(packed)
21.40
Bell Mine
Chemical
Hydrated
Lime
Warner
Company
99% -325
100% -30
25
22.20
Nittany
Hydrate
Warner
Company
24% -100
100% -4
42
12.95
Hydrated
Lime
New Enterprise
Stone Lime
Co.
95% -325
100% -200
NA
25.50
68
-------
Table 2-6 - Comparison of Volume of Precipitate and Bulking Ratio Achieved (Produced
by Specific Grades of Limestone and Hydrated Limes from Nearby
When Added as a Water Slurry to Synthetic Acid Mine Water)
*Less than 5.
**Less than 10.
***No reaction, additive settled to
bottom as lumps.
BR Bulking Ratio
Pulverized Limestone
Cold Bond
Typical Code 55 Dry Screenings Gold Bond Wet Kiln Bell Mine pennsylvania Asphalt Agricultural
Grams of Limestone Limestone CAL-AC #20 #10 PLS Sludge #90 PLS 10. 1 Stone Filler Limestone
Reactant PPT P PT PPT PPT PPT PPT PPT — PPT
per Liter Vol BR Vol BR Vol BR Vol BR Vol BR Vol BR Vol BR Vol BR Vol BR Vol BR
of SAX4 (ml (ml) (ml) (ml) (ml) (ml) (ml) (ml) (ml) (ml)
0.5
1.0
1.5
2.0
3.0
4.0
5.0
*
10
15
20
20
20
20
-
12.8
12.8
12.8
8.6
6.4
5.1
**
**
**
**
10
15
20
-
-
-
-
1.7
1.9
2.0
** -
15 3.8
25 4.2
30 3.8
40 3.3
45 2.8
50 2.5
***
***
***
***
***
***
*
-
-
-
-
-
-
-
20
30
25
25
30
35
35
40.0
30.0
16.7
12.5
10.0
8.8
7.0
**
**
**
**
**
**
10
-
-
-
-
-
-
1.3
15
20
20
20
25
20
20
15.0
10.0
6.7
5.0
4.2
2.5
2.0
**
**
**
10
15
20
-
-
-
-
3.3
3.8
4.0
**
10
20
25
30
35
25
-
10.0
13.3
12.5
10.0
8.8
5.0
25
30
35
25
30
30
30
12.5
15.0
11.7
6.3
5.0
3.9
3.0
Grams of
Reactant
per Liter
of SAMW
Hydrated Lime
Typical
Lime
Wash.
Chemical
Hydrate
Chemical
Hydrated
Lime, #26
Bell Mine
Chemical
Hydrated
Li
Nittany
Hydrate
- New
Enterprise
Hydrated
Lime
PPT
Vol
(ml)
BR
PPT
Vol
(ml)
BR
PPT
Vol
(ml)
BR
PPT
Vol
(ml)
BR
PPT
Vol
(ml)
BR
PPT
Vol
(ml)
BR
0.5
1.0
1.5
2.0
3.0
4.0
5.0
7
90
85
75
70
75
75
80
67.2
31.7
18.6
13.1
9.3
7.0
6.0
90
120
80
60
70
60
70
51.5
34.4
15.3
8.6
6.7
4.3
4.0
90
90
85
65
60
60
70
36.0
18.0
11.3
6.5
4.0
3.0
2.8
65
70
60
55
50
50
65
29.0
15.6
8.9
6.1
3.7
2.8
2.9
10
15
20
30
35
40
45
6.7
5.0
4.5
5.0
3.9
3.3
3.0
100
105
75
55
55
50
60
67.0
35.0
16.7
9.2
6.1
4.2
4.0
7
-------
Table 2-7 - Comparison of pH Resulting from Addition of Specific
Grades of Limestones and Hydrated Limes from Nearby Quarries
(Injected as a Water Slurry to Synthetic Acid Mine Water)
Pulverized Limestone Hydrated Lime
-4
Cd
U
4)
I Cd I
4JCI)
4)4)
U
-4E
4)0 C d _)..-4
c i
4) 4) 4) cd 4 ) 0 0 4) ci
9 . 44) >4 ) 4J-4 .-4 N GJ ’
04-i . iO yb Q• -4 O / .. . 4C/) 4 ‘ 0 -1 XCd4) Cd4) ‘e 4 ) >..4) 4 . 4)
r4 td $) L . . .- > . 0 .i ci 4J (4 LI lJ U 4J 4 )
V) .4 4) . , . (44) LI .,i . .-iCd -4Cd • Cd (4(4 L1 Cd
I . —‘ •- .- #
.40 .-4 0 0 -4 ciE 4) E .-I ’ ‘ J
-l Ii 0 U N 0 — 4) C 4) 4 Ifl . 4 Cd . >-. . 4) ‘ 4 >-. 4)
c ç , ).. ) L) L C1) ( ‘ (z . < . . (,- L ) -) X Z Z
—.1 ____ _________________________________________ ___________________________
C
0.5 4.5 3.3 3.65 3.1 3.9 3.3 3.9 3.6 3.95 3.9 5.0 4.1 4.4 3.7 3.2 4.1
1.0 4.5 3.4 3.8 3.15 4.3 3.5 4.35 3.7 4.1 4.1 5,5 5.5 5.9 4.6 3.4 8.9
1.5 4,5 3.8 3.7 3.25 4.7 3.6 5.1 3.75 4.2 5.0 5,5 10.6 10.6 4.7 3.5 10.3
2.0 4.5 3.8 4.0 3.35 4.8 3.7 5.0 3.8 4.3 5.1 6,0 11.0 10.8 10.3 3.7 10.5
3.0 4.5 3.8 4.1 3.5 4.8 3.7 5.1 3.9 4.5 5.0 --- 11.1 11.0 10.4 3.8 10.5
4.0 4.5 3.9 4.1 3.8 4.8 3.7 5.1 3.9 4.6 4.9 8,5 11.1 11.2 10.8 3.8 10.7
5.0 4.5 4.1 4.3 3.85 4.8 3.7 5.0 3.9 5.2 4.9 11.0 11.5 11.7 11.0 3.8 10.8
-------
9.2 (excluding the Nittany Hydrate). However, when comparing at a
given addition level, the volume of precipitate is more important
than the bulking ratio because the actual volume is of greatest
practical interest. In terms of volume of precipitate, the volumes
at the 2 g/l addition level varied from 55 to 65 ml (excluding the
Nittany Hydrate).
SUMMARY
The initial investigation indicated that hydrated limes were more
effective than pulverized limestones. Hydrated dolomitic limes appeared
to be more effective than high-calcium limes; however, high-calcium
limestone appeared to be more effective than doloinitic limestone.
Because dolomitic limestone was not readily available at the demonstra-
tion mine site, only high-calcium limestones and hydrated limes were
included in the evaluation of specific grades available locally. In
this evaluation, it appears that where limestone is used, the limestone
should be Gold Bond #10 Pulverized Limestone, as supplied by the National
Gypsum Co. Where hydrated lime is used, it should be the Washington
Chemical Hydrate, as supplied by Standard Lime Refractories Co.
71
-------
TEST 3
PLUGGING CHARACTERISTICS OF THE PRECIPITATES
The second main objective in connection with the underground precipita-
tion concept for abatement of pollution from acid mine water is to form
precipitates that will seek out and plug drainage outlets. From this
standpoint, bulking ratio is not as important as plugging ability; how-
ever, high bulking precipitates having superior plugging ability are the
most desirable.
LABORATORY PROCEDURE
Since there was no experimental procedure available to evaluate the plug-
ging characteristics of the precipitates, a suitable test method had to
be developed. The apparatus first used in this investigation consisted
essentially of a vertically positioned glass tube, 2 inches in diameter
and 4 feet long, with the lower end inserted in a Buchner filter, with a
rubber sleeve to form a watertight seal. A layer of coarse sand (-10+14)
was placed in the tube, on top of the perforated filter plate, and a
layer of fine sand (-60+100) was placed over the coarse sand. A short
length of rubber tubing and hose clamp were placed on the funnel outlet,
and 2000 ml of synthetic mine water (see Test 2) was placed in the tube.
A slurry of the reactant was then added to the mine water, and the result-
ing mixture allowed to stand undisturbed for 18 hours. After that time,
the hose clamp was removed and the time required to draw off 100 ml of
the liquid from the bottom of the funnel was determined. A similar draw-
off of 100 ml was made when the liquid head had been reduced to 17 inches.
This test is identified in this program as the static plugging test
because the slurry addition is done as a single addition to a static pool
of water.
To more closely approximate actual field conditions, the static head
condition was replaced by one in which water flowed at a constant rate
before the addition of the slurry, also at a constant rate. The appara-
tus was as above, except that the funnel effluent was unrestricted after
passing through the sand bed, and a continuous feed of synthetic mine
water was supplied to the top of the tube. The incoming feed rate was
adjusted to 545 ml per minute to yield one tube volume change in 5 min-
utes. When approximately 1000 ml of water was contained in the glass
tube, a constant feed of water slurry of the reactant was started. The
funnel discharge rate was constantly measured, and the time required to
reduce the discharge rate to one drop per second was noted; then both
water feed and slurry feed were stopped. Eighteen hours after the feeds
were stopped, the tube was refilled to the original height, and the time
between drops was measured. The tube was refilled daily to the original
73
-------
height and the time between drops noted. This test is identified in this
program as the vertical dynamic plugging test because the water and
slurry are added at a continuous constant rate and because the glass tube
is positioned vertically.
The test was then further modified to simulate a horizontal mine adit
with a vertical borehole placed behind a rubble pile at the effluent end.
The tube was placed in a “horizontal” position (1% slope down to the
effluent end), and the Buchner funnel was replaced with a piece of wire
retaining screen. Layers of coarse and fine sands were placed behind the
wire screen, and the mine water feed was started. The flow was adjusted
to 700 mi/mm to simulate the linear velocity of a mine flow of approxi-
mately 450 bpm in a 7 by 7 foot mine adit (1 foot per second) When the
water feed had been stabilized, the water slurry feed, adjusted to a pre-
selected rate, was started. The slurry was added through a vertical side
tube situated just behind the sand layers. Discharge rate through the
wire screen was measured; when the flow rate reduced sufficiently, the
time between drops was measured. This test is identified in this program
as the horizontal dynamic plugging test.
