WATER POLLUTION CONTROL RESEARCH SERIES • 12010 DIM 08/70
   Pyrite Depression by Reduction
                  of
     Solution Oxidation Potential
ENVIRONMENTAL PROTECTION AGENCY • WATER QUALITY OFFICE

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                    WATER POLLUTION CONTROL RESEARCH
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 PYRITE DEPRESSION BY REDUCTION

                OF

  SOLUTION  OXIDATION POTENTIAL
Department  of  Mineral  Engineering

        University  of  Utah

    Salt Lake  City, Utah  84112
                for


    ENVIRONMENTAL PROTECTION AGENCY
        WATER QUALITY OFFICE
     Grant  Number   12010 DIM


         December, 1970

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                        EPA Review Notice
This report has been reviewed by the Water Quality Office of the
Environmental Protection Agency and approved for publication.
Approval does not signify that the contents necessarily reflect
the views and policies of the Water Quality Office 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
     A study of pyrite depression by reducing agents with
potassium ethylxanthate as collector indicates that pyrite
may be depressed effectively in the flotation of both lead
and copper sulfide ores without the use of poisonous cyanide
salts.  More specifically, the use of sodium sulfite as the
depressant may result in metallurgical, economical, environ-
mental and safety advantages over the poison, cyanide.   For
example, in the case of the copper ore, the best results
with cyanide as the depressant were a rougher concentrate
recovery of 90.2% and a grade of 4.3% Cu.   However, when
sulfite was used as the  depressant for the same recovery
a grade of 7.3% Cu was obtained.
     Experimental results support the theory that dixanthogen
is the collector species responsible for pyrite flotation.
The study shows that pyrite depression is  possible by
maintaining a reduced solution oxidation potential thus
preventing dixanthogen formation.   Depression was effected
with the following reducing agents and in  all cases the
results were similar; sulfite, sulfide, thiosulfate, hypo-
phosphite and oxalate.  The proposed mechanism of depression
involves the adsorption of the reductant on surface active
sites, thus preventing the adsorption and  dissociation  of
molecular oxygen to nascent oxygen.   In the case of sulfite
the adsorption reaction is shown  below:

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            ss                            ss           cr
        /           .                / V     /
      Fe          + S03  aqueous   *  F\     /°~S\
          X                            ^S £        \
            SS                            SS           0
      Pyrite Surface                 Pyrite Surface
     This report was submitted  in  fulfillment of Grant
Number 12010 DIM between  the  Environmental Protection Agency
 (EPA)   and the Grantee.
     Key Words :
     f 1 otati on
     py ri te
     depression
     reducing  agents
     cyanide
     sulfite
     ethyl xanthate
     oxidation potential
                            11

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                            CONTENTS

SECTION                                                        PAGE
ABSTRACT 	   1
CONCLUSIONS & RECOMMENDATIONS  	 vii
INTRODUCTION	   1
EXPERIMENTAL TECHNIQUES  	   5
     Reagents  	   5
     Flotation Experiments with Singular Minerals	   6
     Zeta Potential Experiments  	   8
     Oxidation Potential Measurements  	 	   9
     Froth Flotation Experiments with Ore Samples  	  10
EXPERIMENTAL RESULTS 	  12
     Flotation Experiments with Singular Minerals  	  12
     Zeta Potential Experiments	21
     Oxidation Potential Experiments	21
     Froth Flotation Experiments with Ore Samples  	  27
DISCUSSION	39
ACKNOWLEDGEMENTS	46
REFERENCES	47
PUBLICATIONS 	  50
                               ill

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                             FIGURES

FIGURE                                                        PAGE

   1    Schematic diagram of flotation  apparatus  	  7

   2    Flotation recovery of pyrite, 100  x  200 mesh, as a
       function  of pH with 2 x  10-4 M  KEX and at  four  levels
       of addition of sodium sulfite	13

   3    Flotation recovery of pyrite, 100  x  200 mesh, as a
       function  of pH with 2 x  10-4 M  KEX in the  presence
       and absence of zinc sulfite	14

   4    Flotation recovery of pyrite, 100  x  200 mesh, as a
       function  of pH with 2 x  10-4 M  KEX and at  four  levels
       of addition of sodium sulfide	16

   5    Flotation recovery of pyrite, 100  x  200 mesh, as a
       function  of pH with 2 x  10-4 ^  KEX in the  presence and
       absence of sodium thiosulfate   	 17

   6    Flotation recovery of pyrite, 100  x  200 mesh, as a
       function  of pH with 2 x  10-4 M  KEX in the  presence and
       absence of sodium hypophosphite  	 18

   7    Flotation recovery of pyrite, 100  x  200 mesh, as a
       function  of pH with 2 x  10-4 M_  KEX and at  three levels
       of addition of sodium oxalate   	 19

   8    Flotation recovery of pyrite, 100  x  200 mesh, as a
       function  of pH with 2 x  1Q-4 M.  KEX and 1 x 10'3 M
       sodium sulfite for two different conditioning times  . . 20

   9    Flotation recovery of pyrite, 100  x  200 mesh, as a
       function  of pH at two levels of addition of KEX  .... 22

  10    Flotation recovery of pyrite, 65 x 100 mesh, as a
       function  of pH with  2 x  10~4 N[ KEX in the  presence and
       absence of sodium sulfite	23

  11    Flotation recovery  of pyrite, minus  200 mesh, as a
       function  of pH with  2 x  10-4 M^ KEX in the  presence and
       absence of sodium sulfite	24

  12    Flotation  recovery  of galena, 100  x  200 mesh, as a
       function  of pH with  10-3 ^ additions of several
       reducing  agents and  2  x  10-4 M KEX   	25

                             i v

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FIGURE                                                        PAGE

  13   Zeta potential  of pyrite as a function of pH in the
       absence and presence of various additions of sodium
       sulfite ........................  26

  14   Solution oxidation potential as a function of pH,
       pyrite (100 x 200 mesh), 2 x TO"4 M KEX,  and various
       levels of addition of sodium sulfide (European
       Convention) . .....................  28

  15   Percent recovery and grade percent of chalcopyrite-
       pyrite ore with KEX as a function of sodium cyanide
       addition  .......................  31
  16   Percent recovery and grade percent of chalcopyrite-
       pyrite ore with KEX as a function of sodium sulfite
       addition  .......................   32

  17   Percent recovery and grade percent of galena-pyrite
       ore with KEX as a function of sodium cyanide
       addition  .......................   36

  18   Percent recovery and grade percent of galena-pyrite
       ore with KEX as a function of sodium sulfite
       addition  .......................   37

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                             TABLES
TABLE                                                          PAGE

   I   Experimental Flotation Results Obtained with
       Chalcopyrite-Pyrite Ore with 2.0 Ib.  per ton CaO
       and Various Amounts of Sodium Cyanide Depressant ...   29

  II   Experimental Flotation Results Obtained with
       Chalcopyrite-Pyrite Ore using Various Amounts of
       Sodium Sulfite Depressant at pH 8  	   30

 III   Experimental Flotation Results Obtained with Galena-
       Pyrite Ore using Various Amounts of Sodium Cyanide
       Depressant at pH 8.0	   34

  IV   Experimental Flotation Results Obtained with Gal ena-
       Pyrite Ore using Various Amounts of Sodium Sulfite
       Depressant at pH 8.0	   35
                               vi

