WATER POLLUTION CONTROL RESEARCH SERIES
1401QFII03/71
   Evaluation  of  Pyritic Oxidation
        by Nuclear  Methods
ENVIRONMENTAL PROTECTION AGENCY  WATER QUALITY OFFICE

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Evaluation  of  Pyritic  Oxidation by Nuclear Methods
                                by
                         Mellon Institute
                    Carnegie-Mellon University
                        4400 Fifth Avenue
                  Pittsburgh, Pennsylvania  15213
                              for the
                  ENVIRONMENTAL PROTECTION AGENCY
                          Program Number
                       Grant No. 14010 FII
                            March 1971
           For sale by the Superintendent of Documents, U.S. Government Printing Office
                     Washington, D.C., 20402 - Price BO cents

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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.

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                               ABSTRACT

          EVALUATION OF PYRITIC OXIDATION BY NUCLEAR METHODS

                          by Robert A. Baker
Laboratory studies demonstrated the feasibility of using the Mossbauer
effect and a backscattering mode of detecting 14.4 Kev gamma rays to
spectroscopically monitor the oxidation processes taking place on pyrite
materials.  A cobaltous oxide form of cobalt-57 was the radiation
source.

Spectra were obtained of pyritic surfaces under 2 mm of water.  Differen-
tiation of nonoxidized and oxidized pyritic surfaces was possible with
further separation of the spectra to show individual oxidation product
peaks suggesting ferric hydroxide and ferric sulfate.

This report was submitted in fulfillment of Research Grant No. 14010
FII between the Federal Water Pollution Control Administration and
the Mellon Institute, Carnegie-Mellon University.
Key Words:  Mdssbauer effect, backscatter detection, mine drainage,
            pyrite, iron-57, cobalt-57,  iron.
                                   iii

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                               CONTENTS
Section




   I.     Conclusions




  II.     Recommendations




 III.     Introduction




  IV.     Experimental Equipment




   V.     Experimental Procedure




  VI.     Results




 VII.     Acknowledgments




VIII.     References




  IX.     Glossary
Page




 1




 3




 5




 9




15




17




27




29




31

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                                FIGURES

Numb er                                                           Page

  1       Assembly of M6ssbauer Scattering Proportional Counter   10

  2       Mossbauer Detector During Assembly - Two Views          11

  3       Experimental Equipment - Two Views                      13

  4       Spectrum of Stainless Steel Made with Prototype
          Backscattering Detector                                 18

  5       Spectrum of Stainless Steel Made with Redesigned
          Backscattering Detector                                 18

  6       Spectrum of Ferric Hydroxide                            20

  7       Spectrum of Ferric Sulfate                              20

  8       Spectrum of Dry Pyrite Slab                             22

  9       Spectrum of Pyrite Slab Under 2 mm of Water             22

 10       Spectrum of Unreacted Pyrite Particles                  23

 11       Spectrum of Biologically and Chemically Reacted         23
          Pyrite  Particles
                                  vn

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                              TABLES

Number                                                         Page
  I.    Evaluation of Cobalt-57 Source Quality                   17

 II.    Comparison of Prototype and Redesigned Detectors         17

III.    Mossbauer Spectra of Ferric Hydroxide and Ferric
        Sulfate-Peak Analyses                                    19

 IV.    Mossbauer Spectra of Dry and Wetted Pyrite-Peak
        Analyses                                                 21

  V.    Mossbauer Spectra of Unreacted and Oxidized Pyritic
        Mineral-Peak Analyses                                    24
                                ix

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                               Section I

                              CONCLUSIONS
It has been demonstrated in this short feasibility study that the
Mossbauer effect, a nuclear resonance absorption phenomenon, may be
used in conjunction with a scattering-mode detection system to monitor
chemical oxidation of pyritic material.

The technique is sensitive to differences in extra-nuclear electron
distributions and permits nondestructive observation of the chemical
state being studied.  Differences between ferric and ferrous iron
and between pyrite and oxidation products are measured.

Spectra of pyritic surfaces were obtained without difficulty when
these were covered by a film of water 2 mm in depth.

The spectrographic measurements were favored when the surface of the
material being measured was flat and at right angles to the radiation
beam.  Particles of larger size or highly irregular surfaces are
geometrically less favored for analyses.

Oxidized pyritic material gave Mossbauer spectra which could be
separated to indicate presence of ferric hydroxide and ferric sulfate.

Oxidation reaction rates with the particular pyrite under study were
sufficiently slow so that spectra could be taken over extended periods
such as 8 to 24 hours without significant differences in the spectral
response.  This facilitates long-term scanning and hence the likelihood
of detection of low concentrations of reaction products.

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                               Section II

                            RECOMMENDATIONS


Major effort in this feasibility study was devoted to construction of
a backscattering detector and verification that 14.4 Kev gamma rays
could be used to monitor the chemical state of pyritic surface through
a film of water.  It was beyond the scope of the study to quantitatively
characterize the response of the analytical system to the various
ferrous and ferric compounds known or suspected of being involved in
the pyritic oxidation process.  The concentration and time of absorption
relationships should be established for these compounds.

In future research, a cobalt-57 source of 200 millicuries intensity
in the form of cobaltous oxide should be used.  This would enhance the
analytical efficiency of the system over that with the 100 millicurie
source used in the feasibility study.

Once the aforementioned steps have been taken, the system should be
applied to a study of the oxidation reactions of pyrites with and
without organisms.  The nature and rate of formation of the reaction
products on the surface should be compared with those existing in the
aqueous solution.  Comparison of the biologically seeded and nonseeded
systems should indicate the nature of the role of the microorganisms
in the oxidation process.

