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Minerals Engineering 19 (2006) 659–665

Pyrite activation in amyl xanthate flotation with nitrogen

J.D. Miller a,*, 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, USAb Malozemoff Technical Facility, Newmont Mining Corporation, 10101 East Dry Creek Road, Englewood, CO 80112, USA

Received 13 July 2005; accepted 6 September 2005Available 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 tothe N2TEC flotation technology currently being used for the recovery of auriferous pyrite at Newmont�s 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 responsiblefor a loss in pyrite recovery. This supposition was confirmed with laboratory experiments, and a program was initiated to study flotationchemistry variables by electrochemically controlled contact angle measurements. Experimental results show that activation of pyrite insuch 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 tocollector (PAX) consumption and the initial state of the pyrite surface. Experimental results show the importance of the pyrite surfacestate 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

Newmont Mining Corporation has used the patentedN2TEC technology (Gathje and Simmons, 1997; Simmonsand Gathje, 1998) for auriferous pyrite recovery at its LoneTree Mine Complex, since March 1997. The Lone TreeMine Complex, owned and operated by Newmont MiningCorporation, was originally developed as a high-gradeoxide heap leach. With the addition of the whole-ore auto-clave, refractory sulfide ores containing gold grades as lowas 3.1 g/t could be processed economically. However, a sig-nificant portion of the sulfide resource (<3.1 g/t Au) couldnot be economically processed. Investigation of processingoptions for this low-grade sulfide resource eventually led tothe development of the N2TEC flotation process. Applica-

0892-6875/$ - see front matter � 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.mineng.2005.09.017

* Corresponding author. Tel.: +1 801 5815160; fax: +1 801 5814937.E-mail address: jdmiller@mines.utah.edu (J.D. Miller).

tion of this technology led to improvements in both goldrecovery and selectivity for auriferous sulfide ores (Sim-mons, 1997; Gathje and Simmons, 1997; Simmons andGathje, 1998; Simmons et al., 1999).

In the N2TEC process, processing (grinding through flo-tation) takes place in an inert atmosphere. The processoperates in a potential range between �0.1 and �0.5 Vvs. Ag/AgCl (Simmons, 1997) and uses potassium amylxanthate (PAX) as the collector. Shortly after the plantwas commissioned at Lone Tree in March 1997, the aurif-erous pyrite recovery decreased substantially. This decreasein pyrite recovery was thought to be the result of cyanide inthe flotation mill water. To overcome the pyrite depressionan investigation was initiated to evaluate different activa-tors in order to alleviate or solve this problem. This paperreviews results from previous studies (Miller et al., 2002)regarding the low potential hydrophobic pyrite surfacestate and looks at the effect of activation on the pyrite sur-face state in the absence and presence of cyanide.

660 J.D. Miller et al. / Minerals Engineering 19 (2006) 659–665

2. Background

The conventional theory of xanthate flotation of pyriteconsiders xanthate adsorption an electrochemical processthat involves the formation of the xanthate dimer (dixanth-ogen) (Fuerstenau et al., 1985; King, 1982). Dixanthogen isformed by the anodic oxidation of the xanthate ion at thepyrite surface, coupled with the cathodic reduction ofadsorbed oxygen:

2X� $ X2 þ 2e� ð1Þ1

2O2 adsð Þ þH2Oþ 2e� $ 2OH� ð2Þ

Electrochemical measurements for the amyl xanthate/di-amyl dixanthogen couple, has shown the standard half-cellpotential to be E0 = �0.158 V vs. SHE (Winter andWoods, 1973). From the Nernst equation, with dixantho-gen referenced to the liquid state, E = E0 � 0.059 ÆlogbX�c. Thus, in 1 · 10�3 M PAX solutions, a hydropho-bic pyrite surface state should not be observed at potentialsless than 0.019 V vs. SHE or �0.223 V vs. SCE, if dixanth-ogen is responsible for hydrophobicity at the pyrite surface.Earlier studies utilizing electrochemically controlled con-tact angle measurements, have shown that a hydrophobicpyrite surface state could be established at low potentialsand low pH in a nitrogen atmosphere, as is shown inFig. 1 (Miller et al., 2002).

These early studies suggested that the reduction of pyritesurface compounds in a nitrogen atmosphere may have cre-ated a ‘‘clean’’, low polarity pyrite surface, which perhapsfacilitated PAX adsorption and thus account for the lowpotential, low pH hydrophobic pyrite surface state (Milleret al., 2002).

