14010 FPR 04/71
Acid Mine Drainage Formation
   and Abatement

The Water Pollution Control Research Reports describe the
results and progress in the control and abatement of pollu-
tion in our Nation's waters.  They provide a central source
of information on the research, development, and demonstra-
tion activities in the Environmental Protection Agency,
Water Quality Office, through in-house research and grants
and contracts with Federal, State, and local agencies,
research institutions, and industrial organizations.

A triplicate abstract card sheet is included in the report
to facilitate information retrieval.  Space is provided on
the card for the user's accession number and for additional

Inquires pertaining to Water Pollution Control Research
Reports should be directed to the Head, Project Reports
System, Office of Research and Development, Environmental
Protection Agency, Water Quality Office, Washington, D.C.

Acid Mine Drainage Formation and Abatement
       The Ohio State University Research Foundation
                   13H Kinnear Road
                  Columbus Ohio 43212
                        for the


                  WATER QUALITY OFFICE
                    Program Number
                FWPCA Grant No. 14010 FPR
                      APRIL 1971

This report has been reviewed by the Environmental Protection
Agency and approved for publication.  Approval does not signify
that the contents necessarily reflect the views and policies
of the Environmental Protection Agency, nor does mention of
trade names or commercial products constitute endorsement or
recommendation for use.


The central theme of this report pertains to at-source control of
pyrite oxidation.  The current level of knowledge of acid mine drain-
age formation is critically reviewed, with emphasis on reaction
kinetics and reactant and product transport.  A reaction system
model is developed which provides a conceptual framework for sub-
sequent discussion dealing specifically with the physical, chemical,
and biological characteristics of pyritic systems encountered in
mining situations.  Practical considerations of at-source control
of acid mine drainage formation in underground mines, spoil banks,
and refuse piles are presented in the final section of the report.
Deficiencies in current knowledge which are brought out by this
report include: Descriptions of the physical environment existing
at pyrite oxidation sites in natural systems are far more incomplete
than the current understanding of pyrite oxidation kinetics; oxygen
transport is poorly described at this time, but is probably the rate-
controlling factor in most instances; serious questions exist as to
the effectiveness of air-sealing techniques as currently practiced;
the significance of bacterial catalysis of pyrite oxidation under
field conditions has not been established.

This report was submitted in fulfillment of Research Grant No.
l-WP-01328-01 between the Federal Water Pollution Control Adminis-
tration and The Ohio State University Research Foundation.
Key Words:  Acid mine water,* Pyrite,* Oxidation,* Pollution abatement,*
            Ferrobacillus, Strip mines, Underground mining, mine wastes













        (K. S. Shumate, E. E.  Smith, P. R.  Dugan,
         R. A. Brant, C. I. Randies)

        (K. S. Shumate and R.  A. Brant)

      THE CHEMICAL SYSTEM  (E. E. Smith)

        (P. R. Dugan and Ci. I. Randies)

        (R. A. Brant and K. S. Shumate)













Pertinent Rate Processes in Acid Mine Drainage

Micro View of Pyritic System

Local Transport and Reaction Environment

General Underground Mine Environment

Simplified Model of Pyritic System

Solution and Steady State Rate Equation

Possible Scheme for Mechanisms of Pyrite Oxidation






                               SECTION I

          Throughout this report, the authors have attempted to state
pertinent conclusions in the appropriate chapters.  In summary, we have
attempted to provide a critical and quantitative description of the
"real world" of acid mine drainage.  The major points developed in the
report are:

1.  The only pyritic material in natural systems which can be oxidized
at significant rates is that which is situated above the ground water
table, and which is exposed to an oxygen-containing atmosphere.  Pyrite
which is continually submerged in a surface or ground water pool will
be effectively blocked from oxygen, and no significant oxidation will

2.  A model has been developed which allows a quantitative description
of the rate of pyrite oxidation and acid product release in terms of the
physical, chemical, and biological characteristics of the system.

3.  Basic chemical reaction kinetics have been established for pyrite
oxidation by both 02 and Fe+3, which are the only oxidizing agents of
significance in natural systems.  The fundamental mechanism of pyrite
oxidation has not been established.  Os, however, is the ultimate oxidiz-
ing agent in all systems.

U.  Autotrophic bacteria of the Ferrobacillus - Thiobacillus group can
catalyze pyrite oxidation under favorable environmental conditions.  The
relative significance of chemical versus biological rates in natural
systems has not been established.

5.  Air sealing, without elimination of breathing induced by barometric
pressure changes, as is currently practiced, is not effective in giving
positive control of acid production in underground mines.  Mine flooding
is a positive means of eliminating acid production.

6.  Currently available field data are of such a nature that firm con-
clusions cannot be drawn as to pyrite oxidation or acid release rates,
and based on these data, quantitative determinations of the effectiveness
of abatement programs are questionable.  Data have not been obtained
which allow firm interpretations of abatement procedure effects in terms
of a rational reaction system model.  After application of an abatement
procedure, it will be necessary to collect mine drainage data for an
extended period of time, perhaps as long as five to ten years, before a
sound estimate may be made of the new acid production rate.  This is a
result of the slow response time of natural pyritic systems to imposed
changes.  The slow rate of product removal from the sites of pyrite oxi-
dation is largely responsible for this slow response.  The collection of

gas-phase oxygen data from within the systems may materially reduce the
time required to estimate the effect of an abatement procedure on pyrite
oxidation rates.

                               SECTION II

          The design of successful and economically feasible abatement
procedures for at-source control of acid mine drainage depends on the
ability to quantitatively describe rates of acid generation, and the
factors controlling these rates.  All pyritic systems behave in accord-
ance with the same fundamental principles, but the individuality of each
specific situation precludes the usefulness of empirical correlations
and generalized qualitative conclusions.  The following recommendations
relate to gaps in present knowledge which present obstacles to the
rational handling of real mine drainage situations.

1.  A rational reaction system model should be used to bridge the gap
between laboratory research and field applications.  Laboratory investi-
gations should be designed so that variable conditions which simulate
the natural environment are not only controlled, but are also described
in terms of physical, chemical, and biological environments, and perti-
nent mass transports and reaction kinetics.  Conversely, field projects
should be designed to allow the collection of data which can be inter-
preted in terms of the rational reaction system model.  Because of vari-
able hydrologic influences and slow system response to imposed changes,
short-term monitoring programs should be viewed with extreme caution.
2.  Mathematical descriptions of natural pyritic systems in terms of
rational reaction system models should be developed for the various major
types of systems.  Models should relate pyrite oxidation and product
removal rates to basic system characteristics.  Such models will provide
practical tools for the engineering design of abatement programs in
abandoned, operating, and proposed mining operations.

3.  The relative significance of biological and chemical rates of pyrite
oxidation must be established for the various types of mining situations.
Future work on abatement techniques depends significantly on this infor-
mation .

h.  With regard to underground mines, the development and trial of bulk-
head seals and sealing techniques should be continued, and mine flooding
practiced where possible.  The effectiveness of air seals placed far in
from the outcrop should be determined, and methods to prevent or counter-
act the "breathing" of air-sealed mines should be investigated.  The
effects of air and bulkhead seals used in conjunction with partial flood-
ing should be investigated.

5.  In the area of mine drainage treatment, emphasis should be given to
the investigation of biological treatment as a possible alternative to
chemical treatment.

6.  Although kinetic expressions for pyrite oxidation rates have been
developed, the fundamental mechanisms of these reactions have not been
determined.  It is recommended that efforts continue to determine basic
reaction mechanisms.

                              SECTION III

          Within the past decade, both State and Federal authorities
have become increasingly concerned about the problem of acid mine drain-
age.  The extent to which mine drainage is impairing surface water quality
has been described in recent reports1*2 and such information will not be
discussed here.  It is significant, however, that affected states have
established, or are establishing, more stringent regulations relating to
mine drainage quality than have existed in the past.  As in the case of
any industrial waste, there are basically two approaches to controlling
mine-acid pollution; i.e., abatement at the source, and treatment of the
waste.  Because acid mine drainage production has been shown to often
continue unabated for scores of years following the abandonment of mining
operations, treatment implies a cost that will continue for an indeter-
minantly long period of time.  Present engineering technology, however,
is sufficient to design and operate such treatment facilities.  A recent
report by Hill3 discusses the state of the art and research needs of
mine drainage treatment.

          Abatement at the source, the ultimate alternative to treatment,
is more controversial than treatment because there is serious doubt in
the minds of many as to the feasibility or even the possibility of such
an approach in many situations.  This is particularly true in the case
of abandoned underground mines.  Both the abatement of acid production
from abandoned operations, and the planning of existing and proposed
mining operations to provide for at-source abatement, depend on the same
basic principles.  The understanding of these principles is incomplete,
however, and there appears to be some confusion in the interpretation of
laboratory and field data.

          A primary purpose of this report, therefore, is to evaluate
the "state of the art" of acid mine drainage at-source abatement, and to
present a fundamental reaction system model which will hopefully resolve
some of the conflicting concepts, and offer a sound basis for understand-
ing, evaluating, and subsequently ameliorating the problem.  An attempt
is made within the present sphere of knowledge to more accurately describe
and define the important physical, chemical, and biological characteris-
tics which have a direct bearing on the rate of acid formation and acid
drainage resulting from the production of coal.  While this report is
written with specific reference to coal mining, the principles developed
apply generally to other pyritic systems.

          In addition to the discussion of at-source abatement, the bio-
logical system section of this report presents a discussion of the appli-
cation of biological treatment to acid drainage situations, and presents
also a brief discussion of the effects of acid drainage on the ecology
of receiving waters.

          The report is not intended to provide an annotated bibliographi-
cal review of mine drainage literature, since this is available else-
where.4  It is intended instead to provide a critical analysis of the
current level of understanding of the oxidation of pyritic materials in
mining environments, and to define specific areas in which additional
research and development is necessary to the practical solution of the
problem.  As the reader will see, there is disagreement in many instances
between the interpretations and conclusions of the authors of this report,
and other investigators active in this field.  There is also some dis-
agreement between the authors of specific sections of this report, par-
ticularly in regard to the important question of the significance of
microbial catalysis of pyrite oxidation.  Only through free discussion
of such points will progress be made in this field, and it is hoped that
this report will invite discussion, with faith in the fact that lively
argument promotes lasting understanding.

                              SECTION IV


 K. S. Shumate, E. E. Smith, P. R. Dugan, R. A. Brant, C. I. Randies
          It is becoming increasingly evident that much of the consider-
ation given to acid mine drainage formation and discharge has been taken
out of context.  In many instances, the problem has either been over-
simplified, or it has been assumed to be too complex to be handled by
other than gross empirical approaches.  As a result, misconceptions have
been generated from time to time, and there often appears to be con-
flicting data between laboratory and field investigations.  It is con-
sidered necessary, therefore, to present a conceptual model of pyrite
oxidation for use as a frame of reference for the discussion of acid
mine drainage control.  This model is nothing more than a description
of the reaction system, and can be readily expressed in both qualitative
and mathematical terms.  The pyritic system* description is intended to
account for those physical, chemical, and microbial factors which in-
fluence the production (the rate of discharge of pollutants to the
receiving stream) of acid mine drainage.  It considers the transport of
the mobile reactants (oxygen or ferric ion and water) to the pyrite, the
oxidation reaction leading to the formation of oxidation products
(hydrogen ion, sulfate ion, etc.), and the removal and transport of
products to the system boundary (mine opening, receiving stream, etc.).
This model is neither new nor controversial.  Rather, it is a restate-
ment of fundamental principles found in standard references pertinent
to the description of reaction systems.

          To avoid a premature involvement with mathematical expressions,
the system will first be outlined in a qualitative form.  A more detailed
discussion of physical, chemical, and biological considerations is given
in subsequent chapters.

          The oxidation of pyritic materials associated with coal and
other mined minerals has often been described by the following equations:
*The term "pyritic sytem" as used in this paper means any acid-producing
 situation associated with mining activity, such as gob piles,  spoil
 banks, underground mines, etc.

          FeS2(s) + 3-1/2 02 + H20 -» 2S04= + Fe+2 + 2H+          (l)

          Fe+2 + I/if 02 + H+ -> Fe+3 + 1/2 H20                    (2)

          Fe+3 + 3 H20 -^Fe(OH)3 +  + 3H+                         (3)
Since these are familiar to everyone involved in acid mine drainage work,
it is convenient to outline the model in relation to these equations.
It must "be remembered that these are gross stochiometric equations, and
although they indicate initial react ants and final products of oxidation,
they do not define reaction mechanisms, nor do they indicate intermediate
products which may cancel out of the overall equations.  Further, they
do not indicate all of the factors affecting the rates of each reaction,
nor do they specifically indicate the locations within a given system
at which the reactions take place.  It is likely that the simplicity of
these reactions, as they are popularly written, may itself be a factor
in the tendency toward over-simplification in the analysis of pyritic
oxidation systems.

          Often, the three equations are added, giving the overall stoch-
iometric relationship:

     FeS2(s) + 3-3A °2 + 3-1/2 H20 -» 2H2S04 + Fe(OH)3 I          (k)

This expression does indeed identify the initial reactants, and focuses
attention on the fact that sulfuric acid and ferric hydroxide are the
products of the complete reaction scheme.  It is the presence of these
products in surface waters which is to be avoided or, at least, controlled,
Once oxidation products are present in a stream, the only alternative is
treatment of the drainage.  This paper, however, addresses itself to the
goal of abatement of pyrite oxidation at the source.  In this regard, it
is misleading to represent the summation of Eqs. (l), (2), and (3) in
the form of Eq. (If), because this obscures the fact that the reactions
1 - 3 do not generally take place at the same location within the reaction
system.  Further, Eq. (l) does not represent the only possible reaction
of pyrite with an oxidizing agent to yield S04=, IT1", and Fe+2.  It has
been conclusively demonstrated that Fe+3 can also be an effective oxidiz-
ing agent.  To simplify the discussion at this point, the model will be
developed with 02 as the oxidizing agent which must be transported to
the pyrite surface.  Oxidation by Fe+3 will be discussed in a later sec-
tion of this section, and the relative importance of the two mechanisms
will be developed in subsequent sections of this report.

          Referring initially to Eq. (l), several pertinent points may
be drawn from fundamental considerations of this first reaction step.
These points are:

1.  In a natural pyritic system, the reaction shown in Eq.  (l)  is not at
equilibrium.  Pyrite in mining environments is continuously being oxidized
because the system is always open, in some degree,  to the entry of atmos-
pheric oxygen.  It is the rate of oxidation that determines the magnitude
of the mine drainage problem, and it is therefore realistic to  consider
Eq. (1) in terms of rate expressions.  Control of the reaction  must stem
from control of a rate-determining step in the reaction.   Equilibrium
constants merely indicate that the reaction will occur, but do  not give
any information as to the rate.

2.  The system is heterogeneous, involving the reaction of crystalline
pyrite (FeS^) with oxygen (gaseous or dissolved in  water),  and  water
(liquid or water vapor).  The reaction site is at the pyrite surface,
and it is the environment at this surface which determines  the  rate of
the reaction.  This rate may be expressed in kinetic terms  as a function
of the concentration of reacting species.  The "concentration"  of FeS2
is proportional to the surface area of the pyrite crystals, while other
chemical species may be represented in conventional concentration terms,
such as partial pressures (gas) or molar concentration (liquid).

3.  Equation  (l) indicates that oxygen is the ultimate electron acceptor
in the oxidation of pyrite, but does not necessarily imply a direct reac-
tion of oxygen with pyritic sulfur to form sulfate.  For  example, it is
possible that electrons may be transferred through a cyclic oxidation-
reduction of iron.  Such intermediates simply cancel out  in the stochio-
metric representation in Eq. (l).  Similarly, catalysis of this reaction
by various possible means, particularly by bacterial action, is not
reflected in Eq. (l).

U.  In discussing the system it is necessary to include terms describing
reaction kinetics (a function of the environment at the reaction site),
and also, terms describing the rate of transport of reactants to the
site.  Depending on the system, either reaction kinetics  or reactant
transport might be rate limiting.  Reaction kinetics expressions describe
the resistance to reaction at the site, while reactant transport expres-
sions describe the resistance to transport to the site.  These  resist-
ances can be thought of as resistances in series, and somewhat  analogous
to resistances in an electric circuit.  If, in a given system,  either
resistance is much larger than the other, it becomes the  rate-limiting
step, or the  step which would afford the most effective control of the

5.  The amount of oxygen dissolved in water entering a natural  system
supplies only an insignificant portion of the total demand for  oxygen
required at observed rates of pyrite oxidation.  Therefore, to  support
these rates, oxygen must enter the system as a gas.  Furthermore, oxygen
transport within the system must also be predominantly in the gas phase,
because the rate of diffusion of oxygen in water is extremely slow, and
pyrite covered by more than a centimeter or two of water  will be effec-
tively shielded from exposure to oxygen.  Thus, one must look to the

 factors controlling gas-phase 02 transport  for  a description  of this
 major and indispensible  link in the overall reaction chain.

           A typical element of pyrite undergoing active  oxidation might
 be visualized in the diagramatic form shown by  Fig.  1.
 02 (Atmospheric)
 Transport by convection or
 diffusion through porous
 media separating pyrite from
 open atmosphere.

 Diffusional transport of 02
 through water film, if
 Oxidation Product Removal-
                                      Liquid phase (seepage) or vapor
                                      phase (diffusion or convection)
                                      transport to pyrite surface,  to
                                      be adsorbed there,  or to be
                                      incorporated in water film, if
-*|7^- Pyrite surface covered by liquid
  ' water film of variable thickness,
  K with lower limit being adsorbed
  £ water vapor.
 /*r Reaction (l) occurs at pyrite
 // surfaceo
           Oxidation products accumulate at the pyrite surface,  or if a
 significant water film is present, they may diffuse away from site,  or
 be carried away in seepage.  However, if the thickness of the water  layer
 separating the pyrite from the vapor phase oxygen source is on  the order
 of a centimeter or more, oxygen diffusion through the water will be
 severely limited.  Pyrite 'buried' below the ground water table will
 undergo little or no oxidation.

        Fig. 1 - Pertinent Rate Processes in Acid Mine Drainage
These steps are put in more easily visualized form in Figs. 2, 3, and k
which show the reaction sites, the immediate reactant and product trans-
port environment, and the overall system environment, respectively, for
a possible drift mine situation.  Similar diagrams could have been drawn
for a gob pile, strip pit, or any type of natural pyrite oxidation system.

          Figure 2 represents the immediate vicinity of pyrite crystals
undergoing active oxidation.  The oxidation reaction shown by Eq. (l)
occurs at the pyrite surface, at a rate dictated by conditions at that
surface (02 concentration, nature of pyrite, etc.).  As previously stated,
the rate of reaction for both Case A and Case B (Fig. 2) depends.on the
concentrations of reactants at the point of reaction.  Furthermore, oxygen
must be transported to the point of reaction, and this transport requires

                                    Case A
   02  02
  02    02
   " o2
   02   02

o2 c    o2
02   2  02
  " 02
                  02  °202
                    02 02
                                                for  the  oxidation of
                                          pyrite in  the  absence of liquid
                                          •water. Hygroscopic  acid salts
                                          are  dissolved  by water from air
                                          to form concentrated solutions.
                                         Seepage movement of acid salt
                   Porous Media
                (unsaturated with
                 water, continuous
                 vapor phase)
                 0   °2   0
               /  2 02  02 2
              / 02  02  Q2 n
                   02  02
              X o2  o2   o2
              X        °2
                 02 Transport
                    Water Film
                                        Case  B
                                       Oxidation of FeS2 by 02
                                  Fe+3 " _  Fe+2  Movement by seepage,
                                               -*- diffusion,  or both
                Fig. 2.  Micro View of Pyritic System

 an expenditure of energy.   Unless  there is  a forced draft  (convection)
 of air through the porous  media and past the pyrite,  the 02 must move to
 the pyrite by molecular diffusion.   If 02 transport is by  diffusion, the
 energy expenditure appears as  a negative concentration gradient in the
 direction of transport. Referring to  Case  A,  the 02  concentration (par-
 tial pressure) at a buried pyrite  surface must,  in  general, be less than
 1/5 of an atmosphere.   Only if there is convective  transport of 02 can
 the oxygen concentrations  in the outside air and at the pyrite surface
 be similar.  If a film of  water (laminar flow seepage or stagnant film)
 cavers the pyrite, a second energy expenditure is required to drive the
 diffusive transport of oxygen  through  the film,  resulting  in a second
 concentration drop. This  applies  to Case B, where  the oxygen concentra-
 tion at the water-vapor interface must be greater than at  the water-
 pyrite interface.  It  is important  to  note  that  both  reactant transport
 and reaction rates at  the  pyrite surface are concentration-dependent
 terms in this type of  system,  and  are  inseparably coupled.  This is why
 it is often found convenient to draw the analogy between these two types
 of resistances (transport  and  reaction)  and a  simple  electrical circuit
 with two resistances in series.  Just  as  flow  of current in a simple
 two-resistance circuit depends  on the  magnitude  of  both resistances, so
 is the rate of pyrite  oxidation dependent on the magnitude of the trans-
 port and reaction resistances.

