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Sulfidization flotation performance of malachite in the presence of calcite
Minerals Engineering 132 (2019) 293–296
Contents lists available at ScienceDirect
Minerals Engineering journal homepage: www.elsevier.com/locate/mineng
Sulfidization flotation performance of malachite in the presence of calcite Cheng Liu
a,b,⁎
, Shaoxian Song
a,b,⁎
c
, Hongqiang Li , Guanghua Ai
T
d
a
School of Resources and Environmental Engineering, Wuhan University of Technology, Wuhan 430070, China Hubei Key Laboratory of Mineral Resources Processing and Environment, Wuhan University of Technology, Luoshi Road 122, Wuhan, Hubei 430070, China School of Xingfa Mining Engineering, Wuhan Institute of Technology, Wuhan 430073, China d Faculty of Resource and Environmental Engineering, Jiangxi University of Science and Technology, Ganzhou, Jiangxi 341000, China b c
A R T I C LE I N FO
A B S T R A C T
Keywords: Malachite Sulfidization Calcite Slimes coating
The effect of calcite on malachite sulfidization flotation was investigated by micro-flotation tests, adsorption, sedimentation and zeta potential test. The micro-flotation results showed that the finer the calcite particles size is, the lower the malachite recovery will be in the sulfidization flotation of malachite at around pH 9.5. The addition of calcite slimes prevented the S species adsorption at malachite surface. Zeta potential distribution measurements confirmed that slimes coating of calcite on malachite surface is detrimental to sulfidization flotation of malachite.
1. Introduction Copper is an important nonferrous metal that used in the galvanizing, alloys, as well as other industries (Li et al., 2008). Sulfide minerals such as chalcopyrite, chalcocite, and covellite are the primary source for copper production and they are becoming depleted (Lotter et al., 2016; Chen et al., 2014), therefore beneficiation copper oxide resources have become more important in recent years. This situation increases the need to process these ores to produce a marketable product. Copper oxide minerals are common found in silicate and carbonate minerals, malachite being a typical oxide mineral of copper, and possessing a hydrophilic surface which does not respond well to traditional sulphide copper collectors such as xanthanes (Liu et al., 2018a, 2018b; Feng et al., 2017, 2018). Previous investigation shown that sulfidization-xanthate flotation is the commonly used method for beneficiation of malachite and other oxidized copper, lead and zinc minerals (Malghan, 1986; Feng et al., 2016; Wu et al., 2017). Sulfidization reaction is a important factor for the sulfidization xanthate flotation of malachite, the optimal acid/alkali pulp is at approximately pH 9.5, at pH 9.5, HS− is the dominant species that interacted with the copper site and formed copper sulfide component on malachite surface, and the surface hydrophobicity of malachite is improved, hence effective adsorption of sulfide species on malachite surface will improve the flotability of malachite (Feng et al., 2017; Veeken et al., 2003). However, malachite usually associated with other carbonate gangue in ore deposits (Ding, 2014), especially calcite minerals (Oprea et al., 2004). Due
⁎
to its low hardness, calcite is easily slimed in grinding process. The calcite slimes may influence the sulfidization flotation performance of malachite in real ore flotation. However, very little research has been conducted concerning the interaction between malachite and calcite and implications for malachite sulfidization-flotation and the interactive mechanism is unclear. Hence, a better understanding of the interaction between malachite and calcite has a practical importance for sulfidization flotation of malachite. So the aim of this study was to investigate the effect of calcite on the sulfidization flotation of malachite. This was accomplished through the use of a series of experiments and analytical techniques, including micro-flotation tests, adsorption, sedimentation and zeta potential tests. 2. Experimental 2.1. Samples and reagents Malachite and calcite samples used for the experiments were obtained from Yunna Province of China. The samples were crushed and ground using an agate mortar. Size fractions of −150 μm + 74 μm, −74 μm + 37 μm, −10 μm calcite and −74 + 38 μm malachite were utilized for the flotation tests. The −5 μm size fractions were prepared for zeta potential measurements. The X-ray diffraction (XRD) analyses indicated that the purity of both samples were higher than 98%. Sodium butyl xanthate (SBX) with 88% purity was used as the collector, which was obtained from Zhuzhou Flotation Reagent
Corresponding authors at: School of Resources and Environmental Engineering, Wuhan University of Technology, Wuhan 430070, China. E-mail addresses: [email protected] (C. Liu), [email protected] (S. Song).
https://doi.org/10.1016/j.mineng.2018.11.051 Received 10 April 2018; Received in revised form 3 August 2018; Accepted 30 November 2018 0892-6875/ © 2018 Elsevier Ltd. All rights reserved.
Minerals Engineering 132 (2019) 293–296
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Company. Analytical-grade Na2S·9H2O and used methyl isobutyl carbinol (MIBC) were used as sulfidizing agent and frother, respectively. Analytical-grade NaOH and HCl were utilized as the pH modifiers in the experiments, and distilled water with a resistivity of 18.2 Ω cm was used for all the tests.
