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Flotation separation behavior of chalcopyrite and sphalerite in the presence of locust bean gum
Minerals Engineering 143 (2019) 105940
Contents lists available at ScienceDirect
Minerals Engineering journal homepage: www.elsevier.com/locate/mineng
Flotation separation behavior of chalcopyrite and sphalerite in the presence of locust bean gum
T
⁎
Bo Fenga,b, Yutao Guoa, Wenpu Zhanga, Jinxiu Penga, Huihui Wanga, Zhiqiang Huanga, , Xiaotong Zhoub a b
Jiangxi Key Laboratory of Mining Engineering, Jiangxi University of Science and Technology, Ganzhou, China State Key Laboratory of Rare Metals Separation and Comprehensive Utilization, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Chalcopyrite Sphalerite Locust bean gum Separation Adsorption mechanism
Locust bean gum was tested as a potential selective depressant in the flotation separation of chalcopyrite and sphalerite using potassium butyl xanthate (PBX) as collector. In single mineral flotation, locust bean gum depressed sphalerite, while chalcopyrite was floatable. This illustrated that locust bean gum could be used to separate chalcopyrite from sphalerite. Adsorption tests and zeta potential measurements indicated that locust bean gum can adsorb on the surfaces of both chalcopyrite and sphalerite, but the adsorption amount on sphalerite was higher than that on chalcopyrite. XPS analysis showed that locust bean gum adsorbed on the sphalerite surface through chemical interaction between ZnOH or ZnO on the sphalerite surface and hydroxyl groups of locust bean gum. Locust bean gum adsorbed more easily on the sphalerite surface, perhaps due to sphalerite being easier to oxidize than chalcopyrite.
1. Introduction Sulfide minerals are major sources of base metals, such as copper, lead, zinc, and nickel. For economic and technological reasons, the mineral feed to metal smelters must meet high-grade and low-impurity requirements. However, sulfide minerals are always interlaced with other sulfide and nonsulfide minerals in an ore (Huang, 2013). Therefore, to meet smelter requirements, froth flotation is used to improve the content of a specific sulfide mineral in an ore and remove deleterious impurities (Bulatovic, 2007). In the flotation separation of complex sulfide ores, depressants are usually added to selectively prevent a certain mineral from floating (Bıçak et al., 2012; Chandra and Gerson, 2009). Most depressants currently used in the sulfide flotation industry are inorganic depressants, such as sodium cyanide (NaCN), potassium dichromate (K2Cr2O7), and lime (CaO) (El-Shall et al., 2000; Mu et al., 2016). These inorganic depressants are highly effective, but toxic and hazardous, resulting in potential harm to both humans and the environment. Much research has focused on studying potential nontoxic replacements for toxic inorganic depressants (Gül et al., 2008; Sarquís et al., 2014). Naturally occurring polymers, such as starch, dextrin, cellulose, and guar gum, have been tested or used as selective depressants (Liu and Zhang 2000; Pawlik et al., 2003; Shortridge et al., 2000; Wang
⁎
et al., 2005). The adsorption mechanism between polysaccharides and minerals is complex (Bulatovic, 2007). However, the lack of thorough understanding regarding the adsorption mechanism of polysaccharides on minerals hinders their application in mineral processing (Laskowski et al., 2007). Locust bean gum is a galactomannan vegetable gum extracted from seeds of the carob tree and has been used as a useful depressant for the flotation separation of chalcopyrite from talc (Feng et al., 2018). However, locust bean gum has yet to be used as a depressant in Cu–Zn separation. This study aimed to determine the role of locust bean gum in the flotation of chalcopyrite and sphalerite, while the adsorption mechanism of locust bean gum on sphalerite is also discussed. 2. Materials and methods 2.1. Samples and reagents Natural chalcopyrite and sphalerite samples used in this study were purchased from the Mineral Specimens Laboratory, Zhejiang University, China. The samples were crushed and those with high purity were selected. These samples were then ground and screened to collect the desired fractions. Mineral particles of −150 + 37 μm were selected for microflotation and adsorption tests. Mineral particles of −10 μm
Corresponding author. E-mail address: [email protected] (Z. Huang).
https://doi.org/10.1016/j.mineng.2019.105940 Received 8 April 2019; Received in revised form 12 August 2019; Accepted 13 August 2019 Available online 23 August 2019 0892-6875/ © 2019 Elsevier Ltd. All rights reserved.
