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Preferential oxidation of chalcopyrite surface facets characterized by ToF-SIMS and SEM
Applied Surface Science 252 (2006) 7155–7158 www.elsevier.com/locate/apsusc
Preferential oxidation of chalcopyrite surface facets characterized by ToF-SIMS and SEM Mohammad Al-Harahsheh a, Frank Rutten b,*, David Briggs b, Sam Kingman a b
a School of Chemical, Environmental and Mining Engineering, The University of Nottingham, Nottingham NG7 2RD, UK Centre for Surface Chemical Analysis and School of Pharmacy, The University of Nottingham, Nottingham NG7 2RD, UK
Received 12 September 2005; accepted 15 February 2006 Available online 15 May 2006
Abstract The use of hydrometallurgical methods for the production of copper from chalcopyrite has become more attractive due to environmental drivers such as lower energy demand and less gaseous emissions such as SO2. Unfortunately, chalcopyrite is known to be a highly unreactive mineral in hydrometallurgical processes. This work reports that a freshly cleaved chalcopyrite surface exhibits highly selective reactivity depending on the exposed fracture planes. ToF-SIMS was used to qualitatively characterise various fracture planes from freshly cleaved chalcopyrite particles, prior to and after hydrometallurgical treatment (leaching). It was found that prior to treatment certain areas exhibit pronounced contamination from atmospheric hydrocarbons upon fracture, whereas others were highly unreactive and remarkably free from adventitious hydrocarbon contamination. The positive ion spectra recorded from these areas are indeed dominated by peaks from Fe and Cu elements and related compounds. The negative ion spectra for the reactive areas showed a high content of oxidised (sulphur) species. After leaching, the differences between the sites of low and high reactivity were more subtle than prior to this treatment, whereas SEM analysis showed clear evidence for selective attack of ferric sulphate to specific planes after such treatment. Attempts are made to rationalise these observations with regards to selective dissolution based on different exposed chemistries at various cleavage planes within chalcopyrite crystals. # 2006 Elsevier B.V. All rights reserved. Keywords: ToF-SIMS; Imaging; Chalcopyrite; Mining; Fracture surface; Metal extraction
1. Introduction Chalcopyrite (CuFeS2) is one of the most economically important copper sulphide minerals in terms of availability, and is the world’s major source of copper. The majority of copper is produced by breaking down chalcopyrite by heat, using socalled pyrometallurgical processing. Interest in hydrometallurgy (solution processes) has risen recently due to current drivers to protect the environment from sulphur dioxide emissions which occur during pyrometallurgical operations and also to reduce energy consumption. However, leaching of chalcopyrite for copper recovery is currently uneconomic due to the inert nature of chalcopyrite during oxidation in aqueous solutions. A number of theories have been proposed to account for the observed slow oxidation of chalcopyrite. It is suggested that formation of an elemental sulphur layer on the surface of * Corresponding author at: Boots Science Building, School of Pharmacy, The University of Nottingham, University Park, Nottingham NG7 2RD, UK. E-mail address: [email protected] (F. Rutten). 0169-4332/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2006.02.274
chalcopyrite may act as a diffusion barrier for the transport of ions and electrons [1,2]. Others suggest that this barrier layer is instead comprised of a copper-rich polysulphide layer, CuSn [3–5]. X-ray photoelectron spectroscopic (XPS) analysis conducted by Balaz et al. [6] revealed the existence of sulphur in three chemical forms, S2, S0 and S6+, when using combined bacterial and chemical leaching. In a similar study Klauber et al. [7] suggest the formation of elemental sulphur as a main product and disulphide S22 as a secondary one with no evidence for polysulphide chain formation beyond 2. Furthermore, it has been reported that elemental sulphur can be formed on selective sites and fissures on chalcopyrite fracture surfaces [8]. Dutrizac also showed that sulphur particles form at discrete sites on the surfaces of a ‘‘massive’’ (large, not size-selected) chalcopyrite particle [2]. This work showed that sulphur globules were different in size, suggesting deposition on preexisting sulphur grains via formation of H2S. The wide disagreement concerning the nature of the passivating layer necessitates substantial further research in this area. It is therefore very important to tackle the issue from