Malachite -4 Malachite+5 10 M Na2S -3 Malachite+1 10 M Na2S Calcite -3 Calcite+1 10 M Na2S
90 80 70 Recovery(%)
2.2. Micro-flotation tests The flotation tests were carried out in a mechanical agitation flotation machine. Pure mineral particles (2 g) and deionized water (40 mL) were mixed in the plexiglass cell. When needed, calcite was added prior to the conditioning of malachite. A fresh prepared Na2S·9H2O solution with a desired dosages were added to sulfidize the malachite surface for 5 min, stock solutions were poured into the pulp suspension and conditioned for 5 min, and the pulp pH was adjusted to 9.5 by NaOH or/and HCl. the collector SBX and MIBC were added sequentially into the suspension, and conditioned for 3 min and 1 min, respectively. The flotation was conducted for a period of 4 min. After that, both the floated and unfloated products were collected, then filtered and dried. The recovery was calculated by the dry weights and Cu grade analysis of the concentrate and tailings.
60 50 40 30 20 10 0
0
1
2
3 4 5 6 -4 SBX concentration ( 10 M)
7
8
Fig. 1. Effect of SBX dosage on the flotation of malachite and calcite at pH 9.5.
flotation recovery of two minerals in the absence and presence of sodium sulphide when SBX was used as collector. As shown in Fig. 1, in the absence of Na2S, the floatability of malachite and calcite using the SBX collector is weak. A low recovery of approximately 20% of the malachite was obtained with 8 × 10−4 mol/L SBX, and calcite could not be floated in the presence of SBX. This phenomenon may be attributed to the high solubility of copper xanthate which cannot stably exist on malachite surface, resulting in weak floatability (Feng et al., 2017). Fig. 1 also shows that the flotation recovery of malachite increased significantly in the presence of Na2S while in the same concentration of SBX collector, and the higher Na2S concentration is, the higher recovery of malachite will be. The sulfidization of malachite is attributed to interaction between HS− and copper site at mineral surface (Feng et al., 2018). However, the calcite also could not be floated in the presence of Na2S, indicating that sulfide ions does not interact with calcium site at calcite surface. The single mineral flotation results indicate that it may be possible to separate malachite from calcite by sulfidization-xanthate flotation. Hence we test the separation performance of malachite from calcite in the mixed malachite-calcite system and the result is shown in Fig. 2. It can be seen from Fig. 2 that calcite interferes with flotation of malachite and their effect is related to their size, the malachite decreased with the calcite particles size reducing. In the presence of −150 + 74 μm
2.3. Adsorption tests Procedures for the sulfidizing agent Na2S·9H2O adsorption tests are as follows: 2 g of malachite sample was introduced into 40 mL of the fresh prepared Na2S·9H2O solution with a desired concentration at a pH value of 9.5. When required calcite was added prior to the conditioning of malachite. Various process-time was conditioned by magnetic stirrer, after that the suspension was filtered, and sulfur ions concentration of the filtrate was measured by inductively coupled plasma (ICP)-optical emission spectroscopy (OES). The amount of sulfur ions in the solutions was measured to obtain the sulfur ions initial concentration reduction due to malachite adsorption. 2.4. Sedimentation tests The sample sedimentation rate was characterized by its turbidity. Sedimentation were performed using a Turb 555 IR nephelometer. For the sedimentation tests, 0.1 g of sample was added to a certain volume (100 mL) of deionized water. When needed, 0.5 g malachite was added in the calcite slimes suspension. The suspension was stirred for 3 min using a magnetic stirrer, 25 mL suspensions was pipetted out by transfer pipette for turbidity measurement. The nephelometer is connected to a computer which collects the data as a function of sedimentation time. 2.5. Zeta potential tests Zeta potential tests were performed using a Zetaphoremeter III (SEPHY/CAD) instrument. Suspensions of 0.01 wt% solid concentration were prepared by dispersing a certain amount of mineral particles in a 1 × 10−3 M KCl background electrolyte solution. The suspension was magnetically stirred in a beaker for 6 min at a desired pH value. After 20 min of settling, the pH value of the suspension was measured and the supernatant was collected for zeta-potential measurements. The zetapotential of each sample was measured by three times, and the average value was reported and the standard deviation was calculated. In addition, each individual measurements can get the distribution of electrophoretic mobility. 3. Results and discussion 3.1. Micro-flotation results
Fig. 2. The effect of calcite size/dosage on the sulfidization flotation of malachite at pH 9.5 [Na2S] = 1 × 10−3 mol/L; [SBX] = 8 × 10−4 mol/L.
Micro-flotation tests were performed in order to investigate the flotation performance of malachite and calcite. Fig. 1 shows the 294
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Fig. 3. Adsorption of S species onto the malachite surfaces with and without calcite.
