WATER POLLUTION CONTROL RESEARCH SERIES
DAST 33
14010 EIZ 01 70
Studies on
Limestone Treatment
of Acid Mine Drainage
U.S. DEPARTMENT OF THE INTERIOR • FF ERAL WATER POLLUTION CONTKOi
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WATER POLLUTION CONTROL RESEARCH SERIES
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Studies on Limestone TreatmeM&f
of
Acid Mine Drainage
Optimization and Development of Improved Chemical Techniques
for the Treatment of Coal Mine Drainage
by
Bituminous Coal Research, Inc.
350 Hochberg Road
Monroeville, Pennsylvania
for the
COMMONWEALTH OP PENNSYLVANIA
DEPARTMENT OF MINES AND MINERAL INDUSTRIES
and
THE FEDERAL WATER POLLUTION CONTROL ADMINISTRATION
DEPARTMENT OF THE INTERIOR
Program Number
' Grant No. lUOlO EIZ
January 1970
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This report has been reviewed "by the Federal
Water Pollution Control Administration and
approved for publication. Approval does not
signify that the contents necessarily reflect
the views and policies of the Federal Water
Pollution-Control Administration.
For sale by the Superintendent ot Documents, V.8. Government Printing Office
Washington, D.C. 20*02 - Price $1.25
ii
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ABSTRACT
Four actual coal mine waters have been neutralized with limestone both
on a batch scale and by utilizing a continuous flow apparatus. Varia-
tions in treatment procedure were necessary depending on the character-
istics of the individual waters.
A standardized test was established to evaluate the reactivity of the
limestones. The following variables are of importance in evaluating
limestones for coal mine water neutralization: (a) particle size,
(b) Ca and Mg content, and (c) surface area.
Ferrous iron oxidation has been accomplished with both synthetic and
actual coal mine water at low pH in the presence of coal-derived
activated carbon.
Electrophoretic mobility studies on precipitates obtained by both lime
and limestone neutralization of coal mine water yielded information
which can be applied for more effective sludge removal.
Magnetic sludges were prepared using two different iron-bearing waters.
The conversion of precipitates to a magnetic form results in signifi-
cant reductions in settled sludge volumes as well as increases in
solids content, compared to the initially formed sludge obtained by
lime neutralization alone.
Data obtained in these studies indicate that the limestone process
offers considerable promise for an improved lower cost method for treat-
ing several types of coal mine waters.
This report was submitted by Bituminous Coal Research, Inc., in fulfill-
ment of a project FWPCA Grant No. 63-01-68, among the Federal Water
Pollution Control Administration, the Pennsylvania Coal Research Board,
the United Mine Workers of America, and Bituminous Coal Research, Inc.
Key Words
Coal Mine Drainage Carbon Catalyst
Neutralization Sludge
Limestone Magnetic Sludge
Oxidation Coagulation
Ferrous Iron , Waste Water
iii
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CONTENTS
Abstract Page
Section 1 Conclusions and Recommendations 1
Section 2 Introduction 3
Section 3 Experimental 9
Section ^ Discussion 23
Section 5 References 95
Abstract Cards 97
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FIGURES
Figure Page
1 Flow Diagram of Conceptual Limestone
Treatment Process .................................. 5
2 Apparatus for Neutralization of Synthetic
and Actual Coal Mine Waters ........................ 11
3 Apparatus for Ferrous Iron Oxidation in the
Presence of Coal-Derived Carbons ................... 15
k Continuous Flow Test Apparatus ....................... 19
5 General View of Continuous Flow System ............... 20
6 Neutralization of Synthetic Coal Mine Water
with No. 1809 Limestone ............................ 31
7 Neutralization of Synthetic Coal Mine Water
with No . 1337 Limestone ............................ 32
8 Effect of Group A Limestones on Synthetic
Coal Mine Water .................................... 36
9 Effect of Group B Limestones on Synthetic
Coal Mine Water ......... . .......................... 37
10 Effect of Group C Limestones on Synthetic
Coal Mine Water .................................... 38
11 Effect of Limestone No. 1809 on Synthetic
Coal Mine Water .................................... 39
»i
12 Model Curve for Judging Effectiveness of Limestones . . ^7
13 Neutralization of South Greensburg Coal Mine
Drainage - Effect of Amount of No. 1809
Limestone on Fes+
1^- Neutralization of Keystone Coal Mine Drainage with
No. 1809 Limestone - Effect of Aeration on Fe2* ____ 50
15 Neutralization of Keystone Coal Mine Drainage with
No. 1809 Limestone - Effect of Aeration on pH ...... 51
vi
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FIGURES (continued)
Figure
16
17
18
19
20
21
22
23
2k
25
26
27
28
PQ
Effect of Activated Carbon on Ferrous Iron Oxidation
Tarrs Coal Mine Discharge ...
Effect of Coagulant Aids on Zeta Potential
Effect of Ludox HS-*K), Ludox AS, and Solution No. 2k
on Zeta Potential of Fe(OH)s
Effect of Na^gO, , Calgon C-55, and Calgon 37
on Zeta Potential of Fe(OH)2
Effect of Lomar D, Primafloc A-10, Purifloc A-21,
and Calgon 2ko on Zeta Potential of Fe(OH)?
Effect of Poly-Floe 1130 on Zeta Potential of
Fe (OH)O
Effect of M and D Clay, "Red Dog," and Fly Ash
on Zeta Potential of Fe(OH)2
Effect of Calgon 2^0, and Calgon 2kO and Fly Ash
on Zeta Potential of Fe(OH)s
Effect of Fly Ash and Calgon 2kO , "Red Dog" and
Calgon 2Uo, and M and D Clay and Calgon 2kO
on Zeta Potential of Fe (OH)2
Effect of Treatment with Fly Ash and Calgon 2ko
on Settling of Fe (OH)2 Sludge
Effect of Poly-Floe 1130, Calgon C-55, Primafloc A-l6
and Solution No. 2k on Zeta Potential of Fe(OH)3...
Effect of Purifloc A-21, Ludox AS, and Lomar D
Effect of Calgon 2kO, Ludox HS-ifO, and Calgon 37
Effervh of Ua>, P~CL on Zeta Potential of Fe(OH\»
Pagt
6k
67
69
70
72
73
75
76
78
8k
85
86
87
vii
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TABLES
Table Page
1 Analyses of Three General Categories of Coal Mine
Water Selected for Study ............................ 2k
2 Limestones Selected for Study ......................... 25
3 Analyses of Thirteen Limestones Originally Selected
for Study - Case I through Case IV .................. 26
4 Analyses of Fourteen Limestones Selected for Study -
Case V .............................................. 27
5 X-ray Analyses of Fourteen Limestones ................. 29
6 Density and Surface Area of Fourteen Limestones ....... 30
7 Effect of Particle Size of Limestones on pH of
Synthetic Coal Mine Water - Case 1 .................. 33
8 Effect of Magnesium Content of Limestone on pH,
One Hour After Neutralization and Oxidation -
Case 1 .............................................. 35
9 "Efficiency" of Limestones - Case II .................. ho
10 Mathematical Relationships Considered in Evaluating
Limestones - Case II ................................ U2
11 "Efficiency" of Limestones - Case III
12 "Efficiency" of Limestones - Case IV
13 "Efficiency" of Limestones - Case V
l4 Batch-scale Limestone neutralization of
South Greenslmrg Coal Mine Drainage ................. 52
15 Batch-scale Limestone Neutralization of Keystone
Coal Mine Drainage .................................. 53
16 Batch-scale Limestone Neutralization of Tarrs
Coal Mine Drainage ........................ . ......... 5^
17 Batch-scale Limestone Neutralization of Thorn Run
Coal Mine Drainage ............................ ; ..... 55
viii
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TABLES (continued)
Table
18 Evaluation of Prepared Carbon Catalysts for
Fes+ Oxidation 58
19 Evaluation of Life of a Prepared Activated
Carbon Catalyst 59
20 Evaluation of Commercially Available Activated Carbons
as Catalysts for Fe2+ Oxidation 6l
21 Evaluation of Life of a Commercially Available
Activated Carbon Catalyst 62
22 Effect of Materials Other than Carbon on Ferrous
Iron Oxidation 65
23 Effect of Coagulant Aids on Fe (OH)a 68
2k Effect of Coagulant Aids on Fe(OH)s and Fe(OH)3 88
25 Froth Flotation Tests 89
ix
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CONCLUSIONS AND RECOMMENDATIONS
Based on the experimental data obtained in this study, we conclude
the following:
Coal mine water can "be neutralized with limestone. Variations
in treatment procedures for coal mine water are necessary depending
on characteristics of the individual waters.
The limestone process for treating coal mine water involves
essentially the same unit operations as the lime neutralization
process for coal mine water. A typical sequence of unit operations
is: (a) holding, (b) adding the neutralizing agent and mixing,
(c) aerating, and (d) sludge settling and disposal.
A method has been established to evaluate the effectiveness of
individual limestones as neutralizing agents for coal mine water.
Evaluation of ik limestones utilized in this research program has
established the properties of these stones which are responsible for
their effectiveness as neutralizing agents. The criteria for effec-
tive limestones are: (a) minimum particle size, preferably minus
325 mesh (less than ^k microns), (b) relatively high calcium content,
approaching pure CaCOs, (c) relatively low magnesium content, thus
eliminating dolomites, CaMgCcOsJg, and magnesites, MgCCfe, an^ (<0
relatively high specific surface area.
The rate of ferrous iron oxidation in actual coal mine water
can be increased by aeration in the presence of coal-derived acti-
vated carbon. None of the other materials tested was found to be
as effective.
As indicated by electrophoretic mobility measurements, the rate
of settling of ferrous hydroxide formed by lime neutralization of
synthetic coal mine water can be increased by the addition of coagu-
lant aids.
Magnetic sludges can be obtained by controlled, partial oxida-
tion of an alkaline (pH 8) suspension of ferrous hydroxide prepared
by the addition of lime to coal mine water having a relatively high
ferrous/ferric iron ratio, and an aluminum/total iron mole ratio
less than 0.12. The conversion to a magnetic sludge proceeds at a
satisfactory rate at temperatiires of 80 C or above. Concentration
of the raw sludge, by means such as gravity separation and/or centri-
fugation, is desirable to minimize the volume of material that re-
quires heating.
Aluminum, in an Al/Fe mole ratio of greater than 0.12, interferes
strongly with the formation of magnetic sludges. When aluminum is
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present in amounts below this mole ratio, magnetic sludge can be ob-
tained, but it is lighter in color, more gelatinous, and bulkier than
magnetic sludges prepared in the absence of aluminum.
Conversion of ferrous hydroxide precipitated from actual coal
mine water to a magnetic form results in at least a five-fold reduc-
tion in settled sludge volume and in a six-fold increase in solids
content as compared to sludges formed by lime neutralization alone.
It is recommended that the following work be conducted to further
optimize the limestone process:
Further development of information on the limestone process uti-
lizing the continuous flow system. Additional data are needed on:
(a) the effect of excess limestone, similar to that from studies al-
ready carried out on batch scale, (b) the effect of sludge recircula-
tion, including volume of sludge, retention times, and the point of
addition, and (c) the effect of coagulant aids on sludge settling.
Further examination of properties of various limestones, such as
surface area and reactivity toward synthetic and actual coal mine
water, to develop a method for selecting the most effective limestones.
These examinations should be directed toward establishing the order of
importance of those properties responsible for the effectiveness of
limestone as a neutralizing agent for coal mine water.
Further development of the limestone process by operation of on-
site research unit(s) based on results from laboratory tests. En-
gineering evaluations would be made of both portable and stationary
field research unit(s). In addition to costs, the number and location
of discharges to be treated, the rate of flow, the number of lime-
stones to be utilized in treatment tests, and other process variables
would be subjects for consideration. Based on data from the field
research unit(s), a full-scale treatment plant would be designed and
evaluated. Engineering drawings of any major items of specialized
equipment should be included in the evaluation together with cost
estimates.
Final development of the process for industrial use by construc-
tion and operation of a full-scale treatment plant based on data from
the field research unit(s).
It is recommended that the conversion to a magnetic form of ferrous
hydroxide sludges obtained by lime neutralization of coal mine water be
explored further as a means of producing more dense sludges, improving
settling rates, facilitating sludge handling, and increasing plant ca-
pacity.
It is further recommended that additional research be conducted on
optimizing the oxidation of ferrous iron in mine drainage by activated
carbon.
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INTRODUCTION
This is the final and summary report on the Pennsylvania Coal
Research Board Project CR-75 activated July 1, 1967, with financial
support from the United Mine Workers of America, the Pennsylvania
Coal Research Board, and Bituminous Coal Research, Inc., and expanded
February 7» 19^8* with additional financial support for the program
through Grant WPRD 63-01-68 to the Commonwealth of Pennsylvania by the
Federal Water Pollution Control Administration.
Work on the project was conducted according to the BCR Research
Proposal submitted to the Pennsylvania Coal Research Board on
December 20, 1966, and as revised in BCR Research Program Proposal
RPP-llOR2 dated June 12, 1967. In regularly scheduled meetings be-
tween the sponsors and the project personnel during the course of the
program, the various facets of the program were clarified and work
areas more clearly defined. The experimental work was conducted during
the period July 1, 1967 to June 30, 1969.
Objectives
The objective of the overall long-range program, is to design and
develop to pilot-plant stage an improved process for the control and
prevention of pollution of waters by drainage from coal mines, con-
ducting laboratory studies to obtain needed design data.
The objectives of the studies conducted in the period covered by
this report were: (a) to improve and optimize the chemical techniques
involved in the treatment of coal mine drainage with emphasis placed
on limestone neutralization processes, and (b) to further develop,
using laboratory pilot scale equipment, the most promising system as
judged on the basis of engineering evaluations.
Nature and Scope of the Problem
Acid mine drainage results from the dissolution of oxidation prod-
ucts of pyrite in normally neutral to mildly alkaline ground water.
The oxidation of pyrite occurs by exposure to air and water of pyritic
materials associated with the coal seam. Acid drainage seriously pol-
lutes some 5,700 miles of the 10,500 miles of streams affected by all
forms of mine drainage and represents a significant environmental prob-
lem in portions of the Appalachian Region.(l) Inactive sources con-
tribute 78 percent of the acid and active sources 22 percent.(2)
Lime neutralization treatment in conjunction with aeration and
settling ponds is the process most generally used or considered for use
in treating coal mine drainage. For example, it has been stated that of
252 mine drainage locations requiring treatment facilities in the state
of Pennsylvania, 2^3 are using a lime neutralization treatment.
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The claimed advantages of limestone neutralization over lime neu-
tralization are: (a) lower costs for chemical reagent, (b) decreased
hazard to the operator handling a less reactive reagent, (c) little or
no harmful effect on streams and stream life from an accidental over-
treatment, and (d) potential for decreased sludge volume by an increased
solids content in sludge.
Two recent reports (3»^) of limestone neutralization studies de-
scribe treatment of coal mine water containing iron principally in the
ferric state, Fe3* . A greater problem exists in the treatment of coal
mine water containing iron principally in the ferrous state, Fe8* .
Oxidation of the ferrous iron, Fe , •whether induced or natural, and
subsequent hydrolysis leads to the production of more free acid, H1" .
This can be represented by the following reaction.
Fe2* + QS + HgO -»Fe(OH)a + if
It is significant that in the formation of a ferric precipitate,
which can be a chemical form other than Fe(OH)3, the overall reaction in-
cludes the production of an excess of H1" thus leading to an acidic con-
dition requiring further neutralization.
While considerable -work has been done in this country and abroad on
the treatment of coal mine drainage with lime and limestone (5,6,7>8),
many gaps exist in the data. Because of this lack of information,
diverse opinions of the applicability of lime and limestone neutraliza-
tion have been held by -workers in the field (7,9,10). Little systematic
research has been conducted to resolve the differences in results achiev-
ed. The present program of laboratory investigation vas designed to re-
solve some of these differences by exploring various facets of the neu-
tralization process and to arrive at a promising system for coal mine
drainage neutralization.
Approach to the Problem and Research Procedure
The neutralization of coal mine drainage entails a series of indiv-
idual unit operations namely, (a) holding, (b) adding and mixing of the
neutralizing agent, (c) aeration, and (d) solids separation and disposal.
One concept of the limestone treatment process is given in Figure 1.
A study of the individual factors affecting each of the unit opera-
tions was undertaken to optimize the overall neutralization process.
Assessment of Coal Mine Water Composition
Coal mine water is, by its very nature, a variable entity. Chemi-
cal composition and flow rate from a single discharge varies depending
on pumping operations, path through the mine, amount of rainfall, and
temperature. Even more variation is found in discharges from different
locations .
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Sludge
Recirculation
(Optional)
Coal
Mine
Water
Holding
Tank
Limestone
Reactor
Aerator
Settling
Tank
Sludge To
Disposal
Pulverized
Limestone
Storage
Tank
Oxidation
Catalyst
(Optional)
Air
Coagulant Aid
(Optional)
Treated Water
To
Receiving Stream
Bituminous Coal Research, Inc. 2030G54
Figure 1. Flow Diagram of Conceptual Limestone Treatment Process
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Therefore, it was necessary to characterize several coal mine dis-
charges in detail, to select certain waters representing a wide range in
compositional characteristics, and to determine the amenability of these
waters to the treatment process.