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           CONCLUSIONS AND RECOMMENDATIONS
     As was anticipated from the fact that dixanthogen is
the collector species responsible for pyrite flotation, all
reducing agents studied had the ability to depress pyrite
when ethylxanthate was used as collector.   Sulfite, a good
reducing agent, appears to function exceptionally well as
a pyrite depressant.  Sulfite can be used as effectively as
cyanide in  galena-pyrite and chalcopyrite-pyrite ores with
ethyl xanthate as the collector.  In fact, sulfite exhibits
no depressant effect on chalcopyrite, whereas excessive
cyanide can completely depress chalcopyrite.  In the case
of the chalcopyrite-pyrite ore, a significant improvement
in concentrate grade was obtained when sulfite rather than
cyanide was used as the depressant.  Equivalent metallurgical
results were obtained with either sulfite or cyanide as
depressants in the galena-pyrite ore.
     Sulfite was shown to be potential determining for pyrite,
which supports the mechanism proposed for pyrite depression
by reducing agents.  The solution potential  reducing agents
adsorb at the pyrite surface, preventing the adsorption and
dissociation of molecular oxygen to nascent oxygen and in
this manner, prevent oxidation of xanthate to dixanthogen
and subsequent flotation.  Meaningful oxidation potentials
could not be obtained with a platinum electrode when oxyanion
reductants  were used to effect pyrite depression.  However,
the platinum electrode can be used as a monitor when sulfide
                           vii

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ion is used as the depressant.
     Laboratory study has shown that poisonous  cyanide salts
need not be used, both from metallurgical  and economical
criteria, for the depression of pyrite in  sulfide flotation
systems.  This is a most important conclusion in  view of
the recent interest of government and society on  water
pollution and safety.  Consequently, it is recommended that
this study be broadened in order to demonstrate that
similar results can be obtained on an industrial  scale.   For
such a study to be feasible an  united effort and  complete
cooperation between the University, EPA ,and industry is
requi red.
                          vi i i

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                     INTRODUCTION
     One of the principle means of processing the Nation's
raw materials involves the technique of froth flotation.
Froth flotation is the process whereby surfactants (termed
collectors) are adsorbed on selected minerals in a particulate
suspension.  This renders the selected minerals hydrophobic
and on passing air through the suspension, the hydrophobic
particles concentrate in a froth column thus effecting their
separation from the worthless gangue particles.  Almost all
sulfide ores are processed by the froth flotation technique,
and in so doing the rejection or depression of pyrite, a
common sulfide mineral, to the worthless gangue or tailing
product  is frequently required to make an effective
separation.  Industrially this is most readily accomplished
with xanthate as collector for the valuable sulfides such
as chalcooyrite and galena, and poisonous cyanide salts
as a pyrite depressant, i.e., the cyanide salts prevent
adsorption of the collector on the pyrite surface and
subsequent flotation.
     Dixanthogen, an oxidation product of xanthate,  is the
species responsible for pyrite flotation .  In most  sulfide
flotation systems pyrite depression is desired, therefore,
it should be possible to use various chemicals to reduce
the oxidation potential  of the solution and depress  pyrite
by preventing the formation of the collector, dixanthogen.
On this basis,the purpose of our research was to establish
                          1

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 that  pyrite  could be effectively depressed with non-toxic
 reducing  agents which  do not have  the adverse ecological
 and emotional problems associated  with the poisonous cyanide
 sal ts.
                                                p -3
      The  first industrial technique of flotation  '  was to
 collect mineral particles in an oily layer which  could then
 be separated from the  gangue and water.  The oil  flotation
 procedure has been replaced by a method known as  froth
 flotation, where bubbles carrying  mineral particles rise to
 the surface and are removed in the froth, leaving the gangue
 behind.
      The observation that different collectors changed
 flotation results and  the patenting of xanthate,  dithio-
 carbonate, in 1925 increased the use of flotation as a
 separation technique in mineral processing operations.
 Attention was then centered on means of floating  one sulfide
 mineral away from others.  This was accomplished  by using
 various chemical  reagents as depressants  and activators.
 The depressants allowed one or more minerals to float while
 suppressing others with the gangue, while the activators
 caused otherwise unfloatable minerals to  become floatable.
     The first depressants  were alkalis  and cyanide compounds
which were followed by  many organic and inorganic compounds.
The depressant effect of alkalis was investigated by Wark
                             ef-
                            5-9
and Cox ,  and the depressant effect of cyanide has  been the
topic of many investigations
                            2

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     Gaudin   has shown that many anions act as depressants
for sulfide minerals, but little information on mechanisms
was given.  The mechanisms for depression of sulfide
minerals have remained obscure, because the mechanisms for
flotation have been obscure.  This is evidenced by the
number of theories proposed to explain the flotation
mechanisms        Gaudin   proposed that the adsorption of
xanthate on sulfide minerals was the result of an ion
                         1 2
exchange mechanism.  Wark   proposed that xanthates adsorb
on a sulfide mineral by exchanging with hydroxyl and sulfur
ions on the surface.  Mellgren   presented evidence which
supports a theory of insoluble salt formation between the
collector and the mineral  as a mechanism for flotation.
Another mechanism,, given by Cook and Nixon  , is the chemical
adsorption of a neutral molecule on the surface.
     The mechanism for xanthate flotation of pyrite has
been considered extensively '  5~zo.  Recently, Fuerstenau
showed that the oxidation  product, dixanthogen, is the species
responsible for pyrite flotation when xanthate is used
as the collector.   Majima  and  Takeda18 verified the exist-
ence of dixanthogen on pyrite  with infrared spectroscopy.
Most probably dixanthogen  is formed by adsorbed nascent
oxygen oxidation  of xanthate.
     Since the pyrite flotation mechanism has been well
established,  it should be  possible to analyze the depression
of pyrite.   The cyanide depression mechanism of pyrite has
                           3

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been determined .   However, the mechanism of pyrite
depression with other depressants, especially reducing
agents, has not been analyzed in light of the recent theory
advanced for pyrite flotation.   Because of the environmental
and safety problems presented by cyanide depress ion, research
was initiated to determine the  flotation response of pyrite
in the presence of non-toxic reducing agents.

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               EXPERIMENTAL TECHNIQUES
     The investigation included the four following tech-
niques:  flotation experiments  with singular minerals,
zeta potential  experiments, oxidation potential  measurements,
and froth flotation experiments with ore samples.
Reagents
     The reagents as discussed  here, will  apply  to all  of
the experiments in this investigation.
     Commercial potassium ethylxanthate (KEX)  was  purified
by dissolving the xanthate in a minimum amount of  acetone
and recrystal1izing the xanthate by the addition of cold
               ?n
petroleum ether  .  After recrystal1ization the  material
was filtered, washed with petroleum ether, and dried.   This
purification method gives a purity of better than  99 percent.
The purified xanthate was stored in an airtight  container
in a refrigerator until used.
     Deionized, distilled water was used in all  experiments
except for the froth flotation  experiments on ore  samples,
where tap water was used.
     Pure pyrite mineral specimens and the galena-pyrite
ore were obtained from Park City, Utah.  Pure galena was
obtained from Minerals Unlimited.  The chalcopyrite-pyrite
ore was typical of the southwestern copper porphory ores.
     All of the chemicals used  in this investigation were
of reagent grade quality or better.
                             5

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Flotation Experiments with Singular Minerals
                                             21
     A modified Hallimond tube flotation cell    was  used
to determine the effect of certain reducing agents on the
flotation response of pyrite and galena with potassium
ethylxanthate as the collector.   The apparatus,  described
in Figure 1, consisted of a fritted-glass bottom tube
through which air was controlled by a manometer, constant
head reservoir, and a gas measuring burette.  A  magnetic
stirrer with a teflon-coated stirring bar was  used to
maintain constant agitation.
     The following procedure was used for both pyrite and
galena mineral samples:
     1.  The mineral was dry-ground with a porcelain mortar
and pestle, then sized with Tyler standard sieves within
24 hours prior to the flotation  test.
     2.  A sized 1.0 gram sample was used as the flotation
sample.
     3.  The flotation sample was deslimed 5 times with
deionized water prior to each test.
     4.  Deionized water, xanthate, and reducing agent
were mixed to yield the desired  concentration  of 130 mill-
iliters total volume.
     5.  The desired solution pH was obtained  with either
KOH or HC1.
     6.  The deslimed mineral was added to the solution.
     7.  The pulp was conditioned for 3 minutes.
                           6

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            Constant head
             water tank
 Manometer
                                Air measuring
                                burette
Compressed-    Air Reservoir
air Line
                                        Hallimond tube
                                        floation cell
Figure  1.   Schematic diagram of flotation
            apparatus.