Minerals Engineering 143 (2019) 105940
B. Feng, et al.
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2θ(degree) Fig. 1. XRD diagrams of chalcopyrite and sphalerite.
represent one standard deviation around the average value.
Table 1 Elemental analysis results for chalcopyrite and sphalerite (%). Sample
Cu
Fe
S
Zn
Chalcopyrite Sphalerite
32.91 0.07
29.06 –
33.25 31.56
– 64.39
2.4. Zeta potential measurements Zeta potential measurements were performed using a ZetaPALS Zeta Potential Analyzer. These experiments were conducted at room temperature using KCl solution (1 mM). A mineral powder sample (1 g) was mixed with the KCl solution (50 mL). The pH was adjusted to the desired value and maintained by adding HCl and KOH solutions. Locust bean gum was added and conditioned for 10 min. The mineral suspension was then poured into a rectangular cell in which electrodes were inserted for measurement. Each experiment was conducted three times, with the average value reported. Error bars represent one standard deviation around the average value.
were used in zeta potential and XPS tests. According to XRD (Fig. 1) and elemental analyses (Table 1), the purity of chalcopyrite was 95.23% (Cu 32.91%) and the purity of sphalerite was 95.95% (Zn 64.39%). The specific surface areas of the minerals were analyzed using the Brunauer–Emmett–Teller (BET) method. The specific surface areas of chalcopyrite and sphalerite were 0.476 and 0.155 m2/g, respectively. Locust bean gum (molecular weight, 250,000–300,000) and collector potassium butyl xanthate (PBX) were purchased from Shanghai Siyu Chemical Technology Co., Ltd. Hydrochloric acid (HCl) and potassium hydroxide (KOH) were used as pH modifiers. Potassium chloride (KCl) was used to prepare the supporting electrolyte solution. All reagents used in this study were of analytical-grade purity. Distilled water was used in all tests.
2.5. X-ray photoelectron spectroscopy (XPS) For XPS analysis, sphalerite (1 g) was mixed with locust bean gum solution at a concentration of 100 mg/L and pH 7. The suspension was conditioned for 30 min, and the mineral solids were filtered, washed with distilled water, and dried under vacuum before XPS analysis. To minimize oxidation, XPS analysis was performed within 12 h of sample preparation, conducted using an AXIS 165 X-ray photoelectron spectrometer (Kratos Analytical).
2.2. Flotation tests For the single mineral flotation tests, sphalerite or chalcopyrite particles (2 g) were precleaned in HCl solution (0.1 mol/L). After rinsing with distilled water and filtering several times, the particles were mixed with distilled water (40 mL) in a 50-mL flotation cell. Locust bean gum was added as depressant, followed by an amount of PBX, and then the pH was immediately adjusted to the desired value with HCl and KOH. After adding frother methylisobutylcarbinol (MIBC), the pulp was floated for 3 min. The mineral recovery was calculated from the dry weights of the flotation concentrates and tails. Each experiment was conducted three times, with the average value reported. Error bars represent one standard deviation around the average value.
3. Results and discussion The effect of pH on the flotation of chalcopyrite and sphalerite was studied, with the results shown in Fig. 2. PBX had a good collecting ability for both sulfides, with pH having little effect on sulfide flotation. The recoveries of both chalcopyrite and sphalerite were very high at all tested pH levels when the PBX concentration was 1 × 10−4 mol/L. The results indicated that separating chalcopyrite and sphalerite was not possible in the absence of a depressant. The effect of PBX dosage on the flotation of chalcopyrite and sphalerite at pH 7 was studied, with the results shown in Fig. 3. The recoveries of both chalcopyrite and sphalerite increased with increasing PBX dosage, reaching maximum values when the PBX dosage was 2 × 10−4 mol/L. Fig. 4 shows the effect of locust bean gum dosage on the flotation of chalcopyrite and sphalerite. These results indicated that sphalerite was apparently depressed by locust bean gum, with its recovery sharply decreased from 83% to 0% by 400 kg/t of locust bean gum. However, the chalcopyrite recovery was only slightly affected, remaining at around 70% when the locust bean gum dosage exceeded 400 kg/t. The depression effect of locust bean gum on chalcopyrite and sphalerite at different pH values was also studied, with the results
2.3. Adsorption tests For the adsorption tests, sphalerite or chalcopyrite powder (1 g) was placed in a beaker with distilled water (100 mL) and mixed for 3 min. Locust bean gum solution of the desired concentration was added and mixed for a further 1 h, ensuring that the adsorption process had reached equilibrium. The slurry was then centrifuged and the locust bean gum concentration remaining in the supernatant was measured by determining the total organic carbon (TOC) content of the supernatant using a TOC analyzer (vario TOC, ELEMENTAR, Germany). This value was compared to a known calibration standard. Each experiment was conducted three times, with the average value reported. Error bars 2
Minerals Engineering 143 (2019) 105940
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Fig. 2. Effect of pH on the flotation of chalcopyrite and sphalerite (c (PBX) = 1 × 10−4 mol/L).