Evaluation of Limestone
Limestones vary considerably in composition and structure. There-
fore, if limestones are to be used as neutralizing agents for coal mine
water, it is necessary to establish the criteria for evaluating them
for this purpose. The effect of chemical composition, particle size,
surface area, and other properties of the limestones on reactivity with
coal mine water was studied.
Batch-scale Neutralization of Actual Coal Mine Water
The objectives of this study were to establish (a) the effective-
ness of limestone as a neutralizing agent for coal mine water, (b) the
types of coal mine water amenable to treatment with limestone, and
(c) the techniques and unit operations involved in limestone neutral-
ization.
Oxidation of Ferrous Iron
The ferrous iron present in some coal mine water is more resis-
tant to oxidation by aeration than that in other discharges. To pro-
mote the neutralization with limestone in such a water, it may be
necessary to find a catalyst for the oxidation of ferrous iron in an
acid medium.
Initial studies involved preparation and testing of a catalyst
derived from coal. Later, emphasis was placed on the further investi-
gation of coal-derived, commercially available activated carbons for
use as catalysts.
Non-oxidative Neutralization and Addition of Coagulant Aids
As far as is known, direct, non-oxidative neutralization for the
removal of iron has neither been evaluated nor applied in practice. The
availability of such a technique would eliminate the need for oxidation
of ferrous iron to ferric iron. Studies were conducted to determine the
extent to which iron could be precipitated as ferrous hydroxide with lime
and removed without oxidation of the iron to the ferric state. Studies
were also made on addition of coagulant aids to improve the settling
characteristics of sludges.
Magnetic Sludge Studies
Previous work at BCR and elsewhere has confirmed that a magnetic
sludge may form during lime neutralization of coal mine water. A sludge
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of this type could be more easily removed by commercially available wet
or dry magnetic separators. One objective of the present study was to
explore the conditions under which magnetic sludge forms. A sludge of
this type would be denser and settle faster than the sludge usually
formed by lime or limestone neutralization.
Miscellaneous Studies
Areas explored in miscellaneous studies were: (a) the effect of
coagulant aids on the Fe(OH)3 sludge that will be formed in a limestone
neutralization process, (b) flotation, as a technique to separate the
sludge from the treated water, (c) use of a calcium ion electrode to
detect changes in concentration (activity) of Ca2* during neutralization,
and (d) activities on ASTM Committee D-19 on water, related to the anal-
ysis of coal mine water.
Continuous Flow Tests
A small laboratory pilot plant was utilized to examine the lime-
stone treatment process for coal mine water under flow conditions which
approximate actual treatment plant operations more closely than batch
tests.
Process Evaluations
Near the end of this present study, the overall technical and econ-
omic feasibility of chemical techniques developed during the course of
the program, and the merit of further development of these techniques on
a laboratory-scale were considered. Data obtained from the laboratory
studies were used for process engineering evaluations.
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EXPERIMENTAL
Apparatus and general procedure for conducting experiments are
described below in the various categories: (a) assessment of coal
mine water composition, (b) evaluation of limestones, (c) batch-scale
neutralization of actual coal mine water, (d) oxidation of ferrous iron,
(e) non-oxidative neutralization and addition of coagulant aids, (f)
magnetic sludge studies, (g) miscellaneous studies, (h) continuous flow
tests, and (i) process evaluation. (See schedule of work as given in
Figure 2 above).
Assessment of Coal Mine Water Composition
After examination of a number of coal mine water discharges in
the vicinity of the BCR laboratories, four were selected for study
on this program. These discharges are classified into three cate-
gories: (a) ferrous iron water containing little or no aluminum,
(b) ferrous iron water containing a substantial amount of aluminum,
and (c) ferric iron water.
Samples were analyzed routinely for: (a) ferrous iron colori-
metrically using the o-phenanthroline method, (b) cations, Si, Al, Fe,
Ca, Mg, Mn, and Na by emission spectrographic techniques, (c) acidity
by adding hydrogen peroxide, boiling, cooling to room temperature, and
titrating to pH 8.2, and (d) pH.
Evaluation of Limestones
The reactivity of lU selected limestones was evaluated by con-
sideration of (a) their physical and chemical properties, and (b)
their effectiveness in neutralizing synthetic coal mine water.
Chemical Properties of the Limestones
The chemical composition of the individual limestones was de-
termined by conventional emission spectrographic techniques using a
Jarrell-Ash1 Model 78-000 1.5 meter Wadsworth grating spectrograph.
Structure was determined by x-ray diffraction analyses utilizing a
Picker Nuclear powder diffraction unit.
Physical Properties of the! Limestones
Densities of the Ik limestones were determined with a Beckman
air pycnometer. Surface areas were measured by the standard BET
1 Mention of commercial products throughout this report does not imply
endorsement by the Federal Water Pollution Control Administration.
9
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(Brunauer, Emmett, and Teller) technique using nitrogen as the adsorbate
at liquid nitrogen temperatures or "by a modified BET technique using a
Micromeritics Model 2200 surface area analyzer.
Neutralization Reactions
In five series of neutralization tests (Cases I-V) the reactivity
of the limestones toward synthetic coal mine water was observed by vary-
ing the amount of limestone, the amount and type of oxidant, and the
time at which the oxidant was added.
The general procedure for conducting the neutralization reactions
follows:
Varying amounts of limestone and oxidizing agent (air or hydrogen
peroxide) were added to 1500 ml of a synthetic coal mine water con-
taining 220 ppm of Fe8* added as ferrous sulfate and having the pH ad-
justed to 3-0 with sulfuric acid. The solution (mixture) was stirred
continuously for a 5-5 hour period and changes in pH recorded with
time. Samples were withdrawn periodically and analyzed for Fe8*. The
amount of limestone added was based on the acidity of the synthetic
coal mine water; the amount of hydrogen peroxide was based on the con-
centration of Fe3*. The apparatus for conducting these experiments is
shown in Figure 2. An Orion Model ^K)l meter with a Sargent/Jena com-
bination electrode was used to measure pH and a Houston Instrument
Omnigraphic T-Y recorder, Model HR-80, was employed to record changes
in pH.
Case I
Thirteen stones were tested. The amount of limestone added was
twice the stoichiometric amount based on acidity of the synthetic coal
mine water. This amount was selected from studies on batch-scale neu-
tralization of actual coal mine water, (see Figure 13). The amount of
limestone was also based on the assumption that the stones consisted of
pure CaCCfe. The amount of hydrogen peroxide added was three drops, ap-
proximately 0.4 times the amount necessary to completely oxidize the
ferrous iron present. The limestone was added at the start of the test.
The Hs.03 was added either (a) when pH reached 6.0 after addition of lime-
stone- (and would have continued to increase), or (b) when pH had leveled
off at a value less than 6.0. In most instances, a coarse, a medium,
and a fine fraction of .each stone were tested.
Case II
Thirteen stones were tested. As in Case I, the amount of limestone
added was twice the stoichiometric amount based on acidity of the syn-
thetic coal mine water and was also based on the assumption that the
stones consisted of pure CaCOs. Three drops of 30 percent hydrogen per-
oxide ^ere added, approximately 0.^ times the amount necessary to com-
10
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Figure 2. Apparatus for Neutralization of Synthetic and Actual Coal
Mine Waters
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pletely oxidize the ferrous iron present.
All experiments in Cases II-V were conducted with 325 x hoo mesh
limestones, and with the limestone and the oxidizing agent (hydrogen
peroxide or air) being added together.
Case III
Thirteen stones were tested. The limestone again was assumed to be
pure CaCOk, and the amount added was twice the stoichiometric amount
based on acidity of the synthetic coal mine water. The amount of 30 per-
cent peroxide added was increased to 0.5 ml, approximately 1.6 times the
stoichiometric amount necessary to completely oxidize the ferrous iron
present.
Case IV
Thirteen stones were tested. An excess amount, 0.5 ml, of 30 per-
cent hydrogen peroxide was,added, as in Case III. An. adjustment was
made in the amount of limestone to compensate for materials in the stones
other than CaCOg or MgCOs. The weight of limestone chosen was sufficient
to provide twice the equivalent stoichiometric amount of pure CaCQs based
on acidity. This amount was calculated using the formula:
wt = (2X) x 100
(% CaO)+ (% MgO) (55.08/40.32)
where
Wt = weight of limestone in grams
X = stoichiometric amount of pure CaCOg
based on acidity
Case V
Fourteen stones were tested. The amount of limestone added was
twice the stoichiometric amount based on the acidity of the synthetic
coal mine water and was also based on the assumption that the stones con-
sisted of pure CaCGb . Instead of adding hydrogen peroxide, air at a rate
of 2500 ml/min was bubbled continuously into the solution through a frit-
ted glass disk at the bottom of the beaker.
Batch-s^cale Neutralization of Actual Coal Mine Waters
A study was made of the conditions under which actual coal mine wa-
ter could be neutralized with limestone on a batch scale. Using data
from the preliminary study, a standardized procedure was chosen for
batch-scale limestone neutralization of four actual coal mine waters!-™
South Greensburg, Keystone, Tarrs, and Thorn Run. Differences in re-
sponse of these waters to this standardized procedure were observed.
12
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Compositional differences among the four waters were confirmed by ele-
mental analysis.
Conditions for the neutralization experiments were: a sample of
each water was treated on the same day as received in the laboratory,
the first one at 18 C and then a second at 22 C. Temperature of the
water as sampled ranged from 11 to lU C. Twice the stoichiometric
amount (based on determined acidity of the samples and assuming the
limestone to be pure CaCCfe) of No. 1809 limestone, 325 x koo mesh, was
added to 1500 ml of the actual coal mine water in a 2000 ml beaker.
Then for 90 minutes the mixture was stirred at a constant rate and
aerated at 2500 ml/min with compressed air introduced through a medium
porosity fritted glass disk. The apparatus used is illustrated in
Figure 3.
A series of analyses was performed on 100 ml aliquots of each
water (a) as received, (b) after treatment for 90 minutes, (c) after
treatment for 90 minutes and having stood undisturbed overnight, and
(d) after treatment for 90 minutes, having stood overnight, and then
having been aerated and stirred for an additional 30 minutes.
Ferrous iron was determined colorimetrically using o-phenanthro-
line. Sulfates were determined gravimetrically. Acidity was determined
by adding hydrogen peroxide, heating, and titrating to pH 8.2. Si, Al,
Fe, Ca, Mg, Mn, and Na were determined using an emission spectograph.
Eh was measured using platinum-calomel electrodes. Electromotive force
(EMF) values were determined and converted to the standard hydrogen
electrode scale (Eh) by the addition of the saturated calomel reference
electrode potential, 2^2 millivolts. For the sake of conformity with
most existing pertinent literature, the so-called European sign con-
vention for electrode potentials was adopted; standard redox potentials
for couples above hydrogen in the electromotive force series were given
negative signs while those below were considered positive.
Conductivity was measured using a Hach conductivity meter, Model
2200. Dissolved oxygen was determined with a Yellow Springs, Model 5^,
oxygen meter equipped with a Clark-type membrane-covered polarographic
probe. Turbidity was determined using a Hach laboratory turbidimeter.
Dissolved solids were determined gravimetrically by evaporating a
weighed amount' of solution to dryness. The zeta potential was calcula-
. ted from electrophoretic mobility data determined with a Zeta-Meter
(Zeta-Meter, Inc., New York, New York). This instrument also allowed
determination of conductivity with electrophoretic mobility.
i
Oxidation of Ferrous Iron
The objective of this study, to find a catalyst for the oxidation
of ferrous iron in an acid medium, was carried out (a) by preparing a
catalyst from cpal3 (b) by testing the prepared catalyst, (c) by testing
commercially available activated carbons, and (d) by testing other
13
-------
materials which might have catalytic properties.
Catalyst Prepared from Coal
The first experiments dealt primarily with the development of sat-
isfactory procedures for preparing an active material from coal. As a
result of many experiments, the following procedure for making an active
carbon evolved:
Devolatilization of minus Uo mesh coal at 500 to 800 C.
Crushing resultant coke to minus ko mesh.
Activation in air of crushed coke at 300 to 600 C.
Calcination at 700 to 1000 C.
Test for Catalytic Activity
The standard test, developed to evaluate carbons and other materials
as aids in the oxidation of ferrous iron, consisted of the following
steps:
A quantity (l6 g) of the test material was washed twice with 20
ml portions of 6 N HC1, twice with 20 ml portions of deionized water,
then washed two more times with a special test solution prepared by
adding 200 ppm of ferrous iron as ferrous sulfate to deionized water
and adjusting the pH to 3.0 with sulfuric acid. The washed material
was then placed in a reactor tube (Figure 3)1 together with 150 ml of
test solution. Air was bubbled at a selected rate into the mixture
through a medium porosity fritted disk at the bottom of the reactor
tube. The decrease in ferrous iron in the sample was determined
periodically by dichromate titration using a Sargent Model D record-
ing titrator. At the end of a specified period of time, the test
solution was removed and 150 ml of fresh test solution added to start
a new cycle or test.
Kon-oxidative Neutralization and Addition of Coagulant Aids
Studies of the non-oxidative neutralization process involved: (a)
precipitation of ferrous hydroxide from synthetic coal mine water by
addition of lime, and measurement of eleetrophoretic mobility (zeta
potential) of the precipitated ferrous hydroxide as formed^ and as changed
by the addition of coagulant aids (electrolytes, polyeleetrolytes, -and
inert solids); and (b) utilization of data from (a) in settling tests.
Materials
Synthetic Coal Mine Water
Fresh quantities of synthetic coal mine water were prepared as
needed. Ferrous sulfate was added to deionized water to yield a solu-
tion containing 250 ppm of Fe2* . The pH of the solution was then ad-
justed to 3-0 by addition of sulfuric acid.
H
-------
(2030P26)
Figure 3. Apparatus for Ferrous Iron Oxidation in the Presence of Coal-
Derived Carbons
-------
Ferrous Hydroxide Suspension
Reagent grade lime, Ca(OH)s, was added as a solid to synthetic coal
mine water in quantity equal to the stoichiometric amount based on
acidity of the coal mine water. The resultant suspension attained a pH
in the range 10.5 to 11.5-
Polyelectrolytes and Electrolytes
Polyelectrolytes were prepared according to specifications of the
manufacturer; this involved, initially, preparation of a concentrated
solution by non-shear mixing of the polyelectrolyte with deionized water.
Then, a 1000 ml stock solution containing 1000 ppm of polyelectrolyte
was prepared by dilution of the concentrate with deionized water. Fresh
stock solution was prepared as often as necessary because of deteriora-
tion due to aging. Essentially the same procedure was employed in pre-
paring stock solutions of the electrolytes.
Inert Solids
The inert solids selected for testing were: (a) M and D clay, a
ball clay, (b) "red dog" collected from a pile of burned-out coal refuse
material in Westmoreland County, Pennsylvania, and (c) fly ash collected
from a stack at a pulverized coal-fired electric utility power station.
These materials were added as solids without further preparation.
Electrophoretic Mobility Studies
Selected amounts of coagulant aids were added to 100 ml portions of
ferrous hydroxide suspension and stirred for one minute. Electrophoretic
mobility of the resultant mixture was then measured and a graph prepared
of the observed zeta potential values versus concentration of each co-
agulant aid.
In certain tests, the inert solid was added to synthetic coal mine
water first, followed by lime, and then finally by the polyelectrolyte.
Settling Rate Studies
Coagulant aids were added to 2000 ml of ferrous hydroxide suspen-
sion; the entire mixture was stirred for one minute, and then transferred
to a 2000 ml graduated cylinder. The line of demarcation between solids
and water was observed periodically for times up to 2.5 hours.
Magnetic Sludge Studies
To explore conditions under which a magnetic sludge can be formed
during coal mine water neutralization, tests were conducted using both
synthetic and actual coal mine water. The following procedure for these
tests was adopted:
16
-------
Synthetic test solutions were prepared "by adding specified
amounts of ferrous sulfate to deionized water and adjusting the pH
to 3-0 with sulfuric acid. Test samples of actual mine water were
obtained from either the South Greensburg or the Keystone discharge.
A 1500 ml sample of test solution was transferred to a 2000 ml
beaker; then a mechanical stirrer, thermometer, and EMF and pH
electrodes were introduced. Slow, constant-speed stirring was com-
menced, and initial values of Eh, pH, and temperature were recorded.
Either IN NaOH solution or solid hydrated lime, Ca(OH)s, was added
to precipitate ferrous hydroxide. Eh, pH, and temperature were re-
corded at the start and periodically thereafter at about 15 minute
intervals. Stirring was stopped momentarily while changes in Eh,
pH, temperature, magnetic response (determined qualitatively with a
small permanent magnet), and color of the precipitate were observed.