Potential (mV vs. SCE)-600 -50 0 -40 0 -300 -200 -100 0 100

Con

tact

Ang

le (

degr

ees)

0

10

20

30

40

50

60

70

80

90

Nitrogen

Air

Fig. 1. Electrochemically controlled contact angle measurements forpyrite in a 1 · 10�3 M PAX solution, pH 4.68, in air and in nitrogen(Miller et al., 2002). (Dotted line indicates the standard half-cell potentialfor the amyl xanthate/di-amyl dixanthogen couple at an amyl xanthateconcentration of 1 · 10�3 M.)

3. Experimental section

3.1. Materials

In all experimental work, Milli-Q deionized water with aresistivity of 18 MX cm was used. Lead nitrate and coppersulfate solutions were used for pyrite treatment. A solutionof the copper cyanide complex (K2Cu(CN)3), preparedfrom copper sulfate and potassium cyanide, was used tostudy the effect of cyanide. The potassium amyl xanthate(PAX) collector used in all experiments was purified threetimes by dissolution in acetone and recrystallization withethyl ether. All additional chemicals used were of analyticalreagent grade quality.

The pyrite electrodes used were prepared as previouslydescribed (Miller et al., 2002), from a massive, high quality,crystalline specimen purchased from Ward�s Natural Sci-ence Establishment.

For each test where a nitrogen atmosphere was required,the electrolyte was purged with nitrogen for at least 2 hprior to the experiment.

3.2. Electrochemically controlled contact angle

measurements

As described in earlier work (Miller et al., 2002), electro-chemically controlled contact angle measurements weremade utilizing a three-compartment electrochemical cell,with a parallel plate window in the working compartment.This cell was placed on the optical bench of a Rame-Hartgoniometer, which was then used to measure the contactangles (Du Plessis, 2004).

A EG&G PAR 173 Potentiostat/Galvanostat pro-grammed with an IBM PC-XT computer, with Model250 Electrochemical Analysis System software, was usedto control the potential of the pyrite electrode at room tem-perature (22 �C). For a typical experiment, the voltage wasset at the desired level and after 1 min at the desired poten-tial, the activator was added. The electrode surface wasthen allowed to react at this potential for 10 min. Subse-quently the xanthate collector was added and the electrodesurface was allowed to react for a further 4 min at thedesired potential. Finally, the contact angle was measuredat the required potential.

3.3. Bubble attachment time measurements

A high-speed video camera was used to measure bubbleattachment time. The procedure involved releasing a smallbubble from the tip of a capillary glass tube next to the pyr-ite surface. The video camera is used to record the releaseof the bubble, contact against the mineral surface and bub-ble attachment. The bubble attachment process is thenreviewed in slow motion and the bubble attachment timedetermined within 1–2 ms (depending on the recordingspeed).

Potential (mV vs. SCE)-800 -700 -600 -500 -400 -300 -200

Con

tact

Ang

le (

degr

ees)

0

10

20

30

40

50

60

70

80

90

pH 9.20

pH 4.68

Fig. 2. Electrochemically controlled contact angle measurement in nitro-gen-purged solutions, for pyrite treated with 1 · 10�3 M Pb(NO3)2 and5 · 10�5 M PAX for two different pH conditions (Du Plessis et al., 2002).

J.D. Miller et al. / Minerals Engineering 19 (2006) 659–665 661

3.4. Electrochemical considerations

Cyclic voltammetry experiments were conducted in athree-compartment electrochemical cell as described in ear-lier work (Miller et al., 2002).

3.5. XPS surface analysis

A V6 Scientific 220I XL Electron Spectrometer with amonochromatized Al Ka X-ray source was used to obtainthe XPS spectra of cathodically treated pyrite (�0.3 V vs.SCE). Spectral analysis was accomplished with use of theHandbook for X-ray Photoelectron Spectroscopy (Maulerand Stickle, 1995).

