Pyrite flotation in the presence of metal ions and sphalerite

In~RlllfflOml. JOUXnmltof

ELSEVIER

Int. J. Miner. Process. 52 (1997) 187-201

Pyrite flotation in the presence of metal ions and sphalerite Q. Zhang, Z. Xu, V. Bozkurt, J.A. Finch * Department of Mining and Metallurgical Engineering, McGill Unicersio', 3450 University Street, Montreal, QU H3A 2A7, Canada Received 5 July 1996; accepted 9 July 1997

Abstract The effect o f Cu 2+, Fe 2+ and Ca 2~ ions on pyrite floatability with xanthate as a function of pH in the presence and absence o f sphalerite was studied. In the alkaline pH region, these ions activated the pyrite when alone but not when sphalerite was present. Zeta-potential measurements and infrared surface characterization confirmed the different interaction with xanthate depending whether the pyrite was alone or with sphalerite. © 1997 Elsevier Science B.V.

Keywords: pyrite; sphalerite; flotation; mineral interaction; metal ions: zeta potential; l~q'lR

I. Introduction

Sulphide mineral ores remain the major source of base metals. The flotation of valuable minerals of copper, lead and zinc from pyrite, the main sulphide gangue, has received considerable attention (Forssberg, 1985; Dobby and Rao, 1989). Recently, there has been growing suspicion that metal ions play a role in limiting selectivity of sulphide flotation. These metal ions result from the use of recycle water, the presence of semisoluble minerals and from superficial oxidation of sulphide minerals and steelgrinding media. Their detrimental effect is associated with either depression of the target minerals or activation of the unwanted mineral (e.g. pyrite). Understanding the role of metal ions is essential for their effects to be countered. In this communication, the action of Cu ~+, Fe 2+ and Ca "~÷ ions on the flotation of pyrite,

* Corresponding author. Phone: + 1-514-398 4755; Fax: + 1-514-398 4492; E-mail: [email protected] 0301-7516/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PII S0301 -75 1 6 ( 9 7 ) 0 0 0 6 4 - l

188

Q. Zhang et al. / lnt, J. Miner. Process. 52 (1997) 187-201

alone or mixed with sphalerite, is reported. Copper ions are routinely used to activate sphalerite, and in some operations are used to activate pyrrhotite (Chang et al., 1954; Busheli, 1962; Rao, 1971a,b) and pyrite (Gehhardt and Richardson, 1987). The undesirable activation of pyrite in sphalerite flotation is, therefore, a possible cause for concern. Ferrous ions have been shown to activate sphalerite under certain conditions (Leroux et al., 1987; Zhang et al., 1992). However, the mechanism proposed was not necessarily limited to sphalerite. Possible activation of pyrite by ferrous ions is therefore a possibility. Finally, calcium ions, because they are usually present in large quantities (either from use of recycle water, presence of calcium-containing minerals a n d / o r use of lime for pH adjustment) and are considered as depressants for pyrite (Fuerstenau et al., 1985), were also selected for study. The classical approach to a fundamental study of metal ion effects would be to use single minerals. It is, however, becoming increasingly evident that this can be misleading (Trahar et al., 1994; Nagaraj and Brinen, 1995). An example in our laboratories has been the different response of pyrrhotite and pentlandite to xanthate adsorption when in the presence of each other (Xu and Finch, 1996). Consequently, this study of the effect of metal ions on pyrite/xanthate interaction included the presence of sphalerite. The interaction was followed by microflotation, infrared surface analysis, and zeta-potential measurement. The implications for flotation practice are considered.