In cases where aeration was utilized to accelerate the oxidation of
ferrous iron, air flow was measured with a small rotameter. The
rate of stirring was held constant in all runs.
The effects of reaction pH, impurities, reaction temperature,
and sludge concentration on formation of magnetic sludge were noted.
Miscellaneous Studies
Effect of Coagulant Aids on Fe(OH)3
The effect of selected coagulant aids on zeta potential of ferric
hydroxide resulting from limestone neutralization of synthetic coal
mine water was examined.
The ferric hydroxide was prepared in the following manner: Lime-
stone No. 1809, 325 x hOO mesh, was added to 1500 ml of synthetic coal
mine water containing 250 ppm of Fe2* and adjusted to pH 3-0 with sul-
furic acid. The amount of limestone used was twice the stoichiometric
amount based on acidity of the synthetic coal mine water sample. Con-
version of the ferrous iron to ferric hydroxide, Fe(OH)3, was completed
in 90 minutes by aeration. Final pH of the mixture was 7-8.
Various amounts of selected coagulant aids were added to 100 ml
aliquots of the resultant ferric hydroxide-limestone mixtures. Electro-
phoretic mobility of the sludge particles was then measured using a
Zeta-Meter; a graph was prepared of calculated zeta potential values
versus concentration of each coagulant aid.
Flotation Studies
A limited study involving separation of ferric hydroxide formed by
limestone neutralization of actual coal mine water was conducted uti-
lizing standard froth flotation equipment and procedures. Samples
(2500 ml) of limestone-neutralized South Greensburg discharge obtained
17
-------
from continuous flow apparatus experiments were stirred and aerated at
constant rates in a sub-aeration type Wemco Pagergren apparatus. Selec-
ted froth promoters, sample conditioners, and coagulant aids were added
in various combinations. The amount of sludge solids that reported to
the froth and tailings was then determined.
Calcium Ion Electrode Studies
The calcium ion electrode was investigated for use in measuring the
solubility of limestones in mine water. A calibration curve was prepared
using solutions of pure CaClg with concentrations from 1 x 10~a to
1 x 10"3 M. Activity or concentration of Ca2* ion versus the electrode
potential as measured with the Orion calcium ion electrode was plotted
on semi-log graph paper.
ASTM Activities
As members of ASTM Committee D-19 on Water, project personnel par-
ticipated in the development and round robin testing of a method for de-
termination of acidity "specifically for mine drainage, surface streams
receiving mine drainage, industrial waste acids and their salts, and
similar waters bearing substantial amounts of ferrous iron or other poly-
valent cations in a reduced state."
The round robin sampling, testing, and compilation of data have not
been completed by the committee. If satisfactory results are obtained
in the round robin, the method is to be proposed as a tentative standard
at the January 1970 ASTM D-19 meeting.
Continuous Flow Tests
A continuous flow test apparatus was designed and constructed for
use in evaluating the limestone neutralization process.
Figure k is an artist's conception of the continuous flow system.
A photograph of the actual system is shown in Figure 5. A description
of materials, equipment, and operation follows:
Reservoir: The reservoir has a total capacity of 210 gallons
and consists of two Glascote glass-lined tanks each having bottom
discharge and lids. The tanks have 150-gallon and 60-gallon capaci-
ties .
Sample Cooling and Circulating System; A Forma "Forma-Temp"
portable cooler is used to maintain the sample at temperatures as low
as k6 F. The cooler has a rated capacity of UOOO Btu/hr. Circula-
tion of the sample between the two reservoirs is accomplished by use
of a Gorman Rupp Model 11698, 5^00 Series pump, with a Gorman Rupp
Model 12500-21 oscillating pump used for priming.
18
-------
Legend
A — Limestone Reactor
B — Reservoir
C — Reservoir
D — Vibra Screw Feeder
E — Aeration Tank
F — Settling Tanks
Bituminous Coal Research, Inc. 2030G56
Figure 4. Continuous Flow Test Apparatus
-------
(2030P7)
Figure 5. General View of Continuous Flow Syst
em
-------
Limestone Reactor: The stirred tank reactor consists of a
6o-gallon stainless steel tank equipped with four 2-inch stainless
steel baffles. Stirring is accomplished by use of a "Lightnin"
Model ND-1A. 1/k horsepower, 1750 rpm motor, 350 rpm propeller,
portable mixer equipped with two ?•7-inch diameter propellers. The
sample is transferred to the stirred tank reactor from the reservoir
using a Gorman Bupp Model 11698, 5600 Series pump. The flow rate is
controlled by a 1/2-inch Whitey Model 1BS8-316 stainless steel needle
valve, and is measured by a Brooks Model 1305 flowmeter. Compressed
air is introduced into this tank through a manifold consisting of h
spherical gas diffuser stones (Fisher Scientific) mounted at the end
of 3/l6-inch stainless steel tubing.
Limestone Feeder: Pulverized limestone is fed to the reactor
by a Vibra Screw feeder equipped with a 1/^-inch diameter feed screw.
Aeration Tank; The polyethylene cylindrical tank has a capacity
of 80 gallons and has an air manifold identical to the one mentioned
above. Gravity flow from the stirred tank reactor into the aeration
tank is controlled by a polypropylene ball valve.
Activated Carbon Reactor; The circular, 1^-inch diameter stain-
less steel basket is 4 inches deep and is divided into four quarters.
Carbon is equally distributed into four sections and held loosely
with porous cloth. The entire apparatus is covered with 18 mesh
stainless steel woven wire cloth and is immersed in the aeration
tank a few inches above the gas diffuser stones.
Settling Tanks; Two 90-gallon settling tanks are used to col-
lect the sludge. These tanks are constructed of 316 stainless steel.
Piping; Piping is stainless steel, except for the large diameter
flexible Tygon connectors between the settling tanks.
An auxiliary portable pumping system consists of a Gorman Rupp
Model 11698, 5600 Series, and a Gorman Rupp Model 12500-21 oscilla-
ting pump.
The general procedure used for treating coal mine water in this
system follows:
A total of 125 gallons of coal mine water was treated over a
2.5 hour period under flow conditions. The limestone reactor was
filled initially with 50 gallons of coal mine water, the appropriate
amount of limestone added, and the mixture stirred for 50 minutes.
After this initial period, the flow of coal mine water was ad-
justed to 1 gpm both from the reservoirs to the limestone reactor and
from the limestone reactor to the aeration tank.
21
-------
Additional limestone was added at a constant rate of twice the
stoichiometric amount based on acidity.
Compressed air was fed into the aeration tank as it was being
filled to the 50 gallon mark; aeration was continued and the level
held at 50 gallons by pumping the aerated sample into the settling
tank. Water remaining in the aeration tank at the end of the test
was pumped into the settling tanks.
Aliquots (200 ml) were withdrawn periodically from the mixing
tank, the aeration tank, and the two settling tanks; the pH and fer-
rous iron concentration were determined on each.
-------
DISCUSSION
Assessment of Coal Mine Water Composition
Analytical data covering the four coal mine waters selected for
study on this program are given in Table 1. Although every coal mine
discharge is unique, these four discharges represent three significant
categories for purposes of this study: South Greensburg and Keystone
discharges represent category (a), a ferrous iron water containing
little or no aluminum; Tarrs falls into category (b), a ferrous iron
water containing a substantial amount of aluminum. The Thorn Run dis-
charge represents category (c), a ferric iron water.
Evaluation of Limestones
Limestone is a general term embracing carbonate rocks or fossils;
it is composed primarily of calcium carbonate or combinations of cal-
cium and magnesium carbonate with varying amounts of impurities, the
most common of which are silica and aluminum (ll). If "limestone" is
to be used as a neutralizing agent for coal mine water, the questions
arise as to which type of limestone, or are all limestones equally
effective?
To attempt to answer these questions, various types of limestones
were secured specifically for this study. They are listed in the or-
der received, in Table 2, together with the reasons for their
selection.
A series of neutralization reactions was devised to measure the
pH response (reactivity) resulting from addition of these stones to a
synthetic coal mine water (acidified ferrous sulfate solution); a
suitable oxidizing agent was also added. Differences in pH response
were then related to the chemical composition and physical properties
of the limestone.
Chemical Properties of the Limestones
Table 3 contains a summary of the analyses of the thirteen lime-
stones originally selected for study. These analyses were performed
on the overall batch of limestone as received and were used in eval-
uating the experiments listed below under Case I through Case IV.
After completion of Case IV experiments, the analyses were re-
peated on the narrow particle size range material used in Case II
through V experiments. The results of these analyses are listed in
Table 4. Limestone No. 1462 was added to the list as an example of a
magnesite, MgCO^, because experimental evidence obtained during the
23
-------
TABLE 1. ANALYSES OF THREE GENERAL CATEGORIES OF COAL
MINE WATER SELECTED FOR STUDY
Fes* % Acidity,
Spectrographic Analysis, ppm of Total ppm as S04S",
Category Source pH Fe Al Mn Ca Mg_ Si Na Fe CaCOa ppm
a South
Greensburg k.7 123 8 h 210 Ik 1^ 88 91 250 llto
a
Keystone 6.0 330 <3 ^ 235 9*f 7 1000 95 265 3630
b
Tarrs 2.? 122 55 ^ 191* 83 hi — 79 752
c
Thorn Run 2.If 168 102 16 192 78 28 38 5 1285
-------
TABLE 2. LIMESTONES SELECTED FOR STUDY
BCR
Sample No.
1335
1337
1352
1355
1362
Source
1U62
1809
2135
2136
2177
Hills Material Co.
Rapid City, South Dakota
Mineral Pigments & Metals
Chas. Pfizer
Gibsonburg, Ohio
H. E. Millard Lime & Stone Co., Inc.
Annville, Pennsylvania
Elkins Limestone
Elkins, West Virginia
Nickajack Dam-Fernvale Co.
Limestone TVA
Giant Portland Cement Co.
Egypt, Lehigh County, Pa.
Basic, Inc.
Gabbs, Nevada
Basic, Inc.
Gabbs, Nevada
J. E. Baker Co.
York, Pennsylvania
Winfield Lime & Stone Co., Inc.
West Winfield, Pennsylvania
Appalachian Stone Co.
Lake Lynn Plant
Mercersburg, Pennsylvania
Greer Limestone Co. '
Greer, West Virginia
McClout Yards
Marine City, Michigan
German Valley Limestone Co . >
Riverton, West Virginia via
Mr. Ronald Hill
Reason for Choice
Good performance in air
pollution studies at BCR
High Mg
High Mg
High Si
High Fe t
High Al
First thought to be a
magnesite, later proved
to be a dolomite
Magnesite
Poor performance in air
pollution studies at BCR
Used at Rochester &
Pittsburgh Coal Co. for
coal mine water
neutralization
Used by Bureau of Mines
for coal mine water
neutralization studies
Used by Bureau of Mines
for coal mine water
neutralization studies
Used in S0a removal
tests at an electric
power generation plant
Used at Norton Mine
Drainage Treatment
Laboratory
-------
TABLE 3. ANALYSES OF THIRTEEN LIMESTONES ORIGINALLY SELECTED TOR STUDY.
CASE I THROUGH CASE IV
Spectrochemical Analyses, Mineral Samples
Reported as Percent by Weight of Ignited Sample (900 C)
BCR
Sample
No.
1335
1337
1352
1355
1362
1364
1461
1654
1809
2135
2136
2145
2177
Loss on
Ignition SiOg
42.9 3.2
47.
43.
33.
33.
33.
50.
46.
4l.
35.
37.
41.
43.
5
2
3
6
1
2
0
5
6
3
4
0
0.78
7.4
27-5
15.2
23.1
2,61
2.56
5.90
19.4
15.4
2.05
1.0
0.67
0.15
2.31
5.75
3.70
8.20
0.45
0.6l
1.99
5.4o
4.io
0.60
0.43
FeaOa
0.38
0.25
1.85
2.48
21.0
2.60
0.86
1.87
1.50
2.38
1.78
0.48
0.15
MgO
0.69
45.0
30.0
1.85
3.20
3.30
90.0
36.0
1.34
2.55
2.90
1.69
1.16
CaO
94.0
53-0
56.0
60.0
55.0
58.0
4.35
58.0
88.0
68.0
71.0
92.0
97.0
TiOa
0.05
0.02
O.l4
0.33
0.29
0.35
0.03
0.05
0.07
0.23
0.18
o.o4
o.o4
0.02
<0.02
0.08
0.44
0.08
0.61
0.02
0.08
0.07
0.36
0.46
0.03
0.02
KgO
<0.1
00.1
0.77
0.87
0.66
i.4o
0.10
<0.1
0.28
1.03
0.79
0.1
O.I
MnOa
0.03
O.03
O.03
0.05
0.44
0.08
0.03
6.i4
o.i4
0.03
0.03
0.03
0.03
-------
TABLE 1*. ANALYSES OP FOURTEEN LIMESTONES SELECTED FOR STUB?.
CASE V
Spectrochemical Analyses, Mineral Samples
Reported as Percent by Weight of Ignited Sample (900 C)
BCR
Sample
No.
1335
1337
1352
1355
1362
1361*
ll*6i
11*62
165!*'
1809
2135
2136
2ll*5
2177
Loss on
Ignition
1*2.8
1*6.5
1*2.6
31*. o
36.1
30.1*
1*7.2
1*8.1*
1*5.8
1*2.1
3l*.6
36.7
1*1.7
1*2.7
SiOg
3.35
1.1*0
8.00
25.5
10.6
28.5
1.05
3.90
2.05
l*.6o
19.5
15.8
5.00
1.1*1
0.77
<0.3
2.75
1*.1*0
2.17
10.7
<0.3
1.2l*
0.51*
1.50
6.10
1*.1*0
1.69
0.1*2
0.33
0.32
1.08
1.95
12.8
3.70
0.30
1.U6
1.83
1.30
2.70
1.70
0.88
<0.3
MgO
0.72
1*3.0
30.0
1.80
3.80
I*. 20
1*5.0
80.0
38.0
1.06
2.1*0
2.80
1.1*8
0.90
CaO
91*. o
55.0
-56.0
61*.o
69.0
1*6.5
53.0
11.5
56.0
89.0
66.0
72.0
90.0
95.0
TiOa
0.05
<0.03
0.11
0.25
0.12
0.50
<0.03
0.03
<0.03
0.05
0.27
0.23
0.07
<0.03
0.02
<0.02
0.08
0.1*0
0.03
0.70
<0.02
<0.02
<0.02
0.02
0.33
0.36
0.03
0.02
KaO MnOg
<0.1 <0.03
<0.1 <0.03
0.87 <0.03
0.91 0.03
0.20 0.37
2.25 0.07
<0.1 <0.03
<0.1 <0.03
-------
Case I through Case IV experiments indicated that sample No. ll*6l was
not a magnesite.
Table 5 contains the results of x-ray analyses on the fourteen
limestones selected for study. This analysis indicates only the
structure of compounds present. The amount of each compound present
cannot be obtained from these data. Those compounds present in rel-
atively small amounts may not be detected at all.
Physical Properties of the Limestones
Density and surface area of the limestones tested in these ex-
periments are listed in Table 6. In cases where surface area was
measured by both the standard and the modified BET technique, agree-
ment between the two methods was good. Limestone No. 2135 has greater
than 11 times the surface area of limestone No. 1337j even though the
particle size of each limestone was 37 to 1& microns (325 x too mesh).
Neutralization Reactions
The results of the five series of neutralization tests, Case I
through Case V, are as follows:
Case I
The type of neutralization curve produced by the addition of finely
divided (minus 325 mesh) limestone, BCR No. 1809, to synthetic coal mine
water is shown in Figure 6- A pH of 6.0 was attained within 3 minutes
after limestone addition. At that time H^Oa was added, and the pH de-
creased initially as a result of the oxidation of ferrous iron to the
ferric, Fe3*, state.. After oxidation was complete, the neutralizing
ability of the limestone then became the controlling factor and the pH
again increased to a maximum of 7.7.
Figure 7 illustrates a less effective limestone, BCR No. 1337.
After addition of this limestone to synthetic coal mine water, the pH
leveled off at a maximum of 5.6. Addition of HgOg resulted in a de-
crease in pH due to ferrous iron oxidation, but recovery of pH was not
rapid. Maximum pH recorded after addition of peroxide was only 5.5-
Each of the other stones was tested in similar fashion. All data
from this Case I series of tests and the respective particle size frac-
tions of limestones used are listed in Table 7.
The effect of particle size is most noticeable. The coarser
sizes—50 x 60, or 60 x 100 mesh—show much slower and incomplete
neutralization than the more finely divided sizes—325 x too mesh or
minus too mesh—of the same limestone. Maximum pH attained after oxi-
dation as well as time of maximum pH attainment after limestone
28
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TABLE 5. X-RAY ANALYSES OF FOURTEEN LIMESTONES
BCR
Sample
No. Compounds Identified.