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                               Section III

                              INTRODUCTION
The objective of this research was to demonstrate  the  feasibility of using
the Mossbauer effect and backscattering mode detection of  14.4 Kev gamma
rays to spectroscopically monitor pyritic oxidation.   Successful demonstra-
tion will provide a valuable technique for defining  the nature of the
oxidation processes.  Such knowledge is necessary  if practical methods of
eliminating or restricting acid mine drainage formation are  to evolve.
When coal mine pyrite, FeS2 ,  is oxidized in the presence of water, acidity
is formed.  Acidity  is attributed  to $2    oxidation  to sulfate and to
Fe(II) oxidation to  ferric  iron and its hydrolysis.
Yellow-brown  ferric sulfate  and  ferric hydroxide precipitates which form
are known as  "yellow-boy"  in the colloquial  language of  the coal  industry.
The acidity and dissolved  salt content impair  the quality of the  receiving
body of water and  restrict usefulness of  the resource.   Hence,  the need to
prevent these discharges.  Despite much study,  the understanding  of the
pyrite oxidation is still  incomplete.  Singer  and Stumm  (1968)  found  that
sulfate retards Fe(II)  oxidation.  Though the  oxidation  rate is first order
with respect  to Fe(II)  it  is slower  than  in  the presence of sulfate.  The
rate of ferric hydrolysis  is linear  second-order with respect to  Fe(III) and
faster in the presence  of  sulfate.   They  proposed that in the absence of
bacteria the  rate  determining step is the Fe(II) oxidation.  Schematically:


                        FeS.   ; - > SO."2 +  Fe(II)
                           2 slow      4

and
                                     slow
                        Fe(II) + 02 - T>  Fe(III)

                                   fast
                   Fe(III) + FeS2 - * Fe(II) + S04


The FE(II) oxidation rate  is dependent upon  the anionic  species under acidic
conditions (Huffman and Davidson, 1956).   Since the hydroxyl ligand has a
strong Fe(III) affinity  it  was postulated  to  be  a factor  in Fe(II) oxidation.
The hydrolysis of  free  Fe(III) is therefore  involved in  Fe(II)  dissolution
from the pyrite.   Garrels  and Thompson (1960)  studied pyrite oxidation by
iron sulfate  and showed that the rate is  independent of  total Fe(II)  ions
on the pyritic surface.  Oxidation of pyrites  to release ferrous  and  sul-
fate ions was observed  only  at sites occupied  by ferric  ions.   This oxida-
tion rate is  slow  relative to the adsorption process, hence the  latter controls.

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The specific role of acidophilic chemoautotrophic bacteria in pyritic
conversion to acid mine drainage is still undefined.  These Fe(II)- and
Ss~'-'--utilizing organisms are active at pH 2 to 4.5 and use carbon di-
oxide as their carbon source.  Since oxidation of FeSs may proceed solely
by chemical routes the microorganisms are not essential to acid formation.
Their role may be:  (1) as a direct catalyst to alter the overall chemical
reaction rates, or (2) as specific catalytic agents which alter the rate
of intermediate reactions and the nature of the resulting by-products but
not the overall rate.  The microorganisms may remove electrons from sur-
face pyritic iron to start a reaction chain and/or catalyze sulfur oxida-
tion or they may simply increase Fe(III) concentration and hence the Fe(III)
to Fe(II) ionic ratio.  The ferric ion is reduced to ferrous ion by the
pyrite and the pyrite is oxidized to the ferrous ion.

Silverman and Ehrlich (1964) outlined two alternate mechanisms for
bacterial conversion of 82"  .  One involves Fe(III) oxidation of pyrites
to obtain Fe(II) which the organism oxidizes back to Fe(III).   The
alternate mechanism is independent of Fe(III) and requires only contact
between the bacteria and Se'11.  It is likely that both mechanisms could
take place in a given system depending on the nature of the pyritic
material.  Silverman (1967) further elaborated on the mechanism of the
bacterial action and proposed that two mechanisms of bacterial pyrite
oxidation operate concurrently.  These were termed the direct contact
and indirect contact mechanisms.  The direct contact mechanism requires
physical contact between the bacteria and the pyrite particles.  The
indirect contact mechanism requires that the bacteria oxidize Fe(II) to
the Fe(III) state thereby regenerating the Fe(III) ions required for
chemical oxidation of pyrite.  During this investigation it was reported
that Fe(III) oxidizes pyrite in the absence of bacteria and oxygen.
Smith and Shumate (1970) claim that direct oxygen oxidation and Fe(III)
oxidation of pyrite are independent processes and that the latter is a
chemical analogy of the microbially enhanced pyrite oxidation process.

The role of S^'   and the ferrous ion is twofold in the metabolism of
these bacteria.  They supply both the energy and reducing power for
carbon dioxide fixation.  Dugan and Lungren (1965) have proposed, in
the case of the Fe(II), a model to explain the coupling of the energy
released from Fe(II) in the form of an electron to the carbon reduction
mechanism within the cell.   In this model, an initial iron and oxygen
complex is oxygenated but not oxidized in the absence of electron
transport.  Subsequently, this complex reacts with iron oxidase or
oxygenase to effect the electron transport.  It is not evident from
this study whether the complex is formed in solution or on the pyrite
surface.

