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The critical degree of mineral surface oxidation in copper sulphide flotation
Minerals Engineering 145 (2020) 106075
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The critical degree of mineral surface oxidation in copper sulphide flotation ⁎
T
Tiisetso Moimane, Chris Plackowski, Yongjun Peng
School of Chemical Engineering, The University of Queensland, St Lucia, Brisbane, QLD 4072, Australia
A R T I C LE I N FO
A B S T R A C T
Keywords: Chalcocite Chalcopyrite Critical degree of oxidation Flotation Surface analysis
It is well documented that surface oxidation of copper sulphide minerals has some detrimental effects on their flotation performance. However, little work has been done to quantitatively relate surface oxidation to flotation performance, which makes it inherently difficult for processing plants to optimise flotation conditions for oxidised ores. In this study, an array of oxidised chalcopyrite and chalcocite samples was prepared and characterisation of the surface oxidation species was carried out by X-ray Photoelectron Spectroscopy (XPS). The degree of surface oxidation was quantified as the ratio of hydrophilic species to hydrophobic species and correlated with copper sulphide flotation recovery. A quantitative relationship between them was established and a critical degree of oxidation, beyond which flotation becomes impossible, was identified to be 11.7 for chalcopyrite and estimated to be in the range of 1.74–4.85 for chalcocite, indicating that chalcocite flotation is much more sensitive to surface oxidation. This study will enable provision of guidelines to better manage oxidised copper ores to circumvent the loss of recovery and will also help in developing potential solutions that could be applied to flotation of minerals with different degrees of oxidation.
1. Introduction Copper sulphide minerals, found in the primary and secondary enrichment hydrothermal zones, yield the most copper production throughout the entire globe. The most commonly found copper sulphides in the primary zone are chalcopyrite (CuFeS2) and bornite (Cu5FeS4) while the secondary enrichment zone hosts mainly chalcocite (Cu2S) and covellite (CuS). Both the primary and secondary copper sulphides, together with associated precious metals such as gold, are recovered from raw ores by froth flotation, a separation process based on exploiting differences in surface properties to effect separation between valuable and gangue minerals. As these copper sulphide minerals are semiconductors, their surfaces are reactive and oxidise upon exposure to air and aqueous solutions during stockpiling, crushing, grinding and flotation. As a result, oxidation plays a crucial role in flotation as it alters the surface properties of the minerals and affects adsorption of collectors onto the minerals. Extensive research, employing electrochemical and surface sensitive analytical techniques, has been conducted over the years to understand this oxidation process and its ramifications on copper sulphide flotation (Gardner and Woods, 1979; Buckley and Woods, 1984; Vaughan et al., 1997; Fullston et al., 1999; Yin et al., 2000; Ghahremaninezhad et al., 2013; Hirajima et al., 2017). The unanimous view amongst researchers is that this oxidation
⁎
process could culminate in effects either desirable or detrimental to mineral flotation. “Mild oxidation” could lead to enhanced hydrophobicity of the copper sulphide minerals owing to surfaces rich in intrinsically hydrophobic species such as elemental sulphur and polysulphides (Heyes and Trahar, 1977). This constitutes the well-known collectorless flotation phenomenon of copper sulphides such as chalcopyrite. Chalcocite collectorless flotation, although weak and not as extensive as that of chalcopyrite, has also been reported (Heyes and Trahar, 1979). In contrast, “significant oxidation” culminates in great amounts of hydrophilic metal hydroxides and oxides precipitating on the mineral surfaces (Senior and Trahar, 1991; Smart, 1991), thereby increasing the hydrophilicity of the mineral surfaces, thus rendering the minerals unamenable to flotation and consequently leading to losses in mineral recoveries. However, “mild” and “significant” oxidation are relative terms and cannot be adopted in quantitatively defining the degree to which a mineral surface is oxidised. Little work has been done to quantitatively relate the degree of surface oxidation to copper sulphide flotation, which makes it inherently difficult for processing plants to optimise flotation conditions for oxidised ores and explore potential solutions that could be tailored to flotation of minerals with different degrees of oxidation. Therefore the unanswered fundamental question is: how much is “mild” and how much is “significant” with regard to the degree of mineral surface oxidation? Moreover, a parameter of paramount
Corresponding author. E-mail address: [email protected] (Y. Peng).
https://doi.org/10.1016/j.mineng.2019.106075 Received 2 February 2019; Received in revised form 29 June 2019; Accepted 7 October 2019 0892-6875/ © 2019 Elsevier Ltd. All rights reserved.
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importance, the “critical degree of surface oxidation”, defined as the degree of surface oxidation beyond which mineral recovery by true flotation becomes virtually impossible, needs to be determined. A previous study by Newell et al. (2007) has demonstrated that sulphides with various degrees of surface oxidation and susceptibility to oxidation respond differently to the sulphidisation process used for restoration of their floatability. Moreover, the current sulphidisation process has also proved to suffer from drawbacks in restoring the floatability of heavily oxidised sulphides (Newell et al., 2007). Understanding the degree of surface oxidation may provide guidelines to the sulphidisation process. Therefore in the quest to quantitatively relate surface oxidation to copper sulphide flotation and to determine the critical degree of surface oxidation, the present study focused on representatives of both primary and secondary type copper sulphides viz. chalcopyrite and chalcocite. This is based on the premise that these are the most commonly floated copper sulphide minerals. Moreover, it is also to represent both ends of the “oxidation susceptibility spectrum”, with the former being the least prone while the latter is the most prone, of the copper sulphides to oxidation as previously established in zeta potential measurements (Fullston et al., 1999).
Sodium hydroxide solution (1%) was used to adjust and maintain the pulp pH at 9.5. Air was then introduced into the flotation cell at a flow rate of 6 L/min. Four flotation concentrates were collected after cumulative times of 1, 3, 6 and 10 min employing froth scraping at an interval of 10 s. Flotation tests were conducted in duplicates to ensure good reproducibility and to determine experimental errors. The experimental errors, represented by error bars in the flotation data presented in Section 3, were found to be between 1 and 2%, which reflected good reproducibility of the results. Prior to flotation, samples for surface characterisation by X-ray Photoelectron Spectroscopy (XPS) were collected and frozen in liquid nitrogen. This was done to avoid inadvertent further oxidation before characterisation in order to ensure that any oxidation species formed are exclusively attributable to the deliberate chemically induced oxidation by hydrogen peroxide. 2.3. Mineral surface characterisation by Cryo-XPS XPS analyses were carried out using a KRATOS Axis Ultra X-ray Photoelectron Spectrometer, incorporating a 165 mm hemispherical electron energy analyser. The incident radiation source is monochromatic Aluminium (Al) X-ray Kα x-rays (1486.6 eV) operating at 150 W (15 kV, 15 mA). The sample analysis size spot is about 300 × 700 µm. The frozen slurry samples were defrosted just prior to characterisation. The solids were placed on the sample holder and immediately transferred into the loading chamber of the spectrometer. All XPS measurements were conducted under cryogenic conditions to avoid evaporation of volatile species such as elemental sulphur on the mineral surfaces under the ultra-high vacuum conditions. This was achieved by pre-cooling the samples in the loading chamber to −160 °C before evacuation and maintaining that temperature during analysis in the sample analysis chamber (SAC) using liquid nitrogen cooling. Samples were analysed at a base pressure of 10−9 torr. Survey scans were carried out from 0 to 1200 eV at a pass energy of 160 eV in 1.0 eV steps and a dwell time of 100 ms. High resolution scans of Cu 2p, Fe 2p, O 1s, C 1s, and S 2p were collected at a pass energy of 20 eV in 100 meV steps and using 2 or 3 sweeps. All the spectra were charge corrected using adventitious carbon at 284.8 eV and analysed using the CasaXPS software (version 2.3.14).
2. Experimental methods and materials 2.1. Minerals and chemical reagents Chalcopyrite and chalcocite mineral samples, supplied by GEODiscoveries, Australia, were crushed using a jaw crusher and a rolls crusher and screened to collect the −3.35 + 0.71 mm size fractions. The processed mineral samples were then sealed in polyethylene bags and stored in a freezer to minimise further surface oxidation. The chemical compositions of chalcopyrite and chalcocite, obtained by employing Inductively Coupled Plasma Mass Spectroscopy (ICP-MS), are presented in Tables 1 and 2, respectively. X-ray powder diffraction (XRD) analysis showed a chalcopyrite purity of 85 wt.%, with quartz, lime and sphalerite being the main impurities, and a chalcocite purity of 96 wt.%. The thionocarbamate based RTD11A, from Tall Bennet, was used as the collector and DSF004 from Orica was used as the frother. They were both of industry grade and used as received. Hydrogen peroxide (30% w/v, AR grade) was used as the oxidising agent. Pulp pH was adjusted using sodium hydroxide (AR grade). Grinding and flotation were carried out using Brisbane tap water.