MgCOg, CaMg(CCb)8
1337 CaMg(C03)a
lU6l CaMg(C03)3
165U CaMg(C03)s, CaC03
1352 CaMg(C03)3, CaCOa
136U CaC03, SiOa, [eSiO-
1355 CaCOa, SiOa
1362 CaC03, SiOa, ff-Fea03, Ca(MgPe)(C03)8
2136 CaC03, SiOa
2135 CaCOa, Si08
1335 CaC03
21^5 CaCX)3, SiOa
1809 CaC03, SiOa
2177 CaCOs
29
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TABLE 6. DENSITY" AND SURFACE AREA OF FOURTEEN LIMESTONES
BCR
Sample
No.
1335
1337
1352
1355
1362
1364
1461
ll*62
1654
1809
2135
2136
2145
2177
Density,
D,
g/ml
2.70
2.74
3-57
2.63
3.02
2.87
2.94
3.27
2.32
3.18
2.64
2.46
2.59
2.54
Surface
Area, SA,
m/g
0.88*
0.62*
2.29*
2.94*
2.53*
2.13*
1.11*
1.98*
1.22*
1.76*, 1.72*
7.18*
5.39*, 5.13*
2.05*
1.17*
* Standard BET
* Modified BET
30
-------
120
TIME, minutes
150
180
Bituminous Coal Research, Inc. 2030G13
Figure 6. Neutralization of Synthetic Coal Mine Water with No. 1809 Limestone
-------
8-1
7~
6-
Q.
5-
4-
Addition
Limestone Addition
;30
60
I
90
TIME, minutes
120
150
180
Bituminous Coal Research, Inc. 2030G14
Figure 7. Neutralization of Synthetic Coal Mine Water with No. 1337 Limestone
-------
TABLE 7. EFFECT OF PARTICLE SIZE OP LIMESTOHKS OH pH OF ffifHTHETIC
COAL MINE WATEE. CASE I*
After Limestone Addition
Before Hp02 Addition
BCK
Sample
No.
1335
1337
1352
1355
1362
1364
11+61
1654
1809
2135
2136
2145
Mesh Size
Tested
-4oo
140 x 200
50 x 60
-400
140 x 200
50 x 60
-4oo
100 x 140
50 x 60
-400
140 x 200
50 x 60
-400
140 x 200
50 x 60
-4oo
140 x 200
50 x 60
325 x 4oo
100 x i4o
50 x 60
325 x 4oo
200 x 325
60 x 100
-325
100 x 200
•- 60 x 100
-4oo
140 x 200
50 x 60
-400
140 x 200
50 x 60
325 x 4oo
60 x 100
Original
pH of
Synthetic
Mine Water
2.8
3.0
3.0
3.0
3.1
3.0
3.1
2.9
3.1
3.0
3.0
3.0
3.0
3.1
2.9
3.0
3.0
3.0
• 3.0
3-0
3.0
2.9
2.9
3.0
2.9
3.0
3.0
3-0
3-0
3.0
3.0
3-0
3.0
3.0
3.0
Maxijuuin
PH
Attained
6.0
5.9
5.8
5.6
5.8
5.5
6.1
5.9
5.8
6.1
6.0
5.9
6.2
6.2
6.0
6.2
6.1
6.0
5.6
5.6
5.4
5.9
5.7
5.6
6.0
5.9
5.9
6.0
6.0
6.0
6.0
6.0
5-9
6.0
6.2
Time after
Limestone
Addition,
min
5
15
28
25
70
120
6
26
44
5
22
32
12
12
30
6
16
36
9
45
70
14
22
44
3
3
12
1
5
17
2
3
25
3
4
After H20p Addition
Minimum
PH
Attained
3-9
3.4
3.2
3-2
3.4
3.1
3.6
3.2
3.1
4.5
3.7
3.6
3-7
3.4
3.2
3.8
3.4
3.4
3.1
3.2
2.9
3.2
3.3
3.1
3.9
3.9
3.5
4.2
4.0
3.7
4.2
3.9
3.4
3.9
4.1
Maximum pH
Attained
after
Oxidation
7.9
5.6
5.3
5.5
5.5
5.0
5.8
5-3
3.2
7.7
5.7
5.4
7.5
5.6
5.7
7.6
5.5
5.2
5.3
5.0
3.1
5.3
5.3
3.2
7.7
7.9
5.6
7.6
6.5
5.5
7.8
7.5
5.3
7.8
7.7
Time of
Maximum
pH after
Ha°5
Addition,
Min
l6o
42
64
96
140
240
85
128
40
122
24
38
240
86
105
222
44
105
50
120
93
50
45
4o
100
no
54
187
20
20
211
186
55
100
88
2177 325 x 400
3.0
6.1
3.8
7.8
118
* Insufficient oxidizing agent—KgO,,, for complete oxidation
of ferrous iron, added after the limestone.
-------
addition, "but prior to oxidation, are the test indicators of effective
neutralization for this series of experiments.
Using these criteria, the stones have teen grouped in three gen-
eral categories: Group A, the most effective neutralizing agents—No.
1335, 1355, 1809, 2135, 2136, 21^5, and 2177; Group B, intermediate--
No. 1362 and 1364; and Group C, the least effective neutralizing
agents—No. 1337, 1352, 1^6l, and 165^.
An interesting trend is shown in Table 8. The pH attained one hour
after addition of HgOg, before equilibrium (complete ferrous iron oxida-
tion) had been attained, was arbitrarily chosen as an indication of
neutralizing efficiency. With few exceptions, neutralizing efficiency
of a stone decreases as the percentage of MgO present in the stone
increases.
No similar trend is apparent with percentage of CaO present; for
example, stones No. 165^ and 1355 have similar CaO contents yet are
widely spaced in Table 8. More is involved than mere high calcium oxide
content. No other trends could be found from chemical composition and
neutralization efficiency. The data, however, show limestones to be
more effective than dolomites or magnesites.
Case II
Figures 8, 9, and 10 represent the pH curves generated by 325 x kOQ
mesh samples of all the test limestones when the oxidant was added at
the same time as the limestone to synthetic coal mine water. The stones
have been grouped according to overall appearance of the curve rather
than the pH attained at one point in time or some other arbitrary stand-
ard. Figure 11 (one of the curves from Figure 8) shows that ferrous
iron has not been completely oxidized by the addition of 3 drops of
hydrogen peroxide, the amount used in this test. Figure 11 also reveals
the reason for the inflections in these curves. The initial effect of
the addition of limestone was an increase in pH. Then the oxidation of
ferrous iron retarded the pH increase until all the iron was oxidized;
the system was then allowed to achieve maximum pH as a result of the
neutralizing action of the limestone present. Those limestones repre-
sented in Figures 9 and 10 produced a pH greater than 7 only after sev-
eral days subsequent to ferrous iron oxidation.
The test data are listed in Table 9; the 13 limestones tested are
arranged in order of increasing reactivity to coal mine water or ef-
ficiency based on Figures 8, 9, and 10. A mathematical relationship
was noted between efficiency and some property or combination of proper-
ties of the limestones. Efficiency, in this case, is directly related
to area under the individual curves in Figures 8, 9, and 10; the
greater the area, the greater change in pH as a result of limestone ad-
dition. Reactivity in this context is synonymous with efficiency.
-------
TABLE 8. EFFECT OF MAGNESIUM CONTENT OF LIMESTONE ON pH,
ONE HOUR AFTER NEUTRALIZATION AND OXIDATION. CASE I*
BCE
Sample
Wo.
1461
1337
165U
1352
136U
1362
2135
2136
1335
1355
2177
2145
1809
pH Attained
One Hour after HgOg
Addition
5.3
5.3
5-3
5.8
6.0
6.0
6.1
6.3
6.k
6.6
6.6
7.0
7-3
Spectrochemical Analyses,
MgO Percent of Ignited
(,900 C) Sample
90.0
1*5.0
36.0
30.0
3-30
3.20
2.55
2.90
0.69
1.85
1.16
1.69
* Insufficient oxidizing agent—Hg03, for complete oxidation
of ferrous iron, added after the limestone.
35
-------
U)
x
a
1
7-
5-
4-
3-1
1809
1335 —
2177
I
60
120
180
TIME, minutes
240 300 330
Bituminous Coal Research, Inc. 2030G39
Figure 8. Effect of Group A Limestones on Synthetic Coal Mine Water
-------
120
180
TIME, minutes
240
1
300 330
Bituminous Coal Research, Inc. 2030G38
Figure 9. Effect of Group B Limestones on Synthetic Coal Mine Water
-------
8 -i
7 -
6 -
300 330
Bituminous Coal Research, Inc. 2030G37
Figure 10. Effect of Group C Limestones on Synthetic Coal Mine Water
-------
7-
6-
X
Q.
5-
4-
0 ppm Fe8+
40
16
^220 ppm Fe8+
—i—
60
120
180
TIME, minutes
240 300 330
Bituminous Coal Research, Inc. 2030G40
Figure 11. Effect of Limestone No. 1809 on Synthetic Coal Mine Water
-------
TABLE 9. "EFFICIENCY" OF LIMESTONES. CASE I»
BCR
Sample
No.
1337
165^
lU6l
L352
L364
1355
1362
2136
2135
1335
21^5
1809
2177
Relative
Area Spectrochemical Analysis
Under CaO Percent of (900 C)
Curve Ignited Sample
30
37
38
55
62
68
Qh
9u
95
97
98
99
100
53-0
58.0
^•35
56.0
58.0
60.0
55.0
71.0
68.0
9^.0
92.0
88.0
97.0
CaO + (SA x D)*
5^.7
60.8
7.6
6^.2
6^.1
67.7
62.6
8^.3
86.9
96.U
97.3
93-6
100.0
4- Insufficient oxidizing agent—HgOa, for complete oxidation
of ferrous iron, added with the limestone.
* (Surface Area x Density)
-------
The data show increasing efficiency with increasing percentage of
CaO in the limestone sample. Stones with a lower percentage of CaO may
be equally efficient if their specific surface area is high, as indica-
ted in Table 9 by limestones No. 2135 and 2136.
A mathematical expression for the relationship between efficiency
and some property or properties of a given limestone would be most use-
ful as a means of evaluating limestones. Mathematical relationships
considered in evaluating Case II data are listed in Table 10. The one
selected [CaO + (Surface Area x Density)] has been useful to date but
needs to be revised and improved as more data become available.
Case III
The data from the thirteen stones tested in Case III are listed in
Table 11. A sufficient quantity of hydrogen peroxide was available to
oxidize all ferrous iron present. In the case of the least efficient
limestones, some ferrous iron was still present 5 minutes after addi-
tion of the stone and peroxide. No major differences between results
of Case II and Case III were noted when the limestones were listed in
order of increasing efficiency as determined from the area under the
curves.
Case IV
Data from Case IV are given in Table 12. Some iron remained un-
oxidized by the least efficient stones. Few differences from Case II
and Case III results were noted when the amounts of limestone were
adjusted to compensate for impurities in the stones.
Limestone No. ll»6l, by virtue of the low CaO value, should have
been the least reactive of the thirteen in this series of tests as
well as in all of the past series. The area under the curve was not
the least of the thirteen as one would expect. (See Tables 9, U, and
12.) In addition, x-ray analysis (qualitative) showed only the pres-
ence of dolomite in this stone and no indication of magnesite. Clearly
this sample had been mislabeled, and limestone No. l^tol is, in fact, a
dolomite rather than a magnesite. Limestone No. lb623 a magnesite from
Basic, Inc., Gabbs, Nevada, was then included in the Case V tests and,
as expected, it was found to be the least effective neutralizing agent.
Case. V
The data from testing the fourteen stones using air as the oxidant
in Case V are listed in Table 13- Levels of pH attained 30, 60, and
300 minutes after addition of limestone and start of aeration are
listed together with the [CaO + (Surface Area x Density)] values.
These values do not vary substantially in the Case II through V
experiments.
-------
TABLE 10. MATHEMATICAL RELATIONSHIPS CONSIDERED IN EVALUATING LIMESTONES. CASE
fc
BCR
Sample
No.
1337
165!*
lUfiL
1352
1361*
1355
1362
2136
2135
1335
21^5
1809
2177
Relative
Area
Under
Curve
30
37
38
55
62
68
8U
9^
95
97
98
99
100
CaO X SA*
32.9
70.8
U.8
128.2
123.5
176.1*
139.2
382.7
1*88.2
82.7
188.6
15**.9
113.5
CaO X SA
MgO
0.7
2.0
0.1
*.3
37.^
95. ^
U3.5
132.0
191.^
120.0
111.6
115.6
97.8
CaO + SA
53.6
59.2
5.U
58.3
60.1
62.9
57.5
76.1*
75.2
9^.9
9^.0
89.8
98.2
CaO + (SA)3
53.U
59.5
5.6
61.2
62.5
68.6
61.U
100.0
119.5
9^.8
96.2
91.1
98.U
CaO + (SA X D**)
5^.7
60.8
7.6
6U.2
6U.1
67.7
62.6
&.3
86.9
96.h
97.3
93.6
100.0
4- Insufficient oxidizing agent—Ha08, for complete oxidation
of ferrous iron, added with the limestone.
* Surface Area ** Density
-------
TABLE 11. "EFFICIENCY" OF LIMESTONES. CASE III4-
BCR
Sample
No.
1337
165^
l46l
1364
1352
1355
1362
1335
2136
2135
2145
1809
2177
Relative
Area
Under
Curve
32
36
55
68
75
75
87
92
93
95
98
99
100
Fe8*, ppm
5 Minutes After
Addition of Reagents
12
10
15
2
1
10
0
0
0
0
0
0
0
CaO + (SA x D)*
54.7
60.8
7.6
64.1
64.2
67.7
62.6
96.4
84.3
86.9
97.3
93-6
100.0
4- Sufficient oxidizing agent—1^02, for complete oxidation
of ferrous iron, added with the limestone.
* (Surface Area x Density)
43
-------
TABLE 12. "EFFICIENCY" OP LIMESTONES. CASE IW
ECR
Sample
No.
1654
1337
1461
1352
1361*
1355
1335
1362
2135
2136
1809
2177
2145
Relative
Area
Under
Curve
32
33
40
78
87
89
91
94
96
97
98
99
100
Factor used
in Adjusting
Amount of
Limestone*
0.95
0.89
0.79
1.05
1.6k
1.6k
1.08
1.73
1.44
1.37
1.15
1.04
1.09
Fea+, ppm
5 Minutes after
Reagent Addition
13
0
Ik
1
0
0
0
0
0
0
0
0
0
CaO + (SA x D)*
60.8
54.7
7.6
64.2
64.1
67.7
96.4
62.6
86.9
84.3
93.6
100.0
97.3
4- Sufficient oxidizing agent—HgOg, for complete oxidation of ferrous
iron, added -with the limestone. Amount of limestone utilized reflects
compensation for impurities in the stone other than CaCOg or MgCQj.
± _, . _ Weight of limestone needed, compensating for impurities
a or Weight of limestone needed, assuming pure CaCOg
* (Surface Area x Density)
44
-------
TABLE 13. "EFFICIENCY" OF LIMESTONES. CASE V4-
BCR
Sample
No.
3.462
1337
lU6l
1654
1352
1364
1355
1362
2136
2135
1335
2145
1809
2177
Relative
Area
Under
Curve
30
46
48
49
^9
50
52
69
87
87
94
95
96
100
30
min
3.6
5.3
5.4
5.5
5.5
5.6
5.6
5.7
5.7
5.8
5-9
6.0
6.1
7.6
pH after
60
min
3-9
5.3
5.4
5.5
5.5
5.5
5.5
5.6
5.9
5.9
7.4
7.8
7.8
8.0
300
min
4.9
5.3
5.3
5.3
5.4
5.4
5-5
7.4
7.8
7.8
7.9
7.9
7.9
8.0
CaO + (SA x D)*
18.0
56.7
56.3
58.8
64.2
52.6
71.7
76.6
85.2
85.0
96.4
95-3
94.6
98.0
•1- Sufficient oxidizing agent—air, for complete oxidation of ferrous
iron, introduced at the same time as limestone addition and continued
throughout the reaction period.
* (Surface Area x Density)
45
-------
The experimental conditions observed under Case V are recommended
as the best method to date of evaluating limestones as neutralizing
agents for coal mine water. These conditions are: addition of 325 x
UOO mesh limestone and air to a solution of synthetic coal mine water
containing 200 to 250 ppm of Fe3* added as ferrous sulfate and having
the pH adjusted to 3.0 with sulfuric acid; stirring continuously for a
5.5 hour period and recording the changes in pH with time. The amount
of limestone should be twice the stoichiometric amount based on the
acidity of the synthetic coal mine water and based on the assumption
that the stone contained pure CaC03. Air should be bubbled into the
solution through a fritted glass disk at the bottom of the container
throughout the reaction at a rate of 2500 ml/min.
A composite graph of all results from the past tests should be
used to judge the results of this experiment. Such a composite is
presented in Figure 12. The curve from an effective limestone would
fall into area A on Figure 12, while curves from ineffective lime-
stones would resemble those in areas B or C.
There was no essential difference in the results of the Case II
through Case V experiments; therefore, air was selected as the oxidant.