These often unreconcilable reports prompted a pilot plant investigation
by this laboratory of the microbiological and chemical aspects of pyritic
oxidation.  These studies utilized continuous flow, environmentally con-
trolled units to simulate conditions in an actual mine.  The results, Baker
and Wilshire (1968, 1970),  provided quantitative information about the kinetic
and hydraulic factors affecting acid mine drainage release.  However, the
exact nature of the reaction mechanism at the mineral surface was still un-
known.   It was concluded that a novel analytical procedure would have to be

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applied.  This is especially true if reactions on the pyritic surface were
to be differentiated from those that occur in the aqueous solution at some
finite distance from the surface.

It was suggested that the Mossbauer effect, a nuclear resonance absorption
phenomena, might provide a means of monitoring pyritic surface reactions.
The technique is sensitive to differences in extra-nuclear electron dis-
tributions and permits nondestructive observation of the chemical state of
the isotope under examination.  The difference between ferric and ferrous
iron and their oxides, sulfates and sulfides may be observed.  Radiation
from cobalt-57 source in a known crystal lattice will preferentially be
absorbed by iron-57 nuclei.  Absorption will only occur when the iron-57
nuclei are incorporated in either a crystal lattice or a sufficiently large
molecule to prevent the recoil which occurs when gamma rays are emitted or
absorbed by the nuclei.  Absorption requires that the energy levels match
precisely.  Precision of the match may be destroyed by the small amount of
energy involved in a Doppler shift produced by velocities on the order of
tenths of a mm per second.

Mossbauer effect may be observed by two modes.  Usually a transmission mode
is used in which the source, absorber and detector are in series.  However,
the nature of the pyritic material to be studied suggested use of the scat-
tering mode in which the source and detector are on the same side of the
sample.  Shielding is arranged so that the detector does not respond to a
significant fraction of the primary radiation emitted by the source.  With
the scattering mode detection system, only atoms in a layer approximately
0.01 mm deep on the mineral surface will respond.

The source and absorber are mounted so that their relative velocity may
easily be varied in a precisely controlled manner.  Resonance absorption
is observed at certain discrete velocities depending on the chemical states.
If the source and absorbing nuclei are in the same state, resonance absorp-
tion will be observed at zero relative velocity.  Differences in chemical
state are observed as a shift from zero velocity and by quadrupole splitting
which is manifest as two peaks.  The degree of shifting and splitting ex-
pected during the measurement of pyritic surfaces will be indicative of the
state of the iron-57.

Use of the Mossbauer effect and the backscattering detection mode to monitor
reactions at the pyritic surface, though theoretically possible, had not
been previously demonstrated.  Of particular concern was the practicality
of making measurements through an aqueous film and the relative time in-
tervals for significant oxidative reaction vs. requisite exposure time
necessary to obtain spectra.  It was proposed to use krypton-methane filled
proportional counters to detect resonantly-scattered 14.4 Kev photons as
the optimum approach to intrinsic detection sensitivity.  This system was
selected in preference to alternates of detection of conversion electrons
or detection of 6.5 Kev x-rays.  The efficiency of the 14.4 Kev system was
expected to be greater because of the lower nonresonance effect.  Clarifi-
cation of these points was the objective of this feasibility study.

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                              Section IV

                        EXPERIMENTAL EQUIPMENT


Major  effort was  devoted to manufacturing,  assembling  and  improving  the
backscattering  detector system.   The basis  of  this work was  a  detector
developed  under sponsorship of  the  U.  S. Atomic Energy Commission.
(Chow,  et  al.,  1969.)   The  design of this prototype unit was modified
to maximize signal  to noise ratio by increasing shielding; improving
detector resolution; and optimizing the geometry of the physical system.

Improved detector shielding reduces the count  rate caused by high energy
radiation  coming  directly from  the  source.  This reduces the background
counting rate and improves  the  signal  to noise ratio.  The reduced
background count  rate for a given source intensity also permits use of
a more  intense  source without loss  of  counter resolution.  Geometric
optimization maximizes  exposure to  direct radiation without sacrificing
efficiency of measuring  the scattered photons.   The following design
innovations were made:   (a)  a circular anode replaced the eight-cornered
design  of  the prototype;  (b) thinner anode supports were made of quartz;
(c) a guard electrode was added at  the lead-in to compensate for field
distortion; (d) a window was used which completed rather than truncated
the toroidal shape  of the detector  active volume.

Figure  1 depicts  the cross-sectional view of the detector and identifies
the parts.  Figure  2 shows  two views of the detector in an early stage
of assembly.  The detector wall encloses a toroidal  volume and consists
of an aluminum body for  the  outermost part of the toroid, a tantalum
shield  for the  inner quarten (nearest the source,  and an aluminum-coated
polypropylene window for the inner  quarter)  nearest the sample.  The
joints, between the tantalum and  the aluminum,  and between the poly-
propylene  and the aluminum,  are sealed with epoxy cement as are the
lead-in supports  for the anode and guard and the gas inlet tubing.
The joint between the window and  the tantalum shield is provided with
a rubber o-ring and an aluminum sleeve and is sealed with a silicone
compound.   Earlier attempts to seal the latter joint with a rigid
epoxy failed because pressure-vacuum cycling during detector filling
caused the thin window to flex and  crack the seal.   An aluminum clamping
plate holds the tantalum shield in place (bolts not shown)  and another
thin plate (1/8"  thick - not shown)   clamps the window edge to the
detector body.   The evaporated aluminum window coating was applied by
vacuum deposition and was shown to make electrical contact with the body
of the detector.
  Ecosil - Manufactured by Emerson & Company, Incorporated, Canton,
  Massachusetts.