3.6. Fourier transform infrared spectroscopy

Mid-infrared spectra were recorded using a Biorad-Dig-ilab FTS-6000 FTIR spectrometer, with a wide band MCTliquid-nitrogen cooled detector. The optical systemincluded a high-intensity ceramic source and a germaniumcoated KBr beam splitter. Dried air was used to purge thesystem, prior to spectra being recorded. Two infrared spec-troscopy techniques were used. A potassium bromidetransmission (KBr) spectrum was taken of a prepared leadxanthate compound. The transmission spectrum was theresult of 512 co-added scans ratioed against 512 co-addedbackground scans, at a resolution of 4 cm�1. The externalreflection spectrum was obtained at a specular reflectanceangle of 30� with a resolution of 8 cm�1.

3.7. Bench-scale flotation tests

Bench-scale flotation tests were carried out under nitro-gen on an auriferous pyrite ore from Lone Tree, Nevada(head assay: 2.64 g Au/ton). For each flotation test, 1 kgof ore was wet ground in a laboratory ball mill at 60% sol-ids (made up with deoxygenated water) for 30 min at65 rpm, to obtain a product 80 wt.% passing 70 lm. Uponcompletion of the grinding stage, the slurry was washed outof the mill into a 2.3 L Denver flotation cell using deoxy-genated water, where the slurry was made up to 34% solids(with deoxygenated water). Adjustments in pH were madeusing a 10% sulfuric acid solution, with an automated pHcontroller, keeping the pH between 5.4 and 5.6. The flota-tion cell was operated at an rpm between 1100 and 1200.As soon as the impeller was turned on, the pH controllerwas put into operation, and the pulp was then conditionedat the required pH for 5 min. When lead nitrate was addedas activator, it was added as a 5% solution, and the pulpwas then conditioned for 2 min. Following activation, thepotassium amyl xanthate (PAX) collector was added as a1% solution and conditioned for 1 min. Subsequently 3–4drops of MIBC and 1–2 drops of Dowfroth 250 were addedas frothers, and then nitrogen (as flotation gas) was bub-bled through the suspension. The first rougher concentratewas collected for 5 min, and following a second PAX addi-

tion, the second rougher concentrate was collected for afurther 5 min.

4. Results and discussion

4.1. The effect of lead activation on the low potential, low pHhydrophobic pyrite surface state in the absence of cyanide

As discussed briefly in the introduction, earlier studieshave concluded that a ‘‘clean’’ pyrite surface, availablefor PAX adsorption, is created by the reduction of pyritesurface compounds in nitrogen. In these early studies(Miller et al., 2002) it was found that both a low pH anda high PAX concentration (1 · 10�3 M) were requirementsfor establishment of the low potential hydrophobic pyritesurface state. In contrast to these results, it was found thatthe low potential hydrophobic pyrite surface state treatedwith lead nitrate (1 · 10�3 M) as activator, could beachieved at substantially reduced PAX concentrations(5 · 10�5 M) as is demonstrated in Fig. 2. Additionally, itwas found that this low potential hydrophobic pyrite sur-face state could now be achieved at both pH 4.7 and 9.2compared to earlier results, where in the absence of leadnitrate as activator, the low potential hydrophobic pyritesurface state could only be established at pH 4.7.

Earlier studies (Miller et al., 2002) have shown thatapplication of an anodization potential to a pyrite elec-trode, will lead to the formation of ferric hydroxide islandson the pyrite surface, thereby artificially creating a hydro-philic pyrite surface. This oxidized pyrite surface shouldthen respond differently to activator and collector treat-ment when compared to a ‘‘fresh’’ pyrite surface. Fig. 3is a summary of the results from contact angle measure-ments under nitrogen conditions, at pH 4.7 with no

PAX Concentration (M)10-7 10-6 10-5 10-4 10-3 10-2

Lea

d C

once

ntra

tion

(M)

10-7

10-6

10-5

10-4

10-3

10-2

No Anodization

1 Minute Anodization

attachment:right of curves

no-attachment:

left of curves

Fig. 3. Concentration limits of lead nitrate and potassium n-amylxanthate required to establish bubble attachment for no anodizationand 1 min anodization (Du Plessis, 2004). (Contact angle solution pH 4.7,nitrogen; anodic pre-treatment: 0.3 V vs. Ag/AgCl for 0 and 1 min,anodization solution pH 9.2.)

662 J.D. Miller et al. / Minerals Engineering 19 (2006) 659–665

anodization pre-treatment and 1 min anodization pre-treatment for various concentrations of lead nitrate andPAX (the lowest concentrations that led to bubble attach-ment were used to determine the concentration limits). It isclear that substantially greater concentrations of leadnitrate and PAX were required to establish a hydrophobicpyrite surface state on an oxidized pyrite surface, comparedto a ‘‘fresh’’ pyrite surface. These results demonstrate thatwith substantial increases in both lead nitrate and PAXconcentration, the artificially created hydrophilic surfacestate can be overcome and a hydrophobic pyrite surfacestate can be established.

