Minerals Engineering 19 (2006) 659–665

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Pyrite activation in amyl xanthate flotation with nitrogen

a,*
J.D. Miller , R. Kappes b, G.L. Simmons b, K.M. LeVier b

a
Department of Metallurgical Engineering, University of Utah, 135 S. 1460 E. Rm412, Salt Lake City, UT 84112, USA
b
Malozemoff Technical Facility, Newmont Mining Corporation, 10101 East Dry Creek Road, Englewood, CO 80112, USA

Received 13 July 2005; accepted 6 September 2005

Available online 9 November 2005

Abstract

The low potential hydrophobic state of pyrite in amyl xanthate (PAX) flotation with nitrogen is of particular interest with regard to
the N2TEC flotation technology currently being used for the recovery of auriferous pyrite at Newmonts Lone Tree Plant in Nevada.
Initially, the N2TEC system had been found to operate satisfactorily, but cyanide in the flotation mill water appeared to be responsible
for a loss in pyrite recovery. This supposition was confirmed with laboratory experiments, and a program was initiated to study flotation
chemistry variables by electrochemically controlled contact angle measurements. Experimental results show that activation of pyrite in
such cyanide solutions can be achieved more effectively with lead than with copper. Subsequently, based on these fundamental studies,
significant improvement at the Lone Tree Plant was achieved by lead activation, in which case the recovery increased to expected levels.
The effect of activator is particularly significant not only with respect to pyrite depression by residual cyanide, but also with respect to
collector (PAX) consumption and the initial state of the pyrite surface. Experimental results show the importance of the pyrite surface
state and the rather interesting features of the activation process.
 2005 Elsevier Ltd. All rights reserved.

Keywords: Gold ores; Sulfide ores; Flotation activators; Froth flotation; Oxidation

1. Introduction tion of this technology led to improvements in both gold

recovery and selectivity for auriferous sulfide ores (Sim-
Newmont Mining Corporation has used the patented mons, 1997; Gathje and Simmons, 1997; Simmons and
N2TEC technology (Gathje and Simmons, 1997; Simmons Gathje, 1998; Simmons et al., 1999).
and Gathje, 1998) for auriferous pyrite recovery at its Lone In the N2TEC process, processing (grinding through flo-
Tree Mine Complex, since March 1997. The Lone Tree tation) takes place in an inert atmosphere. The process
Mine Complex, owned and operated by Newmont Mining operates in a potential range between 0.1 and 0.5 V
Corporation, was originally developed as a high-grade vs. Ag/AgCl (Simmons, 1997) and uses potassium amyl
oxide heap leach. With the addition of the whole-ore auto- xanthate (PAX) as the collector. Shortly after the plant
clave, refractory sulfide ores containing gold grades as low was commissioned at Lone Tree in March 1997, the aurif-
as 3.1 g/t could be processed economically. However, a sig- erous pyrite recovery decreased substantially. This decrease
nificant portion of the sulfide resource (<3.1 g/t Au) could in pyrite recovery was thought to be the result of cyanide in
not be economically processed. Investigation of processing the flotation mill water. To overcome the pyrite depression
options for this low-grade sulfide resource eventually led to an investigation was initiated to evaluate different activa-
the development of the N2TEC flotation process. Applica- tors in order to alleviate or solve this problem. This paper
reviews results from previous studies (Miller et al., 2002)
regarding the low potential hydrophobic pyrite surface
*
Corresponding author. Tel.: +1 801 5815160; fax: +1 801 5814937. state and looks at the effect of activation on the pyrite sur-
E-mail address: jdmiller@mines.utah.edu (J.D. Miller). face state in the absence and presence of cyanide.