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                           NO
                           

                           (5)
          DESCRIPTION
High Vacuum  Valve
Polypropylene  Window
Typical  Sample Location
Aluminum  Body
Grid for  Guard  Voltage
Stupakoff Seals
Connector for  Preamplifier
Tantalum  Shield
Lead Shield
Typical  Source  Location
Clamping Plate (bolts not shown)
Quartz Support Rod (one of seven)
0.00l"dia. Wire  Anode (3"diameter circle)
Evaporated  Aluminum Coating
Aluminum  Tube Insert
"o" Ring
Lead to Anode
Figure  1.   Assembly  of Mossbauer  Scattering Proportional  Counter
                                               10

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Figure 2.   Mossbauer Detector During Assembly - Two Views
                              11

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                                        2
The anode is a 0.001" diameter Neutroloy  wire and is supported at eight
points along its circular form.  The original location of this circular
anode at the center of the circular cross-section of the toroid was found
to yield unsatisfactory resolution.  Optimization of its location led to
the present 3" diameter circle.  Seven of the anode supports are 1 mm
diameter quartz rods which are thinned down at the ends and formed into
loops through which the wire passes.  The lower ends of these rods are
epoxy-cemented into holes in the detector body.  The eighth support is
a .010" O.D. stainless steel tube into which the ends of the anode pass.
This stainless steel tube is soldered to the tube of a stupakoff seal
which is cemented into the detector body.   The anode wire passes through
this tube and is finally soldered at the outer end.  An apprppriate
fitting is provided to make the electrical connection to the preamplifier
(see below).  The guard electrode is constructed of welded tantalum wire
and is soldered to the inner end of a solid-wire stupakoff seal (see
Figure 2).  Additional tantalum and lead shielding is provided at the
source end of the detector for more flexibility in source location as
well as for personnel protection.  The detector is filled with a 90%
krypton-10% methane mixture.

The electronic components of the spectrometer assembly consisted of:
(a)  Nuclear Science Industries Model MM-60 Mossbauer Effect Spectrometer;
(b)  Northern Scientific Model NS-600 pulse height analyzer; (c)   John
Fluke Model 412 B High Voltage Power Supply; (d)   ORTEC Model 109 PC Pream-
plifier; (e)  ORTEC Model 485 Amplifier.   The last unit was added when it
was found that the preamplifier output was not satisfactorily handled by
the amplifier incorporated into the pulse height analyzer.   Interfacing,
including slight modification to the pulse height analyzer was carried
out without difficulty.   Figure 3 gives two views of the analytical
assembly.

An extension rod was designed to fit the Mossbauer drive unit to permit
deeper penetration of the source into the back of the detector.   This
extension was constructed of tantalum to provide additional shielding
for personnel in the rearward direction.   The guard voltage was  provided
by an adjustable high voltage supply but could be provided by means of
a fixed voltage divider from the main high voltage power supply.   A
support stand was designed and constructed for mounting the entire sample-
detector-source-drive unit in a vertical position for its ultimate appli-
cation.

The manufacturer, after considerable delay, supplied a 100 millicurie
cobalt-57 source in the form of cobaltous oxide.   This was only half the
strength ordered but was accepted to permit some testing during the brief
nine-month project period.

When the source was first placed in position within the detector central
hole, an unexpectedly high background was obtained.  After considerable
study of this effect, it was ascertained that the source, though well
within the specifications for radiochemical purity, contained significant
concentrations of cobalt-56 and cobalt-58 and a small amount of cobalt-60.
2
 Molecu-Wire Corporation, Wall Township, New Jersey.
                                  12

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Figure 3.  Experimental Equipment - Two Views
                              13

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It was determined by a lithium-drifted germanium spectrometer that cobalt-
56 and 58 were present in quantities estimated to be of the order of
hundreds of microcuries.   Since these nuclides emit high energy gamma rays
(^00 Kev) , they contribute substantially to the detector background at
low energies despite the  source shielding provided.  [in addition, 0.2%
branch in the decay of cobalt-57 itself also yields gamma-radiation of
high energy (~690 Kev) and of similar intensity.]  These isotopic
impurities are unavoidable in freshly prepared cobalt-57.  As time
passes, their concentrations relative to cobalt-57 will decrease since
the half lives of cobalt-56 and cobalt-58 are 77 and 72 days, respectively.
(The longer-lived cobalt-60 present is more than a factor of ten lower
in concentration.)
                                   14

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                               Section V

                        EXPERIMENTAL PROCEDURE


Samples were mounted beneath the vertically-oriented Mossbauer unit
and as close as possible  to the detector window.  Radiation counts
were measured  over specific time intervals.  At the conclusion of the
absorption period, the  counts were .transferred from the multi-channel
analyzer to tape and printed format via a NS 102, Teletype Series 33
page-printer and tape-punch.  The data were then analyzed by an IBM
360 computer.  A plot tape was produced and used in conjunction with a
Calcomp Plotter to prepare the final absorption spectra.

Detector response characteristics were evaluated by monitoring with a
310 stainless  steel natural absorber, 2" x 2" x 0.01".

Ferric hydroxide was prepared for spectrescopic analysis by reacting a
ferric chloride solution with sodium hydroxide, filtering the precipi-
tate through a O.lu filter and placing the dried precipitate on a watch
glass.  Ferric sulfate was a reagent grade laboratory supply.   This was
also placed in a watch glass prior to analysis.