Fig. 5. Effect of pH on the depression effect of locust bean gum (c (PBX) = 1 × 10−4 mol/L, pH 7, c(locust bean gum) = 2 kg/t).
120
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Fig. 3. Effect of PBX dosage on the flotation of chalcopyrite and sphalerite.
Fig. 6. Adsorption behavior of locust bean gum on chalcopyrite and sphalerite. 100
80
Chalcopyrite Chalcopyrite+Locust bean gum Sphalerite Sphalerite+Locust bean gum
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Fig. 4. Effect of locust bean gum on the flotation of chalcopyrite and sphalerite (c(PBX) = 1 × 10−4 mol/L; pH = 7).
Fig. 7. Zeta potential of chalcopyrite and sphalerite with and without locust bean gum at different pH values.
shown in Fig. 5. The depression effect of locust bean gum on sphalerite was strong at all tested pH values, with the sphalerite recovery slightly decreasing with increasing pH. In contrast, the depression effect of
locust bean gum on chalcopyrite was weak in the pH range of 3–9, and the chalcopyrite recovery significantly decreased when the pH 3
Minerals Engineering 143 (2019) 105940
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C1s
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Fig. 8. XPS spectra of sphalerite (a) without and (b) with locust bean gum.
gum was adsorbed on the surfaces of both minerals. XPS was used to investigate the adsorption mechanism of locust bean gum on sphalerite. Characteristic photoelectron spectra and peaks were detected for zinc, sulfur, oxygen, and carbon, as shown in Fig. 8. Atomic concentrations of the different elements present on the surface were also determined based on the intensity of the signals produced, with the results shown in Table 2. The relative elemental atomic concentrations before adding locust bean gum were as follows: Zn 2p, 36.46%; S 2p, 32.95%; C 1s, 14.4%; O 1s, 14.99%. The appearance of carbon on the sphalerite surface before adding locust bean gum was attributed to hydrocarbon contamination (Boulton et al., 2003; Fairthorne et al., 1997). After adding locust bean gum, the relative elemental atomic concentrations changed to the following: Zn 2p, 14.92%; S 2p, 15.70%; C 1s, 39.08%; O 1s, 30.30%. The increased relative concentrations of in carbon and oxygen showed that locust bean gum had adsorbed on the sphalerite surface. The XPS spectrums of Zn 2p were then collected on sphalerite before and after adding locust bean gum, with the results shown in Fig. 9. Fig. 9(a) shows the Zn 2p spectrum before adding locust bean gum, which was fitted by two peaks, comprising a peak at 1021.14 eV, assigned to ZnS, and a lower intensity peak at 1022.76 eV, assigned to ZnOH or ZnO (Deroubaix and Marcus, 2010; Skinner et al., 1996). Fig. 9(b) shows the Zn 2p spectrum of sphalerite after locust bean gum treatment. Compared with pure sphalerite, the binding energy of ZnS did not change, while the binding energy of ZnOH or ZnO changed from
Table 2 Relative elemental atomic concentrations (%) of sphalerite before and after interacting with locust bean gum. Elements
Sphalerite Sphalerite + locust bean gum
Content Zn 2p
S 2p
C 1s
O 1s
36.46 14.92
32.95 15.70
14.40 39.08
14.99 30.30
exceeded 9. This result indicated that locust bean gum could be used as a depressant to separate sphalerite from chalcopyrite in the pH range of 3–9. The adsorption behavior of locust bean gum on chalcopyrite and sphalerite at pH 7 is shown as Fig. 6. Locust bean gum showed similar adsorption behavior on chalcopyrite and sphalerite, with the adsorption amount increasing as the amount added increased. However, the amount adsorbed on sphalerite was larger than that on chalcopyrite. Fig. 7 shows the effect of pH on the zeta potential values of chalcopyrite and sphalerite before and after adding locust bean gum. In the absence of locust bean gum, both chalcopyrite and sphalerite showed positive zeta potential values in strong acidic solutions, which decreased with increasing pH, with isoelectric points (IEPs) of about 3.5 and 3, respectively. After adding locust bean gum (100 mg/L), the zeta potential magnitudes of both chalcopyrite and sphalerite decreased, but the IEP and signs did not change. This result indicated that locust bean
a
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b
1030
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1025
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Binding energy(eV)
Binding energy(eV)
Fig. 9. Resolved narrow-scan Zn 2p spectra of sphalerite before and after treatment with locust bean gum. 4