3. Results and discussion 3.1. Flotation of chalcopyrite and chalcocite oxidised to various degrees An oxidation methodology was developed to yield different mineral flotation behaviours by conditioning the mineral samples with hydrogen peroxide solutions of different concentrations for 10 min after grinding and prior to flotation. It should be noted that although H2O2 is a strong oxidising agent with an oxidation-reduction potential (ORP) of 1.77 V vs. SHE, the final mixed pulp potential after H2O2 conditioning and prior to collector addition, at pulp pH of 9.5, was in the range of 0.287–0.300 V and 0.280–0.290 V vs. SHE for chalcopyrite and chalcocite, respectively, for the various H2O2 dosages tested. Since thiol collectors interaction with mineral systems is generally accepted to be electrochemical in nature, it is the mixed pulp potential that ultimately determines the extent of electrochemical reactions that the collector molecules undergo, and the Eh ranges within which flotation was conducted in this study are not sufficiently high to culminate into collector decomposition. Therefore to that extent, any residual H2O2 should not have any detrimental effect on the collector chemistry. The
2.2. Mineral grinding and flotation Crushed single mineral samples (100 g) of chalcopyrite or chalcocite were ground in a laboratory stainless steel mill to achieve a P80 of 106 µm (80 wt.% particles less than 106 µm in diameter). After grinding, the slurry was transferred to a 1.5 L mechanical batch flotation cell and conditioned with the collector RTD11A (18 g/t), and the frother DSF004 (60 g/t) for 1 min for each reagent while agitated at 600 rpm. For the oxidation tests, the pulp was conditioned with hydrogen peroxide solution (30% w/v) at the required concentration (wt. %) for 10 min prior to the direct addition of flotation reagents (collector and frother) into the slurry. The final pulp potentials after hydrogen peroxide conditioning were in the ranges of 0.287–0.300 V and 0.280–0.290 V vs. SHE for chalcopyrite and chalcocite flotation, respectively, for the tested dosages, and decreased as flotation proceeded. Table 1 Chemical composition of chalcopyrite (CuFeS2). Species
Al2O3
Bi
CaO
Co
Cu
Fe
Pb
S
SiO2
Ti
Zn
wt.%
0.32
0.11
1.66
0.03
29.3
27.2
0.66
30.8
4.47
0.03
2.67
2
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Table 2 Chemical composition of chalcocite (Cu2S). Species
Ag
Al
As
Bi
Fe
Mg
Mo
Na
Ni
Pb
S
Zn
Cu
wt.%
0.02
0.02
0.02
0.01
0.54
0.01
0.11
0.01
0.02
0.05
13.3
0.01
77.1
and chalcocite at 0 wt.% H2O2 is attributed to differences in the amount of hydrophilic species present on the mineral surfaces. Mineral flotation recovery progressively decreased as a result of an increase in hydrogen peroxide concentration. This is because the mineral surfaces are being progressively oxidised with the concomitant metal dissolution and formation of hydrophilic metal oxides and hydroxides that precipitate on the mineral surfaces. The reduction in recoveries is attributed to the increment of the fraction of hydrophilic oxidation species coating the mineral surfaces, thereby decreasing the surface hydrophobicity of the sulphide minerals. Moreover, the presence of such species on the mineral surfaces has an effect of sterically hindering adsorption of collector molecules to create hydrophobic surfaces necessary for flotation, and together these changes effectively render the mineral surfaces increasingly unamenable to flotation. It can also be observed from Fig. 1 that chalcopyrite flotation recovery started to plateau beyond a hydrogen peroxide concentration of 30 wt.%. Above this point the chalcopyrite surface is sufficiently hydrophilic to be unamenable to recovery by true flotation and the primary mechanism by which the particles are recovered is entrainment. It is interesting to note for chalcocite that flotation recovery drastically dropped to the entrainment level (about 1.80%) by increasing the hydrogen peroxide from 8 to 10 wt.%, illustrating the enormous susceptibility of this copper sulphide to surface oxidation. The types of hydrophilic oxidation species that negatively impact flotation of these copper sulphides are presented and discussed in Section 3.2.
Fig. 1. Chalcopyrite and chalcocite flotation recoveries as functions of hydrogen peroxide concentration (error bars represent standard deviation between duplicate tests).
effect of hydrogen peroxide concentration on mineral flotation recovery is shown in Fig. 1 for both chalcopyrite and chalcocite. At the onset of the oxidation process (0 wt.% H2O2), very good flotation recoveries of 89.3% and 97.5% were obtained for chalcopyrite and chalcocite, respectively. The difference in flotation recovery between chalcopyrite
Fig. 2. Cu 2p3/2 (left) and Fe 2p3/2 (right) XPS spectra of chalcopyrite conditioned with various concentrations of H2O2. 3
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3.2. Cryo-XPS analysis of oxidised chalcopyrite and chalcocite surfaces Surface characterisation was carried out to determine the types and concentrations of the species that formed on the chalcopyrite and chalcocite mineral surfaces upon oxidation after chemical treatment with various concentrations of hydrogen peroxide. The XPS spectra and related discussion are presented in this subsection for both copper sulphide minerals. It should be noted that the selection of samples for surface characterisation was based on a “significant” difference in flotation recovery. For chalcopyrite, the samples conditioned with 0, 10, 20 and 40 wt.% H2O2 were characterised, while for chalcocite, the samples conditioned at 0, 8 and 10 wt.% H2O2 were characterised. Shown in Fig. 2 are Cu and Fe spectra, which were fitted with the 2p3/2 peaks, obtained for chalcopyrite samples conditioned with 0, 10 and 40 wt.% H2O2. From the Cu 2p3/2 spectra, for the mineral surface conditioned with 0 wt.% H2O2, the peak located at a binding energy of 931.7 eV is attributable to Cu(I)-S in the chalcopyrite lattice (Smart, 1991; Ghahremaninezhad et al., 2013; Hirajima et al., 2017). Its intensity decreased as the oxidation process proceeded – that is, an increase in hydrogen peroxide concentration. This occurs with a concomitant increase in the intensity of the Cu(II) peak located at 933.0 eV and an emergence of another Cu(II) peak in the presence of the oxidising agent. This peak is located at 937.9 and 938.5 eV for chalcopyrite conditioned with 10 and 40 wt.% H2O2, respectively. The formation of Cu(II) oxidation species on the chalcopyrite surface is corroborated by the presence of the characteristic Cu(II) satellite peaks located at 941.4 and 943.9 eV (with 10 and 40 wt.% H2O2), which are in agreement with reported values in literature (942–948 eV) (Rosencwaig et al., 1971). These Cu(II) species are primarily in the form of hydroxides and oxides (Cu(II)-O/OH) (McIntyre and Cook, 1975; Smart, 1991). The peak at 707.4 eV in the Fe 2p3/2 spectra is due to the chalcopyrite Fe(II)-S species (Buckley and Woods, 1984). It is worth noting the substantial amount, even more than the chalcopyrite Fe(II)-S species, of ferric (Fe(III)) species present on the mineral surface from the onset (in the absence of hydrogen peroxide) as shown by the peaks located at binding energies of 710.4 and 713 eV, which have been documented to be in the form of hydroxides/oxides/oxyhydroxides (Fe(III)-O/OH/ OOH) (Buckley and Woods, 1984; Smart, 1991). This further attests to the phenomenon of the ease with which iron ions dissolve from chalcopyrite, and the preferential oxidation of the Fe ionic sites prior to Cu and S ionic sites (Buckley and Woods, 1984; Vaughan et al., 1997; Yin et al., 2000; Xiong et al., 2018) owing to the higher chemical reactivity of iron. The amount of the hydrophilic ferric oxidation species increased at the expense of the chalcopyrite Fe(II)-S species as the oxidation process progressed and the latter eventually diminished. The presence of these ferric oxidation species, together with the trace amount of cupric (Cu(II)) species observed in the Cu 2p3/2 spectrum, on the mineral surface indicates that mineral oxidation had already occurred even in the absence of the oxidising agent. This is attributable to the presence of dissolved oxygen during grinding and in the flotation system, as well as a high concentration of hydroxyl species in the pulp in alkaline conditions, typical of the sulphide flotation process. The S 2p spectra of chalcopyrite are presented in Fig. 3 and were fitted with the 2p1/2 and 2p3/2 spin-orbit doublet with an intensity ratio of 1:2 and binding energy separation of 1.2 eV (Smart et al., 1999). The S 2p3/2 component located at 161.0 eV in the sample conditioned with 0 wt.% H2O2 is attributable to the chalcopyrite monosulphide S2 − species (Buckley and Woods, 1984; Zachwieja et al., 1989). It was observed from the Cu 2p3/2 and Fe 2p3/2 spectra that the chalcopyrite surface was oxidised from the onset with 0 wt.% H2O2. It is also evident from the S sites that oxidation had already occurred, illustrated by the presence of the disulphide (S22 −) and polysulphide (S2n−)/elemental sulphur (S0 ) species, as shown in the S 2p spectrum. These peaks (2p3/2 components) are located at binding energies of 162.0 and 163.1 eV respectively, and are in agreement with values reported in the literature (Zachwieja et al., 1989; McCarron et al., 1990; Smart et al., 1999; Harmer et al.,
Fig. 3. S 2p XPS spectra of chalcopyrite conditioned with various concentrations of H2O2.
2006). Upon the chemical treatment with hydrogen peroxide, sulphate (SO24−) species, located at 168.5 eV (10 wt.% H2O2) and 168.7 eV (40 wt.% H2O2) (Wagner, 1990; Smart et al., 1999; Harmer et al., 2006), were formed at the expense of the lower binding energy species (disulphide, monosulphide and polysulphide/elemental sulphur) as they progressively oxidised. The results for surface characterisation of chalcocite are presented in Fig. 4. The chalcocite Cu 2p3/2 spectra are similar to those of chalcopyrite (Fig. 2). The peak located at 932.8 eV is characteristic of the Cu (I)-S species in the chalcocite lattice (Mielczarski, 1987; Mielczarski and Suoninen, 1988), which oxidises to form Cu(II) species located at 934.3 and 936.4 eV with 8 wt.% H2O2, and 934.3 and 936.8 eV with 10 wt.% H2O2. These Cu(II) species are ascribed to hydroxides and oxides (Cu (II)-O/OH) (McIntyre and Cook, 1975; Smart, 1991). The chalcocite mineral surface had also been slightly oxidised, prior to deliberate chemical oxidation, as a result of exposure to dissolved oxygen. This is evidenced by the presence of a Cu(II) species peak located at 934.8 eV and the “trace amounts” of sulphite (SO32 −) and sulphate (SO24−) species shown in the S 2p spectrum. These sulphite and sulphate species are located at 166.5 eV (Cai et al., 2009) (reported on a pyrite surface – sulphide minerals have similar anion sublattices) and 168.8 eV (Wagner, 1990; Smart et al., 1999; Harmer et al., 2006), respectively, in addition to the chalcocite monosulphide S2 − located at 162.0 eV 4
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Fig. 4. Cu 2p3/2 (left) and S 2p XPS (right) spectra of chalcocite conditioned with various concentrations of H2O2.
