WATER POLLUTION CONTROL RESEARCH SERIES • 14010 DLI 02/71
Silicate Treatment
for
Acid Mine Drainage Prevention
ENVIRONMENTAL PROTECTION AGENCY • WATER QUALITY OFFICE
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WATER POLLUTION CONTROL RESEARCH SERIES
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20242.
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Silicate Treatment For Acid Mine Drainage Prevention
Silicate and Alumina/Silica Gel Treatment of Coal Refuse
for the Prevention of Acid Mine Drainage
by
Tyco Laboratories, Inc.
Bear Hill
Waltham, Massachusetts 02154
for the
ENVIRONMENTS PROTECTION AGENCY
WATER QUALITY OFFICE
Project No.: 14010DLI
Contract No.: 14-12-560
February. 1971
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price $1
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EPA Review Notice
This report has been reviewed by the Environmental
Protection Agency and approved for publication.
Approval does not signify that the contents neces-
sarily reflect the views and policies of the Environ
mental Protection Agency, nor does mention of trade
names or commercial products constitute endorsement
or recommendation for use.
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ABSTRACT
A treatment technique has been demonstrated on a laboratory scale which
inhibits or prevents the generation of acid mine water from waste coal refuse.
Three variations of the general method were considered:
1. Neutralization of the water-accessible refuse with a dilute
solution of sodium silicate (waterglass)
2. Development of a continuous gel on the refuse surface structure
which sealed off the entire pile from natural runoff waters
3. Development within the pile structure of a continuous silica/
aluminia gel to eliminate percolation through the refuse and
minimize the effect of natural erosion of the gel structure.
Comparison of the effluent water with an untreated pile shows that the neutral-
ized pile was effective for a minimum of 120 in. of equivalent rainfall in inhibit-
ing AMD generation. The surface gel was effective for a longer period of time.
The most effective treatment utilized a mixed alumina/silica gel formed within
the pile at depths up to 6 in. This method was effective for more than 500 in.
of equivalent rainfall, the duration of the test, and appeared to be exceptionally
stable at that time.
The weathering resistance of the treatment methods was evaluated by heat-
ing the gel treated refuse in the laboratory and exposing it to rain, snow,
and freeze-thaw cycles outdoors. Extensive washings of the weathered test
materials established the fact that the treatments were effective for at least
120 in. of equivalent rainfall (the duration of the test) in preventing AMD
generation.
This report was submitted in fulfillment of Contract No. 14-12-560 between
the Federal Water Quality Administration and Tyco Laboratories, Inc.
KEY WORDS
Silica gel Accelerated testing
Acid mine drainage Weatherability
Coal refuse Neutralization
Alumina/silica gel Waterglass
Water pollution Gel forming methods
111
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Table of Contents
Section No.
ABSTRACT
1 CONCLUSIONS
2 RECOMMENDATIONS FOR FUTURE WORK ....
3 INTRODUCTION
4 THE TYCO TREATMENT APPROACH
5 DETAILS OF REFUSE PILE TREATMENTS
6 RESULTS AND DISCUSSION
7 GEL WEATHERABILITY TESTS
8 TREATMENT OF ACID MINE DRAINAGE
9 OTHER EXPERIMENTS
10 MASS BALANCE
11 REFERENCES
12 PUBLICATIONS
Appendix No.
I ANALYTICAL METHODS
II COMPLETE ANALYSIS OF PILE EFFLUENTS . . .
Ill AMD GENERATION MECHANISM
Page No.
.... ii
. . . . 1
. . . . 3
. . . . 5
. . . . 7
. . . . 11
. . . . 15
.... 27
.... 33
. . . . 53
. . . . 57
.... 69
.... 71
Page No.
.... 73
.... 75
.... 93
V
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List of Illustrations
Figure No. Page No.
1. Gel Times at 25.0 °C of 3.22 Ratio Sodium
Silicate as a Function of pH 13
2. Iron Content of Wash Effluent From Four
Tests Piles Compared to Control Pile 16
3. pH of Wash Effluent From Pile B (Neutralized
Pile) Compared to Pile A (Control) 17
4. pH of Wash Effluent From Pile C (Silica Gel-
Surface Gel) Compared to Pile A (Control) 18
5. pH of Wash Effluent From Pile D (Alumina/
Silica Gel - Surface Gel) Compared to Pile
A (Control) 19
6. pH of Wash Effluent From Pile E (Alumina/
Silica Gel-Gelled in Depth) Compared to
Pile A (Control) 20
7. Rate of Iron Removal From Piles 22
8. Rate of Sulfur Removal From Piles 23
9. Determination of the Minimum Amount of
Waterglass Needed to Complex Ferric Iron
in Ferric Sulfate Solution 37
10. Determination of the Minimum Amount of
Waterglass Needed to Complex Ferrous
Iron in Ferrous Sulfate Solution 39
11. Oxidation of Ferrous to Ferric in the
Presence of Silicate 41
12. Amount of Sodium Aluminate Needed to
Precipitate Ferrous Iron 43
13. Amount of Sodium Aluminate Needed to
Precipitate Ferric Iron 44
vn
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List of Illustrations (Cont.)
Figure No. Page No.
14. Determination of Amount of Lime Needed
to Precipitate Ferrous Iron 46
15. Determination of Amount of Lime Needed
to Precipitate Ferric Iron 47
16. Comparison of Settling Rates Using Sodium
Aluminate and Lime to Precipitate Ferrous
Iron o . . 50
17. Comparison of Settling Rates Using Sodium
Aluminate and Lime to Precipitate Ferric
Iron 51
viii
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List of Tables
Table No. Page No.
I. Analysis of Barnes and Tucker Bituminous
Coal Refuse 9
II. Wash Analysis of Heated Pile 28
III. Wash Analysis of Heated Pile 29
IV. Analysis of Collected Water From Outdoor
Test 31
V. Analysis of Effluent Water From Washing
Refuse Used in Outdoor Test 32
VI. Treatment of Ferric Sulfate With Water-
glass and Sodium Aluminate 34
VII. Treatment of Ferrous Sulfate With Water-
glass and Sodium Aluminate 38
VIII. Oxidation of Ferrous to Ferric in the
Presence of Silicate 40
IX. Precipitation of Ferrous Iron by Sodium
Aluminate 42
X. Precipitation of Ferrous and Ferric Iron
With Lime 45
XI. Iron Solution Treatments 48
XII. Settling Rates 49
XIII. Solids Content of Iron Precipitates 52
XIV. Optimization Studies for Alumina/
Silica Gel Composition Showing Gel
Time (sec) and Gel Consistency 53
XV. Analysis of Supernatant AMD in Gel
Stability Tests 54
IX
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List of Tables (Cont.)
Table No. Page No.
XVI. Equilibrium Between Fe3+, Fe2 + , OH",
so42-
XVII. Log Equilibrium Constants for Fe3+,
+, OH", SO42~ Species ................. 58
XVIII. Computer Printout ..................... 60
XIX. Sample Output ....................... 63
XX. Comparison of Parameters for Standard
Samples ........................... 65
XXI. Relative Amounts of Soluble Iron Species ......... 66
XXII. Typical AMD Samples ................... 67
XXIII. AMD Samples Corrected for Sulfate ............ 68
XXIV. Sulfate Analysis, ppm ................... 74
XXV. Sulfate Analysis (PPM) With and Without
Preoxidation ........................ 74
XXVI. Pile: Control ........................ 75
XXVII. Pile B: Neutralized Pile ................... 80
XXVIII. Pile C: Silica Gel (Surface Treatment) .......... 82
XXIX. Pile D: Alumina/Silica Gel (Surface
Treatment) ......................... 86
XXX. Pile E: Alumina/Silica Gel (In -Depth
Treatment) ......................... 90
XXXI. Rapid Washing of Coal Refuse ............... 94
x
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SECTION 1
CONCLUSIONS
The following conclusions are based on the experimental work accomplished
during this program:
1. Neutralization of coal mine refuse by treatment with waterglass
(sodium silicate) is an effective technique for preventing or minimizing acid
mine drainage (AMD) generation for a period in excess of 120 in. of equiva-
lent rainfall.
2. Sealing the coal mine refuse pile surface to water percolation
with silicate-based gels is effective in preventing or minimizing AMD
generation over a long period, perhaps in excess of 400 in. of equivalent
rainfall.
3. Alumina/silica gels are more effective in prolonged sealing of
the refuse structure than are the silica gels because of the lower water
solubility of the alumina/silica gel structures.
4. Surface gels are not stable to extremes in temperature. Both
heating and freezing cause coagulation of the gel with the resultant loss in
continuity. Such broken gels no longer seal the refuse structure, but the
residual effects of the treatment minimize the generation of AMD over pro-
longed periods of time, similar to the effect of neutralizing the material
with silicate.
5. In depth gelation of refuse piles using alumina/silica gels should
be effective in prolonged prevention or retardation of AMD generation regard-
less of the environmental temperature variations.
6. The treatment of AMD water with sodium silicate and sodium alu-
minate in a holding pond is no more effective than the conventional applica-
tion of lime. There is no advantage in settling rates or precipitate volume.
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SECTION 2
RECOMMENDATIONS FOR FUTURE WORK
The viability of using sodium silicate gels with and without sodium aluminate
to inhibit or prevent AMD generation from waste coal refuse has been success1
fully demonstrated in the laboratory. It is therefore recommended that the
following work be continued to demonstrate the effectiveness (including cost
effectiveness) of the treatment procedure:
1. Laboratory optimization of the treatment procedure for
cost, depth of gelation control, quantity of chemicals, and
demonstration of means of field application
2. Selection of several conditions for field evaulation under
carefully chosen conditions to assess and compare percolation
and run-off, and duration of effectiveness
3. Field evaluation over a 2-yr period, followed by deter-
mination of effectiveness of overplanting
4. Comparison of field results with laboratory data to
provide a correlation of results for future utilization of
method.
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SECTION 3
INTRODUCTION
THE ACID DRAINAGE PROBLEM
The discharge of acid mine drainage (AMD) into streams of Appalachia may
qualify as the single most significant pollution problem present today by vir-
tue of the severity of damage to the streams and the effort that will be re-
quired to overcome this problem.1 In Pennsylvania alone, the quantity of
AMD produced is approximately 1.5 x 109 gal/day.1 The magnitude of con-
tinuing treatment cost to eliminate AMD contamination from Pennsylvania's
stream system has been estimated to be in excess of one hundred million
dollars per year after an outlay of several hundred million dollars for treat-
ment facilities.1
All methods of coal mining, whether surface or underground, contribute to
this undesirable phenomenon. The refuse materials from coal mines and
coal cleaning are major sources of AMD, since the breaking and crushing
operations necessary for mining and coal separation provide a tremendous
increase in particulate surface area available for oxidation. In the anthra-
cite region of Pennsylvania alone, there are 270 culm and silt banks esti-
mated to contain seven-hundred and fifty million tons of refuse.2 Approxi-
mately four times this much material exists in the bituminous regions of the
state.2
Extensive work is underway to develop and demonstrate methods for either
preventing the formation of AMD or treating it before its seepage into streams.
Prevention is far to be preferred, because it would hopefully offer a final
solution to the problem rather than require a continuing and perhaps grow-
ing treatment cost. Methods considered for prevention include diversion of
the surface drainage, elimination of air, passivation of the rock surfaces,
deactivation of bacteria associated with AMD formation, cultivation of sul-
fate-reducing bacteria (within the rock strata) to reverse the action of the
sulfate-forming bacteria, and modification of pH ( within the rock strata)
above that conducive to AMD formation.
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Under the subject contract, Tyco Laboratories has been engaged in develop-
ing a method which will prevent the generation of AMD by direct treatment
of the coal mine refuse. The basis of the method, which has been shown to
be feasible on a laboratory scale, is to isolate the AMD generating sites from
drain water via treatment of the coal refuse with a solution of sodium silicate
or sodium silicate plus sodium aluminate.
BACKGROUND CHEMISTRY: FORMATION OF ACID MINE WATER
Waste coal refuse containing significant amounts of pyrite will, in the pre-
sence of air and water, generate a dilute solution of iron sulfate and sulfuric
acid. Secondary reactions between these ingredients and the local minerals
will add concentrations of aluminum, manganese, calcium, magnesium, and
sodium to the effluent water.
The overall stoichiometry for the acid generation process is:
4 FeS2 + 15 O2 + 14 H2O -* 4 Fe (OH)3 + 8 H2SO4 ( 1)
The mechanism of this reaction is under study; there is some evidence that
microorganisms also contribute to pyrite oxidation.3>4} 5
This reaction proceeds in stages, the first involving the formation of soluble
ferrous sulfate:
2 FeS2 +702+2H2O-^2 FeS04 + 2 H2 SO4 ( 2^
Air will then slowly oxidize ferrous iron to ferric:
4 FeSO4 +2 H2SO4 + O2 -> 2 Fe2(SO4)3 +2 H2O ( 3)
which, as the acid becomes more dilute and/or the soluble iron content in-
creases, will hydrolyze:
Fe2( S04) 3 -I- 6 H2O - 2 Fe (OH) 3 + 3 H2SO4 ( 4)
The quantity of these pollutants in acid mine water is variable, and depends
on the particular pyrite-coal source and the history of the water before
reaching the analyst. The worst cases have a pH less than 2.5 and soluble
iron contents up to 10, 000 ppm.6
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SECTION 4
THE TYCO TREATMENT APPROACH
MECHANISMS
To prevent the generation of acid mine water, it is necessary to interrupt
reaction ( 1) at some point. Tyco's approach has been to prevent access of
the pyrite to water via the formation of a silica gel over the potentially ac-
tive acid generation sites. This treatment is based on the following reaction:
Na2SiO3 +H2SO4 ^(SiO2) +Na2SO4+H2O (5)
When a solution of sodium silicate ( waterglass) is neutralized below pH
10.7, silicic acid is first formed;
SiO32 + 2 H+ - H2SiO3 ( 6)
Initially, silicic acid and metasilicic acid ( Eq. 6) are monomeric. On aging,
a three-dimensional structure of Si-O-Si bonds is formed and the solution
sets into a gel. The rates at which these reactions take place depend, in a
complex fashion, on pH, temperature, and sodium silicate concentration.