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     8.  The pH of the pulp was measured and recorded after
conditioning.
     9.  The pulp was transferred to the Hallimond tube
flotation cell and floated for 2 minutes at constant agitation
and at 70 milliliters per minute air flow rate.
    10.  The pH was measured after flotation to determine
if a significant change occurred.
    11.  The concentrate and tailing products were dried,
weighed and the percent recovery calculated.
Zeta Potential Experiments
     The zeta potential  of pyrite was determined at various
concentrations of sodium sulfite and at various pH values.
The pH at which the zeta potential  of the pyrite surface
reached zero was determined graphically, and this pH is
called the zero-point-of-charge (ZPC).
     The equipment consisted of a Zeta Meter to determine
the zeta potential at the pyrite surface and a Beckman
Zeromatic II pH meter to measure pH.   A magnetic stirrer
with a teflon-coated magnetic stirring bar was used to
maintain agitation during conditioning.
     The following procedure was used to obtain the desired
sample conditions for the zeta potential determinations.
     1.  The pyrite was  dry-ground with  a porcelain mortar
and pestle,  then screened through a 200 mesh Tyler sieve.
     2.  The minus 200 mesh pyrite was  weighed out into
50 milligram samples.
                           8

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     3.  Deionized water and sodium sulfite were added
to a 150 mi Hi liter beaker to give a total volume of 100
milliliters and the desired concentration of sodium sulfite.
     4.  The 50 milligram pyrite sample was added to the
water and sodium sulfite solution.
     5.  The pK of the sample was adjusted with either HC1
or KOH.
     6.  The sample was conditioned for 3 minutes to
approximate the flotation conditions of the pyrite.
     7.  The pH of the sample was measured and recorded.
     8.  The resulting suspension was decanted into a
plexiglass electrophoretic cell, electrodes inserted, and
placed under the microscope.
     9.  A potential was applied across the electrodes.
    10.  The average time for a particle to move horizon-
tally between  two lines of the grid was recorded.  This  time
was translated into zeta potential from standard charts.
The measured zeta potentials were plotted against pH, and
a ZPC was determined from the resulting curve.
Oxidation Potential Measurements
     The apparatus used in these measurements consisted  of
a Beckman Zeromatic II pH meter, a calomel reference
electrode, a platinum electrode, a glass electrode, magnetic
stirrer with teflon-coated magnetic stirring bar, and a
250 milliliter beaker.
     The following procedure was used in preparing the samples
                           9

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and making measurements.
     1.  The pyrite was dry-ground with a porcelain mortar
and pestle, then sized with Tyler sieves.
     2.  A 1.0 gram sample, 100 X 200 mesh, was used as in
flotation experiments.
     3.  Deionized water, xanthate, and reducing agent were
mixed to yield the desired concentrations of 130 milliliters
total volume.
     4.  The pH was adjusted with either KOH or HC1.
     5.  The deslimed pyrite was added to the above solution.
     6.  The pulp was conditioned for 3 minutes.
     7.  The pH was measured and recorded.
     8.  The solution oxidation potential was measured and
recorded.
     9.  The Eh was calculated from the cell potential,
Eh = Ecell + Eref.
Froth Flotation Experiments with Ore Samples
     Experimental equipment consisted of an ore crusher, a
rod mill,  a Wemco froth flotation cell, a Beckman Zeromatic
II pH meter, and a Mettler top load electronic balance.
     The following procedure was used on both the galena and
the chalcopyrite ores.
     1.  Approximately 100 Ibs of ore was crushed, then
coned and  quartered, and  split with a riffle until approx-
imately 500 gram samples  resulted.
     3.  500 grams of a sample was  weighed out on the top
                          10

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loading balance and placed in the rod mill  with 333
milliliters of tap water.
     3.  The ore was ground at 60 percent solids in the rod
mill for 3 minutes and the resulting pulp was transferred
to the flotation cell with 1667 milliliters of tap water.
     4.  Varying amounts of sodium sulfite  or sodium cyanide
and 0.05 pounds per ton KEX were added to the cell.
     5.  The pH was adjusted and the pulp was conditioned
at 20 percent solids for 5 minutes.
     6.  3 drops of Aerofroth 65 were added, the air was
turned on, and the sample  was floated for 8 minutes.
     7.  The concentrate and tailing products were dried,
weighed, and analyzed to test the effectiveness of the
depressant.
                          11

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                 EXPERIMENTAL RESULTS
     The flotation response of pyrite and galena in a
Hallimond cell with KEX as the collector and various reducing
agents as depressants was investigated.   Zeta potential
and solution oxidation potential  measurements were made  on
these systems.  Flotation tests  with lead and copper ore
samples were made to compare the  effectiveness of sodium
cyanide and sodium sulfite as depressants for pyrite.  The
experimental data from these tests are presented in this
section.
Flotation Experiments with Singular Minerals
     Various reducing agents at different concentration  levels
were tested to determine their ability to depress pyrite
and to establish the mechanism for depression with KEX as
the flotation collector.
     The flotation response of pyrite with KEX in the presence
of various additions of sodium sulfite is shown in Figure 2.
When no sodium sulfite is present, complete depression is
effected above pH 10; whereas, with increasing sulfite
additions the pH for depression is lowered to what appears
to be a minimum of pH 5 for additions of 10"3 M, and greater.
     The flotation response of pyrite with KEX in the presence
and absence of zinc sulfite is shown in Figure 3.  When
zinc sulfite is present, complete depression is effected
above pH 5.
                           12

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u>
        oc
        UJ

        §
        u
        UJ
        IT
U
O
cr
UJ
a.
            100
            80
    60
            20
Sodium Suffite


• None

o
                   D  |x|o"2M
                                      6       8      10

                                  FLOTATION     pH
                                                             14
        Figure  2
Flotation  recovery of  pyrite,
of pH with  2  x  10-4 M  KEX  and

sodium sulfite.
                                        TOO  x  200 mesh, as a function
                                        at  four  levels of addition of

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   100
    80
o:
u

IĞ>
    40
   20
u
o:
Zinc Sulfite:



o  None


a  Ixio"3M
                     468


                        FLOTATION    pH
                                  10
12
14
Figure 3.   Flotation  recovery of pyrite, TOO x 200 mesh, as a function

           of pH  with  2  x  10~4 M_ KEX in the presence and absence of

           zinc  sulfite.