0892-6875/$ - see front matter  2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.mineng.2005.09.017
660 J.D. Miller et al. / Minerals Engineering 19 (2006) 659–665

2. Background 3. Experimental section

The conventional theory of xanthate flotation of pyrite 3.1. Materials

considers xanthate adsorption an electrochemical process
that involves the formation of the xanthate dimer (dixanth- In all experimental work, Milli-Q deionized water with a
ogen) (Fuerstenau et al., 1985; King, 1982). Dixanthogen is resistivity of 18 MX cm was used. Lead nitrate and copper
formed by the anodic oxidation of the xanthate ion at the sulfate solutions were used for pyrite treatment. A solution
pyrite surface, coupled with the cathodic reduction of of the copper cyanide complex (K2Cu(CN)3), prepared
adsorbed oxygen: from copper sulfate and potassium cyanide, was used to
2X $ X2 þ 2e ð1Þ study the effect of cyanide. The potassium amyl xanthate
(PAX) collector used in all experiments was purified three
1 times by dissolution in acetone and recrystallization with
O2 ðadsÞ þ H2 O þ 2e $ 2OH ð2Þ
2 ethyl ether. All additional chemicals used were of analytical
Electrochemical measurements for the amyl xanthate/di- reagent grade quality.
amyl dixanthogen couple, has shown the standard half-cell The pyrite electrodes used were prepared as previously
potential to be E0 = 0.158 V vs. SHE (Winter and described (Miller et al., 2002), from a massive, high quality,
Woods, 1973). From the Nernst equation, with dixantho- crystalline specimen purchased from Wards Natural Sci-
gen referenced to the liquid state, E = E0  0.059 Æ ence Establishment.
logbXc. Thus, in 1 · 103 M PAX solutions, a hydropho- For each test where a nitrogen atmosphere was required,
bic pyrite surface state should not be observed at potentials the electrolyte was purged with nitrogen for at least 2 h
less than 0.019 V vs. SHE or 0.223 V vs. SCE, if dixanth- prior to the experiment.
ogen is responsible for hydrophobicity at the pyrite surface.
Earlier studies utilizing electrochemically controlled con-
3.2. Electrochemically controlled contact angle
tact angle measurements, have shown that a hydrophobic
measurements
pyrite surface state could be established at low potentials
and low pH in a nitrogen atmosphere, as is shown in
As described in earlier work (Miller et al., 2002), electro-
Fig. 1 (Miller et al., 2002).
chemically controlled contact angle measurements were
These early studies suggested that the reduction of pyrite
made utilizing a three-compartment electrochemical cell,
surface compounds in a nitrogen atmosphere may have cre-
with a parallel plate window in the working compartment.
ated a ‘‘clean’’, low polarity pyrite surface, which perhaps
This cell was placed on the optical bench of a Rame-Hart
facilitated PAX adsorption and thus account for the low
goniometer, which was then used to measure the contact
potential, low pH hydrophobic pyrite surface state (Miller
angles (Du Plessis, 2004).
et al., 2002).
A EG&G PAR 173 Potentiostat/Galvanostat pro-
grammed with an IBM PC-XT computer, with Model
90 250 Electrochemical Analysis System software, was used
to control the potential of the pyrite electrode at room tem-
80
perature (22 C). For a typical experiment, the voltage was
70 set at the desired level and after 1 min at the desired poten-
tial, the activator was added. The electrode surface was
Contact Angle (degrees)

60 then allowed to react at this potential for 10 min. Subse-

quently the xanthate collector was added and the electrode
50
surface was allowed to react for a further 4 min at the
40 desired potential. Finally, the contact angle was measured
at the required potential.
30

20 Nitrogen 3.3. Bubble attachment time measurements

Air
10 A high-speed video camera was used to measure bubble
0 attachment time. The procedure involved releasing a small
-600 -50 0 -40 0 -300 -200 -100 0 100 bubble from the tip of a capillary glass tube next to the pyr-
Potential (mV vs. SCE) ite surface. The video camera is used to record the release
of the bubble, contact against the mineral surface and bub-
Fig. 1. Electrochemically controlled contact angle measurements for
ble attachment. The bubble attachment process is then
pyrite in a 1 · 103 M PAX solution, pH 4.68, in air and in nitrogen
(Miller et al., 2002). (Dotted line indicates the standard half-cell potential reviewed in slow motion and the bubble attachment time
for the amyl xanthate/di-amyl dixanthogen couple at an amyl xanthate determined within 1–2 ms (depending on the recording
concentration of 1 · 103 M.) speed).
 J.D. Miller et al. / Minerals Engineering 19 (2006) 659–665 661