1015
Minerals Engineering 143 (2019) 105940
B. Feng, et al.
References
1022.76 to 1021.08 eV. This indicated that oxides on the sphalerite surface participated in the interaction between sphalerite and locust bean gum, and that the interaction was chemical.
Bıçak, Ö., Ekmekçi, Z., Can, M., Öztürk, Y., 2012. The effect of water chemistry on froth stability and surface chemistry of the flotation of a Cu–Zn sulfide ore. Int. J. Miner. Process. 102, 32–37. Boulton, A., Fornasiero, D., Ralston, J., 2003. Characterisation of sphalerite and pyrite flotation samples by XPS and ToF-SIMS. Int. J. Miner. Process. 70 (1–4), 205–219. Bulatovic, S.M., 2007. Handbook of Flotation Reagents: Chemistry, Theory and Practice: Volume 1: Flotation of Sulfide Ores. Elsevier. Chandra, A.P., Gerson, A.R., 2009. A review of the fundamental studies of the copper activation mechanisms for selective flotation of the sulfide minerals, sphalerite and pyrite. Adv. Coll. Inter. Sci. 145 (1–2), 97–110. Deroubaix, G., Marcus, P., 2010. X-ray photoelectron spectroscopy analysis of copper and zinc oxides and sulphides. Surf. Inter. Anal. 18 (1), 39–46. El-Shall, H.E., Elgillani, D.A., Abdel-Khalek, N.A., 2000. Role of zinc sulfate in depression of lead-activated sphalerite. Int. J. Miner. Process. 58 (1–4), 67–75. Fairthorne, G., Fornasiero, D., Ralston, J., 1997. Effect of oxidation on the collectorless flotation of chalcopyrite. Int. J. Miner. Process. 49 (1–2), 31–48. Feng, B., Peng, J., Zhang, W., Ning, X., Guo, Y., Zhang, W., 2018. Use of locust bean gum in flotation separation of chalcopyrite and talc. Miner. Eng. 122, 79–83. Gül, A., Yüce, A.E., Sirkeci, A.A., Özer, M., 2008. Use of non-toxic depressants in the selective flotation of copper-lead-zinc ores. Can. Metall. Q. 47 (2), 111–118. Huang, P., 2013. Chitosan in differential flotation of base metal sulfides. Laskowski, J.S., Liu, Q., O'Connor, C.T., 2007. Current understanding of the mechanism of polysaccharide adsorption at the mineral/aqueous solution interface. Int. J. Miner. Process. 84 (1–4), 59–68. Liu, Q., Zhang, Y., 2000. Effect of calcium ions and citric acid on the flotation separation of chalcopyrite from galena using dextrin. Miner. Eng. 13 (13), 1405–1416. Mu, Y., Peng, Y., Lauten, R.A., 2016. The depression of pyrite in selective flotation by different reagent systems–a literature review. Miner. Eng. 96, 143–156. Pawlik, M., Laskowski, J.S., Ansari, A., 2003. Effect of carboxymethyl cellulose and ionic strength on stability of mineral suspensions in potash ore flotation systems. J. Coll. Inter. Sci. 260 (2), 251–258. Sarquís, P.E., Menéndez-Aguado, J.M., Mahamud, M.M., Dzioba, R., 2014. Tannins: the organic depressants alternative in selective flotation of sulfides. J. Cleaner Prod. 84, 723–726. Shortridge, P.G., Harris, P.J., Bradshaw, D.J., Koopal, L.K., 2000. The effect of chemical composition and molecular weight of polysaccharide depressants on the flotation of talc. Int. J. Miner. Process. 59 (3), 215–224. Skinner, W.M., Prestidge, C.A., Smart, R.S.C., 1996. Irradiation effects during XPS studies of Cu(II) activation of zinc sulphide. Surf. Inter. Anal. 24 (9), 620–626. Wang, J., Somasundaran, P., Nagaraj, D.R., 2005. Adsorption mechanism of guar gum at solid–liquid interfaces. Miner. Eng. 18 (1), 77–81.