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     The flotation response of pyrite with KEX in the
presence of various additions of sodium sulfide is  shown  in
                         _3
Figure 4.  Addition of 10   M. sodium sulfide is required
                                        -5
to depress pyrite, while additions of 10   M_ sodium sulfide
have no effect on the flotation response.
     The flotation response of pyrite with KEX in the presence
and absence of sodium thiosulfate is shown in Figure 5.
Sodium thiosulfate acts as a depressant at pH 7 and above,
but shows little effect below pH 7.
     The flotation response of pyrite with KEX in the presence
and absence of sodium hypophosphite  is shown in Figure 6.
Sodium hypophosphite is a pyrite depressant above pH 6,  but
shows little effect on pyrite below  pH 6.
     The flotation response of pyrite with KEX in the
presence of various additions of sodium oxalate is  shown
in Figure 7.  Sodium oxalate is not  as effective as the
other reducing agents in pyrite depression.  Depression
occurs only above pH 8.
     Figures 2 thorugh 7 show that sulfite is one of the
most effective depressants tested.  These  figures aloo show
that the best pyrite depression occurs in  basic media and
that below pH 4.5, no depression is  observed with any
depressant.
     Figure 8 indicates that the effectiveness of sodium
sulfite is long-lasting, in that pyrite is depressed as
well, or even better, after a ten minute conditioning time
                           15

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  100
   60
OL
UJ
O  60
u
LJ
cc
u
g
bJ
   40
   20
Figure 4.
Sodium Suffide:
o None
a lxlo"5M
• ix io"4M
• lx|0~*M
                            6       8      10
                         FLOTATION    pH
                                          12
14
  Flotation  recovery of pyrite, 100  x  200 mesh, as a
  function of  pH with 2 x 10-4 y\ KEX,  and at four levels
  of addition  of sodium sulfide.

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  IOO
   80
tr
UJ
UJ
or
ui
o
(T
bl
a.
   40
   20
Figure 5
KEX: 2x 1C)4 M

Sodium Thiosulfote


o  None


n  lxio"5
                             6       8

                          FLOTATION
                                   IO
                    12
                               PH
 Flotation recovery of

 of pH with 2 x 10-4 M

 sodium thiosulfate.
pyrite, 100 x  200  mesh,

KEX in the presence  and
   14
as a function

absence of

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              100
oo
            cc
            UJ


            I
            bJ
            CC
z
UJ
u
cc
              80
   60
               40
               20
Sodium Hypophosphite


 o  None

 n  |x io"5M
            Figure  6,
                                        6      8

                                     FLOTATION    pH
                                            10
                                             12
           Flotation  recovery^of pyrite, 100 x 200 mesh,

           of  pH with 2 x 10 4 M^ KEX in the presence and

           sodium  hypophosphite.
14
                                                 as  a  function

                                                 absence  of

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  100
>-
QC
  80
8 60
ui
a:
u
ac
in
a.
   4O
   20
KEX: 2xlO~4M
Sodium Oxalatc:
•  None
o  I x lo"4 M
a  I x |0"SM
                    46       8      10
                        FLOTATION     pH
                                         12
14
Figure 7.   Flotation recovery of pyrite,  100  x 200 mesh as a function
           of pH with 2 x TO'4 n KEX and  at  three levels of addition
           of sodium oxalate.

-------
ro
o
          too
        > 80

        or
        Id


        §60
        u
        a:
UJ
o
oe
          40
        Figure 8.
                                            KEX= 2 x |Q"4M

                                            Sodium  Sulfite: IO"3M


                                            o  10  Minute

                                            P  3   Minute
                                                          n
                              4       6       8      10

                                 FLOTATION     p H
                                                     12
14
           Flotation recovery  of pyrite,  100  x  2QO mesh, as a function
           of pH with 2 x 10-4 j^ KEX  and  1  x  10~  M sodium sulfite
           for two different conditioning  times.

-------
as it was after a three minute conditioning time.
     As can be seen in Figure 9, pyrite flotation  response
does not change considerably from a KEX concentration of
2xx 10   mole per liter to a KEX concentration of  5 x 10~
mole per liter.  This determination was made because the
ore samples were floated at a KEX level of about 5 x 10~
mole per liter.
     Figures 10 and 11 illustrate that the size of the pyrite
particles are relatively unimportant in the sodium sulfite
depression system.
     Oxyanion reductants do not affect the flotation response
of galena, as Figure 12 illustrates.  The galena floats  as
well in the presence of the reductants as in their absence.
Zeta Potential Experiments
     The zeta potential of pyrite in the absence of sulfite
and at two levels of sulfite addition  was  determined as
a function of pH.  See Figure 13.  It appears  that the
sulfite anion has a special affinity for the pyrite surface,
in that the ZPC is  pH 7 with no sulfite addition,  pH 6
with 10"4 M sulfite, and pH 5 with  10"3 M sulfite.
Oxidation Potential  Measurements
     Solution oxidation potential measurements of  each
pyrite flotation system were attempted; however, in oxyanion
reductant systems,  it was not possible to obtain meaningful
measurements.  No variation in the  platinum-calomel cell
potential could be  detected, even though the concentration
                          21

-------
           too
ro
or
UJ


I
UJ
oc
         UJ
         o
         tr
         ui
         a.
            80
            60
           40
           20
                   o 2 x io"4M KEX
                    n 5 x 10"5M
KEX
                              4      6       8      IO


                                 FLOTATION     pH
                           12
                                                          14
         Figure 9.  Flotation  recovery of pyrite,  100 x 200 mesh as a function

                   of pH  at  two levels of addition  of KEX.

-------
ro
         100
       >80
       QL
       LJ

       8 60
       UJ
          40
        UJ
        0.
          20
       Figure 10
                                KEX*. 2 x |0"4 M

                                Sodium Sulfite:

                                o None

                                D |x|o"5
                            4      €      8      10

                                FLOTATION     pH
                                       12
               14
Flotation recovery.of  pyrite, 65
of pH  with 2 x 10   M.  KEX in the
sodium sulfite.
x 100  mesh, as a function
presence  and absence of

-------
           100
>
OC
LU

O
            80
PO
         LJ
         O
         QC
         UJ
         0.
   40
            20
 Sodium Sulfite: _

o None

a I x I0"3 M
                                      6      8      10

                                  FLOTATION    pH
                                                           14
          Figure  11.  Flotation recovery of pyrite
                     function of pH with 2 x 10~4
                     absence of sodium sulfite.
                                         minus 200 mesh, as a
                                        M  KEX  in the presence
               and

-------
ro
on
100


> 80
oc
UJ
O
Ğ M

u 60
o:

h-
w 4O
o
o:
Q.
20

I

KEX
V w . -i VX • • 0 w - u ^fc , ,
-4 \
:2x|Q U \
Depressant: \

\
a None I
o I

• 1
• |

—



-
i
0 2
xlO"3M Sodium Sulfite 1
ttr I
xlO"3M Sodium Thiosulfote 1
xlo"5M Sodium Hypophosphite 1

1
A
i
I
-
iii it i
46 8 10 12 14
                                    FLOTATION   pH


          Figure  12.  Flotation recovery of galena, 100  x 200  mesh,  as  a
                     function of pH with 10'3 M, additions of  several  reducing
                     agents and 2 x 1Q-4 KEX.

-------
no
        + 50
        +40
     *Ğ
     ? +30
      >
     I +20

     j +10
UJ
o
a.

£
-IO

- 20
        -40

        -50
                                           No2S03 Addition:
                                               None
                                               I  x 10
                                               I  x
                                          8
                                           10
                                                12
14
                                      PH
      Figure 13
            Zeta potential  of pyrite as a function of pH in  the  absence
            and oresence  of various additions of sodium sulfite.