           Figure  3 is  a sketch  of an expanded view  of the sample under-
 ground mine pyrite oxidation system.   This  figure points out the three
 major factors which must be  taker! into account in the description of any
 pyrite oxidation  system.

 1.   One must  be able to describe the necessary gas-phase 02 transport to
 the  pyrite.   This  means  that the 02 concentration at the "free air"
 boundary,  the Q2  concentration  at the  air-water film interface, and the
 02 concentration  at the  pyrite  surface must all be known.  The overall
 "driving  force" of 02  transport in the absence of convective transport*
 is the  difference between the free air concentration and the concentration
 at the  pyrite  surface where 02 accepts electrons from pyrite.  The oxygen
 concentration  gradient  at any point determines the rate of oxygen trans-
 port through  the porous media and through any water film present on the
 pyrite.  This  gradient is shown schematically in Fig. 3 as  a decrease in
 02 concentration in the direction of transfer.  In the case of convective
 transport through the porous media, the concentration drop  would be pri-
marily  across the water film.

 2.  The concentration of 02 at the pyrite surface determines the rate of
pyrite  oxidation, which under steady-state conditions must  in turn be
equal to the rate of oxygen transport.   It should be noted  that since
02 transport must be in the gas phase through all but the last few
*Convective transport induced by atmospheric pressure fluctuations,  or
 "mine breathing."  This will be discussed in the next section.

                            02  Diffusion  Through
                                Porous  Media
                                    Seepage  and  / or
                                    Condensation  Water
            Surface  of Pyrite
            or Reaction Surface
                     Products of  Oxidation Removed
                     in  Seepage  Water.

                   02  Diffusion Through  Water  Layer
                  £:'&j Oxygen  Molecules
                                                                                 Seepage Water
Fig. 3.   Local Transport and Reaction Environment

millimeters of transport path, the amount of water in contact with pyrite
is relatively small, and hence, once oxidation is initiated, pH values
in this film will be quite low and salt concentrations will be quite high,
approaching saturation.  Chemical and biological kinetics of pyrite oxi-
dation must conform to these conditions.  The two rate processes, oxygen
transport and pyrite oxidation, will adjust themselves to the conditions
prevailing.  They will attain equal steady-state rates, and are inseparably
coupled in this manner.  Depending on the system, either can be "rate
controlling," and a successful abatement procedure must strike at the
rate controlling process.

3.  The transport process of ultimate concern is the rate of transport
of oxidation products, particularly iron, H+, and S04=, away from the
site to the receiving stream.  In the situation shown in Fig. k, the
vehicle of product transport out of the system is the flowing ground water.
In another situation, it might be the intermittent percolation of rain
water down through the overburden.  In any case, the regions of active
pyrite oxidation cannot be continuously saturated with ground water, or
the oxidation would be blocked because of lack of oxygen.  Referring to
Fig. If, one may consider the seepage or diffusion of oxidation products
as being tributary to the ground water flow.  Oxidation products may
either diffuse along water films to a region of active ground water flow
or, because of the hygroscopic nature of these salts, they may condense
water from the surrounding air to promote sufficient seepage to carry
products to regions of active ground water flow.  It is likely that many
sites of active oxidation do not continuously contribute oxidation prod-
ucts at or near the site.  When an intermittent flow of percolating rain
water or a rising ground water table approaches or intersects the region
of product storage, there will be a surge of acid products from the system.
This is regularly noticed in many instances during the spring increases
in ground water flow.  Even though many oxidation sites may be flooded
out during such a period, and the total rate of pyrite oxidation may be
at a minimum, the rate of transport of products out of the system might
be at its maximum.  It is important to note that the two processes (oxygen
transport and pyrite oxidation kinetics) which control the rate of pyrite
oxidation cannot at this time be directly measured in natural systems.
One must examine effluent drainage and, from this, attempt to infer the
extent and rate of pyrite oxidation.  Because of the intermittent and
unpredictable nature of this product removal mechanism, inferences as to
effects of abatement procedures on oxidation rates must be made with
considerable caution.

          Returning to equations 2 and 3? locations within the system
at which these reactions might occur can be defined.  It was indicated
above that oxidation-reduction of the Fe+£ - Fe+3 couple is very likely
a link in the electron transport chain leading to oxidation at the pyrite
surface.  However, the drainage from a site of pyrite oxidation is not
likely to contain much iron in the Fe+3 form (because of the slow rate
of Fe+2 oxidation in acid solution and the rapid rate of Fe+3 reduction
at the pyrite surface) unless bacterial action can catalyze the oxidation

                                                           Pervious  Sandstone
                                                             '   Fractured
                    -*• Water Movement
                    -> Oxygen Movement
                    E3 Water Saturated Region
                    H| Active  Pyrite  Oxidation
                                                                                impervious  Clay
                                           Fig.  k.   General Underground Mine Environment

rate  of  Fe+2  to Fe+3.   It should be noted that such catalysis has not
yet been directly observed in a natural environment, where the active
regions  cannot  be saturated with water, although the numbers of organisms
found in some drainages may indicate that catalysis occurs.

          After Fe+2 ion is transported away from the site of oxidation,
and mixed with  ground  waters which may raise the pH, the rate of
Fe+2  -»Fe+3 oxidation  may be greatly increased.  The growth of bacteria.,
particularly  in pooled water exposed to oxygen, as on the floor of a
mine,  may result in almost complete conversion of Fe+2 to Fe+3 in the
drainage before it leaves the mine.  The soluble iron at the site of
oxidation, however, may be essentially all in the Fe+2 state.  The char-
acteristic "yellow boy" precipitate formed by the reaction shown in
equation 3 is dependent on both Fe"1"3 concentration and on the pH, the
reaction becoming more complete as pH increases toward neutrality.  Both
reactions 2 and 3 may  begin to occur at the site of oxidation, but will
not proceed in  large degree until the concentrated acid seepage is diluted
with  ground water and  the pH begins to rise.  The reactions may become
very pronounced as diluted acid flows along the floor of the mine, and
will go  essentially to completion in the receiving waters below the mine.
However,  oxidation and precipitation reactions which occur after the
strong acid solution leaves the pyrite and finds its way to flowing
ground water  will have no effect on the rate of pyrite oxidation unless
additional pyrite is contacted along the way.

     Reaction Rates
          For purposes of demonstration,  the model will be developed for
the specific case outlined in the  figure  below,  and assuming Eq. (l) to
be the predominant pyrite oxidation reaction.  Again,  this limitation
of the pyrite oxidation reaction to the case of  direct oxidation by Q2
is done only to simplify presentation of  the model.
Concentre dor,
Cos Phase
  Permeoble media
liquid water flow periodic,  ,
unsaturated.or absent
I Pyrite
                                     Region of Active
                                     Saturated F'lo*
             Fig. 5.  Simplified
             Model of Pyritic

          Here,  it  is  assumed that the oxygen  concentration  c at the
porous media boundary  A is  CL, that oxygen transport through the porous
media is by diffusion  only  (no convective transport), that a water film
covers the pyrite,  and that the pyrite is oxidized directly  by 02 at the
pyrite surface.  Working with a unit area of pyrite,

                              rr = kiC3    ,                      (5)

               rr = rate of reaction (moles Oa/hr consumed),
               k]_ = reaction rate constant,
               03 - 02 cone, at pyrite surface, and
               n = apparent order of reaction.

To simplify this example, it will be assumed that n = 1.  At steady state,

     r^  = rate of Os transport through porous media  (moles
     rt2 = rate of 02 transport through water film (moles 02/hr).

Further, rti = ^j- (cj. - ca)     and   rta = ^f (c2 -  c3),        (7)

where     Dj_ = diffusivity of 02 through the porous media,

          I>2 = diffusivity of Q2 through the water,

          L  = length of diffusion path through porous media,

          X  = length of diffusion path through water film,

          C2 = Os cone, at porous media - water film interface, and

          Ca = Os cone, at pyrite surface.

Rearranging Eqs . (7)

          Cl -c
and                 YX                                   (8)
          c2 - C3 = — rt  = — rr     .
                    L>2       D2

Adding Eqs. (8)
and                                                              (9)
          rr =   —- (c.-ca)

Note that for a given value of GJ. - cs (the overall driving force for
oxygen transfer) an increase in L or X, or a decrease in Dj. or 1*2, will
lead to a decrease in rr.  However, for a given oxidation site in a given
system, L, X, DI, and D2 will be constant and Eq. (9) may be rewritten as

                           rr = km (Cl-c3)     ,                (10)

where km is the overall oxygen transfer coefficient for the system.  Com-
bining Eqs. (5) and (10) [with n = 1 in Eq. (5)1
This gives the oxygen concentration at the pyrite surface in terms of
the concentration of oxygen at the outside atmospheric boundary A, the
mass transport characteristics of the system (1%), and the kinetic rate
constant (kx ) .

Rearranging Eq. (ll)
=  r	;
Thus, the rate of oxidation may be expressed as a function of km, k^,
and the concentration of oxygen at the outside atmospheric boundary of
the system cx.  This is analogous to a simple electrical circuit with
two resistances, Rj. and R2j in series, in which case
               I = 	=	 E
where I = current flow and E'= potential drop.
          In looking at the problem in the manner shown above, it is not
necessary to assume a first-order reaction as shown in Eq. (5), nor is
it necessary to assume a single site with single values of L and X.

This was done only to simplify this example.  The model can be expanded
to fit complex situations, with the major limitation being valid data on
the factors determining mass transport and kinetics.  For example kj^ is
a function, in general, of the scale of the system, the number of sites,
and of the factors determining both molecular diffusion and convective
transport of oxygen, and of the electron transport intermediates in the
water film, if present.  Similarly, ^ is a function of oxygen, ferrous,
and ferric ion concentrations at the pyrite surface, the nature and sur-
face area of the exposed pyrite, and catalytic factors such as bacterial
activity.  All of these factors must be accounted for in a description
of the reaction system.

          In any specific case, either mass transport or kinetics might
be the rate-determining factor, depending on the relative values of kx
and km.  For example, take the case where r-^ (rate of 02 transport)
= 1%! (ci-ca), and rr = k^a.  As before, rr = r-t, and the simultaneous
solution of the expressions for r-t and rr will yield the rate of trans-
port (or of reaction) and the concentration of oxygen at the pyrite sur-
face which will be maintained at steady state.  This solution, which was
carried out analytically above, is demonstrated graphically below.
                                                          Solution.Case B
                       C, = Oxygen Concentration at Pyrife Surface
          Fig.  6.   Solution and Steady State  Rate  Equation
Three cases are shown:  Case A, kx » km; Case B, kx<« km ; and Case C,

          In Case A, it is seen that a change in either k]_ or ]% will
yield a significant change in the steady-state reaction rate; that is,
both are rate controlling.  In Case B, the steady-state reaction rate is
very sensitive to changes in kl9 but is insensitive to changes in ]%;
thus, the kinetics are rate controlling.  The reverse is true in Case C,
where mass transport is rate controlling.  To control pyrite oxidation
at the site, we must direct our efforts toward the control of the rate-
controlling step, which will vary from one situation to another.  It is
the ultimate effect of such procedures as mine sealing on the rate-
controlling step which is of importance.  A description of pyritic sys-
tems as a rational reaction system provides a rational tool for the
abatement of pyrite oxidation at the source.
                      OXIDATION BY FERRIC IRON

          It was stated above that both 02 and Fe+3 are potential oxidiz-
ing agents of pyrite in natural systems.  Rewriting Eq.  (1)  in more general

    FeS2(s) + electron acceptor -*-Fe+2 + 2S'VI)  + reduced electron acceptor

If ferric iron is the electron acceptor, then the pyrite oxidation
reaction may be rewritten as

          FeS2(s) + 1^ Fe+3 + 6H20 -^15Fe+2 + 2S04= + 16H+    .     (13)
The only available supply of the ferric iron required in this reaction
is through the continuous reoxidation of ferrous iron by oxygen, as shown
in Eq. (2).  Rewriting Eq. (2) to show the oxidation of ik moles of Fe+2,
               2 + 3-1/2 02 + lte+ ->>lUFe+3 +  7H20

Adding Eqs0 (13) and (lU) gives the overall reaction

          FeS2(s) + 3-1/2 02 + H20 -»- Fe+2 + 2S04= + 2H+     .     (15)

          Equation (15) is identical to Eq. (1)  and by either path
(02 or Fe+3 oxidation) the net reaction is the same.  In both cases,
oxygen must be supplied to the system at a rate equivalent to the rate
of pyrite oxidation.  The important difference lies in the fact that if
pyrite is oxidized by oxygen, 02 must be continuously supplied at the
pyrite surface, while for oxidation by ferric iron, ferric iron must be
continuously supplied.  For the continuous steady-state reaction, rates
of transport and reaction are related by the following expressions :

     Oxygen Oxidation

          Rate of 02 transport to            Rate of pyrite
          pyrite surface           ~         oxidation by 02

     Ferric Iron Oxidation

Rate of 02 trans-     Rate of oxida-     Rate of Fe+3     Rate of oxida-
port to -water      =  tion of         =  transport to  =  tion of pyrite
overlying FeS2        Fe+2 to Fe+3       pyrite sur-      by Fe+3
                      by 02 (bac-        face
                      terially cata-

A model description of the latter system (ferric oxidation) differs from
the oxygen oxidation system only in that two transport steps and two
reaction kinetics terms must be accounted for, rather than one transport
step and one reaction kinetics term.  Mass transport and reaction kinetics
will be specifically discussed in subsequent chapters.

          Just as reaction rates can be modeled rationally, so also can
product release rates be similarly modeled.  Referring to Fig. 5,  prod-
ucts of oxidation will move away from the site by either diffusion or
convection, depending on whether the water film on the pyrite is moving
or stagnant.  If there is no water film, the products will remain  at the
site.  The rate and frequency with which the products are removed  from
the system will depend on the mechanism of transport away from the site,
and the relative position of flowing ground water.  As ground water levels
rise, they will flush out products held near the site, or moving very
slowly in the vicinity of the site.  It is significant to note that rising
ground water may "flood out" oxidation sites, temporarily decreasing the
rate of oxidation, but at the same time, the rate of removal of oxidation
products from the system may be a maximum value.  The overall process of
product removal can be adequately represented by well-established  expres-
sions describing mass transport and ground water flow.  The primary factor
to bear in mind is the fact that the distance from the site to a region
of active ground water flow is variable with time and will vary with
changing ground water patterns.

          It is believed that through the description of pyrite  oxidation
systems in the context of the model presented above,  the discussion of
such systems will become clearer and problems of communication can be
considerably lessened.  This model provides a basic framework for  the
discussions in the following sections of this report, and,  it is further

hoped that it will have a clarifying influence on the general understand-
ing of pyrite oxidation in  "natural" systems.  This same type of model
has similar applications to other heterogeneous reaction systems.

                              SECTION V

                         THE PHYSICAL SYSTEM

                    K.  S. Shumate and R.  A.  Brant
          In the previous section,  pyritic systems were discussed in the
context of generalized reaction systems.  The purpose of this section is
to discuss the physical characteristics of pyritic systems which have an
important influence on the rate of  pyrite oxidation.   In order to set
the stage for this discussion several previously mentioned fundamental
characteristics are re-emphasized below.

          First, if pyrite is to be oxidized continuously, then all
reactants must be continuously made available at the reactive site; i.e.,
the pyritic surface.  In natural systems, the reactants are H20, FeS2,
and an oxidizing agent which can be either 02 or Fe+3 ion.  The FeS2 is
immobile, and initially present in the system, with the total amount of
FeS2 representing the total reaction capacity of the system.  H20 is
present in sufficient quantity in any damp environment in which there is
liquid water, or relative humidities approaching 100%.  The oxidizing
agent, whether  it be 02 or Fe+3, is not initially present in the system
in appreciable  quantities, and if it is not continuously supplied, the
reaction will soon  stop.  Further', the only source of Fe+3 is through
the oxidation of Fe+2 released from the pyrite, and 02 is the only avail-
able oxidizing  agent which can accomplish this reaction.  Therefore,
regardless of the oxidizing agent which is active at the pyrite surface,
02 must be continuously  supplied to the system at a rate chemically
equivalent to the rate of pyrite oxidation.  Since the amount of oxygen
which can enter the system as oxygen dissolved in water is insignificant
when compared to the amounts of oxidation products commonly observed in
acid drainages, it  follows that effectively all of the oxygen taking
part in the overall reaction must enter the system in the gas phase.*

          There are only two mechanisms by which 02 can be transported;
i.e., convective transport and molecular diffusion.  With regard to the
former mechanism, there are three major possibilities for the generation
*In accordance with Eq.  (h), the reaction of 1 mg 02 with pyrite will
 produce 1.6? mg acidity, as CaCOs.  The saturation value of dissolved
 oxygen in water is approximately 9 mg/£.  Therefore, oxygen dissolved
 in water before the water  contacts the pyrite can account for, at the
 most, approximately 9 x 1.6? = 15 mg/,0 acidity.

of significant oxygen movement.  First, and most obvious, would be the
continuous renewal of 02 at the surface of a spoil bank or refuse pile
by wind currents.  Because of the slow rate of the pyrite oxidation
reaction, little air movement would be necessary to maintain atmospheric
oxygen concentrations at pyritic surfaces directly exposed to the atmos-
phere .

          A second potentially important source of air movement appli-
cable to underground mines would be the effective ventilation of signif-
icant mine volumes by thermal convection currents, generated by tempera-
ture differentials inside and outside the mine.  In this case, pyritic
materials exposed at the surface within the mine could be continuously
supplied with oxygen.

          The third significant mechanism for the generation of convective
transport is the "breathing" of any semi-confined gas volume due to fluc-
tuations in atmospheric pressure.  The principle is most readily expressed
in terms of the ideal gas law,

                               Pv = nRT     ,
          P = absolute pressure,
          v = gas volume,
          n = number of moles of gas in volume v,
          R = universal gas constant, and
          T = absolute temperature.

Rewriting this expression in differential form, with v, R, and T held

                       dn/dP = v/RT = constant,

or, the number of moles of gas which must enter or leave any semi-confined
(vented) gas volume during a given pressure fluctuation is directly pro-
portional to the volume.

          This volume might be the interconnected pore spaces in a gob
pile or spoil bank, or the mined volume of an underground mine.  Since
atmospheric pressure fluctuations of one per cent or more (per cent of
absolute pressure) over a few days time are not uncommon, refuse piles
and underground mines will breathe one per cent or more of their vented
gas volumes in and out during these periods.  An atmospheric pressure
increase will force outside atmosphere into the system, and an atmospheric
pressure decrease will draw mine atmosphere out.  If the vented, semi-
confined gas volume is large, this can result in a significant amount of
oxygen transport.  Further, if pyritic material lies along the vent path-
ways or in the region to which gas is continually being supplied or
removed, it will have access to a more or less continuous supply of

          It should be noted that convective transport is a transfer
mechanism which is applicable to any fluid system, either gaseous or
liquid.  However, in mining situations, convective transport need only
be considered as it applies to the gas or vapor phase.  The only liquid
phase present is adsorbed water vapor, stagnant water films overlying
the pyritic surfaces, or slowly seeping ground water.  In all cases, the
water is either not flowing, or undergoing laminar flow, and there is no
turbulent mixing in the water phase.  Therefore, any movement of 02 across
the water barriers separating the pyritic surfaces from 02 in the vapor
phase must be by molecular diffusion, and will occur whenever there is
a concentration gradient of 02 through the water layer.  Similarly,
molecular diffusion of 02 through a mixture of gases will always occur
whenever there is an 02 concentration gradient.  When dealing with molec-
ular diffusion in any fluid phase, the rate of 02 transport can be rep-
resented by the expression:

                              — -  t) —

          N = rate of 02 transport, &** moles ,

          A = cross sectional area of fluid normal to the direction
              of transport, cm2,

         — = concentration gradient of 02 in the fluid along the
              direction of transport, gram moles 02. transport
                                         cm  -  cm
              is in the direction of the negative concentration
              gradient, or in the direction of decreasing concen-
              tration, and
          D = coefficient of diffusivity, £2-   .