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different angles in an attempt to understand the mechanism by which chalcopyrite is oxidised and passivated. It is of particular interest to further explore and understand the nature of the selective reactivity of various fractured chalcopyrite surfaces. In this paper novel evidence on this subject based on ToF-SIMS and SEM is presented. ToF-SIMS as a monolayer surface analytical technique is used here in an attempt to provide further information about the nature of the passivating layer and the selective reactivity of various chalcopyrite surfaces. 2. Experimental Chalcopyrite samples were obtained from Gregory, Bottley and Lloyd (London, UK). Chemical analysis by ICP-AES showed it contained 33.9% Cu, 30.3% Fe and 35.6% S. Ferric sulphate leaching was carried out in 0.25 M Fe2(SO4)3–0.5 M H2SO4 at 90 8C, prepared using reagent grade H2SO4, Fe2(SO4)3.nH2O (all Aldrich) and Milli-Q (Millipore Corp.) ultrapure water. SEM evaluation was carried out in a Philips XL30 instrument using a beam voltage of 20 kV. The ToF-SIMS work was performed on a ToF-SIMS IV instrument (ION-TOF GmbH, Mu¨nster, Germany) equipped with a gallium liquid metal ion gun. Typical conditions include a pulsed current of 1.5 pA and an energy of 25 kV, analyzing an area of 500 mm 500 mm. Full raw datasets (RDS) were acquired throughout. To minimize potential contamination freshly prepared chalcopyrite samples were used for ToF-SIMS analysis, which were transferred into the vacuum chamber immediately after fracture. 3. Results 3.1. SEM analysis When chalcopyrite (38–53 mm) was leached for 3 h, no evidence was observed for attack, other than the formation of a small number of micron-sized sulphur globules. Only ca. 2% of the copper was extracted at this stage. Fig. 1 shows the same chalcopyrite particles after 10 h, when sulphur is observed on specific parts of some particles, whereas other planes are not affected.
Fig. 1. SEM back scattered image of chalcopyrite particles leached for 10 h.
3.2. ToF-SIMS analysis Samples were prepared by fracturing a piece of crystalline chalcopyrite (5 mm) using a carefully cleaned pestle and mortar. The freshly fractured particles were mounted and transferred to the ToF-SIMS chamber for analysis immediately after breakage. After analysis, the samples were removed from the chamber, carefully recording their position in the sample holder. The samples were then subjected to leaching for 3 h, carefully removed from the solution and washed several times with Milli-Q ultrapure water and left to dry in air for 30 min. The leached samples were mounted in exactly the same position as before leaching and loaded into the ToF-SIMS chamber for analysis. 3.2.1. Analysis of the freshly cleaved chalcopyrite surface Images were acquired from a number of locations on the sample in order to identify any differences on the surfaces exposed by fracture. This initial analysis revealed the presence of two distinctly different types of areas, esp. evident in C3H5+ ion maps (see insert in Fig. 2). Spectra were then generated from the RDS recorded during image acquisition from the two regions of interest (Fig. 2). The two areas seemed to have distinctly different reactivities: only one picking up significant amounts of hydrocarbons (HC) from the ambient atmosphere. This area was found to be rich in HCs as well as oxidized species (esp. oxy-sulphur species) (see pane A). Surprisingly, the other area strongly resembled what might be expected from a clean, pure chalcopyrite surface, the intensity of HC signals in this area being very low (pane B). Clearly pane B is dominated by peaks associated with Cu and Fe, whereas pane A shows a range of hydrocarbon peaks as well as peaks for Cu and Fe. The normalised intensities of a number of selected ions summarise this observation in Fig. 3, in which values for the high HC area are divided by those for the low HC area. Significant increases in the relative amounts of oxidized species (SOx and FeOx) and Sn species in high HC areas can be
Fig. 2. Positive spectra of a freshly fractured chalcopyrite surface obtained from regions of interest on C3H5+ ion map as indicated, collected from areas with (A) high and (B) low levels of HCs. Peak identifiers in brackets denote minor components.