RESULTS
Results of tests using the static plugging test are shown in Table 3-1.
High-calcium hydrated lime, monohydrated dolomitic lime, and pulverized
high-calcium limestone were evaluated at various addition levels. All
decreased the flow rate of water through the sand layer at the bottom end
of the tube to a great degree. The high-calcium hydrated lime wis more
effective than the monohydrated dolomitic lime; both limes were more
effective than the pulverized limestone.
Results of the tests using the vertical dynamic plugging test are shown
in Table 3-2. Again, all three materials were able to decrease the flow
rate of water through the sand layer to a great extent--in some cases,
rather quickly; in others, after a short time. Some tests developed
channeling through the sand and had to be discontinued. In these tests
the monohydrated dolomitic lime appeared to be more effective than the
high-calcium hydrated lime. However, the most effective reduction in
flow rate was obtained with a massive dose rate using high-calcium lime-
stone. In this test, 23 grams of limestone were added per liter of mine
water. Time to reduce flow (from 545 mi/mm) to one drop per second
could not be measured within the time limit of the working day. At the
end of the first day, the rate was reduced to 1.4 seconds between drops.
At the end of 7 days, this rate had been reduced to 17 seconds between
drops. At the end of 14 days, the rate was 43 seconds between drops.
The horizontal dynamic plugging test was developed to investigate the
possibility that the precipitates formed in the mine water would not flow
horizontally to plug a vertically positioned sand bed. These tests were
performed using high-calcium hydrated lime and pulverized high-calcium
limestone. Results, shown in Table 3-3, are typical of a number of test
74
-------
Table 3-1 - Decrease in Flow Rate Through Sand
Due to Precipitation in Acid Mine Water
(Using Static Plugging Test)
Lime Preduct
Reactant
Addition
(g/l)
Time For Flow of 100 ml (mm)
At 44-Inch Head
At 17-Inch Head
High-calcium
Hydrated Lime
0.5
1.0
1.5
2.5
7.5
20.2
31.5
31.5
41.0
70.0
205.0
150.0
Monohydrated
Dolomitic Lime
0.5
1.0
1.5
2.0
2.5
3.5
10.0
NA
14.0
20.0
14.0
16.5
21.0
24.5
57.0
67.0
67.0
58.5
Pulverized
High-Calcium
Limestone
0.5
1.0
1.5
2.5
3.5
0.4
0.8
NA
2.0
5.t
1.3
2.7
2.2
10.5
14.5
Water Only
0
0.05
0.09
75
-------
* Teat
** Teat
Time
Table 3-2 - Decrease in Flow Rate Through Sand Due to Precipitation in Acid Mine Water (AMW)
(Using Vertical Dynamic Plugging Test)
discontinued after 4 days
discontinued after 7 days
vent beyond working day
C’
Inflow (545 mi/mm)
Outflow
‘C
Run
No.
Total
Volume
of
MW
(ml)
Total
Volume
of
Additive
Slurry
(1)
Concentra-
tiort of
Additive
in Slurry
(7.)
Total Wt
of
Additive
Added to
AMW
(gh)
Wt of
Additive
to
Volume
of ANW
(gil)
Time to
Reduce
Flow to
1 drop/sec
(mm)
pH to
Effluent
at
18 hr
Time Between Drops (sec)
.
After
1 Day
After
3 Days
After
5 Days
After
7 Days
After
14 Days
‘
80
66
69
75
83
84
86
10
10
10
10
10
10
10
0.5
0.5
1.0
0.5
0.5
0.5
0.5
0.4
1.0
0.5
2.0
3.0
4.0
5.0
2
5
5
10
15
20
25
0.2
0.5
0.5
1.0
1.5
2.0
2.5
9
19
36
6
10
4
3.5
6.0
6.0
8.0
11.5
12.5
12.5
12.5
1.5
0.5
0.0
3.0
5.0
0.0
0.8
0.5
0.5
1.5
2.3
5.0
1.5
3.0
*
0,8
2.2
-
6.0
2.6
3.5
*
0.9
-
1.4
9.5
3.9
3.2
*
1.5
3.1
2.9
**
.
2.0
79
71
68
85
76
85A
82
10
6
6
10
4
10
3
0.5
1.0
1.0
0.5
0.5
0.5
0.5
0.4
0.5
1.0
4.0
2.0
3.0
3.0
—
2
5
10
20
10
25
15
0.2
0.84
1.67
2.0
2.5
2.5
5.0
14
36
***
4
10
4
7.5
5.5
u.s
12.5
12.5
12.5
12.5
12.5
4 5
1.2
1.2
3.8
3.8
3,5
6.0
4.0
-
5.0
-
5.5
8.0
-
4.5
7.0
9.0
5.0
7.2
9.0
2.5
3.5
11.0
7.0
8.0
8.3
0.0
3.3
4.0
14.5
11.0
10.0
7.0
g
67
70
72
73
74
10
10
10
10
3
0.5
1.0
1.0
1.0
0.5
1.0
0.5
2.0
4.0
13.8
5
5
20
40
69
0.5
0.5
2.0
4.0
23.0
18.0
8.0
5.0
***
***
4.0
4.0
5.0
5.0
5.5
1.0
1.1
0.5
1.3
1.4
1.8
1.1
1.8
2.8
3.2
1.8
1.2
-
5.0
6.0
1.7
1.5
1.8
8.0
17.0
1.4
1.0
2.0
15.0
43.0
-------
Table 3-3 - Decrease in Flow Rate Through Sand
Due to Precipitation in Acid Mine Water
(Using Horizontal Plugging Test)
TestRun
A
B
C
Treatment
Slurry of high-
calcium hydrated
lime
Slurry of high-
calcium hydrated
lime and pulver-
ized high-calcium
limestone
Slurry of pulver-
ized high-calcium
limestone followed
calcium hydrated
lime
Initial Flow
Rate
(ml 1mm)
700
700
700
Effluent Flow
Rate - Sand in
Place (mi/mm)
400
450
430
Effluent Flow
Rate - After
Treatment
(drops/sec)
1
2
2.2
Effluent Flow
Rate - After
1 Week
(drops/sec)
8.7*
4
3
Effluent Flow
Rate - After
2 Weeks
(drops/sec)
--
4
7.5
*Char el developed in sand, test discontinued.
runs carried out, and illustrate that the precipitates formed in the acid
mine water do, in fact, seek out the drainage channels and plug them.
They also show that plugging with precipitates formed using only hydrated
lime is more susceptible to subsequent channeling than for those result-
ing from the addition of limestone as well. The limestone does not yield
as voluminous a precipitate and hence, being of greater density, is not
as apt to develop a channel. The reduction in flow rate is not as great
as in the vertical test for a comparable time, but limestone is effective
enough to reduce a flow of 400 to 450 ml/min to a flow of drops.
77
-------
In evaluating the test data from flow tests as described herein, it
must be recognized that, because of the nature of the materials being
tested and the reactions involved, different test runs can result in
wide, yet insignificant, variations in flow rates, and flow rates
during test runs extending over long periods of time can fluctuate
widely. Therefore, the decision as to whether a given change in flow
rate is significant is a subjective one that must be based on consid-
eration of many factors, including results from other test runs.
SUMMARY
Results of these plugging tests indicate that precipitates resulting
from the neutralization of acid mine water, while being bulky, are
also capable of plugging the voids in a porous obstruction through
which the water must pass. If the precipitate is excessively bulky,
as with the addition of hydrated lime, there is the possibility that
it might pass through the pores of the obstruction, but if this occurs,
adding limestone for a short period results in a less bulky precipitate
which will tend to plug up any channel that develops.
It appears that the most useful test is the vertical dynamic plugging
test, from the standpoint of testing possible additives for injection
into the acid mine water. The horizontal test is useful, but takes
more time to set up and perform.
78
-------
TEST 4
STUDIES TO OPTIMIZE SIZING.OF FEED MPLTERIALS AND
COMPOSITION VERSUS PRECIPITATE BULKING
To determine the most efficient utilization of the neutralization
reaction and resultant precipitation of metallic ions front the water,
studies were conducted in which the particle size of the additive
material, the solids content of the slurry, and the quality of the
water used to make up the slurry were varied.
LABORATORY PROCEDURE
For these studies, the bulking ratio test procedure described for
Test 2 was used. Results, however, are reported as volume of
precipitate rather than the bulking ratio because the actual volume
produced is more meaningful than bulking ratio in terms of precipitate
formed in a mine adit.
EFFECT OF VARYING PARTICLE SIZE
A monohydrated dolomitic lime and a high-calcium hydrated lime were
evaluated at addition levels of 0.5 g/l and 1.0 gIl, in the range of
particle sizes available: high-calcium hydrated lime in two ranges
(-325 mesh and +325 mesh); monohydrated dolomitic lime in three ranges
(-324 mesh, -200 +325 mesh, and -100 +200 mesh). Results (see
Table 4—i) for the high-calcium hydrated lime were inconclusive because
of the limited ranges of particle sizes. In the case of the monohy-
drated dolomitic lime in three ranges (-324 mesh, -200 +325 mesh, and
-100 +200 mesh). Results (see Table 4-1) for the high-calcium hy-
drated lime were inconclusive because of the limited ranges of particle
sizes. In the case of the monohydrated dolomitic lime, the two finer
ranges were superior to the coarser range. This effect was noted at
both addition levels.
Next, a high-calcium limestone (100% -1/8-mesh material) and a high-
calcium chemical hydrate (100% -30-mesh material) were crushed and
screened into seven ranges for each material. The individual ranges
were then evaluated at a dosage level of 2 g/l. Results are shown in
Tables 4-2 and 4-3.
Table 4-2 indicates that, for limestone, a finer particle size is more
efficient. The limestone must be ground to -200 mesh or finer for
efficient utilization of its neutralizing power, because the calcium
sulfate formed in the reaction is deposited as a hard coating on the
limestone particles and prevent further reaction of the stone with the
acid. A smaller particle size initially exposes more surface to the
acid water and therefore permits a higher proportion of the limestone
to react.