A second set of reactions can also be involved, i.e., the precipitation of iron
silicate. According to the literature,7 most transition metal silicates, in-
cluding both ferrous and ferric silicate, are extremely insoluble, forming
the basic chemical structure of most rock formations. A solution of a solu-
ble silicate, in which the anions exist as monomers, dimers, and possibly
trimers, reacts rapidly to form insoluble precipitates. The extent to which
this takes plate is a function of pH and the oxidation state of the iron. Ferrous
silicate is apparently more insoluble than ferric silicate (see data in Section 5)
At high pH, e.g., ~ 10, soluble complex ions are also formed. However, under
the conditions of AMD generation, i.e., at low pH, the addition of sodium
silicate can result in the formation of some insoluble iron silicate mixed in
with the gel developed according to reaction (5).
Thus, there are three mechanisms by which treatment of coal mine refuse
will silicate can inhibit the generation of acid mine water:
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1. Blocking AMD generation with a water impermeable silica
gel
2. Precipitation of iron silicate which (a) scavenges soluble iron
and (b) also coats the pyrite particles
3. Neutralization of AMD acid, as per reaction (5).
Our experiments have indicated that all three mechanisms are operative.
When a surface gel is formed, most water is diverted from the pile. On
disrupting the gel, the effluent water composition becomes similar to that
from the neutralized pile. Insoluble iron silicate is observed on removing
samples of refuse from inside the pile.
EXPERIMENTAL METHODS
Treatment techniques were evaulated by testing piles of actual coal mine
refuse under simulated natural conditions. The test piles each consisted
of 200 kg of representative refuse, formed to a cone 3 ft in base diameter
and 18 in. high. A measured artificial rainfall .'(generally 100 liters/day which
is about 6 in. of water) was maintained on essentially an 8-hr per day, 5-day
work schedule, with percolated and runoff water samples being collected on
a daily basis. The wash water samples were analyzed for total iron, ferrous
iron, sulfate, pH, calcium carbonate acidity, and soluble silica (see
Appendix I).
The test piles were placed in plastic basins on a tilted table to allow easy
collection of the runoff. An overhead sprinkling system was constructed to
simulate intermittent rainfall. The plastic basins had two sample points
from which the runoff and percolated wash water were collected: one col-
lecting from a 14-in.-diameter center area and the other from the outer an-
ulus. The data reported are for composite samples of the two collection
points.
The specific refuse material used for evaluation was a washed waste coal
refuse originating from the lower Kittanning Seam. The analysis is given
in Table I.
8 -
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Table I. Analysis of Barnes and Tucker Bituminous Coal Refuse
Size
Passed Retained
% Pyritic Sulfur % Fe2O3
Wt % (Dry Basis) ( Ignited Basis) % Sulfur* % Ash* % Moisture*
CD
1/2 in.
3/8 in.
1/4 in.
8 mesh
30 mesh
1/2 in.
3/8 in.
1/4 in.
8 mesh
30 mesh
2.5
10.5
25.3
46.2
13.8
1.7
4.14
3.12
1.52
2.70
5.24
3.32
14.53
11.45
7.73
10.31
17.47
17.75
5.41
3.62
1.89
3.30
6.53
4.63
2.82
54.11
58.01
53.45
55.25
44.14
0.98
1.01
1.08
1.14
1.30
1.80
*As received.
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SECTION 5
DETAILS OF REFUSE PILE TREATMENTS
SILICATE MATERIAL
The sodium silicate solution used in the laboratory experiments to deter-
mine the lag time for gelation was produced by Philadelphia Quartz (type N)*
and has the following composition:
%SiO2:28.7
% Na2O:8.9
% H2O: 62.4
SiO2/Na2O:3.22
Density: 41°Be (at 68 °F) , 1.39 g/ml
NEUTRALIZED PILE ( PILE B)
A pile of coal mine refuse was neutralized by treatment with 31 of a water-
glass solution containing 4% SiO2. Neutralization was defined as the condi-
tion when the effluent solution of the pile during the waterglass treatment
had the same pH as the fresh silicate solution. Examination of the pile
showed that the particles of coal refuse were coated with a thin layer of
some gel-like material. This coating did not block the flow of water through
the pile, but did tend to prevent contact of the water with the surface of the
coal.
SILICA GEL: SURFACE TREATMENT (PILE Q
It was intended that one pile of coal mine refuse should have a thin layer of
silica gel to form a sealant layer. To accomplish this, it was necessary to
determine the conditions under which waterglass would gel. It was known
that acidifying the sodium silicate solution would cause gelation, and it was
felt that it might be possible to allow the acid in the refuse pile to act as the
acidifying material.
First, some tests were made to determine the gelling properties of the type N
silicate. Reagent grade sulfuric acid was used to lower the pH. Distilled
water was used for diluting the commercial silicate and making up all
solutions.
*the use of this particular commercial product does not constitute
endorsement or recommendation by the Federal Water Quality Administration.
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Gel times were determined by adding a dilute solution of H2bO4 to sodium
silicate solutions (in which the concentration of SiO2 ranged from 1 to 28.0%),
mixing well, and allowing the mixture to stand in 100 -ml beakers kept at
25 °C until gelling.
The data obtained from these experiments are as follows:
Concentration: 1% SiO2
pH 9.5 8.0 7.0 4.0
Gel time, sec 5 x 105 2100 2580 4 x 105
Concentration: 2% SiC-2
pH 8.5 6.5 6.0 2.5
Gel time, sec 1800 370 415 5 x 105
Concentration: 3% SiO2
pH 9.0 8.5 7.5 6.5
Gel time, sec 320 170 90 250
Concentration: 4% SiC-2
pH 9.0 7.5 6.5 1.0
Gel time, sec 90 20 100 8 days
Several high concentrations of SiO2 solutions (10 to 28.0% SiO2) were tested
for gel time at various pHs. Gel was formed instantly.
The data obtained from these experiments agree with the data published by
Philadelphia Quartz Company, as presented graphically in Fig. 1.
Several experiments on small pyritic piles were set up to determine which
waterglass should be used in treating the larger piles. In the first experi-
ment, 250 g of the fresh, high sulfur coal refuse described above were
slowly washed with 1000 ml distilled water. The washing was collected
and analyzed. The analysis showed:
pH:3.3
Acidity: 540 ppm as CaCOa
Ferrous iron: 429 ppm
Total iron: 1177 ppm
SO4:475ppm
This refuse was neutralized, without gel formation, with 100 ml of water-
glass solution continaing 3% SiC-2 at pH 11.3.
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UJ
Fig. 1. Gel times at 25.0 °C of 3.22 ratio sodium silicate as a function of pH
The pile was slowly washed with 250 ml of distilled water and the effluent
collected and analyzed. This analysis showed:
pH:5.7
Acidity: 200 ppm as CaCOs
Ferrous iron: 13.6 ppm
Total iron: 181.2 ppm
SO4: 247 ppm
In the second experiment, gel was formed on the top of and partially inside
a 500-g pile of fresh refuse by treating with waterglass solution containing
5% SiO2 at pH 9.5. The treated pile was left for 1 hr to harden the gel and
was then washed slowly with measured amounts of distilled water. The
effluent pH was 4.0 after washing with 200 ml distilled water. Acidity was
100 ppm as CaCO3.
To determine the reason that the AMD continued to be produced from this
treated pile, it was cut into two halves. When examined, it was noted that
gel was formed irregularly and that some pieces of refuse were not coated
with gel. Water permeability of the pile was unimpaired.
Based on these experiments, it was decided to form the gel on Pile C using
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a silicate solution containing 4% SiO2 and to acidify the solution to pH 9.5
before application. The actual treatment of Pile C was accomplished by
passing the solution through the pile several times until gelation occurred.
The gel formed was somewhat nonuniform, but the treatment was continued
until the entire pile was covered with gel. In order to increase the resi-
dence time of the silicate solution in the pile, some of the gel was formed
by thickening the silicate solution with Cab-O-Sil, a very fine silica powder.
This increase in residence time greatly simplified the formation of a con-
tinuous gel across the pile. A total of approximately 4 i of concentrated
waterglass was used.
ALUMINA/SILICA GEL: SURFACE TREATMENT ( PILE D)
The difficulty in forming the silica gel on the pile prompted a search for
better gelation methods. In addition to the thickening procedure described
it was found that a strong, continuous gel could be formed rapidly by
mixing the sodium silicate with sodium aluminate. In fact, this method
worked too well and the gel formed before the solution could be applied to
the pile. This situation was remedied by first treating a pile with 1 i of
sodium silicate diluted to a solution containing 4% SiO2 and then immediately
treating the pile with 10 4 of 5% sodium aluminate. A strong gel was formed,
primarily on the surface of the pile; very little of the material ran through
the pile.
ALUMINA/SILICA GEL: IN-DEPTH TREATMENT ( PILE E)
Gel was formed by slowly spraying the pile with sodium silicate solution
(SiO2/Na2O: 3.22) containing 4% SiO2 in order to let the solution go deeply
through the pile. This was followed by spraying with sodium aluminate so-
lution having a concentration of 5%. This procedure was repeated until the
gel formed a layer inside the pile and covered the surface. The difference
between this treatment and that of Pile D was that the silicate solution was
allowed to penetrate into the pile before the aluminate was added. Thus,
when the aluminate was sprayed on, it could not form a sealant layer of
gel on the surface, but had to penetrate into the pile to form a gel. Succes-
sive treatment finally formed a blocking layer which caused a fairly uniform
layer of gel to be built up.
The pile was immediately disturbed and it was found that the gel indeed had
formed in the interior, but did not fill all the spaces between the rock part-
icles. This caused the washing water to pass very slowly through the pile (as
compared to the relatively rapid flow of water through the untreated pile).
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SECTION 6
RESULTS AND DISCUSSION
PILE TREATMENTS
Five test piles were set up during the course of the experimentation and
were evaluated as described above. The treatments used are summarized
as follows (details of the treatment procedures are given in Section 4):
Pile Treatment
A Control — No treatment
B Neutralized pile — a minimum amount of sodium silicate solu
tion was permeated throughout the pile to neutralize acid via
reaction (5), while not forming a continuous gel
C Silica gelled pile — sufficient silicate was used to form a
coherent gel on the surface of the pile
D Alumina/silica gelled pile — this treatment was similar to
(C), except that sodium aluminate was added to form a
more insoluble gel
E In-depth alumina/silica gelled pile — a mixed gel was
formed beneath the surface of the pile to obtain pro-
tection from errosion and mechanical disruption of the
gel
TEST RESULTS
The pH and the dissolved iron content of the samples are shown in Figs. 2
through 6, the complete analysis of all the piles is given in Appendix II,
Tables XXVI through XXX. The wash volumes used were converted to
inches of water so that the results could be examined in terms of rainfall.
Pennsylvania, for example, receives an average of 40 in. of rain per year.
One comment on the iron analysis is pertinent. Most of the analyses are
for samples passed through conventional laboratory filter paper. Late in
the program, it was demonstrated that this procedure was inadequate for
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6
a,
c
cu
4->
§
u
c
o
0)
i—i
O
CO
CO
control
neutralized
silica gel
j^. alumina/silica gel Surface treatment)
E; alumina/silica gel fn-depth treatment)
A:
B:
C;
D
1000
500
100
50
10
vWWvWV
I
I
1
1
0
40
80
120
400
440
160 200 240 280 320 360
Cumulative Effluent, inches of water
Fig. 2. Iron content of wash effluent from four test piles compared to control
pile
480
-------
o-o« Pile B
0 40 80 120 160 200 240 280 320
Cumulative Effluent, inches of water
360
400
440
Fig. 3. pH of wash effluent from Pile B (neutralized pile)
compared to Pile A (control)
-------
CO
1
PH
40
Pile C
80
120
160
200
240
280
320
360
400
440
48(
Cumulative Effluent, inches of water
Fig. 4o pH of wash effluent from Pile C (silica gel-surface gel)
compared to Pile A (control)
-------
I
I—'
CO
5 —
4 _
3 —
0
40
80
160 200 240 280 320
Cumulative Effluent, inches of water
360
400
440
480
Fig. 5. pH of wash effluent from Pile D (alumina/silica gel - surface gel)
compared to Pile A (control)
-------
•ooo-0-o.o.oo.cbo.
Pile E
to
o
1
1
1
1
0 40 80 120 160 200 240 280 320
Cumulative Effluent, inches of water
360
400
440
481'
Fig. 6. pH of wash effluent from Pile E (alumina/silica gel-gelled in depth)
compared to Pile A (control)
-------
removing finely divided iron hydroxide. Calculations of the total soluble,
chemically complexed ferric iron as a function of pH indicate negligible
amounts (< 1 ppm) at and above pH 6. Experimental results confirm this
conclusion. Therefore, the total dissolved iron values presented in
Appendix II include suspended solid iron hydroxide for those samples with
high pH. This applies to Piles B and C for the first 80 in. of equivalent rain-
fall; Pile D: 240 in.; Pile E; over 280 in.
DISCUSSION
Examination of the wash effluent analysis data for the control pile (A) shows
that the effluent composition was comparable to that found in actual field
studies.8 The pH was about 2.0 and the iron content was 1000 to 5000 ppm
(see Table XXVI in Apendix II).
The neutralization treatment (B) is effective for about 120 in. of equivalent
rainfall in causing a reduction in the acid mine drainage produced by the wash-
ing of coal mine refuse. After this period, the treatment's effectiveness is
reduced, but still yields acid flows at a lower level than untreated refuse.
This reduction in effectiveness is undoubtedly associated with the washing
out of the silica from the pile (see Table XXVII in Appendix II) and as the
silicate is washed out, the refuse is again exposed to the wash water.
However, even after much of the silicate is washed out, the AMD production
never approaches the level of the untreated pile (A). This is shown in Figs.
7 and 8 which compare the extent of iron and sulfur removal from the five
different piles over several years of equivalent rainfall. (Note logarithmic
scales on ordinates of both graphs.)
For treatment C (surface gelled with silica), as with the neutralized pile,
the pH is increased and iron content is depressed. The silica is also slowly
being washed out of this pile, although the rate is somewhat lower, i.e., about
40 ppm for Pile C versus 60 ppm for Pile B. It would be anticipated that the
gel will eventually lose its integrity and allow the production of AMD.
However, for the first 80 in. of equivalent rainfall, the appearance of the
surface of the gel did not change appreciably and the wash water continued
to run off the surface of the pile, not penetrating to the interior. The iron
content of the effluent water was slowly increasing, but still remained an
order of magnitude lower than the untreated pile.