Fig. 6. Zeta potential distributions of malachite and calcite with and without Na2S at pH 9.5. 50 40
(a)Malachite
30 20
Frequency (%)
10
Fig. 4. Turbidity measurements of calcite and calcite/malachite mixture at pH 9.5.
40
(b)Calcite
30 20 10 0
30 Calcite Malachite
20
Zeta potential (mV)
0 40
40
(c) Mixed malachite and calcite
30
10
20 10
0
0 -40
-10
-35
-30
-25
-20
-15
-10
-5
0
5
10
Zeta potential (mV)
-20
Fig. 7. Zeta potential distributions of malachite and calcite at pH 9.5 (a) individual malachite, (b) individual calcite and (c) binary mixed malachite and calcite suspension.
-30 -40 -50
7
8
9
10
11
fraction calcite, malachite recovery did not change. However, when 30 g/L −10 m fraction calcite particles were added, the recovery of malachite decreased significantly (from 80% to 15%).
12
pH Fig. 5. Zeta-potential of malachite and calcite as a function of solution pH.
3.2. The mechanism of calcite slimes depress the malachite sulfidization flotation The above mentioned flotation results indicated that the calcite 295
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slimes (−10 μm) significantly depressed the malachite floatability, hence the depression mechanism of the calcite slimes on the malachite sulfidization flotation was discussed in the following wok. Firstly, the adsorption behaviour of sulfide ions on malachite surface with and without calcite slimes was studied and the result is presented in Fig. 3, as shown in Fig. 3, in the absence of calcite slimes, sulfide ion species in the pulp suspension were transferred onto the malachite surface and the adsorption amount of sulfide ions onto the malachite surfaces increased with the increases of sulfidization time when it was less than 8 min, the adsorption amount of S species reached a maximum and remained constant when the sulfidization time is over 8 min. The adsorption amount of sulfide ions onto the malachite surface in the presence of calcite slimes was lower than that in the absence of calcite slimes, indicating that with the addition of calcite in malachite pulp prevents the S species adsorption on malachite surface. Adsorption result indicated that interaction may be occurred between malachite and calcite. To confirm the interaction between malachite and calcite particles, the turbidity measurements were performed at pH 9.5 and the result is presented in Fig. 4. In this work, malachite particle size is far larger than that of calcite slimes. So the turbidity value of calcite slimes can be used as theoretical turbidity. Fig. 4 also shows that the sedimentation rate of malachite and calcite mixture decreased as the increase of sedimentation time, and the turbidity value is lower than that of single calcite slimes, probably indicating that hetero-coagulation occurred in malachite-calcite system. The zeta potential reflects the surface charges of mineral particles, and the particles interaction is related to the surface characters, hence the malachite and calcite zeta potentials were tested and the results were presented in Fig. 5, as shown in Fig. 5, the IEP (isoelectric point) of calcite and malachite occurred at pH 9.5 and 7.5, respectively, similar to the previous literature (Li et al., 2015; Liu et al., 2016a, 2016b). The zeta potential of calcite is close to zero around 9.5, while that of malachite is negative. At such low zeta potential values, heterocoagulation between malachite and calcite particles is anticipated, and this can be explained by classic DLVO theory (Feng et al., 2015; Chen et al., 2016). In order to investigate the hetero-coagulation form of malachite with calcite, the zeta potential distributions of individual malachite or/ and calcite particles with and without Na2S and mixed malachite-calcite particles were tested at pH 9.5. Fig. 6(a) shows the individual zeta potential distribution peak of bare malachite being centered at −14.80 mV, and that of the Na2S pre-treated malachite being centered at −42.50 mV, indicating that the S species adsorbed at malachite surface, but the zeta potential distribution peak of Na2S pre-treated calcite was almost the same as that of bare calcite (around −4 mV), suggesting no interaction occurred between S species and calcite surface. In Fig. 7, the zeta potential distribution measurement of malachite and calcite mixture can be used to confirm hetero-coagulation between malachite and calcite particles. The volume ratio of malachite and calcite is 1:1 and the zeta potential distribution result is shown in Fig. 7(c). It can be seen from Fig. 7(c) that the malachite and calcite mixture presented a single modal zeta potential distribution the distribution peak is centered at −5.71 mV. Since this single peak value is similar to the distribution peak of individual calcite (Fig. 7(a)), it can be concluded that all the malachite particles are almost fully coated by calcite particles (Xu et al., 2003, Chen et al., 2016), combine with the adsorption test (Fig. 3), indicates the adsorption of S species onto calcite slimes coating malachite surface was depressed because the calcite slimes cannot interact with S species (see Fig. 6(d)), which matched well with the sulfidization flotation behaviour of malachite in the presence of calcite slimes around pH 9.5.