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3.2.2. Analysis of the leached chalcopyrite surface Analysis after treatment showed less pronounced differences between the two types of sites identified before leaching. It is possible that the leaching was somewhat too aggressive for the very limited SIMS analysis depth, causing any potential differences between the two areas to have been smoothed out. However, the ratio of the oxidized species in the areas with high HC was still slightly higher than those obtained from the spectra of the surface with low HC. Further in-depth analysis of the acquired data from the leached surface falls outside the scope of this brief publication and will be considered in a future, more detailed publication.
in ferric sulphate solution due the galvanic interaction between the two minerals [11,12]. The difference in reactivity of various sites on chalcopyrite surfaces as well as other sulphide minerals could well be related to variation in the surface chemistry of different cleavage planes, which are moreover proposed to, in specific cases, undergo surface reconstruction resulting in the generation of 50% pyrite-like phase on particular cleavage planes [13,14], thus potentially leading to the formation of a more reactive chalcopyrite/pyrite-system as described above. In our SIMS spectra, ions like Cu+, Fe+, FeH+ and CuH+ dominate in regions with low HC coverage as is clearly evident from the freshly cleaved surface. This would be expected from a clean, pure chalcopyrite surface not exposed to any oxidative environment and not altered in a substantial way from the moment of fracture, thus exposing the bulk composition of that particular plane. However, ions like Fe2O+, CuS2+, Fe2S+, FeS2+, CuS+, Cu2S+ and FeS3+ can be seen in higher proportion across the HCrich area, suggesting that the latter have experienced significant alteration and oxidation upon fracture. One may therefore speculate that such a surface might represent the case where a reconstruction process, such as that proposed by Klauber [13], could have occurred. A similar trend can be observed for the negative ions: species like O, S, HS are more abundant on the non-treated surfaces containing low levels of HC, compared to those rich in HC. However, the ions related to oxidised oxysulphur species and Sn as well as clusters like FeO, CuS, CuO, FeS2, CuS2, FeS, CuO2, and Fe2O3 are significantly more intense in the spectra acquired from regions with high HC content. An especially interesting case concerns the thiosulphate ion S2O3, which is ca. eight times more prominent in the area with high HC levels. Thiosulphate is expected to form as a result of pyrite oxidation [15], therefore it can be speculated that S2O3 may well be an intermediate oxidation product of the pyrite-like surface which could be formed as a result of the proposed surface reconstruction. After treatment both areas show a trend similar to before treatment with, however, much reduced differences. The leaching time was appropriate for subsequent SEM analysis, however, it may well have been too harsh for the much more restricted analysis depth of SIMS. Further work is required to investigate the observed phenomena. An in-depth evaluation of the acquired data has been published elsewhere [16] as this falls outside the scope of the current paper.
4. Discussion
5. Conclusions
Examination of the SEM micrograph shown in Fig. 1 and the ToF-SIMS data shown in Figs. 2 and 3 suggests a preferential attack at particular fracture planes of the same particle of a freshly fractured chalcopyrite surface. Heterogeneous chemistry of mineral surfaces has previously been observed during froth flotation of sulphide minerals by ToF-SIMS and was attributed to mineral surface heterogeneity arising from defects, impurities, lattice imperfections and small variations in stoichiometry [9,10]. Furthermore, it was shown that when chalcopyrite is in intimate contact with pyrite (FeS2), it shows pronounced enhancement in the reactivity when it was leached
Preferential oxidation of specific chalcopyrite surfaces upon fracture was observed. SEM and ToF-SIMS analyses were used to characterize the selectivity of the different chalcopyrite areas with a view to hydrometallurgical processing. This selectivity appeared to be linked to the reactivity of the freshly cleaved chalcopyrite surface as determined using ToF-SIMS analysis. Fully understanding the selectivity of the oxidation process is crucially important for Cu extraction from chalcopyrite by hydrometallurgical means to become feasible, which would have important beneficial implications for the environment. This study highlights preliminary results of an investigation
Fig. 3. Ratio of relative intensity (normalised to total intensity) of area rich in hydrocarbon (Hi) to area low in hydrocarbons (Lo). Relative ratio = (IHi/TotHi)/ (ILo/TotLo). # indicates overlapping peaks.
observed. The ratio of negative species like O, S, HS, Cl and F was found to be very close to unity suggesting similar relative abundance of these species in both areas. However, the ratio of the oxidized sulphur species like Sn, MSn and SOn was found to be up to seven times higher in the areas with high HC contamination. This is indicative of superior oxidation and higher reactivity of those sites with high HC intensity upon exposure to air when fractured. Further evidence for this was obtained when the sums of the intensity of Sn, MSn and SOn species were (table in Fig. 3). The total normalized P compared signals of S for both n þ HS species are generally P the same P kinds of surfaces. However, the signals of SO MS n and n obtained from the HC regions are about 2.6 and 3 times higher than those obtained from the low HC area, respectively.