- 21 -
-------
100-
CD
>
O
6
0)
G
o
G
CD
O
^
CD
CX,
0 2
8 10 12 14 16 18
Equivalent Years Rainfall
Fig. 7. Rate of iron removal from piles [A - control pile, B - neutralized
pile, C - silica gel (surface treatment), D - alumina/silica gel
(surface treatment), and E - alumina/silica gel (in-depth treat-
ment) ]
- 22 -
-------
100
T3
CD
CD
Pi
a
c
CD
O
!H
CD
10
Pile D
Pile B
0
6 8 10 12 14 16 18
Equivalent Years Rainfall
Fig. 8. Rate of sulfur removal from piles [ A control pile, B neutralized
pile, C silica gel ( surface treatment), D - alumina/silica gel
( surface treatment), and E aluminia/silica gel (in-depth treatment) ]
- 23 -
-------
After 80 in. of equivalent rainfall, the pile was disturbed. Several cracks
were made in the suface of the gel and the washings were continued. The
pile was then violently disturbed by turning the surface over. Examination
of the interior of the pile showed very little internal gel, none of it con-
tinuous. Washings were continued.
The detailed data ( Table XXVIII in Appendix II) show that breaking the gel on
the surface of the pile allowed water to enter the interior, resulting in the for-
mation of AMD. Comparison with Pile A, however, reveals that although the
pH drops and the iron and sulfate increase sharply, all values are lower than
the untreated pile.
Pile D was given a thin sealant layer of alumina/silica gel and was washed
with water on a daily basis. It is evident that not only are the iron and sul-
fur compositions at reduced, stable levels, but the silica in the effluent is
much lower than in the silica gel protected pile as expected. This result
indicates that thepile will retain its stability for a longer period of time.
The continuous dropping of the wash water on certain spots on the surface of
the pile caused local errosion faults in the continuous gel structure which
were large enough to permit water to enter the interior of the pile and start
to create AMD. These faults in the gel structure were due to the fact that
the washing was not completely random, but tended to drop selectively in
certain spots (this would not be the case under ordinary rainfall conditions).
Since these faults were due to an experimental artifact and were not representa-
tive of the system in general, it was decided to seal the holes with gel and con-
tinue the test, making an effort to "rain" on the pile in a more random manner.
The pile was therefore repaired, and it is obvious from the analysis data that
the protection against AMD formation was resumed immediately.
The best results were obtained from the pile treated in depth with the alumina/
silica gel. The decreased solubility of the gel enhanced the long term stability
of the gel, while the deeper layer of gel increased its resistance to erosion
and cracking. This fact can be confirmed upon considering that Pile E had
been violently distrubed on day 1 of the treatment period, yet the wash efflu-
ent showed the lowest concentrations of pollutants. Clearly, this is a very
promising treatment technique.
In summary, examination of the sulfur and iron removal rates for the various
treatments show that they are all markedly superior to the untreated condition.
Each treatment has its own advantages and disadvantages which will determine
its use in specific situations. The neutralization technique appears to have
the shortest lifetime, yet it is undoubtedly the cheapest since it would use the
least amount of treatment material. Its lifetime can be increased through the
use of aluminate in the neutralization procedure to reduce the solubility of the
sealing precipitate.
- 24 -
-------
The surface treatment with silicate gel alone is not as durable as that with
the alumina/silica gel because of higher gel solubility, but it is cheaper than
the mixture. The surface treatment with the alumina/silica gel is less expen-
sive than the in-depth treatment, but the in-depth treatment is certainly the
most effective. The proper treatment method must be chosen by optimization
of both cost and effectiveness criteria.
- 25 -
-------
SECTION 7
GEL WEATHER ABILITY TESTS
A series of tests were run to determine the effect of temperature extremes on
the stability and effectiveness of the gel treatment. The tests were
performed at two levels: small laboratory heating and freezing tests and
larger outdoor freezing tests. The indoor tests were carried out by
forming sealant layers of gel on l~lb piles set up in small flat con-
tainers.
EFFECT OF HIGH TEMPERATURE ON ALUM IN A/SILICA GEL
There were two purposes in performing high temperature tests on alumina/
silica gel in refuse piles. One was to see how the gel withstood simulated
summer conditions and the other was to see if the gel technique could be
used on hot piles where the inside of the refuse pile was burning.
The "summer" test consisted of placing 1 kg of refuse in a shallow dish
and forming the alumina/silica gel on the small pile. The treated pile
was then placed under an infrared lamp which was adjusted so that the
ambient temperature was between 85 and 90 °F. During the 1-week period
of the test, the gel slowly dried out and took on the appearance of dried
plaster.
At the end of the week, the pile was sprayed with water to determine the
stability of the gel and its ability to prevent AMD generation. The washing
was continued for 17 days (the results are shown in Table II) . It was
apparent that the gel was slowly washing away, and at the end of the test
period there was little evidence of gel structure. However, when the pile
dried out, the particles of refuse were covered with a very thin layer of
white material which was apparently silica or alumina or a mixture of both.
The results in Table II show that although the sealant layer of gel per se
was gone, the residual silica or alumina continued to prevent AMD genera-
tion. It should be noted that in these tests 50 6. of water are equivalent to
about 110 in. of rainfall.
- 27 -
-------
Table II. Wash Analysis of Heated Pile
(Simulated "Summer" Test)
Day
1
4
7
9
11
14
15
16
17
Cumulative Volume
of Wash, * I
0.5
2
5
10
15
20
30
40
50
pH
12
8.3
7.5
7.2
7.2
7.0
7.0
6.8
6.5
* 0.46 i of water is equivalent to 1 in. of rain.
A second test was run to simulate the treatment of a hot pile. Here, a 1-kg
pile of refuse was treated with alumina/silica gel and placed in an oven at
130 °F, which is approximately the surface temperature of a hot pile. After
2 days of baking, a 15-day series of water washings was started. The ef-
fluent analysis is given in Table III. The visual results were very similar
to the lower temperature test: the gel hardened during baking and was
eroded during washing. Despite the fact that the continuity of the sealant
layer was interrupted, no AMD was produced during the equivalent of 120 in.
of rainfall.
The temporarily high pH of the effluent is undoubtedly due to the washout of
the gel-forming materials as silicate and aluminate. Here again, the refuse
retained a white layer when it was dried at the end of the equivalent of 110 in.
of rainfall. This indicates that there is still residual silica adhering to the
refuse which should seal the rock and thus prevent or at leat minimize AMD
generation.
- 28 -
-------
Table III. Wash Analysis of Heated Pile
(Simulated Hot Pile)
Cumulative Volume
Day of Wash, * I pH
1 5 10.8
2 10 8.0
3 15 7.2
4 20 7.0
7 25 7.0
8 30 7.0
9 35 6.8
10 40 6.8
11 45 6.6
14 50 6.6
15 55 6.5
* 0.46 8. of water is equivalent to 1 in. of rain.
"ANTIFREEZE" SELECTION
Several experiments were carried out to develop an antifreeze system that
would prevent the the interstitial water in the gel from freezing. The tests
consisted of gelling small laboratory piles weighing 500 g each, set up on a
watch glass, and keeping them in the freezer at a temperature of -8 °C for
various periods of time.
Sodium Chloride: Experimentation using NaCl as an antifreeze, in which
the concentrations of the solution range from 5 to 10%, showed that the
higher concentrations of NaCl form a water soluble gel with the silicate
solution alone. When 500-g laboratory piles were gelled by adding 10% NaCl
to the alumina/silica gel (in which the concentration of Si02 ranged from
5 to 10%), a gel was formed that resisted freezing at -8 °C. However, when
the pile was sprayed with water, the NaCl was washed out. The chemical
analysis showed that 93% of the added NaCl was removed during washing.
Calcium Chloride: This salt was ineffective as an antifreeze additive,
since it formed a gel with the silicate solution which broke on freezing. At
the same time, it reacted with sodium aluminate and formed a white pre-
cipitate of Ca(OH)2.
- 29 -
-------
Ammonium Chloride: These experiments showed that a water soluble gel
was formed by the addition of NHt Cl to the silicate solution with the release
of NH3 gas. Again, chloride ion was detected in the wash effluent. Also,
NH4 Cl reacts with the sodium aluminate to yield the gelatinous precipitate
of aluminum hydroxide.
Ethyl Alcohol: This material formed a strong gel with the concentrated
solution of silicate, but the gel was found to be soluble in water. When we
tried to mix ethyl alcohol with sodium aluminate (5%) and then added this
mixture to a waterglass solution containing 4% SiOg, it was found that the
resultant gel has some solubility in water. The solubility of the gels formed
using ethyl alcohol prevents its use as an antifreeze additive.
Prestone Ethylene Glycol: This material was also ineffective, since it
formed a soluble gel.
Polyethylene Glycol 400: This material was also ineffective, since it
formed a soluble gel.
Propylene Carbonate: This material formed a gel which was found to de-
compose when sprayed by acid mine water. Carbon dioxide gas was evolved,
indicating that the carbonate was decomposed by the acidic water, thus
destroying the gel.
Polyethylene Glycol 20,000: This material formed freeze-resistant gels
when added to the silicate and aluminate mixtures. The concentrations of
polyethylene glycol 20, 000 used ranged from 5 to 10%. This was added to
silicate solutions containing from 4 to 8% SiCfe and sodium aluminate solu-
tions containing 5 to 10% aluminate.
At low additive concentrations, the gel was quite weak in consistency. Al-
though the higher concentrations gave stronger gels, it was found that this
gel tends to separate from rock particles on spraying with water.
Glycerin: When glycerin was added (10% concentration) to the silicate
and sodium aluminate, it produced a gel with characteristics similar to
those produced from polyethylene glycol 20, 000.
- 30 -
-------
EFFECTS OF LOW TEMPERATURE ON ALUMINA/SILICA GEL
Two outdoor tests were set up to evaluate the effect of low temperatures on
the alumina/silica gel. Both were performed in 3-gal pails containing about
25 Ib of the refuse. One sample was treated with the gel in a manner
similar to Pile E of the large scale test group, while the other sample
was treated with a gel containing 0.5% by weight of polyethylene glycol
(20, 000).
Both pails were placed outdoors in an exposed place and allowed to endure
the full effect of a New England winter. During the 45 days of the test, the
temperature ranged between 3 and 53 °F. There was snow on 8 days and
rain on 7 days. At the end of this 6-week period, the pails were examined
and it was found that virtually no gel was visible. Upon drying, a layer of
white material, which was probably residual alumina and silica, could be
seen on the surface of the refuse pieces.
The liquid that had collected in the bottom of each pail was drained out and
analyzed with the results shown in Table IV. It is clear that although the gel
was no longer sealing the refuse, the acid production of the material was very
low. It should be noted that the pails did not have drain holes in the bottom so
the water could not drain out, thus the refuse was soaked in water for much
of the 6 weeks of the test.
Table IV. Analysis of Collected Water From Outdoor Test
Acidity, Soluble Silica,
Test pH ppm CaCOs ppm
With antifreeze 5.9 30 50
Without antifreeze 5.8 50 80
In order to see if the refuse that had been used in this test was still pro-
tected from producing AMD under more normal drainage conditions, sam-
ples from each test were placed in a dish and washed with water. The
washings were collected and analyzed as shown in Table V. It would
seem that the residual alumina and silica on the refuse surface maintained
a protective layer, despite the absence of a coherent gel, and still pre-
vented the production of AMD.
- 31 -
-------
Table V.
Test
With antifreeze
Without antifreeze
Analysis of Effluent Water From Washing
Refuse Used in Outdoor Test
pH
6.2
6.1
Acidity,
ppm CaCOs
10
15
Soluble Silica,
ppm
15
20
- 32 -
-------
SECTION 8
TREATMENT OF ACID MINE DRAINAGE
SILICATE TREATMENT OF ARTIFICIAL ACID WATERS
The purpose of these experiments was to study the reaction of ferrous and
ferric ions (present as sulfates) with silicate ions (present as waterglass)
over a range of concentrations. The goal was to determine the effectiveness
of waterglass in precipitating or complexing the iron.
The test procedure was to add 10 ml of ferrous ( or ferric) sulfate solution
of a chosen concentration to 10 cc of sodium silicate ( waterglass) solution
of a given concentration. The iron was kept in the range of 100 to 1200 ppm
in order to simulate actual acid waters. After the reagents were mixed, the
solution was filtered to remove any resultant precipitate and the filtrate was
analyzed for pH and iron concentration. The filtrate was then treated with
0.5 ml of concentrated ( 10%) sodium aluminate solution to test the presence
of free iron ions in the presence of silicates. It had been determined pre-
viously that the aluminate would precipitate free iron, but would not react
with iron in any complex form. The aluminate-treated solution was filtered
to remove precipitates and the filtrate was again analyzed for pH and iron
content.
Table VI presents the raw data obtained when ferric sulfate was treated
with waterglass and sodium aluminate. Examination of the data shows that
there are three different situations:
1. No precipitate from silicate addition and no precipitate from alu-
minate addition. In this case, it is clear that the addition of the silicate
caused the complexing of the iron into soluble iron silicates. The addition of
the sodium aluminate could not break the iron silicate complex, although the
aluminate would ordinarily precipitate all the iron. The analytical procedure
for determining iron was chosen so that both free iron ions and complexed
iron could be detected.
2. No precipitate from silicate addition, but some precipitate from
aluminate addition. It appears that in this case the addition of silicate
caused some of the iron to complex, but not all of it. When the aluminate is
added, the free iron ions are precipitated.
- 33 -
-------
Table VI. Treatment of Ferric Sulfate With Waterglass and Sodium Aluminate
Silicate Concentration, * M
Fe3+ Concen-
tration, * ppm Treatment
2122
(pH= 1.9)
424
(pH=2.4)
Silicate
0.4
No ppt
pH = 10.8
0.2
No ppt
pH= 6.8
0.02
[Fe] = 1050 [Fe] = 1050
0.01
No ppt
pH= 2.2
[Fe] = 1040
0.004
No ppt
pH= 2.2
[Fe] = 1040
Aluminate No ppt No ppt
pH = 11.5 pH = 9.3
[Fe] = 1050 [Fe] = 1040
Yellow-brown Yellow-brown
ppt ppt
pH= 6.5 pH = 6.5
[Fe] = 0 [Fe] = 0
Silicate No ppt
pH= 11.3
[Fe] =210
No ppt Yellow-brown Yellow-brown Yellow-brown
ppt ppt ppt
pH=11.0 pH=2.9 pH=2.6 pH - 2.6
[Fe] = 210 [Fe] = 67 [Fe] = 178 [Fe] = 160
Aluminate Glassy gel No ppt
pH= 12.2 pH= 11.7
[Fe] = 210 [Fe] = 210 [Fe] = 0
Yellow-brown Yellow-brown Yellow-brown
ppt ppt ppt
pH= 10.8 pH = 10.2 pH = 10.1
[Fe] = 67
[Fe] - 44
* After dilution, concentrations are one-half these figures.