          It is seen that for a given concentration gradient — , the
rate of transport per unit area  ^  is directly proportional to the
diffusivity D.  The magnitude of this coefficient is strongly dependent
on the nature of the fluid phase, being generally much higher in gases
than in liquids.  For example, for the diffusion of 02 through air at
25°C and 1 atm pressure, D = 0.206 ^— .  For the diffusion of 02 through
                                 2 sec
water at 25*C, D = 0.18 x 10~4 — .  Thus, the diffusivity of 02 in air
is slightly more than 10,000 times as great as the diffusivity of 02 in
water.  Water, however, is a more efficient diffusion barrier to the
transport of 02, as compared to air, by a factor of more than 10,000,
because of the low solubility of 02 in water.  For example, take a water
film 1 mm thick, exposed to air on one side and pyrite on the other; let
the dissolved oxygen concentration on the air side be saturated with 02

at 9 mg/£  and let the dissolved oxygen at the pyxite surface be U.5
Under these conditions, using the diffusivity given above,
        *     0.5-9)
                                o.l cm
          dc _       .5   gram
          dx ~ " 32 x 10s     cm4          *

     D = 0.18 x 10-4 3£ x 3.6 x 103 SS£ = 0.6U8 x 10'1 S2*
                     sec             nr                 nr

     » = - (0.6*8 x 10-1) x -J^-5 - 1 X 10-^ gram moles
     A                      32 x 10s              hr - cm^
Now, consider pyrite covered by a stagnant  layer of air 1 mm thick.  Let
the oxygen concentration at the outside boundary of the air layer be
20 per cent, which is approximately the chemical equivalent of 9 nig/,0 of
02 dissolved in water (air at 1 atm pressure,  20 per cent oxygen, and
25°C is an equilibrium with about 9 mg/£ 0$ dissolved in water).  Further,
let the oxygen concentration at the air-pyrite interface equal 10 per
cent, approximately equivalent to U.5 mg/^  dissolved oxygen in water.
Under these conditions, and using an oxygen diffusivity in air of
0.206 cm2 /sec, the rate of 02 transport across the 1 mm air layer is
calculated by Eq. (16) as approximately 3 X 10~2 gram moles/hr-cm2, or
3 X 10s times as great as in the case of diffusion through a 1 mm water
layer.  Similarly, if the stagnant air layer is 300 meters thick, with
aJi oxygen drop across the layer from 20 per cent to 10 per cent, the rate
of oxygen transport would be approximately  1 x 10"7 gram moles/hr-cm2,
or the same as the 1 mm water layer.  Thus, one can consider water (stag-
nant, or in laminar flow) to be 300,000 times  more effective than stag-
nant air as a barrier to oxygen diffusion.

          In the case of oxygen diffusion into a water film, with bac-
terial catalysis of Fe+2 to Fe+3, and transport of Fe+3 to the pyrite
surface to drive the oxidation of pyrite (see page 21), diffusion rates
become more difficult to analyze because of the complexity of the system.
However, molecular diffusion rates for iron ions in water are of the
same order of magnitude as for oxygen, and the extreme effectiveness of
water as a diffusion barrier for any electron acceptor, whether it is
02 or Fe+3, must still be considered.


          In order to provide a feeling for the effect of varying water
layer thickness on the rate of oxidation of pyrite, consider one gram
of pyrite exposed to air (20 per cent 02) and having a relative humidity
of 100 per cent.  Assume that the rate of oxygen utilization in pyrite
oxidation is 15 |-ig per hour per gram (a reasonable rate for finely
divided sulfur ball material), and that the effective cross sectional
area for 02 transport to the pyrite is 10 cm2.  If the pyrite is then
covered with water and agitated, the dissolved oxygen throughout the
water will approach saturation, and the oxidation rate will remain at
15l-ig per hour*.  However, there is no agitation of water layers in a
mining situation, so the only 02 transport to the pyrite is by molecular
diffusion.  Consider first a 1-mm water layer over the pyrite (either a
quiescent or laminar flow layer).  Assume that the rate of oxidation of
pyrite is directly proportional to the oxygen concentration at the pyrite
surface.** Then

                               W = kc2                          (1?)
      c2 = 02 concentration at the pyrite surface  (mg/£)s and
       W = rate of oxygen utilization
Assuming the saturation dissolved oxygen value at 20 per cent oxygen is
9 mg/,0, then when c2 = 9 mg/^, W = 15 i_tg/hr.

          Therefore, for this system, k = -£• = 1.6?.  The diffusivity of

                                              2                 2
oxygen in water is approximately 1.8 x 10~5 £5L_ = 6.^8 x 10~2 ^5-     }
                                            SCC                ill*
where     A = 10  cm2
          „   gram moles 02
          D = 6M x 10-2 S.
* Smith5 has  shown that for the  oxidation of pyrite by  oxygen, the  oxi-
  dation rate for pyrite  exposed to  air  at  a given oxygen  content is the
  same  as for pyrite  exposed  to  water  saturated with  oxygen with respect
  to the given air oxygen content.
**An oversimplification,  but  close to  that  observed for the oxidation of
  pyrite by oxygen, and sufficiently accurate  for the purpose of this


           „ _ gram moles Oa
           C -r-	**
1 gram mole of 02 = 32 x 106 ng, so N.=
                                        32 x 10fc
also 1 gram mole = 32 x 103 mg, so c« 2S = c' x 10'3 _2SL = 32 x 103 c __^. ,
                                       Si             cm               cm"
              32 x 10s

Therefore, substituting into Eq.. (l6),

          10        dx       0.1

where cj, = 02 concentration in mg/g, at the pyrite surface and c-j* = 02
concentration in mg/^ at the air-water film interface .


          W = 102 x Dc^ - 102 x Dc2
If we assume that the outside of the film is saturated with oxygen  (with
respect to air at 20 per cent Oa) at a value of 9 mg/^, then c^ ^ 9
          W = (102 x 6.U8 x ID'2 x 9) - (102 x 6.U8 x KT2 c2).  (18)

This is the transport rate, which, at steady state, must also be equal
to the Oa utilization rate

          W = 1.6? 02

Combining Eqs. (18) and (19), and solving for W,
          W = 58.3 - ^^                                        (20)
and            p
          W= 5^3

          W = 11.9 i-ig/hr

Thus, with a 1-mm film of water, the oxidation rate has dropped signi-
ficantly from 15 i^g/hr (no water film) to 11.9
          If the film is increased to a thickness of 1 cm, then Eq. 20

          W = 5.83 - ^

Similarly, a 2-cm thick overlying layer results in an equilibrium rate
of 2.U |ig/hr, and a 10 cm thickness of overlying water decreases the
rate to 0.56 ng/hr, or less than h per cent of the rate with no overlying
water film.

          In the case of the bacterially catalyzed oxidation of Fe+2 to
Fe+3 in the water film and oxidation of the pyrite by Fe+3, the calcula-
tion of water layer effect becomes much more complex.  However, the
mobile electron acceptors, 02 and Fe+3, still must move through the water
by diffusion, and the overall effect will be similar.

          It should be noted that the above calculations are sensitive
to the value assigned to the effective transport area, or to the avail-
able transport area per gram of exposed pyrite.  The authors feel that
the value assigned is reasonable, but there is no direct confirmation of
this assumption.

          Generally speaking, as the effective transport area A per unit
of pyrite activity decreases, the effectiveness of the water film as an
oxygen barrier increases.  For example, if a transport area of less than
10 cm2 were available to carry oxygen to the pyrite in the above example,
the equilibrium oxidation rate would be less than the values shown above
for the various film thicknesses.

          Natural pyritic systems may logically be separated into two
categories:  (a) Situations in which the pyrite is largely left in place,
but is exposed to oxidizing environments, (e.g., underground mines); and
(b) relocated materials, which includes both spoil piles and refuse piles,
A physical characterization of any type of pyritic system, however, must
include the following basic information:

1.  Type and location of pyritic material.

2.  Location of zones where pyrite is submerged below the  free water
surface of pooled water or bodies of ground water,  in which case the
pyrite is sealed off from oxidation.

3.  Nature and location of underground water flow patterns,  which provide
the vehicle for removing oxidation products from the  system.

U.  Physical characteristics of the structure surrounding  exposed* pyrite,
which determine the availability of 02 to pyrite by either convective
transport or molecular diffusion.

The various types of mining situations differ widely  in  these  respects,
and representative types will be discussed  separately.
     Underground Mines

          Underground mining situations  constitute the most  complex
pyritic systems.  Variables  include the  amount  of pyrite  and its  degree
of exposure; the rate at which surfaces  are refreshed; the location and
flow rate of underground water; the nature and  location of points of air
entry; and the amount, nature, and influence  of collapse  on  both  air and
water movement.  Further,  the presence of neutralizing minerals such as
CaCOs, Ca(HC03)2, and Mg(HCOs)2 are influential in changing  the charac-
teristics of the effluent  drainage.  To  generalize and simplify the sit-
uation without a knowledge and understanding  of these many aspects is to
invite confusion.  The statements  that follow represent a listing of
pertinent physical factors to be considered in  the evaluation of  an acid
producing mine and the indications and prognoses for  remedial measures.

          Most underground mining  to this date  is of  the  room and pillar
type, and up-dip drift mines in bituminous coal regions often produce
large quantities of acid drainage. However,  the geometry and location
of the coal bed may lead to  significant  drainage from other  mine  types,
such as shaft mines in the anthracite regions.   Knowledge of water sources
and water movement within  the system are of prime importance to the under-
standing of acid production  rates, and in the consideration  of remedial
methods.  A feature of primary significance is  the function  of a  mine as
an aquifer drainer.  A mine, by virtue of the extensive surface area that
is exposed, functions as a stimulator or accelerator  of drainage  of the
overlying formation.  Where  highly permeable  strata immediately overlie
the coal, mining activity  induces  an immediate  response in terms  of high
drainage rates.  Where relatively  tight  (impermeable) over-strata
 ^Exposed pyrite may be defined as pyrite to which a continuous oxygen
  supply is available; e.g., pyrite covered by several inches of water is
  not exposed pyrite, because of the low diffusivity of oxygen in water.

separate the mined zone and aquifer,  the response is delayed until col-
lapse exposes the water-bearing zones to the displaced areas.

          The rapid release of water  during the normal or  seasonal period
of high flow and during occasional heavy rainfalls cause abrupt flow
changes, and help flush and drain the reactive surfaces of the mine envi-
ronment.  This gives a cycle of (a) low or zero rate of water movement
past the pyrite, during which oxidation products accumulate near the
site, and (b) a flushing-washing cycle that dissolves the  salts and gives
an initially highly concentrated drainage solution.  This  cycle imposes
a quality shock on the receiving streams.  The resulting periodic acid
surge, which normally occurs annually, is often superimposed on a rela-
tively constant "base rate" of acid drainage from mines.6

          During the low-flow portion of the hydrologic cycle, gas trans-
port with resulting oxidation is at its maximum and product transport at
its minimum; during the wet hemicycle, the oxidation is at a minimum and
the product transport at its maximum.

          Consideration in describing fluid (air and water) transport
should be given to the following features:

1.  Permeability and porosity

     Significant porosity and permeability are usually found in
     sandstone.  However, all sandstone is not porous, for the
     interstices may be filled with smaller particles of bulking
     cement  (hydrated iron oxide, clay, gypsum, calcite, or silica).

2.  Jointing

     Joints are systematic cracks in the rock that arise from load
     release, and usually run at an angle to the bedding.   Several
     related sets may be present at any one location.  These are
     the conductors or pervious elements in rocks that would other-
     wise be impervious, and are not  manifest at moderate to great
     depth.  Coal, however, is characterized by very close sets of
     joints called cleat, and some fractions (vitrain) have a micro-
     cleat.  Joints are often widened by natural forces (gravity,
     weathering, mass wasting, and vegetation), especially near the

     Bedding plane joints are related to the history of sedimenta-
     tion and the eventual development of planes of weakness or
     separation parallel to the bedding.  Often these are  distinct
     planes between layers of rock, and virtually all bedded sedi-
     mentary rocks reflect this phenomenon.  These weaknesses are
     often revealed in the mining process where blasting may effect
     separation, or where the creation of the void or mined areas
     amplifies the inherent weakness  of the rock.  Porous  strata,

      joints, and bedding planes (when separated) are the basic
      passageways for fluids, both air and water.  The passageways
      created by mining are important and may in places obscure
      (such as in collapse areas) the primary route of fluid travel
      through rock.

           Gas transport can be at a high rate where convection is unin-
 hibited throughout a mining complex.  Where openings are closed the air
 must seek  other avenues such as through the permeable zones mentioned

           Water transport is a gravity phenomenon.  Infiltrated precipi-
 tation  may course its way through pervious rock but its course is basi-
 cally downward, and the regions of flow will, normally not be saturated
 with water.  The flow of ground water below the water table tends to be
 in a more  horizontal direction, and pyrite below the ground water table
 is effectively sealed off from oxidation.  Occasionally artesian condi-
 tions occur that cause water levels to rise in some mines.  Natural
 drainage finds its path through the mine as a function of the geologic
 structure  and of gravity,  and each mine win have individual character-
 istics.  The percolation of water over internal waste, and over and
 through pillars to eventually reach the mine courses is controlled by
 porosity and joints, and the interception of water in the more remote
 areas of the mine.
     Strip Mines

          In strip mines, the pyritic materials in the high wall consti-
tute a special case of pyritic materials left in place.  Because there
is no underground mined volume, oxygen transport to the pyrite is
restricted to regions relatively close to the high wall surface.  Aside
from this restriction, the system characteristics of high walls will be
similar to those of underground mines.  However, the pollution potential
of a stripped area resides primarily in the pyrite incorporated in the
spoil pile, since the total exposed surface area of this pyrite will
generally be much greater than pyrite exposed to oxidation in the high

          Depending on the placement of material in the spoil piles,
pyritic materials may be at or near the surface.  It is unlikely that
materials buried several feet or more beneath the surface can undergo
significant oxidation because of the restriction of 02 diffusion to these
depths, and the reaction zone is most probably restricted to the outer
layers of the pile.  This provides easy access and observation, but also
presents a rapidly refreshed surface, unlimited air contact with the
pyritic surfaces, and susceptibility to an immediate rapid "flush-out"
during periods of precipitation.  In the past the most reactive materials
have been put at the outermost surfaces of spoil piles.  There is an
increasing awareness of the problems generated by this practice, and in
general efforts are currently being made to reduce pyrite exposure by


the burial of high pyrite content materials deep within the spoil piles.
In some areas the strata are sufficiently impregnated with pyrite to defy
even these procedures; however, present strip mining practices have
brought improvements to both the land surface and to drainage water  from
the affected areas.
     Refuse Piles

          Refuse piles are very similar to spoil banks as far as morphol-
ogy is concerned.  The pyrite content is often much higher,  however,  and
the matrix generally contains large proportions of clay minerals of the
kaolinite or illite groups.  Pyritic materials are distributed throughout
the pile, rather than being localized, as in the case of spoil piles.
The passage of gas or water through a "tight" refuse pile may be highly
restricted.  Recent examination of refuse piles of clayey nature7 showed
only a 6- to l4-inch zone to have been altered by weathering; below this
zone, the main body of refuse material shows little or no pyrite oxida-
tion.  A similar situation occurs in many spoil piles, but where the
materials are largely of porous nature, percolation and breathing factors
become much more pronounced, resulting in thicker zones of weathering.

          It should be noted that even though significant pyrite oxida-
tion is likely to occur only in the surface layers of spoil  and refuse
piles, water of phenomenally high acidity may accumulate in  ground water
pools within the piles, because of the leaching of concentrated solutions
from the outer surface during periods of precipitation.

                              SECTION VI

                          THE CHEMICAL SYSTEM

                              E. E. Smith
          In this section, the chemistry (i.e., the chemical mechanism
and chemical reaction kinetics involved in pyrite oxidation) will be
examined.  In relation to the conceptual model this section will be con-
cerned with chemical rather than physical processes.  The transport of
reactants to the reaction site are eliminated as constraints on reaction
rate, either by design of the experiment or by definition of the reacting

          Because the pyrite oxidation reaction is so slow under normal
conditions, experimental conditions can be used to isolate different
mechanisms and individually evaluate the kinetics involved.  Two mechan-
isms have been studied:  (l) 02 oxidation, or oxidation by adsorbed
oxygen, in which case oxygen must "be transported to the pyrite surface;
and (2) Fe+3 oxidation or oxidation by ferric ions, in which case Fe+3
ions must be transported to the pyrite surface.  The following discussion
presents the different methods used to evaluate pyrite oxidation in rela-
tion to these mechanisms.

          Two basic approaches to the study of pyrite oxidation have been
used; i.e.,  (l) the geochemical approach, and  (2) reaction kinetics.

          In this discussion, the geochemical area is broadened to include
any study which seeks to interpret the pyrite reaction system by use of
chemical thermodynamic principles, or equilibrium relationships.  Gener-
ally this approach uses equilibrium or thermodynamic data to evaluate
reaction mechanisms which are possible under the conditions imposed on
or by the system.  Garrels and Christ8 provide the most detailed descrip-
tion of concepts used by the several workers in this area.  Sato9
described the geochemical environment of sulfide ores in terms of E^ and
pH.  From field measurement and experimental oxidations of iron-containing
solutions, the probable ranges of En and pH for a weathering environment
were determined.  The oxidation potential for the weathering environment
was reported to depend mostly on the reduction mechanism of oxygen.

          In a companion paper, Sato10 attempted to clarify the oxidation
mechanism of pyrite by using experimentally determined single electrode
potentials of sulfide minerals.  Since the electrode potential is deter-
mined by the rate-limiting oxidation-reduction reaction, Sato interpreted
his results as indicating that the rate-limiting oxidation process is the
oxidation of pyritic sulfur to S°, leading to the initial release of

ferrous ions and 82 molecules, which are apparently released simultane-

          Clark11 also used the E^-pH representation to define stability
fields for pyrite and the pertinent ionic species involved.   He described
pyrite oxidation as an electrochemical process involving the "corrosion"
of pyrite, and thermodynamic calculations were made to show  that ferric
ions and oxygen are potential oxidizing agents.

          Hem12'13 and his co-workers made detailed experimental studies
of the ferrous/ferric equilibrium in natural waters and inferred that
natural waters are sufficiently close to equilibrium to allow calculation
of both the concentrations and forms of the dissolved iron species.
These studies were not specifically related to mine waters,  nor to any
water having the low pH typical of acid mine drainage.

          From geochemical analyses of mine water,  Barnes and Clarke14
concluded that oxygen need not be a major oxidizing agent in pyrite oxi-
dation.  The reduction of water to hydrogen was proposed as  a possible
substitute.  Others have shown, from both experimental15 and thermody-
namic11 considerations, that the oxidation of  pyrite in the  absence  of
oxidizing agents such as oxygen or Fe+3 ions cannot be explained.

          More recently Barnes and Romberger16 used E^-pH diagrams to
represent stabilities of minerals and aqueous  species in solution at
different concentrations of iron, carbon,  and  sulfur.  These diagrams
led them to conclude that the leading question in the chemistry of acid
mine drainage is how low pH is reached at low  E^.  (it should be noted
that these authors were basing their conclusions on the nature of efflu-
ent water and/or water pooled within the mine, which does not represent
the composition of water at the pyrite reaction sites within a mine.)

     Kinetics of 02 Oxidation

          Earlier reports by Braley,17  Burke and Downs,18 and Nelson
et al.19 disagreed on the effect of oxygen concentration on rate of
pyrite oxidation, indicating that rate  varies as a function of oxygen
concentration from zero to first power.