-------
of reductant was changed by several orders of magnitude.
Meaningful solution oxidation potential readings were
obtained in the sodium sulfide system, as illustrated in
Figure 14.  The potential readings in this figure have been
converted to Eh (hydrogen electrode reference), and are
plotted against pH.  The dotted line drawn through the data
represents the 50 percent recovery isotherm, as determined
from flotation experiments.  Above the dotted line, good
flotation response is obtained and below the dotted line,
poor flotation response is obtained.
Froth Flotation Experiments with Ore Samples
     Tables I and II show the flotation results of the
chalcopyrite-pyrite ore when sodium cyanide and sodium
sulfite, respectively, were the depressants.  By comparing
these two tables the relative effectiveness of each depressant
can be determined.   The columns labeled Fe Units and Cu Units,
are weights of the respective elements based on a total
weight of 100 grams.  The distribution percentages of Fe and
Cu show that sodium sulfite is just as effective as sodium
cyanide for depressing pyrite in a chalcopyrite ore.
Graphical representation in Figures 15 and 16 show that
Fe percent recovery falls off with increasing depressant
addition in both cyanide and sulfite systems.  This means
that both sodium cyanide and sodium sulfite can effectively
depress pyrite.
     Comparison of the Cu percent recovery of both curves,
                          27

-------
IS5
00
          +0-5
          +0-4

          +0-3

          +0-2
       o
      bj  -i
          -0-2

          -03

          -0-4
      Figure 14.
 KEX' 2 x I0"4 M
 Sodium Sulfide
 o  None
 D  I x  K>~* M
 •  I x  10  M
 A  |xlO"5M
                                             8
                                   10
12
14
                                        PH
Solution  oxidation  potential  as  a  function of pH, pyrite
(100 x 200 mesh), 2  x  10-4 M  KEX,  and various levels of
addition  of sodium  sulfide TEuropean Convention).

-------
                                             TABLE I

                           Experimental  Flotation Results  Obtained With
                           Chalcopyrite-Pyrite Ore With  2.0  1b  per ton
                            CaO and Various  Amounts of NaCN Depressant
vo
PH
8.5
8.65
8.65
8.80
Depressant
Amount
None
0.05 Ib
per ton
0.10 Ib
per ton
0.50 Ib
per ton
Product
Product Wt, grains
Concentrate
Tail
Total
Concentrate
Tail
Total
Concentrate
Tail
Total
Concentrate
Tail
Total
82
412
72
425
60
443
40
434
Wt,%
16.6
83.4
100.0
14.5
85.5
100.0
12.0
88.0
100.0
8.5
91.5
100.0
Fe,
20.
2.
15.
2.
16.
6.
9.
4.
%
4
6
7
9
6
4
3
6
Cu,%
4.30
0.09
4.30
0.08
4.60
0.12
2.30
0.67
Fe
Units
3.39
2.17
5.56
2.26
2.46
4.72
2.00
5.67
7.67
0.74
4.00
4.74
Cu
Units
0.710
0.075
0.785
0.620
0.067
0.687
0.560
0.106
0.666
0.180
0.580
0.760
Fe Distri-
bution^
60.9
39.1
100.0
47.8
52.2
100.0
26.1
73.9
100.0
15.6
84.4
100.0
Cu Distri-
bution,%
90.5
9.5
100.0
90.2
9.8
100.0
84.2
15.8
100.0
31.0
69.0
100.0

-------
CO
o
                                               TABLE II

                             Experimental Flotation Results Obtained With
                             Chalcopyrite-Pyrite Ore Using Various Amounts
                                  of Sodium Sulfite Depressant at pH 8
Depressant
Amount
None
0.25 Ib
per ton
0.50 Ib
per ton
0.75 Ib
per ton
1.00 Ib
per ton
Product
Concentrate
Tail
Total
Concentrate
Tail
Total
Concentrate
Tail
Total
Concentrate
Tail
Total
Concentrate
Tail
Total
Product
Wt, grams
53
443
55
443
44
453
43
453
39
461
Wt,%
10.7
89.3
100.0
11.0
89.30
100.0
8.9
91.1
100.0
8.7
91.3
100.0
7.8
92.2
100.0
Fe,%
26.8
2.3
24.4
2.3
28.0
7.7
23.8
4.9
28.0
14.5
Cu,%
5.90
0.08
5.80
0.08
7.30
0.08
6.20
0.13
7.70
0.10
Fe
Units
2.84
2.04
4.88
2.68
2.04
4.72
2.46
7.00
9.46
2.04
4.44
6.48
2.18
13.34
15.52
Cu
Units
0.620
0.070
0.690
0.640
0.070
0.710
0.640
0.072
0.712
0.536
0.118
0.654
0.600
0.092
0.692
Fe Distri-
bution,/^
58.3
41.7
100.0
56.8
43.2
100.0
26.0
74.0
100.0
31.6
68.4
100.0
14.1
85.9
100.0
Cu Distri
bution,%
90.2
9.8
100.0
90.2
9.8
100.0
89.9
10.1
100.0
82.0
18.0
100.0
86.0
13.4
100.0

-------
   10
                                         • Iron  Recovery

                                         o Copper Recovery

                                         A Copper  Grode
            0-2     0-4    06     0-8     1-0     1-2

               SODIUM  CYANIDE ADDITION (Pounds/Ton)
                                               1-4
                                                    100
                                                    80
                                                                    UJ

                                                                60  §
                                                                    u
                                                                40
                                                                20
                                                                    ui
                                                                    u
                                                                    flC
                                                                    Ul
                                                                    Q.
Figure  15,
Percent recovery  and grade percent of chalcopyrite-pyrite ore
with KEX as  a  function of sodium cyanide addition.

-------
        10
CO

ro
                                                    • Iron Recovery

                                                    o Copper Recovery

                                                       Copper Grade
                                                    100
                                                                     80
                                                                         o
                                                        I-

                                                    40  g
                                                        o
                                                        cr
                                                        UJ
                                                        Q.

                                                    20
                 0-2     0-4     0-6    0-8    1-0     1-2

                   SODIUM  SULFITE  ADDITION (Pounds/Ton )
                                               1-4
      Figure 16,
Percent recovery  and  grade  percent of chalcopyrite-pyrite

ore with  KEX  as  a  function  of sodium sulfite solution.

-------
reveals that sodium cyanide not only depressed pyrite
but also depressed the chalcopyrite.  Recovery dropped
from about 90 percent at .05 Ib per ton to 30 percent
at 0.5 Ib per ton.  Sodium sulfite had little effect on
the flotation recovery of chalcopyrite.  Recovery decreased
from 90 percent at 0.25 Ib per ton to 86 percent at 1.0
Ib per ton.   Comparison of concentrate grade, percent Cu,
of the cyanide and sulfite systems indicates the same
results, sulfite is a depressant for pyrite but not for
chalcopyrite whereas, cyanide can be depressant for both
pyrite and chalcopyrite.   For example, with sodium sulfite
the percent copper in the concentrate increases from about
6 percent at 0.25 Ib per ton to almost 8 percent at 1.0 Ib
per ton.  This is to be compared with results in the cyanide
system in which the percent copper in the concentrate
drops from about 4.5 percent at low levels of cyanide to
about 2.5 percent at 0.5 Ib per ton.
     Table III and IV show the flotation results of the
galena-pyrite ore when sodium cyanide and sodium sulfite
were the depressants.  Again, the columns labeled Fe Units
and Pb Units refer to the weight of the respective elements
based on a total weight of 100 grams.  Comparison of these
tables gives the relative effectiveness of each depressant.
Both depressants are effective for pyrite depression.
     Figures 17 and 18 graphically demonstrate that both
cyanide and sulfite depress pyrite in a galena-pyrite ore.
                          33