3.4. Electrochemical considerations tion, the second rougher concentrate was collected for a
further 5 min.
Cyclic voltammetry experiments were conducted in a
three-compartment electrochemical cell as described in ear- 4. Results and discussion
lier work (Miller et al., 2002).
4.1. The effect of lead activation on the low potential, low pH
3.5. XPS surface analysis hydrophobic pyrite surface state in the absence of cyanide

A V6 Scientific 220I XL Electron Spectrometer with a As discussed briefly in the introduction, earlier studies
monochromatized Al Ka X-ray source was used to obtain have concluded that a ‘‘clean’’ pyrite surface, available
the XPS spectra of cathodically treated pyrite (0.3 V vs. for PAX adsorption, is created by the reduction of pyrite
SCE). Spectral analysis was accomplished with use of the surface compounds in nitrogen. In these early studies
Handbook for X-ray Photoelectron Spectroscopy (Mauler (Miller et al., 2002) it was found that both a low pH and
and Stickle, 1995). a high PAX concentration (1 · 103 M) were requirements
for establishment of the low potential hydrophobic pyrite
3.6. Fourier transform infrared spectroscopy surface state. In contrast to these results, it was found that
the low potential hydrophobic pyrite surface state treated
Mid-infrared spectra were recorded using a Biorad-Dig- with lead nitrate (1 · 103 M) as activator, could be
ilab FTS-6000 FTIR spectrometer, with a wide band MCT achieved at substantially reduced PAX concentrations
liquid-nitrogen cooled detector. The optical system (5 · 105 M) as is demonstrated in Fig. 2. Additionally, it
included a high-intensity ceramic source and a germanium was found that this low potential hydrophobic pyrite sur-
coated KBr beam splitter. Dried air was used to purge the face state could now be achieved at both pH 4.7 and 9.2
system, prior to spectra being recorded. Two infrared spec- compared to earlier results, where in the absence of lead
troscopy techniques were used. A potassium bromide nitrate as activator, the low potential hydrophobic pyrite
transmission (KBr) spectrum was taken of a prepared lead surface state could only be established at pH 4.7.
xanthate compound. The transmission spectrum was the Earlier studies (Miller et al., 2002) have shown that
result of 512 co-added scans ratioed against 512 co-added application of an anodization potential to a pyrite elec-
background scans, at a resolution of 4 cm1. The external trode, will lead to the formation of ferric hydroxide islands
reflection spectrum was obtained at a specular reflectance on the pyrite surface, thereby artificially creating a hydro-
angle of 30 with a resolution of 8 cm1. philic pyrite surface. This oxidized pyrite surface should
then respond differently to activator and collector treat-
3.7. Bench-scale flotation tests ment when compared to a ‘‘fresh’’ pyrite surface. Fig. 3
is a summary of the results from contact angle measure-
Bench-scale flotation tests were carried out under nitro- ments under nitrogen conditions, at pH 4.7 with no
gen on an auriferous pyrite ore from Lone Tree, Nevada
(head assay: 2.64 g Au/ton). For each flotation test, 1 kg
of ore was wet ground in a laboratory ball mill at 60% sol- 90
ids (made up with deoxygenated water) for 30 min at
65 rpm, to obtain a product 80 wt.% passing 70 lm. Upon 80
completion of the grinding stage, the slurry was washed out
70
of the mill into a 2.3 L Denver flotation cell using deoxy-
Contact Angle (degrees)

genated water, where the slurry was made up to 34% solids 60

(with deoxygenated water). Adjustments in pH were made
using a 10% sulfuric acid solution, with an automated pH 50
controller, keeping the pH between 5.4 and 5.6. The flota-
40
tion cell was operated at an rpm between 1100 and 1200.
As soon as the impeller was turned on, the pH controller 30
was put into operation, and the pulp was then conditioned
at the required pH for 5 min. When lead nitrate was added 20 pH 9.20
as activator, it was added as a 5% solution, and the pulp pH 4.68
10
was then conditioned for 2 min. Following activation, the
potassium amyl xanthate (PAX) collector was added as a 0
1% solution and conditioned for 1 min. Subsequently 3–4 -800 -700 -600 -500 -400 -300 -200
drops of MIBC and 1–2 drops of Dowfroth 250 were added Potential (mV vs. SCE)
as frothers, and then nitrogen (as flotation gas) was bub- Fig. 2. Electrochemically controlled contact angle measurement in nitro-
bled through the suspension. The first rougher concentrate gen-purged solutions, for pyrite treated with 1 · 103 M Pb(NO3)2 and
was collected for 5 min, and following a second PAX addi- 5 · 105 M PAX for two different pH conditions (Du Plessis et al., 2002).
662 J.D. Miller et al. / Minerals Engineering 19 (2006) 659–665