79
-------
Table 4-1 - Comparison of Solution pH and Volunie of Precip-
itate Produced by Addition of High-Calcium Hydrated Lime and
Monohydrated Dolomitic Lime, as a Water Slurry, to Synthetic
Acid Mine Water - Effect of Varying Particle Size
Additive
Material
Size Range
(Mesh)
Dosage 0.5 gIl
Dosage = 1.0 g/l
pH
Volume of
Precipitate
(ml)
pH
Volume of
Precipitate
(ml)
High-Calcium
Hydrated
Lime
-325
+325
5.5
5.5
125
130
5.5
5.5
110
120
Monohydrated
Dolomitic
Lime
-325
-200 +325
-100 +200
5.0
5.0
4.5
75
70
20
5.5
5.5
5.0
180
110
40
Table 4-3 indicates that fineness of grind is not as critical for
high-calcium chemical hydrate as it is for limestone. This is due
to the fact that a chemical grade of hydrated lime, as used in this
test, is a high-quality product from which coarse uncalcined or
poorly calcined particles have been removed by screening after
hydration. A hydrated lime whose screen analysis indicates the
presence of coarse uncalcined particles would not be a true hydrated
lime and, hence, would behave more like a limestone.
EFFECT OF VARYING SLURRY CONCENTRATION
The next variable of interest is the slurry concentration; the
percent solids. The specific grades of locally available limestones
and limes (the characteristics of which are shown in Tables 2-4 and
2-5) were evaluated at five slurry concentrations ranging from 1%
to 50% solids. The dosage levels used for each material are based
on achieving a pH of about 4, with the limestones H 11 with the
hydrated limes. Results obtained (shown in Table 4-4 and 4-5)
indicate that within the limits of this evaluation, slurry concen-
tration does not appear to influence the effectiveness of the
reactant. However, differences for some of the materials seem to
indicate that the dosage level may have a bearing on the effect-
iveness of utilization. A much more extensive evaluation would be
required to derive more conclusive data.
80
-------
Table 4-2 - Comparison of Solution p1-I and Volume of Precipitate Produced
by Addition of High-Calcium Limestone, as a Water Slurry, to
Synthetic Acid Mine Water - Effect of Varying Particle Size
Size Range
(Mesh)
pH
Volume of
Precipitate
(ml)
-400
5.1
20
—325 +400
5.1
25
-200 +325
4.0
20
-100 +200
3.8
< 10
-20 +100
3.8
< 10
-8 +20
3.2
< 10
-4 +8
3.1
Original
Lumps
NOTES: Material Added: Gold Bond #20, Ground and Screened
Dosage Level: 2 g/l
Slurry Concentration: 4% Solids
Table 4-3 - Comparison of Solution pH and Volume of Precipitate Produced
by Addition of High-Calcium Hydrated Lime, as a Water Slurry, to
Synthetic Acid Mine Water - Effect of Varying Particle Size
Size Range
(Mesh)
pH
Volume
Precipi
(ml)
of
tate
-400
11.2
70
-325 +400
11.0
75
-200 +325
10.7
75
-140 +200
10.6
75
-100 +140
11.0
70
-70 +100
10.7
60
-50 +70
11.0
60
NOTES: Material Used: Bell Mine Chemical Hydrate
Dosage Level: 2 g/l
Slurry Concentration: 4% Solids
81
-------
Table 4-4 - Comparison of Volume (ml) of Precipitate Produced by Specific
Grades Limestones and Hydrated Limes When Added as a Water Slurry in
Synthetic Acid Mine Water - Effect on Varying Slurry Concentration
Pulverized Limestone Hydrated Lime
o -4
0
4 )
4.) 4)
41)
U E
U
o 4) 41) G ) o 4) ft
U ,-4 ,-4 ‘-4 —4 > 4) —s -i J 4-’ ‘-4 ‘ ‘ —
LI) 0 —. 0 C l ) —.. 0 Cl) ‘ . -r i C /) ‘l . ‘ -.. .-4 0’’. b41 4) . . C 4) .i -I C (1)
b4 . b41 Ob0 l b +Jbř )b0 04.ŕbO UbO 4 - 0
00 (I ) C )., 4) •r C . . .4
k 4) 41) L’) r1 r -l r1 C l) t ’I) i-i ,- -rI 0 . 1i t’) LI) LI)
r1 0 r40 r - 4 U) 0
— 0 ‘.1 4-’ 4-) 0 14 4 ) 0 4.) 4)0) 4J 4) ‘I 4.) U) 4.) bO • r . 4 ) C 4.) , 4.) 41) 4.) 4) 4.1
C/) U . )C L 5 C CC) C 1 LL03 U c U $
1 20 60 25 35 35 <10 20 40 40 60 70 45
S 20 40 20 40 30 10 15 25 70 50 60 50
10 20 45 20 23 30 10 15 20 60 50 50 50
25 20 40 20 40 30 10 10 25 50 50 50 50
50 20 40 20 30 30 10 15 20 50 50 50 50
-------
Table 4-5 - Comparison of pH Resulting From the Addition of Specific
Grades of Limestones and Hydrated Limes Injected as a Water Slurry to
Synthetic Acid Mine Water - Effect of Varying Slurry Concentration
Pulverized Limestone Hydrated Lime
o
c ) -
U)
U) c i 0)
U) $ — U)Q)
—4 L) E 1 -. •H
•Sb •
-
00 0u U) - U) 0 0) Lt) 1.i
U —I ‘—‘ — — U)
\ 0 LID 0 . . .. 0 Cl) 0 ( ID S r1 ( /D ‘. . ‘ 4 . ‘ r-l 0 -.. (1) -. .. C 3 (3) .. t-l C 4..) 4.) (1) •—_
LJD4J 0 . b0 Z bo ObO .I b0 # b0 4- bO O4JbU Xoc 4-.)bO
4 -) c ja) 0 ( 1 ) •r4C (3 •r 4C •i-1
1 - i (1) 0) I ‘) 4 —‘ - U) ) - - •r4 0) ‘-4 E 1- / D ‘-4 E (I) $- LtD
E >. . -1 ,- 0 -40 .- 1 E - U) E
0 r4 4 4 < 4.3 0 4 ) 0 C) 0 . 4-3 —l 4.3 (F)•r( 4- bO -l 4.3 C d - . 4.3 - . 4-3 0) .r-l C) 43
( I) L ).- c L)Cd Cd Cd - Cd cd U Cd Z Cd
1
3.7
4.0
4.0
4.9
5,0
3.5
3.8
4.4
10.8
11.5
11.7
11.5
5
3.4
3.8
3.8
4.7
3.9
3.3
3.9
4.0
9.9
11.1
11.4
11.4
10
4.0
4.2
4.3
5.0
3.7
3.2
3.9
3.9
10.3
10.9
11.6
11.5
25
4.0
3.9
3.9
5.0
3.7
3.4
3.8
4.0
10.3
10.6
11.5
11.2
50
3.6
3.7
3.8
4.8
3.6
3.1
3.9
3.7
9.8
11.0
10.6
11.4
-------
EFFECI’ OF VARYING QUALITY OF WATER USED TO PREPARE SLURRY
The third variable studied was the quality of water used to prepare
the slurry. Pure water would not normally be available to make up
the slurry at the field site, and the mine effluent or a nearby stream
would have to be used. However, as the treatment of the mine water
proceeded, the quality of the water would change.
Therefore, on the first day of this evaluation both deionized water
and synthetic acid mine water were used to make up the slurry to
perform the bulking ratio test, using the four locally available hy-
drated limes. On the following day the test was repeated, this time
using supernatant liquid from the first day’s series of eight tests
to make up the respective slurries. Results are shown in Table 4-6.
When deionized water with a pH of 7 was used, the final pH at
18 hours ranged from 11.1 to 11.3. However, when synthetic acid mine
water with a pH of 3 was used, the final pH at 18 hours ranged from
10.0 to 11.5. This indicates that at startup pure water would be more
desirable than acid mine water. However, comparison of the data for
the second set of tests (performed with slurries made up with water
that had been treated the day before) shows that all eight tests
resulted in a solution pH within the narrow range of 10.9 to 11.5.
Also, a comparison of data for the specific limes shows that after the
first day’s treatment, si)bsequent treatment is independent of the
quality of the water used at startup.
SUMMARY
These studies indicate that: (1) particle size of the slurry solids
is important for limestone, not so critical in the case of a good
quality, correctly calcined and slaked hydrated lime, except as an
indication of quality; (2) slurry concentration is not critical,
provided a good dispersion is obtained; and (3) quality of water used
to make up the slurry is not critical, especially after the water
treatment has been started.
For purposes of the demonstration at the mine site, the limestone used
will be specified in the size range of 200 to 400 mesh when its func-
tion is to take part in the neutralization reaction, and coarser when
it is used as a particulate filler. The hydrated lime used will be
specified in the size range of 140 to 400 mesh to assure a good quality
material. The slurry concentration will be limited to a maximum of
5% to assure adequate dispersion of the solids. The water used for
making up the slurry will be mine drainage water.
84
-------
Ln
Table 4-6 - Comparison of Solution pH and Volume of Precipitate Produced by Addition of
High-Calcium Hydrated Lime, as a Water Slurry, to Synthetic Acid Mine Water
Water Used
to
Prepare Slurry
Start-
ing pH
Washington Chemical
Hydrate
(at 2 g/l)
Chemical Hydrated
Lime #26
(at 3 g/l)
Bell Mine Chemical
Hydrated Lime
(at 5 g/l)
New Enterprise Hydrated
Lime
(at 5 g/l)
H
Precip-
itate
Volume
(ml)
H
I ’
Precip-
itate
Volume
(ml)
H
Precip-
itate
Volume
(ml)
Precip-
itate
Volume
(ml)
Initial
-
18 hr
Initial
18 hr
Initial
18 hr
Initial
18 hr
Deionized
Water
Synthetic Acid
Mine Water
Decantate from
Deionized
Water Test
Decantate from
SAMW Test
7
3
11.1-
11.3
10.0-
11.5
11.7
10.0
11.5
11.7
11.1
10.0
10.9
10.9
60
85*
55
55
12.0
10.5
11.7
11.7
11.2
10.4
11.1
11.1
60
70
60
55
11.9
11.3
11.2
11.5
11.3
10.7
10.9
10.9
70
65
55
55
12.0
11.9
11.5
11.6
11.1
11.5
11.3
1l.S
65
65
60
60
* Probably high due to experimental limitations of test method.