-------
CO
                                             TABLE III

                           Experimental Flotation Results Obtained With
                            Galena-Pyrite Ore Using Various Amounts of
                                Sodium Cyanide Depressant at pH 8.0
Depressant
Amount
None
0.10 Lb
Per Ton
0.25 Lb
Per Ton
0.50 Lb
Per Ton
0.75 Lb
Per Ton
1.00 Lb
Per Ton
Product
Concentrate
Tail
Total
Concentrate
Tail
Total
Concentrate
Tail
Total
Concentrate
Tail
Total
Concentrate
Tail
Total
Concentrate
Tail
Total
Product
Wt, grams
251
244
102
393
106
389
99
400
112
387
117
380
Wt,*
50.7
49.3
100.0
21.6
79.4
100.0
21.4
78.6
100.0
19.8
80.2
100.0
22.5
77.5
100.0
23.6
76.4
100.0
Fef%
20.9
12.8
5.8
32.6
4.7
22.7
11.6
22.1
5.8
18.3
8.1
23.3
Pb.X
30.5
2.0
46.0
6.0
54.6
6.2
49.0
8.0
43.3
7.0
43.3
7.8
Fe
Units
10.6
6.3
16.9
1.19
25.85
27.04
1.00
17.85
18.85
2.30
17.70
20.00
1.30
14.20
15.17
1.91
17.80
19.71
Pb
Units
15.50
0.99
16.49
9.48
4.76
14.24
11.70
4.88
16.58
9.71
6.42
16.13
9.75
5.42
15.17
10.20
5.95
16.15
Fe Distri-
bution,/^
62.7
37.3
100.0
4.4
95.6
100.0
5.4
94.6
100.0
11.5
88.5
100.0
8.4
91.6
100.00
9.7
90.3
100.0
Pb Distri-
bution,%
94.0
6.0
100.0
66.4
33.6
100.0
70.6
29.4
100.0
60.4
39.6
100.0
64.2
35.8
100.0
63.0
37.0
100.0

-------
CO
CJ1
                                                TABLE IV

                              Experimental Flotation Results Obtained With
                               Galena-Pyrite Ore Using Various Amounts of
                                   Sodium Sulfite Depressant at pH 8.0
Depressant
Amount
None
0.25 Lb
Per Ton
0.50 Lb
Per Ton
0.75 Lb
Per Ton
1.00 Lb
Per Ton
Product
Concentrate
Tail
Total
Concentrate
Tail
Total
Concentrate
Tail
Total
Concentrate
Tail
Total
Concentrate
Tail
Total
Product
Wt, grams
251
244
148
349
111
383
87
410
91
407
Wt,%
50.7
49.3
100.0
29.8
70.2
100.0
22.5
77.5
100.0
17.5
82.5
100.0
18.2
81.8
100.0
Fe,*
20.9
12.8
11.6
20.9
16.3
23.0
9.9
25.0
7.6
12.5
Pbt%
30.5
2.0
43.3
4.7
46.6
4.3
44.0
4.7
56.6
6.0
Fe
Units
10.6
6.3
16.9
3.5
14.6
18.1
3.4
17.8
21.5
1.7
20.6
22.3
1.4
10.2
11.6
Pb
Units
15.50
0.99
16.49
12.90
3.30
16.20
10.50
3.33
11.58
7.70
3.88
11.58
10.30
4.90
15.20
Fe Distri-
bution^
62.7
37.3
100.0
19.1
80.9
100.0
17.0
83.0
100.0
7.8
92.2
100.0
11.8
88.2
100.0
Pb Distri-
bution^
94.0
6.0
100.0
79.5
20.5
100.0
76.0
24.0
100.0
66.7
33.3
100.0
68.0
32.0
100.0

-------
CO
         too
                                                  • Iron Recovery

                                                  o Lead Recovery

                                                  A Lead Grode
                   0-2     0-4     0-6     0-8     1-0      1-2

                     SODIUM  CYANIDE  ADDITION (Pounds/Ton)
                                                1-4
                                                     100
                                                      80
                                                                          >-
                                                                          a:
                                                                          a:
                                                                        20
                                                                          IS
      Figure 17
Percent recovery  and  grade  percent of galena-pyrite ore with

KEX as  a function  of  sodium cyanide addition.

-------
  100
                                                      too
                                                 Iron Recovery
                                              o Lead Recovery
                                                 Lead Grade
             0-2     04     0-6    0-8     1-0      1-2
               SODIUM  SULFITE  ADDITION (Pounds/Ton)
                                                1-4
Figure  18.
Percent  recovery and grade percent of  galena-pyrite ore with
KEX as  a function of sodium sulfite addition.

-------
The lead recovery drops slightly in both the cyanide and
sulfite systems, which is an indication that both cyanide
and sulfite may have a small depressing effect on galena.
Lead recovery in the cyanide system drops quickly from
about 95 percent to about 65 percent with small  additions
of the depressant.   On the other hand, lead recovery in the
sulfite system is not affected to the same extent.   In this
case, the lead recovery decreases slowly and only at large
additions of sodium sulfite (1.0 Ib per ton) is  the recovery
less than 70 percent.   In both systems iron recovery is
reduced to 10 percent at moderate additions of depressant.
                         38

-------
                DISCUSSION OF RESULTS
     The common technique of cyanide depression of pyrite
in flotation milling of a complex sulfide ore has been
                       r o
thoroughly investigated " .   The mechanism responsible
for depression is the formation of a ferrocyanide complex
                     5
on the pyrite surface .   The industrial use of cyanide is
undesirable, however, both from the standpoint of the
potential pollution problem and safety hazard it presents.
     The depression of pyrite with reducing agents has not
been investigated as extensively as has cyanide.  However,
                                                    22
reducing agents have been observed to depress pyrite
Sulfite, which is a good reducing agent, has been observed
                 22 25
to depress pyrite     .   In  addition, ferrous ion, which
is also a good reducing agent, has been observed to depress
pyrite .
     Since dixanthogen is the species responsible for pyrite
flotation, any chemical  which is more reducing than the
xanthate-dixanthogen couple  should be capable of depressing
pyrite.  The average value of the standard half cell
potential (E°), according to the European sign convention,
for the xanthate-dixanthogen system was found to be minus
0.044 volt by Huiatt20 and minus 0.049 volt by Majima17.
The half cell reactions  and  their corresponding potentials
for the reducing agents  considered in this study are
presented in the following equations, written according
                               26
to the European sign convention  :
                          39

-------
     SOg" + 20H" = S0^~ + H20 + 2e"         E°  =  -0.93
     H2PO~ + 30H" = HPO~~ + 2H20 + 2e~      E°  =  -1.57
     S" = S + 2e"                         E°  =  -0.48

     H2C2°4(aq) ' 2C02(^ + 2H+ + 2e"      E°  =  -°'49
      2
             60H" = 2SOI" + 3H00 + 4e"      E°  =  -0.58

The flotation results of pyrite using the reducing  agents,
which are represented in the preceding half cell  reactions,
are shown in Figures 2 through 7.   The figures  indicate
that all these reducing agents act as depressants for  pyrite.
These results present more evidence that  dixanthogen  is  the
species responsible for pyrite flotation, since in  these
systems the dixanthogen molecule would be thermodynamically
unstable.  Other indirect evidence for dixanthogen  as  the
collector species for pyrite arises because:   ferric  xanthate
is an unstable compound, decomposing into ferrous ion  and
dixanthogen;   ferrous xanthate is too soluble  to form at
the concentration used, and while electrostatic adsorption
is possible in acid solutions it should not be  possible  in
basic solutions where both the pyrite surface and xanthate
ion are negatively charged.
     Comparison of Figures 2 through 7, indicate that  sulfite
is one of the better depressants for pyrite.   This  can
be  accounted  for, since sulfite is  such a strong
                          40