-------
Table VI. (Cont.)
Silicate Concentration, M
CO
en
Fe3+ Concen- Treatment
tration, ppm
0.4
0.2
0.02
0.01
0.004
218
(pH=2.4)
Silicate No ppt
pH= 11.4
[Fe] =110
Aluminate No ppt
pH = 11.6
[Fe] = 110
No ppt
pH = 11.2
[Fe] = 110
No ppt
pH 11.7
[Fe] =110
No ppt
pH= 7.8
[Fe] = 110
No ppt
pH= 11.3
[Fe] =110
Yellow-brown
ppt
pH = 2.9
[Fe] = 15
No ppt
pH= 11.3
[Fe] = 0
Yellow-brown
ppt
pH= 2.8
[Fe] = 40
No ppt
pH = 10.9
[Fe] = 40
-------
3. Silicate addition causes precipitation, and aluminate addition pro-
duces further precipitation. In this case, the silicate causes the precipita-
tion of the iron as iron silicate. The iron silicate precipitates at pH values
below about 7, but not above that. Therefore, if insufficient silicate is added
to raise the pH from the acid level of the iron sulfate solution to a point
above 7, the iron silicate will precipitate. If the pH is raised above 7 by
waterglass addition, the iron is complexed and cannot then be precipitated.
The amount of waterglass needed to cause the iron to complex without pre-
cipitating can be determined by means of a graph such as Fig. 9. Here, the
iron and silicate concentrations in the mixed solution ( from Table VI ) are
plotted for the condition where all the iron is complexed. The minimum sil-
icate required for any concentration of iron is determined by drawing a line
through the origin and the data points representing the least amount of sili-
cate that was used to complex a given amount of iron. The ratio of silicate
to iron along this line is a constant and has a value of six parts of waterglass
( 100% sodium silicate with a weight ratio of SiO2/Na2O of 3.22) to one part
of iron. This is a rather high value and will undoubtedly prove to be very
costly, but the work does establish the concept of being able to make the iron
inert and not subject to precipitation. The advantage of this treatment would
be that the acid mine water could be treated without the necessity of settling
and collecting a hard to handle, low-solids precipitate.
A similar series of experiments was performed with ferrous sulfate solu-
tions as shown in Table VII. The data are plotted in Fig. 10. It is not as
obvious how the minimum line should be drawn, but using the origin and
point A, a line can be drawn that will create a region that includes all other
points. The minimum weight ratio is again about six parts silicate to one
part iron; there is some evidence that suggests that the minimum line should
be steeper than that drawn. This would give a lower ratio of silicate to iron,
which can be derived from the fact that the pH of the solution at point A is
still quite basic (pH = 10.3) and the minimum point should be close to pH 7
(that is, lower silicate content). In any case, the line is steeper than that
drawn through point A, but not as steep as that drawn through point B which
is outside the complexing region obtained from Table VII. The weight ratio
for the line drawn through point B is 4.3 parts silicate to 1 part iron.
OXIDATION OF FERROUS TO FERRIC IN THE PRESENCE OF SILICATE
The previous experimentation raised the question of how stable the ferrous
silicate complex was to oxidation of the iron. Since it is known that most of
the iron content of acid waters is in the ferrous form, this might have some
bearing on the treatment. An iron silicate complex solution was formed by
- 36 -
-------
1200 -
0
0
0.050 0.100 0.150
SiO2 Concentration, mol SiO2/jf
I
0.200
Fig,, 9. Determination of the minimum amount of water glass needed to complex
ferric iron in ferric sulfate solution
- 37 -
-------
ca
oo
Table VII. Treatment of Ferrous Sulfate With Waterglass and Sodium Aluminate
Silicate Concentration, * M
Fe2 + Concen-
tration, * ppm Treatment 0.4 0.2
Silicate Faint pptf No pptf
0.04
0.02
0.01
0.004
2200
1050
Blue-green Blue-green Blue-green Blue-green
ppt ppt ppt ppt
pH=ll pH=10.3 pH>5 pH-5.4 pH = 4.7 pH = 4.9
[Fe] = 1005 [Fe] = 1095 [Fe] = 703 [Fe] = 893 [Fe] = 893 [Fe] = 972
Aluminate No pptf No pptf Blue-green Blue-green Blue-green Blue-green
ppt ppt ppt
pH=12.3 pH=12.2 pH = 9.2 pH = 9.2 pH = 9.0
[Fe] = 1005 [Fe] = 1050 [Fe] = 0 [Fe] = 20 [Fe] = 0
Silicate No pptf No pptf
pH 11.5 pH= 10.8
Blue-green Blue-green Green ppt
ppt ppt
pH=6.5 pH=5.8 pH=4.6
lAluminate No pptf No pptf
ppt
pH= 6.5
[Fe] = 55
Yellow ppt
pH= 5.6
[Fe] = 530 [Fe] = 530 [Fe] = 223 [Fe] = 357 [Fe] = 424 [Fe] = 480
Blue-green Blue-green Green ppt Green ppt
ppt ppt
pH=12 pH=12.3 pH=10.4 pH = 10.2 pH = 10.0 pH = 10.1
[Fe] = 530 [Fe] = 530 [Fe] = 0 [Fe] = 20 [Fe] = 44 [Fe] = 50
*After dilution, concentration are one-half these figures.
fThe filtrate ( or solutions) turned deep blue.
-------
1200
0
0
0.200
0.050 0.100 0.150
SiO2 Concentration, mol 8162/.£
Fig. 10. Determination of the minimum amount of waterglass needed to com-
plex ferrous iron in ferrous sulfate solution
- 39 -
-------
mixing 100 ml of ferrous sulfate solution ( 2122 ppm as ferrous) with 100 ml
of sodium silicate solution ( 0.15M). Examination of Fig. 10 shows that this
mixture is in the band that should be fully complexed (and was verified by
the fact that the resultant solution, which is 0.75M in silicate, has a pH of
9.3).
Portions of this mixture were analyzed for ferrous at various time intervals.
For each sample of the mixture that was analyzed, a portion of the original
ferrous solution was also analyzed for ferrous as a control. The results are
shown in Table VIII and plotted in Fig. 11. The data show clearly that the
presence of silicate accelerates the rate of ferrous oxidation. The fact that
the control sample of ferrous sulfate did not appear to oxidize at all over a
period of almost 3 days is somewhat surprising, although it is known that
without aeration this oxidation takes place quite slowly.
Table VIII. Oxidation of Ferrous to Ferric in the Presence of Silicate
Ferrous Ferrous Amount
Concentration Concentration Ferrous
Time Elapsed, With Silicate, Without Silicate, Oxidized,
hr ppm PPm %
0.33 770 1060 27.4
1 614 1060 42.1
3 470 1060 55.7
5 357 1060 66.3
70 90 1060 91.5
PRECIPITATION OF FERROUS AND FERRIC IRON
USING SODIUM ALUMINATE
Since experimentation showed that sodium aluminate could be used to preci-
pitate all the iron in acid water, a series of experiments was run to deter-
mine the minimum amount of aluminate needed to do this and to compare
the results with lime treatment.
The procedure used was to add the same volume of 10% sodium aluminate
solution to different volumes of an iron sulfate solution of known concentra-
- 40 -
-------
100
CD
N
•i—I
T3
•g 80
O
c
ro
O
60
O
40
20
0
0.1
1.0
10
Time, hr
Figo 11. Oxidation of ferrous to ferric in the presence of silicate
-41 -
-------
tion. The precipitate was filtered out and the filtrate analyzed for iron. The
results of these experiments for ferrous and ferric solutions are shown in
Table IX. If these data are plotted, as in Figs. 12 and 13, it can be deter-
mined that 2.48 g of sodium aluminate are needed to precipitate 1 g of fer-
rous iron and 1.24 g are needed to precipitate ferric iron.
Table IX . Precipitation of Ferrous Iron by Sodium Aluminate
Volume of
Iron in Solution,
ml
Iron
Concentration
in Filtrate, ppm
Ferrous Solution ( 1040 ppm) *
60 352
50 218
45 128
40 34
35 0
Ferric Solution (1060 ppm) *
60
50
45
40
35
358
235
156
45
0
Amount Iron
Precipitated,
%
66.2
79.0
87.7
96.7
100.0
66.4
77.9
85.2
95.8
100.0
Weight
Ratio,
Aluminate: Iron
1.60
1.92
2.14
2.40
2.75
0.79
0.94
1.05
1.18
1.35
*0.5 ml of 10% sodium aluminate added to given volumes of iron
sulfate solution.
PRECIPITATION OF FERROUS AND FERRIC IRON USING LIME
Experiments were run to precipitate ferrous and ferric iron with lime to
compare the results with those for sodium aluminate precipitation. Varying
weights of lime (CaO) were added to identical volumes of ferrous sulfate
and ferric sulfate solutions containing known iron concentrations. The mix-
- 42 -
-------
90 -
T3
-------
3+
Weight Ratio: Sodium Aluminate/Fe , g/g
Fig. 13. Amount of sodium aluminate needed to precipitate ferric iron
-44 -
-------
tures were shaken vigorously for at least 3 hr, then filtered and the filtrate
analyzed for iron. The composition of the mixtures and the analytical re-
sults are shown in Table X . The results are shown graphically in Figs.
14 and 15, and indicate that the precipitation of ferrous and ferric iron re-
quires about 1.2 and 1.3 g of lime per gram of iron, respectively. For the
ferric iron, this is about the same as with sodium aluminate and is about
half the amount needed for ferrous precipitation with aluminate.
Table X. Precipitation of Ferrous and Ferric Iron With Lime
Weight of CaO Added
to 50 Ml of Iron Concentration Amount Iron
Iron Solution, g in Filtrate, ppm Precipitated, % CaO/Fe*
Ferrous Solution ( 1016 ppm)
0.03 390.9 61.5 0.590
0.04 234.5 76.9 0.787
0.05 145.2 85.7 0.984
0.06 — 100.0 1.181
Ferric Solution ( 1005 ppm)
0.02 815.4 18.9 0.397
0.03 636.7 36.6 0.595
0.04 446.8 55.5 0.793
0.05 278.2 72.2 0.993
*CaO/Fe = e of CaQ
50 x ppm Fe x 10"
SETTLING RATE AND SOLIDS CONTENT OF IRON PRECIPITATES
USING LIME AND SODIUM ALUMINATE
Settling Rates: Solutions containing about 1000 ppm Fe were treated as
shown in Table XI . The mixtures were shaken vigorously for 30 min and
- 45 -
-------
100 -
90
O
S
(D
+
80
(U
O
70
O
60
0.5 0.6
0.7 0.8
0.9
1.0
2+
1.1
1.2
Weight Ratio: CaO/Fe g/g
Fig. 14o Determination of amount of lime needed to precipitate ferrous iron
-46 -
-------
100
90
80
70
CD
O
e GO
CD
o;
+
CD
c
CD
O
$H
CD
50
40
30
20
10
0.2 0.4 0.6 0.8 1.0 1.2 1.4
3+
Weight Ratio: CaO/Fe , g/g
Fig. 15. Determination of amount of lime needed to precipitate ferric iron
- 47 -
-------
one of each type ( sample numbers 1, 3, 5, 7) were put in graduates and
allowed to settle. The level of the top of the suspension was recorded as
time passed using the graduations on the cylinder for reference ( 500 at the
top of the graduate). The readings taken are shown in Table XII and plotted
graphically in Figs. 16 and 17. It is quite obvious that there is no advantage
in settling rate to using sodium aluminate to precipitate iron from acid mine
drainage, in fact the rate is slower and more sludge is produced.
Table XI. Iron Solution Treatments
Test No.
1
2
3
4
5
6
7
8
Iron Solution
Aluminate Added
500 ml ( 1000 ppm Fe) 1.5 g in 20 ml H2O
1.5 gin 20 ml H2O
500 ml ( 1000 ppm Fe3 + ) 1.4 g in 20 ml H2O
1.4 g in 20 ml H2O
Lime Added
1.2 g in 20 ml H2O
1.2 g in 20 ml H2O
1.5 g in 20 ml H20
1.5 g in 20 ml H2O
Solids Content of Iron Precipitates: The remaining samples from Table XI
(numbers 2, 4, 6, 8) were placed in separatory funnels and allowed to set-
tle for 75 min (except sample-no. 2 which settled for 4 hr). The settling
time chosen was that time at which the suspension did not seem to be settling
further. The settled sludge was then removed from the bottom of the funnel
and its solids content determined. The results of these experiments are
shown in Table XIII,
The results of all the tests shown here indicate that there is no advantage to
using sodium aluminate to precipitate iron from acid mine drainage.
- 48 -
-------
Table XII. Settling Rates
Test Sample
T^ 3+ / -,-,%+/
Fe / Fe /
* Lime ( 7) Aluminate ( 1) Lime ( 3)
492
390
290 470
190
150 360
125
112 282
105
240
93 215
480 200
190
465
455
440
430
417
405
50
*Numbers in parentheses refer to test numbers in Table VII.
Time,
min
0
1
5
8
10
12
14
15
17
20
23
25
30
35
36
40
45
50
55
60
65
70
75
90
120
150
180
210
240
3 days
Fe3 + ,
Aluminate
500
490
455
430
405
385
357
335
308
260
232
210
190
180
170
- 49 -
-------
500
Ol
o
CO
•M
• I—i
5
>%
b
400 -
O
•t-H
CO
C
0)
o^
CO
CD
Sodium aluminate
200 -
o
20
40
60
80
100 120
Time, min
140
160
180
Fig. 16. Comparison of settling rates using sodium aluminate and lime to
precipitate ferrous iron
-------
500
400
300
200
100 -
Sodium aluminate
-Q—
0
10
20 30
Time, min
40
50
60
70
Fig. 17. Comparison of settling rates using sodium aluminate and lime to pre-
cipitate ferric iron
- 51 -
-------
Table XIII. Solids Content of Iron Precipitates
Weight of Weight of Solids
Sludge, g Dry Ppt, g Content, %
2 + /aluminate(2) 45.34 0.19 0.4
2 + /lime(4) 25.52 0.36 1.4
Fe3 + /aluminate ( 6) 23.75 0.55 2.3
/lime(8) 16.67 0.55 3.3
- 52 -
-------
SECTION 9
OTHER EXPERIMENTS
OPTIMIZATION OF ALUMINIA/SILICA GEL CONCENTRATION
In order to optimize the composition of the alumina/silica gel for in-depth
gelation, a series of tests was run using several different combinations of
solution concentrations. The criteria used for optimization were gelation
time and the strength of the gel. The results are given in Table XIV. The
data in this table give a qualitative evaluation of the consistency of the gel
as well as the time it took to gel.