-------
TEST 5
EFFECT OF AIR AGITATION ON BULKING RATIO
AND ON PLUGGING CHARACTERISTICS
The purpose of introducing air into the acid mine water is to convert
iron from the ferrous state to the ferric state so that the iron
precipitation will start at a lower pH. If all the iron were con-
verted to the ferric state, it could all be precipitated without
having to raise the pH above 8. Therefore, the conversion of
ferrous ions to Lerric would result in a greater volume of pre-
cipitate. However, this increase is offset to some degree by the
fact that the ferric oxide hydrate precipitates are denser than the
ferrous oxide hydrate precipitates. Thus, while all of the iron would
be precipitated at the lower pH, the increase n volume of precipitate,
if any, would not be comparable to the precipitation of that same iron
as ferrous oxide hydrate at the higher pH.
LABORATORY PROCEDURE
The effects of air agitation to the bulking properties and plugging
properties were studied. Bulking was evaluated using the bulking ratio
test described for Test 2, performed with and without a 5-minute period
of air agitation, at several dosage levels of high-calcium limestone.
The air was introduced by inserting a rubber hose attached to a pump
(such as that used to aerate fish aquaria) into the water contained
inthe cylinder, and bubbling air up through the water. The test was
also performed varying the air agitation period for a fixed dosage
level of high-calcium limestone. Plugging was evaluated using the
static plugging test described for Test 3, performed with and without
a 5-minute period of air agitation, at several dosage levels of
high-calcium hydrated lime.
RESULTS
Results of the bulking tests (shown in Tables 5- ]. and 5-2) indicate
that the use of air does not appreciably affect the volume of precipi-
tate. These tests were done with high-calcium limestone, which can
only raise the pH to 5. Apparently, the lengths of time used for
air agitation were insufficient to effect any large-scale conversion
from ferrous to ferric.
Results of the plugging tests (shown in Table 5-3) indicate that air
agitation is helpful in some instances. At a dosage level of 2.5 grams
of high-calcium hydrate lime per liter of mine water, there was an
appreciable decrease in percolation rate through the sand in the air-
agitated test compared with the test with no air agitation.
87
-------
S1JI!4ARY
Air agitation may be beneficial under certain conditions in connection
with plugging a drainage opening. From a bulking standpoint, air
agitation does not appear to be useful and may even be detrimental
to achieving as high a bulking ratio as possible.
The tests would indicate, and other investigators have published
supporting confirmation, that the ferrous to ferric conversion proceeds
slowly at low pH and more rapidly at higher pH. Hence, at low pH, air
agitation would have to be continued for a much longer period of time
than at high pH for the same degree of conversion of ferrous to ferric.
88
-------
Table 5-1 - Effect of Aeration on Precipitation Resulting
From the Addition of Varying Quantities of High-Calcium
Limestone to Synthetic Acid Mine Water
Weight of
Additive
(g/l)
Volume of Precipitate After
18 hours (ml)
With 5 Minutes
Air Agitation
No Air
Agitation
0.1
0.2
0.5
1.0
3.0
5.0
5
<< 5
< 5
10
15
15
<< 5
<< 5
<5
10
20
20
Table 5-2 - Effect of Varying Time of Air Agitation on
Precipitation Resulting From the Addition of High-
Calcium Limestone to Synthetic Acid Mine Water
Time Duration of
Air Agitation
(mm)
Volume of Precipitate
After 18 hours
(ml)
5
8
10
15
20
10
10
10
15
15
Note: Dosage Level = I g/l
89
-------
‘ 0
0
Table 5-3 - Effect of Aeration on Plugging Effectiveness of Precipitates
Resulting from the Addition of Varying Quantities of High-Calcium
Hydrated Lime to Synthetic Acid Mine Water
Weight of
Additive
(g/l)
Time for Flow of 100 ml, at
44 Foot Head (mm)
Discharge
pH
With 5 Minutes No Air
Air Agitation Agitation
With 5 Minutes No Air
Air Agitation Agitation
0.5
15
2.5
3.5
5.5
20.0
38.0
33.0
16.0
19.0
20.0
35.0
5
13
13
13
5
10
12.5
13
Control
(Water Alone)
0.05
3
-------
TEST 6
EFFECT OF STATIC HEAD ON PLUGGING CHARACTERISTICS
If it is assumed that precipitates formed underground in acid mine water
can effectively reduce the mine effluent flow by filling the voids in a
drainage, the question remains whether this sealed barrier will remain
watertight at an increased pressure and, if not, at what pressure the
seal will break down.
LABORATORY PROCEDURE
The vertical dynamic plugging test was used in this study, except that
the glass tube was replaced by a steel tube, so as to withstand the
anticipated applied pressure. The additive used was Washington Chemical
Hydrated Lime, added as a 2% water slurry. When the flow of mine water
through the barrier was reduced from the initial 545 ml/min to a rate of
1 drop/sec, the time required as noted and the flows of mine water and
slurry were stopped. After 18 hours, the time between drops was noted.
The inlet end of the tube was then pressurized to 4.3 psig (corresponding
to 10 feet of water). The time between drops was noted. The pressure
was then increased to 8.7 psig (corresponding to 20 feet of water) and
the time between drops noted. This was repeated, progressively increas-
ing the pressure, until the flow could be measured in mi/mm, or until
the effluent end blew out.
RE SULTS
The results, shown in Table 6-1, indicate that the initial slight pressur-
ization increases the water flow somewhat; however, further increases in
pressure increase the flow only slightly. A pressure is reached where
the seal becomes porous. At this point, the flow increases markedly.
SUMMARY
The tests indicate that the seal formed as the precipitate in the acid
mine water plugs the voids in the drainage channel does not become porous
as the pressure is increased until a substantial pressure (corresponding
to approximately a 100-foot head of water) has been reached. This is for
a seal which is relatively ttfresh?e and formed from a single injection of
additive. If we assume that additional precipitate, formed with the addi-
tional injection of additive, flows to reinforce the precipitate already
in the voids, it is conceivable that the seal will be able to hold much
higher pressures. Additional testing would be required in this area.
91
-------
Table 6-1 - Effectiveness of Seal Under Increasing Pressure
Startup Phase
Test 1 Test 2 Test 3
Initial Acid Mine Water 545
Flow Rate, mi/mm
Washington Chemical Hydrate
(added as 2% water slurry) 1.73
(g/l)
Time to reduce flow to
1 drop/sec (mm) 5 5 6
Time between drops at
18 hrs (sec) 32.0 45.0 10.0
Pressure Phase
Pressure
(psig)
Equivalent Head
of Water* (ft)
Time Between Drops (sec)
0
4.3
8.7
13.0
17.3
21.7
32.5
43.4
65.0
86.7
108.4
130.1
0
10
20
30
40
50
75
100
150
200
250
300
32.0
5.6
5.8
6.2
5.0
5.4
4.1
1.0
264**
790**
---
---
45.0
7.0
5.2
4.1
4.6
3.1
3.0
2.2
2.7
3.0
---
10.0
6.0
4.0
3.8
3.9
3.4
3.4
3.4
2.8
2.4
>700**
---
* Does not include 4-foot water column in tube.
** mi/mm flow rate.
*** Effluent end blew out.
92
-------
TEST 7
COMPOSITION OF ACID MINE WATER
WHICH CAN BE TREATED EFFECTIVELY
Because of the wide range of composition of acid mine waters, the neutra-
lization of a specific acid mine water might present a problem. There-
fore, a study was conducted to determine whether limitations might prevent
the treatment of some acid mine waters.
A range of synthetic mine waters was prepared containing varying concen-
trations of iron (Fe ) ions and sulfuric acid representative of the
metal ions and acidity encountered in acid mine waters. These waters
were then neutralized using high-calcium hydrated lime and limestone.
The volume of precipitate formed and the pH of the solution were used to
evaluate the effectiveness of the treatment.
LABORATORY PROCE DURE
A series of 12 synthetic mine waters, in which the iron concentration
was set at four levels, while the sulfuric acid concentration was set at
three, was prepared. All other mineral constituents that might be
encountered in actual acid mine waters were neglected in this study on
the assumption that they would probably be present in relatively small
quantities and their effects would be minor.
The respective concentrations of iron and acid and the corresponding cal-
culated total acidity are shown in Table 7-1.
The initial pH of each of the 12 synthetic mine waters was first
measured; the 950 milliliters of each water were placed in a separate
graduated cylinder. A 6% slurry (3 g/50 ml) of a high-calcium limestone
in deionized water was added to each of the cylinders. The cylinders
were allowed to stand undisturbed for 18 hours, the solution pH was
measured, and the volume of precipitate noted. One gram of the limestone
was then added to each of the cylinders (after first slurrying it with
50 milliliters of solution from the cylinder). The cylinders were
allowed to stand undisturbed for 24 hours, and the pH and volume of pre-
cipitate were noted. This procedure was repeated daily until 12 grams
of limestone had been added to each cylinder. Results of this series
are shown in Tables 7-2 through 7-4.
This series of tests was then repeated using a high-calcium hydrated lime
as the additive except that the first addition was 1 gram in 50 milli-
liters rather than 3 grams in 50 milliliters as in the case of limestone.
Also, when the pH in any cylinder was raised to more than 12, no further
addition of lime was made to that cylinder. Results of this series are
shown in Tables 7-5 through 7-7.
93
-------
Table 7-1 Composition of Synthetic Mine Waters
Experi-
mental
Water
No.