The beneficial effect of lead nitrate as activator for thistype of system was also seen in bubble attachment timemeasurements (Du Plessis et al., 2002). For an untreatedpyrite surface in a nitrogen-purged 1 · 10�3 M PAX solu-tion at pH 4.7 and �0.3 V vs. SCE, a bubble attachmenttime of 203 ms was observed. However, when the pyritesurface was treated with 1 · 10�3 M lead nitrate solutionprior to PAX addition, a bubble attachment time of82 ms was observed, demonstrating a significant improve-ment in bubble attachment rate with lead activation.

Bench-scale flotation tests in nitrogen also supported thebeneficial effect of lead activation on auriferous pyriterecovery (Du Plessis et al., 2002). Without lead activation,the overall rougher sulfide recovery was 74% compared to83% at the same PAX dosage level with lead activation.

4.2. The effect of lead activation on the low potential, low pH

hydrophobic pyrite surface state in the presence of cyanide

As mentioned earlier, shortly after the Lone TreeN2TEC flotation plant was commissioned, auriferous pyr-

ite recovery decreased substantially. This decrease in aurif-erous pyrite recovery appeared to be the result of cyanidepresent in the flotation mill water.

Since cyanide serves as a well-known depressant for pyr-ite (Elgillani and Fuerstenau, 1968), cyanide adsorption atactive sites on the pyrite surface can be expected. Addition-ally, xanthate adsorption by pyrite in the presence of cya-nide is known to be significantly inhibited (Gaudin et al.,1956). Cyanide is also responsible for inhibiting the electro-chemical oxidation of xanthate (Janetski et al., 1977; DeWet et al., 1997). Elgillani and Fuerstenau (1968) con-cluded that insoluble ferric ferrocyanide would form at apyrite surface in the presence of cyanide in alkaline solu-tions. This ferric ferrocyanide species could then ultimatelybe responsible for the loss in pyrite hydrophobicity. Anadditional detrimental effect of cyanide could be theremoval of adsorbed metal-collector species from the pyritesurface. This metal-collector species could be taken intosolution as a soluble cyanide complex, and again pyritedepression would result.

It is well-known that the cyanide anion does not readilycomplex with lead at moderate concentrations (Fuerstenauet al., 1985). Thus the use of lead nitrate as activator shouldfacilitate xanthate adsorption at the lead-treated pyrite sur-face (cyanide ions will not be competing with xanthate ionsfor active lead sites), which would then lead to the lowpotential hydrophobic pyrite surface state being sus-tained even in the presence of relatively high cyanideconcentrations.

The use of lead nitrate as an activator in the presence ofsignificant concentrations of cyanide was found to be quiteeffective at sustaining the hydrophobic pyrite surface state.Electrochemically controlled contact angle measurementresults revealed that the hydrophobic pyrite surface stateat low potentials in the presence of cyanide, was dependenton both the lead nitrate concentration as well as the PAXconcentration (Figs. 4 and 5).

The sensitivity of the pyrite surface state to activatorconcentration is revealed in Fig. 4 for a constant PAX con-centration of 1 · 10�4 M. At a high lead nitrate concentra-tion (1 · 10�3 M) the hydrophobic pyrite surface statecould be sustained, even at cyanide concentrations as highas 20 ppm. However, when the lead nitrate concentration isreduced by an order of magnitude (1 · 10�4 M) the hydro-phobic pyrite surface state could only be sustained up tocyanide concentrations of 8–9 ppm.

Fig. 5 demonstrates the effect of PAX concentration onthe pyrite surface state for a constant lead nitrate concen-tration (1 · 10�3 M). It is clear again that at high PAX con-centrations (1 · 10�3 and 1 · 10�4 M) the hydrophobicpyrite surface state could be sustained at high cyanide con-centrations. In the case of 1 · 10�3 M PAX, the hydropho-bic pyrite surface state could be established at cyanideconcentrations as high as 70 ppm. When the PAX concen-tration is reduced significantly to 5 · 10�5 M, pyrite hydro-phobicity could only be realized at cyanide concentrationsbelow 18 ppm.