(Mielczarski, 1987; Mielczarski and Suoninen, 1988; Termes et al., 1987). The treatment of the chalcocite mineral with hydrogen peroxide led to further oxidation of the monosulphide species, culminating in the formation of disulphide S22 − species located at 162.7 eV (8 wt.% H2O2) and 163.0 eV (10 wt.% H2O2). Fascinating to note is the formation of the polysulphide/elemental sulphur species, which are intrinsically hydrophobic, located at 164.3 eV, with 8 wt.% H2O2 concentration that ultimately oxidised to form sulphates with 10 wt.% H2O2.
Table 3 The atomic concentration of each species on chalcopyrite (CuFeS2) surface with various extents of oxidation and the degree of surface oxidation for each condition. Species
0 wt.% H2O2
10 wt.% H2O2
20 wt.% H2O2
40 wt.% H2O2
S2 −
7.867 3.394 1.572 6.223 12.72
1.228 8.649 0.1864 4.015 3.505
0.7126 10.43 0 5.398 2.268
0.2433 6.962 0 4.937 0.9108
S22 −
6.239
2.296
1.704
0.6411
S2n−/S0
5.997
1.603
1.459
0.6128
SO24−
0
4.042
3.985
2.151
∑ hydrophilic species
9.617
16.71
19.82
14.05
∑ hydrophobic species Oxidation index
13.86
2.831
2.171
0.8561
0.694
5.90
9.13
16.4
Cu(I)-S Cu(II)-O/OH Fe(II)-S Fe(III)-O/OH
3.3. The degree of copper sulphide mineral surface oxidation The quantitative information (atomic concentrations) of the surface species on chalcopyrite and chalcocite shown by the XPS spectra in the preceding section is presented in Tables 3 and 4, respectively. As can be expected, the tables demonstrate a decrease in the atomic concentrations of the metal sulphide species (Cu(I), Fe(II) and S2 −) hosted by the chalcopyrite and chalcocite lattices, with a concomitant increase in the amount of oxidation species forming on the mineral surfaces upon chemical treatment with hydrogen peroxide. The atomic concentrations of the surface species were further used to calculate the degree of mineral surface oxidation for both copper sulphides. The surface hydrophobicity and floatability of the copper sulphides upon oxidation in typical alkaline flotation conditions are primarily controlled by two opposite processes, dissolution of metal ions that produces sulphur-rich hydrophobic surfaces, and precipitation of metal hydroxide and oxide that produces hydrophilic surfaces (Fairthorne et al., 1997). It is therefore the proportions of hydrophilic and hydrophobic surface species that determines whether the mineral is sufficiently hydrophilic for depression or sufficiently hydrophobic for flotation. Therefore in order to quantify the degree of mineral surface oxidation, the ratio of hydrophilic species to hydrophobic species was computed and denotes the oxidation index in Tables 3 and 4. The calculation was done by taking the sum of the atomic concentrations of the
Atomic concentration (%)
hydrophilic oxidation species: Cu(II)-O/OH, Fe(III)-O/OH, SO32 − and SO42 −, and dividing it by the atomic concentrations of the hydrophobic polysulphide/elemental sulphur (Sn2 −/ S 0 ) oxidation species, and the metal ion species (Cu(I)-S and Fe(II)-S) from the unoxidised phase of the copper sulphides. The rationale for incorporating the unoxidised metal ionic sites with the hydrophobic contribution is premised on the fact that this is a collector-based flotation system, and collector adsorption occurs at these sites thus rendering the mineral surfaces hydrophobic. Presented in Fig. 5 is the degree of mineral surface oxidation as a function of hydrogen peroxide concentration for both chalcopyrite and chalcocite. The degree of surface oxidation shows a linear dependence on hydrogen peroxide concentration for chalcopyrite. Chemically treating the chalcopyrite surface with 10, 20 and 40 wt.% H2O2 5
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Table 4 The atomic concentration of each species on chalcocite (Cu2S) surface with various extents of oxidation and the degree of surface oxidation for each condition. Species
Atomic concentration (%) 0 wt.% H2O2
8 wt.% H2O2
10 wt.% H2O2
S2 −
39.60 5.413 15.49
11.12 21.36 4.983
6.250 29.65 2.576
S22 −
0
2.103
0.7004
S2n−/S0
0
1.758
0
SO32 −
1.295
0
0
SO24−
1.145
1.008
0.6815
∑ hydrophilic species
7.853
22.36
30.33
∑ hydrophobic species Oxidation index
39.60
12.88
6.250
0.198
1.74
4.85
Cu(I)-S Cu(II)-O/OH
Fig. 6. Chalcopyrite and chalcocite flotation recoveries as functions of degree of surface oxidation (error bars represent standard deviation between duplicate tests).
could only be achieved by the surface treatment of chalcopyrite with 40 wt.% H2O2. Moreover, a H2O2 concentration of 8 wt.% yielded an increment factor of 9 for chalcocite – a factor that was achieved with slightly more H2O2 concentration of 10 wt.% for chalcopyrite. However, at the onset of the oxidation process (in the absence of H2O2), chalcopyrite surface oxidation was higher (by a factor of about 3.5) than that of chalcocite, and this is attributed to the presence of a significant amount of ferric oxidation species, as revealed by the XPS data, owing to the high reactivity of iron. This is the reason why chalcopyrite flotation recovery was lower than chalcocite flotation recovery without the oxidation treatment.
3.4. The critical degree of surface oxidation for chalcopyrite and chalcocite flotation Fig. 5. The degree of mineral surface oxidation for chalcopyrite (CuFeS2) and chalcocite (Cu2S) under various H2O2 concentrations.
Flotation recoveries as a function of the degree of mineral surface oxidation for both chalcopyrite and chalcocite are presented in Fig. 6. As can be anticipated, mineral flotation recoveries decreased with an increase in the degree of surface oxidation, with flotation of the former adopting a well-defined sigmoid shape while the latter showed a dramatic decay beyond the initial stage of surface oxidation. The chemically untreated mineral surfaces, with degrees of oxidation of 0.694 for chalcopyrite and 0.198 for chalcocite, yielded very good flotation recoveries of 89.3 and 97.5%, respectively. A degree of surface oxidation of 5.90 led to a 17.4% drop in chalcopyrite flotation recovery, while a 55.9% drop was observed at a degree of surface oxidation of 9.13. For heavily oxidised chalcopyrite surfaces, with a degree of surface oxidation of 16.4, 5.95% recovery was obtained, accounting for an 83.4% recovery drop from the recovery of chemically untreated chalcopyrite. For chalcocite, a degree of surface oxidation of 1.74 yielded a flotation recovery of 71.7%, accounting for a 25.8% loss in recovery. The heavily oxidised chalcocite surface at a degree of oxidation of 4.85 yielded a mere 1.80% recovery, representing a 95.3% loss in flotation recovery. It must be noted that while such a tremendous recovery loss was observed in chalcocite flotation, for the mineral surface treated with 10 wt.% H2O2, a 71.9% flotation recovery could still be obtained for chalcopyrite, although with a 17.4% loss in recovery. This demonstrates that chalcocite flotation was much more affected than chalcopyrite by the oxidation process. The flotation behaviour of chalcopyrite was best described by the Dose-Response function (Eq. (1)), which was adopted to determine its critical degree of surface oxidation. This is herein defined as the degree of surface oxidation beyond which mineral recovery by true flotation
increased the degree of surface oxidation by factors of 9, 13 and 24, respectively, compared to that treated with 0 wt.% H2O2. Chalcocite surface oxidation exhibited a rather different dependency on hydrogen peroxide concentration compared to chalcopyrite surface oxidation, as already demonstrated by its flotation behaviour, the results of which are shown in Fig. 1. The dependence of the degree of surface oxidation on hydrogen peroxide concentration for chalcocite was best described by a Boltzmann growth function. Incremental changes by factors of 9 and 24 for chalcocite conditioned with 8 and 10 wt.% H2O2, respectively, in the degree of surface oxidation were observed. Unlike the gradual increase in the degree of surface oxidation observed for chalcopyrite, the curve for chalcocite suggests that its surface oxidation degree increased minimally below 8 wt.% H2O2 while it increased drastically, directly to highest levels, above 8 wt.% H2O2. This further demonstrates the peculiar oxidation behaviour of chalcocite and the differences in oxidation of these copper sulphides owing to their different electrochemical properties. It is vital to note the factors by which the degree of mineral surface oxidation increased subject to treatments with various concentrations of hydrogen peroxide for chalcopyrite and chalcocite. From the increment factors and their corresponding hydrogen peroxide concentrations quoted above, it is evident that the chalcocite surface was much more sensitive to oxidation than the chalcopyrite surface. An increment factor of 9 in the degree of surface oxidation was obtained by the treatment with 10 wt.% H2O2 for chalcopyrite, while this oxidiser concentration yielded an increment factor of 24 for chalcocite, which 6
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an instrument to predict flotation mineral recoveries as a result of the degree to which the surfaces have been oxidised. Therefore it will serve as a guideline to help flotation plants to better manage oxidised ores to circumvent losses in recoveries as well as to explore potential solutions that could be tailored to flotation of ores with different degrees of oxidation. The critical degree of surface oxidation was mathematically determined for the primary copper sulphide chalcopyrite, while it was estimated for the secondary copper sulphide mineral chalcocite, to be 11.7 and in the range of 1.74–4.85, respectively. This is of paramount importance as it serves as a stepping-stone in exploring novel ways to modify surface properties of the minerals, which are otherwise completely unamenable to the most efficient sulphide mineral separation technology, in a quest to reverse the adverse effect of oxidation and restore their floatability.
becomes virtually impossible, due to great quantities of hydrophilic oxidation species precipitating on the mineral surface, and the predominant mechanism by which mineral particles report to the concentrate is entrainment. Similar sigmoidal functions, in particular the Boltzmann function, have also been used on experimental data showing characteristic sigmoidal shapes to determine the critical particle contact angle for mineral flotation (Gontijo et al., 2007) and the critical degree of surface oxidation for coal flotation (Chang et al., 2017, 2018).