4. Conclusion The current work confirmed that micro-flotation tests achieved flotation recovery of the malachite in the presence of sodium sulfide when SBX was used as collector. The floatability of the malachite decreased when calcite particles were added, and the finer the calcite particles is, the lower the malachite recovery will be. Adsorption test showed that calcite slimes prevented the adsorption of S species at malachite surface. Sedimentation tests showed that hetero-coagulation occurred in malachite-calcite system, zeta potential distribution indicated the hetero-coagulation form is that the malachite particles are almost fully coated by calcite slimes, and then depressing the adsorption of S species at malachite surface. In these solutions, the copper sulfide can not be formed on malachite surface and resulted in the depressed flotation of malachite. Acknowledgments The authors acknowledge the support of the National Natural Science Foundation of China (Nos. 51804238, 51474167, 51674183 and 51564014). References Chen, T., Zhao, Y., Song, S., 2016. Electrophoretic mobility study for heterocoagulation of montmorillonite with fluorite in aqueous solutions. Powder Technol. 309, 61–67. Chen, X.M., Peng, Y.J., Bradshaw, D., 2014. The separation of chalcopyrite and chalcocite from pyrite in cleaner flotation after regrinding. Miner. Eng. 58, 64–72. Ding, P., 2014. Experimental study on beneficiation of carbonate-type silver-bearing oxidized copper ore. Kunming University of Sci. and Technol. Master Thesis (in Chinese). Feng, B., Lu, Y., Luo, X., 2015. The effect of quartz on the flotation of pyrite depressed by serpentine. J. Mater. Res. Technol. 4 (1), 8–13. Feng, Q., Zhao, W., Wen, S., 2018. Surface modification of malachite with ethanediamine and its effect on sulfidization flotation. Appl. Surf. Sci. 436, 823–831. Feng, Q.C., Zhao, W.J., Wen, S.M., Cao, Q.B., 2017. Copper sulfide species formed on malachite surfaces in relation to flotation. J. Ind. Eng. Chem. 48, 125–132. Feng, Q.C., Wen, S.M., Zhao, W.J., Deng, J.S., Xian, Y.J., 2016. Adsorption of sulfide ions on cerussite surfaces and implications for flotation. Appl. Surf. Sci. 360, 365–372. Liu, C., Feng, Q., Zhang, G., Chen, W., Chen, Y., 2016a. Effect of depressants in the selective flotation of scheelite and calcite using oxidized paraffin soap as collector. Int. J. Miner. Process. 157. Liu, C., Ai, G.H., Song, S.S., 2018a. The effect of amino trimethylene phosphonic acid on the flotation separation of pentlandite from lizardite. Powder Technol. 336, 527–532. Liu, C., Chen, Y.F., Song, S.S., Li, H.Q., 2018b. The effect of aluminum ions on the flotation separation of pentlandite from lizardite. Colloids Surf. A: Physicochem. Eng. Asp. 555, 708–712. Li, J., Lu, H., Liu, S., Xu, Z., 2008. Optimizing the operating parameters of corona electrostatic separation for recycling waste scraped printed circuit boards by computer simulation of electric field. J. Hazard. Mater. 153 (1–2), 269–275. Li, F., Zhong, H., Xu, H., Jia, H., Liu, G., 2015. Flotation behavior and adsorption mechanism of α-hydroxyoctyl phosphinic acid to malachite. Miner. Eng. 71, 188–193. Liu, G.Y., Huang, Y.G., Qu, X.Y., Xiao, J.J., Yang, X.L., Xu, Z.H., 2016b. Understanding the hydrophobic mechanism of 3-hexyl-4-amino-1, 2,4-triazole-5-thione to malachite by ToF-SIMS, XPS, FTIR, contact angle, zeta potential and micro-flotation. Colloids Surf. A: Physicochem. Eng. Asp. 503, 34–42. Lotter, N.O., Bradshaw, D.J., Barnes, A.R., 2016. Classification of the major copper sulphides into semiconductor type and associated flotation characteristics. Miner. Eng. 96–97, 177–184. Malghan, S.G., 1986. Role of sodium sulfide in the flotation of oxidized copper, lead, and zinc ores. Min. Metall. Process. 3, 158–163. Oprea, G., Mihali, C., Danciu, V., Podariu, M., 2004. The study of 8-hydroxyquinoline and salicylaldoxime action at the malachite flotation. J. Min. Metall. A Min. 125 (1), 449–478. Wu, D., Ma, W., Wen, S., et al., 2017. Enhancing the sulfidation of smithsonite by superficial dissolution with a novel complexing agent. Miner. Eng. 114, 1–7. Veeken, A.H.M., Akoto, L., Hulshoff Pol, L.W., Weijma, J., 2003. Control of the sulfide S2concentration for optimal zinc removal by sulfide precipitation in a continuously stirred tank reactor. Water Res. 37, 3709–3717. Xu, Z., Liu, J., Choung, J.W., Zhou, Z., 2003. Electrokinetic study of clay interactions with coal in flotation. Int. J. Miner. Process. 68 (1), 183–196.