2. Experimental section 2.1. M i n e r a l s

The sphalerite (Sp) and pyrite (Py) samples (37-74 txm size fraction) were isolated from ore samples from Brunswick Mining and Smelting (New Brunswick, Canada) by alternate use of a shaking table and a Mozley separator. The single minerals obtained were treated three times with a 5% HC1 solution to remove soluble impurities. Residual sulphur, formed as a result of the acid treatment, was removed by washing the samples with acetone, followed by de-oxygenated-distilled water. The product was then dried in a vacuum oven at ~ 70°C and stored under nitrogen. For both sphalerite and pyrite, X-ray diffraction analysis showed that no significant amounts of other mineralogical phases were present. Chemical analysis indicated a purity over 97% for pyrite while sphalerite contained 63.8% Zn and 2.8% Fe. The sample of this size range was used in the flotation and IR studies. For zeta-potential measurements, it was further ground (in an agate mortar and pestle) to ca. 20 I~m immediately prior to use. 2.2. C h e m i c a l s

Sodium iso-propyl xanthate [iprx, (CH3)2CHOCS2Na] from American Cyanamid was further purified using standard procedures and stored in petroleum ether (Rao, 1971a,b), ACS reagent grade copper sulphate, zinc sulphate, ferrous sulphate and calcium chloride (Fisher Scientific) were used as received. Hydrochloric acid and

Q. Zhang et al./ Int. J. Miner. Process.52 (1997) 187-201

189

mineral 1

~

eral2

Fig. 1. Set-up for conditioning of pyrite alone (mineral 1) and in presence of sphalerite (mineral 2).

sodium hydroxide used as pH modifiers were also of ACS reagent grade. De-oxygenated double distilled water was used in all the experiments.

2.3. Microflotation The set-up for conditioning the pyrite (Fig. 1) permitted the mineral to be treated alone (as mineral 1) or in the presence of sphalerite (as mineral 2), where the two minerals were in separate compartment but shared the same solution. One gram of mineral was conditioned for 10 min in 30 ml of de-oxygenated water at a given metal ion concentration, after which the supernatant was replaced with a premeasured amount of xanthate stock solution, and conditioning continued for another 10 min. Conditioning was provided by a laboratory shaker (New Brunswick Scientific Co., Inc., USA) at 200 rpm. To ensure that the minerals in the separate compartments shared the same solution in the case of the mixed-mineral tests, the level of the solution in the beaker was maintained above the top of the glass partition, as indicated in Fig. 1. The pyrite along with the supernatant was then transferred to a modified Hallimond tube (Fuerstenau et al., 1957), and flotation was conducted for 2 min with an air flow rate of 74 m l / m i n . The solids in floats and tails were weighed separately after filtration and drying, and the recovery was calculated.

2.4. Zeta-potential Zeta-potential of pyrite was measured using a Lazer Zee TM Meter (Model 501: Pen Kem, Inc., USA). All measurements were conducted in a 0.1 M NaC1 background electrolyte solution. A 0.05 g sample of pyrite, alone or mixed with sphalerite (which was of much greater size), was placed in a 100 ml beaker and mixed, for 5 min, with 80 ml distilled water containing the metal ions of interest. (In some of the experiments, a pre-determined amount of xanthate was added at this stage and mixing continued for another 5 min.) The coarse sphalerite particles were then allowed to settle and supernatant containing the fine target mineral particles was taken for zeta-potential measurement. The results presented in this paper are the average of three independent measurements with a typical variation of + 2 mV. Repeat tests showed that the conditioning procedure was capable of producing reproducible mineral surfaces suitable for studying the effect of various treatments.

Q. Zhang et al. lint. J. Miner. Process. 52 (1997) 187-201

190

2.5. FTIR-spectrum The attenuated total reflectance (ATR) spectroscopic technique was used to characterize the surface species on the mineral particles treated. (Sample preparation was the same as used for the microflotation tests.) A sample of the mineral along with some solution was taken using a pipette and placed on a strip of filter paper. This was repeated till the filter paper was covered by a thin layer of particles. The sample was then lifted along with the filter paper and pressed onto a zinc selenide (ZnSe) ATR crystal. IR spectra were obtained using an IFS-66 FTIR spectrometer (Bruker) with a baseline horizontal ATR sampling unit (Spectra Tech). The clean ATR crystal was used as background for the spectra presented in this communication. The spectrum was obtained by accumulating 200 scans using an MCT detector at a wavenumber resolution of 4 c m - 1 and presented without any baseline correction. As a check, a spectrum from the ZnSe crystal in contact with 10 a M xanthate solution was acquired: no characteristic bands were observed in the spectral region presented in this communication. The crystal was cleaned with acetone, exposed to ultraviolet radiations for 10 min (to decompose any residual xanthate species), rinsed with 100% ethanol, and blow-dried with filtered dry nitrogen after each measurement. For the purpose of IR band identification, the spectrum was also collected using external reflectance infrared spectroscopy (at a fixed incident angle of 45 °) using a copper foil pre-treated in a 0.5 m M i PrX solution, rinsed with petroleum ether and dried with dry nitrogen. This treatment removes all dixanthogen components and leaves 100