-------
reducing agent (E° = -0.93) and since sulfite is potential
determining for pyrite, as shown in Figure 13.
     Because sulfite is potential determining for pyrite,
the depressant effect should arise both from its reducing
interactions in solution and its adsorption on  the pyrite
surface.  The latter effect is probably more important,
because recent work indicates that the oxidation of
xanthate to dixanthogen is accomplished catalytically by
                                    1 8 20
nascent oxygen on the pyrite surface  '  .   The sulfite
would then prevent the adsorption of molecular  oxygen and
formation of active nascent oxygen sites as indicated by
the following reaction:
            SS                             SS       0=
                                             \
         Fe            + SOI          + Fe    0 — S
           \                 (aqueous)     \
            "(surface)                    SS       °
Such a mechanism accounts for depression by occupying the
sites for the effective oxidant and is substantiated by
zeta potential measurements.  The results illustrated in
Figure 13 show that the zeta potential becomes  more negative
as sulfite is added.   This is in accord with  the proposed
mechanism.  Other reducing agents, which also act as
depressants, probably function in a similar manner.
     Figure 12, shows that reducing agents are  not depressants
for galena and that it should be possible to  separate galena
                          41

-------
from pyrite in an ore containing both minerals.   This may
he somewhat surprising because galena as well as all other
sulfides adsorb oxygen at their surface readily.  Conse-
quently, one might expect depression as in the case of
pyrite.  Such is not the case, because unlike ferrous
ethyl xanthate, lead ethyl xanthate is a very stable compound
and has been observed by infrared techniques on  the galena
       27
surface  .   As a result, galena is not depressed by
reducing agents.
     To depress pyrite from galena and other sulfides, it
would be desirable to be able to monitor the solution
oxidation potential  and determine whether enough reducing
agent is in solution to prevent dixanthogen formation.
Meaningful  measurements of solution oxidation potentials
were not possible with oxyanion reductants because these
reductants  are not reversible to the platinum electrode,
probably due to the  fact that there is an oxygen transfer
involved in the oxidation-reduction couple, in addition to
the simple  electron  transfer.  However, meaningful measure-
ments were  made using sulfide ion for the depressant, as
shown in Figure 14.   Comparison of Figure 14 with Figure 4
indicates that for a pH less than 8, pyrite depression
occurs at Eh values  less than 0.1 volt; and that good
flotation occurs at  Eh values greater than 0.1 volt.  Above
pH 8, it is believed that pyrite depression occurs for an
entirely different reason.  It is well known that pyrite is
                          42

-------
depressed 1n a basic media of pH ]1 and above.  This
phenomenon is attributed to the formation of ferric hydroxide,
on which dixanthogen cannot adsorb.  This reasoning is
supported by the fact that flotation cannot be effected at
high pH even when a moderate oxidizing agent is added to
the system to form dixanthogen.  If measurements of oxyanion
solution potentials were possible, it is expected that an
Eh response similar to the sulfide system would exist.
     Sodium sulfite has relatively long-lasting effectiveness,
since it depresses pyrite well, even after a ten minute
conditioning time.  This is demonstrated in Figure 8 and
indicates that the oxidation kinetics of sulfite in the
pyrite system is slow and therefore not a hindering factor
in depression.
     The flotation results shown in Figures 2, 10 and 11
indicate that depression of pyrite is not a function of
particle size, since almost identical flotation curves were
obtained for three different mesh  sizes.
     An evaluation of the theory proposed was  made by
testing both a lead and copper ore.  The results of tests
on the copper ore are shown in Table I   and II.  These
results show that both sodium cyanide and sodium sulfite
are depressants for pyrite, since  in both cases the weight
percent of concentrate, the percent of iron in the concentrate
and the iron distribution in the concentrate decrease as
the level  of depressant addition increases.   The copper
                          43

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distribution in the concentrate drops from 84 percent with
0.10 Ib per ton sodium cyanide to 31 percent with an addition
of 0.5 Ib per ton.  This response is not observed  when
sodium sulfite is used as the depressant, since recovery is
still 86 percent even at an addition of 1.0 Ib per ton.
These results indicate that cyanide will depress both
chalcopyrite and pyrite with additions of more than 0.10
Ib per ton, but that sulfite is a depressant for pyrite only
and will  not influence chalcopyrite flotation at any level.
Figures 15 and 16 illustrate these results graphically.
Approximately five times more sulfite than cyanide is
required for adequate depression of pyrite; however, the
rougher concentrate grade is significantly greater with
sulfite,  7 percent Cu, than with cyanide, 4.3 percent Cu,
at the same recovery.  The minimum price of alkaline sulfites
is 4 cents a pound, while the price of sodium cyanide is
                      28
about 20 cents a pound  .   At these prices.the cost of using
sulfite is the same as the cost for using cyanide.   Because
the economics are the same and because sulfite is more
efficient metallurgically, it appears that sulfite would
be a better depressant for pyrite in copper porphory ores.
In addition,pol1ution danger is reduced and monitoring costs
for the poisonous cyanide are eliminated.
     It has been reported that sulfite is an effective
                     23
depressant for galena   and that galena is not influenced
          2Q
by cyanide  .  However, the results of this investigation
                          44

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tabulated in Tables III and IV and illustrated in
Figures 17 and 18, do not support prior findings.  Galena
floats as well with sulfite additions as with cyanide
additions.  Both cyanide and sulfite appear to depress
galena to a slight extent in ore flotation but the effect
seems greater with cyanide than with sulfite.  Pyrite is
effectively depressed with both cyanide and sulfite, but
more sulfite is required than cyanide to accomplish the
same results.  Other than the level of reagent addition,
there seems to be little difference in metallurgical results
of sulfite and cyanide in the case of the lead ore.  To
depress pyrite more sulfite than cyanide is required; however,
this is offset by the fact that cyanide is five times more
expensive than sulfite.  Therefore, on the basis  of both
metallurgy and economics, sulfite and cyanide are equivalent
as pyrite depressants for lead ore.
                          45

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                     ACKNOWLEDGMENTS








This work was accomplished under the direction of Dr. Jan D.



Miller, Assistant Professor of Metallurgy, Department of Mineral



Engineering, University of Utah with the assistance of Walter G.



Peterson, former graduate student in metallurgy.  Mr. Peterson



did much of the experimental work on this project and his Master's



thesis was the basis for this report.







This work was performed in fulfillment of Environmental Protection



Agency Grant No. 12010 DIM.

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                            REFERENCES

 1.  Fuerstenau, M. C., Kuhn, M. C.f and Elgillani, D.  A.,  "The  Role
     of Dixanthogen in Xanthate Flotation of Pyrite," AIME  Trans.,
     241 (1968) 148-156.

 2.  Fuerstenau, D. W. ed., Froth Flotation, Fiftieth Anniversary
     Volume, The American Institute of Mining, Metallurgical,  and
     Petroleum Engineers, Inc., N.Y., 1962, 39-68.

 3.  Adamson, A. W., Physical Chemistry of Surfaces, Second Edition
     Interscience Publishers, N.Y., 1967, 478.

 4.  Fuerstenau, D. W., Froth Flotation. Fiftieth Anniversary  Volume,
     The American Institute of Mining, Metallurgical and Petroleum
     Engineers, Inc., N.Y., 1962, 144-164.