Fe
(mg/i)
H 2 S0 4
(mg/i)
Due to
Fe
(mg/i)
Free
(due to
H 2 S0 4 )
(mg/i)
Total
(mg/i)
1
100
1,000
179
1,020
1,199
2
1,000
1,000
1,790
1,020
2,810
3
5,000
1,000
8,950
1,020
9,970
4
10,000
1,000
17,900
1,020
18,920
5
100
5,000
179
5,100
5,279
6
1,000
5,000
1,790
5,100
6,890
7
5,000
5,000
8,950
5,100
14,050
8
10,000
5,000
17,900
5,100
23,000
9
100
iO,000
179
10,200
10,379
10
1,000
10,000
1,790
10,200
11,990
11
5,000
10,000
8,950
10,200
19,150
12
10,000
10,000
17,900
10,200
28,100
In the reaction H 2 S0 4 + CaCO 3 —.-CaSO 4 + H 2 C0 3 :
1 mol of H 2 S0 1 mol of CaCO 3
or 98 # H 2 S0 4 0 100 # CaCO 3
•. 100 mg/i H 2 S0 4 i02 mg/i CaCO 3
In the reaction FeSO 4 + CaCO 3 + H 2 0—. Fe0 + CaSO 4 + H2C0 3 :
1 mol of Fe (equivalent to 1 mol of S0 4 =) l mol of CaCO 3
or 56 # Fe l00 # CaCO 3
100 mg/i Fe i79 mg/i CaCO 3
Total acidity is the sum of the free acidity (due to the H 2 S0 4 )
and the acidity due to the iron (PeSO 4 )
94
-------
Table 7-2 - Neutralization of Range of Acid Mine Waters
With High-Calcium Limestone - 1,000 mg/i H2S0 4
(Synthetic Mine Waters 1 through 4)
Total
Weight
of
Add itiVe
(grams)
100 mg/i Fe
TA = 1,199
1000 mg/i Fe
TA = 2,810
5000 mg/i Fe
TA = 9,970
10,000 mg/i Fe
TA 18,920
pH
Vol of
PPT (ml)
p1-I
Vol of
PPT (ml)
pH
Vol of
PPT (ml)
pH
Vol of
PPT (ml)
0
3
4
5
6
7
8
9
10
ii
12
2.0
4.0
6.0
6.0
7.0
7.0
7.0
7.0
7.0
7.5
7.5
0
<10
10
10
10
10
10
10
10
15
15
2.0
4.0
5.0
5.5
5.5
5.5
6.0
6.0
6.5
6.5
7.0
0
<10
<10
<10
10
15
15
20
20
20
20
2.0
4.0
4.0
4.5
4.5
4.5
4.,5
4.5
5.0
5.0
5.5
0
12
15
15
15
20
25
30
30
30
30
2.0
4.0
4.0
4.0
4.0
4.0
4.0
4.5
4.5
4.5
5.0
0
20
25
25
30
30
30
30
30
30
30
-------
Table 7-3 - Neutralization of Range of Acid Mine Waters
With High-Calcium Limestone - 5,000 mg/i l-1 2 S0 4
(Synthetic Mine Waters 5 through 8)
Total
Weight
of
Additive
100 mg/i Fe
TA = 5,279
—
1000 mg/i Fe
TA = 6,890
5000 mg/I Fe
TA = 14,050
10,000 mg/I Fe
TA = 23,000
Vol of
Vol of
Vol of
Vol of
(grams)
pH
PPT (ml)
pH
PPT (ml)
pH
PPT (ml)
pH
PPT (ml)
0 1.0 0 1.0 0 1.0 0 1.0 0
3 4.0 <10 4.0 <10 4.0 <10 4.0 <10
4 4.5 <10 4.0 <10 4.0 20 4.0 <10
5 6.0 20 5.5 15 5,5 40 5.5 20
6 6.0 30 6.0 20 6.0 40 5.5 30
7 6.0 35 6.0 30 6.0 40 5.5 40
8 6.0 40 6.0 30 6.0 40 6.0 40
9 6.0 40 6.0 30 6.0 40 6.0 40
10 6.5 40 6.0 35 6.0 45 6.0 40
11 6.5 40 6.0 40 6.0 45 6.0 40
12 6.5 40 6.0 40 6.0 50 6.0 40
-------
Table 7-4 - Neutralization of Range of Acid Mine Waters
With High-Calcium Limestone - 10,000 mg/i H 2 S0 4
(Synthetic Mine Waters 9 through 12)
Total
Weight
of
Additive
(grams)
100 mg/i Fe
TA = 10,379
1000 mg/i Fe
TA = 11,990
-—
5000mg/i Fe
TA = 19,150
10,000 mg/i Fe
TA = 28,100
pH
Vol of
PPT (ml)
pH
Vol of
PPT (ml)
pH
Vol of
PPT (ml)
pH
Vol of
PPT (ml)
0
3
4
5
6
7
8
9
10
11
12
<1.0
2.0
2.0
2.5
3.5
4.5
6.0
6.0
6.0
6.0
6.0
0
<10
10
40
95
120
130
140
14O
145
145
<1.0
2.0
2.0
2.0
2.0
2.5
3.5
4.5
5.5
6.0
6.0
0
<10
<10
30
120
130
150
150
160
160
160
<1.0
2.0
2.0
2.0
2.0
3.0
4.0
4.5
5.0
5.5
5.5
0
<10
<10
30
135
140
180
180
180
180
180
<1.0
2.0
2.0
2.5
3.0
4.0
4.5
4.5
4.5
4.5
5.0
0
<10
<10
50
130
130
130
140
140
140
145
-------
Table 7-5 - Neutralization of Range of Acid Mine Water
With High-Calcium Hydrated Lime - 1,000 mg/i H 2 S0 4
(Synthetic Mine Waters 1 through 4)
00
Total
Weight
of
Additive
(grams)
100 mg/i Fe
TA = 1,199
1000 mg/i Fe
TA = 2,810
5000 mg/i Fe
TA = 9,970
10,000 mg/i Fe
TA = 18,920
pH
Vol of
PPT (ml)
pH
Vol of
PPT (ml)
pH
Vol of
PPT (ml)
pH
Vol of
PPT (ml)
0
1
2
3
4
S
6
2.0
6.0
11.0
>12.0
-
-
-
0
20
45
20
-
-
-
2.0
5.0
8.0
11.0
>12.0
-
-
0
65
160
140
140
-
-
2.0
3.0
6.0
6.0
9.0
11.5
>12.0
0
50
260
290
290
400
370
2.0
5.0
6.0
6.0
8.5
11.5
>12.0
0
60
160
230
370
420
640
-------
Table 7-6 - Neutralization of Range of Acid Mine Waters
With High-Calcium Hydrated Lime - 5,000 mg/i H 2 S0 4
(Synthetic Mine Waters 5 through 8)
0
Total
Weight
of
Additive
(grams)
100 mg/i Fe
TA = 5,279
1000 mg/i Fe
TA = 6,890
5000 mg/i Fe
TA 14,050
10,000 mg/i Fe
TA 23,00
pH
Vol of
PPT (ml)
—
pH
Vol of
PPT (ml)
pH
Vol of
PPT (m l)
pH
Vol of
PPT (ml)
0
1
2
3
4
5
6
7
1.0
2.0
4.0
5.0
8.5
11.5
>12.0
-
0
0
5
10
55
80
75
-
1.0
2.0
3.0
5.0
8.5
11.0
>12.0
-
0
0
20
50
60
250
200
-
1.0
2.0
2.0
3.0
5.5
9.0
>12.0
-
0
0
20
50
140
260
380
-
1.0
2.0
2.0
3.0
4.0
8.0
11.0
>12.0
0
0
25
55
140
250
440
630
-------
Total
Weight
of
Additive
(grams)
100 mg/i Fe ”’
TA = iO,379
1000 mg/i Fe
TA = 11,990
5000 mg/i Fe ’
TA = i9,l50
10,000 mg/i Fe
TA = 28,100
pH
Vol of
PPT (ml)
pH
Voi of
PPT (ml)
pH
Vol of
PPT (ml)
pH
Vol of
PPT (ml)
0
1
2
3
4
5
6
7
8
<1
1.0
2.0
2.5
3.0
>12.0
-
-
-
0
0
5
20
60
130
-
-
-
<1
1.0
2.0
2.0
2.5
3.0
12.0
>12.0
-
0
0
0
5
30
40
210
240
-
<1
1.0
2.0
2.0
2.5
3.0
3.0
12.0
>12.0
0
0
0
20
40
50
530
690
720
<1
1.0
2.0
2,0
2.0
3.0
3.0
11.5
>12.0
0
0
5
20
50
80
530
710
790
Table 7-7 - Neutralization of Range of Acid Mine Waters
With High-Calcium Hydrated Lime - 10,000 mg/i H 2 S0 4
(Synthetic Mine Waters 9 through 12)
0
0
-------
RE SULTS
The data shown in Tables 7-2 through 7-7 indicate that if a sufficient
amount of additive is used, all the synthetic mine waters in the range
studied could be neutralized. However, the effectiveness of the neutra-
lization to precipitate the mineral content is not the same for all the
waters studied. Also, the neutralization reaction does not proceed along
a predicted curve, but rather is influenced by the buffering action of
the mineral content. In many cases, successive additions of limestone
or lime do not increase the pH, until a point is reached when the addi-
tion of “one more gram” results in a large increase in pH. When these
tests were started, it was hoped that plots of the different variables
could be prepared; however, this could not be done because of their
limited scope.
As expected, the waters with the higher iron content yielded higher
volumes of precipitates; however, the increase in volume was not as great
as might be expected. For example, referring to Table 7-5, the water
containing 100 mg/l Fe” yielded a total precipitate volume of 45 milli-
liters at a pH of 11, for an addition of 2 grams of hydrated lime. The
water containing 100 mg/i Fe yielded a total precipitate volume of
140 milliliters at a pH of 11, for an addition of 3 grams of hydrated
lime. There was not a tenfold increase in volume of precipitates for a
tenfold increase in iron content. This phenomenon is due in part to the
fact that precipitation of iron hydroxides from iron sulfate solutions is
a highly complex reaction, depending on the formation of numerous com-
plexes of iron oxides associated with varying quantities of water. Part
of this phenomenon is also due to the presence of free acidity, as shown
by a comparison of 100 mg/I Fe water in Tables 7-5, 7-6, and 7-7.
Increasing the free acidity of the water required more hydrated lime to
raise the pH to any given level, but when that pH had been reached, the
volume of precipitate was much higher.
SUMMARY
The precipitation of the metallic iron content of acid mine waters,
especially iron, during the neutralization is a complex reaction, depend-
ing on many variables. Part of this complexity is the multitude of forms
in which the iron oxide hydrates can exist, both in themselves and when
precipitated in the presence of other metal ions. The results of these
two series of tests indicate that any water whose analysis falls within the
wide range of acid mine waters encountered can be treated effectively. The
degree of effectiveness, and other specific variables, can only be deter-
mined in the field for waters that are actually encountered. More defin-
itive data would require a test program of greater scope than the contract
will allow.
101
-------
TEST 8
GELLING OF ACID MINE WATER WITH SYNTHETIC
GELLING AGENTS
Another approach to underground precipitation in acid mine water is
that of gelling the water to form either a rigid or semirigid solid.