(
)
y = A1 + (A2 − A1)/ 1 + 10(logx 0 − x ) p
(1)
In Eq. (1), y and x represent chalcopyrite recovery and the degree of surface oxidation, respectively. The other parameters, A1 (bottom asymptote), A2 (top asymptote), logx 0 (point of inflection) and p (the slope determined from the sigmoidal curve fitting), were determined to be A1 = 5.95, A2 = 89.3, logx 0 = 7.93 and p = −0.321. In estimating the critical degree of surface oxidation for flotation, the intercept between the tangent of the curve (the straight line drawn through the point of inflection) and the degree of surface oxidation on the x-axis should be identified. The critical degree of surface oxidation in chalcopyrite flotation was thus estimated to be 11.7. At this point, the proportion of hydrophilic oxidation surface species is about 12 times greater than that of the hydrophobic surface species. Above this degree of surface oxidation, mineral particle recovery is attributed exclusively to entrainment and only about 11.0% recovery could be achieved when the chalcopyrite mineral surface was critically oxidised. Contrary to chalcopyrite flotation, chalcocite flotation as a function of the degree of surface oxidation was best described by a second-order polynomial function, as expressed by Eq. (2):
y = intercept + B1X + B 2X 2
Acknowledgements The authors would like to express their gratitude to the following companies and institutions; Newmont USA Limited, Newcrest Mining Limited and the Australian Research Council (ARC) for financial support to the ARC Linkage project (LP160100619), Engineering the sulphidising reactions for flotation of low quality ores. Dr Barry Wood from the Centre for Microscopy and Microanalysis (CMM) at the University of Queensland (UQ) is greatly acknowledged for his assistance with X-ray Photoelectron Spectroscopy (XPS) characterisation. Dr Yangyang Huai from UQ School of Chemical Engineering is also acknowledged for his contribution during discussions in relation to collector chemistry.
(2) References
The parameters y and x represent chalcocite recovery and the degree of surface oxidation, respectively. The other parameters were determined, from curve fitting, to be intercept = 100.4 , B1 = −14.4 , and B2 = −1.22 . Due to the nature of the function describing chalcocite flotation (a second order polynomial function with second derivative of a constant – hence no inflection point), it was inherently impossible to mathematically determine the exact point (critical degree of oxidation) at which the mechanism by which mineral particles report to the concentrate transitions from true flotation to entrainment. However, from Fig. 6 it is evident that the critical degree of oxidation for chalcocite is much less than that of chalcopyrite, and it can be deduced to lie between 1.74 and 4.85 from the line graph. It is crucial to note that a degree of surface oxidation of about 5 was sufficient to render the chalcocite surface critically oxidised, about 2.4 times less than the 11.7 beyond which the chalcopyrite surface reached a state of critical surface oxidation, further illustrating the resistance of the latter copper sulphide to surface oxidation. This infers that chemical methods usually tailored, such as sulphidisation, to restore the floatability of oxidised copper sulphides through formation of metal sulphide phases or species that would facilitate collector adsorption prior to flotation, should consider formation of a metal sulphide phase that is intrinsically resistant to surface oxidation, such as a primary type copper sulphide mineral like chalcopyrite. This can potentially improve the efficiency of the current sulphidisation process in place to address the challenge of oxidation, as it has proved to suffer from drawbacks such as failing to restore floatability of sulphides that are heavily oxidised and those that are sensitive to surface oxidation (Newell et al., 2007).
Buckley, A.N., Woods, R., 1984. An X-ray photoelectron spectroscopic study of the oxidation of chalcopyrite. Aust. J. Chem. 37, 2403–2413. Cai, Y., Pan, Y., Xue, J., Sun, Q., Su, G., Li, X., 2009. Comparative XPS study between experimentally and naturally weathered pyrites. Appl. Surf. Sci. 255, 8750–8760. Chang, Z., Chen, X., Peng, Y., 2017. Understanding and improving the flotation of coals with different degrees of surface oxidation. Powder Technol. 321, 190–196. Chang, Z., Chen, X., Peng, Y., 2018. The effect of saline water on the critical degree of coal surface oxidation for coal flotation. Miner. Eng. 119, 222–227. Fairthorne, G., Fornasiero, D., Ralston, J., 1997. Effect of oxidation on the collectorless flotation of chalcopyrite. Int. J. Miner. Process. 49, 31–48. Fullston, D., Fornasiero, D., Ralston, J., 1999. Zeta potential study of the oxidation of copper sulfide minerals. Colloids Surf., A 146, 113–121. Gardner, J., Woods, R., 1979. An electrochemical investigation of the natural flotability of chalcopyrite. Int. J. Miner. Process. 6, 1–16. Ghahremaninezhad, A., Dixon, D., Asselin, E., 2013. Electrochemical and XPS analysis of chalcopyrite (CuFeS2) dissolution in sulfuric acid solution. Electrochim. Acta 87, 97–112. Gontijo, D.F., Fornasiero, D., Ralston, J., 2007. The limits of fine and coarse particle flotation. Canadian J. Chem. Eng. 85, 739–747. Harmer, S.L., Thomas, J.E., Fornasiero, D., Gerson, A.R., 2006. The evolution of surface layers formed during chalcopyrite leaching. Geochim. Cosmochim. Acta 70, 4392–4402. Heyes, G., Trahar, W., 1977. The natural flotability of chalcopyrite. Int. J. Miner. Process. 4, 317–344. Heyes, G., Trahar, W., 1979. Oxidation-reduction effects in the flotation of chalcocite and cuprite. Int. J. Miner. Process. 6, 229–252. Hirajima, T., Miki, H., Suyantara, G.P.W., Matsuoka, H., Elmahdy, A.M., Sasaki, K., Imaizumi, Y., Kuroiwa, S., 2017. Selective flotation of chalcopyrite and molybdenite with H2O2 oxidation. Miner. Eng. 100, 83–92. Mccarron, J., Walker, G., Buckley, A., 1990. An X-ray photoelectron spectroscopic investigation of chalcopyrite and pyrite surfaces after conditioning in sodium sulfide solutions. Int. J. Miner. Process. 30, 1–16. Mcintyre, N., Cook, M., 1975. X-ray photoelectron studies on some oxides and hydroxides of cobalt, nickel, and copper. Anal. Chem. 47, 2208–2213. Mielczarski, J., 1987. XPS study of ethyl xanthate adsorption on oxidized surface of cuprous sulfide. J. Colloid Interface Sci. 120, 201–209. Mielczarski, J., Suoninen, E., 1988. XPS study of the oxidation of cuprous sulphide in aerated aqueous solutions. Colloids Surf. 33, 231–237. Newell, A., Skinner, W.M., Bradshaw, D., 2007. Restoring the floatability of oxidised sulfides using sulfidisation. Int. J. Miner. Process. 84, 108–117. Rosencwaig, A., Wertheim, G., Guggenheim, H., 1971. Origins of satellites on inner-shell photoelectron spectra. Phys. Rev. Lett. 27, 479. Senior, G., Trahar, W., 1991. The influence of metal hydroxides and collector on the flotation of chalcopyrite. Int. J. Miner. Process. 33, 321–341.
4. Conclusions A method for quantitatively relating the degree of mineral surface oxidation to copper sulphide flotation, which involves quantification of the proportions of hydrophilic and hydrophobic surface species by the surface sensitive technique XPS, has been developed. This will serve as 7
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T. Moimane, et al. Smart, R.S.C., 1991. Surface layers in base metal sulphide flotation. Miner. Eng. 4, 891–909. Smart, R.S.C., Skinner, W.M., Gerson, A.R., 1999. XPS of sulphide mineral surfaces: metaldeficient, polysulphides, defects and elemental sulphur. Surf. Interface Anal. 28, 101–105. Termes, S., Buckley, A., Gillard, R., 1987. 2p electron binding energies for the sulfur atoms in metal polysulfides. Inorg. Chim. Acta 126, 79–82. Vaughan, D., Becker, U., Wright, K., 1997. Sulphide mineral surfaces: theory and experiment. Int. J. Miner. Process. 51, 1–14. Wagner, C., 1990. Photoelectron and Auger energies and the Auger parameter: a data set.
Pract. Surf. Anal. Xiong, X., Hua, X., Zheng, Y., Lu, X., Li, S., Cheng, H., Xu, Q., 2018. Oxidation mechanism of chalcopyrite revealed by X-ray photoelectron spectroscopy and first principles studies. Appl. Surf. Sci. 427, 233–241. Yin, Q., Vaughan, D., England, K., Kelsall, G., Brandon, N., 2000. Surface oxidation of chalcopyrite (CuFeS2) in alkaline solutions. J. Electrochem. Soc. 147, 2945–2951. Zachwieja, J.B., Mccarron, J.J., Walker, G.W., Buckley, A.N., 1989. Correlation between the surface composition and collectorless flotation of chalcopyrite. J. Colloid Interface Sci. 132, 462–468.