 5.  Mark, I. W. and Cox, A.  B., "Principles of Flotation,  III.  An
     Experimental Study of the Influence of Cyanide, Alkalis,  and
     Copper Sulfate on the effect of Xanthates at Mineral Surfaces,"
     AIME Trans., 112 (1934)  245.

 6.  Elgillani, D. A. and Fuerstenau, M. C., "Mechanisms  Involved in
     Cyanide Depression of Pyrite," AIME Trans., 241 (1968)  437-443.

 7.  Majumdar, K. K., "On the Role of Alkali Cyanides in  the Depression
     of Pyrite," J. Sci. Ind. Res., 11B (1952) 344.

 8.  Majumdar, K. K., "Depression of Pyrite by Cyanide  Ions,"  The
     Mining Magazine, 97 (1957)  137-139.

 9.  Majumdar, K. K., "On the Mechanism of  Depression of Pyrite," J.
     Sci.  Ind. Res., 13B (1954)  586.

10.  Gaudin, A. M., Flotation, McGraw-Hill  Book Co., Inc.,  N.Y., 1957,
     308.

11.  Gaudin, A. M., Flotation, McGraw-Hill  Book Co., Inc., N.Y., 1957,
     242.

12.  Sutherland, K. L.  and Mark, I.  W.,  Principles  of Flotation.
     Australasian Institute of Mining and Metallurgy, Melbourne, 1955,
     110.

13.  Taggart, A.  F., Handbook of Mineral  Dressing. John Wiley  and Sons,
     Inc.,  N.Y., 1945,  12.

14.  Cook,  M. A.  and Nixon, J.  C.,  "Theory  of Water-Repellent  Films on
     Solids Formed by Adsorption from Aqueous  Solutions of Heteropolar
     Compounds,"  J. Phys.  Chem., 54  (1950) 445-459.

                                47

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 15.  Mellgren, 0., "Heat of Adsorption and Surface Reactions of
     Potassium Ethylxanthate on Galena," AIME Trans., 235 (1966)  46.

 16.  Gaudin, A. M., Dewey, F., Duncan, W. E., Johnson, R. A., and
     Tangel, 0. F., "Reactions of Xanthates with Sulfide Minerals,"
     AIME Trans.,  112 (1934) 319-346.

 17.  Gaudin, A. M., deBruyn, P. L., and Mellgren 0., "Adsorption  of
     Ethylxanthate on Pyrite," AIME Trans., 207 (1956) 65.

 18.  Majima, H. and Takeda M., "Electrochemical Studies of the Xanxate-
     Dixanthogen System on Pyrite," AIME Trans., 241 (1968) 431.

 19.  Rao, S. R., and Patel, C.  C., "Behavior of Xanthates on Iron
     Pyrite Surfaces in Presence of 0?, CO? and Their Mixtures,"  J.
     Mines, Metals, and Fuels, 8 (I960) 18.

 20.  Huiatt, J. L., "A Study of the Oxidation of the Flotation
     Collectors Potassium Ethylxanthate and Ammonium Diethyl Dithio-
     phosphate," M.S.  Thesis, University of Utah (1969) 6-34.

 21.  Hallimond, A. F., "The Role of Air in Flotation at Great Dilutions,"
     The Mining Magazine, 72 (1945) 201.

 22.  Filimonov, V. N., Vershinin, E.  A., and Bocharov, V. A., "Effect
     of Sodium Sulfite on the Oxidation by Oxygen during the
     Cyanideless Flotation of Sulfide Minerals," Tsvet. Metal.  7
     (1968) 5-6., Abstracted in Chemical Abstracts,  69 (1968) 69043h.
     (Original Article not Examined).

 23.  Sutherland, K. L., and Mark, I.  W., Principles  of Flotation,
     Australasian Institute of Mining and Metallurgy, Inc., Melbourne,
     1955, 218.

 24.  Taggart, A. F., Elements of Ore  Dressing.  John  Wiley and Sons,
     Inc., N.Y., 1951, 276.

 25.  Pol'kin, S. I., Adamov, E. V., Tr. Nauch.-Tekh.  Sess.  Inst.
     "Mekhanobr" (Vses.  Nauch.-Issled. Proekt.  Inst.  Mekh.  Obrab.
     Polez. Iskop.) 5th 1965 (Pub. 1967) 1,375-89 (Russ).  Edited by
     Bogdanov, 0.  S.  Leningrad, USSR., Abstracted in Chemical Abstracts,
     69 (1968) 108818m.   (Original Article not  Examined).

26.  Latimer, W. M., Oxidation  Potentials. Prentice-Hall, Inc.,
     Englewood Cliffs, N.J., 1952, 131, 346-347.

27.  Poling, G. W. and Leja, J., "Infrared Study of  Xanthate Adsorption
     on Vacuum Deposited Films  of Lead Sulfide  and Metallic Copper
     under Conditions  of Controlled Oxidation," J. Phys.  Chem., 67 (1963)
     2121.

                               48

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28.  Caldwell, A.  B.s "A Technical  Buyers  Guide to Mineral Processing
     Reagents," Engineering and Mining  Journal, 169  (1968) 196-197.

29.  Wark, I.  W.,  Principles of Flotation, Australasian Institute of
     Mining and Metallurgy, Inc., Melbourne,  1938, 197.
                              49

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                     PUBLICATIONS
1.   Peterson, Walter G.,  "Pyrite Depression  by  Reduction
    of Solution Oxidation  Potential",  M.S.  Thesis,  University
    of Utah, 1970.
2.   Miller, Jan D.  and Peterson, Walter G. ,  "Pyrite Depression
    by Reduction of Solution  Oxidation Potential",  to  be
    presented at the Annual  A.I.M.E.  Meeting,  New  York,
    February, 1971.   The  same will  be  submitted for publication
    to the Transactions  of A.I.M.E.
                          50

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   Accession Number
                      Subject
                    Field it Group


                         10
                                                SELECTED WATER RESOURCES ABSTRACTS
                                                       INPUT TRANSACTION FORM
 c Organization

        University of Utah
      PYRITE DEPRESSION BY REDUCTION  OF SOLUTION OXIDATION POTENTIAL
10

Author! a)
Miller, Jan D.
11
Date
August 1970
12

Pages
50
i X 1 Project Number
21

, c Contract Number
EPA Grant No. 12010 DIM
Note
   Citation
23
Descriptors (Starred First)

  Flotation,  PyHte, Sulflte, Oxidation Potential
25 Identifiers (Starred First)

      Ethyl  Xanthate, Depression, Cyanide^Reducing Agents, Complex Sulfide  Ores
27
   Abstract
           A study of pyrlte depression  by reducing agents with potassium
     ethylaxanthate as collector  Indicates that pyrlte may be depressed
     effectively 1n the flotation of both lead and copper sulfide ores
     without the use of poisonous cyanide salts.  More specifically,  the
     use of sodium sulflte as the depressant may result in metallurgical,
     economical, environmental and  safety advantages over the poison,
     cyanide as the depressant were a rougher concentrate recovery  of 90.2%
     and a grade of 4.3% Cu.  However,  when sulflte was used as the depres-
     sant for the same recovery a grade of 7.3% Cu was obtained.
                                           Aba tractor
                                                     Jan D. Miller
                                            Institution
                                                    University of Utah
 WRSIC
      (REV. OCT. i9ea)
                                                 SEND TOl WATER RESOURCES SCIENTIFIC INFORMATION CENTER
                                                        U ğ. DEPARTMENT OP THE INTERIOR
                                                        WASHINGTON, D.C. 20240

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