Cyanide Concentration (as copper complex), ppm0 5 10 15 20 25

Con

tact

Ang

le (

degr

ees)

0

10

20

30

40

50

60

70

80

90

1 x 10-3 M Pb(NO3)2

1 x 10-4 M Pb(NO3)2

Fig. 4. Electrochemically controlled contact angle measurements as afunction of cyanide concentration for pyrite in a 1 · 10�4 M nitrogen-purged PAX solution, pH 4.7, at �0.3 V vs. SCE, treated with two levelsof lead nitrate addition (Du Plessis et al., 2002).

Cyanide Concentration (as copper complex), ppm0 20 40 60 80

Con

tact

Ang

le (

degr

ees)

0

10

20

30

40

50

60

70

80

90

5 x 10-5 M PAX

1 x 10-4 M PAX

1 x 10-3 M PAX

Fig. 5. Electrochemically controlled contact angle measurements as afunction of cyanide concentration for pyrite in a 1 · 10�3 M nitrogen-purged lead nitrate solution, pH 4.7, at �0.3 V vs. SCE, treated withvarying levels of PAX addition (Du Plessis et al., 2002).

Cyanide Concentration (as copper complex) (ppm)0 20 40 60 80

Con

tact

Ang

le (

degr

ees)

0

10

20

30

40

50

60

70

80

90

Untreated

Treated with1 x 10-3 M CuSO4

Treated with1 x 10-3 M Pb(NO3)2

Fig. 6. Electrochemically controlled contact angle measurements as afunction of cyanide concentration for pyrite in a 1 · 10�3 M nitrogen-purged PAX solution, pH 4.7, at a potential of �0.3 V vs. SCE, untreatedor treated with 1 · 10�3 M CuSO4 or Pb(NO3)2 (Du Plessis et al., 2002).

J.D. Miller et al. / Minerals Engineering 19 (2006) 659–665 663

In addition to lead activation, copper activation wasalso considered as a potential measure for overcoming pyr-ite depression by cyanide. Fig. 6 compares electrochemi-cally controlled contact angle measurement resultsobtained with no activation, copper activation and leadactivation in the presence of cyanide. It is clear from theseresults that the use of copper as activator in the presence ofcyanide, only resulted in a slight improvement on the unac-tivated case.

Further electrochemically controlled contact angle mea-surement experiments were carried out utilizing flotation

mill water, to confirm that cyanide indeed was responsiblefor the loss in pyrite hydrophobicity, and that the use oflead nitrate as activator would alleviate this problem. Theresults revealed that for untreated pyrite (no activator addi-tion) with 1 · 10�3 M PAX addition and copper-treatedpyrite (1 · 10�3 M) in nitrogen-purged flotation mill waterat �0.3 V vs. SCE, no contact angle could be measured,thereby indicating a hydrophilic pyrite surface state. How-ever, for lead-treated pyrite (1 · 10�3 M) a hydrophobicpyrite surface state could be achieved, with an average con-tact angle of 58� being measured.

4.3. Pyrite surface state analysis

4.3.1. Electrochemical considerations

Cyclic voltammetry experiments were initiated to fur-ther characterize the interaction of lead with pyrite. Resultsfrom cyclic voltammograms carried out subsequent to leadtreatment at �0.5 V vs. SCE for 10 min, are presented inFig. 7. When pyrite is treated with lead, a reaction occursthat results in an anodic peak around �0.5 V vs. SCE onthe positive potential scan. A plateau is reached and thenan anodic current increase is observed at above �0.2 Vvs. SCE. The currents observed were not very significant.According to the Eh-pH (Pourbaix) diagram for thelead–water system, at pH 4.7 and �0.6 V, lead ions arereduced to elemental lead, followed by oxidation to lead(II)at about �0.5 V, thus the following oxidation reaction isprobable:

Pb0 $ Pb2þ þ 2e� ð3Þ

The reversible potential for Pb/Pb2+ half cell at a Pb2+ con-centration of 1 · 10�3 M is about �0.46 V vs. SCE.

Abs

orba

nce

1146

1215

Potential (V vs. SCE)-0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0

Cur

rent

(m

A)

-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

Without PAX (1st scan)

With 5 x 10-5 M PAX (5th scan)

With 5 x 10-5 M PAX (1st scan)

Fig. 7. Cyclic voltammograms for pyrite in 1 · 10�3 M Pb(NO3)2 at pH4.7 (50 mV/s) (Du Plessis et al., 2002).