8
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The critical degree of mineral surface oxidation in copper sulphide flotation ⁎
T
Tiisetso Moimane, Chris Plackowski, Yongjun Peng
School of Chemical Engineering, The University of Queensland, St Lucia, Brisbane, QLD 4072, Australia
A R T I C LE I N FO
A B S T R A C T
Keywords: Chalcocite Chalcopyrite Critical degree of oxidation Flotation Surface analysis
It is well documented that surface oxidation of copper sulphide minerals has some detrimental effects on their flotation performance. However, little work has been done to quantitatively relate surface oxidation to flotation performance, which makes it inherently difficult for processing plants to optimise flotation conditions for oxidised ores. In this study, an array of oxidised chalcopyrite and chalcocite samples was prepared and characterisation of the surface oxidation species was carried out by X-ray Photoelectron Spectroscopy (XPS). The degree of surface oxidation was quantified as the ratio of hydrophilic species to hydrophobic species and correlated with copper sulphide flotation recovery. A quantitative relationship between them was established and a critical degree of oxidation, beyond which flotation becomes impossible, was identified to be 11.7 for chalcopyrite and estimated to be in the range of 1.74–4.85 for chalcocite, indicating that chalcocite flotation is much more sensitive to surface oxidation. This study will enable provision of guidelines to better manage oxidised copper ores to circumvent the loss of recovery and will also help in developing potential solutions that could be applied to flotation of minerals with different degrees of oxidation.
1. Introduction Copper sulphide minerals, found in the primary and secondary enrichment hydrothermal zones, yield the most copper production throughout the entire globe. The most commonly found copper sulphides in the primary zone are chalcopyrite (CuFeS2) and bornite (Cu5FeS4) while the secondary enrichment zone hosts mainly chalcocite (Cu2S) and covellite (CuS). Both the primary and secondary copper sulphides, together with associated precious metals such as gold, are recovered from raw ores by froth flotation, a separation process based on exploiting differences in surface properties to effect separation between valuable and gangue minerals. As these copper sulphide minerals are semiconductors, their surfaces are reactive and oxidise upon exposure to air and aqueous solutions during stockpiling, crushing, grinding and flotation. As a result, oxidation plays a crucial role in flotation as it alters the surface properties of the minerals and affects adsorption of collectors onto the minerals. Extensive research, employing electrochemical and surface sensitive analytical techniques, has been conducted over the years to understand this oxidation process and its ramifications on copper sulphide flotation (Gardner and Woods, 1979; Buckley and Woods, 1984; Vaughan et al., 1997; Fullston et al., 1999; Yin et al., 2000; Ghahremaninezhad et al., 2013; Hirajima et al., 2017). The unanimous view amongst researchers is that this oxidation
⁎
process could culminate in effects either desirable or detrimental to mineral flotation. “Mild oxidation” could lead to enhanced hydrophobicity of the copper sulphide minerals owing to surfaces rich in intrinsically hydrophobic species such as elemental sulphur and polysulphides (Heyes and Trahar, 1977). This constitutes the well-known collectorless flotation phenomenon of copper sulphides such as chalcopyrite. Chalcocite collectorless flotation, although weak and not as extensive as that of chalcopyrite, has also been reported (Heyes and Trahar, 1979). In contrast, “significant oxidation” culminates in great amounts of hydrophilic metal hydroxides and oxides precipitating on the mineral surfaces (Senior and Trahar, 1991; Smart, 1991), thereby increasing the hydrophilicity of the mineral surfaces, thus rendering the minerals unamenable to flotation and consequently leading to losses in mineral recoveries. However, “mild” and “significant” oxidation are relative terms and cannot be adopted in quantitatively defining the degree to which a mineral surface is oxidised. Little work has been done to quantitatively relate the degree of surface oxidation to copper sulphide flotation, which makes it inherently difficult for processing plants to optimise flotation conditions for oxidised ores and explore potential solutions that could be tailored to flotation of minerals with different degrees of oxidation. Therefore the unanswered fundamental question is: how much is “mild” and how much is “significant” with regard to the degree of mineral surface oxidation? Moreover, a parameter of paramount
Corresponding author. E-mail address: [email protected] (Y. Peng).
https://doi.org/10.1016/j.mineng.2019.106075 Received 2 February 2019; Received in revised form 29 June 2019; Accepted 7 October 2019 0892-6875/ © 2019 Elsevier Ltd. All rights reserved.
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importance, the “critical degree of surface oxidation”, defined as the degree of surface oxidation beyond which mineral recovery by true flotation becomes virtually impossible, needs to be determined. A previous study by Newell et al. (2007) has demonstrated that sulphides with various degrees of surface oxidation and susceptibility to oxidation respond differently to the sulphidisation process used for restoration of their floatability. Moreover, the current sulphidisation process has also proved to suffer from drawbacks in restoring the floatability of heavily oxidised sulphides (Newell et al., 2007). Understanding the degree of surface oxidation may provide guidelines to the sulphidisation process. Therefore in the quest to quantitatively relate surface oxidation to copper sulphide flotation and to determine the critical degree of surface oxidation, the present study focused on representatives of both primary and secondary type copper sulphides viz. chalcopyrite and chalcocite. This is based on the premise that these are the most commonly floated copper sulphide minerals. Moreover, it is also to represent both ends of the “oxidation susceptibility spectrum”, with the former being the least prone while the latter is the most prone, of the copper sulphides to oxidation as previously established in zeta potential measurements (Fullston et al., 1999).
Sodium hydroxide solution (1%) was used to adjust and maintain the pulp pH at 9.5. Air was then introduced into the flotation cell at a flow rate of 6 L/min. Four flotation concentrates were collected after cumulative times of 1, 3, 6 and 10 min employing froth scraping at an interval of 10 s. Flotation tests were conducted in duplicates to ensure good reproducibility and to determine experimental errors. The experimental errors, represented by error bars in the flotation data presented in Section 3, were found to be between 1 and 2%, which reflected good reproducibility of the results. Prior to flotation, samples for surface characterisation by X-ray Photoelectron Spectroscopy (XPS) were collected and frozen in liquid nitrogen. This was done to avoid inadvertent further oxidation before characterisation in order to ensure that any oxidation species formed are exclusively attributable to the deliberate chemically induced oxidation by hydrogen peroxide. 2.3. Mineral surface characterisation by Cryo-XPS XPS analyses were carried out using a KRATOS Axis Ultra X-ray Photoelectron Spectrometer, incorporating a 165 mm hemispherical electron energy analyser. The incident radiation source is monochromatic Aluminium (Al) X-ray Kα x-rays (1486.6 eV) operating at 150 W (15 kV, 15 mA). The sample analysis size spot is about 300 × 700 µm. The frozen slurry samples were defrosted just prior to characterisation. The solids were placed on the sample holder and immediately transferred into the loading chamber of the spectrometer. All XPS measurements were conducted under cryogenic conditions to avoid evaporation of volatile species such as elemental sulphur on the mineral surfaces under the ultra-high vacuum conditions. This was achieved by pre-cooling the samples in the loading chamber to −160 °C before evacuation and maintaining that temperature during analysis in the sample analysis chamber (SAC) using liquid nitrogen cooling. Samples were analysed at a base pressure of 10−9 torr. Survey scans were carried out from 0 to 1200 eV at a pass energy of 160 eV in 1.0 eV steps and a dwell time of 100 ms. High resolution scans of Cu 2p, Fe 2p, O 1s, C 1s, and S 2p were collected at a pass energy of 20 eV in 100 meV steps and using 2 or 3 sweeps. All the spectra were charge corrected using adventitious carbon at 284.8 eV and analysed using the CasaXPS software (version 2.3.14).
2. Experimental methods and materials 2.1. Minerals and chemical reagents Chalcopyrite and chalcocite mineral samples, supplied by GEODiscoveries, Australia, were crushed using a jaw crusher and a rolls crusher and screened to collect the −3.35 + 0.71 mm size fractions. The processed mineral samples were then sealed in polyethylene bags and stored in a freezer to minimise further surface oxidation. The chemical compositions of chalcopyrite and chalcocite, obtained by employing Inductively Coupled Plasma Mass Spectroscopy (ICP-MS), are presented in Tables 1 and 2, respectively. X-ray powder diffraction (XRD) analysis showed a chalcopyrite purity of 85 wt.%, with quartz, lime and sphalerite being the main impurities, and a chalcocite purity of 96 wt.%. The thionocarbamate based RTD11A, from Tall Bennet, was used as the collector and DSF004 from Orica was used as the frother. They were both of industry grade and used as received. Hydrogen peroxide (30% w/v, AR grade) was used as the oxidising agent. Pulp pH was adjusted using sodium hydroxide (AR grade). Grinding and flotation were carried out using Brisbane tap water.