,

,

,

i

i

• 80

=m

\ \

i

• • • •

•

,

PyX PyCuX PySpCuX PySpX

60

[,.., 40

20

I

5

~

I

6

,

I

7

,

I

8

,

I

9

,

I

10

11

ptt Fig. 2. The effect o f ! 0 - 5 M Cu ions on pyrite flotation with 10- 5 M iso-propyl xanthate as a function of pH: PyX ~ pyrite alone; PyCuX = copper-activated; l~vSpX = in the presence of sphalerite; PySpCuX = copperactivated in the presence of sphalerite.

Q. Zhang et al. lint. J. Miner. Process. 52 (1997) 187-201 100

I

!

!

i

I

•

I

•

__

• •

80

191 I

PyX PyFeX PySpFeX

60 k

0

40

20

0 5

4

6

7

8

9

10

11

pI-I Fig. 3. The effect of 10 -5 M ferrous ions on pyrite flotation with 10 -5 M iso-propyl xanthate as a function of pH: PyX = pyrite alone; PyFeX = iron-activated; PySpFeX = iron-activated in the presence of sphalerite. 100

80

l

i

i

i

I

e

m~,

• PyX

\

•

~k~m

•

i

PyCaX PySpCaX

40

tX

•

•

20

5

6

7

8

9

10

11

pI-I Fig. 4. The effect of 10 -5 M Ca ions on pyrite flotation with lO -5 M iso-propyl xanthate as a function of pH: PyX = pyrite alone; PyCaX = calcium-activated; PySpCaX = calcium-activated in the presence of sphalerite.

Q. Zhang et al. / Int. J. Miner. Process. 52 (1997) 187-201

192

copper xanthate on the foil. The spectrum was collected using the same instrumental parameters as in ATR experiments, and polished copper foil was used as background. The experiments for the mixed-mineral system were designed to eliminate galvanic effects which otherwise would complicate the analysis. This system is therefore different from that encountered in practice, but nevertheless it is a step closer compared to the traditional single mineral studies. Our focus in this work is to examine the effect of metal ions and a second mineral on xanthate interaction with a target mineral (pyrite). The effect of galvanic interaction and redox potential was not examined, but for the purpose of comparison, we kept the redox potential relatively constant by using de-oxygenated water with a low solid-to-liquid ratio. In the case of mixed-mineral systems, quantifying the adsorption of metal ions or xanthate on individual minerals is difficult even if semi-quantitative XPS analyses were used. For this reason, we used zeta-potential measurement as an analytical tool to provide in situ semi-quantitative information, which proved satisfactory.

3. Results 3.1. Flotation Fig. 2 shows that pyrite alone (i.e. in the absence of metal ions and sphalerite) exhibited the well known flotation response: a minimum around pH 7, with increasing

20

I

I

I

I

I

• -

• ~

Py

PyCu

•

"-~ 0 ...........................................................

•

PyX

"

? U

.......

-20

J o~

-40 I

-60 I

2

,

I

4

,

I

,

6

I

8

i

I

10

t

I

12

pH Fig. 5. Zeta-potential of pyrite as a function of pH: alone (Py) in the presence of 10 5 M Cu ions (PyCu); 10 5 M iso-propyl xanthate (PvX) both Cu ions and xanthate (PyCuX).