4. Conclusions The major conclusions of this study were as follows: (i) PBX showed a good collecting ability for both chalcopyrite and sphalerite. Locust bean gum had a strong depression effect on sphalerite, but a weak depression effect on chalcopyrite. (ii) Locust bean gum was adsorbed on the surface of both chalcopyrite and sphalerite, but the amount of locust bean gum adsorbed on sphalerite was larger than that on chalcopyrite. (iii) Locust bean gum adsorbed on the sphalerite surface through a chemical interaction between ZnOH or ZnO on the sphalerite surface and hydroxyl groups on locust bean gum. Locust bean gum adsorbed more easily on the sphalerite surface, perhaps because sphalerite was easier to oxidize than chalcopyrite.
Acknowledgements The authors acknowledge the support of Natural Science Foundation of China (51664020), Natural Science Foundation of Jiangxi Province (Nos. 20181BAB206021), The Research Fund Program of State Key Laboratory of Rare Metals Separation and Comprehensive Utilization (Gk-201801), College Students' Innovation and Entrepreneurship Training Program (201710407024) and Jiangxi Youth Jinggang Scholar Award Program. We thank Simon Partridge, PhD, from Liwen Bianji, Edanz Editing China (www.liwenbianji.cn/ac), for editing the English text of a draft of this manuscript.
5
Contents lists available at ScienceDirect
Minerals Engineering journal homepage: www.elsevier.com/locate/mineng
Flotation separation behavior of chalcopyrite and sphalerite in the presence of locust bean gum
T
⁎
Bo Fenga,b, Yutao Guoa, Wenpu Zhanga, Jinxiu Penga, Huihui Wanga, Zhiqiang Huanga, , Xiaotong Zhoub a b
Jiangxi Key Laboratory of Mining Engineering, Jiangxi University of Science and Technology, Ganzhou, China State Key Laboratory of Rare Metals Separation and Comprehensive Utilization, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Chalcopyrite Sphalerite Locust bean gum Separation Adsorption mechanism
Locust bean gum was tested as a potential selective depressant in the flotation separation of chalcopyrite and sphalerite using potassium butyl xanthate (PBX) as collector. In single mineral flotation, locust bean gum depressed sphalerite, while chalcopyrite was floatable. This illustrated that locust bean gum could be used to separate chalcopyrite from sphalerite. Adsorption tests and zeta potential measurements indicated that locust bean gum can adsorb on the surfaces of both chalcopyrite and sphalerite, but the adsorption amount on sphalerite was higher than that on chalcopyrite. XPS analysis showed that locust bean gum adsorbed on the sphalerite surface through chemical interaction between ZnOH or ZnO on the sphalerite surface and hydroxyl groups of locust bean gum. Locust bean gum adsorbed more easily on the sphalerite surface, perhaps due to sphalerite being easier to oxidize than chalcopyrite.