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Contents lists available at ScienceDirect
Minerals Engineering journal homepage: www.elsevier.com/locate/mineng
Sulfidization flotation performance of malachite in the presence of calcite Cheng Liu
a,b,⁎
, Shaoxian Song
a,b,⁎
c
, Hongqiang Li , Guanghua Ai
T
d
a
School of Resources and Environmental Engineering, Wuhan University of Technology, Wuhan 430070, China Hubei Key Laboratory of Mineral Resources Processing and Environment, Wuhan University of Technology, Luoshi Road 122, Wuhan, Hubei 430070, China School of Xingfa Mining Engineering, Wuhan Institute of Technology, Wuhan 430073, China d Faculty of Resource and Environmental Engineering, Jiangxi University of Science and Technology, Ganzhou, Jiangxi 341000, China b c
A R T I C LE I N FO
A B S T R A C T
Keywords: Malachite Sulfidization Calcite Slimes coating
The effect of calcite on malachite sulfidization flotation was investigated by micro-flotation tests, adsorption, sedimentation and zeta potential test. The micro-flotation results showed that the finer the calcite particles size is, the lower the malachite recovery will be in the sulfidization flotation of malachite at around pH 9.5. The addition of calcite slimes prevented the S species adsorption at malachite surface. Zeta potential distribution measurements confirmed that slimes coating of calcite on malachite surface is detrimental to sulfidization flotation of malachite.
1. Introduction Copper is an important nonferrous metal that used in the galvanizing, alloys, as well as other industries (Li et al., 2008). Sulfide minerals such as chalcopyrite, chalcocite, and covellite are the primary source for copper production and they are becoming depleted (Lotter et al., 2016; Chen et al., 2014), therefore beneficiation copper oxide resources have become more important in recent years. This situation increases the need to process these ores to produce a marketable product. Copper oxide minerals are common found in silicate and carbonate minerals, malachite being a typical oxide mineral of copper, and possessing a hydrophilic surface which does not respond well to traditional sulphide copper collectors such as xanthanes (Liu et al., 2018a, 2018b; Feng et al., 2017, 2018). Previous investigation shown that sulfidization-xanthate flotation is the commonly used method for beneficiation of malachite and other oxidized copper, lead and zinc minerals (Malghan, 1986; Feng et al., 2016; Wu et al., 2017). Sulfidization reaction is a important factor for the sulfidization xanthate flotation of malachite, the optimal acid/alkali pulp is at approximately pH 9.5, at pH 9.5, HS− is the dominant species that interacted with the copper site and formed copper sulfide component on malachite surface, and the surface hydrophobicity of malachite is improved, hence effective adsorption of sulfide species on malachite surface will improve the flotability of malachite (Feng et al., 2017; Veeken et al., 2003). However, malachite usually associated with other carbonate gangue in ore deposits (Ding, 2014), especially calcite minerals (Oprea et al., 2004). Due
⁎
to its low hardness, calcite is easily slimed in grinding process. The calcite slimes may influence the sulfidization flotation performance of malachite in real ore flotation. However, very little research has been conducted concerning the interaction between malachite and calcite and implications for malachite sulfidization-flotation and the interactive mechanism is unclear. Hence, a better understanding of the interaction between malachite and calcite has a practical importance for sulfidization flotation of malachite. So the aim of this study was to investigate the effect of calcite on the sulfidization flotation of malachite. This was accomplished through the use of a series of experiments and analytical techniques, including micro-flotation tests, adsorption, sedimentation and zeta potential tests. 2. Experimental 2.1. Samples and reagents Malachite and calcite samples used for the experiments were obtained from Yunna Province of China. The samples were crushed and ground using an agate mortar. Size fractions of −150 μm + 74 μm, −74 μm + 37 μm, −10 μm calcite and −74 + 38 μm malachite were utilized for the flotation tests. The −5 μm size fractions were prepared for zeta potential measurements. The X-ray diffraction (XRD) analyses indicated that the purity of both samples were higher than 98%. Sodium butyl xanthate (SBX) with 88% purity was used as the collector, which was obtained from Zhuzhou Flotation Reagent
Corresponding authors at: School of Resources and Environmental Engineering, Wuhan University of Technology, Wuhan 430070, China. E-mail addresses: [email protected] (C. Liu), [email protected] (S. Song).
https://doi.org/10.1016/j.mineng.2018.11.051 Received 10 April 2018; Received in revised form 3 August 2018; Accepted 30 November 2018 0892-6875/ © 2018 Elsevier Ltd. All rights reserved.
Minerals Engineering 132 (2019) 293–296
C. Liu et al.
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Company. Analytical-grade Na2S·9H2O and used methyl isobutyl carbinol (MIBC) were used as sulfidizing agent and frother, respectively. Analytical-grade NaOH and HCl were utilized as the pH modifiers in the experiments, and distilled water with a resistivity of 18.2 Ω cm was used for all the tests.