193

Q. Zhang et al. lint. J. Miner. Process. 52 (1997) 187-201

floatability in acid conditions and a maximum in alkaline (ca. pH 8) (Steininger, 1968; Fuerstenau et al., 1985). The addition of cupric ions enhanced pyrite floatability significantly over the pH range 6 to 10. In contrast, in the presence of sphalerite along with metal ions, the floatability of pyrite decreased significantly over the whole pH range, with the recovery at pH > 5 being lower than that for pyrite alone without copper activation. This reduced floatability suggests competition for xanthate when the two minerals share the same solution. It appears that when copper-activated sphalerite is present, it consumes most of the xanthate available, leaving a lower xanthate concentration for pyrite flotation than if the sphalerite were not present. This was indirectly confirmed by the observation that the flotation of pyrite in the presence of sphalerite but absence of cupric ions remained unchanged, because in the absence of activating metal ions, sphalerite is largely unresponsive to xanthate. This suggests that the presence of sphalerite under these conditions should have little effect on pyrite flotation, as observed. Fig. 3 shows the effect of ferrous ions on pyrite flotation. Similar to cupric ions, ferrous ions increased floatability of pyrite alone, in particular in alkaline media with a maximum recovery at ca. pH 9. Again, in the presence of sphalerite, pyrite flotation was depressed. An activation effect of calcium ions (10 -5 M) on single pyrite flotation was found although it was less than that of either cupric or ferrous ions (Fig. 4). When sphalerite is present, however, pyrite is virtually unfloatable above pH 7.

20

0

I

I

I

I

I

.....................................................................

E -20 e~

= 0 I

I60

•

Py

• l •

PyCu PyCuSp PyCuXSp

I

2

,

I

4

~

I

,

6

I

8

,

I

10

,

I

12

pI-I Fig. 6. Zeta-potentialof pyrite as a function of pH in the presence and absenceof sphalerite: alone (Py); in the presence of 10-5 M Cu ions (PyCu); with added sphalerite (PyCuSp); in 10-5 M iso-propyl xanthate (PyCuXSp).

Q. Zhang et al. / Int. J. Miner. Process. 52 (1997) 187-201

194

The above flotation results all show a common feature: metal ions promoted flotation of pyrite alone, but the presence of sphalerite along with the metal ions depressed the floatability.

3.2. Zeta-potential Fig. 5 shows that pyrite alone had an iso-electrical point (iep) at ca. pH 3. This value is lower than that reported by Fuerstenau and Mishra (1980), but similar to that by Fornasiero et al. (1992). The discrepancy appears to be related to the initial oxidation state of pyrite: the more oxidized the pyrite, the higher the iep. By comparison with the iep of pyrite oxidized to various degrees as reported by Fomasiero et al. (1992), the pyrite sample used in this study appears to be slightly oxidized. In the presence o f iprX, the zeta-potential of pyrite decreased marginally (by inspection of the data points), probably reflecting adsorption of negatively charged xanthate anions. A similar observation was made by Fomasiero and Ralston (1992) although Cases et al. (1993) suggest a much larger decrease in zeta-potential in the presence of xanthate. Cupric ions increased the zeta-potential significantly, in particular above pH 6. This increase can be attributed to the adsorption of a cupric ion species (probably Cu(OH) ÷ from reference to the solution stability diagram (Stumm and Morgan, 1996) on the negatively charged pyrite surface. Upon subsequent addition of

20

u

I

I

I

I

I

-20

m eJl

@ !

-40

PyFe -60

• •

I

2

~

• -v

PyFeSp PyFeXSp

i

I

4

"

•

a

i

~

6

I

8

i

I

10

~

I

12

pH Fig. 7. Zeta-potential of pyrite as a function of pH in the presence and absence of ferrous ions and sphalerite: alone (Py); in the presence of 10 -5 M ferrous ions (PyFe); with added sphalerite (PyFeSp); and in 10 -5 M iso-propyl xanthate (PyFeXSp).