          Clark11 found the rate to vary with oxygen to the two-thirds
power.  The nature of the rate-limiting reaction (in a laboratory envi-
ronment), and the effect of oxygen concentration, temperature, and of
water partial pressure in vapor phase*  oxidation, have been reported by
*For purposes of this report a vapor phase environment is defined as
 one in which the vapor phase is the continuous phase; i.e.,  the pyrite
 is not submerged in water and water does not fill the voids  in the solid

Morth and Smith.20  In these studies, experimental conditions were
designed to eliminate diffusional or mass transfer resistances.  The
rate-limiting mechanism was found to be a surface (chemical) reaction
under these conditions.
          Oxygen Concentration

          Jutte21 extended the work relating oxidation rate to oxygen
and nitrogen partial pressure to pressures exceeding 20 atm.  A definite
decrease in reaction rate with nitrogen pressure (at constant oxygen
partial pressure) was noted.

          Using the Hougen and Watson22 adsorption model, a rate equation
was derived23 which correlated well with experimental data:
                              1 + KiOs + K2I
          k  = reaction rate constant,
          02 = concentration of dissolved oxygen,
          KI = adsorption equilibrium constant for oxygen on pyrite,
          K2 = adsorption equilibrium constant for inert material on
               pyrite,   and
          I  = concentration of inert gas.
          Water Concentration

          Water was found?0 to be a reaction medium rather than a react-
ant in the rate-determining reactions in natural environments.  Oxidation
rate was a function of relative humidity in vapor phase oxidation and the
rate at 100 per cent relative humidity was the same as in liquid* (aque-
ous) phase oxidation at the same partial pressure of oxygen.

          Smith, Svanks, and Shumate23 found that change in pH has little
effect on oxidation rate at low pH; i.e., below 3.0-  However, as the pH
is raised, the oxidation rate increases, slowly at first, increasing to
the point where the rate doubles every two pH units above pH of 6.0.
*A liquid phase environment is defined here as one in which water is the
 continuous phase, or the pyrite is submerged in water.

          Pyrite Characteristics

          Birle24 and Clark11 determined surface areas of different types
 of pyrite and reported "sulfur "ball" to have approximately ten times the
 BET  surface area as llmuseum grade" pyrite of the same mesh size.

          A more detailed mineralogies! study of pyrite was made by
 Stiles.25  pyrite found in coals and associated strata were classified
 according to the nature and sequence of decomposition.  Of the seven
 classes suggested, those of highest reactivity were composed of pyrite
 masses containing pyrite crystals up to 5 nm in diameter, agglomerated
 into spheres 10-30 (jm in diameter.  The less reactive types had crystals
 of 0.25 to 2-mm in diameter.  Caruccio26 noted that significant variation
 in grain size accounts for the different reactivities of pyrite samples
 he examined.

          There is no evidence that trace impurities or features other
 than those that could be described by texture have a major effect on
 reactivity.  Different cations, such as chromium,  nickel, copper, and
 similar ions that are reported to accelerate oxidation in other systems,
were added to the reaction mixture with no significant effect.  High
 concentrations of anions such as phosphates did have an inhibitory effect,
 but  in concentrations below 200 mg/,0 negligible inhibition was noted.
 The  0s oxidation rate is remarkably insensitive to concentrations of
 substances other than oxygen.
          Effect of Temperature

          The influence of temperature on rate has been noted by a number
of investigators.18?20'27.  Over the range of temperatures comparable to
natural conditions, the rate approximately doubles for each 10°C rise.
          Desorption of Oxidation Products

          Oxidation rates in both vapor and liquid environments do not
appear to be limited by oxidation products.20  Rates are constant for
long periods of time.  Visible build-up of oxidation products in vapor-
phase oxidations do not influence rate.  The desorption of oxidation
products by adsorbed water is a continuous and effective mechanism for
renewing "reactive sites" on the pyrite surface.
          Summary of 02 Oxidation

          Quantitative information is available on the effect of

          1.  temperature,
          2.  oxygen concentration,
          3.  PH,
          4.  water (concentration) partial pressure,
          5-.  surface area or texture,   and
          6.  concentration of iron, sulfate, and other ions on
              the kinetics of 02 oxidation of pyrite.

          The rate-determining reaction, in the absence of mass transport
limitations, is a heterogeneous surface reaction involving an electron
transfer from pyrite to the oxidizing agent adsorbed on the surface.   A
detailed description of the "reactive site" is not now available,  although
the adsorption of molecular oxygen is undoubtedly a first step in  the
direct aerobic oxidation mechanism.
     Kinetics of Fe+3 Oxidation

          Work by Garrels and Thompson,28 who investigated the oxidation
of pyrite by ferric sulfate solutions, showed a dependence of the pyrite
oxidation rate on the ferric/ferrous ratio, and suggested that the rate-
controlling mechanism is related to adsorption of ferric and ferrous iron
on the pyrite surface.  They also concluded that the rate of oxidation
is chiefly a function of the oxidation-reduction potential (E^) of solu-
tion, and is independent of the total iron concentration.  Over the range
of Eh that could be examined by Garrels and Thompson their results are
valid; however, neither conclusion is basically correct in the light of
more recent data.

          Singer and Stumm15 have interpreted kinetic data of the type
developed by Garrels28 by using a model involving the cyclic oxidation
of ferrous ions to ferric, reduction of ferric by electron transfer with
pyrite, re-oxidation of ferrous by oxygen, etc.  Noting that oxidation
of ferrous-to-ferric ions is slow compared to reduction of ferric ions
by pyrite, Singer and Stumm concluded that the rate-limiting reaction in
the oxidation of pyrite is the oxidation of ferrous to ferric ions.
Based on this model, they reached the conclusions that (l) ferric iron
cannot exist in contact with pyritic agglomerates, and (2) the overall
rate of dissolution of pyrite is independent of the surface structure of

          A more definitive study of Fe+3 oxidation kinetics has been
reported by Smith, Svanks, and Shumate,23 and Smith, Svanks, and Halko.29
Using equipment which enabled them to determine anaerobic oxidation rates
at very high ferric/ferrous ratios (greater than 10,000-to-l) at constant
EMF, these investigators were able to study the effect of ferric/ferrous
ratio and total iron concentration on the rate of pyrite oxidation.

          By applying an adsorption model in which ferrous and ferric
ions compete for adsorption sites on the pyrite surface, a rate equation

•was derived which gave an excellent correlation of the rate data.
Although this  does not constitute proof, the correlation indicates that
an adsorption  phenomenon is a likely mechanism in Fe+3 pyrite oxidation.
If so,  the relative adsorption of ferrous and ferric ions, together with
the rate of production of ferric ions, will determine the Fe+3 oxidation

           A large difference was noted in the adsorption on pyrite of
ferrous ions relative to ferric, for sulfur ball compared to museum grade
pyrite.  In each  case the adsorption equilibrium constant for ferrous is
greater than ferric, but the selective adsorption of ferrous on museum
grade pyrite is much greater than that for sulfur ball.

           The  significance of E^ (or more precisely, EMF for the system
studied) was also  examined.   The data indicated that the oxidation-
reduction  potential of the solution had, in itself,  little effect on
oxidation  rate.  The fundamental variable was the ferric/ferrous rate
which,  in  the  system under examination, determined the EMF (the dependent
variable).  As the EMF was raised to the point where essentially all the
iron was in the ferric form,  the rate leveled off.  In solutions with
very little iron less than 3 ppm) the oxidation rate, even at high EMF's,
was  negligible.

          Simultaneous 02  and Fe+s oxidations were carried out by Smith,
Svariks, andHalko.29  The  rates  were independent of  one another over the
range of conditions investigated; i.e., the 02 oxidation rate was not
influenced by the EMF or total iron concentration in the solution.  At
the  same time,  the partial pressure of oxygen had no effect on the Fe+3
oxidation.  It therefore appears that the "reaction  sites" for 02 and
Fe+3 oxidation of the pyrite  are not the same.

          Based on these data, the rate-determining  regime of pyrite
oxidation was described in terms of the dissolved oxygen concentration
and of the ferric/ferrous  ratio  at the reaction site.  Comparison of
rates shows that in order  for the Fe+3 rate to be significant in an
environment exposed to air with  more than 15 per cent oxygen, the ferric/
ferrous ratio must be greater than 0.3 (2k per cent  ferric).   Such a
high ferric/ferrous ratio  in  waters in contact with  pyrite below pH 3.0
can only be achieved by microbial activity.  At higher pH where the
chemical oxidation rate of ferrous ions is much greater, the  concentra-
tion of ferric ions, because  of  their limited solubility at higher pH
values, is too low to develop a  significant Fe+3 oxidation rate.  These
data also  contradict the model of Singer and Stumm,15 since an appreci-
able concentration of ferric  ions can exist, at steady-state  conditions,
in the presence of pyrite.  In addition, oxidation rate is proportional
to pyrite  surface area in aerobic oxidation.

          Summary of Fe+3 Oxidation

          Quantitative information is available on the effects of ferric/
ferrous ratio and total iron concentration on the Fe+3 oxidation of
pyrite.  The following kinetic model, based on the competitive adsorption
of ferrous and ferric ions on reactive sites of pyrite, provides a good
quantitative expression of oxidation rate as a function of ferric/ferrous
ratio and total iron concentration:
                r =
                  k = reaction rate constant,  and
          ki and k^ = adsorption equilibrium constants for
                      ferric and ferrous ions.


          Thermodynamic or equilibrium relationships between minerals
and solutions are not intended to describe the kinetics of a process or
set of reactions which may occur as the system is displaced from equilib-
rium.  Application of oxidation-reduction potential (En) vs. pH relation-
ships have been very helpful in representing stability fields of minerals
and chemical sediments under conditions close to calculated equilibrium
conditions in which the quality of the solution phase in contact with
the mineral was known.  However, the application of these geochemical
concepts to acid mine drainage is more limited than normally considered.
For defining solubility regimes of solutions such as mine effluents in
relation to the mineral environment, these concepts are useful.  In this
case, reactions involved are fairly rapid, equilibrium conditions are
approached, and reactions occur largely within a solution of determinable

          However, as a means of describing the extent and rate of pyrite
oxidation, the geochemical approach does not appear to be applicable,
and in a sense is misleading.  Two facts account for this observation:
(l) the rate-determining reaction is a surface (not solution) reaction,
and (2) the pyritic system is far removed from equilibrium at the reactive
sites.  As shown by the conceptual model, the major source of acid mine
drainage is from pyrite exposed to a vapor phase.  Solution concentra-
tions as determined on effluent water or ground water from within or
around the mine are therefore not characteristic of the adsorbed water
in contact with the reactive pyrite area.  There is evidence that oxida-
tion of pyrite is not an electrochemical process in the same sense as is
corrosion of metals.  Although reactions involving an oxidation-reduction
step are, by definition, electrochemical in nature, it appears that the
rate of electron transfer (oxidation) is independent of solution E^;

Fe+3 oxidation is determined explicitly by ferric/ferrous  ratio and total
iron concentration, not E^.

          At this point it appears that the chemical oxidation of pyrite
is better interpreted using an adsorption model rather  than an electro-
chemical or thermodynamically defined model.  Changes in chemical oxida-
tion rates with oxygen and ferric and ferrous  ion concentration can be
accurately predicted on the basis of equations derived  from the adsorption

          The bacteria involved in the microbial  catalysis  of pyrite
oxidation have been reported to function through  the  oxidation of ferrous
ions to ferric.  Dugan and Lundgren30  note  the  energy supply for Ferro-
bacillus ferrooxidans to be the oxidation of ferrous  ions.   Large increases
in oxidation rate were noted27'31  when large quantities  of  bacteria were
added to the reaction system.

          Silverman32 suggested that bacteria operate through both a
"direct" and "indirect" contact mechanism in oxidizing pyrite.  Direct
oxidation implies the oxidation of pyrite through direct electron transfer
between the cell and pyrite on which the cell is  adsorbed.   Indirect
oxidation occurs by oxidation of pyrite by  ferric ions,  the ferric ions
being generated by bacterial oxidation of ferrous ions in solution.

          Bailey33 followed the rate of pyrite  oxidation as a function
of ferric ion concentration in a biological system  and observed no sig-
nificant change in rate until the  bacteria  had  oxidized  the iron in solu-
tion to 70 or 80 per cent ferric.   This indicates "indirect" oxidation
is of primary importance although  it does not rule  out a significant
contribution by direct oxidation.

          Recent unpublished data  show that in  terms  of  the ferric/ferrous
ratio generated by bacteria, the corresponding  oxidation rate is equiva-
lent to that predicted on the basis of non-biological Fe+3  oxidation
studies; this would indicate the "indirect" oxidation mechanism by micro-
bial action.

          If this is true, the Fe+3 oxidations  described earlier are
chemically analogous to the microbiological system.  In  the laboratory-
controlled Fe+3 oxidation system,  the  rate  of ferrous-to-ferric oxidation
is controlled at any desired level. In microbial systems,  a steady-state
condition is (or can be) reached in which the rate  of pyrite oxidation,
as determined by ferric/ferrous ratio  and total iron  concentration, is
equal to the rate of ferrous ion oxidation  required to maintain the
ferric/ferrous ratio.

                              SECTION VII

                         THE BIOLOGICAL SYSTEM

                    P. R. Dugan and C. I. Randies
          In general the involvement of biological systems in acid mine
drainage can be arbitrarily divided into three categories:

          A.  The influence of acid drainage on biological systems.
          B.  The influence of organisms on formation of acid drainage.
          C .  Biological means of abatement and treatment.

          Although pertinent literature references number several hundred,
an attempt has been made to cite only recent monographs, reviews, and
reports which are not generally available in the literature.

          Distinction between two categories of microbes is made on the
basis of nutritional requirements.  Both types have been discussed exten-
sively in the literature.34'38

          Autotrophic microorganisms are those organisms which utilize
carbon dioxide, either oxidation of minerals or photosynthesis as their
energy, and a few trace minerals and/or vitamins as additional nutrients.
This type of microbe, which includes the Thiobaccillus-Ferrobacillus
group of bacteria as well as algae, can therefore grow in a minimal
nutritional environment since all of the minimal requirements are readily
available in natural water (acid water in the case of Thiobacillus-

          Heterotrophic microbes are those which depend upon the oxida-
tion of reduced organic compounds for their energy in addition to their
cellular carbon requirements.  They also have nutritional mineral and/or
vitamin requirements similar to the autotrophic organisms.  The hetero-
trophic microbes include the Desulfovibrio-Desulfotomaculum group of
bacteria that have been recommended as possible agents for acid water
treatment.34  In general, specific differences among species of hetero-
trophic microbes is reflected in differences among types of organic com-
pounds required by each species.  This category of organism is somewhat
more fastidious nutritionally than the autotrophic category and nutri-
tional requirements vary widely.

          It should be pointed out that all organisms do not fall neatly
into one category or the other.  Many organisms are known which have the
facility to adapt either to an autotrophic or heterotrophic mode of exist-
ence and are referred to as facultative autotrophs or facultative


           It is generally recognized that acid drainage has a deleterious
influence  on multicellular species of plants and animals.39'40  However,
many protist organisms  (bacteria, algae, yeasts, and filamentous fungi)
have the capacity to live in a mine acid environment.  Indeed, certain
bacteria (i.e., certain Thiobacillus-Ferrobacillus) are acidophilic and
contribute to acid formation via their metabolic activities.  A summary
report of  the activities of microorganisms in acid mine drainage is

          Reports pertaining to isolation and correlation of the iron
and sulfur oxidizing chemoautotrophic bacteria of the Thiobacillus-
Ferrobacillus group indicate that their correlation with acidic coal mine
discharge is nearly 1; i.e., the bacteria can always be isolated from
acidic coal mine drainage.  Although positive correlations do not estab-
lish a cause and effect relationship, considerable evidence has accumu-
lated which strongly implicates the bacteria as contributive agents in
the formation of acid from reduced pyritic materials.34>35>38»41542

          The unique feature of acidic mine environments is the proximity
of pyrite (FeSg) or related mineral to the substance being mined.  In
iron pyrite both the iron and sulfur are in the reduced state (Fe+2 and
S~) and both can be oxidized by bacteria with an ultimate production of
acid (H+).  The resultant end products are ferric iron (Fe+3), sulfate
(S04=), and acid (H*), all, of which characterize acid mine drainage.

          Bacterial oxidation of ferrous iron proceeds in the following
generalized manner:

          Fe+2 -»Fe+3 + electron     ,

where the liberated electron is used by the bacterium as an energy source
and for the ultimate reduction of C02 into new cell material.

          Ferric iron produced biologically will either react with sulfide

          8Fe+3 + S= + kE20 -> 8Fe+2 + S04= + 5H+     ,

and result in recycling ferric to ferrous iron which is then again avail-
able to Ferrobacillus bacteria as an energy source; or ferric iron will
react nonbiologically with water,

          Fe+3 + 3H20 -+Fe(OH)3 + 3H+     ,

to form yellow-brown ferric hydroxide precipitates and acid.

          Acid is also produced microbiologically as the result of direct
oxidation of reduced sulfur compounds.  Several metabolic reactions have
been elucidated and these reactions are the subject of an excellent review
by Trudinger.43  In this context it must be recalled that the biological
oxidation of sulfide to sulfate involves several intermediary steps, not
all of which are completely understood.  No single species of organism
can be expected to possess all of the enzymes necessary for all known
sulfur oxidation pathways.  However, the following generalized reactions
will serve to illustrate how H+ and S04= can be produced as the result
of metabolism of reduced sulfur compounds by bacteria:

     (l)  Oxidation of sulfur probably proceeds by reduction of
          sulfur by glutathione (GSH) to glutathione polysulfide
          and subsequent oxidation of the
          S° + 2GSH  	*• H2S +
   or     S" + GSH	>-GSS0H
             elemental sulfur) /  I      r2  Hthiosulfate)     (21)
in which a net accumulation of thiosulfate and acid could be produced or
further used in biological reactions.

      (2)  Oxidation of thiosulfate (SS03=)

          S203= + 202 + H20 ->2S04= + 2H+                       (22)
          Thiosulfate produced in reaction (21) is ultimately oxidized
biologically to sulfate and acid through several steps.  One likely
mechanism is via the splitting of thiosulfate into sulfide (S=) and
sulfite (S0s=) .  Sulfite can be oxidized to sulfate microbiologically
in two ways; i.e., (a) via sulfite oxidase enzyme (E) which can be gen-
eralized as
          E + S03~ ->ES03~ - *- E~ + S04~ + 2H+
where E represents the enzyme, or (b) the adenosine phosphosulfate (APS)
reductase pathway which is somewhat more involved.37?44

      (3)   Sulfide ion can be oxidized biologically via reactions
           similar to those shown in reaction (21).

          Devising and assessing potential controls of acid formation
 in various types of mines, refuse piles, and associated materials depends
 upon an understanding of the processes involved in the oxidation of
 pyritic materials under the variable conditions existing at the actual

          It is appropriate here under "biology" to look at the problem
 of pyrite oxidation from a somewhat different viewpoint; namely, reaction
 mechanisms in the oxidation.  For purposes of discussion we have set up
 a  minimal reaction scheme (Fig.  7).  This has the virtue of allowing us
 to visualize the process and the factors that might be important in
 determining the rates of the process.  It serves as a guide in directing
 attention to various important facets of pyrite oxidation which may not
 be evident from stoichiometric equations or from reaction kinetics.

          Some factors are obvious from the stoichiometric equations
 commonly employed [Eqs.  (l)-(3),  Section IV]  but other  factors are not
 obvious because of catalytic activity or because they are "crossed out"
 of the reaction equations.  It is also valuable to consider possible
 reaction pathways because the overall reaction kinetics may or may not
 reveal these mechanisms,  and different parts  of the reaction may be
kinetically important under different conditions.