3. Results and discussion 3.1. Flotation of chalcopyrite and chalcocite oxidised to various degrees An oxidation methodology was developed to yield different mineral flotation behaviours by conditioning the mineral samples with hydrogen peroxide solutions of different concentrations for 10 min after grinding and prior to flotation. It should be noted that although H2O2 is a strong oxidising agent with an oxidation-reduction potential (ORP) of 1.77 V vs. SHE, the final mixed pulp potential after H2O2 conditioning and prior to collector addition, at pulp pH of 9.5, was in the range of 0.287–0.300 V and 0.280–0.290 V vs. SHE for chalcopyrite and chalcocite, respectively, for the various H2O2 dosages tested. Since thiol collectors interaction with mineral systems is generally accepted to be electrochemical in nature, it is the mixed pulp potential that ultimately determines the extent of electrochemical reactions that the collector molecules undergo, and the Eh ranges within which flotation was conducted in this study are not sufficiently high to culminate into collector decomposition. Therefore to that extent, any residual H2O2 should not have any detrimental effect on the collector chemistry. The
2.2. Mineral grinding and flotation Crushed single mineral samples (100 g) of chalcopyrite or chalcocite were ground in a laboratory stainless steel mill to achieve a P80 of 106 µm (80 wt.% particles less than 106 µm in diameter). After grinding, the slurry was transferred to a 1.5 L mechanical batch flotation cell and conditioned with the collector RTD11A (18 g/t), and the frother DSF004 (60 g/t) for 1 min for each reagent while agitated at 600 rpm. For the oxidation tests, the pulp was conditioned with hydrogen peroxide solution (30% w/v) at the required concentration (wt. %) for 10 min prior to the direct addition of flotation reagents (collector and frother) into the slurry. The final pulp potentials after hydrogen peroxide conditioning were in the ranges of 0.287–0.300 V and 0.280–0.290 V vs. SHE for chalcopyrite and chalcocite flotation, respectively, for the tested dosages, and decreased as flotation proceeded. Table 1 Chemical composition of chalcopyrite (CuFeS2). Species
Al2O3
Bi
CaO
Co
Cu
Fe
Pb
S
SiO2
Ti
Zn
wt.%
0.32
0.11
1.66
0.03
29.3
27.2
0.66
30.8
4.47
0.03
2.67
2
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Table 2 Chemical composition of chalcocite (Cu2S). Species
Ag
Al
As
Bi
Fe
Mg
Mo
Na
Ni
Pb
S
Zn
Cu
wt.%
0.02
0.02
0.02
0.01
0.54
0.01
0.11
0.01
0.02
0.05
13.3
0.01
77.1
and chalcocite at 0 wt.% H2O2 is attributed to differences in the amount of hydrophilic species present on the mineral surfaces. Mineral flotation recovery progressively decreased as a result of an increase in hydrogen peroxide concentration. This is because the mineral surfaces are being progressively oxidised with the concomitant metal dissolution and formation of hydrophilic metal oxides and hydroxides that precipitate on the mineral surfaces. The reduction in recoveries is attributed to the increment of the fraction of hydrophilic oxidation species coating the mineral surfaces, thereby decreasing the surface hydrophobicity of the sulphide minerals. Moreover, the presence of such species on the mineral surfaces has an effect of sterically hindering adsorption of collector molecules to create hydrophobic surfaces necessary for flotation, and together these changes effectively render the mineral surfaces increasingly unamenable to flotation. It can also be observed from Fig. 1 that chalcopyrite flotation recovery started to plateau beyond a hydrogen peroxide concentration of 30 wt.%. Above this point the chalcopyrite surface is sufficiently hydrophilic to be unamenable to recovery by true flotation and the primary mechanism by which the particles are recovered is entrainment. It is interesting to note for chalcocite that flotation recovery drastically dropped to the entrainment level (about 1.80%) by increasing the hydrogen peroxide from 8 to 10 wt.%, illustrating the enormous susceptibility of this copper sulphide to surface oxidation. The types of hydrophilic oxidation species that negatively impact flotation of these copper sulphides are presented and discussed in Section 3.2.
Fig. 1. Chalcopyrite and chalcocite flotation recoveries as functions of hydrogen peroxide concentration (error bars represent standard deviation between duplicate tests).
effect of hydrogen peroxide concentration on mineral flotation recovery is shown in Fig. 1 for both chalcopyrite and chalcocite. At the onset of the oxidation process (0 wt.% H2O2), very good flotation recoveries of 89.3% and 97.5% were obtained for chalcopyrite and chalcocite, respectively. The difference in flotation recovery between chalcopyrite
Fig. 2. Cu 2p3/2 (left) and Fe 2p3/2 (right) XPS spectra of chalcopyrite conditioned with various concentrations of H2O2. 3
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3.2. Cryo-XPS analysis of oxidised chalcopyrite and chalcocite surfaces Surface characterisation was carried out to determine the types and concentrations of the species that formed on the chalcopyrite and chalcocite mineral surfaces upon oxidation after chemical treatment with various concentrations of hydrogen peroxide. The XPS spectra and related discussion are presented in this subsection for both copper sulphide minerals. It should be noted that the selection of samples for surface characterisation was based on a “significant” difference in flotation recovery. For chalcopyrite, the samples conditioned with 0, 10, 20 and 40 wt.% H2O2 were characterised, while for chalcocite, the samples conditioned at 0, 8 and 10 wt.% H2O2 were characterised. Shown in Fig. 2 are Cu and Fe spectra, which were fitted with the 2p3/2 peaks, obtained for chalcopyrite samples conditioned with 0, 10 and 40 wt.% H2O2. From the Cu 2p3/2 spectra, for the mineral surface conditioned with 0 wt.% H2O2, the peak located at a binding energy of 931.7 eV is attributable to Cu(I)-S in the chalcopyrite lattice (Smart, 1991; Ghahremaninezhad et al., 2013; Hirajima et al., 2017). Its intensity decreased as the oxidation process proceeded – that is, an increase in hydrogen peroxide concentration. This occurs with a concomitant increase in the intensity of the Cu(II) peak located at 933.0 eV and an emergence of another Cu(II) peak in the presence of the oxidising agent. This peak is located at 937.9 and 938.5 eV for chalcopyrite conditioned with 10 and 40 wt.% H2O2, respectively. The formation of Cu(II) oxidation species on the chalcopyrite surface is corroborated by the presence of the characteristic Cu(II) satellite peaks located at 941.4 and 943.9 eV (with 10 and 40 wt.% H2O2), which are in agreement with reported values in literature (942–948 eV) (Rosencwaig et al., 1971). These Cu(II) species are primarily in the form of hydroxides and oxides (Cu(II)-O/OH) (McIntyre and Cook, 1975; Smart, 1991). The peak at 707.4 eV in the Fe 2p3/2 spectra is due to the chalcopyrite Fe(II)-S species (Buckley and Woods, 1984). It is worth noting the substantial amount, even more than the chalcopyrite Fe(II)-S species, of ferric (Fe(III)) species present on the mineral surface from the onset (in the absence of hydrogen peroxide) as shown by the peaks located at binding energies of 710.4 and 713 eV, which have been documented to be in the form of hydroxides/oxides/oxyhydroxides (Fe(III)-O/OH/ OOH) (Buckley and Woods, 1984; Smart, 1991). This further attests to the phenomenon of the ease with which iron ions dissolve from chalcopyrite, and the preferential oxidation of the Fe ionic sites prior to Cu and S ionic sites (Buckley and Woods, 1984; Vaughan et al., 1997; Yin et al., 2000; Xiong et al., 2018) owing to the higher chemical reactivity of iron. The amount of the hydrophilic ferric oxidation species increased at the expense of the chalcopyrite Fe(II)-S species as the oxidation process progressed and the latter eventually diminished. The presence of these ferric oxidation species, together with the trace amount of cupric (Cu(II)) species observed in the Cu 2p3/2 spectrum, on the mineral surface indicates that mineral oxidation had already occurred even in the absence of the oxidising agent. This is attributable to the presence of dissolved oxygen during grinding and in the flotation system, as well as a high concentration of hydroxyl species in the pulp in alkaline conditions, typical of the sulphide flotation process. The S 2p spectra of chalcopyrite are presented in Fig. 3 and were fitted with the 2p1/2 and 2p3/2 spin-orbit doublet with an intensity ratio of 1:2 and binding energy separation of 1.2 eV (Smart et al., 1999). The S 2p3/2 component located at 161.0 eV in the sample conditioned with 0 wt.% H2O2 is attributable to the chalcopyrite monosulphide S2 − species (Buckley and Woods, 1984; Zachwieja et al., 1989). It was observed from the Cu 2p3/2 and Fe 2p3/2 spectra that the chalcopyrite surface was oxidised from the onset with 0 wt.% H2O2. It is also evident from the S sites that oxidation had already occurred, illustrated by the presence of the disulphide (S22 −) and polysulphide (S2n−)/elemental sulphur (S0 ) species, as shown in the S 2p spectrum. These peaks (2p3/2 components) are located at binding energies of 162.0 and 163.1 eV respectively, and are in agreement with values reported in the literature (Zachwieja et al., 1989; McCarron et al., 1990; Smart et al., 1999; Harmer et al.,
Fig. 3. S 2p XPS spectra of chalcopyrite conditioned with various concentrations of H2O2.
2006). Upon the chemical treatment with hydrogen peroxide, sulphate (SO24−) species, located at 168.5 eV (10 wt.% H2O2) and 168.7 eV (40 wt.% H2O2) (Wagner, 1990; Smart et al., 1999; Harmer et al., 2006), were formed at the expense of the lower binding energy species (disulphide, monosulphide and polysulphide/elemental sulphur) as they progressively oxidised. The results for surface characterisation of chalcocite are presented in Fig. 4. The chalcocite Cu 2p3/2 spectra are similar to those of chalcopyrite (Fig. 2). The peak located at 932.8 eV is characteristic of the Cu (I)-S species in the chalcocite lattice (Mielczarski, 1987; Mielczarski and Suoninen, 1988), which oxidises to form Cu(II) species located at 934.3 and 936.4 eV with 8 wt.% H2O2, and 934.3 and 936.8 eV with 10 wt.% H2O2. These Cu(II) species are ascribed to hydroxides and oxides (Cu (II)-O/OH) (McIntyre and Cook, 1975; Smart, 1991). The chalcocite mineral surface had also been slightly oxidised, prior to deliberate chemical oxidation, as a result of exposure to dissolved oxygen. This is evidenced by the presence of a Cu(II) species peak located at 934.8 eV and the “trace amounts” of sulphite (SO32 −) and sulphate (SO24−) species shown in the S 2p spectrum. These sulphite and sulphate species are located at 166.5 eV (Cai et al., 2009) (reported on a pyrite surface – sulphide minerals have similar anion sublattices) and 168.8 eV (Wagner, 1990; Smart et al., 1999; Harmer et al., 2006), respectively, in addition to the chalcocite monosulphide S2 − located at 162.0 eV 4
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Fig. 4. Cu 2p3/2 (left) and S 2p XPS (right) spectra of chalcocite conditioned with various concentrations of H2O2.