Q. Zhang et al. ~Int. J. Miner. Process. 52 (1997) 187-201

195

xanthate at alkaline pH, the zeta-potential decreased significantly. The reduction can be attributed to either the adsorption of negatively charged iprX ions a n d / o r to partial removal of adsorbed cupric ions from the pyrite surface. The increased flotation recovery of pyrite with iprX in the presence of cupric ions suggests that the former is more likely to be the case, i.e. the presence of cupric ions on the surface attracts the negatively charged iprX. Fig. 6 shows the effect of the presence of sphalerite. The zeta-potential in the presence of cupric ions remained the same whether sphalerite was present or not. The subsequent addition of iprx did not change the zeta-potential, which is in marked contrast to the case in the absence of sphalerite. By comparison with Fig. 5, copper ions appear to be still adsorbed on pyrite in the presence of sphalerite, but subsequent xanthate adsorption did not occur. This finding is consistent with the observed flotation behaviour, namely that a significant reduction in pyrite flotation occurred when sphalerite was present (Fig. 2). Shown in Figs. 7 and 8 are the zeta-potential results in the presence of ferrous ions and calcium ions, respectively. Similar to the case with cupric ions, these ions increased the zeta-potential of pyrite significantly. In the presence of sphalerite, however, the zeta-potential response resembled that of pyrite alone and the subsequent addition of i p r X had little effect. This suggests that ferrous and calcium ions have much less affinity for pyrite compared to sphalerite and adsorbed preferentially on sphalerite when these

I

I

I

I

I

I

20

0

m DJi

-20

@

=3. I

-40

-60

• •

I

2

PyCaSp PyCaXSp

,

I

4

• m ~ i

I

,

6

I

8

i

I

10

,

I

12

pI-I Fig. 8. Zeta-potential of pyrite as a function of pH in the presence and absence of calcium ions and sphalerite: alone (Py); in the presence of 10 -5 M calcium ions (PyCa); with added sphalerite (PyCaSp); in 10 -5 M iso-propyl xanthate (PyCaXSp).

196

Q. Zhang et al. / Int. J. Miner. Process. 52 (1997) 187-201

PySpCuX

~

d

Py alone a Cu~PrX e

i

I

i

i

,

I

~

I

,

I

I

i

1350 1300 1250 1200 1150 1100 1050 1000

Wavenumber

i

950

lcm-'l

Fig. 9. FTIR/ATR spectra of pyrite particles treated with l0 s M cupric ions and 5× 10 5 M iso-propyl xanthate in the absence (c) and presence (d) of sphalerite, as compared to that untreated (a) or treated with xanthate only (b), and to external reflectance spectrum of copper toil treated with iso-propyl xanthate.

two minerals are present in the same solutions. The competition mechanism tbr the observed suppression of metal activation in the presence of sphalerite seems to depend on the metal ion: in the case of cupric ions, xanthate adsorption was suppressed while in the case of ferrous and calcium ions, adsorption of the metal ions was suppressed. The overall effect, however, is similar, namely, the presence of sphalerite retarded the flotation of pyrite.

3.3. Infrared spectra Infrared spectroscopy was used to identify and quantify the surface species resulting from interactions between the minerals and iPrX. Fig. 9 shows the spectra obtained with pyrite in the presence of cupric ions. (Only part of the spectral region, from 1350 to 950 cm -1, is shown, over which the characteristic xanthate bands appear.) A featureless spectrum was obtained for the pyrite conditioned in de-oxygenated water (a). Six broad bands at ca. 1267, 1256, 1142, 1088, 1026 and 1008 cm ~ were observed when pyrite was conditioned in 5 × 10- 5 M ~PrX solutions (b), suggesting the adsorption of i PrX on

197

Q. Zhang et al. / lnt. J. Miner. Process. 52 (1997) 187-201

Table 1 Positions of corresponding principal bands (cm- 1) of copper xanthate and dixanthogen formed from ethyl and iso-propyl xanthates Compound

Vibration modes v, (scs, c o c )

v (coc)

v (scs)

(EX) 2 (iprx) 2

1261 1267

1240 1256

1150 1142

1108 1088

1044 1026

1019 1008

CuEX CuiprX

1197 1239

1190 1227

1123 1140

1049 1090

1035 1016

1009 1004

pyrite. C o m p a r i n g these bands with those (1239, 1227, 1216, 1090 and 1016 c m - t ) on copper foil (e), it is evident that the adsorbed species is dixanthogen, as expected in the case of pyrite (Ball and Rickard, 1976; Woods, 1984). The dixanthogen bands corresponded to those of ethyl d i x a n t h o g e n ( L e p p i n e n et al., 1989; Y o o n et al., 1995), but with a slight shift as shown in Table 1. These spectral shifts are associated with substitution of the ethyl group by iso-propyl which is a stronger electron donor. W h e n