1. Introduction Sulfide minerals are major sources of base metals, such as copper, lead, zinc, and nickel. For economic and technological reasons, the mineral feed to metal smelters must meet high-grade and low-impurity requirements. However, sulfide minerals are always interlaced with other sulfide and nonsulfide minerals in an ore (Huang, 2013). Therefore, to meet smelter requirements, froth flotation is used to improve the content of a specific sulfide mineral in an ore and remove deleterious impurities (Bulatovic, 2007). In the flotation separation of complex sulfide ores, depressants are usually added to selectively prevent a certain mineral from floating (Bıçak et al., 2012; Chandra and Gerson, 2009). Most depressants currently used in the sulfide flotation industry are inorganic depressants, such as sodium cyanide (NaCN), potassium dichromate (K2Cr2O7), and lime (CaO) (El-Shall et al., 2000; Mu et al., 2016). These inorganic depressants are highly effective, but toxic and hazardous, resulting in potential harm to both humans and the environment. Much research has focused on studying potential nontoxic replacements for toxic inorganic depressants (Gül et al., 2008; Sarquís et al., 2014). Naturally occurring polymers, such as starch, dextrin, cellulose, and guar gum, have been tested or used as selective depressants (Liu and Zhang 2000; Pawlik et al., 2003; Shortridge et al., 2000; Wang
⁎
et al., 2005). The adsorption mechanism between polysaccharides and minerals is complex (Bulatovic, 2007). However, the lack of thorough understanding regarding the adsorption mechanism of polysaccharides on minerals hinders their application in mineral processing (Laskowski et al., 2007). Locust bean gum is a galactomannan vegetable gum extracted from seeds of the carob tree and has been used as a useful depressant for the flotation separation of chalcopyrite from talc (Feng et al., 2018). However, locust bean gum has yet to be used as a depressant in Cu–Zn separation. This study aimed to determine the role of locust bean gum in the flotation of chalcopyrite and sphalerite, while the adsorption mechanism of locust bean gum on sphalerite is also discussed. 2. Materials and methods 2.1. Samples and reagents Natural chalcopyrite and sphalerite samples used in this study were purchased from the Mineral Specimens Laboratory, Zhejiang University, China. The samples were crushed and those with high purity were selected. These samples were then ground and screened to collect the desired fractions. Mineral particles of −150 + 37 μm were selected for microflotation and adsorption tests. Mineral particles of −10 μm
Corresponding author. E-mail address: [email protected] (Z. Huang).
https://doi.org/10.1016/j.mineng.2019.105940 Received 8 April 2019; Received in revised form 12 August 2019; Accepted 13 August 2019 Available online 23 August 2019 0892-6875/ © 2019 Elsevier Ltd. All rights reserved.
Minerals Engineering 143 (2019) 105940
B. Feng, et al.
3000
3000 V V
V
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I(count/s)
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V V
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V
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2θ(degree) Fig. 1. XRD diagrams of chalcopyrite and sphalerite.
represent one standard deviation around the average value.
Table 1 Elemental analysis results for chalcopyrite and sphalerite (%). Sample
Cu
Fe
S
Zn
Chalcopyrite Sphalerite
32.91 0.07
29.06 –
33.25 31.56
– 64.39
2.4. Zeta potential measurements Zeta potential measurements were performed using a ZetaPALS Zeta Potential Analyzer. These experiments were conducted at room temperature using KCl solution (1 mM). A mineral powder sample (1 g) was mixed with the KCl solution (50 mL). The pH was adjusted to the desired value and maintained by adding HCl and KOH solutions. Locust bean gum was added and conditioned for 10 min. The mineral suspension was then poured into a rectangular cell in which electrodes were inserted for measurement. Each experiment was conducted three times, with the average value reported. Error bars represent one standard deviation around the average value.
were used in zeta potential and XPS tests. According to XRD (Fig. 1) and elemental analyses (Table 1), the purity of chalcopyrite was 95.23% (Cu 32.91%) and the purity of sphalerite was 95.95% (Zn 64.39%). The specific surface areas of the minerals were analyzed using the Brunauer–Emmett–Teller (BET) method. The specific surface areas of chalcopyrite and sphalerite were 0.476 and 0.155 m2/g, respectively. Locust bean gum (molecular weight, 250,000–300,000) and collector potassium butyl xanthate (PBX) were purchased from Shanghai Siyu Chemical Technology Co., Ltd. Hydrochloric acid (HCl) and potassium hydroxide (KOH) were used as pH modifiers. Potassium chloride (KCl) was used to prepare the supporting electrolyte solution. All reagents used in this study were of analytical-grade purity. Distilled water was used in all tests.
2.5. X-ray photoelectron spectroscopy (XPS) For XPS analysis, sphalerite (1 g) was mixed with locust bean gum solution at a concentration of 100 mg/L and pH 7. The suspension was conditioned for 30 min, and the mineral solids were filtered, washed with distilled water, and dried under vacuum before XPS analysis. To minimize oxidation, XPS analysis was performed within 12 h of sample preparation, conducted using an AXIS 165 X-ray photoelectron spectrometer (Kratos Analytical).