10-2 ite recovery decreased substantially. This decrease in aurif-

No Anodization erous pyrite recovery appeared to be the result of cyanide
1 Minute Anodization present in the flotation mill water.
10-3 Since cyanide serves as a well-known depressant for pyr-
ite (Elgillani and Fuerstenau, 1968), cyanide adsorption at
Lead Concentration (M)

active sites on the pyrite surface can be expected. Addition-

10-4 ally, xanthate adsorption by pyrite in the presence of cya-
nide is known to be significantly inhibited (Gaudin et al.,
attachment:
right of curves 1956). Cyanide is also responsible for inhibiting the electro-
10-5 chemical oxidation of xanthate (Janetski et al., 1977; De
Wet et al., 1997). Elgillani and Fuerstenau (1968) con-
cluded that insoluble ferric ferrocyanide would form at a
no-attachment:
10-6 pyrite surface in the presence of cyanide in alkaline solu-
left of curves
tions. This ferric ferrocyanide species could then ultimately
be responsible for the loss in pyrite hydrophobicity. An
10-7 -7 additional detrimental effect of cyanide could be the
-6 -5 -4 -3 -2
10 10 10 10 10 10 removal of adsorbed metal-collector species from the pyrite
PAX Concentration (M) surface. This metal-collector species could be taken into
Fig. 3. Concentration limits of lead nitrate and potassium n-amyl solution as a soluble cyanide complex, and again pyrite
xanthate required to establish bubble attachment for no anodization depression would result.
and 1 min anodization (Du Plessis, 2004). (Contact angle solution pH 4.7, It is well-known that the cyanide anion does not readily
nitrogen; anodic pre-treatment: 0.3 V vs. Ag/AgCl for 0 and 1 min, complex with lead at moderate concentrations (Fuerstenau
anodization solution pH 9.2.)
et al., 1985). Thus the use of lead nitrate as activator should
facilitate xanthate adsorption at the lead-treated pyrite sur-
anodization pre-treatment and 1 min anodization pre- face (cyanide ions will not be competing with xanthate ions
treatment for various concentrations of lead nitrate and for active lead sites), which would then lead to the low
PAX (the lowest concentrations that led to bubble attach- potential hydrophobic pyrite surface state being sus-
ment were used to determine the concentration limits). It is tained even in the presence of relatively high cyanide
clear that substantially greater concentrations of lead concentrations.
nitrate and PAX were required to establish a hydrophobic The use of lead nitrate as an activator in the presence of
pyrite surface state on an oxidized pyrite surface, compared significant concentrations of cyanide was found to be quite
to a ‘‘fresh’’ pyrite surface. These results demonstrate that effective at sustaining the hydrophobic pyrite surface state.
with substantial increases in both lead nitrate and PAX Electrochemically controlled contact angle measurement
concentration, the artificially created hydrophilic surface results revealed that the hydrophobic pyrite surface state
state can be overcome and a hydrophobic pyrite surface at low potentials in the presence of cyanide, was dependent
state can be established. on both the lead nitrate concentration as well as the PAX
The beneficial effect of lead nitrate as activator for this concentration (Figs. 4 and 5).
type of system was also seen in bubble attachment time The sensitivity of the pyrite surface state to activator
measurements (Du Plessis et al., 2002). For an untreated concentration is revealed in Fig. 4 for a constant PAX con-
pyrite surface in a nitrogen-purged 1 · 103 M PAX solu- centration of 1 · 104 M. At a high lead nitrate concentra-
tion at pH 4.7 and 0.3 V vs. SCE, a bubble attachment tion (1 · 103 M) the hydrophobic pyrite surface state
time of 203 ms was observed. However, when the pyrite could be sustained, even at cyanide concentrations as high
surface was treated with 1 · 103 M lead nitrate solution as 20 ppm. However, when the lead nitrate concentration is
prior to PAX addition, a bubble attachment time of reduced by an order of magnitude (1 · 104 M) the hydro-
82 ms was observed, demonstrating a significant improve- phobic pyrite surface state could only be sustained up to
ment in bubble attachment rate with lead activation. cyanide concentrations of 8–9 ppm.
Bench-scale flotation tests in nitrogen also supported the Fig. 5 demonstrates the effect of PAX concentration on
beneficial effect of lead activation on auriferous pyrite the pyrite surface state for a constant lead nitrate concen-
recovery (Du Plessis et al., 2002). Without lead activation, tration (1 · 103 M). It is clear again that at high PAX con-
the overall rougher sulfide recovery was 74% compared to centrations (1 · 103 and 1 · 104 M) the hydrophobic
83% at the same PAX dosage level with lead activation. pyrite surface state could be sustained at high cyanide con-
centrations. In the case of 1 · 103 M PAX, the hydropho-
4.2. The effect of lead activation on the low potential, low pH bic pyrite surface state could be established at cyanide
hydrophobic pyrite surface state in the presence of cyanide concentrations as high as 70 ppm. When the PAX concen-
tration is reduced significantly to 5 · 105 M, pyrite hydro-
As mentioned earlier, shortly after the Lone Tree phobicity could only be realized at cyanide concentrations
N2TEC flotation plant was commissioned, auriferous pyr- below 18 ppm.
 J.D. Miller et al. / Minerals Engineering 19 (2006) 659–665 663