There are numerous materials that can gel a mass of water; the problem
is the introduction of the gelling material into the water external
to the mine adit without gelling taking place until after the mixed
water is returned to the mine voids so that the gel is formed under-
ground. A material that appears to be appropriate for this use is
cellulose gum, marketed as CMC-7H by Hercules, Inc. This gum in-
creases the viscosity of water. In addition, if ions of heavy metals
(such as aluminum or iron) are introduced over an extended period of
time, extensive cross-linking occurs; the ions enter the structure
and make the gels rigid.
LABORATORY PROCEDURE
The manufacturer’s recommended procedures were followed during the
laboratory evaluation of this gum in an attempt to reproduce the
expected results. Starting with deionized water, aluminum ions were
added in the form of aluminum acetate. After thorough dispersion, the
cellulose gum was added and dispersed by hand. Four tests that varied
the aluminum ion content and amount of cellulose gum were performed.
Synthetic mine water with an iron and aluminum content was then sub-
stituted for the deionized water. No more ions of heavy metal were
added. Cellulose gum was then added and dispersed by hand. After
3 hours, the tubes were evaluated for gelling.
The entire series of seven tests was repeated. In the second series,
good dispersion was accomplished with the use of a blender.
RESULTS
Results of these tests are shown in Table 8-1. The first four tests
(in which deionized water and aluminum acetate were used) were
performed to confirm the manufacturer’s literature. The results,
while not verifying the manufacturer’s results, were close enough to
indicate that the minor differences could easily have been caused by
experimental variations. The main point to remember in using this
cellulose gum is that the gelling is largely dependent on the dis-
persion of the gum and the heavy metal ions required for cross-
linking. Where mixing was good, the formation of rigid gels occurred
as expected, though faster than anticipated. Poor mixing resulted
102
-------
in high concnetrations of either gum or ions which, in turn, resulted
in rigid gels in some portions of the tests cylinder and no gels in
other portions. The tests confirmed the need for the proper con-
centrations to achieve the desired degree of rigidity, and the proper
dispersion to achieve the desired concentrations.
The last three tests (in which mine water was used) were performed to
determine whether the naturally occurring heavy metal ions could be
used to cross-link the gum and form a rigid gel. Three ratios
(ranging from 0.2 to 1.0%) of gum synthetic mine water were tried. As
before, results from poor mixing could not be evaluated, other than
to confirm the necessity for good mixing. Results from the well-mixed
series indicated that 0.2% is too low to produce gel; 0.5% resulted in
a soft gel witiri a 24-hour period; and 1.0% resulted in a firm gel,
formed too quickly. For synthetic water, the ideal concentration
lies somewhere between 0.5 and 1.0%.
SUMMARY
The use of cellulose gum for gelling mine water appears to be feasible
under the correct conditions; however, a great deal more laboratory
work must be done before its proper application can be established.
Its attractiveness from a cost standpoint would depend on the quantity
used; its use appears to be limited to the gelling of mine water after
the effluent drainage points have been plugged.
103
-------
Table 8-1 - Gelling of Water by the Use of Cellulose Gum
Test
No.
Water Used
(ml)
Aluminum
Acetate
CMC-7H
Ge1
Time
(hr)
Results
OW
p.14W
Wt
(g)
Conc,
on CNC
(%)
Wt
(g)
Conc. on
AI1W
( )
Poor Mixing (by hand)
Good Mixing (by blinder)
1
1000
-
2
20
10
1.0
1-1/2
Rigid gel formed at top of cylinder,
instantly upon addition of gum. A
precipitate then appeared at bottom
of cylinder within approximately
10 minutes.
Uniform dispersion throughout -
formed uniform rigid gel during
mixing
2
1000
-
1
20
5
0.5
2
As in Test 1 above.
Firm gel with slight water layer
at top of cylinder. Within 30
minutes the entire tube was
filled with a rigid gel.
3
1000
-
0.35
7
5
0.5
24
Firm gel formed throughout 25% of
the water within 24 hours,
Upon mixing formed very viscous
liquid, which became a soft gel
throughout within 24 hours.
4
1000
-
0.04
2
2
0.2
4
Immediate gel formed - in lumps.
Within 4 hours a flexible, soft
extension of the gel formed at top
of cylinder. Gel filled approx-
imately St of volume.
Formed a thickened liquid, but
no gel formed within 4 hours.
5
.
1000
0
0
10
1.0
-
Firm gel resulted immediately which
became rigid within 3 hours,
Firm gel formed while mixing,
no change occurred thereafter.
6
7
-
-
1000
1000
0
0
0
0
5
2
0.5
0.2
-
-
As in Test 5, above.
Gel formed in single lump upon
addition of gum - lumps became
rigid after 3 hours.
No gel formed within first
several hours, very soft gel
filled cylinder within 24 hours.
No appreciable gelling or
thickening occurred.
*Per manufacturer’s literature.
-------
TEST 9
COATING OF MINE SURFACES BY PRECIPITATES
FORMED UNDERGROUND
It was postulated that precipitates formed underground in a mine adit
might form a protective coating and prevent dissolution of the pyrites
with the acid mine water. To explore this possibility, a number of
samples, including pyrites, coal, and shale, were collected from the
demonstration mine site and forwarded to the laboratory.
LABORATORY PROCEDURE
At the laboratory, the samples were placed in vats of synthetic acid
mine water. The required amount of high-calcium hyrated lime in a
10% water slurry was added to the vats. The usual precipitates
(whitish or graygreen) formed and clouded the entire container.
Observations at 18 hours indicated a uniform fallout over the bottom
of the containers and over the specimens. No precipitate adhered to
the vertical surfaces; it tended to turn brown (indicating oxidation
or the iron) after a period of several days.
After one week, the specimens were removed from the tank and examined.
In general, the precipitate was easily washed away; however, where it
was in contact with pyrites, it did not wash away and the presence
of pyrites in the coal was clearly defined. But since the color of
the precipitate at these points was reddish-orange (indicating a
high concentration of ferric oxide), it appears that rather than
sealing off the pyrites, the precipitate accelerated their oxidation.
Therefore, precipitates formed underground in the acid mine water
were eliminated from consideration for sealing in the coal or shale.
Furthermore, experimenters studying the reaction of groundwater
seeping into an underground mine and becoming acidic (because of the
dissolution of iron pyrites) have proven the importance of oxygen
as the ultimate oxidant. From the results of their studies, it is
apparent that most of the dissolution of pyrites takes place in
adits not flooded with mine water; thus, coating the surfaces of
flooded adits appears to be unbeneficial.
No further studies were made of coating mine surfaces as a deterrent
to pollution from acid mine water.
CONCLUSION
It was concluded that the underground precipitation does not result in
the formation of a protective coating on the pyrites particles.
105
-------
TEST 10
AUGMENTATION OF MINERAL CONTENT BY ADDITION OF
WASTE PICKLE LIQUOR
At times it might be desirable or necessary to augment the mineral
content of acid mine water; therefore, the precipitation of such
augmented mine water was studied. Waste pickle liquor (sulfate)
was used as the additional source of mineral content because it is
readily available, high in iron content, and presents a disposal
problem in itself.
LABORATORY P ROCE DURE
The bulking ratio test procedure described for Test 2 was used for
this study. Three experimental waters were prepared by adding pickle
liquor to the synthetic acid mine water to give ratios of acid water
to waste pickle liquor of 99:1, 95:5, and 90:10. A control contain-
ing no waste pickle liquor was also used.
Waste pickle liquor from the Irwin Plant of the U.S. Steel Corpo-
ration was used in the tests and had an approximate composition as
follows:
FeSO 4 13.0% by weight
H 2 S0 4 8.5% by weight
The iron concentration is approximately 50,000 mg/l; free acidity
87,000 mg/l; and total acidity 173,000 mg/l.
Four high-calcium hydrated limes were used, at the optimum addition
level for each, to precipitate the mineral content of the water.
The volume of precipitate and the pH of the solution were measured
after 18 hours.
RESULTS
Results are presented in Table 10-1. The augmentation of the acid
mine water with only 1% of waste pickle liquor produced, on the
average, a doubling of the volume of precipitate. Augmentation with
higher percentage of waste pickle liquor produced a decrease rather
than an increase. This is due to the fact that the addition level
of additive was not increased to neutralize the additional acidity
due to the waste pickle liquor. Increasing the addition of lime
would precipitate more of the mineral content as the pH is increased.
107
-------
Table 10-1 - Precipitation in Acid Mine Water
Augmented With Waste Pickle Liquor
Ratio
of
Acid Mine
Water
to
Waste Pickle
Liquor
Washington
Chemical
Hydrate
Chemical Hydrated
Lime #26
Bell Mine
Chemical
Hydrated Lime
New Enterprise
Hydrated Lime
at 2 g/l
at 3 g/l
at S g/l
at 5 g/l
pH
Vol of
Precipitate
(ml)
pH
Vol of
Precipitate
(ml)
pH
Vol of
Precipitate
(ml)
—
pH
Vol of
Precipitate
( ml)
100:0
(control)
99:1
95:5
90:10
11.0
4.0
1.9
1.7
60
100
15
20
10.8
3.7
2.3
2.0
65
140
60
40
10.3
4.1
2.0
1.6
55
140
40
30
10.5
11.0
2.1
1.8
55
150
30
80
-------
S 1v1MARY
Augmentation of the mineral content of acid mine water to produce
additional volume of precipitate is feasible using waste pickle liquor
(sulfate) from the steel industry. The additional acidity introduced
by the waste pickle liquor increases the quantity of neutralizing
additive required.
109
-------
TEST 11
CONTINUOUS NEUTRALIZATION OF ACID MINE WATER
A third application of underground precipitation for abating pollution
from abandoned coal mines is the continuous injection of a neutral-
izing agent(s) through boreholes located some distance back from the
effluent point so that the mine water will be neutralized and the
resultant sludge will remain in the mine.
LABORATORY PROCEDURE
The horizontal dynamic plugging test described for Test 3 was used,
except that the tube sloped away from the effluent end rather than
toward it. When slurry was injected through the borehole, the
precipitate formed flowed away from the effluent end rather than
toward it (if the flow of mine water was not great enough to overcome
gravity and pull the precipitate up to the effluent end). The slope
was adjusted to 1%, 5%, and 10%. In the first set of tests, the
borehole was placed 4 inches back from the effluent end. Additional
tests were then performed with the borehole placed 14 and 21 inches
back.