2.2. Flotation tests For the single mineral flotation tests, sphalerite or chalcopyrite particles (2 g) were precleaned in HCl solution (0.1 mol/L). After rinsing with distilled water and filtering several times, the particles were mixed with distilled water (40 mL) in a 50-mL flotation cell. Locust bean gum was added as depressant, followed by an amount of PBX, and then the pH was immediately adjusted to the desired value with HCl and KOH. After adding frother methylisobutylcarbinol (MIBC), the pulp was floated for 3 min. The mineral recovery was calculated from the dry weights of the flotation concentrates and tails. Each experiment was conducted three times, with the average value reported. Error bars represent one standard deviation around the average value.
3. Results and discussion The effect of pH on the flotation of chalcopyrite and sphalerite was studied, with the results shown in Fig. 2. PBX had a good collecting ability for both sulfides, with pH having little effect on sulfide flotation. The recoveries of both chalcopyrite and sphalerite were very high at all tested pH levels when the PBX concentration was 1 × 10−4 mol/L. The results indicated that separating chalcopyrite and sphalerite was not possible in the absence of a depressant. The effect of PBX dosage on the flotation of chalcopyrite and sphalerite at pH 7 was studied, with the results shown in Fig. 3. The recoveries of both chalcopyrite and sphalerite increased with increasing PBX dosage, reaching maximum values when the PBX dosage was 2 × 10−4 mol/L. Fig. 4 shows the effect of locust bean gum dosage on the flotation of chalcopyrite and sphalerite. These results indicated that sphalerite was apparently depressed by locust bean gum, with its recovery sharply decreased from 83% to 0% by 400 kg/t of locust bean gum. However, the chalcopyrite recovery was only slightly affected, remaining at around 70% when the locust bean gum dosage exceeded 400 kg/t. The depression effect of locust bean gum on chalcopyrite and sphalerite at different pH values was also studied, with the results
2.3. Adsorption tests For the adsorption tests, sphalerite or chalcopyrite powder (1 g) was placed in a beaker with distilled water (100 mL) and mixed for 3 min. Locust bean gum solution of the desired concentration was added and mixed for a further 1 h, ensuring that the adsorption process had reached equilibrium. The slurry was then centrifuged and the locust bean gum concentration remaining in the supernatant was measured by determining the total organic carbon (TOC) content of the supernatant using a TOC analyzer (vario TOC, ELEMENTAR, Germany). This value was compared to a known calibration standard. Each experiment was conducted three times, with the average value reported. Error bars 2
Minerals Engineering 143 (2019) 105940
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Fig. 2. Effect of pH on the flotation of chalcopyrite and sphalerite (c (PBX) = 1 × 10−4 mol/L).
Fig. 5. Effect of pH on the depression effect of locust bean gum (c (PBX) = 1 × 10−4 mol/L, pH 7, c(locust bean gum) = 2 kg/t).
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Fig. 3. Effect of PBX dosage on the flotation of chalcopyrite and sphalerite.
Fig. 6. Adsorption behavior of locust bean gum on chalcopyrite and sphalerite. 100
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Fig. 4. Effect of locust bean gum on the flotation of chalcopyrite and sphalerite (c(PBX) = 1 × 10−4 mol/L; pH = 7).
Fig. 7. Zeta potential of chalcopyrite and sphalerite with and without locust bean gum at different pH values.
shown in Fig. 5. The depression effect of locust bean gum on sphalerite was strong at all tested pH values, with the sphalerite recovery slightly decreasing with increasing pH. In contrast, the depression effect of
locust bean gum on chalcopyrite was weak in the pH range of 3–9, and the chalcopyrite recovery significantly decreased when the pH 3
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Fig. 8. XPS spectra of sphalerite (a) without and (b) with locust bean gum.