90 90

80 80

70 70
Contact Angle (degrees)

Contact Angle (degrees)

60 60

50 50

40 40

30 30
Untreated
20 20 Treated with1 x 10-3 M CuSO4
-3
1 x 10 M Pb(NO3)2
10 10 Treated with1 x 10-3 M Pb(NO3)2
1 x 10-4 M Pb(NO3)2

0 0
0 5 10 15 20 25 0 20 40 60 80
Cyanide Concentration (as copper complex), ppm Cyanide Concentration (as copper complex) (ppm)

Fig. 4. Electrochemically controlled contact angle measurements as a Fig. 6. Electrochemically controlled contact angle measurements as a
function of cyanide concentration for pyrite in a 1 · 104 M nitrogen- function of cyanide concentration for pyrite in a 1 · 103 M nitrogen-
purged PAX solution, pH 4.7, at 0.3 V vs. SCE, treated with two levels purged PAX solution, pH 4.7, at a potential of 0.3 V vs. SCE, untreated
of lead nitrate addition (Du Plessis et al., 2002). or treated with 1 · 103 M CuSO4 or Pb(NO3)2 (Du Plessis et al., 2002).

90
mill water, to confirm that cyanide indeed was responsible
80
for the loss in pyrite hydrophobicity, and that the use of
lead nitrate as activator would alleviate this problem. The
70 results revealed that for untreated pyrite (no activator addi-
tion) with 1 · 103 M PAX addition and copper-treated
Contact Angle (degrees)

60
pyrite (1 · 103 M) in nitrogen-purged flotation mill water
50
at 0.3 V vs. SCE, no contact angle could be measured,
thereby indicating a hydrophilic pyrite surface state. How-
40 ever, for lead-treated pyrite (1 · 103 M) a hydrophobic
pyrite surface state could be achieved, with an average con-
30
tact angle of 58 being measured.
5 x 10-5 M PAX
20 1 x 10-4 M PAX
1 x 10-3 M PAX
4.3. Pyrite surface state analysis
10