(Mielczarski, 1987; Mielczarski and Suoninen, 1988; Termes et al., 1987). The treatment of the chalcocite mineral with hydrogen peroxide led to further oxidation of the monosulphide species, culminating in the formation of disulphide S22 − species located at 162.7 eV (8 wt.% H2O2) and 163.0 eV (10 wt.% H2O2). Fascinating to note is the formation of the polysulphide/elemental sulphur species, which are intrinsically hydrophobic, located at 164.3 eV, with 8 wt.% H2O2 concentration that ultimately oxidised to form sulphates with 10 wt.% H2O2.
Table 3 The atomic concentration of each species on chalcopyrite (CuFeS2) surface with various extents of oxidation and the degree of surface oxidation for each condition. Species
0 wt.% H2O2
10 wt.% H2O2
20 wt.% H2O2
40 wt.% H2O2
S2 −
7.867 3.394 1.572 6.223 12.72
1.228 8.649 0.1864 4.015 3.505
0.7126 10.43 0 5.398 2.268
0.2433 6.962 0 4.937 0.9108
S22 −
6.239
2.296
1.704
0.6411
S2n−/S0
5.997
1.603
1.459
0.6128
SO24−
0
4.042
3.985
2.151
∑ hydrophilic species
9.617
16.71
19.82
14.05
∑ hydrophobic species Oxidation index
13.86
2.831
2.171
0.8561
0.694
5.90
9.13
16.4
Cu(I)-S Cu(II)-O/OH Fe(II)-S Fe(III)-O/OH
3.3. The degree of copper sulphide mineral surface oxidation The quantitative information (atomic concentrations) of the surface species on chalcopyrite and chalcocite shown by the XPS spectra in the preceding section is presented in Tables 3 and 4, respectively. As can be expected, the tables demonstrate a decrease in the atomic concentrations of the metal sulphide species (Cu(I), Fe(II) and S2 −) hosted by the chalcopyrite and chalcocite lattices, with a concomitant increase in the amount of oxidation species forming on the mineral surfaces upon chemical treatment with hydrogen peroxide. The atomic concentrations of the surface species were further used to calculate the degree of mineral surface oxidation for both copper sulphides. The surface hydrophobicity and floatability of the copper sulphides upon oxidation in typical alkaline flotation conditions are primarily controlled by two opposite processes, dissolution of metal ions that produces sulphur-rich hydrophobic surfaces, and precipitation of metal hydroxide and oxide that produces hydrophilic surfaces (Fairthorne et al., 1997). It is therefore the proportions of hydrophilic and hydrophobic surface species that determines whether the mineral is sufficiently hydrophilic for depression or sufficiently hydrophobic for flotation. Therefore in order to quantify the degree of mineral surface oxidation, the ratio of hydrophilic species to hydrophobic species was computed and denotes the oxidation index in Tables 3 and 4. The calculation was done by taking the sum of the atomic concentrations of the
Atomic concentration (%)
hydrophilic oxidation species: Cu(II)-O/OH, Fe(III)-O/OH, SO32 − and SO42 −, and dividing it by the atomic concentrations of the hydrophobic polysulphide/elemental sulphur (Sn2 −/ S 0 ) oxidation species, and the metal ion species (Cu(I)-S and Fe(II)-S) from the unoxidised phase of the copper sulphides. The rationale for incorporating the unoxidised metal ionic sites with the hydrophobic contribution is premised on the fact that this is a collector-based flotation system, and collector adsorption occurs at these sites thus rendering the mineral surfaces hydrophobic. Presented in Fig. 5 is the degree of mineral surface oxidation as a function of hydrogen peroxide concentration for both chalcopyrite and chalcocite. The degree of surface oxidation shows a linear dependence on hydrogen peroxide concentration for chalcopyrite. Chemically treating the chalcopyrite surface with 10, 20 and 40 wt.% H2O2 5
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Table 4 The atomic concentration of each species on chalcocite (Cu2S) surface with various extents of oxidation and the degree of surface oxidation for each condition. Species
Atomic concentration (%) 0 wt.% H2O2
8 wt.% H2O2
10 wt.% H2O2
S2 −
39.60 5.413 15.49
11.12 21.36 4.983
6.250 29.65 2.576
S22 −
0
2.103
0.7004
S2n−/S0
0
1.758
0
SO32 −
1.295
0
0
SO24−
1.145
1.008
0.6815
∑ hydrophilic species
7.853
22.36
30.33
∑ hydrophobic species Oxidation index
39.60
12.88
6.250
0.198
1.74
4.85
Cu(I)-S Cu(II)-O/OH
Fig. 6. Chalcopyrite and chalcocite flotation recoveries as functions of degree of surface oxidation (error bars represent standard deviation between duplicate tests).
could only be achieved by the surface treatment of chalcopyrite with 40 wt.% H2O2. Moreover, a H2O2 concentration of 8 wt.% yielded an increment factor of 9 for chalcocite – a factor that was achieved with slightly more H2O2 concentration of 10 wt.% for chalcopyrite. However, at the onset of the oxidation process (in the absence of H2O2), chalcopyrite surface oxidation was higher (by a factor of about 3.5) than that of chalcocite, and this is attributed to the presence of a significant amount of ferric oxidation species, as revealed by the XPS data, owing to the high reactivity of iron. This is the reason why chalcopyrite flotation recovery was lower than chalcocite flotation recovery without the oxidation treatment.
3.4. The critical degree of surface oxidation for chalcopyrite and chalcocite flotation Fig. 5. The degree of mineral surface oxidation for chalcopyrite (CuFeS2) and chalcocite (Cu2S) under various H2O2 concentrations.
Flotation recoveries as a function of the degree of mineral surface oxidation for both chalcopyrite and chalcocite are presented in Fig. 6. As can be anticipated, mineral flotation recoveries decreased with an increase in the degree of surface oxidation, with flotation of the former adopting a well-defined sigmoid shape while the latter showed a dramatic decay beyond the initial stage of surface oxidation. The chemically untreated mineral surfaces, with degrees of oxidation of 0.694 for chalcopyrite and 0.198 for chalcocite, yielded very good flotation recoveries of 89.3 and 97.5%, respectively. A degree of surface oxidation of 5.90 led to a 17.4% drop in chalcopyrite flotation recovery, while a 55.9% drop was observed at a degree of surface oxidation of 9.13. For heavily oxidised chalcopyrite surfaces, with a degree of surface oxidation of 16.4, 5.95% recovery was obtained, accounting for an 83.4% recovery drop from the recovery of chemically untreated chalcopyrite. For chalcocite, a degree of surface oxidation of 1.74 yielded a flotation recovery of 71.7%, accounting for a 25.8% loss in recovery. The heavily oxidised chalcocite surface at a degree of oxidation of 4.85 yielded a mere 1.80% recovery, representing a 95.3% loss in flotation recovery. It must be noted that while such a tremendous recovery loss was observed in chalcocite flotation, for the mineral surface treated with 10 wt.% H2O2, a 71.9% flotation recovery could still be obtained for chalcopyrite, although with a 17.4% loss in recovery. This demonstrates that chalcocite flotation was much more affected than chalcopyrite by the oxidation process. The flotation behaviour of chalcopyrite was best described by the Dose-Response function (Eq. (1)), which was adopted to determine its critical degree of surface oxidation. This is herein defined as the degree of surface oxidation beyond which mineral recovery by true flotation
increased the degree of surface oxidation by factors of 9, 13 and 24, respectively, compared to that treated with 0 wt.% H2O2. Chalcocite surface oxidation exhibited a rather different dependency on hydrogen peroxide concentration compared to chalcopyrite surface oxidation, as already demonstrated by its flotation behaviour, the results of which are shown in Fig. 1. The dependence of the degree of surface oxidation on hydrogen peroxide concentration for chalcocite was best described by a Boltzmann growth function. Incremental changes by factors of 9 and 24 for chalcocite conditioned with 8 and 10 wt.% H2O2, respectively, in the degree of surface oxidation were observed. Unlike the gradual increase in the degree of surface oxidation observed for chalcopyrite, the curve for chalcocite suggests that its surface oxidation degree increased minimally below 8 wt.% H2O2 while it increased drastically, directly to highest levels, above 8 wt.% H2O2. This further demonstrates the peculiar oxidation behaviour of chalcocite and the differences in oxidation of these copper sulphides owing to their different electrochemical properties. It is vital to note the factors by which the degree of mineral surface oxidation increased subject to treatments with various concentrations of hydrogen peroxide for chalcopyrite and chalcocite. From the increment factors and their corresponding hydrogen peroxide concentrations quoted above, it is evident that the chalcocite surface was much more sensitive to oxidation than the chalcopyrite surface. An increment factor of 9 in the degree of surface oxidation was obtained by the treatment with 10 wt.% H2O2 for chalcopyrite, while this oxidiser concentration yielded an increment factor of 24 for chalcocite, which 6
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an instrument to predict flotation mineral recoveries as a result of the degree to which the surfaces have been oxidised. Therefore it will serve as a guideline to help flotation plants to better manage oxidised ores to circumvent losses in recoveries as well as to explore potential solutions that could be tailored to flotation of ores with different degrees of oxidation. The critical degree of surface oxidation was mathematically determined for the primary copper sulphide chalcopyrite, while it was estimated for the secondary copper sulphide mineral chalcocite, to be 11.7 and in the range of 1.74–4.85, respectively. This is of paramount importance as it serves as a stepping-stone in exploring novel ways to modify surface properties of the minerals, which are otherwise completely unamenable to the most efficient sulphide mineral separation technology, in a quest to reverse the adverse effect of oxidation and restore their floatability.
becomes virtually impossible, due to great quantities of hydrophilic oxidation species precipitating on the mineral surface, and the predominant mechanism by which mineral particles report to the concentrate is entrainment. Similar sigmoidal functions, in particular the Boltzmann function, have also been used on experimental data showing characteristic sigmoidal shapes to determine the critical particle contact angle for mineral flotation (Gontijo et al., 2007) and the critical degree of surface oxidation for coal flotation (Chang et al., 2017, 2018).