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into the heterogeneity of freshly cleaved chalcopyrite and its response to an oxidizing environment. References [1] M.M. Antonijevic, Z. Jankovic, M. Dimitijevic, Hydrometallurgy 35 (1994) 187. [2] J.E. Dutrizac, Can. Metall. Quart. 28 (1989) 337. [3] R.P. Hackl, D.B. Dreisinger, E. Peters, J.A. King, Hydrometallurgy 39 (1995) 25. [4] H.G. Linge, Hydrometallurgy 2 (1976) 51–64. [5] A.J. Parker, R.L. Paul, G.P. Power, J. Electroanal. Chem. 118 (1981) 305. [6] P. Balaz, D. Kupka, Z. Bastl, M. Achimovicova, Hydrometallurgy 42 (1996) 237.
[7] C. Klauber, A. Parker, W. Van Bronswijk, H. Watling, Int. J. Miner. Process. 62 (2001) 65. [8] D.L. Jones, E. Peters, in: J.C. Yannopoulos, J.C. Agarwal (Eds.), Extractive Metallurgy of Copper, AIME, New York, 1976, pp. 632–653. [9] J. Duan, D. Fornasiero, J. Ralston, Int. J. Miner. Process. 72 (2003) 227. [10] C. Piantadosi, R.S.C. Smart, Int. J. Miner. Process. 64 (2002) 43. [11] M. Al-Harahsheh, PhD Thesis, University of Nottingham, Nottingham, UK, 2005. [12] A.P. Mehta, L.E. Murr, Hydrometallurgy 9 (1983) 235. [13] C. Klauber, Surf. Interf. Anal. 35 (2003) 415. [14] D.J. Vaughan, U. Becker, K. Wright, Int. J. Miner. Process. 51 (1997) 1. [15] J.D. Rimstidt, D.J. Vaughan, Geochim. Cosmochim. Acta 67 (2003) 873. [16] M. Al-Harahsheh, F.J.M. Rutten, D. Briggs, S. Kingman, Int. J. Miner. Process., in press.
Preferential oxidation of chalcopyrite surface facets characterized by ToF-SIMS and SEM Mohammad Al-Harahsheh a, Frank Rutten b,*, David Briggs b, Sam Kingman a b
a School of Chemical, Environmental and Mining Engineering, The University of Nottingham, Nottingham NG7 2RD, UK Centre for Surface Chemical Analysis and School of Pharmacy, The University of Nottingham, Nottingham NG7 2RD, UK
Received 12 September 2005; accepted 15 February 2006 Available online 15 May 2006
Abstract The use of hydrometallurgical methods for the production of copper from chalcopyrite has become more attractive due to environmental drivers such as lower energy demand and less gaseous emissions such as SO2. Unfortunately, chalcopyrite is known to be a highly unreactive mineral in hydrometallurgical processes. This work reports that a freshly cleaved chalcopyrite surface exhibits highly selective reactivity depending on the exposed fracture planes. ToF-SIMS was used to qualitatively characterise various fracture planes from freshly cleaved chalcopyrite particles, prior to and after hydrometallurgical treatment (leaching). It was found that prior to treatment certain areas exhibit pronounced contamination from atmospheric hydrocarbons upon fracture, whereas others were highly unreactive and remarkably free from adventitious hydrocarbon contamination. The positive ion spectra recorded from these areas are indeed dominated by peaks from Fe and Cu elements and related compounds. The negative ion spectra for the reactive areas showed a high content of oxidised (sulphur) species. After leaching, the differences between the sites of low and high reactivity were more subtle than prior to this treatment, whereas SEM analysis showed clear evidence for selective attack of ferric sulphate to specific planes after such treatment. Attempts are made to rationalise these observations with regards to selective dissolution based on different exposed chemistries at various cleavage planes within chalcopyrite crystals. # 2006 Elsevier B.V. All rights reserved. Keywords: ToF-SIMS; Imaging; Chalcopyrite; Mining; Fracture surface; Metal extraction