The pyritic samples used in this study were obtained from Shawville,
Pennsylvania and have been used in previous pilot plant investigations
in this laboratory.  Baker and Wilshire (1968, 1970).   It contains 45%
iron, 0.05% magnesium, 0.26% manganese and 0.08% calcium.  Loss on
ignition is 27.8% which includes entrained coal and conversion of
carbonates or  other anionic forms to oxides.  X-ray analyses indicate
content of 90% or more with minor quantities of siderite, marcasite
and quartz.  If all the iron were assumed to be present as FeS2 then
the material would be 98% pyrite.  The mineral is a microporous solid
with at least  0.036 ml/gm internal voids.  These voids have an internal
specific surface of approximately 1 m /gm.

The pyritic mineral was received as lumps approximately three to five
inches in size.  Outer surfaces were rejected and the material was
prepared either by crushing or by cutting of cross-sectional slabs
with a carborundum disc to obtain a flat surface.  The crushed material
was screened and only the 3.5 to 7 mesh particles were retained for
testing.   These were sterilized for at least 24 hours in an atmosphere
of carboxide (10% ethylene oxide and 90% carbon dioxide) prior to use.
The slabs were approximately three inches in diameter and 0.5-inches
thick.  These were heat sterilized for three days at 112C, after which
the surfaces were polished to remove residual oxides before use.
                                  15

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The pyritic slabs were checked for uniformity of spectral response
over their cross-sectional area.   Holes were drilled at approximately
90 in the sides of the slabs.  Small glass rods were affixed in these
holes and one was colored red to provide a point of reference.  Mossbauer
spectra were obtained at various points in each quadrant of the surface
area and compared.  No differences were found so that only one Mossbauer
spectrum taken at the center of the pyritic slab is presented in this
report.  Spectra were obtained of the dry slab and when the surface
was submerged beneath 2 mm of water.

The reacted pyritic particulates  which were spectroscopically examined
had undergone oxidation for 87 days in a horizontal, packed-bed pilot
plant.   The continuously flowing  unit was seeded with a ternary mix-
ture of chemoautotrophic organisms (Ferrobacillus ferrooxidansf  Ferro-
baeillus sulfooxidans and Thiobaoillus thiooxidans).  Thus, the pyrite
had been subjected to biologically promoted oxidation.   The initially
yellow-gray colored pyrite surfaces were covered by a typical reddish-
brown reaction product at the end of the test period.   These particles
were packed into a shallow plastic plate for analysis.   Details of the
horizontal reactor pilot plant studies have previously been published.
Baker and Wilshire (1968, 1970).
                                 16

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                              Section VI

                                RESULTS


The quality of the cobaltous oxide source was checked with a lithium-
drifted germanium spectrometer for 690 Kev gamma rays and an x-ray
proportional counter for 14.4 Kev activity.  Self-absorption was
compared with a Co57 on chromium source of known high quality.   Table
I.  There is a smaller loss of 14.4 Kev radiation, through self-
absorption, with the cobaltous oxide source than with the more con-
ventional cobalt on chromium source.
                                TABLE I

                Evaluation of Cobalt-57 Source Quality
Co57 Source

On Chromium

Cobaltous Oxide

On Chromium

Cobaltous Oxide
      Energy Level, Kev
           14.4


          690
                  Relative Count Rate    Ratio
                      27,701              0.38
                      71,538
                       4,200              0.58
                       7,215
The prototype and redesigned detectors were compared using the cobaltous
oxide source and a 310 stainless steel reference.  Single peak spectra
were obtained.  Figures 4 and 5.  The prototype detector spectrum was
made over 17.5 hours and that of the redesigned detector over 3.2 hours.
Table II.  The difference in peak position, 1.07 vs 1.09, is insignifi-
cant.  The approximately 20% greater peak amplitude of the spectrum with
the redesigned detector is significant.  At comparable exposure time
the deviation in peak position, amplitude and width would be smaller
with the redesigned detector.  Mechanical difficulties with the seals
were not corrected until the end of this feasibility study.  The
tests described in the subsequent paragraphs were made with the proto-
type detector.  These analytical results would have been enhanced if
time had permitted testing with the redesigned detector.

                               TABLE II

   Comparison of Prototype and Redesigned Detectors Spectral Analyses
              Position, mm/sec   Relative Absorption  Width ,  mm/sec
Detector
         a
Prototype
Redesigned

a
   X
-1.095
-1.069
  a_
0.009
0.021
X
0.025
0.029
a
0.001
0.002
X
0.310
0.297
a
0.013
0.030
Area
0.024
0.027
  17.5 hour scan
  3.2 hour scan
               X, mean
               cr, standard deviation
                               half peak width at
                               half maximum
                                 17

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               o-8.0O  -6.4O   -4.BO   -3.20   -1.60   0.00   1.60    3.20   4.80  6.40   8.00
Figure 4.   Spectrum  of Stainless Steel Made with Prototype Backscattering

             Detector
              S o
              = 8
              S. 
                o
                    1..*'*'
o -8.00  -6.40   -4.80  -3.20   -1.60   OOO  L60

                       Velocity mm/sec
                                                      3^0   4^80   635 - i2)0
Figure 5.  Spectrum  of Stainless Steel Made with  Redesigned Backscattering