RESULTS
Results of these tests are shown in Tables 11-1 through 11-3. In the
first set of tests, reported in Table 11-1, the placement of the slurry
inlet proved to be too close to the effluent end for two reasons:
first, the high pH of the discharge stream for such a low additive
level indicated insufficient neutralization time; second, the plugging
of the sand barrier indicated insufficient distance for settling of
the precipitate to the bottom surface of the tube, at which point it
started to roll back down the tube.
In the tests reported in Tables 11-2 and 11-3, the slurry inlet was
placed 14 and 21 inches back, respectively. These tests were carried
out only until the precipitate had rolled back 50 cm; therefore, some
of the tests were of very short duration. Because of the neutraliza-
tion, the pH of the effluent stream was increased in every test.
Some reduction in the flow was noted, but in no case was the flow reduced
to a drop-by-drop rate. Flow back down the tube was very difficult
to measure with any degree of accuracy. Nevertheless, it appears
that, within the experimental limitations, there was a good correlation
between the various tests.
111
-------
Table 11-1 - Precipitate Flow in Sloped Adit Resulting from Neutralization
of a Flowing Stream of Acid Mine Water with a 2%
Slurry of High-Calcium Hydrated Lime
Slurry Inlet:
4 Inches from Effluent End
Total
Elapsed
Time
(mm)
Total
Slurry
Added
(ml)
1% Slope
5% Slope
10% Slope
Effluent
Flow
Rate
(mi/mm)
Effluent
pH
Effluent
Flow
Rate
(mi/mm)
Effluent
pH
Effluent
Flow
Rate
(mi/mm)
Effluent
pH
0
2
4
6
8
10
12
14
16
18
0
50
100
150
200
250
300
350
400
450
900
900
735
400
250
250
200
2*
2*
2*
3.0
11.5
11.5
11,5
11.5
11.5
11.5
11.5
115
11.5
900
800
560
135
5*
5*
5*
5*
5*
5*
3.0
11.5
11.5
11.5
11.5
11.5
11.5
11.5
11.5
11.5
900
875
740
530
175
160
90
50
-
-
3.0
11.5
11.5
11.5
11.5
11.5
11.5
11.5
-
-
Time for
Precipitate
to Flow Back
50 cm (nun)
16 27
.
9 67
•
3 17
.
Linear Flow
Rate of
Precipitate
Back Down Tube
(ft/mm)
0.101
0.170
0.517
* drops/sec
112
-------
Table 11-2 - Precipitate Flow in Sloped Adit Resulting from Neutralization
of a Flowing Stream of Acid Mine Water with a 2%
Slurry of High-Calcium Hydrated Lime
Slurry Inlet: 14 Inches from Effluent End
Total
Elapsed
Tine
(mm)
Total
Slurry
Added
(ml)
1% Slope
5% Slope
10% Slope
Effluent
Flow
Rate
(ml/min)
Effluent
pH
Effluent
Flow
Rate
(mi/mm)
Effluent
pH
Effluent
Flow
Rate
(ml/min)
Effluent
pH
0
2
4
6
8
10
12
14
16
18
0
50
100
150
200
250
300
350
400
450
900
228
486
372
240
132
-
-
-
-
3.0
3.5
3.2
3.3
3.3
3.9
-
-
-
-
900
522
444
384
292
192
-
-
-
3.0
3.1
3.4
3.3
3.6
3.5
-
-
900
396
-
-
-
-
-
-
3.0
3.4
-
-
-
-
-
-
Time for
Precipitate
to Flow Back
50 cm (mm)
5.58
4.47
1.68
Linear Flow
Rate of
Precipitate
Back Down Tube
(ft/mm)
0.294
0.367
0,980
113
-------
Table 11-3 - Precipitate Flow in Sloped Adit Resulting from Neutralization
of a Flowing Stream of Acid Mine Water with a 2%
Slurry of High-Calcium Hydrated Lime
Slurry Inlet: 21 Inches from Effluent End
Total
Elapsed
Time
(mm)
Total
Slurry
Added
(ml)
1% Slope
5% Slope
10% Slope
Effluent
Flow
Rate
(mi/mm)
Effluent
pH
Effluent
Flow
Rate
(ml/min)
Effluent
pH
Effluent
Flow
Rate
(ml/min)
Effluent
p1-I
0
2
4
6
8
10
12
14
16
18
0
50
100
150
200
250
300
350
400
450
900
330
324
468
464
252
152
132
160
152
3.0
3.5
3.3
3.3
3.4
3,9
3.8
3.9
4.1
4.0
900
504
504
348
348
300
270
300
330
318
3.0
4.0
4.0
4.0
3.7
4.5
3.9
3.8
4.7
3.8
900
594
576
-
-
-
-
-
-
-
3.0
3.1
3.1
-
-
-
-
-
-
-
Time for
Precipitate
to Flow Back
50 cm (mm)
7 75
.
2 45
.
Linear Flow
Rate of
Precipitate
Back Down Tube
(ft/mm)
0.025
0.212
0.67
*762...cm flow in 10 minutes, then precipitate stopped flowing
114
-------
SIJvIMARY
Results of these tests indicated the feasibility of continuous neutral-
ization of acid mine drainage by injection of the slurry into the adit,
and allowing the precipitate to flow back down the adit to lower por-
tions of the mine. The success of this treatment depends on the slope
of the mine adit (in relation to the flow rate of the acid mine water)
and on the injection point being placed far enough from the effluent
end to prevent forward flow of the precipitate. By varying the
quantity and concentration of slurry, the pH of the effluent stream
can be adjusted to any desired level. Additional laboratory work
will be required to obtain more refined data; however, correlation
of such laboratory work with field conditions would be difficult.
Therefore, a small field demonstration, based on present laboratory
tests, would be desirable as the next development step.
115
-------
TEST 12
USE OF FLY ASH
Because of its low cost and widespread availability, fly ash from
coal-burning power generating stations is of interest for possible use
in connection with th underground precipitation concept. However,
while slightly alkaline, fly ash cannot be considered as a neutralizing
agent. Therefore, its use from a bulking standpoint (which depends
upon the neutralization of the acid water with the formation of a
bulky sludge as the mineral content precipitates of the water) does
not appear promising.
The major value of fly ash appears to be its ability to enter into a
reaction to form ettringite (6 CaO • A1 2 0 3 3S04 33 H O) when all
the necessary reactants are present. This reaction is the basis for
the substitution of fly ash for part of the cement to produce a con-
crete with superior properties over nonfly ash concretes. This
indicates that fly ash is valuable in sealing drainage channels.
LABORATORY PROCEDURE
The composition and form of fly ash varies, depending on the types of
fuel being burned and on the pretreatment of the fuel before being
fired. The following fly ashes were included in the laboratory
evaluation:
Fly Ash
Active Components
CaO
MgO
S03
Bituminous
Desulfurization
(Bituminous with High-Calcium Injection
American Lignite
European Lignite
Los
High
High
Medium
Low
Low
High
Medium
Low
High
Medium
Low
In addition, bituminous fly ash interblended with monohydrate doloinitic
and bituminous fly ash interground with monohydrate dolomitic were
included to represent fly ashes that have been modified to augment
the content of reactants in which a fly ash might be deficient.
117
-------
Autogenous Hardening of Fly Ashes
To test the autogenous hardening of fly ash, glass cylinders (2 inches
OD by 6 inches long) were capped at one end with nylon cloth held in
place by a rubber band. These containers were filled and placed capped
end down into a 2-1/2-gallon aquarium that was filled to a depth of
1 inch with deionized water. The aquarium was allowed to stand undis-
turbed for seven days, during which time water was absorbed into the
fly ash. At the end of seven days, the force required for a 0.025-
square-inch rod to penetrate 1 inch into each sample was measured.
Results, shown in Table 12-1, indicate that certain fly ashes will
harden when exposed to moisture.
The test was repeated using three 2-1/2-gallon aquariums. One sample
of each fly ash was placed into each of the aquariums, which are filled
to the depth of 1 inch with:
(1) Deionized water
(2) Synthetic (reconstituted) sea water
(3) Synthetic acid mine water
The aquariums were allowed to stand undisturbed for seven days. Penetra-
tion resistance was measured as before, then allowed to stand undis-
turbed for a total of 70 days, and the penetration resistance was
measured again. Results shown in Table 12-2 again indicate that fly
ashes will harden when exposed to moisture (water quality does not
appear to be important), provided the reactants to form ettringite
are present and sufficiently dispersed. Long-term data indicate that
the hardening process produces extremely high penetration resistance
and a slight expansion in the mass, as indicated by the cracking of
a number of cylinders.
Bituminous fly ash, per Se, does not contain sufficient quantities of
reactants to harden by itself. Interblending bituminous fly ash with
monohydrated dolomitic lime, while augmenting the CaO and MgO content,
does not mix the reactants sufficiently to be effective. Because of
the more intimate mixing of the reactants, intergrinding the two appears
to be beneficial. The desulfurization fly ashes appear to have good
hardening properties because of their high content of reactants re-
suiting from the mixing of limestone with the coal before firing.
American lignite showed good hardening properties because of its high
content of CaO, M 3 O, and S03, while European lignite, with less CaO,
MgO, and SO 3 , did not harden at all.
Plugging Effectiveness of Fly Ashes
The hardening test indicated that when fly ash reacts to form ettingite,
there is a slight expansion of the reaction mass. Thus the fly ash
hardening reaction would be useful in plugging effluent drainage
channels.