1. Introduction Chalcopyrite (CuFeS2) is one of the most economically important copper sulphide minerals in terms of availability, and is the world’s major source of copper. The majority of copper is produced by breaking down chalcopyrite by heat, using socalled pyrometallurgical processing. Interest in hydrometallurgy (solution processes) has risen recently due to current drivers to protect the environment from sulphur dioxide emissions which occur during pyrometallurgical operations and also to reduce energy consumption. However, leaching of chalcopyrite for copper recovery is currently uneconomic due to the inert nature of chalcopyrite during oxidation in aqueous solutions. A number of theories have been proposed to account for the observed slow oxidation of chalcopyrite. It is suggested that formation of an elemental sulphur layer on the surface of * Corresponding author at: Boots Science Building, School of Pharmacy, The University of Nottingham, University Park, Nottingham NG7 2RD, UK. E-mail address: [email protected] (F. Rutten). 0169-4332/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2006.02.274
chalcopyrite may act as a diffusion barrier for the transport of ions and electrons [1,2]. Others suggest that this barrier layer is instead comprised of a copper-rich polysulphide layer, CuSn [3–5]. X-ray photoelectron spectroscopic (XPS) analysis conducted by Balaz et al. [6] revealed the existence of sulphur in three chemical forms, S2, S0 and S6+, when using combined bacterial and chemical leaching. In a similar study Klauber et al. [7] suggest the formation of elemental sulphur as a main product and disulphide S22 as a secondary one with no evidence for polysulphide chain formation beyond 2. Furthermore, it has been reported that elemental sulphur can be formed on selective sites and fissures on chalcopyrite fracture surfaces [8]. Dutrizac also showed that sulphur particles form at discrete sites on the surfaces of a ‘‘massive’’ (large, not size-selected) chalcopyrite particle [2]. This work showed that sulphur globules were different in size, suggesting deposition on preexisting sulphur grains via formation of H2S. The wide disagreement concerning the nature of the passivating layer necessitates substantial further research in this area. It is therefore very important to tackle the issue from
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different angles in an attempt to understand the mechanism by which chalcopyrite is oxidised and passivated. It is of particular interest to further explore and understand the nature of the selective reactivity of various fractured chalcopyrite surfaces. In this paper novel evidence on this subject based on ToF-SIMS and SEM is presented. ToF-SIMS as a monolayer surface analytical technique is used here in an attempt to provide further information about the nature of the passivating layer and the selective reactivity of various chalcopyrite surfaces. 2. Experimental Chalcopyrite samples were obtained from Gregory, Bottley and Lloyd (London, UK). Chemical analysis by ICP-AES showed it contained 33.9% Cu, 30.3% Fe and 35.6% S. Ferric sulphate leaching was carried out in 0.25 M Fe2(SO4)3–0.5 M H2SO4 at 90 8C, prepared using reagent grade H2SO4, Fe2(SO4)3.nH2O (all Aldrich) and Milli-Q (Millipore Corp.) ultrapure water. SEM evaluation was carried out in a Philips XL30 instrument using a beam voltage of 20 kV. The ToF-SIMS work was performed on a ToF-SIMS IV instrument (ION-TOF GmbH, Mu¨nster, Germany) equipped with a gallium liquid metal ion gun. Typical conditions include a pulsed current of 1.5 pA and an energy of 25 kV, analyzing an area of 500 mm 500 mm. Full raw datasets (RDS) were acquired throughout. To minimize potential contamination freshly prepared chalcopyrite samples were used for ToF-SIMS analysis, which were transferred into the vacuum chamber immediately after fracture. 3. Results 3.1. SEM analysis When chalcopyrite (38–53 mm) was leached for 3 h, no evidence was observed for attack, other than the formation of a small number of micron-sized sulphur globules. Only ca. 2% of the copper was extracted at this stage. Fig. 1 shows the same chalcopyrite particles after 10 h, when sulphur is observed on specific parts of some particles, whereas other planes are not affected.
Fig. 1. SEM back scattered image of chalcopyrite particles leached for 10 h.