            Detector
                                           18

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Oxidation products which might be expected on the surface of the
pyritic mineral include ferric hydroxide .and ferric sulfate.  The
Mossbauer spectra of these compounds were measured with a velocity range
f +10 mm/sec.  The ferric hydroxide, Figure 6, was prepared by adding
NaOH to a saturated ferric chloride solution, filtering the resulting
hydroxide and measuring the absorption spectra of the precipitate for
13.75 hours.  The ferric sulfate, Figure 7, was reagent grade chemical
or unspecified water of hydration measured for 9.0 hours.   These com-
pounds were placed in watch glasses for spectral analyses.   Each of the
spectra actually consists of two peaks, although that for sulfate,
Figure 7, may appear as a single peak.   The overall width is too great
for a single peak.  Two peaks, representing the quadrupole splitting,
are present.  Table III.  The ferric hydroxide preparation method
precluded pure compound formation.  The Mossbauer spectral characteristics
for ferric sulfate were compared with literature values.   The main
doublet, Figure 7, is centered at +0.41 mm/sec relative to iron metal.
Fluck, et  al. , (1963), reported a position of +0.101 relative to
cobalt-57 diffused into platinum.  Their ferric sulfate had seven
waters of hydration.  Some variation may be expected if the water of
hydration differs.  The experimental value for the quadrupole splitting
is 0.29 mm/sec vs their reported value of 0.28 mm/sec.   Thus the
experimental results agree very well with those cited by Fluck, et  al.


                               TABLE III
       Mossbauer Spectra of Ferric Hydroxide and Ferric Sulfate-
                             Peak Analyses
                                                         Q
                   Position,         Relative       Width ,
                    mm/sec          Absorption      mm/sec

Compound           I                I            I            Area.
  Hydroxide3    -0.981   0.015      0.013   0.001 0.239  0.025    0.010
                -0.320   0.016      0.015   0.001 0.290  0.024    0.014

Ferric  Sulfateb -0.730   0.029      0.016   0.004 0.191  0.041    0.010
                -0.444   0.038      0.022   0.004 0.270  0.028    0.018
 a 13.75  hour scan
   9.0  hour scan
 X,  mean
 a,  standard deviation
 C half peak width at half maximum
                                   19

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     O -8.00  -6.40   -4.80   -3.20   -1.60   0.00    1.60   3.20   4.80   6.40   8.00
Figure  6.   Spectrum of Ferric Hydroxide
     O -8.00  -6.40   -4.80   -3.20  -1.60  0.00   1.60
                             Velocity mm/sec
 Figure 7.   Spectrum of  Ferric Sulfate
                                               20

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A basic question involved in this feasibility study was determination
of the effectiveness of obtaining  backscattering radiation spectra when
the pyritic mineral surface was under a water film.  In the original
research proposal it was expected that oxidation processes would be
monitored through 0.5 mm depth of water.  In this feasibility study the
water depth over a pyritic slab was set at 2 mm.  Success in measuring
spectra at this condition would assure success with thinner water
films on the mineral surface.  Spectra of the dry pyritic slab and of
the slab through the water film are presented in Figures 8 and 9,
respectively.  The analyses of the double peak spectra are given in
Table IV.  The dry slab was monitored for 17 hours and the wetted slab
for 55 hours.  Loss in peak amplitude is approximately 50%.  This
would be reduced considerably with thinner water films.  An important
finding is that backscattering radiation can be measured through the
aqueous layer.

                               TABLE IV

       Mossbauer Spectra of Dry and Wetted Pyrite-Peak Analyses
                         Water Film 2 mm Thick

          Position, mm/sec  Relative Absorption  Width , mm/sec

Condition    X        0_        X        o_         X             Area

Drya      -0.995    0.006    0.028    0.001     0.215    0.009   0.019

          -0.378    0.006    0.028    0.001     0.215    0.009   0.019
Wetb      -1.004    0.006    0.014    0.000     0.213    0.010   0.009
          -0.377    0.006    0.015    0.000     0.196    0.009   0.009
r\
  17 hour scan

  55 hour scan

X, mean
a, standard deviation
C half peak width at half maximum


The Mossbauer spectrum of the dry pyritic slab was compared with the
pyritic peak values reported by Fluck, et  al.  (1963).  The main doublet
is centered at -0.995 mm/sec or +0.31 mm/sec relative  to iron metal.
Quadrupole splitting is 0.62 mm/sec.  Literature values are +0.32 mm/sec
and 0.62 mm/sec.  Agreement is excellent.

Pilot plant studies of the microbiological factor in acid mine drainage
(Baker and Wilshire, 1968, 1970) utilized 3.5 to 7 mesh pyritic particles.
Figure 10 is the Mossbauer spectrum of this material.  This sample was
                                   21

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    O -S.OO  -6.40  -4.80   -3.20   -1.60   0.00    1.60   3.20   4.80   6.4O   8.00
Figure  8.   Spectrum of  Dry  Pyrite Slab
     O -8.00  -6.40  -4.80   -3.20   -1.60   0.00   1.60   3.2O   4.80   6.40   BOO
 Figure  9.   Spectrum of Pyrite  Slab Under  2 mm of Water
                                                22

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                        1.30   - 0.65  0.00   0.65   I 30    1.95   2.60  3.E5
Figure 10.   Spectrum of Unreacted Pyrite Particles
 ?-3.25 -2.60   -1.95  -1.30
-0.65   0.00   0.65

  Velocity mm/sec
                                              1.95
                                                    2.60
                                                          3.25
Figure 11.   Spectrum of Biologically and  Chemically
                  Reacted Pyrite Particles
                                           23

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not freshly ground so that some chemical alteration of the pyritic
surface may have occurred during storage.  There are two peaks whose
position and relative absorption characteristics are summarized in
Table V.  The main doublet is centered at -1.022 mm/sec (+0.30 mm/sec
relative to iron metal)  and has quadrupole splitting of 0.65 mm/sec.
The values differ somewhat from those of the freshly prepared dry
pyritic slab, Table IV,  probably reflecting the effect of surface
oxidation and the presence of some reaction products.   Of greater con-
sequence is the loss of relative absorption when the pyritic mineral
was in particulate form rather than as a flat surface.  The loss is
approximately 33% (0.028 vs 0.020 relative absorption).  This reflects
the unfavorable geometry involved in applying backscattering detection
to an irregular rather than planar surface.  In subsequent research the
latter configuration is  to be preferred.