'

~

'

'

'

'

'

O'olil

'

Py alone 1350

a

I

I

I

I

I

I

1300

1250

1200

1150

1100

1050

I

I

1000

I

950

Wavenumber[cml] Fig. 10. FrlR/ATR spectra of particles treated with cupric (c), ferrous (d) and calcium (e) ions in the presence of 5 × 10-5 M iso-propyl xanthate as compared to that untreated (a) and treated with xanthate only (b).

198

Q. Zhang et al. / Int. J. Miner. Process. 52 (1997) 187-201

cupric ions were present (c), the intensity of dixanthogen bands increased slightly and three additional bands at ca. 1237, 1227 and 1216 c m - l were observed. These indicate the formation of copper i p r x as there was a close spectral match with the external reflectance spectrum of copper foil treated in i prX (e). These observations confirm the zeta-potential results showing the adsorption of copper ions and collector on pyrite. In the presence of sphalerite, the spectrum (d) becomes featureless, resembling that of the pyrite baseline spectrum (a). These spectroscopic observations further confirm that pyrite is not activated by copper ions when sphalerite is present. It implies that adsorption of xanthate is preferentially on activated sphalerite, which reduces the amount of xanthate available for the pyrite. The spectra of pyrite treated with the ferrous and calcium ions are shown in Fig. 10. (For reference, the spectrum of pyrite treated with cupric ions is also included.) Spectra (d) and (e) showed similar features as in the absence of these metal ions, but with some increase in band intensity. In contrast to copper ions, no additional bands were observed, suggesting that iron and calcium do not form a metal xanthate with i prX.

4. Discussion

4.1. General observations 4.1.1. Pyrite alone The results show that the metal ions, Cu 2+, Fe 2+ and Ca 2~, activate pyrite. The activation is through either the formation of metal xanthate (copper), a n d / o r a 'catalytic' effect of metal ions on dixanthogen formation (all ions studied). In the case of cupric ions, the formation of metal xanthate seems responsible for the increased floatability although the slight increase in dixanthogen formation may be a contributing factor. Whether the copper ions were incorporated into pyrite lattice to induce the copper xanthate formation remains to be determined. The zeta-potential measurement suggests that copper ions were chemisorbed on pyrite. The dixanthogen bands were enhanced when metal ions were present. The observed enhancement appears to be related to the variable valencies of copper and iron ions. Ferric or cupric ions may initially be reduced to a lower oxidation state while adsorbed xanthate is oxidized to dixanthogen. In the case of ferrous and calcium ions, it appears that adsorbed cations (as confirmed by zeta-potential measurements) provided a high density of surface active sites which electrostatically attract negatively charged xanthate. As a result, the xanthate concentration in the surface region may be increased sufficiently to promote the redox reaction in the boundary layer. It is also possible that the adsorbed metal ions reduce the electrochemical potential of xanthate oxidation, although this remains to be explored. 4.1.2. Mixed-minerals competitive adsorption The presence of sphalerite did not materially affect pyrite flotation when metal ions were absent. However, with metal ions present, sphalerite decreased pyrite flotation significantly, the floatability being even lower than for pyrite alone in the absence of

Q. Zhang et al./ Int. J. Miner. Process. 52 (1997) 187-201

199

metal ions. This implies that when in competition with sphalerite, adsorption of xanthate is not favoured on pyrite. Competition is either for activating ions which appears to be the case for ferrous and calcium ions, or for collector, which is apparently the case for cupric ions. The end result is, however, the same: the 'less competitive' pyrite is depressed. These mineral competition effects are reminiscent of a previous study of ours where mixing pentlandite and pyrrhotite enhanced xanthate adsorption on pentlandite and retarded it on pyrrhotite (Xu and Finch, 1996). The interpretation offered was galvanic: in the presence of xanthate, pentlandite had a lower open circuit potential than pyrrhotite and in a mixture became the main site for anodic oxidation of xanthate to dixanthogen. In the present situation, the minerals are not in physical contact, and therefore the galvanic argument is less applicable. The present work reveals that competition does not have to be galvanic in origin and certainly further demonstrates that predictions based on single mineral systems can be quite misleading when applied to mineral mixtures. 4.2. Practical implications