          In regard to Fig. 7, it is not the  intention for this diagram
 to describe the mechanism of pyrite oxidation; it is designed to illus-
trate the probable minimal complexity of the  process and provide a basis
for discussion and experimental work.  It is  possible that the reaction
to 2S does not involve,  as implied by Eq. (23), a removal of 2e (elec-
trons) from the 2S.   The oxidation may involve removal of electrons from
iron in the pyrite,  the  oxidized iron then could pick up electrons from
the 2S~ and be reduced again.  This would involve two iron atoms, or one
iron atom going through  two cycles.  It is also possible that the reac-
tion from 2S to 2S03= takes place in two steps, with the utilization of
 an oxygen molecule in each, and that these may differ mechanistically; e.g.,
                   H20                           3H20

T 2H*
i " "
1/40. . > 1/2 H
I \,'
** ' j_- TH+++
* i e
»*** 4- 3H n

	 >. 1
" * -V^ " ^.
8Fe 	 f- 8Fe**
i x
	 6H20 __
r0 /nu\ -i- ^w*



i V'~-4H'1'

1 --4H*
[i ! s
?H tO 1 - - ly/ > OC1
i_n2oU3j ( • «.j
1 	 2H20 	 1

                       Fig.  7.   Possible Scheme for  Mechanisms of Pyrite  Oxidation

          This -would provide an explanation for thiosulfate observed
 during  alkaline oxidation of pyrite, the iron for the second stage being
 tied up and not available for effective catalysis or electron transfer.
 It  is also  possible that this reaction is facilitated by the alkaline
 environment, or iron tie-up, so that the normal reaction is switched to
 this side reaction.

          It is necessary to accept the stoichiometric equations describ-
 ing pyrite  oxidation because these provide the necessary base for examin-
 ing the mechanisms and kinetics of the acid-forming process, and define
 certain irreducible minima which must be considered.

          There seems little doubt that the problem of acid formation
 involves the oxidation of pyrite in two separable oxidative steps
 [Eqs. (l) and (2)] followed by a nonoxidative formation of ferric iron
 precipitate, depicted in Eq. (3), as ferric hydroxide.  These equations
 suffice for stoichiometric and thermodynamic purposes, but do not neces-
 sarily  serve kinetic or reaction mechanism purposes, beyond supplying
 the bones upon which the body of kinetics and mechanisms is built.

          Participants in the reaction determine the kinetics of those
 reactions that are thermodynamically possible.  Some of the participants
 are obvious from the stoichiometrics of the reaction.  Others are not
 obvious  because they serve catalytic functions or "cancel out" in the
 overall reaction.  Both kinds of participants, which are not basically
 different since they both indeed participate in the reaction, may influ-
 ence ,the kinetics of the reaction.  It is with the second type of partic-
 ipants  that knowledge of reaction mechanisms is particularly pertinent
 and, conversely, where kinetic information can be relevant to determining
 reaction mechanism.

          As an example, if we look at Eq. (l), it is not apparent that
 ferrous  iron has anything to do with the reaction since the ferrous iron
 of  pyrite is not apparently oxidized.  From a kinetic, or mechanistic
 point of view, however, there is growing evidence that the rate-limiting
 step in pyrite oxidation may indeed be this oxidation of ferrous to ferric
 iron.   This fact is obscured by the rapid reduction of the ferric iron
 back to  the ferrous state again.

          In these reactions it is relevant to note that the pyrite con-
 tains two oxidizable constituents, the iron and the sulfur, and that
 93-5 per cent (lU/15) of the oxygen consumed in the overall reaction is
 employed in the oxidation of the sulfur component and only 6.5 per cent
 in  the iron component, while none of the oxygen consumed in Eq.  (l),
 stoichiometrically speaking, is used in iron oxidation.

          If iron were, kinetically or mechanistically speaking, the
 consumer of oxygen in Eq. (l), it being then reduced to ferrous iron, it
would have to be oxidized and reduced 1^ times during the oxidation of
 the sulfide portion.   This is the extreme.   To the extent that  oxygen

might directly participate in oxidation of the sulfide portion, either
by direct oxygenation or by serving as a direct electron acceptor, the
number of times the iron portion would be oxidized or reduced would be

          To put it another way, seven pairs of electrons must be trans-
ferred from the sulfur portion of the molecule to oxygen (2 per oxygen
atom, k per oxygen molecule).  The ferrous iron is capable of transferring
only one electron at a time.  If it is the only mediator between the
oxidation of the sulfur in pyrite and the reduction of oxygen, lU mole-
cules of ferrous iron would have to be oxidized and 14 of ferric iron
reduced for each pyrite molecule oxidized to the ferrous and sulfate
levels .

          A minimum of two turnovers would be necessary because the maxi-
mum amount of oxygen that could be used directly by oxygenation would be
302.  It is unlikely that oxidation from the sulfite to sulfate levels
involves oxygenation, or even direct electron transfer to oxygen, so that
four more electron transfers through ions are likely here.  If so, this
would limit direct oxygenation (direct electron transfer to oxygen) to
the involvement of 202.  In this case, six turnovers of ferrous -ferric
ion would be necessary.

          To illustrate this, let us break down the oxidation of the
other portion of the molecule into three hypothetical but possible steps.

          (S2) = -*2S° + 2e                                      (26)

          [2H+ + 2e + 1/202 ->H20]

          2S° + 202 -+2S02                                       (27)

          S02 + H20 -*S03= + 2H+

                + 2H20 -»2SC)4= + ^H+ + he                        (28)

                he + 02
          Reaction (26) involves going from the oxidation level of the
sulfur in pyrite to the level of sulfur itself, which, by its nature,
would necessarily somehow involve electron transfer.

          Reaction (2?) as depicted would be the only step in which direct
action of oxygen would be possible, although this is admittedly hypothet-
ical.  It could conceivably be an oxygenation, the only probable place
where this could occur, or it could also involve electron transfer either
directly to iron or through iron.

          Reaction (28), as indicated above,  undoubtedly does  not involve
direct oxygenation and probably not direct electron transfer to oxygen.

          These reactions have been selected  for illustration  of what
are probably the minimal steps, mechanistically,  that  can be visualized
in oxidation of the sulfur component of pyrite,  and the  most direct path-
way.  This is relevant kinetically since it indicates  minimal  relations
of participants in the reaction.  For example:

      (l)  This would suggest that  rates of oxidation of  Fe+2 would
          need be 2, 6, or lU times the rates of oxidation of  pyrite,
          assuming this oxidation  is rate limiting  and that ferric
          iron acts as oxidant of  the sulfur  portion of  pyrite in
          these different ways.

      (2)  If reaction (2?) is necessary to the oxidation of the
          sulfur portion of pyrite,  oxidation beyond the level of
          elemental sulfur could not occur anaerobically (e.g.,
          with Fe+3 as oxidant).   Since ferric iron can  apparently
          suffice,  in the absence  of oxygen,  to bring  about the
          oxidation of sulfide sulfur to sulfate, it indicates
          that oxygenation is not  an obligatory  step in  the oxi-
          dation and that all the  oxygen found in the  sulfate  can
          come from water.

          Reaction  (23) in Figure  7 [Eq.  (l)] is highly  exergonic, essen-
tially irreversible,  and hence there are no thermodynamic barriers to
its occurrence.  Further, it is unlikely that changing concentrations of
products can significantly affect  the reversibility of this equilibrium
reaction with attendant rate effects.   That the product  may in some
other way influence rate is not excluded (e.g., S04=,  H+, Fe+2).

          Concentrations of reactants,  however, must be  carefully con-
sidered.   First,  it is obvious that  this reaction cannot possibly proceed
as written unless at  least all three reactants are  present, and that the
influence of at least these three  reactants must be considered.

     (a)   FeSa.  The  insolubility  of this reactant  almost perforce
          means that  we must consider an effective  concentration
          which would be much less than the total concentration
          present.   There does not seem to be any actual measure
          of this effective concentration, but certainly surface
          area would be a closer approximation of effective concen-
          tration than total concentration, and might  be the rele-
          vant measure.

     (b)   Oxygen  concentration will be a factor  in  establishing the
          reaction  rate, providing one 'or both of the  other two
          reactants are not limiting.  Unless some  other oxidizing
          agent is  employed (e.g., Fe+3), there  is  no  alternative.

          When we consider that 3-5 molecules of oxygen are consumed
in reaction (l), with the concommitant change of pyritic sulfur from a
-1 to a + 6 oxidation state,  it is necessary that the reaction be more
complex than written in Eq. (l).

     (c)  HaO.  The presence  of water as a reactant in the equation
          should forestall any comments that it is not a reactant;
          it may also be significant as a reaction medium but this
          would be an additional function.  Not showing up in the
          stoichiometry of the reaction is the fact that wherever
          iron is the intermediary in electron transfer between
          pyrite oxidation and oxygen, water must be the source of
          the oxygen that ends up in the sulfate.  Hence, it is
          most probable that  water is more important than indicated
          by the stoichiometry of the reaction.

          All three of these  materials have, within limits, been shown
to be determining factors in  discussing either the kinetics or the  mech-
anism of pyrite oxidation.

          Reaction (2*0 of Figure 7 [Eq. (2)] is not a highly exergonic
reaction; hence, it is readily reversible.  This places this reaction
in a different light than the other two since it allows the reversible
oxidation and reduction of iron under the conditions of pyrite oxidation
and hence has catalytic potentialities both chemically and biologically.
This is not brought out in the stoichiometry of acid formation because
the ferric iron measured  (or ferrous iron disappearing) is that which
enters reaction  (25).  Stoichiometrically, reaction (23) may be the only
truly pertinent reaction  in acid formation, but kinetically reaction (2^)
may be most important.

          Reaction  (25)  [Eq.   (3)], the hydrolysis of Fe+3, yields the
end product of pyritic iron oxidation and in most circumstances ferric
precipitates do not form  at the site of pyrite oxidation, indicating that
the ferric iron that may  be formed by reaction (2k) at the oxidation site
is rapidly reduced again  rather than hydrolyzed.  Thus, reaction (25)
can be considered a secondary process not directly involved in acid for-
mation per se.

          There seems little doubt that iron oxidation is a significant
factor in pyrite oxidation; this may be through reaction (23) involving
oxidation of the iron in pyrite, which does not show up in the stoichio-
metric equation, or it may be through iron in solution, as in reaction
(24), or both.  Distinguishing between these two possibilities is impor-

          In view of the  admitted slow rate of the chemical oxidation
of ferrous iron by oxygen in acidic solution, and the role of this  oxi-
dation in pyrite oxidation, the role of bacteria catalyzing ferrous iron
oxidation in accelerating pyrite oxidation is readily seen.

          The extent to which the ferric-ferrous  couple participates  in
pyrite oxidation via an electron-transferring function will be  pertinent
to the extent of involvement of iron-oxidizing bacteria in determining
rates of oxidation.  Minimally, two moles of ferrous  iron would need  to
be oxidized per mole of pyrite oxidized,  and, maximally, fourteen moles
would need be oxidized.  From our present imcomplete  knowledge, it would
seem that at least six moles would be needed.



          A report on the potential use of heterotrophic anaerobic bac-
teria (Desulfovibrio and Desulfotomaculum) as a means of reducing sulfate
to mil -Fide in a.Hd mine water has been published.34'4* This  process  has
several advantageous aspects.

     (a)  Sulfide will reduce ferric ions to ferrous  ions and will
          precipitate ferrous ions as insoluble FeS,  thereby  remov-
          ing virtually a.n  iron from solution.
     (b)  It has also been reported that precipitated FeS is amenable
          to mechanical separation which would yield a sludge that
          could be further processed to yield a sulfide reagent for
          further use in treating mine water.45

     (c)  Metabolism of the heterotrophic Desulfovibrio-Desulfotomaculum
          group of bacteria also results in a net increase of pH
          of their environment.

     (d)  Metabolic byproducts of the anaerobic bacteria have an
          inhibitory effect on the chemoautotrophic iron-oxidizing

          Two primary difficulties must be overcome to accomplish sulfate
reduction in acidic waters.  Dissimilatory sulfate-reducing bacteria
require an oxidation-reduction potential of -150 to -200 mV; therefore
the water must be made anaerobic.  Secondly, a source of organic nutri-
ents to supply energy and carbon for the heterotrophic anaerobes is
required.  The addition of organic materials is favorable to the estab-
lishment of anaerobic heterotrophic microflora in acidic water.

        •  The process of biological sulfate reduction can be manipulated
in the laboratory to increase the overall efficiency, and attempts to
scale up the process seem to be successful.  This suggests that such a
process could be  developed into a practical abatement method at specific
locations.  Potential methods for accomplishing this process are lagoon-
ing, design of a  facility similar to those used for anaerobic sewage
digestion, and conversion of  certain mines into anaerobic mines where
the reduction process would proceed directly in the mine.


          The carbonaceous energy source for sulfate reducers could be
wood (saw) dust, sewage, waste paper or other domestic waste, algae,
aquatic weeds, or other waste vegetable material.  Activity of a third
group of bacteria was essential to accomplish this process.  The third
group, referred to as cellulose digesters, also proliferates under acidic
conditions and any low-cost cellulose should be able to supply nutrients
to the sulfate reducers.  The process of microbiological cellulose diges-
tion is exothermic and results in substantial heat liberation which could
be advantageous in treatment of water in cold climates.

          Processes involving the use of lime or carbonate treatment to
precipitate ferric iron or Fe(OH)s from solution are quite sensitive to
pH.  A high degree of iron removal at near neutral pH values depends
upon a high ratio of ferric to ferrous ion.  Autotrophic bacteria
(ThiobacciHus-FerrobaciHus) have been used successfully in the labora-
tory to convert ferrous to ferric ion as a prelude to precipitation with
limestone.42  High-rate microbially catalyzed oxidation of ferrous iron
can be carried out at pH values of 2.5 to 35 while the chemical oxidation
of ferrous iron by oxygen is extremely slow at the lower pH values.
Microbial oxidation of iron to the ferric form at low pH, followed by
neutralization of the waste to precipitate the iron offers the possibility
of higher oxidation rates, closer pH control, and better process effi-
ciency  than when oxidation and neutralization must be carried out simul-
taneously.  It is anticipated that commercial use of the microbial con-
version will require a heat input to raise mine water to optimum tempera-
ture for the biological iron oxidation (20-25°C).  Success of this method
of treatment will depend upon availability of lagoon area, concentration
of iron in solution, and total cost of treatment including the lime
precipitation-neutralization and precipitate removal steps.

          As stated at the beginning of this section and elsewhere34
it is possible to inhibit metabolism of the autotrophic iron and sulfur
oxidizing bacteria in the laboratory with the use of chemicals which are
quite innocuous to most other living organisms; e.g., alpha keto acids
and carboxylic acids.  Preventive methods which utilize antimicrobial
agents should prove successful at specific locations; that is, success
in the prevention of this type of pollution would depend upon the ability
to inhibit causative bacterial metabolism at the origin.  The location
and inhibition of microbial activity should not be problematical in the
case of refuse piles but may be quite difficult in the case of abandoned
drift mines.

          The type of antimicrobial agent to be employed in a field sit-
uation is a matter that must be further explored.  Some fruitful inves-
tigations with regard to inhibition of iron and sulfur oxidation by

autotrophic bacteria have been carried out; however, preliminary evidence
suggests that chemical inhibitors might be more practical with reference
to  cost, availability, ease of application, and lack of toxicity for
organisms other than the iron and sulfur oxidizers.   Further work in this
direction is needed.

          An additional approach relating to pyrite  oxidation abatement
via biological means is the use of bacteriophage to  eliminate bacterial
catalysis.  Reports by Shearer and Everson46 and Shearer et al.47 gave
serious consideration to this possibility.

          Three aspects should be considered with regard to phage inhibi-
tion of the acidophilic autotrophic bacteria:

1.  Convincing evidence for establishing the presence of phage particles
which are virulent for acidophilic Thiobacillus or Ferrobacillus has
yet to be prepared.

2.  In relationship to our general knowledge of bacteriophage, known types
of  phage are highly specific to host strains within  a single species and
host species become modified through genetic and selective processes to
a point where they may not be susceptible to a lytic phage.  This suggests
that use of phage to lyse a spectrum of Thiobacillus -Ferrobacillus strains
of bacteria in the field would not be practical if they were available.
The situation would be somewhat analogous to the unsuccessful attempts
to cure enteric bacterial diseases by placing enterophage in the tract.

3.  Finally, bacteriophages feature protein type shells and are very
sensitive to pH and ionic strength; it is not likely that specific pro-
teins can remain functional over the pH and ionic strength range encoun-
tered in mine acids.

          The most recent report of Shearer and Everson48 indicates that
they now believe Caulobacter species to be responsible for Thiobacillus-
Ferrobacillus inhibition in their experiments, and that the inhibition
is due to the production of specific antibacterial agents by Caulobacter.
It should be noted that most data related to inhibition of acidophilic
autotrophs can be interpreted as the activity of chemical antimicrobial
agents.  Disputes with regard to data interpretation do not discredit
sound experimental data and the experimental observations may be quite
significant.  However, data interpretation is strongly dependent on
experimental design, and extreme caution is required in this context if
such lines of investigation are to be fruitful.

          Regardless of the mechanism of biologically-produced agents
inhibitory to Thiobacillus -Ferrobacillus species, the utility of such
approaches will depend upon the ability to get the agent in contact with
the bacteria in the field.  Evidence for the site of pyrite oxidation
presented in other sections of this report and in the general literature
suggest that.this may be very difficult in underground mines but may be
a promising approach in refuse piles.


          The biological research effort related to the acid mine problem
is minimal by comparison to efforts directed toward chemical neutraliza-
tion.  There appears to be an overwhelming amount of evidence accumulating
in the literature which establishes that (a) pyrite is oxidized at sig-
nificant rates by the acidophilic autotrophic bacteria; (b) these bacteria
are always found in acidic mine drainage; (c) the only known sources of
energy for the bacteria in the mine water environment is the oxidation
of Fe  , S=, or pyritic material; (d) the presence of the bacteria in
the water therefore indicates that a finite amount of reduced iron or
sulfur already had been oxidized to produce the cells observed; and (e)
in a continuous flow situation where approximately 10s cells per ml are
continuously being removed, a finite amount of pyritic material is con-
tinuously being oxidized by the bacteria.

          A gross calculation based upon experimental data indicates that
O.l6 mole of iron oxidized yields approximately 1011 cells, or 0.6U gram
moles of iron oxidized will yield the number of cells found in a gallon
of water.  If the flow of water away from the source is 100 gal/min then
G\ moles of iron would have been oxidized per minute to yield the cells
being lost.  The efficiency of energy conversion has been reported to be
10 to 30 per cent; therefore, 6^ x 3 = 192 gram moles of iron would be
the minimum Fe+2 oxidized per minute in the above example; 192 moles of
Fe+2 is the amount found in about 50 lb of pyrite.  These calculations
are only intended as illustrations and no accounting has been made for
energy released from the sulfide in pyrite, which is about 10 x greater
per mole than that from Fe+2 iron.  Assuming that a.n ferrous and sulfide
in pyrite were oxidized to ferric and sulfate it would have required
oxidation of 5 to 50 lb pyrite per minute to yield the acidophilic auto-
trophs in a stream having a flow of 100 gal/min.

          If the above assessment is reasonable, then the basic question
to be resolved in this regard is "What is the relative significance of
microbial pyrite oxidation in comparison to chemical or nonbiological
oxidation in a variety of field situations?"

          If it is concluded that biological oxidation is significant
in proportion to nonbiological oxidation, then efforts must be expanded
to determine the most effective means of inhibiting the oxidations.  One
promising means is via specific anti-microbial chemicals, providing the
compounds can be placed in proximity to the target organisms in the
field and are relatively specific for the target.  Further efforts should
be undertaken to study the basic metabolism of the organisms in order to
understand what inhibitions are effective, how to use them, and under
what circumstances they would be most effective.

          In situations where acid formation cannot be prevented, more
efficient methods of treatment which appear promising in specific situa-
tions are (a) reduction of sulfate to sulfide via anaerobic bacteria—
a process which has several "spin-off" advantages that might be favorably

compared to chemical neutralization processes,  and (b)  adsorption of
metal ions by biologically produced polyelectrolytes which can then be
removed by conventional waste treatment technology.

          Effects of acid mine drainage on the  biological systems in
nonpolluted receiving waters  should be  more carefully evaluated in order
to determine the extent of treatment and abatement that is necessary.
This should include an assessment  of all components of  the acid mine

                             SECTION VIII


                    R. A.  Brant and K.  S.  Shumate
          Throughout this report,  the writers have attempted to  emphasize
the importance of viewing acid mine drainage production as  a dynamic
reaction system.  In controlling such systems, all  pertinent mass  trans-
ports, reactions, and reaction kinetics must be accounted for, and any
successful abatement procedure must exert positive control  on the  rate
of some step in the overall sequence of mass transports and reactions.
Specific steps which may be subject to practical control are listed below.