664 J.D. Miller et al. / Minerals Engineering 19 (2006) 659–665

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 alteredby 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, andthus it is reasonable to conclude that the formation of ahydrophobic lead amyl xanthate species (present in solu-tion after PAX addition) could be responsible for thelow potential hydrophobic surface state of lead-treatedpyrite.

Wavenumber (cm-1)

9001000110012001300

Abs

orba

nce

10451234

1018

10941130

1204

1221

a

b

Fig. 8. FTIR external reflection spectrum (a) (30�, s polarized) for pyritetreated in 1 · 10�3 M lead nitrate and 1 · 10�3 M potassium n-amylxanthate nitrogen-purged buffered solution (pH 4.7) at �0.3 V vs. Ag/AgCl for 30 min compared to (b) the FTIR transmission spectrum of 1%lead n-decyl xanthate in KBr (Du Plessis, 2004).

4.3.2. X-ray photon spectroscopy surface analysis

XPS surface analysis was carried out for untreated pyr-ite and lead-treated pyrite, in the absence and presence ofPAX. As reported previously (Miller et al., 2002), foruntreated pyrite, a ‘‘clean’’ pyrite surface state is createdwhich facilitates PAX adsorption. For lead-treated pyrite,in the absence of PAX, there was no evidence of lead sta-bilization at the pyrite surface utilizing this spectroscopictechnique. However, due to the ex situ nature of this mea-surement, detection of a low surface coverage for lead atthe pyrite surface may not be possible.

When XPS surface analysis was carried out for pyriteconditioned in a solution containing lead nitrate andPAX under reducing conditions, lead was detected at thepyrite surface (peaks at 138 and 143 eV—not found inthe absence of PAX). These results would then suggest thatlead-amyl xanthate facilitates the stabilization of lead atthe pyrite surface and that it is the formation of a lead-amyl xanthate species at the pyrite surface that is responsi-ble for creation of the low potential, low pH hydrophobicsurface state for lead-treated pyrite under reducingconditions.

4.3.3. Fourier transform infrared spectroscopy surface

analysis

FTIR spectroscopy was utilized to confirm the presenceof a lead-amyl xanthate species at the pyrite surface underreducing conditions. In Fig. 8, a lead xanthate transmissionspectrum (lead n-decyl xanthate) is compared to the exter-nal reflection spectra obtained from a pyrite surface treatedat �0.3 V vs. Ag/AgCl for 30 min (nitrogen) with leadaddition (conditioned for 10 min) followed by xanthateaddition (20 min). It is clear that despite some peak shifts,a reasonable comparison can be made, and thus it can beconcluded that it is a lead-xanthate species that is adsorb-ing at the surface under these conditions. The peak shiftsthat seem to occur could be related to the nature of the spe-cies adsorbing. If the lead-xanthate species is stronglyadsorbed at the pyrite surface, some peak shifts areexpected to occur (Leppinen et al., 1989). Additionally,some peak shifts are also expected to occur due to the effectof hydrocarbon chain length (n-amyl vs. n-decyl leadxanthate).

J.D. Miller et al. / Minerals Engineering 19 (2006) 659–665 665

5. Conclusions

On the basis of this study, the following conclusions canbe made regarding lead activation during N2TEC flotationof pyrite:

• The low potential, low pH hydrophobic pyrite surfacestate can be achieved at substantially reduced PAX con-centrations for pyrite activated with lead.

• The low potential hydrophobic pyrite surface state canbe created at both low pH (4.7) and high pH (9.2) forlead-treated pyrite.

• Bubble attachment kinetics for lead-treated pyriteimproved considerably compared to untreated pyrite.

• A modest concentration of cyanide can lead topyrite depression. However, a hydrophobic pyritesurface state can be sustained in the presence of evenrelatively high concentrations of cyanide with leadactivation.

• FTIR external reflection spectroscopy confirms the pres-ence of a lead-amyl xanthate species at the pyrite surfaceunder reducing conditions in nitrogen.

Acknowledgments

The authors would like to recognize the support givenby Newmont Mining Corporation and the National Sci-ence Foundation as well as the contributions of X. Zhu,D.G. Kotlyar and J.C. Gathje to this research project.

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