The procedure used was to mix 10 ml of a silica solution of the concentra-
tion shown in the table with 10 ml df an aluminate solution (concentration
shown in the table) . Thus, the final solution had a concentration of each
component equal to one-half the concentration given in the table. The opti-
mum solution was considered to be a mixture of 3% silica solution with 3%
aluminate, or a final solution containing 1.5% of each.
Table XIV. Optimization Studies for Alumina/Silica
Gel Composition Showing Gel Time (sec)
and Gel Consistency
Wt % SiO2 in Water-
glass Solution
1
No gel
(60)
Wt % Sodium Aluminate in Solution
No gel
(60)
Very weak
gel(1260)
No gel Weak gel Fair gel
(60) (1800) (410)
No gel Very weak Good gel
(60) gel (2100) (315)
No gel Very weak Good gel
(60) gel (2400) (270)
No gel Very weak Good gel
(60) gel (2400) (230)
Weak gel
(900)
Good gel
(250)
Excellent
gel(160)
Excellent
gel (106)
Excellent
gel(100)
Weak gel
(480)
Good gel
(135)
Excellent
gel (73)
Excellent
gel (55)
Excellent
gel (52)
- 53 -
-------
STABILITY OF ALUMINA/SILICA GEL IN CONTACT WITH AMD
In order to determine the stability of the alumina/silica gel when it was
contacted with AMD, a series of static and dynamic tests was run. The
static tests consisted of forming the gel either in the bottom of a beaker
or jar and then pouring in an AMD formed by passing water over the
coal mine refuse. The system was allowed to sit for several weeks. In
the static test, the gel was formed in a beaker and then transferred in pieces
into a jar. AMD was put into the jar and periodically shaken vigorously.
The most obvious result was that the iron in the AMD precipitated quite
rapidly in the form of iron hydroxide. This was probably due to the high
pH of the gel material. The supernatant solutions were periodically ana-
lyzed to see the effect on the AMD composition. Table XV shows the re-
sults of such an analysis made after 10 days. It can be seen that the pre-
sence of the gel caused most of the acidic constituents of the AMD to be
precipitated out of solution.
Table XV. Analysis of Supernatant AMD in Gel
Stability Tests
AMD + Silica/ AMD + Silica/
Analysis Alumina Alumina
of AMD (Shaken) (Without Shaking)
pH 2.3 8.5 4.5
Acidity on CaCO3, 3950 180
ppm
Total dissolved 1117 5 110
iron
Ferrous 120 0
Sulfate 3260 760 1330
Soluble silica 0 200 80
The gel itself did not appear to be affected in any way, although it was hard
to see if there was any change in the shaken test. The gel mass was covered
with yellowish-brown iron hydroxide which might have masked any erosion.
- 54 -
-------
ANALYSIS OF BACTERIA CONTENT OF WASH EFFLUENT
A sample of the wash effluent from the control pile (pile A) was taken after
about 100 in. of equivalent rainfall had passed through the pile. This sample
was analyzed for bacteria content under the direction of Dr. Harold L. Lovell
of Pennsylvania State University. The analysis shows a bacteria count of
2.4 x 10 cells/ml* as compared to an average cell count of about 100 in the
effluent from a coal mine.9 The cell concentration in effluents from existing
refuse piles is probably somewhat higher than that of the coal mine effluent,
but an exact value is not available at this writing.
The very high cell count in the effluent from the control pile washing helps
explain the fact that almost all the effluent solutions showed very high ferric
and very low ferrous concentrations. It has been shown9 '10 that bacteria in
acid solutions promote the oxidation of ferrous ion with the rate of oxidation
varying directly with the bacteria concentration. Thus the fact that the efflu-
ent from the laboratory piles shows abnormally high bacteria counts is con-
sistent with the very high ferric concentrations.
The reasons for the abnormally high bacteria count are hard to determine in
the absence of controlled experimentation, but the environmental conditions
were certainly conducive to the propagation of biological organisms. The
refuse was kept in a highly humid atmosphere at temperatures consistantly
above 60 °F and the pyrite content was relatively high. These conditions
undoubtedly encouraged the growth of the microorganisms and the resulting
ferrous oxidation.
3)t
This value was obtained by a dilution count procedure developed
at Penn. State University by Stone, Tieman and Lovell.
- 55 -
-------
SECTION 10
MASS BALANCE
METHOD
The major soluble species in an acidic mine water include ferrous iron,
ferric iron, sulfate, water, hydroxyl, and hydrogen ions. These materials
do not exist solely as the bare ions but, in part, as complex ions, e.g.,
[ Fe2(OH)2]4+, FeOH2+, Fe(OH)2+. etc. Since these ions control the chemistry
of AMD waters, an understanding of their distribution as a function of gross
solution composition is required. There is also the more subtle point that
a mass balance is required as a check on the thoroughness and accuracy of
the analysis. A "natural" system such as AMD is generally quite complex
but, more important, variable in composition. The self-consistency of re-
sults provides some confidence that all major species have been accounted
for. As will be seen from the data, some analytical procedures had to be
modified.
The equilibria among the ferric, ferrous, sulfate, hydroxyl, and hydrogen
species are summarized in Table XVI . The equilibrium constants used
are shown in Table XVII.
Table XVI. Equilibrium Between Fe3+, Fe2+, OH", SO42"
Equilibrium Reactions
Equilibrium Expression
2 Fe
3+
= Fe2 (OH)2
4+
K22 =
3+2
Fe3+]
3+
Fe
3+
Fe
3+
2+ +
Fe + H.O = FeOH2 + H
= Fe (OH)2 + + 2
= FeS04+
[ Fe3+]
Kia= [Fe(OH)2+] [H+]2
r r^ 3+i
L Fe J
K0i =
[FeSC>4+]
[Fe3+]
- 57 -
-------
Table XVI. (Cont. )
Equilibrium Reactions
Fe3+ + 2 SO42~ = Fe (SO4)2~
I+ = HSO4"
Fe2+ + S042~ = FeS04
Fe2+ + H20= Fe(OH)+ + H+
Equilibrium Expression
[Fe (804)2"]
[Fe3+] [SO,2-]2
v -
JN-OO —
[SO.2'] [H+]
= [ FeSQ4 ]
[Fe2+] [S042~]
= [ Fe(QH)+] [ H+]
[ Fe2+]
Table XVIL Log Equilibrium Constants * for
Fe , Fe2+, OH", SO42" Species
Constant
K22
Ku
Kl2
KOI
Ko2
Koo
Qoi
Qn
Value
-2.91
-3.05
-6.31
+ 2.31
+ 2.62
+ 2.00
+0.23
-6.74
* Taken from L. G. Sillen, A. Martell, "Stability Constants of
Metal-Ion Complexes, " The Chemical Society, London, 1964.
- 58 -
-------
These constants, particularly K22 and Ku , are all functions of ionic
strength, i.e., the total ion concentration. This dependence remains to be
determined experimentally and is considered as an area of theory refine-
ment.
In addition to the eight equilibria in Table XVI, there are mass balances
on Fe(II) , Fe(III) , SO42~, and H+ to be satisfied:
CFe(lD = [ Fe2+1 + [ FeS°4J + [ FeOH+]
CFe(IID = [ Fe3+] + I FeSO*+] + t Fe(S04)2-] + [ FeOH2+] (g)
+ [ Fe(OH)2+] + 2[Fe2(OH)24+]
Cs = [ S042~] + [ HS04~] + [ FeS04] + [ FeSO4+] + 2 [ Fe(SO4)2~] (10)
CH= 2 CS ~ 2 CFe(lD ~ 3 CFe(HD (11)
= [ H+] + [ HS04~] - [ OH"] - [ FeOH+] - [ FeOH2+]
- 2 [ Fe(OH)2 +] - 2 [ Fe2(OH)24+]
The method of solution consists of the following steps, which comprise
part 2 of the computer program in Table XVIII.
First, the equilibria constants are substituted to eliminate all species
except [ Fe2+] , [ Fe3+] , [ SO42~] , and [ H+] , which are the master variables.
The four mass balances ( Eqs. 8 through 11) then provide four equations in
these four unknowns, provided that all the total concentrations are known.
These are rearranged as follows:
[FeH= - - - (12)
I + QOI [so42-]
[ Fe3+] = CFe(II]) / ( 1 + K"[S°42"]2 + K°» (S04") 2 +^7 (13)
2 K22 [ Fe3+]
[H+]2
- 59 -
-------
Table XVIII. Computer Printout
1.01\ PROGRAM /FE2/ JNB-RJJ VERSION 3/3/70
Ul TYPE"
FE(II) ANi FE(III) IN SULFATE, INCLUDING ACIDITY
»•
.14 ®EMANB IN FORM It CFE, CF2, CS
.141 CFE = .00002 IF CFE = 0
.142 CF2 = .00001 IF CF2 = 0
.145 CF3 = (CFE - CF2>/55.85, CF2=CF2/55.85, CS = CS/96.06
.15 TYPE IN FORM 2: CF2, CF3, CS
.2 CF2 = CF2*.00l, CF3 = CF3*.001, CS=CS*.001
.21 FE = 0.2*CF3, S04 = 0.5*CS. H = .003, CM = 2*CS-2*CF2-3*CF3
.22 TYPE "NEGATIVE ACIBITY" IF cn<0
.23 TYPE CH IF CH<0
U24 0EMAN0 CH IF CH<0
1.25 K22 = 10*-2.91, Kll = 10*-3.05, K12 = 10A-6.31,
K01 = 10*2.31, K02 = 10*2.62, Q01 = 10*.23, QlU10~-6.74
1.29 TYPE"
PH FE+3 S04 FE2(OH)2 FEOH FE(OH)2 FES04 FE
-------
Table XVIII. (Cont.)
FORM 1:
PPM FE TOTAL = #, PPM FEUI) = #, PPM S04 = #
FORM 2:
TOTAL FE(II) = ZZZ.ZZZ MM
TOTAL FECIII) = ZZZ.ZZZ MM
TOTAL S04 = ZZZ.ZZZ MM
FORM 3:
ZZ.ZZ 7.7.7..7.7.7. ZZZ.ZZZ 7.7.7..7.7.7. ZZZ.ZZZ 7.7.7..7.7.7. 7.7.7..7.7.7. 7.7.7..7.7.7. 7.7.7..7.7.7.
FORM 4:
EXCESS ACIDITY = 7.7.7..7.7.7. MM, Z7.Z7.Z7. PPM CAC03
TOTAL ACIBITY = ZZZ.7.ZZ MM, ZZZZZZ PPM CAC03
This program is written in GAL, the conversational algebraic
language of the XDS-940 time-sharing computer system. Part 1
is input, Part 2 is calculation, and Part 3 is output. Symbols
are defined as follows:
CFE Total iron in ppm (redefined to millimolar in 1.145)
CF2 Ferrous iron in ppm "
CS Total sulfate in ppm "
CF3 Ferric iron in millimolar
Note concentrations are redefined to molar in 1.2
FE free ferric iron, molar
S04 free sulfate, molar
H free hydrogen ion, molar
CH total acidity, molar,due to excess acid
K22 formation constant for Fe?(OH)2^ from Fe3+ and H
Kll " FeOH++ "
K12 " Fe(OH)2+ "
KOI " FeSO,+ " and SOA~
K02 " Fe(SO,)- " »
Q01 " FeSO- from Fe++ "
Qll " FeOH+ " and H+
FEN new value of FE in iteration
SON new value of SO^in iteration
Al, A2, A3, F, FPR, etc. intermediate results defined by equations
in the program
C22, C21, etc. concentration of complexes corresponding to K22,etc,
recalculated to millimolar in step 3.25.
CHM total acidity, millimolar, due to excess acid
CHP total acidity, ppm CaC03, due to excess acid
CHT total acidity, millimolar, due to acid plus iron species
GPP total acidity, ppm CaCO^, due to acid plus iron species
Note that no account has been taken of variations in activity
coefficient or the possibility of precipitate (Fe(OH)r}?) formation,
- 61 -
-------
[S042"] = CQ / 1 + Koi [Fe3+] + 2 K02 [ Fe3+] [SO42-] (14)
V
+ Qoi [ Fe2+] + Koo [ Hl
F(H) = 0= CH+-^- +-— -As [H+] (15)
H [Hi [H+]2
where Ai = 1(T14 + Qn [ Fe2+] + Kn [ Fe3+]
As = 2[ Fe3+] (Ki2 + K22 [Fe3+])
A3 = 1 + Koo [S042"]
Second, the equations are solved by an iterative procedure. [ Fe3+] is
assumed initially to be 0.2 Cpe/nl) , [ S042~] is assumed initially to be
0.5 Cg, and [ H+] is as sumea initially to be 0.00 3 M. These are merely
starting values and are not critical. The closer they are to the final
values the faster the equations will converge, but the exact values should
not influence the final answer.
Then, [ Fe2+] , [ Fe3+] , and [ SO42~] are evaluated from Eqs. (12) to (14) ,
and the polynomial in H+ ( Eq. 15) is solved using Newton's method. These
revised values are then used in a further evaluation of the master variables
using the same set of equations. When two successive sets of values con-
verge to one part in 107 , the calculation is complete. Normally, this re-
quires only a few iterations, since the equations have been arranged so
that the revised values make very little change in the master variables
when they are recomputed. The manner in which the equations are rear-
ranged and the order in which they are evaluated is quite critical in ob-
taining a rapid solution — in some of our earlier attempts, a different
rearrangement of Eq. (10) ( substractive rather than divisive) did not
give convergence in solutions which were high in iron content.
The input data then are the total soluble iron content, soluble ferrous iron,
and soluble sulfate. The output ( Table XIX ) is a display of the individual
complex ion concentrations as well as predictions of pH and total acidity.
The correspondence of experimentally determined and predicted pH and
total acidity is a measure of the internal consistency of the theory.