Malachite -4 Malachite+5 10 M Na2S -3 Malachite+1 10 M Na2S Calcite -3 Calcite+1 10 M Na2S
90 80 70 Recovery(%)
2.2. Micro-flotation tests The flotation tests were carried out in a mechanical agitation flotation machine. Pure mineral particles (2 g) and deionized water (40 mL) were mixed in the plexiglass cell. When needed, calcite was added prior to the conditioning of malachite. A fresh prepared Na2S·9H2O solution with a desired dosages were added to sulfidize the malachite surface for 5 min, stock solutions were poured into the pulp suspension and conditioned for 5 min, and the pulp pH was adjusted to 9.5 by NaOH or/and HCl. the collector SBX and MIBC were added sequentially into the suspension, and conditioned for 3 min and 1 min, respectively. The flotation was conducted for a period of 4 min. After that, both the floated and unfloated products were collected, then filtered and dried. The recovery was calculated by the dry weights and Cu grade analysis of the concentrate and tailings.
60 50 40 30 20 10 0
0
1
2
3 4 5 6 -4 SBX concentration ( 10 M)
7
8
Fig. 1. Effect of SBX dosage on the flotation of malachite and calcite at pH 9.5.
flotation recovery of two minerals in the absence and presence of sodium sulphide when SBX was used as collector. As shown in Fig. 1, in the absence of Na2S, the floatability of malachite and calcite using the SBX collector is weak. A low recovery of approximately 20% of the malachite was obtained with 8 × 10−4 mol/L SBX, and calcite could not be floated in the presence of SBX. This phenomenon may be attributed to the high solubility of copper xanthate which cannot stably exist on malachite surface, resulting in weak floatability (Feng et al., 2017). Fig. 1 also shows that the flotation recovery of malachite increased significantly in the presence of Na2S while in the same concentration of SBX collector, and the higher Na2S concentration is, the higher recovery of malachite will be. The sulfidization of malachite is attributed to interaction between HS− and copper site at mineral surface (Feng et al., 2018). However, the calcite also could not be floated in the presence of Na2S, indicating that sulfide ions does not interact with calcium site at calcite surface. The single mineral flotation results indicate that it may be possible to separate malachite from calcite by sulfidization-xanthate flotation. Hence we test the separation performance of malachite from calcite in the mixed malachite-calcite system and the result is shown in Fig. 2. It can be seen from Fig. 2 that calcite interferes with flotation of malachite and their effect is related to their size, the malachite decreased with the calcite particles size reducing. In the presence of −150 + 74 μm
2.3. Adsorption tests Procedures for the sulfidizing agent Na2S·9H2O adsorption tests are as follows: 2 g of malachite sample was introduced into 40 mL of the fresh prepared Na2S·9H2O solution with a desired concentration at a pH value of 9.5. When required calcite was added prior to the conditioning of malachite. Various process-time was conditioned by magnetic stirrer, after that the suspension was filtered, and sulfur ions concentration of the filtrate was measured by inductively coupled plasma (ICP)-optical emission spectroscopy (OES). The amount of sulfur ions in the solutions was measured to obtain the sulfur ions initial concentration reduction due to malachite adsorption. 2.4. Sedimentation tests The sample sedimentation rate was characterized by its turbidity. Sedimentation were performed using a Turb 555 IR nephelometer. For the sedimentation tests, 0.1 g of sample was added to a certain volume (100 mL) of deionized water. When needed, 0.5 g malachite was added in the calcite slimes suspension. The suspension was stirred for 3 min using a magnetic stirrer, 25 mL suspensions was pipetted out by transfer pipette for turbidity measurement. The nephelometer is connected to a computer which collects the data as a function of sedimentation time. 2.5. Zeta potential tests Zeta potential tests were performed using a Zetaphoremeter III (SEPHY/CAD) instrument. Suspensions of 0.01 wt% solid concentration were prepared by dispersing a certain amount of mineral particles in a 1 × 10−3 M KCl background electrolyte solution. The suspension was magnetically stirred in a beaker for 6 min at a desired pH value. After 20 min of settling, the pH value of the suspension was measured and the supernatant was collected for zeta-potential measurements. The zetapotential of each sample was measured by three times, and the average value was reported and the standard deviation was calculated. In addition, each individual measurements can get the distribution of electrophoretic mobility. 3. Results and discussion 3.1. Micro-flotation results
Fig. 2. The effect of calcite size/dosage on the sulfidization flotation of malachite at pH 9.5 [Na2S] = 1 × 10−3 mol/L; [SBX] = 8 × 10−4 mol/L.
Micro-flotation tests were performed in order to investigate the flotation performance of malachite and calcite. Fig. 1 shows the 294
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Fig. 3. Adsorption of S species onto the malachite surfaces with and without calcite.