Air is the cheapest oxidant and is therefore used in coal mine water
treatment operations. There was not too much difference in the results
of the Case IV experiments when a compensation was made for impurities
in the limestone. Therefore, in the method being recommended, lime-
stones are assumed to be pure CaCOa. Ultimately only two categories of
limestones are reasonable—those stones which are effective neutraliz-
ing agents and those which are not—in terms of their ability to effect
a change in pH. For coal mine water treatment, a time factor must be
considered along with the change in pH. As a result of the evaluation
of the 14 limestones, the effective stones are No. 1335, 1809, 2135,
2136, 21^5, and 217?. Those stones which are judged to be ineffective
are No. 1337, 1352, 1355, 1362, 136U, ll*6l, ll*6*2, and 165!*.
In general, based on the five series of experiments, magnesites
are the least effective neutralizing agents, followed closely by dolo-
mitic stones. Stones approaching pure CaC03 are the most effective
neutralizing agents. Stones having a relatively low calcium content,
but a calcite structure and a high surface area, are equally effective
neutralizing agents.
The effectiveness of limestones as neutralizing agents for coal
mine waters can be enhanced by reducing the particle size of the stone.
Batch-scale Neutralization of Actual Coal Mine Waters
Although four actual coal mine waters were initially chosen for
batch-scale limestone neutralization studies, exploratory neutraliza-
tion tests were performed on only three of these waters, namely, South
Greensburg, Keystone, and Tarrs. It was felt that any conditions
4.6
-------
pH
4-1
3-
60
120
180
TIME, Minutes
240
300
Bituminous Coal Research, Inc. 2030GS7
Figure 12. Model Curve for Judging Effectiveness of Limestones
-------
employed in neutralizing these three discharges would also enable us to
neutralize the Thorn Run discharge since this particular discharge con-
tains essentially only ferric iron and would, therefore, be amenable to
limestone neutralization.
Figure 13 shows the effect of varying the amount of limestone used
in neutralizing South Greensburg discharge. Reduction in ferrous iron
concentration was accomplished in all experiments but most rapidly in
that one with an excess amount of limestone. It may be assumed that,
allowing sufficient time, there would have been a further reduction in
iron in the one experiment with the stoichiometric (IX) amount of lime-
stone. In commercial -oractice a slight excess of stone could probably
be tolerated economically to obtain more rapid reaction.
Surprisingly, in the experiment with five times the stoichiometric
amount of limestone, no improvement was observed in the rate at which
ferrous iron was oxidized over that with twice the stoichiometric amount.
Figure l4 shows the results of two experiments using the Keystone
discharge and twice the stoichiometric amount of limestone. One experi-
ment was conducted with aeration, the other without aeration. Figure 15
shows the effect of aeration on pH of the same systems. Ferrous iron can
be oxidized during neutralization of Keystone coal mine drainage without
aeration, but about twice the time is necessary to remove the Fe3*.
Maximum pH and trriniTm-nn Fe2"1" values occur at about the same period.
In the last experiment of this series, Tarrs coal mine drainage
was treated with twice the stoichiometric amount of No. 1809 limestone,
325 x 400 mesh. Stirring and aeration for 90 minutes, however, failed
to reduce the Fes* concentration or to increase the pH above 6.7«
Aeration and stirring were resumed the next day for 30 minutes. This
effected oxidation of the Fes+ and an increase of the pH to 7.
Tests on Actual Coal Mine Water under Standardized Conditions
From data obtained in the exploratory tests above, a standardized
set of conditions was selected for batch-scale limestone neutralization
of the four actual coal mine waters (See "Batch-scale Neutralization of
Actual Coal Mine Waters," under Section 3).
The resultant data are summarized in Tables 1^, 15, 16, and 17.
Complete analyses of the waters as received are given in column A; com-
plete analyses of these waters after treatment for 90 minutes in column
B; after treatment for 90 minutes and allowing to stand overnight, in
column C; and, after treatment for 90 minutes, allowing to stand over-
night, and being stirred and aerated an additional 30 minutes in
column D.
Treatment of South Greensburg coal mine drainage (Table lU) was
accomplished quite effectively. Iron content and acidity were reduced
to low levels after standing overnight (column C). Little difference
48
-------
120-1
105-
90-
75-
cu 60-|
45-
30-
15-
0-
2X
IX
15
30 45
TIME, minutes
i
60
75
I
90
Bituminous Coal Retearch, Int. 3030658
Figure 13. Neutralization of South Greensburg Coal Mine Drainage-
Effect of Amount of No. 1809 Limestone on Fe*+
49
-------
360-1
315-
270-
225-
.- 180-
m
£
135-
90-
45-
o-
Without Aeration
With Aeration
I
0
I
40
I
80
120
TIME, minutes
160
200
240
Bituminous Coal Research, Inc. 2030G15
Figure 14. Neutralization of Keystone Coal Mine Drainage with No. 1809
Limestone—Effect of Aeration on Fes+
50
-------
7.8-1
7.6-
7.4-
7.2-
7.0-
6.8-
6.6-
6.4-
6.2-
6.0-
With Aeration
Without Aeration
40
I
80
120 160 200 240
280
TIME, minutes
Bitumino.us Coal Research, Inc. 2030G17
Figure 15. Neutralization of Keystone Coal Mine Drainage with No. 1809
Limestone—Effect of Aeration on pH
51
-------
TAELE 14. BATCH-SCALE LIMESTONE NEUTRALIZATION OF
SOUTH GREENSBURG COAL MINE DRAINAGE
Initial Reaction Initial Reaction
at 18 C at 22 C
pH
Temperature,
Acidity, ppm
Fes+
Si,
Al,
Fe,
Ca,
Mg,
Mn,
Na,
CC
CaC03
, ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
A
5.1
18
220
in
14
7
109
219
82
4
73
B
6.4
21
60
24
6
<2
20
300
80
4
77
C_
6.8
20
18
3
4
<2
4
355
80
4
93
p_
7.6
20
0
-------
TABLE 15. BATCH-SCALE LIMESTONE NEUTRALIZATION OP
KEYSTONE COAL MINE DRAINAGE
Initial Reaction
at 18 C
Initial Reaction
at 22 C
PH
Temperature, °C
>
m
i84
'»
•>
!>
•»
>>
LJ
t>
°C
CaC03
', ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
A
6.3
18
3^2
325
7
<2
330
255
119
5
1070
B
6.2
22
sa
1U
3
<2
13
355
nif
if
1110
c
6.6
21
13
0
2
2
-------
TABLE 16. BATCH-SCALE LIMESTONE NEUTRALIZATION OF
TAKRS COAL MINE DRAINAGE
Initial Reaction Initial Reaction
at 18 C at 22 C
PH
Temperature,
Acidity, ppm
Fea+
Si,
Al,
Fe,
Ca,
Mg,
Mn,
Na,
S04S
*C
CaCOg
, ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
"", ppm
A
3.1
18
673
8U
^5
62
122
237
<*
5
<30
iWa
B_
6.6
21
100
1*
17
<2
1*
500
9U
5
<30
1U22
C_
6.5
20
66
25
12
<2
22
500
90
5
<30
1U68
D_
6.9
20
25
6
9
<2
8
510
90
5
<30
1^72
A
3.0
22
673
8U
^5
62
122
237
9*
5
<30
ll*l
B
6.1
22
95
3U
16
<2
36
470
92
5
<30
l¥K)
C_
6.U
20
75
20
12
<2
22
500
9U
5
<30
1U85
D
7.0
20
ItO
*
9
<2
7
520
9U
5
<30
ll^8U
Eh, mv +662 +392 +367 +U72 +662 +382 +372
Conductivity, |jmhos/cm 2170 2170 2150 2l6o 2170 2170 2150 2l6o
Dissolved oxygen, ppm 8887 8878
Turbidity, JTU UlllUlll
Electrophoretic mobility — +0.6 +0.7 +0.5 — +0.7 +0.6 +0.5
Zeta potential, mv — +8 +9+7 +9 +8 +7
Dissolved solids, ppm 2U60 2200 2330 2160 2^*60 2170 2120 25^0
A = Raw mine water
B = A, after treatment for 90 minutes
C = B, allowed to stand overnight
D = C, stirred and aerated an additional 30 minutes
54
-------
TABLE 17. BATCH-SCALE LIMESTONE NEUTRALIZATION OF
TH5RN RUN COAL MINE DRAINAGE
Initial Reaction Initial Reaction
at 18 C at 22 C
PH
Temperature,
Acidity, ppm
>Fes+
Si,
Al,
Fe,
Ca,
Mg,
Mn,
Ha,
°C
CaCOa
, ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
A
3.2
18
U?8
18
20
51
69
250
66
13
30
B
7.2
20
16
-------
was noted "between initial reaction at 18 C and 22 C (column B).
Treatment of Keystone coal mine drainage (Table 15) proceeded ef-
fectively with only minor differences between reaction at 18 C and
22 C. Again iron content and acidity were reduced to low levels after
the sample was allowed to stand overnight.
Treatment of Tarrs discharge (Table 16) proceeded slowly. Acidity
and iron content were not lowered substantially even after the sample
was allowed to stand overnight. Only after stirring and aeration for an
additional 30 minutes were the iron content and acidity further reduced.
Aluminum was also removed, however, this treatment did not affect man-
ganese concentration.
The most effective treatment occurred with Thorn Run discharge
(Table 1?). Low levels of acidity and iron content were observed after
treatment for only 90 minutes (column B).
In all cases, an increase in concentration of Ca, and therefore
hardness, was noted as a result of the limestone neutralization. Dis-
solved oxygen usually attained a final value of 8 ppm in the treated
water. No significant increase in dissolved solids or conductivity was
noted.
Electrostatic charge on the sludge particles as reflected by
electrophoretic mobility and zeta potential, was reduced on standing
(columns B, C, and D) in most cases; this should mean a more rapid set-
tling of sludge.
Turbidity was reduced to 1 JTU, the value also obtained on tap
water.
The four actual mine waters have been treated successfully but with
varying degrees of difficulty. These batch-scale tests point out the
need for a general set of conditions for neutralization with limestone,
which can be varied as required by the characteristics of the individual
water.
Oxidation of Ferrous Iron
Ferrous iron in some actual coal mine waters is not oxidized read-
ily by aeration alone. (See Table l6.) A method to enhance this oxida-
tion in the limestone neutralization process is needed. The use of car-
bon catalysts to promote the air oxidation of Fe3* in an acid medium (12,
13) and the use of activated carbon alone as a solid catalyst (l4, 15)
have been studied by others. However, so far as is known, no work has
been done on the use of such carbons for the oxidation of Fe8* in coal
mine water. This study was undertaken to test the applicability of car-
bon catalysts described in the literature to coal mine water treatment.
56
-------
Catalyst Preparation
Initially these catalysts were prepared from a number of materials.
Preliminary studies were conducted to evaluate a variety of carbon
catalyst preparation schemes. Carbons, produced from coconut char,
foundry coke, and hardwood sawdust, were subjected to activation by air
and by chemical action. Most carbons prepared in this manner had high
catalytic activity but lacked the desired mechanical strength. The
general procedure for preparing an active carbon was both laborious and
complex. (See Experimental Section.)
Four typical prepared materials were selected for study. Carbon
33^-92-2 was made from Sewell coal devolatilized at 800 C for ^5 min-
utes, activated at 300-375 C for 1 hour and calcined at 750 C for 3.5
hours. Carbon 33^-92-3 was also made from Sewell coal devolatilized
at 510 C for 2.5 hours, activated at 375 C for 1 hour and calcined at
950 C for 1 hour. The calcination at 950 C was accomplished in N2
saturated with water at 90 C, essentially a steam activation step.
Carbon 33^-92-1 was a steam-activated coke from Rochester and Pittsburgh
Coal Company which was further steam activated in our laboratories by
heating at 950 C for 1 hour in Bg saturated with water at 90 C. The
fourth carbon, 33^-75-2, was made from Sewell coal and devolatilized at
700 C for 15 minutes, activated at U80 C for 90 minutes, and calcined
at 800 C for 3 hours.
Testing Prepared Activated Carbons
The four carbons were evaluated in the standard test. Data from
33l*-92-l, 33^.92-2, and 33^-92-3 are listed in Table 18. Percent Fe2*
converted is adequate in all but 33^-92-1. The life of the catalyst
was examined using the fourth carbon, 33**-72-2 with only k g of carbon
being used with 50 ml portions of test solution. Aeration at hOQ
ml/min was carried out for 15-minute cycles. The carbon was filtered
off with no washing after each cycle. The data are presented in Table
19. A constant level of activity was maintained throughout the test.
The results show that the catalyst maintained activity at low pH for
20 cycles. In a coal mine drainage treatment process, the life of the
carbon must be long and mechanical losses low. These tests indicate
that the catalyst life is at least 300 minutes without being re-
generated.
Testing Commercially Available Activated Carbons with Synthetic Coal
Mine Water
Testing of commercially available, coal-derived activated carbons
was initiated since preparing the,carbon from coal in our laboratories
left little time for actual testing of the materials made. In the
preliminary experiments, using limestone together with the carbon in
the test solution during aeration, the carbon soon became coated with
precipitated oxidation products; for this reason, use of the
57
-------
W
TABLE 18. EVALUATION OP PREPARED CARBON AS CATALYSTS FOR Fe8* OXIDATION
Carbon
Sample
Number
33^92-1
33^-92-2
33^-92-3
Air
Rate,
ml/min
too
too
too
Duration
of Test,
min
15
15
15
Percent Fe?+ Converted
Cycle
1
33
28
83
Cycle
2
32
39
76
Cycle Cycle
31* 36
^7 50
76
Cycle
32
58
—
Cycle
6
..
55
«
-------
TABLE 19. EVALUATION OF LIKE OF A PREPARED ACTIVATED CARBON CATALYST
Cycle
No.
1
2
3
k
5
6
7
8
9
10
Percent Fe
Oxidized
^7
^7
1*9
50
52
51
51
58
56
55
Cycle
No.
11
12
13
1U
15
16
17
18
19
20
Percent Fe
Oxidized
56
53
53
55
60
57
56
55
56
5U
59
-------
combination of carbon and limestone was discontinued, even though the
rate of oxidation was increased satisfactorily.
Early experiments with commercially available activated carbons
were also concerned with testing a number of coal-derived carbons and
varying the quantity of carbon and duration of the test (cycle). The
carbons were either used "as is" out of the container or were subjected
to steam activation by heating at 950 C for 1 hour in an atmosphere of
Kg saturated with water at 90 C. An aeration rate of 400 ml/min was
employed in »n of these tests. Results of these experiments are
listed in Table 20. No satisfactory increase in the rate of oxidation
with the carbon present was noted in the first 15-minute cycle; the
rate of oxidation did increase with increasing number of cycles both in
cases where the carbon had been steam activated (Sample No. 334-97-15A
and Sample No. 334-96-l^A) and when used as received (Sample No.
334-96-13C).
To examine the effect of increasing the number of cycles on the
oxidation rate, Nuchar WV-W was used as received in the standard test.
The data are listed in Table 21. After a few unproductive cycles, a
rate of oxidation between 60 and 80 percent was attained in a 60-minute
cycle. The catalyst maintained this activity for 24 cycles, a total of
22-3/4 hours. When the duration of the cycle was reduced to 30 minutes
(cycle 21) or 15 minutes (cycle 22), there was a corresponding decrease
in percent Fe2* oxidized.
It has been suggested that a build-up of bacteria during the first
few unproductive cycles is responsible for the increased catalytic
activity. While there is no direct evidence against such a build-up,
this mechanism does not seem likely based on the immediate catalytic
activity exhibited by the steam activated material (See Table 20,
Carbon Sample No. 334-96-l4c and 334-97-16).
It was thought that the difficulty in limestone treatment of Tarrs
discharge, as shown in Table 16, might have been due to the presence of
aluminum as well as ferrous iron in this water. To examine the effect
of aluminum, the following experiment was conducted. Approximately
150 ppm, as AlgtSOtJa 18 HgO, was added to the test solution. The
1-hour reaction showed no diminishing of efficiency; if anything, the
efficiency was slightly increased.
In summary, the commercially available activated carbons are ef-
fective catalysts, either (a) after further steam activation or (b)
after merely undergoing a few relatively unproductive cycles. A cycle
of 60 minutes duration is necessary to accomplish 60 to 80 percent ox-
idation of ferrous iron in synthetic coal mine water at pH 3«0.
Testing Commercially Available Activated Carbons with Actual Coal Mine
Water
Tarrs discharge, an actual coal mine water, was then tested. This
60
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TABLE 20. EVALUATION OF COMMERCIALLY AVAILABLE ACTIVATED CARBONS FOR Fe8+ OXIDATION
Carbon
Sample
No.