An additional value obtainable from the mass balance is the free acidity,
i.e., the amount of sulfur ic acid not involved with soluble metal ion com-
plexes. In principle, this should be directly computable from pH. The pH
electrode measures the negative log of the hydrogen ion activity (-log AR+) ,
not concentration. The activity is a function of a number of factors suclias
ionic strength. An approximate correction for this factor was included in
the computer program. The "predicted" free acidity does not involve this
- 62 -
-------
Table XIX. Sample Output
ACID MINE WATERS 3/13/70 JNB PAGE 1
>LOAD
FROM /@FE2/
>BO PART 1
FECII) AND FE(III) IN SULFATE. INCLUDING ACIDITY
PPM FE TOTAL = 275, PPM FE(II) = 15, PPM S04 = 560
TOTAL FE(II) = 0.269 MM
TOTAL FE(III) = 4.655 MM
TOTAL S04 = 5.830 MM
NEGATIVE ACIDITY
CH = -2.8437538E-03
CH = 0
PH FE+3 S04 FE2(OH)2 FEOH FE(OH)2 FES04 FECS04)2 FE++
2.76 1.314 4.024 0.68S» 0.667 0.209 1.079 0.009 0.267
EXCESS ACIBITY r 0.000 MM. 0 PPM CAC03
TOTAL ACIDITY = 14.503 MM, 726 PPM CAC03
PPM FE TOTAL = 275, PPM FE(II) - 15, PPM S04 = 720
TOTAL FECII) = 0.269 MM
TOTAL FE(III) = 4.655 MM
TOTAL S04 = 7.495 MM
PH FE+3 S04 FE2(OH)2 FEOH FE(OH)2 FES04 FE(S04)2 FE++
2.75 1.262 5.196 0.610 0.628 0.193 1.338 0.014 0.266
EXCESS ACIBITY = 0.487 MM, 24 PPM CAC03
TOTAL ACIBITY = 14.991 MM, 750 PPM CAC03
PPM FE TOTAL = 1195, PPM FECII) = 0: PPM S04 = 3745
TOTAL FECII) = 0.000 MM
TOTAL FECIII) = 21.397 MM
TOTAL S04 = 38.986 MM
PH FE-i-3 S04 FE2COH)2 FEOH FECOH)2 FES04 FE(S04)2 FE++
2.19 4.764 14.562 0.668 0.657 0.056 14.164 0.421 0.000
EXCESS ACIBITY = 13.782 MM. 690 PPM CAC03
TOTAL ACIBITY = 77.972 MM, 3902 PPM CAC03
- 63 -
-------
activity problem and, once a complete mass balance is obtained, should
provide a more accurate evaluation of the free acid to be treated.
APPLICATION TO STANDARD SAMPLES
The program was first checked out with simple sulfuric acid solutions
containing known amounts of ferric and ferrous sulfate. A comparison
of known, measured, and predicted parameters is shown in Table XX
The known and predicted acidities compared to within 5%; the titrated
values generally tend to be low, by about 6% on the average.
Table XXI shows the distribution of the various complex iron species, as
predicted by the equilibrium constants of Table XVI . The dominant fer-
rous iron species is Fe2+ while, depending on pH, the principle ferric iron
species are the Fe (SOi)+ complex and the bare Fe3+. Note that the amount
of ferric iron present as hydroxyl complexes is a pronounced function of
pH; a pH change of 2.58 to 1.8 lowers the concentration of Fe2(OH)22+ from
10.6 to 0.72%.
APPLICATION TO AMD SAMPLES
The mass balance equations were then applied to AMD waters, generated
in the manner described. A large number of evaluations were made.
The data given below (Table XXII) are representative of the results.
Consider the ten samples listed in Table XXII. For a number of samples,
e.g., 1, 3, 4, 7, 8, 9, the agreement is reasonable. However, the re-
maining samples show pronounced discrepancies; in all cases, the mea-
sured acidities are higher than predicted. This is what could be expected
if another anion, besides sulfate, was present. A likely possibility from
the AMD generation mechanism is sulfite (SO32~). Indeed, as mentioned,
oxidizing the solution before titration did, in some cases, lead to additional
sulfate. Sulfurous acid is titratable to a phenolphthalein end point, and would
therefore contribute to the measured acidity and pH.
The data for samples 10, 9, 7, and 6 were remeasured on this basis.
The results are shown in Table XXIII.
- 64 -
-------
Table XX. Comparison of Parameters for Standard Samples
Oi
Ol
Sample
1
2
3
4
5
6
Composition
8
FeSCX ( 1050 ppm Fe)
FeSO4 ( 1050 ppm Fe) in
( 1000 ppm)
Fe2(SO4)3 ( 1050 ppm) in
Fe2(SO4)3 (737 ppm) in
Fe2(SO4)3 (1050 ppm) in
( 1000 ppm)
Fe2(SO4)3 (737 ppm) in H2SQ4
( 1000 ppm)
Fe ( 1950 ppm) + HaSO4
PH
Measured Predicted
Total Acidity (ppm CaCOs)
Known Measured Predicted
1.95
4.9
2.25
2.2
2.7
2.1
2.5
1 R
1.84
4.5
2.0
2.58
2.64
2.01
2.0
1 ft
1020
1870
2870
2210
1870
3870
2950
1000
1840
2800
2600
1900
3600
2650
7^n«
1021
1882
2903
2864
1982
3885
3000
1 AZ1
-------
Table XXL Relative Amounts of Soluble Iron Species (Mol % Total Fe)
Fe2+ pH (Calc.)
99.1 4.5
98.9 2.0
2.58
2.01
1.8
Sample
2
3
4
5
6
Fe2+
17.
25.
20.
7
4
3
Fe2(OH)24+
10.
1.
0.
6
6
72
Fe(OH)2+
6.
2.
1.
0
3
13
Fe(OH)2 +
1.
0.
0.
3
13
04
Fe(SO4) +
52.3
67.2
74.4
Fe(SO4
1.5
1.8
2.73
-------
Table XXII. Typical AMD Samples
pie No.
1
2
3
4
5
6
7
8
9
10
PH
Measured
2.5
2.4
2.7
2.7
2.5
2.05
2.2
2.1
2.1
2.5
Predicted
2.30
2.42
2.2
2.22
2.6
2.54
2.38
2.19
2.43
2.58
Acidity
Measured Predicted
3950
5705
3150
3230
4200
5505
2803
3904
4153
3353
3396
3909
2969
3162
3269
4849
2657
3902
3820
2763
Total Fe,
ppm
1117
1370
880
980
1306
1804
871
1195
1324
1028
Ferrous Iron,
ppm
120
110
88
90
270
—
—
—
—
Sulfate,
ppm
3260
3752
2850
3035
2850
4315
2550
3745
3669
2471
-------
Sample
No.
6
7
9
10
Table XXIII. AMD Samples Corrected for Sulfate
pH Acidity SO4
Measured Predicted Measured Predicted SO42~ + SOs
2-
2-
2.05
2.2
2.1
2.5
2.25
2.28
2.28
2.2
5505
2803
4153
3353
5518
2810
4087
3426
4315
2550
3667
2471
5296
2697
3923
3288
Judging from the results, this approach to the mass balance problem
appears to be valid. One important result of this analysis was the defini-
tion of a soluble "reduced sulfate." It is equally apparent that further re-
finement is necessary, in particular to add to the computer program a
subroutine which accounts for the deviations of the activity coefficients
from unity. It will also be necessary to account for the contributions from
soluble calcium and aluminum species.
- 68
-------
SECTION 11
REFERENCES
1. Vanderhoof, R. A., "Stream Pollution by Coal Mine Drainage in
Appalachia, " U. S. Department of the Interior, FWPCA, Cincinnati,
Ohio (1967, rev. 1969).
2. Peters, J. W., Spicer, P. S., Lovell, H. L., Special Report SR-67,
Pennsylvania State University to Coal Research Board, Commonwealth
of Pennsylvania (January 1968).
3. Waksman, S.A. and Joffe, S. S., Science, 53_, 216 (1921).
4. Ashmead, D., Colliery Guardian, 190, 694-8(1955).
5. McGoran, C. J. M., Duncan, D.W., and Walden, C. C., Canadian J.
Microbiol. 15(1), 135-8(1969).
6. Hill, R. "Mine Drainage Treatment — State of the Art and Research
Needs, " U. S. Department of the Interior, FWQA, Cincinnati, Ohio
(December 1968), p. 8.
7. Vail, J. G., "Soluble Silicates, " Vol. 1, Chapter 5, Reinhold Pub.
Corp., New York, 1952.
8. "Acid Mine Drainage in Appalachia,"Regional Commission, 1969.
9. Lovell, H. L., private communication based on unpublished research
under FWQA project # WPRD-34-01-68.
10. Glover, H. G., presented at the 22nd Annual Purdue Ind. Waste Conf.,
May 1967. "The Control of Acid Mine Drainage Pollution by Biochemical
Oxidation and Limestone Neutralization Treatment, " May 1967.
- 69 -
-------
SECTION 12
PUBLICATIONS
A presentation of much of the data included in this document was made at
the Third Symposium on Coal Mine Drainage Research, Pittsburgh, Pa.,
May 19, 1970 in the paper "Presentation of Acid Mine Drainage: Silicate
Treatment of Coal Mine Refuses Piles" by Arthur Walitt, Raymond Jasinski,
and Bertram Keilin.
- 71 -
-------
APPENDIX I
ANALYTICAL METHODS
The parameters determined routinely were pH, acidity (calcium carbonate),
total soluble iron, ferrous iron, and sulfate. Determinations of aluminum
and calcium were made on selected samples. The analytical methods were
based on those given in: "Standard Methods for the Examination of Water
and Waste Water, " 12th ed., American Public Health Association, New York
(1965) .
pH was measured with a standard Beckman pH meter calibrated at pH 2 with
standard buffer solution. It was found that standardization at pH 6 introduced
an error of 0.2 unit at pH 2.
Total iron was determined, after filtering the sample, by first reducing
with SnCh solution followed by destruction of the excess SnCl2 with HgCb,
followed by titration with dichromate using diphenylamine sulfonate as the
indicator. The accuracy of the method was proven by titrating standard fer-
ric and ferrous sulfate solutions.
Ferrous iron was measured by direct titrations with dichromate using diphe-
nylamine sulfonate as an indicator.
Total acidity was measured by titration of the untreated solution at room tem-
perature to a phenolphthalein end point. This value therefore includes the free
acid as well as the resulting from the hydrolysis of soluble iron. Data are re-
ported in terms of the equivalent ppm calcium carbonate.
Sulfate was determined primarily by precipitation with benzidine hydrochlo-
ride followed by titration of the released HC1 with sodium hydroxide to the
phenolphthalein end point. This method is rapid, although apparently less
accurate than the standard gravimetric barium sulfate technique. Table I
shows the sulfate analysis by the two techniques.
Neither of the two methods necessarily gave total soluble sulfur content.
It was found that, depending on the specific AMD sample, a reduced sulfate,
presumably sulfite ion, was often present. The addition of bromine water
was sufficient to oxidize this material. The results of the sulfate analysis
with and without this pretreatment are shown in Table II.
- 73 -
-------
Table XXIV. Sulfate Analysis, ppm
Gravimetric,
Sample Benzidine HC1 Gravimetric B-HC1
1 2430 2481 1.015
2 3230 3288 1.015
3 38,060 38,602* 1.014
4 3568 3745 1.05
* Standard known amount 39,100 ppm.
Table XXV. Sulfate Analysis (PPM) With
and Without Preoxidation
After Oxid.,
Sample As Received After Oxidation As Received
1 2430 3220 1.33
2 3667 3923 1.07
3 4315 5296 1.23
4 2550 2697 1.06
5 445 480 1.08
6 285 290 1.02
7 405 405 0.0
As can be seen, the ratio of the two "sulfates" varies from sample to sam-
ple, even though the AMD samples all came from the same pile of waste
coal refuse.
Soluble silica was determined as molybdenum blue by reduction of a pre-
formed yellow silico-molybdate complex. This complex is formed as the
acid at a pH of 1.6. After its reduction to the molybdenum blue, the con-
centration of the sample is determined by comparison with a standard silica
color disk.
- 74 -
-------
APPENDIX II
COMPLETE ANALYSIS OF PILE EFFLUENTS
Table XXVI. Pile A; Control
Volume
of Water,
Day* 4
It
6
7
8
10
13
14
16
23
24
27
28
29
30
31
20
20
40
20
100
50
50
1
50
20
100
100
100
100
100
100
100
pH
1.8
2.05
2.0
2.15
2.0
2.0
2.3
2.4
2,
2,
05
15
2.1
1.8
2.3
2.5
2.3
2.2
2.3
2.3
2.5
Acidity
as CaCO3,
ppm
32,629
16,114
20, 500
14, 160
18, 100
15,600
6,265
4,604
10, 000
8,670
9, 350
16,220
4,360
3,150
3,950
3,460
3,200
3,353
3,250
Dissolved Ferrous Soluble
Iron, Iron, Sulfate, Silica,
ppm ppm ppm ppm
6134
2837
5250
2620
3860
2569
1787
1117
2624
3871
3518
4300
1210
980
1117
1284
950
1040
940
1586
739
614
430
490
167
90
60
112
390
130
580
110
90
120
112
90
90
80
14,272
11,893
11,800
4,738
7,457
7,136
6,660
4,281
7,612
9,500
5,327
8,270
4,370
3,950
3,260
2,660
1,940
2,280
2,280
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
*The data are grouped by weeks, with the day numbers indicating
time elapsed from the start of the experiment.
•fOn days 1 and 2, the pile effluent was separated into the inner core
sample and the outer annulus sample. The top figure for each day is the
inner sample. Data for all other days refer to composite samples which
reflect the average composition of the total wash volume.
- 75 -
-------
Table XXVI. (Cont.)
Day
34 i
35
36
37
43
44
45
48
49
50
52
55
56
57
58
59
62
63
64
65
66
Volume
of Water,
a
2
80
100
100
100
60
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
pH
2.2
2.3
2.5
2.5
2.5
2.0
2.3
2.3
2.3
2.5
2.5
2.5
2.3
2.5
2.5
2.3
2.3
2.3
2.4
2.5
2.55
2.6
Acidity
as CaCO3,
ppm
5,105
4,030
3,150
3,230
3,280
5,060
4,430
4,200
3,700
2,960
2,350
2,220
2,260
1,950
1,890
2,040
1,980
1,900
1,770
1,400
1,000
670
Dissolved
Iron,
ppm
1370
950
880
980
1009
2680
1843
1306
1360
970
840
780
715
650
630
715
760
730
680
510
460
340
Ferrous
Iron,
ppm
110
85
88
90
100
366
290
270
245
210
160
100
90
80
70
85
90
60
60
45
38
20
Sulfate,
ppm
3,752
3,230
2,850
3,035
2,204
4,180
3,270
2,850
2,480
2,000
1,780
1,560
1,350
1,280
1,180
1,230
1,190
1,045
960
870
740
665
Solu
Silic
ppn
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
|On day 34, the top figures are the analysis of the first 2-£ wash;
the other figures are the analysis of the composite samples.