4.3.1. Electrochemical considerations

0
0 20 40 60 80 Cyclic voltammetry experiments were initiated to fur-
Cyanide Concentration (as copper complex), ppm ther characterize the interaction of lead with pyrite. Results
Fig. 5. Electrochemically controlled contact angle measurements as a from cyclic voltammograms carried out subsequent to lead
function of cyanide concentration for pyrite in a 1 · 103 M nitrogen- treatment at 0.5 V vs. SCE for 10 min, are presented in
purged lead nitrate solution, pH 4.7, at 0.3 V vs. SCE, treated with Fig. 7. When pyrite is treated with lead, a reaction occurs
varying levels of PAX addition (Du Plessis et al., 2002). that results in an anodic peak around 0.5 V vs. SCE on
the positive potential scan. A plateau is reached and then
an anodic current increase is observed at above 0.2 V
In addition to lead activation, copper activation was
vs. SCE. The currents observed were not very significant.
also considered as a potential measure for overcoming pyr-
According to the Eh-pH (Pourbaix) diagram for the
ite depression by cyanide. Fig. 6 compares electrochemi-
lead–water system, at pH 4.7 and 0.6 V, lead ions are
cally controlled contact angle measurement results
reduced to elemental lead, followed by oxidation to lead(II)
obtained with no activation, copper activation and lead
at about 0.5 V, thus the following oxidation reaction is
activation in the presence of cyanide. It is clear from these
probable:
results that the use of copper as activator in the presence of
cyanide, only resulted in a slight improvement on the unac- Pb0 $ Pb2þ þ 2e ð3Þ
tivated case.
Further electrochemically controlled contact angle mea- The reversible potential for Pb/Pb2+ half cell at a Pb2+ con-
surement experiments were carried out utilizing flotation centration of 1 · 103 M is about 0.46 V vs. SCE.
664 J.D. Miller et al. / Minerals Engineering 19 (2006) 659–665

0.04 4.3.3. Fourier transform infrared spectroscopy surface

analysis
0.02
FTIR spectroscopy was utilized to confirm the presence
of a lead-amyl xanthate species at the pyrite surface under
reducing conditions. In Fig. 8, a lead xanthate transmission
0.00 spectrum (lead n-decyl xanthate) is compared to the exter-
Current (mA)

nal reflection spectra obtained from a pyrite surface treated

-0.02 at 0.3 V vs. Ag/AgCl for 30 min (nitrogen) with lead
addition (conditioned for 10 min) followed by xanthate
addition (20 min). It is clear that despite some peak shifts,
-0.04
a reasonable comparison can be made, and thus it can be
Without PAX (1st scan) concluded that it is a lead-xanthate species that is adsorb-
With 5 x 10-5 M PAX (5th scan)
-0.06 -5 st
ing at the surface under these conditions. The peak shifts
With 5 x 10 M PAX (1 scan)
that seem to occur could be related to the nature of the spe-
-0.08 cies adsorbing. If the lead-xanthate species is strongly
-0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 adsorbed at the pyrite surface, some peak shifts are
Potential (V vs. SCE) expected to occur (Leppinen et al., 1989). Additionally,
Fig. 7. Cyclic voltammograms for pyrite in 1 · 103 M Pb(NO3)2 at pH some peak shifts are also expected to occur due to the effect
4.7 (50 mV/s) (Du Plessis et al., 2002). of hydrocarbon chain length (n-amyl vs. n-decyl lead
xanthate).

After PAX addition the small anodic peak at about

0.5 V vs. SCE was suppressed, indicating that the elec-
trochemical properties of lead-treated pyrite were altered
by the addition of PAX. The increased anodic current at
0.28 V could be due to xanthate oxidation to dixantho-
gen. However, a colloidal precipitate of lead amyl xan-
thate was present in solution after PAX addition, and
Absorbance

thus it is reasonable to conclude that the formation of a

hydrophobic lead amyl xanthate species (present in solu- 1146
tion after PAX addition) could be responsible for the
1215
low potential hydrophobic surface state of lead-treated
pyrite.
1234 1045

4.3.2. X-ray photon spectroscopy surface analysis

a
XPS surface analysis was carried out for untreated pyr-
ite and lead-treated pyrite, in the absence and presence of
PAX. As reported previously (Miller et al., 2002), for
untreated pyrite, a ‘‘clean’’ pyrite surface state is created
which facilitates PAX adsorption. For lead-treated pyrite,
1018
in the absence of PAX, there was no evidence of lead sta-
bilization at the pyrite surface utilizing this spectroscopic
Absorbance