Fig. 6. Zeta potential distributions of malachite and calcite with and without Na2S at pH 9.5. 50 40
(a)Malachite
30 20
Frequency (%)
10
Fig. 4. Turbidity measurements of calcite and calcite/malachite mixture at pH 9.5.
40
(b)Calcite
30 20 10 0
30 Calcite Malachite
20
Zeta potential (mV)
0 40
40
(c) Mixed malachite and calcite
30
10
20 10
0
0 -40
-10
-35
-30
-25
-20
-15
-10
-5
0
5
10
Zeta potential (mV)
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Fig. 7. Zeta potential distributions of malachite and calcite at pH 9.5 (a) individual malachite, (b) individual calcite and (c) binary mixed malachite and calcite suspension.
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fraction calcite, malachite recovery did not change. However, when 30 g/L −10 m fraction calcite particles were added, the recovery of malachite decreased significantly (from 80% to 15%).
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pH Fig. 5. Zeta-potential of malachite and calcite as a function of solution pH.
3.2. The mechanism of calcite slimes depress the malachite sulfidization flotation The above mentioned flotation results indicated that the calcite 295
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slimes (−10 μm) significantly depressed the malachite floatability, hence the depression mechanism of the calcite slimes on the malachite sulfidization flotation was discussed in the following wok. Firstly, the adsorption behaviour of sulfide ions on malachite surface with and without calcite slimes was studied and the result is presented in Fig. 3, as shown in Fig. 3, in the absence of calcite slimes, sulfide ion species in the pulp suspension were transferred onto the malachite surface and the adsorption amount of sulfide ions onto the malachite surfaces increased with the increases of sulfidization time when it was less than 8 min, the adsorption amount of S species reached a maximum and remained constant when the sulfidization time is over 8 min. The adsorption amount of sulfide ions onto the malachite surface in the presence of calcite slimes was lower than that in the absence of calcite slimes, indicating that with the addition of calcite in malachite pulp prevents the S species adsorption on malachite surface. Adsorption result indicated that interaction may be occurred between malachite and calcite. To confirm the interaction between malachite and calcite particles, the turbidity measurements were performed at pH 9.5 and the result is presented in Fig. 4. In this work, malachite particle size is far larger than that of calcite slimes. So the turbidity value of calcite slimes can be used as theoretical turbidity. Fig. 4 also shows that the sedimentation rate of malachite and calcite mixture decreased as the increase of sedimentation time, and the turbidity value is lower than that of single calcite slimes, probably indicating that hetero-coagulation occurred in malachite-calcite system. The zeta potential reflects the surface charges of mineral particles, and the particles interaction is related to the surface characters, hence the malachite and calcite zeta potentials were tested and the results were presented in Fig. 5, as shown in Fig. 5, the IEP (isoelectric point) of calcite and malachite occurred at pH 9.5 and 7.5, respectively, similar to the previous literature (Li et al., 2015; Liu et al., 2016a, 2016b). The zeta potential of calcite is close to zero around 9.5, while that of malachite is negative. At such low zeta potential values, heterocoagulation between malachite and calcite particles is anticipated, and this can be explained by classic DLVO theory (Feng et al., 2015; Chen et al., 2016). In order to investigate the hetero-coagulation form of malachite with calcite, the zeta potential distributions of individual malachite or/ and calcite particles with and without Na2S and mixed malachite-calcite particles were tested at pH 9.5. Fig. 6(a) shows the individual zeta potential distribution peak of bare malachite being centered at −14.80 mV, and that of the Na2S pre-treated malachite being centered at −42.50 mV, indicating that the S species adsorbed at malachite surface, but the zeta potential distribution peak of Na2S pre-treated calcite was almost the same as that of bare calcite (around −4 mV), suggesting no interaction occurred between S species and calcite surface. In Fig. 7, the zeta potential distribution measurement of malachite and calcite mixture can be used to confirm hetero-coagulation between malachite and calcite particles. The volume ratio of malachite and calcite is 1:1 and the zeta potential distribution result is shown in Fig. 7(c). It can be seen from Fig. 7(c) that the malachite and calcite mixture presented a single modal zeta potential distribution the distribution peak is centered at −5.71 mV. Since this single peak value is similar to the distribution peak of individual calcite (Fig. 7(a)), it can be concluded that all the malachite particles are almost fully coated by calcite particles (Xu et al., 2003, Chen et al., 2016), combine with the adsorption test (Fig. 3), indicates the adsorption of S species onto calcite slimes coating malachite surface was depressed because the calcite slimes cannot interact with S species (see Fig. 6(d)), which matched well with the sulfidization flotation behaviour of malachite in the presence of calcite slimes around pH 9.5.