Mass Transport Controls

     a.  Control of water available to participate in the reaction
         at the pyrite surface.

     b.  Control of oxygen available for pyrite oxidation.

     c.  Control of the rate at which acid products are flushed
         away from the pyrite surface.

Reaction Kinetics Controls

     a.  Control of the rate of the oxidation of pyrite by  oxygen,
         by the application of an inhibitor or passivating  agent
         to the pyrite surface.

     b.  Control of the rate of a microbially catalyzed reaction
         by the application of agents inhibitory or bactericidal
         to the bacteria involved in the catalysis.

          The two major types of acid drainage sources are  underground
mines and relocated pyritic materials; the latter category  includes refuse
piles and strip mine spoil banks.  Because the characteristics of  the
two types of systems are greatly different, at-source abatement  procedures
will be discussed separately for each case.

     Mass Transport Control

          Water Availability at the Pyrite Surface

          It has been demonstrated20 that with a relative humidity of
100 per cent, water availability does not exert a rate-limiting effect
on the oxidation of pyrite by oxygen.  Thus, in any environment wet

 enough to provide a continuous occurrence of moisture in the vicinity
 of pyritic material, there is little hope of limiting water availability
 at the oxidation site.  For example, in the Appalachian coal fields, the
 relative  humidity in underground workings is sufficiently high that the
 chemical  oxidation of pyrite by oxygen is not limited by water availabil-
 ity.   Generally speaking, if there is sufficient water to produce mine
 drainage,  there will be sufficient water for .the pyrite oxidation reaction,
 Water  diversion is a separate consideration dealing primarily with oxida-
 tion product transport, and will  be discussed in a later section.
          Oxygen Available for pyrite Oxidation

          Past and current attempts to control pyrite oxidation in under-
 ground mines have revolved mainly around the control of oxygen access
 to the exposed pyrite, and virtually a.n  schemes have employed mine seals
 of one type or another.  Fundamentally, mine sealing projects aimed at
 oxygen transport control can be divided into two categories:  (a) control
 of the rate of oxygen entry to the mine void, which in turn will control
 mine atmosphere composition; and (b) establishment of an aqueous diffusion
 barrier, as in the partial or complete flooding of a mine.   Both of these
 abatement mechanisms will be operative to some degree in any sealed mine.
 Any type of seal across a mine opening will prevent convective transport
 through that opening and will suppress thermal convection currents within
 the mine.  On the other hand, an air-tight seal will force fbreathing'
 through the overburden, as discussed in Section V.  If a seal causes par-
 tial flooding, some exposed pyritic material may be submerged and effec-
 tively isolated from the mine atmosphere, and at the same time, the
 'breathing* volume is reduced.  The relative intensity of these various
 effects will vary widely from one situation to another.  Oxygen entry
 control and mine flooding will be discussed separately below.
          Oxygen Entry Control.   The sealing of a mine to prevent all
oxygen entry is simple in concept, but difficult to attain.   If oxygen
entry were eliminated, the oxygen in the mine atmosphere would eventually
drop to zero because of gradual  consumption of the oxygen present.  If
the mine atmosphere of a sealed  mine levels off at some finite oxygen
concentration, it is positive proof that the mine is still providing for
oxygen transport into the mine at a rate sufficiently high to maintain
an appreciable rate of pyrite oxidation.  This appears to generally be
the case where mines have been sealed and the atmosphere periodically

          The types of seals which have been tried fall into the categor-
ies of air seals, meant to stop  passage of air, and bullchead seals, meant
both to hold water within the mine and to stop air passage.   Air seals
may be wet, in which case they pass water through a trap arrangement,
or they may be dry, with no provision for the passage of water.  There
is a long record of both wet and dry air seals used separately or in

conjunction, and recent literature contains many descriptions of such
efforts.  However, whether or not they are particularly effective in
bringing about significant reductions in acid production rates is ques-
tionable.  Several air (wet) seal and bulkhead developments are currently
being given close scrutiny.  The U. S. Bureau of Mines has constructed
a  series of seals in a mine near Pittsburgh, and published reports
describe the project and its effectiveness.49'52 Similarly, a project
near Elkins, W. Va.,53 has generated information.  Projects such as these
are yielding valuable and urgently needed information.  It must be
stressed, however, that the interpretation of field data is a difficult
and uncertain task, and in the case of underground mines it is necessary
to collect pre-sealing base line data for a period of at least one year
and preferably for several years.  In the opinion of the authors, post-
sealing data must be followed for at least five years before a reasonably
firm evaluation can be made.  The primary reason for this is the wide
variation in ground water flow patterns from year to year and the slow
response of underground flow systems in regard to the transport of prod-
ucts of pyrite oxidation.  Based on 28 months of presealing data and 32
months of post sealing data, Moebs49 found that the effluent acid load
was reduced about 50 per cent in the subject mine.

          There are also data interpretation problems other than those
associated with hydrologic variability.  For example, with regard to wet
air seals, the data of Moebs52 shows a drop in effluent acidity occurring
almost simultaneously with the completion of the seals.  While this might
be equated with a drop in pyrite oxidation, other considerations may
account, at least in part, for this phenomenon.  In the construction of
some wet air seals, a pool of water several feet deep is created.  Such
a  pool may act as a stilling basin in which high masses of solute-rich
water will seek the bottom part of the pool.  Certain of the flow streams
which drain regions of pyrite oxidation will contain extremely high con-
centrations of oxidation products when they seep into the pool.  On the
other hand, much of the water entering mines through the exposed roof
may contain very little solute, particularly if the roof shale has been
drawn or is absent.

          The probable points of entry of highly acid water to the mine
void are related to the location of pyritic materials in the coal and
associated strata, and merit some discussion.  When one thinks of a
mine with a sandstone roof, the term "acid sandstone" comes to mind.
This term is widely used, and is usually confused with pyritic sandstone
which contains pyrite that will rapidly oxidize and produce acid products.
The term should be abandoned, because it is a misleading generality, and
in most cases such materials do not contribute significantly to acid
mine drainage.

          In moist mines with sandstone roofs, the water entering the
mine void directly through the sandstone contains little acid.  That
which percolates through pyrite-bearing materials (e.g., coal in place,
shale, refuse, and exposed pyrite on the floor) picks up high concentra-
tions of acidity.   Because of specific gravity differences, the roof


 drainage may tend to stratify above  the  strongly acid drainage in the
 pool caused by the seal.  When the pool  fills, the lighter, less acidic
 water may pour over the lip of the interior baffle wall and emerge at
 the outby baffle as a relatively good quality water.  The conclusion
 (though possibly erroneous) is immediately available that a dramatic
 change has taken place in the production of pyrite oxidation products.
 In time, dynamic equilibrium will be reached in the pool, and the acid
 will tend to leave the pool as rapidly as it enters.  Since the streams
 of highly acidified water may flow at very low rates relative to the
 total drainage rate, the time to reach this equilibrium may be consider-
 able, and the true effect of the seal on acid production may not be
 observed in the effluent drainage for an extended period of time.  The
 time required will depend largely on the relative flow rates of the acid
 and fresh water streams within the mine.  It is necessary to sample the
 pooled water within the mine  at various  depths and locations to determine
 to what degree this phenomenon is occurring.

           A third problem in  the  evaluation of data from sealed mines
 revolves around the significance  of  gas  composition in the sealed mine
 atmosphere, and the tendency  of sealed mines to breathe under atmospheric
 pressure fluctuations,  as  discussed  in Section V of this report.  Sealed
 mines have demonstrated mine  atmosphere  02 compositions of from 20 per
 cent down to 10 per cent or a little  less at the point of sampling, which
 is usually near a seal.*9*51  Also,  even in mines which have been sealed
 as carefully as possible,  there have  been no documented cases of signifi-
 cant pressure differentials between the mine and the outside atmosphere,
 indicating that the mines  are breathing  efficiently with atmospheric
 pressure variations. This  convective breathing is the only means of
 significant oxygen transport  into the mine.  As pointed out in Section V,
 if the equilibrium oxygen concentration  in the mine is greater than zero,
 then the gross oxygen intake  is  greater  than the oxygen utilization within
 the mine.  The net oxygen  intake  (the sum of oxygen intake and exhaust
 under pressure fluctuations) will equal  the total 02 utilization within
 the mine, which will in turn be  approximately equal to the sum of oxygen
 used for carbonaceous material  conversion to carbon dioxide, and of oxygen
 utilization in pyrite oxidation.  A knowledge of mine atmosphere volume,
. atmospheric pressure variation, and mine atmosphere composition (02 and
 C02, including variations  from point  to point within the mine) would
 allow a rough calculation of pyrite oxidation rate.  Such data are scarce,
 however, the most complete set having been published and discussed by
 Moebs.49  It is strongly urged that  such data be collected, as a second
 means of evaluating seal effectiveness.

           At this time, it should be  concluded that breathing through
 the enclosing rocks is  the basic failure and limiting constraint in air-
 sealed mines.  If a sealed mine is breathing, the locations of the points
 of air entry may be of considerable  significance.  It is not likely that
 the overburden enclosing sealed above-drainage mines would ever be suf-
 ficiently homogeneous with regard to air permeability and sufficiently
 uniform in depth to allow uniform breathing over the entire overburden

area.  Rather, the regions of air entry will be at locations where the
overburden is either fractured or thin.  Whether or not the soil overlying
regions of air entry is heavily vegetated may be of significance.  Bare
porous rock, such as may be present near the mine outcrop,  offers little
capacity for consuming oxygen as air is pulled in and out through breath-
ing action, and air entering the mine will be essentially at 20 per cent
oxygen.  If, on the other hand, the air must pass through an accumulation
of organic matter at the surface, such as a layer of heavy  vegetation,
oxygen will be utilized through aerobic biological action in this layer.
The oxygen-consuming ability of soil layers high in organic material is
reflected in the observation that oxygen is often absent in vadose or
phreatic waters, and the deeper soil atmospheres are generally lacking
in oxygen because of the demands on the entering atmosphere for its oxygen
content.54  The effectiveness of vegetative or organic layers as an oxygen
filter will depend on the relative rates of oxygen utilization in the
oxygen-consuming layers and the rate of air transport through the layers
by mine breathing.  The rate of air influx is dependent on  the mine void
volume and the rate and amplitude of atmospheric pressure fluctuations,
as described in Section V.  If the areal extent of the regions through
which air is being drawn is also known, then a calculation  could be made
of the oxygen consumption rate of the soil which would be required for
the prevention of oxygen entry.  The practical aspects of such an approach
have not been investigated, although it is likely that data are available
from agricultural studies on the oxygen consumption rates in soil under
various conditions.  With regard to the problem of finding  the breathing
vents of sealed mines ^ the results of a recently conducted  effort are
presented by Moebs.49  In the absence of definitive information, the
filling in of subsidence holes, with revegetation of the fill or mulch
covering, may effectively return such sites to a precollapse condition
with respect to 02 transport.  Whether the effect of such an action will
be significant depends on the individual situation.

          The possibility of applying sewage sludges or other oxygen-
demanding materials to breathing areas might be considered.  At this time,
information on the oxygen consumption kinetics, air permeability, dura-
bility, and effective useful life of such materials is not  available.
It must be remembered that the design life of any at-source abatement
procedure, such as mine drainage treatment, must be interminable, and in
the long run, operation or maintenance costs will far outweigh initial
placement or construction costs.

          If the vegetative layer of the confining overburden of a given
mine is an effective oxygen filter, then the point of placement of the
seals becomes important.  Many old seals were placed very close to the
outcrop, thus allowing the possibility of breathing through bare rock,
as well as placing them in a position of greatest instability and open
attack by mass wasting and weathering effects.  Some newer  approaches
place the seal more remotely and thus in a more stable position.  Several
current projects may respond favorably to the new, more substantial
approaches, both by reducing breathing through bare rock, and by assuring
integrity of the seal.   In any case, selection of the seal  site should


be based on a detailed knowledge of enclosing rocks, the seal should be
designed against immediate and potential  instability, and an evaluation
should be made of the route through which oxygen will enter the mine
through breathing.  With regard to the management of active mines and
the planning of new mines, due consideration should be given to the pos-
sibility of effectively air-sealing sections of a mine before abandonment
of the complex.  The following types of air seals have been used in the
past, and each should be effective as a closure if the integrity of the
seal is maintained:
                                                           (Wet seals)
                                                           (Dry seals)
             I  Native rock, clay pipe and mortar

            II  Brick or block, clay pipe and mortar

           III  Block and use of overflow dams to
                provide water trap

            IV  All of the above without trap drains

             V  All of the above plus backfilling and
                compaction of immediate outby area

            VI  Clay pack

           VII  Other: grout packing of dry openings
                containing collapse

Recent advances in sealing techniques may or may not be significant  in
approaching a solution to the problem.  Diversion of water by the  use  of
fiH in subsidence areas may fulfill a conceptual need, but the  signifi-
cance of this practice in modifying the total water budget and in  reducing
air breathing has not been demonstrated in the field.  The use of  a  seal-
ant (e.g., polyurethane foam) around an air seal is probably  significant,
especially in connection with porous or jointed rocks that can readily
conduct air around the seal.  The concept of sealing not  only the  opening
but the associated enclosing rocks is certainly an advance, as is  the
design of a sump pool of large  size.  With regard to air  seals in  general,
such questions arise as:  Will  these  "curtains" have a reasonable  lon-
gevity?  Will these relatively  fragile structures hold against stresses
transmitted through the rock?   It must be stressed that any mine seal
will require regular maintenance and inspection.

          The most important question which should be asked,  however,
is in regard to the concept of air sealing.   Is air  sealing without  the
elimination of atmospheric pressure induced breathing fundamentally  valid?
It is not feasible to make a statement  except  to point out that  past
experience with air seals has not  demonstrated great success, and  present
efforts may lend themselves to premature conclusions unless extreme  care

is exercised in the collection and analysis of pre- and post-sealing data.

          To summarize the discussion on air sealing,  it must be empha-
sized that sealing an opening and sealing a mine against oxygen entry are
quite different.  Leitch55 stated ^0 years ago that "sealing must be air
tight."  More specifically, the sealing technique must prevent oxygen
entry, whether the mine is actually air-tight or not.   If little or no
oxygen gains access to exposed pyrite, then acid production will be
stopped.  However, it must be concluded that air-sealing techniques which
have been applied to above-drainage mines do not prevent oxygen entry.
There is no reason to assume that in the general case  air sealing will
decrease acid formation to the degree that subsequent  drainage treatment
can be avoided.  It is even conceivable that air sealing could aggravate
acid production in certain instances.  For example, consider a situation
in which significant concentrations of pyrite are present in shale at or
near the top of the coal seam.  If the overburden is thin and fractured
in places, and if the shale layers are relatively permeable to gas flow,
then the shale may act as a conductor of air flow between the coal face
in the mine and the fractures in the overburden.  Before sealing, atmospheric
pressure changes would have resulted in breathing in and out of the mine
entries and ventilation shafts, this being the path of least resistance
to convective transport.  Oxygen transport to pyrite in the shale layers
would be largely limited to molecular diffusion.  After sealing, atmos-
pheric pressure-induced breathing will again follow the paths of least
resistance, which may now be along the shale layers connecting the mine
with overburden fractures.  Thus, pyrite in these layers would be sub-
jected to the convective transport of air back and forth between the
overburden fracture vents and the mine, and oxygen concentrations in the
shale could be much higher than prior to sealing, leading to a higher
pyrite oxidation rate.

          It must be stated that currently available data do not allow
a sound interpretation of the results of air sealing,  particularly in
terms of sealing effects on fundamental mass transport and reaction rates.
In the absence of data to the contrary, the authors feel that, in general,
air sealing as currently practiced cannot curtail acid production to the
degree necessary to make the procedure economically feasible.

          A modified air sealing procedure which would counteract the
breathing action of a mine may hold promise as a future development.
There has been preliminary work on inert gas blanketing of mines,51'56
but no large-scale demonstration has been completed.  If inert gas is
introduced into a mine so that a slight positive pressure is always main-
tained there will be no oxygen entry, and pyrite oxidation will cease.
Depending on the size of the mine and the permeability of the overburden,
this may require unrealistically large quantities of gas.  It should be
noted, however, that nearly complete oxygen exclusion  can be obtained if
inert gas is added to a sealed mine only during periods of atmospheric
pressure increase.  A positive internal pressure would not be necessary
during these periods as it is necessary only to assure that the mine

pressure never drops below atmospheric pressure.   Here again,  the  possi-
bility of applying such a technique to successive sections  of  an active
mine should be considered.  On abandonment, it might be necessary  to use
inert gas only in portions of the mine near the outcrop or  having  thin
confining overburden.

          Mine Flooding.  The flooding of a mine  is  the most singularly
effective method for stopping the formation of iron  sulfate and sulfuric
acid.  Mine breathing is eliminated, since there  is  no semi-confined gas
volume, and the aqueous barrier eliminates significant oxygen  transport
by diffusion.  In the ideal case, all points of entry to a  mine could be
sealed -with bulkhead seals, and the mine,  or a portion thereof, simply
allowed to fill with water.  The concept  and development of hydraulic
bulkheads is not new, and has been used in mining practice  for some time.
Garcia and Cassidy57 reported in 1938 on  their use in Illinois mines.
Interviews with mining engineers show that internal  sealing was in use
in Ohio in the 1930*s, and probably the methods were used widely else-
where.  Bulkheads are currently used in active mines to stem the flow
from abandoned areas, and recent Federal Water Quality Administration
contracts have dealt with the remote placement of seals by  use of  bags and
by other techniques such as grouting and  self-sealing limestone. (58,59).

          In the case of below-drainage mines, flooding on  abandonment
is a likely possibility,  and it would be well to  plan a mining operation
so as to make this feasible from an engineering standpoint. Above-
drainage underground mines, on the other hand, present a more  difficult
problem.  In planning new above-drainage mining operations, attention
should be given to the possibility of flooding part  .or all  of  the  mine
on abandonment, with the placement of a minimum number of bulkhead seals.
Such approaches should be considered as mining down  slope,  leaving several
hundred feet of outcrop coal, and making  ^11- new  mines shaft mines.  The
topography and geological structure of an  area are the major factors in
assessing the feasibility of such approaches.

          In the case of existing abandoned underground operations, a
careful investigation of the feasibility of mine  flooding is a necessary
prerequisite to planning an at-source abatement program.  Due  considera-
tion must be given to the ability of the mine to  hold water, the number
of seals necessary to flood a significant  portion of the mine, and the
capacity of the seals and the mine itself to withstand the  hydraulic
heads which would be encountered.  While  severe outcrop leakage problems
will make flooding impractical in many instances, outcrop sealing  tech-
niques such as grouting, lime and limestone sealing, and the application
of sodium silicate gels and other materials may be practical in certain
instances.  The in situ precipitation of materials which may be of value
in sealing leakage areas is currently under investigation.60

          In Pennsylvania the Department  of Mines and Minerals, working
with Gwin Engineers, Inc.,61'62 designed and  is installing concrete
seals in mine openings of difficult or dangerous  access in  the Moraine

State Park, Pennsylvania.  The deep mine seals employed feature the
injection of retaining bulkheads of free flowing or blown aggregate at
two points in the main entry.  The aggregate bulkheads are injected with
grout, and the seal is completed by pressure grouting the intervening
space and the outcrop on both sides of the seal.  The deep mine sealing
program at this location was seventy percent complete at the end of 1969.62
At that time, the deep mine sealing program had shown a 76 percent
improvement in water quality, reducing deep mine effluent acid from
96,000 pounds (July-December, 196?) to 23,000 pounds (July-December, 1969).
Of the 23,000 pounds reported for the latter half of 1969, 9000 pounds
were produced from mines which had had no reclamation work.

          The remote placement of seals utilized at the Moraine State
Park would appear to represent a sound approach except for possible set-
tling into the floor or erosion of the floor beneath the seal over a
period of time.  Techniques have been devised to prepare an adequate base
by remote methods.  Actually, it is not known just what effect a load
will have on the altered clay floor.  It is possible that pressure grout-
ing into and against the rib section may give sufficient lateral and
vertical integrity to preclude problems associated with weak base mate-
rials.  Outcrop leakage adjacent to the seal must be treated by a second-
ary grouting system to produce either a grout curtain or to create an
integral monolithic body in the adjacent unstable area.