1221
technique. However, due to the ex situ nature of this mea-
surement, detection of a low surface coverage for lead at
the pyrite surface may not be possible. 1204
When XPS surface analysis was carried out for pyrite
conditioned in a solution containing lead nitrate and 1130 1094
PAX under reducing conditions, lead was detected at the
pyrite surface (peaks at 138 and 143 eV—not found in
the absence of PAX). These results would then suggest that 1300 1200 1100 1000 900
lead-amyl xanthate facilitates the stabilization of lead at b Wavenumber (cm-1)
the pyrite surface and that it is the formation of a lead-
amyl xanthate species at the pyrite surface that is responsi- Fig. 8. FTIR external reflection spectrum (a) (30, s polarized) for pyrite
treated in 1 · 103 M lead nitrate and 1 · 103 M potassium n-amyl
ble for creation of the low potential, low pH hydrophobic xanthate nitrogen-purged buffered solution (pH 4.7) at 0.3 V vs. Ag/
surface state for lead-treated pyrite under reducing AgCl for 30 min compared to (b) the FTIR transmission spectrum of 1%
conditions. lead n-decyl xanthate in KBr (Du Plessis, 2004).
 J.D. Miller et al. / Minerals Engineering 19 (2006) 659–665 665

5. Conclusions Du Plessis, R., 2004. The Thiocarbonate Flotation Chemistry of Aurif-

erous Pyrite. PhD dissertation, University of Utah, Salt Lake City,
Utah.
On the basis of this study, the following conclusions can Du Plessis, R., Kotlyar, D.G., Simmons, G.L., Miller, J.D., 2002. The
be made regarding lead activation during N2TEC flotation effect of activation on the low potential hydrophobic state of pyrite in
of pyrite: amyl xanthate flotation with nitrogen. SME Preprint, 02-155.
Elgillani, D.A., Fuerstenau, M.C., 1968. Mechanisms involved in cyanide
• The low potential, low pH hydrophobic pyrite surface depression of pyrite. Transactions AIME (Society of Mining Engi-
neers) 241, 436–445.
state can be achieved at substantially reduced PAX con- Fuerstenau, M.C., Miller, J.D., Kuhn, M.C., 1985. Chemistry of
centrations for pyrite activated with lead. Flotation. SME Inc., Littleton, pp. 74–78.
• The low potential hydrophobic pyrite surface state can Gathje, J.C., Simmons, G.L., 1997. Method for processing gold-bearing
be created at both low pH (4.7) and high pH (9.2) for sulfide ores involving preparation of a sulfide concentrate. United
lead-treated pyrite. States Patent 5 653 945.
Gaudin, A.M., De Bruyn, P.L., Mellgren, O., 1956. Adsorption of ethyl
• Bubble attachment kinetics for lead-treated pyrite xanthate on pyrite. Transactions AIME (Society of Mining Engineers)
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• A modest concentration of cyanide can lead to Janetski, N.D., Woodburn, S.I., Woods, R., 1977. An electrochemical
pyrite depression. However, a hydrophobic pyrite investigation of pyrite flotation and depression. International Journal
surface state can be sustained in the presence of even of Mineral Processing 4, 227–239.
King, R.P., 1982. Principles of Flotation. South African Institute of
relatively high concentrations of cyanide with lead Mining and Metallurgy, Johannesburg, pp. 99–108.
activation. Leppinen, J.O., Basilio, C.I., Yoon, R.H., 1989. In situ FTIR study of
• FTIR external reflection spectroscopy confirms the pres- ethyl xanthate adsorption on sulfide minerals under conditions of
ence of a lead-amyl xanthate species at the pyrite surface controlled potential. International Journal of Mineral Processing 26,
under reducing conditions in nitrogen. 259–274.
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Miller, J.D., Du Plessis, R., Kotlyar, D.G., Zhu, X., Simmons, G.L., 2002.
Acknowledgments The low potential hydrophobic state of pyrite in amyl xanthate
flotation with nitrogen. International Journal of Mineral Processing
The authors would like to recognize the support given 67, 1–15.
Simmons, G.L., 1997. Flotation of auriferous pyrite using Santa Fe Golds
by Newmont Mining Corporation and the National Sci- N2TEC flotation process. SME Preprint 97-27.
ence Foundation as well as the contributions of X. Zhu, Simmons, G.L., Gathje, J.C., 1998. Method for processing gold-bearing
D.G. Kotlyar and J.C. Gathje to this research project. sulfide ores involving preparation of a sulfide concentrate. United
States Patent 5 837 210.
Simmons, G.L., Orlich, J.N., Lenz, J.C., Cole, J.A., 1999. Implementation
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