Figure 11 is the Mossbauer spectrum of the particulate pyritic form
after biologically promoted oxidation in a continuous  pilot plant for
87 days.  The particulates were coated with typical yellow-brown reaction
products.  The spectral analysis is based on four peaks.   Table V.

                                TABLE V
          Mossbauer Spectra of Unreacted and Oxidized  Pyrite-
                             Peak Analyses
                                                         /-i
             Position, mm/sec   Related Absorption  Width ,  mm/sec
Condition
         o
Unreacted
Oxidizedb
X
-1.022
-0.373
-1.119
-0.800
-0.434
-0.279
CT
0.007
0.008
0.031
0.057
0.131
0.177
X
0.020
0.019
0.006
0.005
0.004
0.003
a
0.001
0.001
0.001
0.001
0.005
0.006
X
0.211
0.236
0.258
0.258
0.258
0.258
a
0.012
0.013
0.021
0.021
0.021
0.021
Area
0.014
0.014
0.005
0.004
0.004
0.003
  23.5 hour scan

  24.0 hour scan

X, mean

a, standard deviation
Q
  half peak width at half maximum


Comparison of this spectrum with those of the unreacted pyrite and the
expected ferric reaction products suggests that a composite of all these
components is present.   The middle pair of peaks most nearly approximate
the ferric sulfate and the outer peaks the pyrite.   Shift in peak positions
is most likely attributable to presence of other reaction products such
                                  24

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as the hydroxide.  Detailed analyses of the oxidation processes and their
reaction products will require further study.  The major finding is the
successful demonstration of the application of the Mossbauer effect-
backscattering  detection experimental technique to the problem of
monitoring pyritic surface oxidation.  Spectra of this pyritic material
exposed to an oxidizing aqueous media for several days showed no
significant differences from those of unreacted mineral.  Oxidation
reaction rates were sufficiently slow so that radiation scans could be
taken over extended periods such as 8 to 24 hours without significant
differences in spectral response at the beginning and end of the
period.  This facilitates long-term scanning and hence the likelihood
of detection of low concentrations of reaction products.
                                   25

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                            Section VII

                          ACKNOWLEDGMENTS
During this investigation, Drs. Paul A. Flinn and B. Keisch of Carnegie-
Mellon University provided technical guidance regarding the Mossbauer
and detector systems.  Albert G. Wilshire conducted the tests.

The Research was supported by the Federal Water Quality Administration
through Research Grant 14010 FII.  Technical liaison was provided by
Ronald Hill, Chief, Mine Drainage Pollution Control Activities, FWQA.
                                    27

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                              Section VIII

                               REFERENCES
 1.  Baker, R. A., and Wilshire, A. G. , "Acid Mine Drainage - Pilot
     Plant", Final Report to Appalachian Regional Commission from Mellon
     Institute, August 1, 1967 to November 30, 1968.

 2.  Baker, R. A., and Wilshire, A. G,, "Microbiological Factor in Acid
     Mine Drainage Formation:  A Pilot Plant Study", Environmental Science
     and Technology, 43 401-407 (1970).

 3.  Chow, H. K., Weise, R. F., and Flinn, P. A., "Mossbauer Effect Spectrometry
     for Analysis of Iron Compounds", Report to Division of Isotopes,
     A.E.G., Contract AT-(30-1)-4023,  (1969).

 4.  Dugan, P. R., and Lundgren, D. G., "Energy Supply for the Chemoauto-
     troph Ferrobacillus Ferrooosidans" 3 J. Baot.3 893 825-834 (1965).

 5.  Fluck, E., Kerler, W., and Neuwirth, W., "Der Mossbauer-Effekt und
     Seine Bedeutung fur Die Chemie", AngeW. Chem.3 753 461-472 (1963).

 6.  Garrels, R. M., and Thompson, M. E., "Oxidation of Pyrite by Iron
     Sulfate Solutions", American Journal of Soienoe, 258-A, 75-67 (1960).

 7.  Huffman, R. E., and Davidson, N., "Kinetics of Ferrous Iron-Oxygen
     Reaction in Sulfuritic Acid Solution", Journal of the American Chemical
     Sooiety, 783 4836-4842 (1956).

 8.  Silverman, M. P., "Mechanism of  Bacterial Pyritic Oxidation", J.
     Bacter., 943 1046-1051 (1967).

 9.  Silverman, M. P., and Ehrlich, H. L., "Microbial Formation and De-
     gradation of Minerals", Advances in Applied Microbiology (W.  W.  Umbreit,
     Ed.)3 63 153-206  (1964).

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

11.  Smith, E. E., and Shumate, K. S., "The  Sulfide to Sulfate Reaction",
     Final Report to Federal Water Quality Administration, Program Number
     14010 FRS by Ohio State University Research Foundation, (1970).
                                  29

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                               Section IX

                                GLOSSARY
Chemoautroph - An organism which utilizes carbon dioxide as sole source
of carbon to obtain energy required for metabolism by oxidation of
inorganic sources.

Key - Thousand electron-volts of energy.  One electron-volt is approxi-
mately 1.6 x 10 12 ergs.