          Bulkheads, even if they are found to be unable to completely
flood the mining void, may well produce an effective seal in the area
that they do hydraulically influence,, and they might be effectively used
in conjunction with carefully placed air seals.  The optimum method of
construction will vary widely with the characteristics of individual
sites, with cost being a major consideration.  Often, the expense of
clearing the portal prior to building a seal is the largest single item
in the total seal cost.
          Control of Flushing of Acid Products from Areas of
          Pyrite Oxidation

          The concept of water diversion is an approach which falls in
the category of product transport control, as opposed to reactant trans-
port control.  In any type of pyritic system, it is evident that if the
system can be hydraulically isolated so that no water leaves the system,
then no drainage is produced even though pyrite oxidation may continue
with the build-up of products in the system.  In the case of above-
drainage underground mines, in many parts of Appalachia the fall of
ground water levels during the summer and autumn represents an example
of natural seasonal water diversion, and the rise of ground water levels
during the winter and spring results in a flushing out of accumulated
acid products.  In the same sense, drainage diversion may slow the rate
of product release, but unless all water entry to and drainage from the
system can be elioninated, the system drainage may ultimately reach a new

 equilibrium, lower in flow rate, but proportionally higher in acid prod-
 ucts.   That is, the rate of acid product release may eventually attain
 the same  level as before drainage diversion, with the only difference
 being  that the volume of drainage is less.  Depending on the structure
 of a given mine, it may also be that drainage diversion will effectively
 isolate certain areas, so that acid output from the total system will be
 lowered.  It is potentially significant to note that an unexpected flush
 of water  through a system which has been accumulating oxidation products
 will inevitably produce a flow of concentrated acid which could impose a
 serious shock loading on the receiving stream.

          A novel approach to drainage diversion which has been proposed
 by Ahmed63 is the concept of dewatering mines by using wells to pull down
 the water table.  While the effect would probably be similar to more
 conventional drainage diversion practices, this concept might be appli-
 cable to a wider range of situations.

          Existing field data are too  incomplete at this time to allow
 any generalizations on the long-term effect of drainage diversion in
 underground workings.   A conservative  approach would indicate that while
 drainage diversion may provide temporary relief, and might therefore be
 very applicable to the control of acid release in sections of working
 mines,  continuing control after abandonment will ultimately depend on
 oxygen  transport control.
     Reaction Kinetics Control

          Inhibition of the Chemical Oxidation of Pyrite

          The concept of applying inhibitors to the reactive pyrite sur-
face has received moderate attention for a rather long period of time,
with no indication of major success  in the field.  Barnes  and Romberger16
discuss the principles of inhibition or passivation, and conclude that
this approach is impractical because of the probable necessity of high
passivating reagent concentration, the difficulties in applying such
agents to the reactive pyrite, and the continuous exposure of new pyrite
by caving and slumping.  If further  work is done in this area, attention
should be given not only to the types of inhibitors which  might be
applied, but also to the means of application.  In the case of refuse
and spoil piles, where only the pyritic materials in the first few feet
below the surface will be significantly exposed to oxygen, it is conceiv-
able that inhibitory agents could be effectively applied in liquid solu-
tion.  On the other hand, this will  not be possible in the case of under-
ground mines.  Even if access to all parts of an abandoned mine were
possible, liquid applications to the walls and roof would  not reach pyrite
exposed along cracks and joints behind these surfaces.  In the case of
operating mines, the continuous application of an inhibitor might be
feasible, although the expense and useful life of such applications has
not been thoroughly investigated. It is more likely that  inhibitory
agents for abandoned underground mines would have to be applied in the


vapor phase, and would necessarily consist of volatile compounds.  An
abstract by Bloom et al.64 reports that low molecular weight silane (SiH4)
derivatives are potential volatile inhibitors, although the writers of
this report do not know of any field experiments to date.
          Inhibition of Biological Catalysis of Pyrite Oxidation

          The role of biological catalysis in increasing the rate of pyrite
oxidation is still a major question in the understanding of acid mine
drainage formation.  In the laboratory, the presence of iron-oxidizing
autotrophs in significant numbers has caused increases in pyrite oxidation
rate by factors of 50 or more.5*27'38  Recent reports5'65 have given data
on the environmental conditions under which microbial catalysis might be
expected.  However, we cannot state with assurance that microbial activity
exerts a significant effect on pyrite oxidation rates in natural systems.
The total pyrite oxidation rate is the sum of the rate due to chemical
oxidation by oxygen, and the rate due to the activity of microorganisms.
While the kinetics of the chemical rate are fairly well known, the rate
due to microorganisms will be a function of the microbial population and
the specific activity per microbial cell.  Cell activity is a function
of pH, oxygen concentration, and the availability of microbial nutrients
such as nitrogen and carbon dioxide.  Until more is known about these
functional relationships, and until the environment at the pyrite surface
in natural systems is described more fully, the role of bacterial catalysis
in natural systems cannot be fully assessed.  The following points,
although insufficient to give a complete definition of the significance
of bacterial catalysis, should be borne in mind in any consideration of
bacterial activity:

     (a)  Wild strains of Ferrobaeillus-Thiobacillus species grow
          readily in systems containing only pyrite and water,
          reach a maximum population usually on the order of 10s
          cells/ml, and appear to tolerate pH values down to
          about pH 1.2.  The maximum rate of oxygen utilization
          by these organisms is on the order of 10~7 ^g Og/cell-hr.

     (b)  As mentioned in Sections VI and VII, a possible catalytic
          role of these organisms could be through the oxidation of
          Fe+2 to Fe+3 in solution, thereby making Fe+3 available
          to oxidize pyrite.  The results of Lauss indicate that
          this is indeed the predominant mechanism.  Whether the rate
          of pyrite oxidation by Fe+3 is greater than the rate of
          pyrite oxidation by 02 will depend on the relative con-
          centrations of Fe+2, Fe+3  and 02 at the pyrite surface.

     (c)  In view of the fact that the pyrite cannot be submerged
          in water without limiting 02 transport which is required
          for both chemical and microbial oxidation, then there is
          a limit on how much water can surround the pyrite and
          still allow the pyrite to oxidize.  This restriction on

          water volume per unit area of pyrite places a restriction
          on the number of organisms the system can contain,  and
          hence, on the rate of oxidation by the total microbial
          population.  Also, a low water volume to pyrite area
          ratio will cause a rapid decrease in pH as the oxidation
          proceeds, which may inactivate any organisms in close
          proximity to the pyrite.

     (d)  The specific location in the system where microorganisms
          oxidize Fe+2 is of prime importance in determining
          whether the organisms exert any catalytic effect on
          pyrite oxidation itself.  If the Fe+2 is flushed away
          from the pyrite before  it is oxidized to Fe"1"3 by the
          microorganisms, then unless this Fe+3 is recycled back
          to the pyrite, or comes in contact with other pyrite
          further down the flow path, there will be no microbial
          catalysis of pyrite oxidation.

     In other words,  under the assumptions of paragraph  (b) above,
     there may  be  significant microbial  catalysis  of iron oxidation,
     with little or no effect on  the pyrite  oxidation rate.
     Although autotrophic organisms are  observed in  mine drainage
     and  in drainage  impoundments, it  cannot be readily determined
     whether the organisms grew in close proximity to pyrite, or
     grew on Fe+2  after  it was flushed away  from  the pyrite.  Only
     in the former case  will there be microbial catalysis of the
     pyrite oxidation rate.  It should be noted that acid drainage
     flowing through  pools on the floor  of underground mines may
     provide sufficient  detention times  for  the growth of bacteria
     to high concentrations.  In  such  a  situation, bacteria will
     be observed in the  drainage, and the Fe+3/Fe*2  ratio in the
     drainage will be high, but there may still be little or no
     bacterial activity  at the sites of  pyrite oxidation.  Exist-
     ing  field data are  not sufficient to allow a firm evaluation
     of this point.

          In the opinions of the  authors of  this  section, significant
bacterial catalysis of pyrite oxidation  in underground mines is unlikely.
If bacterial activity is significant, then bactericides might be a means
of positive control.  Because of  necessity of bringing the bactericidal
agent into contact with  the oxidizing pyrite, which  is generally not
exposed at the coal face but is buried some  distance  back of the face,
the agent will probably  have to be applied as a vapor.  At the time of
this writing, the authors are aware of no field applications of bacteri-
cidal agents or inhibitors which  have shown  any sustained effects on
acid drainage formation  in underground mines.


          The preceding discussion of possible approaches to at-source
abatement of pyrite oxidation and/or acid drainage from underground mines
is predicated on the assumption that pyritic material remaining in the
mine must be left in place.  An alternative which might be economically
feasible in some underground situations is that of stripping out the coal
from the affected area, and employing normal strip mine abatement and
reclamation procedures.

          The technical problems associated with the abatement of pyrite
oxidation in refuse and spoil piles are more straightforward than in the
case of underground mines, largely because the reactive pyrite is readily
accessible.  As indicated in Section V, oxidation will be limited to the
surface layers of the piles, and in the case of strip mining the placement
of pyritic materials deep within the pile will eliminate the possibility
of significant oxidation.  The permanent flooding of pyritic materials
in either refuse or spoil, where possible, will eliminate oxidation.
Existing refuse piles, which represent perhaps the most difficult problem,
may be quite large and are normally heavily loaded with pyritic material
throughout the pile.  In the case of both refuse piles and spoil banks
with pyritic material exposed at the surface, there are three possibili-
ties of abatement; i.e., (a) development of an oxygen transport barrier
at the pile surface, (b) control of the reaction rate through either
chemical inhibitors or bactericidal agents, and (c) prevention of water
infiltration into the pile surface.
     Mass Transport Control

          Oxygen Available for Pyrite Oxidation

          The establishment of a cover over exposed pyritic material
immediately suggests the possibility of both artificial covers and natural
vegetative covers.  It is convenient to discuss these separately.

          Artificial Cover.  Any artificial cover which is waterproof
will also exclude oxygen from the pyrite.  Plastic films,.bituminous
concrete, and surface sealants such as lime and sodium silicate have all
been suggested as possible cover materials; several types of applications
are currently under investigation.ss~ss  There is no doubt that an imper-
meable barrier will effectively do the multiple job of controlling oxygen
availability, controlling erosion of the surface, and excluding water
from the pile.  Acid production will be essentially stopped, and with
ground water replenishment also eliminated, acid seepage from the pile
will gradually cease.  The primary consideration, then, is one of initial
cost and the cost of continuing maintenance.  It is probable that

artificial covers will be economically attractive only in the case of
short-term, temporary abatement projects.
          Vegetative Cover.  A vegetative cover has the attraction that
is is potentially permanent and self-healing, as well as being more
satisfactory from an aesthetic standpoint than artificial covers.  It
precludes, however, the possibility of complete elimination of either
oxygen or water entry into the pile.  Further, grading and surface drain-
age must be carefully designed to prevent erosion of the cover, and both
spoil or refuse neutralization and the application of fertilizers would
normally be required.

          A vegetative cover might function in two basic ways; i.e., it
might provide  sufficient oxygen consumption capacity in the root zone
and humus to prevent oxygen penetration to the buried pyritic material,
or it might merely act as  an erosion control device.  If oxygen does
penetrate the  vegetative cover and reaches the buried pyritic material,
the pyrite will  eventually be oxidized, but no new pyrite will be exposed
by erosion.  The pyrite oxidation rate of such a system would gradually
decay because  of increasing diffusive resistances to oxygen transport as
the reactive zone  moves deeper into the pile.  In any particular case,
both mechanisms  would be operative to some degree.

          There  is a lack  of  field  data relating to the effectiveness of
vegetative covers  as a means  of  controlling  acid production.  However,
the continued  monitoring of the  reclamation  program near ELkins, West
Virginia,50 and  current work  by  the Truax-Traer Coal Company near DuQuoin,
Illinois,66 are  generating valuable data.  Fundamentally, the behavior
of any vegetative  cover depends  on the reactivity  of the pyritic surface
to be covered, the diffusivity of oxygen through any soil separating the
pyrite from the  atmosphere, and  the oxygen-consuming capacity of the
soil-humus layers.  Good7  estimated the average acid production rate of
a UO-acre refuse pile in Illinois to be U to 5 tons of acidity  (as CaCOa)
per day.  Using this reactivity, and assuming a dry, granular soil, it
would be necessary to cover pyritic material with  more than 10 feet of
soil to significantly limit pyrite oxidation by using the soil alone as
a diffusion barrier.  The  presence of moisture in  the soil decreases
oxygen diffusivity, as does a decrease in grain size and porosity, with
tightly packed, saturated  clay being essentially impermeable.  Because
of wide variations in performance, soil covers less than 10-15 feet thick
cannot be generally considered effective diffusion barriers.  With the
establishment of a vegetative cover, however, the  use of a relatively
thin soil cover over the pyritic material may be of considerable value,
even though the soil layer itself might not be an  effective diffusion

          At the present time, it has been widely  demonstrated that with
proper fertilization and neutralization, grasses can often be readily
grown directly on  'hot* spoil and on refuse containing high concentrations

of pyrite.  Such plantings, however, should be observed for several
seasons.  If there is sufficient limestone in the neutralized material
to essentially neutralize all the acidity which will ultimately be pro-
duced in the reactive surface layer (pyrite oxidation proceeds readily
at alkaline pH values), then the root zone may never become acid,  and
the vegetation may survive indefinitely as long as ground water conditions
do not allow acid to rise from below into the root zone.  On the other
hand, it is possible that a stand of grass planted on refuse would do
well for a season or two, and then die when the available limestone is
depleted by continuing acid formation.  There is also the possibility
that a sufficient oxygen-consuming layer might be developed rapidly enough
that after a season or so, little oxygen penetrates to the pyrite, and
it would not matter greatly whether the limestone were depleted or not.
Definitive field data do not exist at this time on the evaluation  of such
direct-planting covers.

          A second type of vegetative cover would be one in which  the
refuse (or acid spoil) is covered with a layer of sweet soil, with or
without neutralization of the refuse or spoil before covering.  In this
case, there is no pyrite directly in the root zone, and the soil would
become contaminated with acid only if acid salts are carried upward from
the buried refuse by capillary rise.  A layer of limestone at the  surface
of the refuse would provide temporary neutralization capacity to counter-
act this effect.  Aside from this, the behavior of such a cover will be
similar to a cover planted directly in neutralized refuse.  That is,
there will be some oxygen utilization in the humus and root zones, and
some diffusive resistance to oxygen transport through the soil to  the
buried pyritic material.  The amount of diffusive resistance offered by
the soil will depend on the nature and degree of compaction of the soil,
the moisture content, and the depth of the root zone.  Generally speaking,
it would appear that shallow-rooted perennial grasses would be ideally
suited for vegetative covers.

          While definitive field data on the effectiveness of shallow
soil covers are not presently available, several projects50*66'62  may
provide such data in the near future.  It should be recognized, however,
that while survival of a vegetative cover controls erosion and eliminates
exposure of new pyrite, it is not in itself an indication that pyrite
oxidation has been stopped.  Only sub-surface soil and gas samples can
provide data for the estimation of pyrite oxidation rates.  If the reac-
tion has been stopped, acid products will eventually be flushed away
from the pyritic material by infiltrating precipitation.  This flushing
effect may be quite slow, however, and it may require several years to
indicate positive improvement.  An analysis of subsurface gas samples
for oxygen and carbon dioxide will yield direct information on the rate
and extent of oxygen entry into the refuse or spoil layers, and can pro-
vide an immediate indication of the effect of any cover on pyrite  oxida-
tion rates.  While data of this type are lacking at this time, such data
are being generated.66

      Reaction Kinetics Control

           The concept of applying agents  to  refuse  and spoil which will
 inhibit  either  chemical  pyrite  oxidation  or  microbially catalyzed pyrite
 oxidation  is  conceptually more  attractive than in the  case  of -underground
 mines.   Agents  can be added in  liquid form by spraying directly on the
 surface.  Aside from the ease of application,  however,  there are as many
 problems as for underground mines.   Inhibitors of the  chemical reaction
 which are  effective at economic dosages have not  been  demonstrated under
 field conditions,  and in any case,  the problem of erosion would have to
 be  solved  separately.

           Although many  liquid  agents have been studied which will inhibit
 the autotrophic bacteria suspected of having a rate-controlling effect
 on  pyrite  oxidation69  (e.g., hexanoic acid and alkylbenzene sulfonate),
 again there are no confirming field data. Of more  significance, however,
 is  the fact that the magnitude  of the effect of bacteria on total pyrite
 oxidation  rates is subject  to serious question.  While a refuse or spoil
 pile appears  to offer a  far better environment for  bacterial catalysis
 of  -pyrite  oxidation than underground mines,  the work of Lau65 indicates
 that pyrite-to-water ratio  will exert a limiting  effect. In the opinions
 of  the authors  of  this section, it is doubtful that the bacterial con-
 tribution  to  pyrite oxidation in refuse piles  can exceed 50 per cent of
 the total  pyrite oxidation  rate.  Further, as  in  the case of inhibition
 of  the chemical reaction, erosion would have to be  controlled separately.
 It  is doubtful  that reaction rate control, even if  suitable inhibiting
 agents become available, will be feasible for  any other than temporary
 alleviation applications.
     Product Transport Control

          As an introduction to this section,  it is helpful to visualize
the condition of a refuse or spoil pile which  has  stood exposed to the
elements for a number of years.  Raindrop impact and storm runoff washes
fines (clay, etc.) from the outer mantle of the pile, exposing any pyritic
material present to oxygen.  Pyrite oxidation  proceeds more or less con-
tinuously, with a buildup of acid products near the site of oxidation.
During a rain (or period of snow melt) some of the acidity is carried
away in surface runoff, and the remainder, perhaps as much as 30-^0 per
cent, is carried into the pile with the infiltrating precipitation.  A
ground water pool may build up within the pile, and the water in the
pile will either seep out around the perimeter, or seep into the original
ground below the pile.  Consequently, once a pile  has aged, it is more
or less completely permeated with acid and acid salts.

          Taking this model pile as an example, let us assume that a
vegetative cover has been developed on the pile, and that it is successful
in stopping pyrite oxidation.  Infiltrating precipitation may require
many years to clear the pile interior of previously formed acid products.
This effect will have to be accounted for in efforts to evaluate abatement

techniques on refuse and spoil piles.  Further, residual acid ground-water
seepage occuring after a vegetative cover has been established may cause
additional problems in that such seepage might emerge at the surface near
the toe of the revegetated slopes.  If the vegetative cover at the toe
of a steep slope is destroyed by acid seepage, subsequent erosion may
damage or destroy the remainder of the cover and re-expose pyrite to
oxidation.  In anticipation of such problems, subsurface toe drains are
being employed at the refuse pile study in Illinois.66

          Artifical covers, unlike vegetative covers, hold the possibility
of completely excluding precipitation from entry into the pile.  If this
is done, then acid products will be retained in the refuse or spoil,
unless the terrain and hydrology of the system are such as to allow ground
or surface water to enter the pile from adjacent areas.

          In general, the concept of water diversion in the case of
refuse piles and spoil banks is more straightforward than in the case
of underground mines.  First, there is the real possibility of completely
excluding direct precipitation entry by the construction of an impermeable
surface seal.  In many systems, this will be the sole point of water
entry.  Second, the cover, if truly impermeable, will also shut off oxygen
entry to the pyrite and completely stop pyrite oxidation.  Cost and long-
term durability information for impermeable seal materials is not gener-
ally available.

          A final subject which relates to acid product transport control
and water diversion is that of grading the side slopes.  It is a practice
in some areas to grade a refuse pile to a steep slope in order to reduce
the time runoff water is in contact with the refuse surface.  While such
a practice might decrease infiltration to some degree, it will have no
direct effect on pyrite oxidation rate, and the exposed pyrite will oxi-
dize at essentially the same rate, whether the water runs off slowly or
rapidly.  Steep slopes will simply increase erosion and make it more
difficult to establish and maintain a vegetative cover.