3.2. ToF-SIMS analysis Samples were prepared by fracturing a piece of crystalline chalcopyrite (5 mm) using a carefully cleaned pestle and mortar. The freshly fractured particles were mounted and transferred to the ToF-SIMS chamber for analysis immediately after breakage. After analysis, the samples were removed from the chamber, carefully recording their position in the sample holder. The samples were then subjected to leaching for 3 h, carefully removed from the solution and washed several times with Milli-Q ultrapure water and left to dry in air for 30 min. The leached samples were mounted in exactly the same position as before leaching and loaded into the ToF-SIMS chamber for analysis. 3.2.1. Analysis of the freshly cleaved chalcopyrite surface Images were acquired from a number of locations on the sample in order to identify any differences on the surfaces exposed by fracture. This initial analysis revealed the presence of two distinctly different types of areas, esp. evident in C3H5+ ion maps (see insert in Fig. 2). Spectra were then generated from the RDS recorded during image acquisition from the two regions of interest (Fig. 2). The two areas seemed to have distinctly different reactivities: only one picking up significant amounts of hydrocarbons (HC) from the ambient atmosphere. This area was found to be rich in HCs as well as oxidized species (esp. oxy-sulphur species) (see pane A). Surprisingly, the other area strongly resembled what might be expected from a clean, pure chalcopyrite surface, the intensity of HC signals in this area being very low (pane B). Clearly pane B is dominated by peaks associated with Cu and Fe, whereas pane A shows a range of hydrocarbon peaks as well as peaks for Cu and Fe. The normalised intensities of a number of selected ions summarise this observation in Fig. 3, in which values for the high HC area are divided by those for the low HC area. Significant increases in the relative amounts of oxidized species (SOx and FeOx) and Sn species in high HC areas can be
Fig. 2. Positive spectra of a freshly fractured chalcopyrite surface obtained from regions of interest on C3H5+ ion map as indicated, collected from areas with (A) high and (B) low levels of HCs. Peak identifiers in brackets denote minor components.
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3.2.2. Analysis of the leached chalcopyrite surface Analysis after treatment showed less pronounced differences between the two types of sites identified before leaching. It is possible that the leaching was somewhat too aggressive for the very limited SIMS analysis depth, causing any potential differences between the two areas to have been smoothed out. However, the ratio of the oxidized species in the areas with high HC was still slightly higher than those obtained from the spectra of the surface with low HC. Further in-depth analysis of the acquired data from the leached surface falls outside the scope of this brief publication and will be considered in a future, more detailed publication.
in ferric sulphate solution due the galvanic interaction between the two minerals [11,12]. The difference in reactivity of various sites on chalcopyrite surfaces as well as other sulphide minerals could well be related to variation in the surface chemistry of different cleavage planes, which are moreover proposed to, in specific cases, undergo surface reconstruction resulting in the generation of 50% pyrite-like phase on particular cleavage planes [13,14], thus potentially leading to the formation of a more reactive chalcopyrite/pyrite-system as described above. In our SIMS spectra, ions like Cu+, Fe+, FeH+ and CuH+ dominate in regions with low HC coverage as is clearly evident from the freshly cleaved surface. This would be expected from a clean, pure chalcopyrite surface not exposed to any oxidative environment and not altered in a substantial way from the moment of fracture, thus exposing the bulk composition of that particular plane. However, ions like Fe2O+, CuS2+, Fe2S+, FeS2+, CuS+, Cu2S+ and FeS3+ can be seen in higher proportion across the HCrich area, suggesting that the latter have experienced significant alteration and oxidation upon fracture. One may therefore speculate that such a surface might represent the case where a reconstruction process, such as that proposed by Klauber [13], could have occurred. A similar trend can be observed for the negative ions: species like O, S, HS are more abundant on the non-treated surfaces containing low levels of HC, compared to those rich in HC. However, the ions related to oxidised oxysulphur species and Sn as well as clusters like FeO, CuS, CuO, FeS2, CuS2, FeS, CuO2, and Fe2O3 are significantly more intense in the spectra acquired from regions with high HC content. An especially interesting case concerns the thiosulphate ion S2O3, which is ca. eight times more prominent in the area with high HC levels. Thiosulphate is expected to form as a result of pyrite oxidation [15], therefore it can be speculated that S2O3 may well be an intermediate oxidation product of the pyrite-like surface which could be formed as a result of the proposed surface reconstruction. After treatment both areas show a trend similar to before treatment with, however, much reduced differences. The leaching time was appropriate for subsequent SEM analysis, however, it may well have been too harsh for the much more restricted analysis depth of SIMS. Further work is required to investigate the observed phenomena. An in-depth evaluation of the acquired data has been published elsewhere [16] as this falls outside the scope of the current paper.