- 76 -
-------
Table XXVI. ( Cont.)
Day
69
70
71
72
73
76
77
78
83
84
85
87
90
91
92
93
94
97
98
99
100
101
104
105
106
107
108
111
112
113
114
115
Volume
of Water,
i
100
100
100
100
100
100
100
40
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
pH
2.4
2.6
2.6
2.6
2.6
2.4
2.6
2.4
2.3
2.6
2.6
2.65
2.5
2.65
2.6
2.6
2.65
2.6
2.65
2.6
2.6
2.7
2.5
2.7
2.8
2.8
2.8
2.7
2.7
2.7
2.7
2.7
Acidity
as CaCO3,
ppm
1,210
630
540
510
530
560
490
550
750
410
390
375
510
350
420
380
330
400
290
260
240
250
360
250
200
230
200
270
240
200
200
240
Dissolved
Iron,
ppm
360
310
278
250
240
290
210
320
430
210
160
150
190
150
150
130
130
140
110
80
66
56
110
80
66
56
56
80
66
60
70
80
Ferrous
Iron,
ppm
25
20
18
15
15
20
15
25
40
12
10
8
10
10
10
10
8
5
0
0
0
0
8
0
0
0
0
0
0
0
0
0
Sulfate,
ppm
650
580
545
470
450
490
430
580
640
380
230
210
420
230
275
240
200
230
190
190
170
150
220
190
170
190
190
230
220
190
240
230
Soluble
Silica,
ppm
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
- 77 -
-------
Table XXVI. (Cont.)
Volume Acidity Dissolved Ferrous Soluble
of Water, as CaCO3, Iron, Iron, Sulfate, Silica,
Day a pH ppm ppm ppm ppm ppm
118
119
120
121
122
125
126
127
128
129
139
140
141
142
143
146
147
148
149
150
153
154
155
156
157
160
161
162
163
164
167
168
169
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
2,6
2.8
2.6
2.7
2.6
2.5
2.6
2.6
2.5
2.6
2.1
2.2
2.4
2.4
2.5
2.4
2.5
2.5
2.5
2.5
2.2
2.4
2.4
2.5
2.5
2.4
2.6
2.6
2.7
2.7
2.5
2.6
2.6
250
200
230
250
300
320
290
270
310
250
530
280
210
260
280
350
240
200
210
190
260
220
200
190
180
220
180
170
150
150
190
160
160
90
80
82
80
60
95
72
65
72
55
275
95
65
80
80
95
80
70
70
65
90
75
80
80
70
90
60
60
55
60
75
60
70
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
250
190
210
290
300
330
290
290
290
240
460
260
185
240
265
320
220
190
190
185
205
195
190
190
170
200
165
165
140
145
170
155
150
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
- 78 -
-------
Table XXVI. (Cont.)
Day
170
171
174
175
176
177
178
181
182
183
184
185
188
189
190
Volume
of Water,
a
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
pH
2.6
2.7
2.6
2.6
2.7
2.7
2.7
2.6
2.7
2.7
2.8
2.8
2.6
2.8
2.8
Acidity
as CaCO3,
ppm
180
150
210
200
200
180
160
190
160
150
130
130
170
150
140
Dissolved
Iron,
ppm
80
50
100
80
80
70
60
70
50
50
50
40
65
60
50
Ferrous
Iron,
ppm
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Sulfate,
ppm
170
140
200
185
190
170
150
170
150
150
120
130
150
150
140
Soluble
Silica,
ppm
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
- 79 -
-------
Table XXVII. Pile B: Neutralized Pile
Volume
of Water,
Day* i pH
1 20 2.4
2 20 10.5
3 20 5.5
6 20 10.3
7 20 10.1
8 100 9.8
10 50 9.3
13 50 9.5
14 20 8.6
16f 50 8.8
8.3
201 50 7.6
6.8
21 50 6.8
22 50 7.0
23 100 6.8
24 100 6.5
27 100 6.5
28 100 6.5
29 100 6.5
30 100 6.5
31 100 6.5
34 100 6.5
35 100 6.5
36 100 6.5
37 100 6.5
*Pile was treated on days 0, 1, and 3 until the effluent stream had
the same pH as the fresh silicate solution.
•f Includes finely suspended iron hydroxide.
f On days 16 and 20, the first and last 2 i only of the 50- i total were
analyzed and reported. For material balances, the composite analysis was
estimated as the average of these two figures.
- 80 -
Acidity Dissolved
as CaCO3, Iron,
ppm ppmt
11, 510 3462
— 73
1000 390
— 50
— 12
— 40
— 17
— 16
— 44
— 39
— 42
— 11
— 11
— 11
— 11
— 11
— 11
— 15
— 11
— 27
— 15
— 11
— 22
— 27
— 33
— 28
Ferrous
Iron, Sulfate,
ppm ppm
726 7136
— 2854
45 1500
— 960
— 475
— 1283
— 1903
— 1410
— 1820
— 1638
— 1120
— 1615
— 1140
— 1320
— 980
— 730
— 680
— 360
— 380
— 320
— 285
— 285
— 190
— 190
— 130
— 100
Soluble
Silica,
ppm
—
—
—
—
400
350
320
400
320
230
160
160
90
110
120
100
100
80
60
60
70
60
70
60
60
40
-------
Table XXVII. (Com.)
Volume Acidity Dissolved Ferrous Soluble
of Water, as CaCO3, Iron, Iron, Sulfate, Silica,
Day i pH ppm ppm ppm ppm ppm
43 60 3.5 420 45 13 290 80
44 100 3.5 395 52 13 355 30
45 100 3.0 450 61 16 380 30
48* 100 2.8 650 85 10 420 60
3.0 570 100 15 360 50
49 100 3.0 480 90 15 475 20
*On day 48, the top figures are the analysis of a sample collected
from the inner core, while the other sample, on the same day, was collected
from the outer annulus.
- 81 -
-------
Table XXVIII. Pile C: Silica Gel (Surface Treatment)
Day
1
2
3
6
7
9t
13t
14
15
16
17
20
21
22
23
24
27
28
29
30
36 J
37
38
Volume
of Water,
-------
Table XXVIII. (Cont.)
Day
Volume
of Water,
S>
pH
Acidity Dissolved Ferrous Soluble
as CaCOs, Iron, Iron, Sulfate, Silica,
ppm ppm ppm ppm ppm
41
42
43
45
48
49
50
51
52
55
56
57
58
59
62
63
64
65
66
69
70
71
76
77
78
80
83
84
85
86
87
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
40
100
100
100
100
100
100
100
100
100
2.8
3.0
3.0
3.0
2.9
3.0
3.2
3.0
3.0
2.9
2.9
2.8
2.8
2.8
2.7
2.8
2.8
2.8
2.8
2.6
2.8
2.7
2.6
2.8
2.8
2.9
2.9
2.9
2.9
2.8
2.9
780
630
690
650
830
720
580
760
830
880
770
820
790
730
770
510
480
460
430
470
350
380
450
320
205
190
200
190
210
230
240
265
230
250
270
250
230
200
220
230
270
212
201
201
170
190
110
78
72
78
85
80
95
130
80
56
56
60
56
66
66
50
48
45
40
30
20
13
11
11
13
15
10
10
10
8
10
8
6
5
5
5
5
8
15
5
0
0
0
0
0
0
0
860
780
810
780
540
420
380
420
440
400
360
280
285
230
290
215
180
180
160
170
120
160
180
110
95
90
100
90
110
130
130
70
60
80
60
50
50
40
40
40
45
40
30
30
20
25
20
20
20
20
10
10
12
15
8
6
6
8
5
6
4
4
- 83 -
-------
Table XXVIII. (Cont.)
Day
Acidity Dissolved Ferrous Soluble
as CaCO3, Iron, Iron, Sulfate, Silica,
ppm PPm PPm PPm ppm
90
91
92
93
94
97
98
99
100
101
104
105
106
107
108
111
112
113
114
115
118
119
120
121
122
132
133
134
135
136
139
140
141
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
2.8
2.9
2.9
2.9
2.9
2.8
2.8
2.7
2.7
2.7
2.6
2.6
2.6
2.7
2.6
2.6
2.7
2.6
2.7
2.7
2.6
2.7
2.7
2.6
2.6
2.4
2.5
2.7
2.7
2.6
2.5
2.6
2.6
240
200
180
150
170
190
160
180
180
160
240
260
220
250
310
400
320
350
300
250
300
280
260
240
200
310
210
190
190
200
250
190
160
80
66
56
50
56
80
66
72
80
66
115
90
110
90
100
100
95
88
70
50
75
60
50
50
60
140
75
75
70
65
75
60
50
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
_ .
_____
—
—
—
—
0
0
0
160
110
95
80
120
160
140
110
110
95
190
190
160
170
200
250
310
330
300
270
290
270
250
175
-L 1 *J
190
290
195
170
180
190
225
190
155
8
4
2
2
4
6
4
4
6
2
8
6
6
4
4
8
\j
4
^L
2
2
2
6
2
2
2
£j
2
6
4
2
2
2
6
2
2
- 84 -
-------
Table XXVIII. (Cont.)
Day
142
143
146
147
148
149
150
153
154
155
156
157
160
161
162
163
164
167
168
169
170
171
174
175
176
177
178
181
182
183
Volume
of Water,
£
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
pH
2.7
2.7
2.6
2.6
2.6
2.7
2.7
2.7
2.7
2.8
2.8
3.0
2.9
3.0
3.0
3.1
3.0
2.9
2.9
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
2.9
3.0
3.0
Acidity
as CaCOs,
ppm
150
130
170
150
160
140
140
150
130
110
120
90
100
100
100
90
120
190
200
200
170
170
160
130
110
100
110
110
90
100
Dissolved
Iron,
ppm
40
40
70
50
50
40
40
40
30
30
25
15
30
20
30
20
30
50
50
40
30
30
40
20
25
20
30
30
20
20
Ferrous
Iron,
ppm
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Sulfate,
ppm
145
130
160
140
140
130
125
145
120
105
105
85
95
90
90
85
110
170
190
190
160
150
160
120
100
100
110
110
80
100
Soluble
Silica,
ppm
2
2
4
2
2
2
2
4
2
2
2
2
2
2
2
2
4
8
4
2
2
2
4
2
2
2
2
2
2
2
- 85 -
-------
Table XXIX. Pile D: Aluminia/Silica Gel (Surface Treatment)
Day
1
3
4
6t
10 f
11
12
13
14
17
18
19
20
21
24
25
26
27
33
34
35
38
39
40
42
Volume
of Water,
a
20
100
20
50
100
100
50
100
100
100
100
100
100
100
100
100
100
100
60
100
100
100
100
100
100
pH
10.8
10.4
9.4
8.7
8.2
6.8
6.5
6.5
6.5
6.5
6.5
6.5
6.5
6.5
6.3
6.3
6.5
6.5
6.5
6.3
6.3
5.5
5.0
4.5
6.7 |
6.5
6.5
6.5
Acidity
as CaCO3,
ppm
—
|
—
—
—
5
10
10
10
—
—
—
—
—
—
—
—
—
—
60
120
350
—
—
—
Dissolved
Iron,
ppm*
6
11
6
18
5
5
5
5
5
6
11
15
39
12
25
28
15
12
22
28
39
53
65
78
22
27
22
24
Ferrous
Iron, Sulfate,
ppm ppm
— 250
— 220
— 280
— 245
— 162
— 260
— 180
— 190
— 180
— 230
— 260
— 280
— 190
— 110
— 100
— 85
— 85
— 85
— 100
— 130
— 95
13 140
18 165
33 195
— 95
— 95
— 80
— 80
Soluble
Silica,
ppm
40
40
10
10
5
6
4
5
6
8
12
15
12
8
6
5
4
4
8
15
15
15
10
12
5
5
4
4
*mcludes finely suspended iron hydroxide.
fOn days 6 and 10, only the first and last 2 1 of the total wash were
analyzed.
{Erosion holes plugged with alumina/silica gel.
- 86 -
-------
Table XXIX ( Cont.)
Day
45
46
47
48
49
52
53
54
55
56
59
60
61
62
63
66
67
68
73
74
75
77
80
81
82
83
84
87
88
89
90
91
Volume
of Water,
£
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
40
100
100
100
100
100
100
100
100
100
100
100
100
100
100
Acidity
as CaCO3,
pH ppm
6.5 —
6.5 —
6.5 —
6.7 —
6.7 —
6.5 —
6.3 —
6.3 —
6.3 —
6.2 —
6.2 —
6.2 —
6.2 —
6.2 —
6.2 —
6.0 —
6.1 —
6.2 —
6.1 —
6.0 —
6.0 —
6.0 —
5.6 —
5.5 —
5.5 —
5.6 —
D« D
5.4 —
D« D
5.4 —
5.4 —
5.4 —
Dissolved Ferrous
Iron, Iron, Sulfate,
ppm* ppm ppm
20
18
18
15
15
12
12
15
12
12
15
12
12
15
15
20
12
15
20
25
30
30
55
60
66
55
70
90
66
56
56
44
Soluble
Silica,
ppm
70
80
70
60
60
55
47
45
45
47
55
50
50
50
55
70
60
70
85
95
110
100
330
350
375
310
330
360
380
380
330
365
6
4
5
4
4
5
5
5
4
5
6
4
4
4
4
6
4
6
8
8
4
4
6
4
6
4
4
6
4
4
2
4
* Includes finely suspended iron hydroxide.
- 87 -
-------
Table XXIX ( Cent.)
pH
Acidity
as CaCO3,
ppm
Dissolved Ferrous Soluble
Iron, Iron, Sulfate Silica,
ppm ppm ppm ppm
94
95
96
97
98
101
102
103
104
105
108
109
110
111
112
115
116
117
118
119
129
130
131
132
133
136
137
138
139
140
143
144
145
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
5.2
4.7
4.4
4.4
4.2
4.0
4.0
4.2
3.8
3.6
3.2
3.4
3.2
3.1
3.1
2.7
2.7
2.6
2.7
2.7
2.5
2.5
2.5
2.7
2.5
2.5
2.5
2.5
2.5
2.5
2.3
2.4
2.4
— ._— .