Control
Carbon
Description
Pittsburgh Activated Carbon Company
92- k
92- 5
92- 6
94-12
97-15A
97-15B
OL, as received
CAL, as received
SGL, as received
BPL, as received
BPL, "steam activated
BPL, steam activated
Quantity Duration
of of
Carbon, Test, Cycle Cycle Cycle Cycle
g/1
0
Percent Fe2* Oxidized
min
60
80
80
80
80
107
107
15
15
15
15
15
30
3^
k6
32
21
33
kk
18
22
22
16
63
69
Ik
13
79
West Virginia Pulp and Paper Company
93- 7 Nuchar W-G, as received
93- 9 Nuchar C-115-N, as received
93-10 Nuchar C-190-N, as received
93-11 Aqua Nuchar A, as received
96-13A Nuchar WV-W, as received
96-13B Nuchar W-W, as received
96-13C Nuchar W-W, as received
96-l^A Nuchar W-W, steam activated
96-lUB Nuchar W-W, steam activated
$6-lkC Nuchar W-W, steam activated
97-16 Nuchar W-W, steam activated
80
80
80
80
160
160
160
160
160
160
107
15
15
15
15
15
30
60
15
30
60
60
16
22
27
22
20
15
50
k6
79
85
8k
20
20
2k
16
__
__
38
66
93
--
__
--
--
—
—
_-
__
56
79
--
--
—
--
—
—
—
__
__
68
86
__
__
--
-------
TABLE 21. EVALUATION OF LIFE OF COMMERCIALLY AVAILABLE
ACTIVATED CARBOH CATALYST
Reaction Time, Percent Fe2*
min Oxidized
1 60 2
2 60 3*J.
3 60 50
k 60 60
5 60 6l
6 60 52
7 60 66
8 60 70
9 60 73
10 60 74
11 60 65
12 60 73
13 60 76
l*f 60 76
15 60 77
16 60 75
17 60 67
18 60 72
19 60 73
20 60 73
21 30 61
22 15 to
23 60 62
2k 60 68
62
-------
water, containing 52 ppm of Fe8* at pH 3.10, was aerated at a rate of
kQO ml/rain in the presence of 16 g of activated carbon (Nuchar WV-W),
and also with no carbon present. (See Figure l6.) The rate of ferrous
iron oxidation was increased significantly by the presence of the ac-
tivated carbon. After 60 minutes, pH decreased to 2.89. At least in
this particular coal mine water, oxidation of 80 percent of the ferrous
iron can be accomplished in 15 minutes without first raising the pH by
the addition of a neutralizing agent. Further, the low pH at the end
of the oxidation reaction ensures against the iron precipitating on the
carbon and rendering it inactive and necessitating constant backwashing.
Testing Other Materials
Materials other than activated carbon were also tested in the same
manner as the carbons using synthetic coal mine water. In all cases,
the aeration rate was kOQ ml/min. Table 22 lists these materials,
showing their effect on ferrous iron oxidation and terminal pH achieved.
(The test solution in these cases contained 212 ppm Fe2* as ferrous
sulfate adjusted to pH 3.0 with sulfuric acid.) These materials, some
of which have a surface area as great as carbon, accelerated the rate
of oxidation only when they also effected an increase in pH. It is
felt that the increase in pH was responsible for the increased rate of
oxidation rather than any mechanism similar to that of the carbon.
Stumm and Lee (l6) report a hundredfold increase in the rate of oxida-
tion of ferrous iron per unit increase in pH.
Ho insight regarding the mechansim of this carbon catalysis of
ferrous iron oxidation or the increase in catalytic activity after the
first few unproductive cycles was obtained by (a) Soxhlet extraction and
analysis of the filtrate, (b) pyrolysis of the carbon and analysis of
the resultant gases, or (c) x-ray analysis of the commercially avail-
able, coal-derived carbons both as received and when good catalytic
activity was attained.
The surface of activated carbon has a variety of organic func-
tional groups containing oxygen and hydrogen. Activated carbon has
been described as a disordered agglomerate of layers of large polynu-
clear benzenoid hydrocarbons. Oxygen, which is adsorbed in amounts
proportional to the amount of oxygen in solution, probably reacts as a
diradical —0—0— (l?), in conjunction with hydrogen ions, to extract
electrons from the adsorbed ferrous ions.(13)
Non-oxidative Neutralization and Addition of Coagulant Aids
ELectrophoretic mobility measurements have shown that particles of
freshly prepared ferrous hydroxide formed by the non-oxidative neutral-
ization of synthetic coal mine water have an electrostatic charge of -+9
to +16 millivolts. Reduction of this charge to a minimum will reduce
the forces of mutual repulsion; this can be accomplished by the addi-
tion of specific amounts of an anionic electrolyte or polyelectrolyte.
Gentle agitation at this point will then increase the number of col11-
63
-------
lOO-i •-— •
I m^^ ^^ i
90-
80-
70-
O 60-
Q
X
O
ui
(J
DC
50-
40-
30-
20-
10-
No Carbon Present
r
Carbon Present
I
10
i
20
30 40
TIME, minutes
I
50
1
60
Bituminous Coal Research, Inc. 2030G41
Figure 16. Effect of Activated Carbon on Ferrous Iron Oxidation Tarrs
Coal Mine Discharge
6-4
-------
TABLE 22. EFFECT OF MATERIAIB OTHER THAN CARBON ON FERROUS IRON OXIDATION
Ul
Material
AlaOa
Clay No. 1
Clay No. 2
Clay No. 3
Clay No. 3
Clay, M and D
Fly Ash
Fly Ash
Molecular Sieve, kA
Molecular Sieve, 5A
Molecular Sieve, 13X
White Sand
Sludge
Description
Minus 200 mesh
Kaolin, minus 200 mesh
Bentonite, minus 200 mesh
Attapulgite, minus 200 mesh
Same as above, "but fired at lkOO° F for 10 min
Ball clay, mostly kaolinite
Similar to coal ash but not completely burned,
minus bOO mesh
Same as above, sintered, 1/2-inch x 1/2-inch
Hewlett-Packard, 60 x 80 mesh
F and M Scientific, 30 x 60 mesh
F and M Scientific, 30 x 60 mesh
Common, hardware store variety
From limestone neutralization of South Greensburg
Terminal
PH
3-2
3.1
6.2
5.6
3.3
*.5
5.9
5.3
10.0
6.k
7.3
3.2
6.6
Percent
Fe2*
Oxidized
5
15
69
61
21
73
77
0
82
78
89
3
73
coal mine drainage
-------
sions so that the short range van der Waals1 forces can furnish the
attraction required to cause coagulation and thus markedly increase the
settling rate. The electrophoretic mobility studies were undertaken to
examine the effect of various coagulant aids (electrolytes, polyelec-
trolytes, and inert solids) on the electrostatic charge of ferrous hy-
droxide particles and.'to apply the information gained toward improved
settling of these particles.
Electrophoretic Mobility Studies
The effect of coagulant aids on the electrostatic charge (zeta po-
tential) on particles in suspension is illustrated in Figure 17. Addi-
tion of < 1 ppm of some types of coagulant aids will achieve the iso-
electric point (curve A); an excess amount of this same type is actually
detrimental since it produces a more dispersed suspension. However,
the isoelectric point is never achieved with other types of coagulant
aids (curve B). It is at or near the isoelectric point, where the
forces of mutual repulsion are minimized, the coagulation and faster
settling can occur. Furthermore, high molecular weight, viscous poly-
mers, introduced at this point are adsorbed on the suspended solids,
thereby producing stable floes and improving the settling rate of the
solid particles. Some polymers act as electrolytes as well, and thus
fill the dual role by both minimizing the charge on the particles and
enhancing the formation of stable floes.
Effect of Coagulant Aids Alone
Various types of coagulant aids were first tested to establish
their effectiveness in minimizing the electrostatic charge on the
ferrous hydroxide particles. This effectiveness was indicated by the
amount of aid required to reduce the zeta potential to zero. Types
of aids tested included: (a) anionic polyelectrolytes, (b) anionic
electrolytes, and (c) inert solids.
Altogether, 11 electrolytes and polyelectrolytes and 3 inert
solids were tested. A description of the materials tested is given
in Table 23 together with the results obtained.
The first set of tests (Figure 18) shows the effect of 3 siliceous
materials, all of which can be considered anionic polyelectrolytes, on
the zeta potential of ferrous hydroxide. In only one case, with
solution Wo. 21*-, was the isoelectric point achieved; even here, charge
reversal was not achieved.
In the second set, three other anionic materials were tested
(Figure 19). The isoelectric point was reached with the anionic elec-
trolyte, 1^84 Ps(y, at a concentration of 100 ppm. The isoelectric point
was attained by the addition of approximately 75 ppm of Calgon C-55, a
mixture of materials recommended for silt control by Calgon Corporation.
This mixture appears to be both anionic and polymeric. Addition of
Calgon C-55 in concentrations greater than 75 ppm changes the zeta po-
66
-------
1
6
LU
N
ZONE OF PARTICLE REMOVAL
ZETA POTENTIAL = 0±5 mv
COAGULANT AID, ppm
Bituminous Coal Research, Inc. 2030G59
Figure 17. Effect of Coagulant Aids on Zeta Potential
-------
TABLE 23. EFFECT OF COAGULANT AIDS ON Fe(OH)a
Additive
Source
oo
Ludox
Ludox AS
Solution No. 2k
Calgon C-55
Calgon 37
Lomar D
Primafloc A-10
Purifloc A-21
Calgon 2UO
Poly-Floe 1130
M and D Clay
"Red Dog1'
Fly Ash
Description
Concentration at
Isoelectric Point, ppm
Added to Fe(OH)s
E. I, duPont de Nemours & Co.
E. I. duPont de Nemours & Co.
Philadelphia Quartz Co.
Fisher Scientific Co.
Calgon Corporation
Calgon Corporation
Diamond Shamrock Chemical Co.
Nopco Chemical Division
Rohm and Haas Co.
Dow Chemical Co.
Calgon Corporation
Betz Laboratories, Inc.
Kentucky-Tennessee Clay Co., Inc.
Sewickley Township
Westmoreland County, Pennsylvania coal ash, minus 200 mesh
Sodium stabilized
colloidal silica
Ammonia stabilized
colloidal silica
Activated silica sol
Anionic electrolyte
Anionic mixture
Clay-anionic polyelectrolyte
mixture
Naphthalene sulfonate polymer
Anionic polyelectrolyte
Anionic polyelectrolyte
Anionic polyelectrolyte
Anionic polyelectrolyte
Ball clay, minus ^JOO mesh
Similar to (completely burned)
Colfax Power Station
Duquesne Light Co.
Similar to coal ash but not
completely burned, minus
mesh
100
100
75
35
19
15
9
5
1
*
*
500
*Isoelectric point never achieved - remained electropositive
-------
+ 15-
+ 10-
Ul
0-
-
-10-
-15-
. / Ludox AS
Solution 24
\
0
SO
100
COAGULANT AID, ppm
150
200
Bituminous Coal Research, Inc. 2030G6O
Figure 18. Effect of Ludox HS-40, Ludox AS, and Solution No. 24 on Zeta
Potential of Fe(OH)2
69
-------
+ 20-1
+ 15-
+ 10-
ui
§
o-
-5-
-10-
-15-
Na4P807
I
40
I
80
120
160
200
COAGULANT AID, ppm
Bituminous Coal Research, Inc. 2030G61
Figure 19. Effect of Na4PtOj, Calgon C-55, and Calgon 37 on Zeta
Potential of Fe(OH)2
70
-------
tential from positive to negative. The third curve in Figure 19 shows
the effect of Calgon 37, which contains clay as a bulk additive in ad-
dition to the anionic polyelectrolyte; the isoelectric point was
reached after addition of 35 ppm of the aid.
Figure 20 shows the effect of typical anionic polyelectrolytes as
determined in the third set of tests. Efficiency, in terms of the
least amount of aid necessary to achieve the isoelectric point, de-
creased from Calgon 2^0 through Purifloc A-21 and Primafloc A-10, to
Lomar D. The most efficient aid from among all those tested was Calgon
2^K); approximately 5 ppm was sufficient to achieve the isoelectric
point.
Based on the results from the three sets of tests above, Calgon
2.kQ was chosen as the standard to be used in further work. However, a
more efficient coagulant aid has since been found, namely Paly-Floe
1130. The isoelectric point was achieved (Figure 21) with only 1 ppm
of aid. Other equally efficient coagulant aids are probably available.
It is recognized that efficiency must ultimately be determined on the
basis of cost per unit of coagulant aid necessary to achieve the iso-
electric point.
l
In the fourth set of tests, the effect of three inert solids, a
clay, "red dog", and a fly ash on ferrous hydroxide particles was de-
termined (Figure 22). The isoelectric point was not achieved with up
to 1700 ppm of clay, or up to 700 ppm of "red dog." A concentration
of approximately 500 ppm of fly ash, however, achieves the isoelectric
point, thus indicating that the fly ash is not truly inert. Fly ashes
are known to vary considerably in composition and to contain water-
soluble material which may be either alkaline or acidic in nature.
Effect of a Combination of Coagulant Aids
To determine the effect of adding both an inert solid and a poly-
electrolyte to ferrous hydroxide particles, a single test was made.
Figure 23 shows the effect of the addition of fly ash prior to the ad-
dition of Calgon 2^0, both added to ferrous hydroxide suspension. The
curve for the addition of Calgon 2^0 alone to ferrous hydroxide sus-
pension is also included in this figure for comparison. The amount of
fly ash used, 500 ppm, was chosen from Figure 22; it was added to the
ferrous hydroxide suspension 30 seconds before the addition of Calgon
24o. The amount of Calgon 2*K) necessary to achieve the isoelectric
point was reduced by 1 ppm.
Next, the effect of a change in the order of addition of materials
was examined. Figure 2k shows the effect of 500 ppm each of fly ash,
"re^d dog", and clay added to the synthetic coal mine water prior to the
lime, then the lime, followed in 30 seconds by Calgon 2^*0. The iso-
electric point was achieved with fly ash and only 2 ppm of Calgon
when they were added in this order.
71
-------
+ 20-1
+ 15-
+ 10-
> +5-
<
1 oJ
-5-
-10-
-15-
Primafloc A-10
Lomar D
Calgon 240
Purifloc A-21 *
T
0
I
5
I
10
I
20
15 20 25
COAGULANT AID, ppm
.. Bituminom Coal Research, Inc. 2030G62
Figure 20. Effect of Lomar D/ Primafloe A-10, Purifloc A-21, and Calgon
240 on Zeta Potential of Fe(OH)s
72
-------
15-,
+ 10-
+ 5-
I
5 o-
2
N
-5-
-10-
-15-
POLY-FLOC 1130, ppm
Bituminous Coal Reseirch, Inc. 2030G63
Figure 21. Effect of Poly-Floe 1130 on Zeta Potential of Fe(OH)8
73
-------
15-1
+ 10-
+ 5-
i °H
-10-
-15-
M and D Clay
i
0
500
1000
COAGULANT AID, ppm
1500
2000
Bituminous Coal Research, Inc. 2030C64
Figure 22. Effect of M and D Clay, "Red Dog/' and Fly Ash on Zeta
Potential of Fe(OH)?
7-4
-------
20-i
+ 15-
+ 10-
> +5-
Ill
5 o
S
N
-5-
-10-
-15-
Calgon 240 and Fly Ash
Calgon 240
I
2
I
4
I
6
8
I
10
COAGULANT AID, ppm
Bituminous Coal Research, Inc. 2030G65
Figure 23. Effect of Calgon 240, and Calgon 240 and Fly Ash on Zeta
Potential of Fe(OH)5
75
-------
+ 15-
+ 10-
+ 5-
<
p
Ul
5
i
-10-
-15-
M and D Clay and Calgon 240
Fly Ash and
Calgon 240
"Red Dog"and Calgon 240
r
o
i
2
I
4
I
6
I
8
\
10
COAGULANT AID, ppm
Bituminous Ceal Research, Inc. 2030666
Figure 24. Effect of Fly Ash and Calgon 240, "Red Dog" and Calgon 240,
and M and D Clay and Calgon 240 on Zeta Potential of Fe(OH)2
76
-------
Settling Rate Studies
Finally, the effect of a combination of inert solid and polyelec-
trolyte on settling rate was studied. Figure 25 shows the settling
rate of the sludge without treatment, and the rate with the addition of
fly ash followed "by lime and then Calgon 2ho. The use of fly ash-Calgon
2^0 combination increased the settling rate appreciably; the time re-
quired to reach a minimum sludge volume was reduced from about 100 min-
utes to about 35 minutes. In addition, there was about 25 percent re-
duction in total sludge volume. Settling of the sludge with clay or
"red dog" added together with Calgon 2*K) was similar to that achieved
with fly ash and Calgon
While time did not allow a more comprehensive study of settling
rate as affected by coagulant aids, improvement in settling of this par-
ticular sludge suggests further examination should be made of these
materials as aids in settling sludges produded by any type of coal mine
water neutralization.
Magnetic Sludge Studies
In the study of magnetic sludge formation, tests were conducted on
both synthetic and actual coal mine waters. .Reaction parameters studied
were pH, presence of impurities (principally aluminum), temperature, and
sludge concentration.