Cupric ions are the activator of choice for sphalerite and selective flotation against pyrite is generally successful. Part of the mechanism, from the observations here, may be that in addition to direct activation of sphalerite, there is depression of pyrite caused by the presence of sphalerite. It has been reported that addition of cupric ions appears to retard the flotation of pyrite, which contributes to increased sphalerite concentrate grades (Xu et al., 1992). The findings suggest that while metal ions can activate pyrite, in the presence of sphalerite this may be less of a problem. Does this mean that inadvertent activation is not an issue? Not really. Two places where this activation may occur are: toward the end of a flotation bank where the sphalerite is exhausted, or in refloating a middling stream low in sphalerite. Recent work has shown the benefits of restricting the length of a flotation bank and limiting the use of recycle (Shannon et al., 1993). Part of the success may stem from the beneficial effect the presence of some sphalerite has on depressing pyrite. Deliberate addition of sphalerite to achieve this condition, while an intriguing research idea, is probably not practical. Lastly, knowing where metal ion activation effects are likely to occur may help design corrective action such as altering the pH modifier (e.g. using soda ash to remove the metal ions as carbonate precipitates) or addition of complexing agents, such as diethylene triamine (Marticorena et al., 1994).

5. Summary and conclusions (1) Cu 2+, Fe z+ and Ca 2+ all activated flotation of pyrite alone. All ions promoted dixanthogen formation. In addition, Cu 2+ promoted xanthate chemisorption (forming copper xanthate). (2) The presence of sphalerite along with these metal ions depressed pyrite floatability.

200

Q. Zhang et al. l i n t . J. Miner. Process. 52 (1997) 187-201

(3) T h e e f f e c t o f sphalerite o n pyrite flotation arises f r o m the c o m p e t i t i o n for e i t h e r x a n t h a t e (in the c a s e o f C u 2+) or a c t i v a t i n g species (Fe 2+ o r Ca2+).

Acknowledgements T h e a u t h o r s w i s h to a c k n o w l e d g e the f i n a n c i a l s u p p o r t o f the N a t u r a l S c i e n c e s a n d E n g i n e e r i n g R e s e a r c h C o u n c i l o f C a n a d a , a n d the C a n a d i a n M i n i n g I n d u s t r y R e s e a r c h O r g a n i z a t i o n w h o c o - o r d i n a t e d the s p o n s o r s h i p o f C o m i n c o , Inco, F a l c o n b r i d g e , N o randa, H u d s o n B a y M i n i n g a n d S m e l t i n g a n d Teck. W e also w i s h to t h a n k Drs. S t e p h a n e B r i e n n e a n d R a m R a o for m a n y helpful d i s c u s s i o n s .