(
)
y = A1 + (A2 − A1)/ 1 + 10(logx 0 − x ) p
(1)
In Eq. (1), y and x represent chalcopyrite recovery and the degree of surface oxidation, respectively. The other parameters, A1 (bottom asymptote), A2 (top asymptote), logx 0 (point of inflection) and p (the slope determined from the sigmoidal curve fitting), were determined to be A1 = 5.95, A2 = 89.3, logx 0 = 7.93 and p = −0.321. In estimating the critical degree of surface oxidation for flotation, the intercept between the tangent of the curve (the straight line drawn through the point of inflection) and the degree of surface oxidation on the x-axis should be identified. The critical degree of surface oxidation in chalcopyrite flotation was thus estimated to be 11.7. At this point, the proportion of hydrophilic oxidation surface species is about 12 times greater than that of the hydrophobic surface species. Above this degree of surface oxidation, mineral particle recovery is attributed exclusively to entrainment and only about 11.0% recovery could be achieved when the chalcopyrite mineral surface was critically oxidised. Contrary to chalcopyrite flotation, chalcocite flotation as a function of the degree of surface oxidation was best described by a second-order polynomial function, as expressed by Eq. (2):
y = intercept + B1X + B 2X 2
Acknowledgements The authors would like to express their gratitude to the following companies and institutions; Newmont USA Limited, Newcrest Mining Limited and the Australian Research Council (ARC) for financial support to the ARC Linkage project (LP160100619), Engineering the sulphidising reactions for flotation of low quality ores. Dr Barry Wood from the Centre for Microscopy and Microanalysis (CMM) at the University of Queensland (UQ) is greatly acknowledged for his assistance with X-ray Photoelectron Spectroscopy (XPS) characterisation. Dr Yangyang Huai from UQ School of Chemical Engineering is also acknowledged for his contribution during discussions in relation to collector chemistry.
(2) References
The parameters y and x represent chalcocite recovery and the degree of surface oxidation, respectively. The other parameters were determined, from curve fitting, to be intercept = 100.4 , B1 = −14.4 , and B2 = −1.22 . Due to the nature of the function describing chalcocite flotation (a second order polynomial function with second derivative of a constant – hence no inflection point), it was inherently impossible to mathematically determine the exact point (critical degree of oxidation) at which the mechanism by which mineral particles report to the concentrate transitions from true flotation to entrainment. However, from Fig. 6 it is evident that the critical degree of oxidation for chalcocite is much less than that of chalcopyrite, and it can be deduced to lie between 1.74 and 4.85 from the line graph. It is crucial to note that a degree of surface oxidation of about 5 was sufficient to render the chalcocite surface critically oxidised, about 2.4 times less than the 11.7 beyond which the chalcopyrite surface reached a state of critical surface oxidation, further illustrating the resistance of the latter copper sulphide to surface oxidation. This infers that chemical methods usually tailored, such as sulphidisation, to restore the floatability of oxidised copper sulphides through formation of metal sulphide phases or species that would facilitate collector adsorption prior to flotation, should consider formation of a metal sulphide phase that is intrinsically resistant to surface oxidation, such as a primary type copper sulphide mineral like chalcopyrite. This can potentially improve the efficiency of the current sulphidisation process in place to address the challenge of oxidation, as it has proved to suffer from drawbacks such as failing to restore floatability of sulphides that are heavily oxidised and those that are sensitive to surface oxidation (Newell et al., 2007).
Buckley, A.N., Woods, R., 1984. An X-ray photoelectron spectroscopic study of the oxidation of chalcopyrite. Aust. J. Chem. 37, 2403–2413. Cai, Y., Pan, Y., Xue, J., Sun, Q., Su, G., Li, X., 2009. Comparative XPS study between experimentally and naturally weathered pyrites. Appl. Surf. Sci. 255, 8750–8760. Chang, Z., Chen, X., Peng, Y., 2017. Understanding and improving the flotation of coals with different degrees of surface oxidation. Powder Technol. 321, 190–196. Chang, Z., Chen, X., Peng, Y., 2018. The effect of saline water on the critical degree of coal surface oxidation for coal flotation. Miner. Eng. 119, 222–227. Fairthorne, G., Fornasiero, D., Ralston, J., 1997. Effect of oxidation on the collectorless flotation of chalcopyrite. Int. J. Miner. Process. 49, 31–48. Fullston, D., Fornasiero, D., Ralston, J., 1999. Zeta potential study of the oxidation of copper sulfide minerals. Colloids Surf., A 146, 113–121. Gardner, J., Woods, R., 1979. An electrochemical investigation of the natural flotability of chalcopyrite. Int. J. Miner. Process. 6, 1–16. Ghahremaninezhad, A., Dixon, D., Asselin, E., 2013. Electrochemical and XPS analysis of chalcopyrite (CuFeS2) dissolution in sulfuric acid solution. Electrochim. Acta 87, 97–112. Gontijo, D.F., Fornasiero, D., Ralston, J., 2007. The limits of fine and coarse particle flotation. Canadian J. Chem. Eng. 85, 739–747. Harmer, S.L., Thomas, J.E., Fornasiero, D., Gerson, A.R., 2006. The evolution of surface layers formed during chalcopyrite leaching. Geochim. Cosmochim. Acta 70, 4392–4402. Heyes, G., Trahar, W., 1977. The natural flotability of chalcopyrite. Int. J. Miner. Process. 4, 317–344. Heyes, G., Trahar, W., 1979. Oxidation-reduction effects in the flotation of chalcocite and cuprite. Int. J. Miner. Process. 6, 229–252. Hirajima, T., Miki, H., Suyantara, G.P.W., Matsuoka, H., Elmahdy, A.M., Sasaki, K., Imaizumi, Y., Kuroiwa, S., 2017. Selective flotation of chalcopyrite and molybdenite with H2O2 oxidation. Miner. Eng. 100, 83–92. Mccarron, J., Walker, G., Buckley, A., 1990. An X-ray photoelectron spectroscopic investigation of chalcopyrite and pyrite surfaces after conditioning in sodium sulfide solutions. Int. J. Miner. Process. 30, 1–16. Mcintyre, N., Cook, M., 1975. X-ray photoelectron studies on some oxides and hydroxides of cobalt, nickel, and copper. Anal. Chem. 47, 2208–2213. Mielczarski, J., 1987. XPS study of ethyl xanthate adsorption on oxidized surface of cuprous sulfide. J. Colloid Interface Sci. 120, 201–209. Mielczarski, J., Suoninen, E., 1988. XPS study of the oxidation of cuprous sulphide in aerated aqueous solutions. Colloids Surf. 33, 231–237. Newell, A., Skinner, W.M., Bradshaw, D., 2007. Restoring the floatability of oxidised sulfides using sulfidisation. Int. J. Miner. Process. 84, 108–117. Rosencwaig, A., Wertheim, G., Guggenheim, H., 1971. Origins of satellites on inner-shell photoelectron spectra. Phys. Rev. Lett. 27, 479. Senior, G., Trahar, W., 1991. The influence of metal hydroxides and collector on the flotation of chalcopyrite. Int. J. Miner. Process. 33, 321–341.
4. Conclusions A method for quantitatively relating the degree of mineral surface oxidation to copper sulphide flotation, which involves quantification of the proportions of hydrophilic and hydrophobic surface species by the surface sensitive technique XPS, has been developed. This will serve as 7
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T. Moimane, et al. Smart, R.S.C., 1991. Surface layers in base metal sulphide flotation. Miner. Eng. 4, 891–909. Smart, R.S.C., Skinner, W.M., Gerson, A.R., 1999. XPS of sulphide mineral surfaces: metaldeficient, polysulphides, defects and elemental sulphur. Surf. Interface Anal. 28, 101–105. Termes, S., Buckley, A., Gillard, R., 1987. 2p electron binding energies for the sulfur atoms in metal polysulfides. Inorg. Chim. Acta 126, 79–82. Vaughan, D., Becker, U., Wright, K., 1997. Sulphide mineral surfaces: theory and experiment. Int. J. Miner. Process. 51, 1–14. Wagner, C., 1990. Photoelectron and Auger energies and the Auger parameter: a data set.
Pract. Surf. Anal. Xiong, X., Hua, X., Zheng, Y., Lu, X., Li, S., Cheng, H., Xu, Q., 2018. Oxidation mechanism of chalcopyrite revealed by X-ray photoelectron spectroscopy and first principles studies. Appl. Surf. Sci. 427, 233–241. Yin, Q., Vaughan, D., England, K., Kelsall, G., Brandon, N., 2000. Surface oxidation of chalcopyrite (CuFeS2) in alkaline solutions. J. Electrochem. Soc. 147, 2945–2951. Zachwieja, J.B., Mccarron, J.J., Walker, G.W., Buckley, A.N., 1989. Correlation between the surface composition and collectorless flotation of chalcopyrite. J. Colloid Interface Sci. 132, 462–468.
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