4. Conclusion The current work confirmed that micro-flotation tests achieved flotation recovery of the malachite in the presence of sodium sulfide when SBX was used as collector. The floatability of the malachite decreased when calcite particles were added, and the finer the calcite particles is, the lower the malachite recovery will be. Adsorption test showed that calcite slimes prevented the adsorption of S species at malachite surface. Sedimentation tests showed that hetero-coagulation occurred in malachite-calcite system, zeta potential distribution indicated the hetero-coagulation form is that the malachite particles are almost fully coated by calcite slimes, and then depressing the adsorption of S species at malachite surface. In these solutions, the copper sulfide can not be formed on malachite surface and resulted in the depressed flotation of malachite. Acknowledgments The authors acknowledge the support of the National Natural Science Foundation of China (Nos. 51804238, 51474167, 51674183 and 51564014). References Chen, T., Zhao, Y., Song, S., 2016. Electrophoretic mobility study for heterocoagulation of montmorillonite with fluorite in aqueous solutions. Powder Technol. 309, 61–67. Chen, X.M., Peng, Y.J., Bradshaw, D., 2014. The separation of chalcopyrite and chalcocite from pyrite in cleaner flotation after regrinding. Miner. Eng. 58, 64–72. Ding, P., 2014. Experimental study on beneficiation of carbonate-type silver-bearing oxidized copper ore. Kunming University of Sci. and Technol. Master Thesis (in Chinese). Feng, B., Lu, Y., Luo, X., 2015. The effect of quartz on the flotation of pyrite depressed by serpentine. J. Mater. Res. Technol. 4 (1), 8–13. Feng, Q., Zhao, W., Wen, S., 2018. Surface modification of malachite with ethanediamine and its effect on sulfidization flotation. Appl. Surf. Sci. 436, 823–831. Feng, Q.C., Zhao, W.J., Wen, S.M., Cao, Q.B., 2017. Copper sulfide species formed on malachite surfaces in relation to flotation. J. Ind. Eng. Chem. 48, 125–132. Feng, Q.C., Wen, S.M., Zhao, W.J., Deng, J.S., Xian, Y.J., 2016. Adsorption of sulfide ions on cerussite surfaces and implications for flotation. Appl. Surf. Sci. 360, 365–372. Liu, C., Feng, Q., Zhang, G., Chen, W., Chen, Y., 2016a. Effect of depressants in the selective flotation of scheelite and calcite using oxidized paraffin soap as collector. Int. J. Miner. Process. 157. Liu, C., Ai, G.H., Song, S.S., 2018a. The effect of amino trimethylene phosphonic acid on the flotation separation of pentlandite from lizardite. Powder Technol. 336, 527–532. Liu, C., Chen, Y.F., Song, S.S., Li, H.Q., 2018b. The effect of aluminum ions on the flotation separation of pentlandite from lizardite. Colloids Surf. A: Physicochem. Eng. Asp. 555, 708–712. Li, J., Lu, H., Liu, S., Xu, Z., 2008. Optimizing the operating parameters of corona electrostatic separation for recycling waste scraped printed circuit boards by computer simulation of electric field. J. Hazard. Mater. 153 (1–2), 269–275. Li, F., Zhong, H., Xu, H., Jia, H., Liu, G., 2015. Flotation behavior and adsorption mechanism of α-hydroxyoctyl phosphinic acid to malachite. Miner. Eng. 71, 188–193. Liu, G.Y., Huang, Y.G., Qu, X.Y., Xiao, J.J., Yang, X.L., Xu, Z.H., 2016b. Understanding the hydrophobic mechanism of 3-hexyl-4-amino-1, 2,4-triazole-5-thione to malachite by ToF-SIMS, XPS, FTIR, contact angle, zeta potential and micro-flotation. Colloids Surf. A: Physicochem. Eng. Asp. 503, 34–42. Lotter, N.O., Bradshaw, D.J., Barnes, A.R., 2016. Classification of the major copper sulphides into semiconductor type and associated flotation characteristics. Miner. Eng. 96–97, 177–184. Malghan, S.G., 1986. Role of sodium sulfide in the flotation of oxidized copper, lead, and zinc ores. Min. Metall. Process. 3, 158–163. Oprea, G., Mihali, C., Danciu, V., Podariu, M., 2004. The study of 8-hydroxyquinoline and salicylaldoxime action at the malachite flotation. J. Min. Metall. A Min. 125 (1), 449–478. Wu, D., Ma, W., Wen, S., et al., 2017. Enhancing the sulfidation of smithsonite by superficial dissolution with a novel complexing agent. Miner. Eng. 114, 1–7. Veeken, A.H.M., Akoto, L., Hulshoff Pol, L.W., Weijma, J., 2003. Control of the sulfide S2concentration for optimal zinc removal by sulfide precipitation in a continuously stirred tank reactor. Water Res. 37, 3709–3717. Xu, Z., Liu, J., Choung, J.W., Zhou, Z., 2003. Electrokinetic study of clay interactions with coal in flotation. Int. J. Miner. Process. 68 (1), 183–196.
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