4. Discussion
5. Conclusions
Examination of the SEM micrograph shown in Fig. 1 and the ToF-SIMS data shown in Figs. 2 and 3 suggests a preferential attack at particular fracture planes of the same particle of a freshly fractured chalcopyrite surface. Heterogeneous chemistry of mineral surfaces has previously been observed during froth flotation of sulphide minerals by ToF-SIMS and was attributed to mineral surface heterogeneity arising from defects, impurities, lattice imperfections and small variations in stoichiometry [9,10]. Furthermore, it was shown that when chalcopyrite is in intimate contact with pyrite (FeS2), it shows pronounced enhancement in the reactivity when it was leached
Preferential oxidation of specific chalcopyrite surfaces upon fracture was observed. SEM and ToF-SIMS analyses were used to characterize the selectivity of the different chalcopyrite areas with a view to hydrometallurgical processing. This selectivity appeared to be linked to the reactivity of the freshly cleaved chalcopyrite surface as determined using ToF-SIMS analysis. Fully understanding the selectivity of the oxidation process is crucially important for Cu extraction from chalcopyrite by hydrometallurgical means to become feasible, which would have important beneficial implications for the environment. This study highlights preliminary results of an investigation
Fig. 3. Ratio of relative intensity (normalised to total intensity) of area rich in hydrocarbon (Hi) to area low in hydrocarbons (Lo). Relative ratio = (IHi/TotHi)/ (ILo/TotLo). # indicates overlapping peaks.
observed. The ratio of negative species like O, S, HS, Cl and F was found to be very close to unity suggesting similar relative abundance of these species in both areas. However, the ratio of the oxidized sulphur species like Sn, MSn and SOn was found to be up to seven times higher in the areas with high HC contamination. This is indicative of superior oxidation and higher reactivity of those sites with high HC intensity upon exposure to air when fractured. Further evidence for this was obtained when the sums of the intensity of Sn, MSn and SOn species were (table in Fig. 3). The total normalized P compared signals of S for both n þ HS species are generally P the same P kinds of surfaces. However, the signals of SO MS n and n obtained from the HC regions are about 2.6 and 3 times higher than those obtained from the low HC area, respectively.
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into the heterogeneity of freshly cleaved chalcopyrite and its response to an oxidizing environment. References [1] M.M. Antonijevic, Z. Jankovic, M. Dimitijevic, Hydrometallurgy 35 (1994) 187. [2] J.E. Dutrizac, Can. Metall. Quart. 28 (1989) 337. [3] R.P. Hackl, D.B. Dreisinger, E. Peters, J.A. King, Hydrometallurgy 39 (1995) 25. [4] H.G. Linge, Hydrometallurgy 2 (1976) 51–64. [5] A.J. Parker, R.L. Paul, G.P. Power, J. Electroanal. Chem. 118 (1981) 305. [6] P. Balaz, D. Kupka, Z. Bastl, M. Achimovicova, Hydrometallurgy 42 (1996) 237.
[7] C. Klauber, A. Parker, W. Van Bronswijk, H. Watling, Int. J. Miner. Process. 62 (2001) 65. [8] D.L. Jones, E. Peters, in: J.C. Yannopoulos, J.C. Agarwal (Eds.), Extractive Metallurgy of Copper, AIME, New York, 1976, pp. 632–653. [9] J. Duan, D. Fornasiero, J. Ralston, Int. J. Miner. Process. 72 (2003) 227. [10] C. Piantadosi, R.S.C. Smart, Int. J. Miner. Process. 64 (2002) 43. [11] M. Al-Harahsheh, PhD Thesis, University of Nottingham, Nottingham, UK, 2005. [12] A.P. Mehta, L.E. Murr, Hydrometallurgy 9 (1983) 235. [13] C. Klauber, Surf. Interf. Anal. 35 (2003) 415. [14] D.J. Vaughan, U. Becker, K. Wright, Int. J. Miner. Process. 51 (1997) 1. [15] J.D. Rimstidt, D.J. Vaughan, Geochim. Cosmochim. Acta 67 (2003) 873. [16] M. Al-Harahsheh, F.J.M. Rutten, D. Briggs, S. Kingman, Int. J. Miner. Process., in press.