                               SECTION IX

          This is a compilation of efforts by the following authors
representing several disciplines involved in acid mine investigations at
The Ohio State University:

          R. A. Brant, Geologist, Ohio River Valley Water
                       Sanitation Commission (ORSANCO)
          P. R. Dugan, Professor, Cellular and Microbial
          C. I. Randies, Professor, Cellular and Microbial
          K. S. Shumate, Associate Professor, Civil
          E. E. Smith, Professor, Chemical Engineering

                               SECTION X

 1.  Martin, E. J., and Hill, R. D.,  "Mine Drainage  Research Program of
     the Federal Water Pollution Control Administration," Second Symposium
     on Coal Mine Drainage Research,  Mellon Institute,  Pittsburgh, Pa.,

 2.  Corps of Engineers, "Report For  Development of  Water Resources of
     Appalachia," Appendix C- Prevention of Water Pollution by Drainage
     from Mines, U. S. Army Corps of  Engineers (1969).

 3.  Hill, R. D., "Mine Drainage Treatment, State of the Art and Research
     Needs," U. S. Department of the  Interior, Federal  Water Pollution
     Control Administration, Cincinnati, Ohio, (1968).

 k.  Mine Drainage Abstracts, prepared annually by Bituminous Coal Research,
     Inc., Monroeville, Pa.

 5.  Smith, E. E., and Shumate, K. S., "Sulfide to Reaction Mechanism,"
     Water Pollution Control Research Series, Report No. 1^010 FPS -
     DAST-40, U. S. Dept. Interior, IWPCA, (Feb., 1970).

 6.  Shumate, K. S., and Smith, E'. E., "Development  of  a Natural Laboratory
     for the Study of Acid Mine Drainage Production," Second Symposium
     on Coal Mine Drainage Research,  Mellon Institute,  Pittsburgh, Pa.,

 7.  Good, D. M., ejb al. "The Relation of Refuse Pile Hydrology to Acid
     Production," Third Symposium on  Coal Mine Drainage Research, Mellon
     Institute, (May, 1970).

 8.  Garrels, R. M., and Christ, C. L., Solutions, Minerals, and Equilibria,
     Harper & Row, New York, (1965).

 9.  Sato, M., "Oxidation of Sulfide  Ore Bodies, I,  Geochemical Environments
     in Terms of Eh and pH," Econ. Geology, j>5 0-9^0),  928.

10.  Sato, M., "Oxidation of Sulfide  Ore Bodies, II, Oxidation Mechanisms
     of Sulfide Minerals at 25°C," Econ. Geology, 55 (i960), 1202.

11.  Clark, C. S., "Oxidation of Coal Mine Pyrite,"  J.  Sanitary Eng. Div.
     ASCE, $2_ Proc. Paper U802, (1966), 127.

12.  Hem, J. D., "Restraints on Dissolved Ferrous Iron," U. S. Geological
     Survey, Water Supply Paper 1^59-B, (1960).

13.  Hem, J. D., and Cropper,  W. H.,  "Survey of Ferrous-Ferric Chemical
     Equilibria and Redox Potentials," U. S. Geological Survey, Water
     Supply Paper 1^59-A, (1959).

1^.  Barnes, E., and Clarke, F. E., "Geochemistry of Ground Water in
     Mine Drainage Problems,"  Professional Paper ^73-A, Geological Survey,
     U. S. Department of Interior,  (196U).

15.  Singer, P. C.,  and Stumm, W.,  "Kinetics of the Oxidation of Ferrous
     Iron," Second Symposium on Coal Mine Drainage Research, Mellon
     Institute, Pittsburgh, Pa.,  (1968).

16.  Barnes, H. L.,  and Romberger,  S. B., "Chemical Aspects of Acid Mine
     Drainage," J. Water Pollution  Control Federation, Uo  (1968), 371.

17.  Braley, S. A.,  "Summary Report Mellon Institute Fellowship No. 326B,"
     Mellon Institute of Industrial Research,  (195*0-

18.  Burke, S.  P., and Downs,  R.,  "Oxidation of Pyritic Sulfur in Coal
  •  Mines," AIMME Trans., 130 (1938), U25.

19.  Nelson, H. W.,  et al, "Oxidation of  Pyritic Sulfur in Bituminous
     Coal," I.  E.  C., 25 (1933),  1355.

20.  Morth, A.  H., and Smith,  E.  E.,  "Kinetics of the Sulfide-to-Sulfate
     Reaction," Proceedings, 151st  National Meeting, Am. Ghem. Soc.,
     Pittsburgh, Pa., (March,  1966).

21.  Jutte, R.  B.,Jr., "The Effect  of Oxygen and Nitrogen  in Aqueous
     Solution on the Kinetics  of  the  Sulfide-to-Sulfate Reaction,"
     M. S. Thesis, The Ohio State University,  (1966).

22.  Hougen, 0. A.,  and Watson, K.  M., Chemical Process Principles,
     Part III John Wiley & Sons,  Inc., New York,  (19^7).

23.  Smith, E.  E.; Svanks, K.; and  Shumate, K. S.,  "Sulfide-to-Sulfate
     Reaction Studies," Second Symposium  on Coal Mine Drainage Research,
     Mellon Institute, Pittsburgh,  Pa.,  (1968).

2U.  Birle, J.  D., "Sulfide to Sulfate Reaction Mechanism  in Pyritic
     Materials," M.  S. Thesis, The  Ohio State  University,  (1963).

25.  Stiles, David,  Unpublished data, The Ohio State University.

26.  Caruccio,  F.  T., "An Evaluation  of Factors Affecting  Acid Mine
     Drainage Production," Second Symposium on Coal Mine Drainage
     Research,  Mellon Institute,  Pittsburgh, Pa., (1968).

27.  Konecik, M. G., "The Biological Oxidation of Iron Pyrite," M. S.
     Thesis, The Ohio State University,  (1965).

28.  Garrels, R. M., and Thompson, M. E., "Oxidation of Pyrite by Iron
     Sulfate Solution," Am. J. Sc., 258-A (i960), 57.

29.  Smith, E. E.; Svanks, K.; and HaUto, E., "Aerobic-Anaerobic Oxida-
     tion of Pyrite," Proceedings, 157th National Meeting,  Am. Chem. Soc.,
     Fuel Sym., 13 No. 2, (April, 1969).

30.  Dugan, P. R., and Lundgren, D. G., "Energy Supply for  the Chemoauto-
     trophic Ferrobacillus ferrooxidans," J. Bacteriol., 89 (1965), 825.

31.  Lorenz, W. C., and Torpley, E. C., "Oxidation of Coal  Mine Pyrites,"
     R.I. 62^7, U. S. Bureau of Mines, Washington, D.C., (196*0.

32.  Silverman, M. P., "Mechanism of Bacterial Pyrite Oxidation,"
     J. Bacteriol., Q_ No. k (1967), 1046.

33.  Bailey, J. R., "Biological Oxidation of Pyrite," M. S. Thesis,
     The Ohio State University, (1968).

3*K  Dugan, P. R. and Randies, C. I., "The Microbial Flora  of Acid Mine
     Water and its Relationship to Formation and Removal of Acid,"
     Project Completion Report A-002-OHIO, to Office of Water Resources
     Research, USDI,  (October, 1968).

35.  Ivanov, M. V., "Microbiological Processes in the Formation of
     Sulfur Deposits, (196^-), Trans, from Russian, 1968. Publ.  Israel
     Program for Scientific Translations for U.S. Dept. Agr. and NSF.,
     298 pp.

36.  Kelly, D. P., "Problems of the Autotrophic Micro-organisms,"
     Sci. Prog. Qxf., 55 (1967), 35-51.

37.  Peck, H. D., "Energy Coupling Mechanisms in Chemolithotrophic
     Bacteria," Ann. Rev. Microbial., 22 (1968), 1*89-518.

38.  Silverman, M. P., and Ehrlich, H. L., "Microbial Formation and
     Degradation of Minerals," Adv. in Appl. Microbiol, 6_ (19610,  153.

39.  Riley, C. V., "Limnology of Acid Mine Water Impoundments," First
     Symposium on Acid Mine Drainage Research, Mellon Institute,
     Pittsburgh, Pa., (1965).

hO.  Tubb, R. A., et al., "Potential of a Strip Mined Area  for Fish and
     Wildlife Reclamation," Rpt. 2296, The Ohio State University Research
     Foundation, 8U pp.

Ul.  Sokolova, G. A., and Karavaiko, G. I.,  "Physiology and Geochemical
     Activity of Thiobacilli," (196^). Trans, from Russian,  1968.  Publ.
     Israel Program for Scientific Translations for U.S. Dept. Agr. and
     NSF., 283 PP.

U2.  Whitesell, L. B. Jr.; Huddleston,  R.  L.;  and Allred, R. C.,  "The
     Microbiological Oxidation of Ferrous  Iron in Mine  Drainage Water,"
     Paper presented at 157th National  Meeting, Am.  Chem. Soc.,
     Minneapolis, Minnesota, (April,  1969).

U3.  Trudinger, P. A., "The Metabolism  of  Inorganic  Sulfur Compounds by
     Thiobacilli," Review of Pure and Applied  Chemistry, 17  (1967),

U4.  Tuttle, J. H.; Dugan, P. R.; and Randies, C. I., "Microbial  Sulfate
     Reduction and Its Potential  Utility as an Acid  Mine Water Pollution
     Abatement Procedure," Applied Microbiology,  17  (1969),  297-302.

45.  Zawadzki, E. A.,  and Glenn,  R. A.,  "Sulfide  Treatment of Acid Mine
     Drainage," Summary Rept.,  Bituminous  Coal Research, Monroeville,
     Pa., to FWPCA, (1968), 87 pp.

h6.  Shearer, R. E.,  and Everson, W.  A., "Study of Bacteriophages in
     Controlling Acid Mine Water," First Symposium on Acid Mine Drainage
     Research, Mellon Institute,  Pittsburgh, Pa.,  (1965).

47.  Shearer, R. E.,  et aL, Everson,  W. S., Mausteller, J. W., "Reduction
     of Acid Production in Coal Mines with Use of Viable Anti-bacterial
     Agents," Second Symposium on Coal  Mine Drainage Research, Mellon
     Institute, Pittsburgh, Pa.,  (1968).

U8.  Shearer, Robert  E., and Everson, W. A., "Effect of Antibacterial
     Agents on Mine Drainages," Water Pollution Control Research  Series,
     FWQA publication 1^010 EGJ,  (November, 1968).

ij-9.  Moebs, N. N., and Krickovic, S., "Air-Sealing Coal Mines to  Reduce
     Water Pollution," Bureau of  Mines  Report  No. RI735^, U. S. Dept.
     Interior, (March, 1970).

50.  Hill, R. D., "ElMns Mine Drainage Pollution Control Demonstration
     Project," Third Symposium on Coal  Mine Drainage Research, Mellon
     Institute, (May,  1970).

51.  Shumate, K. S.,  and Smith, E. E.,  "Development  of  a Natural  Labora-
     tory for the Study of Acid Mine  Drainage  Production," Second Sympos-
     ium on Coal Mine Drainage  Research, Mellon Inst.,  (May, 19bt5).

52.  Moebs, N. M., "Mine Air Sealing: A Progress  Report," Second  Symposium
     on Coal Mine Drainage Research,  Mellon Inst.,  (May, 1968).

53.  Hill, R. D., 'The Effectiveness  of Mine Drainage Pollution Control
     Measures at Elkins, W. Va.," Proceedings, 157th Nat. Meeting,
     Am. Chem Soc., Division of Fuel  Chem., 13, No.  2,  (1969).

5^.  Black, A. S., Soil Plant Relationships, John Wiley and Sons, New York,
     (1968), 153-197.

55.  Leitch, R. D., et al., U. S. Bureau of Mines Report,  RI299U,  (1930).

56.  Rice, J. K., "The Use of Inert Gas to Eliminate Acid  Production by
     Abandoned and Active Deep Mines," Third Symposium on  Coal Mine
     Drainage Research, Mellon Institute, (May, 1970).

57.  Garcia, J. A., and Cassidy, S. M., "Bulkheads for Coal Mines,"
     AIME Tech. Pub. No. 789, (1938).

58.  Wenzel, R. W., "Feasibility Study on the Application  of Various
     Grouting Agents, Techniques and Methods to the Abatement of Mine
     Drainage Pollution, Part IV," Halliburton Co., Draft  Final Report
     to U. S. Dept. Interior, FWPCA, Monongahela River Mine Drainage
     Remedial Project, (1968).

59«  Pollution Abatement through New Mine Sealing Techniques, FWQA. Publi-
     cation lUOlO DMO, Washington, B.C., (1970).

60.  Jones, J. B., and Ruggeri, S., "Abatement of Pollution from Abandoned
     Coal Mines by means of In-Situ Precipitation Techniques," Proceedings,
     157th Nat. Meeting, Am. Chem Soc., Division of Fuel Chem., 13,
     No. 2, (1969).

61.  Foreman, J. W., and Tarr, E. G., "Moraine State Park  Mine Drainage
     Project," Second Symposium on Coal Mine Drainage Research, Mellon
     Institute, Pittsburgh, Pa., (1968).

62.  Foreman, J. W., "Evaluation of Pollution Abatement in Moraine State
     Park," Third Symposium on Coal Mine Drainage Research, Mellon
     Institute, Pittsburgh, Pa., (1970).

63.  Ahmad, M. U., Ohio University, Athens, Ohio, Unpublished Communica-
     tion,  (1970).

6U.  Bloom, D. N., et al., Presentation at Am. Inst. Chem. Engrs. work-
     shop; Industrial Process Design for Water Pollution Control, Houston,
     Texas, (April, 1969).

65.  Lau, C. M., et al., "The Role of Bacteria in Pyrite Oxidation
     Kinetics", Third Symposium on Coal Mine Drainage Research, Mellon
     Institute,  (May, 1970).

66.  Ramsey, J. P., "Control of Acid Drainage from Refuse  Piles and
     Slurry Lagoons," Third Symposium on Coal Mine Drainage Research,
     Mellon Institute, (May, 1970).

67.  "Coal Refuse Binder," 5WQA. Project No. 1*4-010 FOA, grant to Black,
     Sivalls, and Bryson, Inc., Pittsburgh, Pa., Grant period 3/70 to 8/70.

68.  Walitt, A., et al., "Silicate Treatment of Coal Mine Refuse Piles,"
     Third Symposium on Coal Mine Drainage Research, Mellon Institute,
     (May, 1970).

69.  Tuttle, J. H., "Aspects of Iron and Sulfur Oxidations by the
     Chemoautotroph Thiobacillus ferrooxidans with Emphasis on Inhibition
     by Organic Compounds," Ph.D. Dissertation, The Ohio State University,

    A iTt'.s.stot) Number
                                              SELECTED WATER RESOURCES ABSTRACTS
                                                     INPUT TRANSACTION  FORM
     Water Quality Office, Environmental Protection Agency
     Acid Mine Drainage Formation  and Abatement
1Q Authors)
i1 he unio state University
Research Foundation

Project Designation
Water Quality Office, EPA Ik
010 FPR
      Water  Pollution Control Research Series, lUOlO FPR
Environmental  Protection Agency, Water Quality Office
Washington.  D.C..  April 1971	
    Descriptors (Starred First)

    Acid mine water,* Pyrite,*  Oxidation}* Pollution abatement,*
    Ferrobacillus, Strip mines, Underground mining, mine wastes
    Identifiers (Starred First)
    The central theme  of this  report  pertains to at-source control of pyrite oxidation.
The current level of knowledge of acid mine drainage formation is critically reviewed,
with emphasis on reaction kinetics and reactant and product transport.  A reaction
system model is developed which provides a conceptual framework for subsequent discus-
sion dealing specifically with the physical, chemical, and biological characteristics
of pyritic systems encountered in mining situations.  Practical considerations of at-
source control of acid mine  drainage  formation in underground mines, spoil banks, and
refuse piles are presented in  the final section of the report.  Deficiencies in current
knowledge which are brought  out by this report include: Descriptions of the physical
environment existing at pyrite oxidation sites in natural systems are far more incomplete
that the current understanding of pyrite oxidation kinetics; oxygen transport is poorly
described at this time, but  is probably the rate-controlling factor in most instances;
serious questions exist as to  the effectiveness of air-sealing techniques as currently
practiced; the significance  of bacterial catalysis of pyrite oxidation under field con-
ditions has not been established.
 WR:102 (REV JULY 1969)
                                          SEND TO:  WATER RESOURCES SCIENTIFIC INFORMATION CENTER
                                                 US DEPARTMENT OF THE INTERIOR
                                                 WASHINGTON. D C  20240
                                                                              CPO: 1969-359-339

 BIBLIOGRAPHIC:  The Ohio State University Research
 Acid Mine Drainage Formation and Abatement,
       Publication No. 1^010 FPR

    The central theme of this report pertains to at-
 source control of pyrite oxidation.  The current level
 of knowledge of acid mine drainage formation is criti-
 cally reviewed, with emphasis on reaction kinetics and
 reactant and product transport.  A reaction system
 model is developed which provides a conceptual frame-
 work for subsequent discussion dealing specifically
 with the physical, chemical, and biological character-
 istics of pyritic systems encountered in mining situa-
 tions.  Practical considerations of at-source control
 of acid mine drainage formation in underground mines,
 spoil banks, and refuse piles are presented in the
 final section of the report.  Deficiencies in current
 knowledge which are brought out by this report
 include: Descriptions of the physical environment
 existing at pyrite oxidation sites in natural systems
 are far more incomplete than the current understanding
 BIBLIOGRAPHIC:  The Ohio State University Research
 Acid'Mine Drainage Formation and Abatement,
       Publication No. HfOlO FPR

    The central theme of this report pertains to at-
 source control of pyrite oxidation.  The current level
 of knowledge of acid mine drainage formation is criti-
 cally reviewed, with emphasis on reaction kinetics and
 reactant and product transport.  A reaction system
 model is developed which provides a conceptual frame-
 work for subsequent discussion dealing specifically
 with the physical, chemical, and biological character-
 istics of pyritic systems encountered in mining situa-
 tions.  Practical considerations of at-source control
 of acid mine drainage formation in underground mines,
 spoil banks, and refuse piles are presented in the
 final section of the report.  Deficiencies in current
 knowledge which are brought out by this report
 include: Descriptions of the physical environment
 existing at pyrite oxidation sites in natural systems
 are far more incomplete than the current understanding
                                                        ACCESSION NO:

                                                        KEY WORDS:

                                                        Acid mine water
                                                        Pollution abatement
                                                        Strip mines
                                                        Underground mining
                                                        Mine wastes
                                                        ACCESSION NO:

                                                        KEY WORDS:

                                                        Acid mine water
                                                        Pollution abatement
                                                        Strip nines
                                                        Underground mining
                                                        Mine wastes
BIBLIOGRAPHIC:  The Ohio State University Research
Acid Mine Drainage Formation and Abatement,
      Publication No. 1U010 FPR

   The central theme of this report pertains to at-
source control of pyrite oxidation.  The current level
of knowledge of acid mine drainage formation is criti-
cally reviewed, with emphasis on reaction kinetics and
reactant and product transport.  A reaction system
model is developed which provides a conceptual frame-
work for subsequent discussion dealing specifically
•with the physical, chemical, and biological character-
istics of pyritic systems encountered in mining situa-
tions.  Practical considerations of at-source control
of acid mine drainage formation in underground mines,
spoil banks, and refuse piles are presented in the
final section of the report.  Deficiencies in current
knowledge which are brought out by this report
include: Descriptions of the physical environment
existing at pyrite oxidation sites in natural systems
are far more incomplete than the current understanding
                                                          ACCESSION NO:

                                                          KEY WORDS:

                                                          Acid mine water
                                                          Pollution abatement
                                                          Strip mines
                                                          Underground mining
                                                          Mine wastes

 of pyrite oxidation kinetics;  oxygen transport is
 poorly described at tMs time, but is probably the
 rate-controlling factor in most instances; serious
 questions exist  as  to the  effectiveness of air-
 sealing techniques  as currently practiced; the signif-
 icance of bacterial catalysis  of pyrite oxidation
 tinder field conditions has not been established.
 of pyrite oxidation kinetics; oxygen transport is
 poorly described at this time, but is probably the
 rate-controlling factor in most instances; serious
 questions exist as to the effectiveness of air-
 sealing techniques as currently practiced; the signif-
 icance of bacterial catalysis of pyrite oxidation
 under field conditions has not been established.
of pyrite oxidation kinetics; oxygen transport is
poorly described at this time, but is probably the
rate-controlling factor in most instances; serious
questions exist as to the effectiveness of air-
sealing techniques as currently practiced; the signif-
icance of bacterial catalysis of pyrite oxidation
under field conditions has not been established.