Studies Utilizing Synthetic Coal Mine Water
Initial tests were conducted on a ferrous sulfate solution contain-
ing 275 ppm Fe2+ and adjusted to pH 3.0 with sulfuric acid. Black mag-
netic precipitates were obtained readily with either sodium hydroxide or
lime added to achieve pH 10.0. However, the products from tests involv-
ing NaOH alkalization appeared to be denser, more granular, and exhib-
ited a stronger magnetic response than those resulting from Ca(OH)a
alkalization. When gentle aeration of the alkaline suspension was em-
ployed, the rate of conversion to a magnetic product was increased
noticeably. For example, with no aeration (stirring only), aeration at
50 ml/min, and aeration at 500 ml/min, magnetic response was observed
after 30, 15, and 5 minutes, respectively. Also, as the aeration rate
was increased, the increase in Eh toward more oxidizing potentials be-
came quite rapid. The fact that magnetic product was formed in all
cases, however, indicates that the magnetic precipitate, once formed,
is resistant to further oxidation to Fe(OH)3.
The effect of initial Fes* concentration on the reaction was also
investigated. Three experiments were conducted at initial Fe3* concen-
trations of 275, 180, and 100 ppm, respectively. Runs were conducted
with no aeration (stirring only), aeration at 50 ml/min, and aeration at
500 ml/min at each respective Fe^+ concentration level. In all cases,
black magnetic products were obtained within 20 minutes; for the runs in-
volving aeration, magnetic response was usually observed within 5 minutes,
77
-------
2000i
1500
1000-
ui
Q
Z
Q
LU
Q
<
O
z
O
3 500
• Fe(OH)s Sludge Untreated
• Fe(OH)s Sludge Treated with
Fly Ash and Calgon 240
V
30
I
60
i
90
120
150
TIME, minutes
Bituminous Coal Research, Inc. 2030G37
Figure 25. Effect of Treatment with Fly Ash and Calgon 240 on Settling
of Fe(OH)2 Sludge
78
-------
Studies Utilizing Actual Coal Mine Waters
In contrast to the results with synthetic coal mine water solutions,
the results with actual coal mine waters showed considerable variability
depending on reaction conditions. Coal mine waters from the Keystone
and South Greensburg sites of the Sewickley Creek basin area were chosen
for use, because of their characteristically high Fe2"1"/Fe3+ mole ratios,
and low aluminum contents.
Early efforts to produce a magnetic product at pH 10.0 were unsuc-
cessful in spite of attempts to promote the conversion, such as:
(a) the addition of iron metal powder (0.5 g) to the sample immediately
prior to alkalization, (b) the addition of iron metal powder followed by
stirring of the sample (at pH 5.0) for 30 minutes prior to alkalization,
(c) heating the sample to 75 to 80 C followed by the addition of iron
metal powder and NaOH alkalization, and (d) mixing the synthetic coal
mine water with the actual coal mine water in the proportions of 2:1,
1:1, and .1:2. actual:synthetic by volume. (The Fe2+ concentrations were
175, 200, and 225 ppm for the 2:1, 1:1, and 1:2 mixtures, respectively.)
In a further attempt, to promote the conversion to a magnetic pre-
cipitate, a portion of a magnetic sludge, previously obtained from lime
alkalization of the synthetic coal mine water, was added to a sample of
actual South .Greensburg coal mine water as seed material. The ultimate
reaction product at pH 10.0 was a rust-brown color and exhibited moder-
ate magnetic response. The rather sluggish behavior of the solid in a
magnetic field, ,and its high Fes+/Fe3'1" ratio (17.7), indicates that the
material may have been a closely consolidated mixture of hydrous ferric
oxide and the original magnetic seeding material. Except for this one
instance, the ultimate reaction products in all of the tests at pH 10.0
involving actual coal mine water consisted of orange, gelatinous, non-
magnetic solids, presumed to be completely oxidized hydrous ferric oxide.
In later experiments, a pH in the range 8.0 to 8.5 was maintained
during the precipitation of iron and the subsequent oxidation reaction,
in an effort to minimize interferences due to coprecipitation of magne-
sium hydroxide which occurs above pH 9.6. A 10 percent lime (Ca(OH)2 )
slurry was used for neutralization in all of these experiments with ac-
tual coal mine waters. In these studies, samples of the ferrous
hydroxide suspensions were selected at random and filtered on Whatman
No. k2. paper. Results of Fe2+ , analyses on the filtrates showed that
essentially no dissolved iron was present. In addition, no residual
dissolved iron was detected in filtrates from the final magnetic sludge
suspensions.
.With the Keystone coal mine water, which is practically free of
dissolved aluminum, precipitated ferrous hydroxide could be readily con-
verted to a dense, black, or dark brown magnetic precipitate near pH 8
provided the following two steps were taken:
79
-------
The initially formed ferrous hydroxide sludge was first concen-
trated by gravity settling or centrifugation followed by decantation
of the supernatant liquid, and then the thickened sludge was heated
to the range 80 to 85 C. Under these same conditions, however, a
magnetic product could not be obtained from South Greensburg mine
vater; the Al/Fe mole ratio in this mine water usually ranges between
O.lU and 0.1?. However, if ferrous sulfate was added either to the
original coal mine water or to the thickened sludge to decrease the
Al/Fe mole ratio to less than 0.12, a magnetic product could be
obtained.
Thus, in a typical experiment, ferrous sulfate was added to raw-
South Greensburg coal mine water to reduce the Al/Fe mole ratio from
O.I1!- to 0.0^ prior to lime addition. In a. second experiment using a
different sample of mine water from the same source, the Al/Fe mole
ratio was reduced from 0.19 to 0.12 in the same manner. In both cases,
dark brown magnetic products were obtained after heating the gravity-
concentrated sludges to about 80 C for 1.5 hours, with stirring and gen-
tle aeration. In the latter experiment the adjusted Al/Fe mole ratio
was confirmed by redissolving a weighed portion of the dried magnetic
sludge itself and analyzing the resulting solution by an emission spec-
trographic technique.
It was observed that the magnetic sludges prepared from South
Greensburg coal mine water, after adjustment of the Al/Fe mole ratio
with ferrous sulfate, were consistently bulkier, less dense, and lighter
in color (various shades of brown) than those prepared from Keystone
coal mine water. For example, the total magnetic sludge obtained from a
16-liter sample of Keystone coal mine water settled to a final volume of
87 ml. In both instances, the initial total iron concentration of the
raw coal mine water (after addition of ferrous sulfate in the case of
the South Greensburg sample) was about 300 ppm. This 3.5-fold differ-
ence in sludge volumes must be presumed due, at least in part, to the
presence of an appreciable amount of co-precipitated aluminum hydroxide
in the South Greensburg coal mine water sludge. In either case, how-
ever, conversion of the precipitated ferrous hydroxide sludges to a mag-
netic form resulted in at least a 5-fold reduction in settled sludge
volumes compared to the initial precipitates from lime neutralization.
The use of metallic iron to increase initial Fe2* concentration,
thereby decreasing the Al/Fe mole ratio, does not appear promising. For
example, in an experiment where South Greensburg coal mine water was
stirred with powdered iron for 30 minutes (at pH 5-0 and 23 C), the sol-
uble iron content increased by only 5 ppm.
The effect of impurities on the formation of a magnetic sludge has
been adequately demonstrated during these studies. For example, the '
fact that magnetic sludges were obtained from Keystone coal mine wate'r
at pH 8.0 but not at pH 10.0 is probably related to the known inhibiting
effect of magnesium hydroxide, which precipitates at pH 9*6.
80
-------
Furthermore, the fact that the South Greensburg coal mine water sludge
could not "be converted to a magnetic form until the aluminum/iron mole
ratio was reduced to 0.12 or less by the addition of ferrous sulfate, as
well as the ease of conversion exhibited by sludges from the aluminum-
free Keystone coal mine water, clearly indicate the inhibition due to
the presence of aluminum. Interestingly, similar results have been re-
ported by others. Kakabadse and Whinfrey (l8) reported that products
from the alkalization of mixed ferric sulfate/ferrous sulfate solutions
to pH 9.6 were ferromagnetic up to an Al/Fe ratio of 0.026, then became
increasingly nonmagnetic, and were completely nonmagnetic above an Al/Fe
ratio of 0.105. More recently, Stauffer (19) has found that the mag-
netic strength of the product, obtained by mixing heated, alkaline sus-
pensions of pure Fe(OH)8 and Fe(OH)3, diminished rapidly when the Al/Fe
mole ratio was greater than 0.123, and ferromagnetic properties had es-
sentially vanished when the Al/Fe mole ratio was 0.18^. The results of
the present study, therefore, are in surprisingly good agreement with
those of Stauffer, considering the fact that our results were obtained
with actual coal mine water samples where other interferences may have
been present.
Of further related interest, Stauffer reported that as the amount
of aluminum in the system increased, the reaction product became a
lighter brown color and appeared to be more gelatinous in texture. This
observation agrees with the results obtained in this study relating to
the preparation of a magnetic sludge from South Greensburg coal mine
water.
The effect of reaction temperature was quite evident in these
studies. At room temperature, the attempted magnetic conversion by
aeration of sludge from lime neutralization of Keystone coal mine water
was unsuccessful. At 50 C under the same conditions, the sludge exhib-
ited weak magnetic response after 2 hours. This response was transient,
however, and oxidation proceeded ultimately to nonmagnetic Fe(OH)3. By
contrast, dense, black magnetic sludges were obtained by the time the
reaction temperature of 80 C was achieved.
Although the data do not afford a precise explanation of this ef-
fect of elevated temperature on ease of magnetic sludge preparation, it
is believed to be related to enhanced ordering and possibly renuclea-
tion and growth of the magnetic iron oxide crystals at the higher tem-
peratures, as well as dehydration (accelerated aging) processes involv-
ing both Fe(OH)2 and Fe(OH)3 prior to their interaction to form the
ferrosoferric oxide. Similar processes may be operative as regards co-
precipitated calcium sulfate, which is the byproduct of lime neutrali-
zation. It is known that insoluble calcium sulfate tends to retard the
formation of a magnetic sludge at or near room temperature. In this
connection, tests with the Keystone coal mine water sludge at room tem-
perature were never conducted for more than a 6-hour period. Although
no magnetic material was ever found within this time interval, the sus-
pended solids characteristically darkened in color from blue-green to
81
-------
dark olive green, indicating some tendency to undergo the desired reac-
tion. After subsequent overnight standing at room temperature, however,
these sludges were invariably light brown or orange in color, and
nonmagnetic.
As mentioned above, a sludge thickening step was found to be advan-
tageous in the magnetic conversion process. In most instances, gravity
settling for about 30 minutes was employed, followed by decantation of
the supernatant liquid. Two anionic coagulant aids were found to be ef-
fective in reducing sludge settling time without having an adverse
effect on its subsequent conversion to a magnetic form. These coagulant
aids were Calgon 2^0 (Calgon Corporation), added to a h to 6 ppm level
in the sludge suspension, and Poly-Floe 1130 (Betz Laboratories, Inc.),
added to a level of 2 ppm.
The effect of further sludge thickening by centrifugation was also
investigated. Batch samples of gravity-settled ferrous hydroxide sludges
were centrifuged for 10 minutes at 1600 rpm. Centrifugation increased
the solids contents from about 2 to 9 percent by weight, a k.5-fold in-
crease. There was some evidence that this additional solids concentra-
tion step resulted in accelerated formation of the magnetic sludge during
heating. There were also indications that reductions in final settled
sludge volume and increases in solids contents of the magnetic sludge
were effected by the centrifugation step. For example, the entire amount
of sludge obtained from lime neutralization of 132 liters (35 gallons) of
Keystone coal mine water was concentrated by centrifuging to 1 liter.
This material was heated to 80-90 C for 2.5 hours; magnetic properties
were oDfeerved after the first 30 minutes. The magnetic sludge settled
overnight to a volume of 230 ml, corresponding to 1.7 ml of sludge per
liter of the original coal mine water sample, and had a solids content
of 17-7 percent be weight. By comparison, a similar experiment with only
gravity-settled solids (also from lime neutralization of Keystone coal
mine water) produced a settled magnetic sludge whose volume corresponded
to J.k ml per liter of coal mine water, and which contained 12.1 percent
solids by weight.
On the other hand, centrifuging did not seem to obviate the need
for elevated reaction temperatures or reduce the effect of interferences
due to cation impurities. Thus, the centrifuged solids from lime neu-
tralization of Keystone coal mine water still could not be converted to
a magnetic sludge at room temperature, and magnetic properties did not
appear in centrifuged, heated South Greensburg sludges until after the
requisite amount of ferrous sulfate had been added.
Finally, it should be pointed out that preliminary sludge thicken-
ing by gravity settling and/or centrifugation may not be absolutely
essential to the magnetic conversion process. However, if a heating
step is required, as the data indicate, it would seem more realistic in
terms of a practical coal mine water treatment process to minimize the
volume requiring heat treatment. This was the reasoning behind those
82
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phases of the experimental work involving preliminary sludge thickening.
Miscellaneous Studies
Effect of Coagulant Aids on Fe(OH)a
Particles of freshly prepared ferric hydroxide formed by limestone
neutralization of synthetic coal mine water carry a positive electro-
static charge (-i4 to +6 millivolts). Neutralization of this charge
should be accomplished by the addition of an anionic polyelectrolyte;
if so, coagulation should take place and thus markedly increase the
settling rate.
A series of graphs, Figures 26 to 29 inclusive, of zeta potential
versus concentration of various coagulant aids was prepared from elec-
trophoretic mobility measurements on ferric hydroxide particles. The
amounts of coagulant aids used are listed in Table 2k together with the
amounts needed with ferrous hydroxide in studies of non-oxidative neu-
tralization. The amount of coagulant aid required to achieve the iso-
electric point with ferric hydroxide is, in general, much less than
that required with ferrous hydroxide.
The results are sufficiently encouraging to warrant further study
in this area, particularly regarding settling rates.
Flotation Studies
Data from six separate flotation experiments are presented in
Table 25. In all cases, there was an insignificant separation of
froth from tailings. Only when fly ash was added (Test No. k) was there
any material in the froth. The method is completely unsatisfactory un-
der these conditions for separating the sludge from the liquid.
Calcium Ion Electrode
Concentration of calcium ion versus electrode potential plotted on
semi-log paper yielded a straight line calibration curve for solutions
containing only CaCls. Introduction of varying amounts of ferrous iron,
ferric iron, or aluminum to the same solutions of CaCl2, however, re-
sulted in randomly scattered points, which could not be utilized to
obtain the concentration (activity) of Caa*.
Although the electrode cannot be used to follow the fate of the
calcium ion during coal mine water neutralization using lime or lime-
stone, it may still be useful in following the rate of dissolution of
limestone in water, in comparing the effect of composition of the stone,
particle size, and surface area on solubility, or it may be used to mon-
itor the amount of calcium ion in the effluent after neutralization, if
all iron and aluminum are removed.
83
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Primafloc A-10
468
COAGULANT AID, ppm
10
12
Bituminous Coal Research, Inc. 2030G67
Figure 26. Effect of Poly-Floe 1130, Calgon C-55, Primafloc A-10 and
Solution No. 24 on Zeta Potential of Fe(OH)3
84.
-------
-MO-i
+ 5-
0-
IU
o
i -10-1
N
-15-
-20-
-25
468
COAGULANT AID, ppm
10 12
Bituminous Coal Research, Inc. 2030O68
Figure 27. Effect of Purifloc A-21, Ludox AS, and Lomar D on Zeta
Potential of Fe(OH)3
85
-------
+ 5-'
0-
t
2
Ul
N
-15-
-20-
-25
468
COAGULANT AID, ppm
10
12
Bituminous Coal Research, Inc. 2030G69
Figure 28. Effect of Calgon 240, Ludox HS-40, and Calgon 37 on Zeta
Potential of Fe(OH)3
86
-------
+ 10
+ 5-
2
2 -IOH
-15-
-20-
-25-
0 20 40 60 80 100 120
Na4PjO7 ppm
Bituminous Coal Research, Inc. 2030G52
Figure 29. Effect of Na4PjO7 on Zeta Potential of Fe(OH)3
87
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TABLE 2U. EFFECT OF COAGULANT AIDS ON Fe(OH)s AND Fe(OH)3
Name
Source
Concentration at
Isoelectric Point, ppm
Added to Fe(OH)a
Concentration at
Isoelectric Point, ppm
Added to Fe(OH)fl
Poty-Floc 1130
Calgon 2^0
Purifloc A-21
Calgon C-55
Ludox AS
Primafloc
A-10
Ludox HS-UO
Lomar D
Calgon 37
Solution 2U
Betz Labora-
tories, Inc.
Calgon Corp,
Dow Chemical Co.
Calgon Corp.
E. I. du Pont
de Nemours, Inc.
Rohm and Haas Co.
E. I. du Pont
de Nemours, Inc.
Diamond Shamrock
Chemical Co.
Calgon Corp.
Philadelphia
1
5
9
75
*
15
*
19
35
<0.1
O.U
O.U
0.8
1.1
1.2
1.5
1.5
1.8
Quartz Co.
(Fisher
Scientific)
100
100
1.8
6.0
Isoelectric point never achieved - remained electropositive.