-------
Table 12-1 - Autogenous Hardening of Fly Ashes
(Short-term Tests, Using De-lonized Water)
Material
Chemical Analysis (%)
Penetration
Force
Required
After
7 Days (psi)
Si0 2
A1 2 0 3
Fe 2 0 3
GaO
MgO
Bituminous Fly Ash
38.5
23.6
25.7
3.7
1.1
1.2
9
Bituminous Fly Ash (90%)
Interbiended with
Monohydrate Dolomitic (10%)
34.65
21.24
23.13
8.24
4.50
1.08
46
Bituminous Fly Ash (91%)
Interground with
Monohydrate Dolomitic (9%)
35.04
21.48
23.39
7.79
4.16
1.09
1075
Desulfurizatjon Fly Ash
(Calcite Injection)
25.8
9.7
14.3
40.4
0.8
6.8
1165
Desulfurizatj.on Fly Ash
(Chalk Injection)
35.8
13.7
15.8
23.9
0.7
2.2
1256
North American Lignite
27.5
10.1
10.6
29.9
16.8
1.2
2152
European Lignite
30-35
15-20
15-20
10-15
3-5
0-3
26
-------
Material
Moisture Source
De-lonized Water
Synthetic Sea Water
Synthetic Acid Mine Water
Penetration Force (psi) Required After
7
Days
70
Days
7
Days
70
Days
7
Days
70
Days
Bituminous Fly Ash
Bituminous Fly Ash (90%)
Interblended with
Monohydrate Dolomitic (10%)
Desulfurization Fly Ash
(Limestone Injection)
Desulfurization Fly Ash
(Chalk Injection)
North American Lignite
European Lignite
0
0
0
600
1600
0
0
0
5200
> 8000
> 8000
0
0
0
0
2000
1800
0
0
400
Cylinder
Cracked
> 8000
3800
0
0
0
0
400
2200
0
0
Negligible
7200
7880
Cylinder
Cracked
0
Table 12-2 - Autogenous Hardening of Fly Ashes
(Long-term Tests, Using Various Waters)
0
-------
The horizontal dynamic plugging test described for Test 3 was used to
evaluate four fly ashes: bituminous fly ash, bituminous fly ash inter-
blended with monohydrated dolomitic lime, desulfurization fly ash, and
North American lignite fly ash. Results shown in Table 12-3 indicate
that bituminous fly ash alone does not have any plugging properties
(as would be expected since bituminous fly ash alone does not harden).
The other three fly ashes were effective, even after being in place
for 24 weeks.
Hardening of Lime/Fly Ash/Gypsum Mixtures
Since the formation of ettringite is responsible for the hardening of
fly ash, and since ettingite is composed of GaO, Al 2 0 3 , and CaSO4, the
effect of gypsum (CaSO 4 ) supplementation to lime/fly ash mixtures was
studied. The penetration test described above was used to determine
the hardening of mixtures of various ratios of lime/fly ash/gypsum.
Results, shown in Table 12-4, indicate that the addition of gypsum
is beneficial, as evidenced by the cracking of 19 of the 48 tubes
after 8 weeks, which was caused by the expansive forces of the
reaction.
The samples with no addition of gypsum did not crack, indicating that
the degree of reactivity is lower when no gypsum is included.
Stabilization of Acid Neutralization Sludges
The possibility of using fly ash to stabilize (harden) sludges resulting
from the neutralization of acid mine waters was investigated. Sludges
were prepared by treating a synthetic waste pickle liquor (150,000
mg/i SO 3 - and 10,000 mg/I Fe ) with different limes to yield sludges
having pH of either 7.2 or 12. After settling overnight, the decantate
in each test was siphoned off and the sludge was mixed with bituminous
fly ash (at varying ratios of sludge to fly ash). Each mixture was
then water-cured, and the development of penetration resistance noted
after 6 weeks.
Results shown in Table 12-5 indicate that bituminous fly ash can be
used to solidify and harden sludges resulting from the neutralization
of acid mine water. Note that the sludge resulting from the use of
high-calcium hydrated lime to neutralize the acid mine water was not
hardened by the fly ash, because of the absence of MgO. Although the
formula for ettringite does not indicate the pressence of MgO, the data
indicate that magnesium is beneficial, perhaps partially substituting
for some of the CaO in the structure.
SUMMARY
It appears that the use of the fly ash in connection with the under-
ground precipitation concept for abatement of pollution from acid mine
121
-------
Table 12-3 - Plugging Effectiveness of Fly Ashes
I’ )
*Ch ne 1
**f4O drops (effluent rate less than evaporation rate)
Material
Flow (drops/see) After
30 mm
18 hr
2 days
3 days
1 wk
2 wk
5 wk
15 wk
24 wk
Bituminous Fly Ash
Bituminous Fly Ash (90%)
Interb].ended with
Monohydrate Dolomitic (10%)
Desulfurization Fly Ash
(Calcite Injection)
North American Lignite
1.0
2.0
1.0
0.07
0.4
0.7
0.6
0.06
0,4
0.5
3.3
0.04
0.3
0.4
1.7
0.035
20
0.3
67
**
4.0
0.3
93
13
0.2
1.0
*
**
1.0
**
*
0.5
**
-------
( 1
Table 12-4 - Hardening of Lime/Fly Ash/Gypsum Mixtures
(Using Various Waters)
Blend Weight Ratios
Penetration Force Required After 8 Weeks (psi)
High-
Calcium
Hydrated
Lime
Bituminous
Fly
Ash
Ground
Gypsum
Interground Samples
Interbiended Samples
Deionized
Water
Synthetic
Sea Water
Synthetic
Acid Mine
Water
Deionized
Water
Synthetic
Sea Water
Synthetic
Acid Mine
Water
1
1
1
1
1
1
1
1
3
12
3
6
3
12
3
12
0
0
1/2
1/2
1
1
2
2
2480
840
2000*
> 8000
3200*
3200
1600*
1600*
6400
1000
2800*
3360*
1400*
1400
1000*
1600
960
1600
2000*
1520*
2200*
1360
1000*
3200
0
Negligible
3800
3200
2000*
No Test
3000*
1800*
1200
1600
7600
3800
1600*
No Test
2000*
800
400
600
> 8000
6400
1600*
No Test
600*
1600
*Cylinder Cracked
-------
Table 12-5 - Stabilization of Acid Neutralization Sludges
Formed from Acid Mine Water
Neutralizing
Agent
Used to
Form Sludge
pH
of
Sludge
Wt. of
Bituminous
Fly Ash
Added to
100 Grams of
Sludge
(g)
Penetration
Resistance
After
6 weeks
(psi)
Monohydrate
Dolomite
7.2
0
5
10
20
30
50
0
0
0
0
560
960
12.0
0
5
10
20
30
50
0
0
1000
2200
4400
2400
High-
Calcium
Hydrate
7.2
0
5
10
20
30
50
0
0
0
0
0
560
12.0
0
5
10
20
30
50
0
0
0
0
0
0
124
-------
drainage is desirable, and opens many possibilities. However, its
usefulness at a specific location will depend on a number of factors.
The usefulness of fly ash is determined by the reaction that produces
the ettringite structure, and the accompanying expansive forces.
Calcium, aluminum, and sulfate ions are necessary for this reaction.
Magnesium is beneficial; apparently it replaces some of the calcium
in the structure. Tests with acid mine water indicate that ferric
iron can replace some of the aluminum in the resulting ettringite
structure. All of the constituents are either present or readily
available when acid mine water is treated with either the proper, or
properly augmented, fly ash.
It does not appear to be desirable to include fly ash in the Phase II
field demonstration at the Driscoll No. 4 Mine, at least initially,
for the following reasons:
(I) The most readily available fly ash for this demonstration
mine site is a bituminous fly ash from the Seward Station,
operated by the Pennsylvania Electric Company, which would
require calcium and magnesium augmentation. This would
mean that hydrated dolomitic lime would be required for
best results, and only high-calcium hydrated lime is
available within a reasonable distance from the mine site.
(Some magnesium ions are present in the mine water, but the
concentration appears to be too low.)
(2) To obtain best results, the fly ash and lime would have to
be interground, necessitating a mill at the site.
(3) Augmentation of the CaSO 4 content appears to be desirable,
if not necessary, to increase the expansion forces during
the reaction.
Funds permitting, fly ash could be used later in the program to plug
one of the drainage effluent points that may develop as the water
level rises in the mine after the successful plugging of the lower
effluent point.
125
-------
SELECTED WATER Rep rt 1, Accession No.
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
4. Title - 5. Repott Date Jul i9 3
ABATEMENT OP MINE DRAINAIZ POLLUTION BY ‘6
WIDERGROUND PRECIPITATION
& PerForming OxESnintJon’
7. Author(s) Repofl to.
10. Project No.
Mr. C. K. Stodd.ard 14010 EJP (#CR84)
9. Organization
Pars sJurden ftion 11, Contract/Grant No.
The Ralph N. Parsons Company, under contract to .
Pennsylvania Dept. of Environmental Resources 13. TypecfRepo,’t and
Period Covered
12. Spon’ toring Organization .
IS. Supplementary Notes
Environmenta l Protection Agency Report
Nttber EPA—670/2—73—092 1 p October 1973.
16. Abstract
- Laboratory- tests with synthetic acid mine water show the sealing effect
of. the gelatinous precipitate that forms when hydrated lime or powdered lime-
stone is added in a simulated mine entry closed by a porous barrier.
Field tests were conducted in a recently abandoned coal mine. Hydrated
lime end limestone slurries were pumped into the mine water behind rubble
barriers through 2-inch steel pipes to test the laboratory findings. The out-
flow was observed at vein attached to the ends of two, 12-inch diameter drain
pipes. The results indicated that only temporary sealing of the outflow was
achieved and that neutralization took place when the interior water flow
conditions were favorable.
Placement of the injection eutlets, dispersion of the lime slurry, volume
of water flowing, and direction of flow in the mine interior to other outlets
are important controlling variables that greatly affect the efficiency of the
sealing and neutralization of the outflowing acid mine water.
A7a. Descriptors
- - Acid Mine Water 7 Mine Water Neutralizationt Mine Water Out-Plow Control,
Mine Water Pollution.
17b. identifiers Coal Mines, Stream Pollution - Mining, Acid Mine Waters 1
Pennsylvania, Underground Mine
17c. COWRR Field & Group - 050
18. Availability
,
19. Sr’izrity C 1 asL 21. Ne. f Send To:
(Report) Pages
0 . WATER RESOURCES SCIENTIFIC INFORMATION CENTER
20. .>ecnxnyi.nass. 22, r i - iCe u, , DEPARTMENT OF THE INTERIOR
(Proge) WASHINGTON, 0. C. 20240
Abstractor Dr. C. K. Stoddard J i j Parsons-Jurden Div. The Ralph M. Parsons C
WRSIC 102 NEV. JUNE 1071)
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