—
___
—
560
550
500
500
450
550
500
500
450
400
490
305
315
340
360
400
380
430
410
450
530
500
500
70
110
110
95
85
110
110
70
100
80
110
130
150
130
130
148
120
110
110
90
230
120
100
90
110
120
120
130
110
130
200
170
160
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
0
0
0
0
0
0
0
0
420
470
420
420
380
418
380
350
330
290
380
330
360
340
280
380
360
380
360
300
405
275
285
310
340
370
340
410
395
420
500
480
470
6
4
6
4
4
8
6
4
4
4
6
4
4
2
2
8
4
4
2
2
12
4
2
2
2
4
2
4
4
2
4
4
2
- 88 -
-------
Table XXIX ( Cont.)
Day
146
147
150
151
152
153
154
157
158
159
160
161
164
165
166
167
168
171
172
173
174
175
178
179
180
Volume
of Water,
i
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
pH
2.5
2.5
2.6
2.7
2.7
2.7
2.7
2.6
2.6
2.7
2.7
2.7
2.7
2.9
2.8
2.9
2.7
2.7
2.9
3.0
3.0
3.0
2.8
2.8
2.8
Acidity
as CaCOs,
ppm
480
460
500
470
480
460
400
430
410
380
360
400
400
310
320
280
280
330
260
230
210
180
220
240
270
Dissolved
Iron,
ppm
150
160
150
140
140
140
100
120
120
100
110
130
100
80
80
90
80
85
70
50
40
30
45
60
85
Ferrous
Iron,
ppm
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Sulfate
ppm
470
450
480
440
460
440
380
400
400
370
330
390
370
280
300
260
260
330
250
200
200
170
220
230
270
Soluble
Silica,
ppm
2
2
6
4
4
4
2
2
2
2
2
2
4
2
2
2
2
2
2
2
2
2
2
- 89 -
-------
Table XXX. Pile E: Alumina/Silica Gel (In-Depth Treatment)
Day
It
•}•
2
3
4
7
8
9
10
11
14
15
16
17
18
21
22
23
28
29
30
32
35
36
37
38
39
42
43
Volume
of Water,
i
50
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
40
100
100
100
100
100
100
100
100
100
100
100
Alkalinity as
CaCO3, ppm*
pH
10.5
9.1
8.3
7.4
6.8
6.8
7.0
7.0
7.0
7.1
7.0
6. a
6.6
6.6
6.5
6.3
6.5
6.3
6.0
6.0
6.0
6.1
6.0
6.0
6.1
6.1
6.0
6.0
P
700
250
110
40
0
10
0
10
12
20
18
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
M
950
320
170
65
20
40
30
60
65
90
85
60
70
70
60
43
70
50
35
20
30
50
40
65
45
30
50
60
Dissolved
Iron,
ppmf
8
15
11
7
5
5
5
5
5
5
5
5
5
5
5
5
5
8
5
5
5
5
8
10
6
5
6
5
Sulfate
ppm
530
380
250
170
190
140
120
140
140
170
150
140
140
160
160
170
180
200
240
190
190
210
190
220
190
175
190
160
Soluble
Silica,
ppm
30
10
6
4
6
5
4
4
4
5
4
4
4
4
6
4
6
8
4
4
6
10
4
6
4
4
6
4
*P alkalinity is obtained by titrating with H2SO4 to the phenophthalein
end point. M alkalinity is obtained by titrating with H2SO4 to the methyl
orange end point. If 2P-M is positive, alkalinity is due to hydroxide. If M-
2P is positive, alkalinity is due to bicarbonate.
•(Includes finely suspended iron hydroxide.
|This pile was violently disturbed on the first day of washing
- 90 -
-------
Table XXX ( Cont.)
Day
44
45
46
49
50
51
52
53
56
57
58
59
60
63
64
65
66
67
70
71
72
73
74
84
85
86
87
88
91
92
93
94
95
Volume
of Water,
i
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
Alkalinity as
pH
6.0
6.0
5.9
6.0
5.9
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.1
6.0
6.0
6.2
6.0
5.8
6.0
6.0
6.0
6.0
CaC03,
P
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
ppm
M
40
70
30
45
40
65
65
50
80
95
70
45
55
70
55
65
60
40
70
80
65
70
90
50
60
60
80
65
40
70
50
55
70
Dissolved
Iron,
ppm
5
5
5
5
8
8
5
5
5
5
5
5
5
10
8
8
10
10
10
8
8
5
5
8
5
5
5
5
5
5
5
5
5
Sulfate,
ppm
100
100
95
95
110
110
95
95
130
110
100
110
95
135
120
130
100
110
130
100
95
76
90
95
80
80
90
80
90
75
85
85
70
Soluble
Silica,
ppm
4
2
2
4
2
4
4
6
8
4
2
2
2
2
2
2
2
2
4
4
2
2
2
10
2
4
2
2
10
6
2
2
2
- 91 -
-------
Table XXX ( Cont.)
Volume Acidity Dissolved Soluble
of Water, as CaCO3, Iron, Sulfate, Silica,
Day i pH ppm ppm ppm ppm
15 95 6
10 80 6
10 90 4
10 115 4
15 120 4
15 95 4
15 95 2
10 100 2
10 90 2
10 65 2
10 50 4
8 40 2
5 40 2
5 55 2
5 40 2
5 40 2
5 40 2
5 40 4
5 30 2
5 30 2
8 60 2
5 40 2
5 40 2
5 40 2
8 40 2
10 60 2
5 80 2
5 50 2
98
99
100
101
102
105
106
107
108
109
112
113
114
115
116
119
120
121
122
123
126
127
128
129
130
133
134
135
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
5.5
5.6
5.6
5.6
5.5
5.7
5.5
5.5
5.6
5.8
5.8
6.0
6.0
5.9
5.9
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
5.9
5.9
6.0
6.0
100
80
100
120
120
100
110
110
90
70
60
40
50
60
40
50
50
40
30
40
60
30
30
20
50
60
20
10
- 92 -
-------
APPENDIX III
AMD GENERATION MECHANISM
Examination of data on Pile A in Appendix II gives some insight into the
mechanism of AMD generation. It is clear that the pile generates an AMD
of a highly concentrated nature, similar to that reported by other investi-
gators. From the data taken on the first and second days, it can be seen
that the inner collection area produced a more concentrated acid water than
the outer area. When the conical shape of the pile is taken into considera-
tion, this result seems reasonable, since the wash water contacted more
acidic rock in the center than in the outer area and therefore should have
been more concentrated.
The results of days 6 through 13 show that regular washings reduce the con-
centration of the AMD, but if the refuse is allowed to sit wet and unwashed
for a few days, the pollutant content of the wash effluent rises again. This
is dramatically verified by the data on days 16 and 23. The pile had been
left for 7 days without being washed, and when the washings were resumed
the resulting AMD was considerably more concentrated than at the beginning
of the 7-day period.
All these observations suggest that the wet pile is slowly generating AMD
and the washings are merely flushing out the previously produced oxidation
products. The fact that the first 20 £ of wash effluent on day 23 were very
concentrated while the next 100 i were far more dilute tends to support this
hypothesis. Yet a small scale laboratory test appears to contradict this con-
cept which has been suggested by other investigators.
A separatory funnel was half filled with fresh coal refuse (about 250 g) and
250-ml quantities of distilled water were passed through the funnel as fast
as it could drain out the bottom (about 2 min per wash). Each successive
wash was started as soon as the previous one had completely drained out of
the funnel. The effluent was analyzed for pH as shown in Table IX. Clearly,
the acid production remained almost constant throughout this test, although
the refuse was completely immersed in water during each wash. The pH
appears to be slowly rising, indicating that the acid water is being washed
out of the rock; yet 2 days later the pH is still at 3.9. Obviously, the con-
cept of AMD being slowly produced and being washed out by "rain" or arti-
ficial washings is not completely satisfactory.
It had been felt that all this washing could have little effect on the composi-
tion of the remaining rock, but the calculation of the total sulfur removed
from the pile proved this untrue. After 570 i of water had passed through
- 93 -
-------
the pile, a total of 3395 g of sulfate or 1132 g of sulfur had been removed
from the rock. If one assumes that the rock is about 12% sulfur, this repre-
sents 4.4% of the total sulfur in the pile.
Table XXXL Rapid Washing of Coal Refuse
Amount of Wash Water pH
500 3.8
750 3.3
1000 3.1
1250 3.3
1500 3.3
1750 3.3
2000 3.3
2250 3.5
2500 3.5
2750 3.7
3000* 3.3
4000f 3.9
* After 1 hr.
' 2 days later.
Examination of the data in Table XXXI shows that the pile is being washed at
a much faster rate than could occur in the natural state. The 570 £ of wash
water is equivalent to about 34 in. of "rain, " almost a year's precipitation
in 3 weeks. From the limited amount of data available, it is not clear what
effect this highly accelerated test rate is having on the data.
-94 -
-------
BIBLIOGRAPHIC:
Tyco Laboratories, Inc., Silicate and Alumina/
Silica Gel Treatment for the Prevention of Acid Mine
Drainage, Final Report FWQA Project No. 14010DLI
April 1870
ABSTRACT
A treatment technique has been demonstrated on
a laboratory scale which Inhibits or prevents the gener-
ation of acid mine water from waste cool refuse. Three
variations of the general method were considered:
1. Neutralization of the water-accessible
refuge with a dilute solution of sodium
silicate (waterglass)
1. Development of a continuous gel on
the refuse surface structure which sealed
off the entire pile from natural runoff
waters
J. Development within the pile structure
of a continuous silica/alumina gel to
eliminate percolation through the refuse
and minimize the effect of natural ero-
sion of the gel structure.
ACCESSION NO.
KEY WORDS
Silica Gel
Acid Mine Drainage
Coal Refuse
Alumina/Silica Gel
Water Pollution
Accelerated Testing
WeatheraWlity
Neutralization
Waterglaas
Gel Forming Methods
BIBLIOGRAPHIC:
Tyco Laboratories, Inc., Silicate and Alumina/
Silica Gel Treatment for the Prevention of Acid Mine
Drainage, Final Report FWQA Project No. 14010DLI,
April 1970
ABSTRACT
A treatment technique has been demonstrated on
a laboratory scale which Inhibits or prevents the gener-
ation of acid mine water from waste cool refuse. Three
variations of the general method were considered:
1. Neutralization of the water-accessible
refuse with a dilute solution of sodium
silicate (waterglass)
2. Development of a continuous gel on
the refuse surface structure which sealed
off the entire pile from natural runoff
waters
3. Development within the pile structure
of a continuous silica/alumina gel to
eliminate percolation through the refuse
and minimize the effect of natural ero-
sion of the gel structure.
ACCESSION NO.
KEY WORDS
Silica Gel
Acid Mine Drainage
Coal Refuse
Alumina/Silica Gel
Water Pollution
Accelerated Testing
Weatherabillty
Neutralization
Waterglass
Gel Forming Methods
BIBLIOGRAPHIC: ACCESSION NO.
Tyco Laboratories, Inc., Silicate and Alumina/
Silica Gel Treatment for the Prevention of Acid Mine
Drainage, Final Report FWQA Project No. 14010DLI,
April 1970
ABSTRACT
A treatment technique has been demonstrated on
a laboratory scale which inhibits or prevents the gener-
ation of acid mine water from waste cool refuse. Three
variations of the general method were considered:
1. Neutralization of the water-accessible
refuse with a dilute solution of sodium
silicate (waterglass)
1. Development of a continuous gel on
the refuse surface structure which sealed
off the entire pile from natural runoff
waters
3, Development within the pile structure
of a continuous silica/alumina gel to
eliminate percolation through the refuse
and minimize the effect of natural ero-
sion of the gel structure.
KEY WORDS
Silica Gel
Acid Mine Drainage
Coal Refuse
Alumina/Silica Gel
Water Pollution
Accelerated Testing
Weatherabillty
Neutralization
Waterglass
Gel Forming Methods
-------
ABSTRACT (Cont.)
Comparison of the effluent water with an untreat-
ed pile shows the neutralized pile was effective for a
minimum of 120 in. of equivalent rainfall in inhibiting
AMD generation. The surface gel was effective for a
longer period of time. The most effective treatment
utilized a mixed alumina/silica gel formed within the
pile at depths up to 6 in. This method was effective for
more than 500 in. of equivalent rainfall, the duration of
the test, and appeared to be exceptionally stable at that
time.
The weathering resistance of the treatment me-
thods was evaluated by heating the ge) treated refuse in
the laboratory and exposing it to rain, snow, and frcezc-
thaw cycles outdoors. Extensive washings of the weath-
ered test materials established the fact that the treat-
ments were effective for at least 120 in. of equivalent
rainfall (the duration of the test) in preventing AMD
generation.
This report was submitted in fulfillment of Con-
tract No. 14-12-560 between the Federal Water Quality
Administration and Tyco Laboratories, Inc.
ABSTRACT (Cont.)
Comparison of the effluent water with an untreat-
ed pile shows*the neutralized pile was effective for a
minimum of 120 in. of equivalent rainfall in inhibiting
AMD generation. The surface gel was effective for a
longer period of time. The most effective treatment
utilized a mixed alumina/silica gel formed within the
pile at depths up to 6 in. This method was effective for
more than 500 in. of equivalent rainfall, the duration of
the test, and appeared to be exceptionally stable at that
time.
The weathering resistance of the treatment me-
thods was evaluated by heating the gel treated refuse in
the laboratory and exposing it to rain, snow, and frcezc-
thaw cycles outdoors. Extensive washings of the weath-
ered test materials established the fact that the treat-
ments were effective for at least 120 in. of equivalent
rainfall (the duration of the test) in preventing AMD
generation.
This report was submitted in fulfillment of Con-
tract No. 14-12-560 between the- Federal Water Quality-
Administration and Tyco Laboratories, Inc.
ABSTRACT (Cont.)
Comparison of the effluent water with an untreat-
ed pile shows the neutralized pile was effective for a
minimum of 120 in. of equivalent rainfall in inhibiting
AMD generation. The surface gel was effective for a
longer period of time. The most effective treatment
utilized a mixed alumina/silica gel formed within the
pile at depths up to 6 in. This method was effective for
more than 500 in. of equivalent rainfall, the duration of
the test, and appeared to be exceptionally stable at that
time.
The weathering resistance of the treatment me-
thods was evaluated by heating the gel treated refuse in
the laboratory and exposing it to rain, snow, and freezc-
thaw cycles outdoors. Extensive washings of the weath-
ered test materials established the fact that the treat-
ments were effective for at least 120 in. of equivalent
rainfall (the duration of the test) in preventing AMD
generation.
This report was submitted in fulfillment of Con-
tract No. 14-12-560 between the Federal Water Quality
Administration and Tyco Laboratories, Inc.
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