Mossbauer Effect - An effect, discovered by R. Mossbauer, in which by
restricting the recoil of radioactive atoms emitting low-energy gamma
rays, the full energy of the gamma ray is available for use in the
study of the resonant absorption thereof.

Toroidal - Doughnut-shaped.

Quadrupole Splitting - The splitting of nuclear energy states effected by
the extra-nuclear electrons of the atom.
                                    31

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 BIBLIOGRAPHIC:   Carnegie-Mellon University,  Mellon
 Institute
 Evaluation of Pyritic Oxidation by Nuclear Methods,
      Publication No.  14010 FII

    Laboratory studies demonstrated the  feasibility
 of  using  the Mossbauer effect and a backscattering
 mode of detecting 14.4 Kev gamma rays to  spectrosco-
 pically monitor the  oxidation processes taking place
 on  pyrite materials.   A cobaltous oxide form of  co-
 balt-57 was  the radiation source.
    Spectra were obtained of pyritic surfaces  under
 2 mm of water.   Differentiation of nonoxidized and
 oxidized  pyritic surfaces was possible with  further
 separation of the spectra to show individual  oxi-
 dation product  peaks  suggesting ferric hydroxide and
 ferric sulfate.
                                                      ACCESSION NO:

                                                      KEY WORDS:

                                                      Mossbauer Effect
                                                      Backscatter Detec-
                                                        tion
                                                      Mine Drainage
                                                      Pyrite
                                                      Iron-57
                                                      Cobalt-57
 BIBLIOGRAPHIC:   Carnegie-Mellon  University, Mellon
 Institute
 Evaluation of Pyritic Oxidation  by Nuclear Methods,
      Publication No.  14010 FII
    Laboratory studies demonstrated the  feasibility
 of using the Mossbauer effect and a backscattering
 mode of detecting 14.4 Kev gamma rays to spectrosco-
 pically monitor the oxidation processes taking place
 on pyrite materials.   A cobaltous oxide form of co-
 balt-57 was the radiation  source.
    Spectra were obtained of pyritic surfaces under
 2  mm of water.   Differentiation  of nonoxidized and
 oxidized pyritic surfaces  was possible with further
 separation of the spectra  to show individual oxi-
 dation product  peaks  suggesting  ferric hydroxide and
 ferric sulfate.
                                                     ACCESSION NO:

                                                     KEY WORDS:


                                                     Backscatter Detec
                                                        .
                                                     ...      .
                                                                8
                                                      yr  

                                                     Chi  17
                                                      obalt-57
BIBLIOGRAPHIC:  Carnegie-Mellon University, Mellon   ACCESSION NO:
Institute
Evaluation of Pyritic Oxidation by Nuclear Methods.   KEY WORDS:
     Publication No. 14010 FII
   Laboratory studies demonstrated the feasibility
of using the Mossbauer effect and a backscattering
mode of detecting 14.4 Kev gamma rays to spectrosco-
pically monitor the oxidation processes taking place
on pyrite materials.  A cobaltous oxide form of co-
balt-57 was the radiation source.
   Spectra were obtained of pyritic surfaces under
2 mm of water.  Differentiation of nonoxidized and
oxidized pyritic surfaces was possible with further
separation of the spectra to show individual oxi-
dation product peaks suggesting ferric hydroxide and
ferric sulfate.
                                                     Mossbauer Effect
                                                     Backscatter Detec-
                                                         ^
                                                          Dralna8e
                                                          e

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   Accession Number
                         Subje
                       Field 8z   up

                        05  A
                                            SELECTED WATfc* RESOURCES ABSTRACTS
                                                    INPUT TRANSACTION FORM
 r  Organization

   Federal Water Quality Administration,  Department of the Interior
   EVALUATION OF PYRITIC  OXIDATION BY NUCLEAR METHODS
10

22
Authors)
Baker, Robert A.
Mellon Institute
Carnegie-Mellon University
4400 Fifth Avenue
Pittsburgh, Pa. 15213
11
Date
December, 19 70
16

12

Pages
Project Number
14010 FII
21

1 c Contract Number
14010 FII
Note
Citation
   EVALUATION OF  PYRITIC OXIDATION BY NUCLEAR METHODS
23
Descriptors (Starred First)
 Mine Drainage, water pollution effects, coal mines, mine wastes
   Identifiers (Starred First)
  I ^                   ^
    Mossbauer  effect,   Backscatter detection, Pyrite, Iron-57, Cobalt-57
27
Abstract
   Laboratory  studies demonstrated the feasibility of using the Mossbauer  effect  and
a backscattering mode of detecting 14.4 Kev gamma rays to spectroscopically monitor
the oxidation  processes taking place on pyrite materials.  A cobaltous  oxide  form of
cobalt-57 was  the radiation source.
   Spectra were obtained of pyritic surfaces under 2 mm of water.   Differentiation
of nonoxidized and oxidized pyritic surfaces was possible with further  separation
of the spectra to show individual oxidation product peaks suggesting  ferric hydroxide
and ferric sulfate.
                                           Abstractor
                                             Dr. Robert A.
                                                         Baker
                                           Institution
                                             Mellon  Institute,  Carnegie-Mellon Univ., Pgh,Pa.
WRjIOZ (REV. OCT. 1968)
WRSIC
                                                SEND TO: WATER R ESOURC ES SC I ENT1 FIC INFORMATION CENTER
                                                        U S. DEPARTMENT OF THE INTERIOR
                                                        WASHINGTON, D.C. 20240
                                                                                        1 96 9  324-444

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