References Ball, B., Rickard, R.S., 1976. The chemistry, of pyrite flotation and depression. In: Fuerstenau, M.C. (Ed.), Flotation. A.M. Gaudin Memorial Volume, Vol. 1., AIMMPE, New York, NY, pp. 458-484. Bushell, C.H.G., 1962. Flotation theory and mill control, In: Fuerstenau. D.W. (Ed.), Froth Flotation--50th Anniversary Volume. AIMMPE, New York, NY, pp. 576-580. Cases, J.M., Kongolo, M., De Donato, P., Michot, L.J., Erre, R., 1993, Interaction between finely ground pyrite and potassium amylxanthate in flotation, 1. Influence of alkaline grinding. Int. J. Miner. Process. 38, 267-299. Chang, C.S., Cooke, S.R.B., Iwasaki, I., 1954. Flotation characteristics of pyrrhotite with xanthate. AIME Trans. 199, 209-217. Dobby, G.S., Rao, S.R. (Eds.), 1989. Processing of Complex Ore. CIM. Montreal. Fornasiero, D., Ralston, J., 1992. Iron hydroxide complexes and their influence on the interaction between ethyl xanthate and pyrite. J. Colloid Interface Sci. 151,225-235. Fornasiero, D., Eijt, V., Ralston, J., 1992. An electrokinetic study of pyrite oxidation. Colloids Surfaces 62, 63-73. Forssberg, K.S.E. (Ed.), 1985. Flotation of Sulphide Minerals. Elsevier, New York. Fuerstenau, D.W., Mishra, R.K., 1980. On the mechanism of pyrite flotation with xanthate collectors. In: Jones, M.J. (Ed.), Complex Sulphide Ores. IMM, London, pp. 271-278. Fuerstenau, D.W., Metzger, P.H., Seele, G.D., 1957. How to use the modified Hallimond tube for better flotation testing. Eng. Min. J. 158 (3), 93-95. Fuerstenau, M.C., Miller, J.D., Kuhn, M.C.. 1985. Flotation Chemistry. AIME, New York. Gebhardt, J.E., Richardson, P.E., 1987. Differential flotation of a chalcocite-pyrite particle bed by electrochemical control. Miner. Metall. Process. 40 (3), 140-145. Leppinen, J.O., Basilio, C,I., Yoon, R.H., 1989. In-situ FF1R study of ethyl xanthate adsorption on sulphide minerals under conditions of controlled potential. Int. J. Miner. Process. 26, 259-274. Leroux, M., Rao, S.R., Finch, J.A., 1987. Selective flotation of sphalerite from Pb-Zn ore without copper activation. C/M Bull. 80 (6), 41-44. Marticorena, M.A., Hill, G., Kerr, A.N., Liechti, D., Pelland, D.A., 1994. INCO develops new pyrrhotite depressant. In: Yalcin, T. (Ed.), Innovations in Mineral Processing. Laurentian University, Sudbury, Canada pp. 15-33. Nagaraj, D.R., Brinen, J., 1995. SIMS study of metal ion activation in gangue flotation. In: Proceeedings 19th International Mineral Processing Congress 3, pp. 252-257. Rao, S.R., 197la. Xanthate and Related Compounds. Marcel Dekker, New York, pp. 15-18. Rao, S.R, 197lb. Thermochemistry of the adsorption of xanthate at pyrrhotite. AIME Trans. 250, 199-203. Shannon, E.R., Grant, R.J., Cooper, M.A., Scott, D.W., 1993. Back to Basics - - The Road to Recovery Milling Practice at Brunswick Mining. In: Proceedings of the 24th Canadian Mineral Processors Annual Meeting, Pap. 2.

Q. Zhang et aL lint. J. Miner. Process. 52 (19971 187-201

201

Steininger, J., 1968. The depression of sphalerite and pyrite by basic complexes of copper and sulfhydryl flotation collectors. Trans. SME 241 (3), 34-42. Stumm, W., Morgan, J.J., 1996. Aquatic Chemistry (3rd ed.). Wiley, New York. Trahar, W.J., Senior, G.D., Shannon, L.K., 1994. Interaction between sulphide minerals--the collectorless flotation of pyrite. Int. J. Miner. Process. 40, 287-321. Woods, R., 1984. Electrochemistry of sulphide flotation. In: Jones, M.H., Woodcock, J.Y. (Eds.), Principles of Mineral Flotation. Australas. Inst. Min. Metall., Victoria, N.S.W., pp. 91-115. Xu, M., Zhang, Q., Rao, S.R., Finch, J.A., 1992. An in-plant test of sphalerite flotation without Cu activation. In: Proceedings of the 24th Canadian Mineral Processors Annual Meeting, Pap. 14. Xu, Z., Finch, J.A., 1996. A direct method for studying collector adsorption on minerals in a mixed mineral system. Trans. IMM, Sect. C 105, C197-199. Yoon, R.H., Basilio, C.I., Marticorena, M.A., Kerr, A.N., Stratton-Crawley, R., 1995. A study of pyrrhotite depression mechanism by diethylenetriamine. Miner. Eng. 8, 807-816. Zhang, Q., Rao, S.R., Finch, J.A., 1992. Flotation of sphalerite in the presence of iron ions. Colloids Surfaces 66, 81-89.