gum was adsorbed on the surfaces of both minerals. XPS was used to investigate the adsorption mechanism of locust bean gum on sphalerite. Characteristic photoelectron spectra and peaks were detected for zinc, sulfur, oxygen, and carbon, as shown in Fig. 8. Atomic concentrations of the different elements present on the surface were also determined based on the intensity of the signals produced, with the results shown in Table 2. The relative elemental atomic concentrations before adding locust bean gum were as follows: Zn 2p, 36.46%; S 2p, 32.95%; C 1s, 14.4%; O 1s, 14.99%. The appearance of carbon on the sphalerite surface before adding locust bean gum was attributed to hydrocarbon contamination (Boulton et al., 2003; Fairthorne et al., 1997). After adding locust bean gum, the relative elemental atomic concentrations changed to the following: Zn 2p, 14.92%; S 2p, 15.70%; C 1s, 39.08%; O 1s, 30.30%. The increased relative concentrations of in carbon and oxygen showed that locust bean gum had adsorbed on the sphalerite surface. The XPS spectrums of Zn 2p were then collected on sphalerite before and after adding locust bean gum, with the results shown in Fig. 9. Fig. 9(a) shows the Zn 2p spectrum before adding locust bean gum, which was fitted by two peaks, comprising a peak at 1021.14 eV, assigned to ZnS, and a lower intensity peak at 1022.76 eV, assigned to ZnOH or ZnO (Deroubaix and Marcus, 2010; Skinner et al., 1996). Fig. 9(b) shows the Zn 2p spectrum of sphalerite after locust bean gum treatment. Compared with pure sphalerite, the binding energy of ZnS did not change, while the binding energy of ZnOH or ZnO changed from
Table 2 Relative elemental atomic concentrations (%) of sphalerite before and after interacting with locust bean gum. Elements
Sphalerite Sphalerite + locust bean gum
Content Zn 2p
S 2p
C 1s
O 1s
36.46 14.92
32.95 15.70
14.40 39.08
14.99 30.30
exceeded 9. This result indicated that locust bean gum could be used as a depressant to separate sphalerite from chalcopyrite in the pH range of 3–9. The adsorption behavior of locust bean gum on chalcopyrite and sphalerite at pH 7 is shown as Fig. 6. Locust bean gum showed similar adsorption behavior on chalcopyrite and sphalerite, with the adsorption amount increasing as the amount added increased. However, the amount adsorbed on sphalerite was larger than that on chalcopyrite. Fig. 7 shows the effect of pH on the zeta potential values of chalcopyrite and sphalerite before and after adding locust bean gum. In the absence of locust bean gum, both chalcopyrite and sphalerite showed positive zeta potential values in strong acidic solutions, which decreased with increasing pH, with isoelectric points (IEPs) of about 3.5 and 3, respectively. After adding locust bean gum (100 mg/L), the zeta potential magnitudes of both chalcopyrite and sphalerite decreased, but the IEP and signs did not change. This result indicated that locust bean
a
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Fig. 9. Resolved narrow-scan Zn 2p spectra of sphalerite before and after treatment with locust bean gum. 4
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References
1022.76 to 1021.08 eV. This indicated that oxides on the sphalerite surface participated in the interaction between sphalerite and locust bean gum, and that the interaction was chemical.
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4. Conclusions The major conclusions of this study were as follows: (i) PBX showed a good collecting ability for both chalcopyrite and sphalerite. Locust bean gum had a strong depression effect on sphalerite, but a weak depression effect on chalcopyrite. (ii) Locust bean gum was adsorbed on the surface of both chalcopyrite and sphalerite, but the amount of locust bean gum adsorbed on sphalerite was larger than that on chalcopyrite. (iii) Locust bean gum adsorbed on the sphalerite surface through a chemical interaction between ZnOH or ZnO on the sphalerite surface and hydroxyl groups on locust bean gum. Locust bean gum adsorbed more easily on the sphalerite surface, perhaps because sphalerite was easier to oxidize than chalcopyrite.
Acknowledgements The authors acknowledge the support of Natural Science Foundation of China (51664020), Natural Science Foundation of Jiangxi Province (Nos. 20181BAB206021), The Research Fund Program of State Key Laboratory of Rare Metals Separation and Comprehensive Utilization (Gk-201801), College Students' Innovation and Entrepreneurship Training Program (201710407024) and Jiangxi Youth Jinggang Scholar Award Program. We thank Simon Partridge, PhD, from Liwen Bianji, Edanz Editing China (www.liwenbianji.cn/ac), for editing the English text of a draft of this manuscript.
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