-------
TABLE 25. FROTH FLOTATION TESTS
Volume
of Water
Treated,
Test No. ml
1 2500
2 2500
3 2500
h 2500
5 2500
6 2500
Additives
Lime
Kerosene
Methylisobutyl Carbincl
(MEBC)
Lime
MIBC
Poly-Floe 1130
MIBC
Poly-Floe 1130
MIBC
Poly-Floe 1130,
Fly Ash
MIBC
Lomar D
MIBC
Arquad 2C-75
Amount
of
Additives
to pH 8
2 drops
2 drops
to pH 8
2 drops
h ppm
2 drops
4 ppm
2 drops
U ppm
2.5 g
2 drops
U ppm
2 drops
k ppm
Air
Flow
Rate,
cfm
1.0
1.0
0.5
0.5
0.5
0.5
Stirrer
Speed,
rpm
650
650
650
650
650
1200
Froth Percent
Time, "by Weight
rpm min Froth Tailings
1 0.0 100.0
0.0 100.0
0.0 100.0
1 13.9
86.1
0.0 100.0
0.0 100.0
-------
ASTM Activities
No single method or set of conditions for the determination of
acidity.of coal mine water is utilized by laboratories involved in such
determinations, whether the acidity determination is pertinent for a
survey of coal mine drainage sources or for neutralization studies.
This has resulted in a lack of reproducibility of acidity values on the
same mine water as determined by two different laboratories. A lack of
understanding of the chemical equilibria involved in this determination
has even resulted in different acidity values on a single sample in the
same laboratory with two different operators.
Experimental conditions not yet resolved in this determination in-
clude: (a) size of sample, (b) internal acid-base indicator versus pH
meter for the end point, (c) heating ver-sus boiling the sample,
(d) duration of heating or boiling, (e) cooling before titrating versus
a hot titration, (f) addition of peroxide (versus no peroxide) to the
sample, and (g) the end point itself.
A standardized method for this acidity determination is a necessity
for coal mine drainage neutralization, particularly when water quality
standards define acidity limits. This, then, is the reason for our in-
volvement in ASTM Committee D-19 on Water—to bring this standardization
nearer.
Continuous Flow Tests
The limestone neutralization of the four actual coal mine waters as
demonstrated previously in batch-scale neutralizations tests, was
studied utilizing the one-gallon-per-minute continuous flow system.
South Greensburg and Keystone
South Greensburg coal mine discharge contained 95 ppm of Tes+ at a
pH of 5-1. In a number of experiments using the general procedure, the
treated water in the settling tank normally contained 50 ppm of Fe * at
pH 6.5. Aeration for 2 to 3 hours in the settling tanks (using air and
a manifold with two gas diffuser stones) reduced this level to about 3
to 10 ppm of Fe3+ and increased the pH to 6.6.
In a variation of the general procedure, an experiment was conduc-
ted in which aeration was first accomplished in the aeration tank for
100 minutes prior to, instead of after, addition of the limestone. This
resulted in a pH of 6.3 and ?6 ppm of Fe3+ in the settling tank. After
further aeration for 1 hour, the concentration of Fe2* was 48 ppra at pH
6A.
In the next two additional experiments the effect of recirculation
of the sludge resulting from the previous treatment of South Greensburg
discharge was studied. No attempt was made to concentrate the sludge.
90
-------
Sludge was added to the water (which had undergone addition of
limestone and mixing) in the aeration tank at a rate of one volume of
sludge per volume of freshly treated water. This, in effect, reduced
the flow rate of freshly treated water from 1.0 gpm to 0.5 gpm. The
water in the settling tank contained 52 ppm of Fe2+ at pH 6.3. Further
aeration for 1 hour in the settling tank resulted in water with 8 ppm
of Fe2+ at pH 6.k.
In the second experiment studying sludge recirculation, the sludge
was added initially to the limestone reactor at a rate equal to the
rate of flow of freshly treated water, resulting in a flow of 0.5 gpm
of coal mine water actually "being treated. The treated water in the
settling tank contained only 10 ppm of Fes+ at pH 6.6. Further aera-
tion for 1 hour in the settling tank resulted in water with pH 7.0 and
containing k ppm of Fe2*.
Keystone coal mine discharge contained 200 ppm of Fe2+ at a pH of
6.2. In a typical experiment, treatment of this discharge resulted in
a water containing approximately 100 ppm of Fes+ at pH 6.5 in the set-
tling tank. Further aeration in the settling tank for 1 hour reduced
the concentration of Fe2+ to 20 ppm at pH 6.5.
The effect of recycled sludge was examined in a manner similar to
that used with the South Greensburg discharge. In a typical experi-
ment, sludge from a previous neutralization of the Keystone discharge
was added to the limestone reactor tank in a volume equal to that of
untreated Keystone mine water, resulting in a flow rate of untreated
water of 0.5 gpm. Treated water entering the settling tank after
aeration now contained only 19 ppm of Fe in contrast to 100 ppm in
the previous experiments with no sludge recirculation. Further aera-
tion of the water in the settling tank showed a treated water with
less than 1 ppm of Fe2+ at pH 6.5.
The translation of limestone neutralization of both South
Greensburg discharge and Keystone discharge from batch scale to con-
tinuous flow was accomplished but with the expected difficulties.
Retention times which were sufficient to accomplish nearly complete
oxidation of ferrous iron on batch scale were not sufficient using
the continuous flow test apparatus. Reduction of iron to a satisfac-
tory level was accomplished in the neutralization of these two waters
by sludge recirculation. There was a difference depending on where
the sludge was added. Better results were obtained when the sludge
was introduced with the untreated mine water in the limestone reactor
tank.
Further studies are necessary to establish the minimum volume of
sludge necessary to effectively aid in the neutralization (and oxida-
tion) since this affects the rate of flow at which the untreated mine
water can be handled in the process.
91
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No claim is made as to the mechansim by which sludge recirculation
aids the process. It has been demonstrated, on batch scale only
(Figure 13), that greater than twice the stoichiometric amount of lime-
stone does not seem to increase the rate of ferrous iron oxidation.
However, the sludge does contain a substantial amount of unreacted lime-
stone in addition to the products which result from the treatment
process.
Tarrs
In all of the continuous flow experiments, a comparison is being
made with the results of the batch-scale neutralization experiments.
(See Discussion Section, Batch-scale Neutralization of Actual Coal Mine
Waters.) With the Tarrs discharge this was not possible for the following
reasons. At the time of sampling the Tarrs discharge for these contin-
uous flow experiments, the water at the point of discharge contained ap-
proximately 4o ppm of Fe8* at pH 3-0» or about half the amount present
in the same discharge when sampled for the earlier studies. (See Dis-
cussion Section, Batch-scale Neutralization of Actual Coal Mine Waters
and Oxidation of Ferrous Iron.) In spite of this reduced concentration
of ferrous iron, the studies were conducted with this water as described.
The general procedure was altered by first aerating the water in
the aerating tank, pumping this water into the limestone reactor, and
then adding limestone. The treated water in the settling tanks typi-
cally contained 5 to 20 ppm of Fes+ at pH 5-9« This iron level was at-
tained with aeration either in the presence or absence of activated
carbon in the aerating tank. Further aeration for 1 hour, in either
case, reduced the concentration of Fe2* to < 1 ppm and increased the pH
about 7.
Neutralization of this discharge using the continuous flow system
proceeded with little difficulty. Satisfactory oxidation of ferrous
iron was accomplished whether the activated carbon was present or not.
It must be stressed again that Tarrs discharge samples for these
continuous flow tests contained much less ferrous iron (in fact, much
less of all contaminants) than when sampled and used in the batch-scale
neutralization experiments. A comparison of batch with continuous flow
treatment, therefore, has little meaning since the quality of the water
had changed significantly. The reasons for the change in composition
of this water should be ascertained. A substitute should be found, if
necessary, for this type of coal mine discharge.
Thorn Run
Using the general procedure, treatment of Thorn Run discharge con-
taining Q ppm of Fe2+ at pH 3.0 resulted in water after aeration and
entering the settling tank containing 2 ppm of Fe2"1" at pH 6.4. Further
aeration increased the pH to 7-3 and decreased the Fe2"1" concentration to
1 ppm.
92
-------
A similar experiment, "but with limestone addition, mixing, and
aeration all carried out in the limestone reactor tank resulted in a re-
duction in Fes* from 23 ppm to 7 ppm and a pH increase from 2.M to 6.8.
In both cases, aluminum, present originally at a concentration of
approximately 50 ppm, was reduced to < 1 ppm.
Treatment of Thorn Ron discharge, which contains iron mostly in
the ferric state, proceeded with no difficulty. Limestone treatment
of this type of coal mine water is most satisfactory.
The results of the continuous flow experiments indicate that neu-
tralization and reduction of iron content can be accomplished by lime-
stone treatment of actual coal mine waters under conditions of flow
which simulate actual treatment plant operations. The results, however,
show that the treatment conditions must be altered depending on the type
of coal mine water.
For example, sludge recirculation was beneficial to the treatment
of the South Greensburg and the Keystone discharges in which ferrous
iron is the predominant species. In addition, the pH values of these
discharges were relatively high, 5-1 for South Greensburg and 6.2 for
Keystone.
Use of a catalyst (for example, activated carbon) to aid in the
oxidation of ferrous iron in a water having a relatively low pH, such
as the Tarrs discharge (at a pH of 3-0) might not only be beneficial
but also necessary.
No further steps in the treatment process, such as sludge recircula-
tion or use of a carbon catalyst, were necessary with the Thorn Run dis-
charge. Since this discharge contained only small amounts of iron in the
ferrous state but relatively large amounts of both iron in the ferric
state (about 60 ppm) and aluminum (about 50 ppm) at a pH of 3-0, the
treatment process involved principally neutralization and little or no
oxidation.
ACKNOWLEDGMENT
This report summarizes work carried out at Bituminous Coal Research,
Inc., under joint sponsorship' of the Federal Water Pollution Control
Administration, Commonwealth of Pennsylvania Coal Research Board, United
Mine Workers of America, and Bituminous Coal Research, Inc.
-------
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treatment plant," Mining Congr. J. 51 (3), 69-71 (1965).
10. Braley, S. A., "A pilot study of the neutralization of acid drain-
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Health, Sanit. Water Board (1951).
11. Boynton, R. S., "Chemistry and Technology of Lime and Limestone,"
New York: John Wiley and Sons, Inc., 1966. p 2.
12. Schumacher, E. A. and Heise, G. W. (to National Carbon Co., Inc.)>
"Activated carbon catalyst bodies and their preparation and use,"
U.S. Pat. 2,365,729 (Dec. 26, 19^*0.
13. Thomas, G. and Ingraham, T. R., "Kinetics of the carbon-catalyzed
air oxidation of ferrous ion in sulfuric acid solutions," Unit
Process Hydromet. 1, 6?-79 (1965).
95
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lU. Lamb, A. B. and Elder, L. W., Jr., "The electromotive activation of
oxygen," J. Am. Chem. Soc. 53, 137-63 (1931).
15. Posner, A. M., "The kinetics of the charcoal catalyzed autoxidation
of Fe8* ion in dilute HC1 solutions," Trans. Faraday Soc. ^9, 389-
95 (1953).
16. Stumm, W. and Lee, G. F., "Oxygenation of ferrous iron," Ind. Eng.
Chem. 53 (2), 1^3-6 (1961).
17. Laidler, K. J., "Kinetic laws in surface analysis," in "Catalysis,"
Vol. 1 (Pt. 1), P. H. Emmett, Ed., New York: Reinhold Publishing
Corp., 195^. P 152.
18. Kakabadse, G. J. and Whinfrey, P., "The effect of certain ions on
the formation of magnetite from aqueous solution," Ind. Chim. Beige
29 (2), 109-12 (196*0.
19. Stauffer, T. E., "The oxygenation of iron(ll)—relationship to coal
mine drainage treatment," M. S. Thesis, Pa. State Univ., 1968.
20. Jukkola, W. H., Steinman, H. E., and Young, E. F., Jr., "Coal mine
drainage treatment," 2nd Symp. Coal Mine Drainage Res. Preprints,
Pittsburgh, Pa., 1968. pp 376-85.
21. Kosowski, Z. V. and Henderson, R. H., "Design of mine drainage treat-
ment plant at Mountaineer Coal Company," Ibid, pp 396-9-
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96
0 V. S. GOVERNMENT PRINTING OFFICE : 1970 O - 381-570
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ABSTRACT
Four actual coal mine waters have been neutralized with
limestone both on a batch scale and by utilizing a contin-
uous flow apparatus. Variations in treatment procedure
were necessary depending on the characteristics of the
individual waters.
A standardized test was established to evaluate the reac-
tivity of the limestones. The following variables are of im-
portance in evaluating limestones for coal mine water
neutralization: (a) particle size, (b) Ca and Mg content,
and (c) surface area.
Ferrous iron oxidation has been accomplished with both
synthetic and actual coal mine water at low pH in the
presence of coal-derived activated carbon.
Electrophoretic mobility studies on precipitates obtained
by both lime and limestone neutralization of coal mine
water yielded information which can be applied for more
effective sludge removal.
ABSTRACT
Four actual coal mine waters have been neutralized with
limestone both on a batch scale and by utilizing a contin-
uous flow apparatus. Variations in treatment procedure
were necessary depending on the characteristics of the
individual waters.
A standardized test was established to evaluate the reac-
tivity of the limestones. The following variables are of im-
portance in evaluating limestones for coal mine water
neutralization: (a) particle size, (b) Ca and Mg content,
and (c) surface area.
Ferrous iron oxidation has been accomplished with both
synthetic and actual coal mine water at low pH in the
presence of coal-derived activated carbon.
Electrophoretic mobility studies on precipitates obtained
by both lime and limestone neutralization of coal mine
water yielded information which can be applied for more
effective sludge removal.
ABSTRACT
Four actual coal mine waters have been neutralized with
limestone both on a batch scale and by utilizing a contin-
uous flow apparatus. Variations in treatment procedure
were necessary depending on the characteristics of the
individual waters.
A standardized test was established to evaluate the reac-
tivity of the limestones. The following variables are of im-
portance in evaluating limestones for coal mine water
neutralization: (a) particle size, (b) Ca and Mg content,
and (c) surface area.
Ferrous iron oxidation has been accomplished with both
synthetic and actual coal mine water at low pH in the
presence of coal-derived activated carbon.
Electrophoretic mobility studies on precipitates obtained
by both lime and limestone neutralization of coal mine
water yielded information which can be applied for more
effective sludge removal.
ACCESSION NO:
KEY WORDS
Coal Mine Drainage
Neutralization
Limestone
Oxidation
Ferrous Iron
ACCESSION NO:
KEY WORDS
Coal Mine Drainage
Neutralization
Limestone
Oxidation
Ferrous Iron
ACCESSION NO:
KEY WORDS
Coal Mine Drainage
Neutralization
Limestone
Oxidation
Ferrous Iron
-------
Magnetic sludges were prepared using two different iron-
bearing waters. The conversion of precipitates to a mag-
netic form results in significant reductions in settled sludge
volumes as well as increases in solids content, compared to
the initially formed sludge obtained by lime neutralization
alone.
Data obtained in these studies indicate that the limestone
process offers considerable promise for an improved lower
cost method for treating several types of coal mine waters.
This report was submitted by Bituminous Coal Research,
Inc., in fulfillment of a project FWPCA Grant No. 63-01-
68, among the Federal Water Pollution Control Adminis-
tration, the Pennsylvania Coal Research Board, the United
Mine Workers of America, and Bituminous Coal Research,
Inc.
Carbon Catalyst
Sludge
Magnetic Sludge
Coagulation
Waste Water
Magnetic sludges were prepared using two different iron-
bearing waters. The conversion of precipitates to a mag-
netic form results in significant reductions in settled sludge
volumes as well as increases in solids content, compared to
the initially formed sludge obtained by lime neutralization
alone.
Data obtained in these studies indicate that the limestone
process offers considerable promise for an improved lower
cost method for treating several types of coal mine waters.
This report was submitted by Bituminous Coal Research,
Inc., in fulfillment of a project FWPCA Grant No. 63-01-
68, among the Federal Water Pollution Control Adminis-
tration, the Pennsylvania Coal Research Board, the United
Mine Workers of America, and Bituminous Coal Research,
Inc.
Carbon Catalyst
Sludge
Magnetic Sludge
Coagulation
Waste Water
Magnetic sludges were prepared using two different iron-
bearing waters. The conversion of precipitates to a mag-
netic form results in significant reductions in settled sludge
volumes as well as increases in solids content, compared to
the initially formed sludge obtained by lime neutralization
alone.
Data obtained in these studies indicate that the limestone
process offers considerable promise for an improved lower
cost method for treating several types of coal mine waters.-
This report was submitted by Bituminous Coal Research,
Inc., in fulfillment of a project FWPCA Grant No. 63-01-
68, among the Federal Water Pollution Control Adminis-
tration, the Pennsylvania Coal Research Board, the United
Mine Workers of America, and Bituminous Coal Research,
Inc.
Carbon Catalyst
Sludge
Magnetic Sludge
Coagulation
Waste Water
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