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Effects of lead ions on the flotation of hemimorphite using sodium oleate
Minerals Engineering 89 (2016) 163–167
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Minerals Engineering journal homepage: www.elsevier.com/locate/mineng
Effects of lead ions on the flotation of hemimorphite using sodium oleate Cheng Liu, Qiming Feng, Guofan Zhang ⇑, Wankun Ma, Qingyou Meng, Yanfei Chen School of Mineral Processing and Bioengineering, Central South University, Changsha 410083, China
a r t i c l e
i n f o
Article history: Received 31 October 2015 Revised 5 February 2016 Accepted 6 February 2016 Available online 9 February 2016 Keywords: Lead ions Hemimorphite Flotation Sodium oleate
a b s t r a c t The effects of Pb(II) ions on the flotation of hemimorphite was investigated by micro-flotation tests, zeta-potential measurements, solution chemistry and Fourier transform infrared spectroscopy. The micro-flotation results indicated that the Pb(II) effectively improved the flotation of hemimorphite minerals. Good floatability of minerals was obtained in the pH region 7 to 9. Adsorption/precipitation of the hydrolyzed species of lead cations occurred in this pH region, these species promote sodium oleate adsorption and from lead oleate on the surface of hemimorphite. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction Zinc is an important base metal that used in the galvanizing, alloys, as well as other industries (Ghosh et al., 2002; Shirin et al., 2006). Hemimorphite is a sorosilicate of formula Zn4Si2O7(OH)2H2O. The termination of the crystal is rather blunt being dominated by a pedion face while the opposite end, is terminated by the point of a pyramid (Anthony et al., 1995). The crystal structure contains tetrahedrons of ZnO3OH, interlocked with Si2O7 groups and water molecules. The zinc is at the center of the tetrahedron while the three oxygens, along with an OH group, are at the four points of the tetrahedron. The mineral is orthorhombic with point group mm2 (Frost et al., 2007; Nakamura et al., 1977). A molecular model of hemimorphite is shown in Fig. 1. In industrial flotation, the existence of unavoidable metal ions such as ions of iron, copper and lead, significantly influence the flotation performance of target mineral (Fan and Rowson, 2000; Zhu et al., 2012). They determined that metal ions formed precipitate, the precipitate and the hydroxy complexes could adsorb onto the surfaces of minerals, and increasing their flotation by promoting collector adsorption. (Zhang et al., 2014; Ejtemaei et al., 2012) examined the flotation responses of quartz and feldspar with collectors in the presence of metal ions. They found that quartz floated in the presence of Pb(II), Zn(II) and Fe(II) ions. On the flotation of hemimorphite with collectors in the absence of metal ions was studies by Liu et al. (2015), Salum et al. (1992), however, no one reported use of lead ions as an activator for hemimorphite
⇑ Corresponding author. E-mail address: [email protected] (G. Zhang). http://dx.doi.org/10.1016/j.mineng.2016.02.002 0892-6875/Ó 2016 Elsevier Ltd. All rights reserved.
flotation, lead ions as an activator for the flotation mechanism of hemimorphite is unclear. Before the study, the hemimorphite activated by lead ions cannot be depressed, whereas Pb(II) ion activation of quartz and calcite as the major gangue mineral found in the zinc oxide ores can be depressed using calcium lignosulfonate as a depressant in the presence of NaOl though single minerals tests. Therefore, achieving a selective separation from the hemimorphite ores is possible in the presence of lead ions. In consequence, the main objective of the present research was to examine the interaction of the hemimorphite surface with lead ions and NaOl. This was accomplished through the use of various techniques, including micro-flotation, zeta-potential analysis, adsorption measurements, lead ions and NaOl species in solution and FT-IR.
2. Materials and methods 2.1. Samples and reagents The ore samples of hemimorphite minerals were obtained from Changsha of Hunan Province, China. The samples were crushed and ground using an agate mortar. The products were then dry sieved to obtain a particle size of 74 lm. The ore was analyzed via a chemical method and phase-examined using powder X-ray diffraction (XRD) showed in Fig. 2. The chemical compositions of the samples are listed in Table 1. According to the result of the XRD analysis, the purities of hemimorphite was very high. Sodium oleate (CH3(CH2)7CH@CH(CH2)7COONa) (NaOl) was used as the anionic collector for the micro-flotation tests. Lead nitrate (PbNO3) was used as the source of lead ions activator. HCl
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2.3. Zeta potential tests Zeta measurements were performed in 1 10 3 mol/L KNO3 background electrolyte solution using Coulter Delsa440sx Zeta analyzer instrument. The suspensions (0.01% mass fraction) with small amount of the minerals were dispersed in a beaker magnetically stirred for 15 min in the presence of different concentration of reagents at various pH values. After 20 min of settling, the pH value of the suspension was measured and the supernatant was obtained for zeta-potential measurements. The zeta-potential of each sample was measured three times in this paper, and the average was reported as the final value. 2.4. FT-IR spectroscopy measurements The FT-IR spectra were obtained using a Spectrum One FT-IR (Japan) spectrometer to characterize the nature of the interaction between the collector and minerals. Approximately 1% (mass fraction) of the solid sample was mixed with spectroscopic grade KBr. The wave number range of the spectra was 400–4000 cm 1. Each spectra was recorded with 30 scans measured at 2 cm 1 resolution. To prepare the samples for FT-IR analysis, pure mineral particles were ground to 5 lm using an agate mortar. A suspension was prepared by adding 2.0 g of the pure mineral particles to 35 mL of deionized water in a Plexiglas cell (40 mL). The suspension was conditioned for 5 min using HCl and NaOH as the pH regulators. Then, the suspension was conditioned for 5 min with lead ions. Afterward, the suspension was conditioned for 3 min with NaOl. Finally, the solid samples were washed three times using distilled water with the same pH and allowed to dry prior to FT-IR analyses.
Fig. 1. Model of hemimorphite structure.
3. Results and discussion 3.1. Micro-flotation The objective of this study was to investigate the effects of lead ions on the flotation of hemimorphite in the presence of NaOl. Fig. 3 shows the flotation recovery of hemimorphite as a function of pH with and without lead ions, and with 2 10 4 mol/L NaOl. The flotation recovery of hemimorphite showed a better floatability throughout the pH range of 4.0–9.0 in the absence of lead ions which is attributed to increases in the concentrations of oleate
Fig. 2. XRD of the hemimorphite sample.
Table 1 Chemical composition of hemimorphite ore.
80
ZnO
SiO2
Al2O3
Fe
Pb
Cu
Other
66.75
24.34
0.086
0.141
0.032
0.018
8.633
70
and NaOH were used for the pH adjustment in the experiments. All the reagents were of analytical grade, and the water used in all the experiments was distilled water. 2.2. Micro-flotation tests
Recovery (%)
60 50 40 30 20
The micro-flotation were carried out in a mechanical agitation flotation machine. The mineral suspension was prepared by adding 2.0 g of mineral to 35 ml of solution. The pulp was continuously stirred for 1 min using a pH regulator, 3 min with the activator, and 3 min with the collector. The pH of the solution was measured before the flotation, and the flotation was conducted for 4 min. The floated and tailing fractions were collected separately and dried and weighed for calculations.
Hemimorphite Hemimorphite+Pb(II)
10
0
4
6
8
10
12
pH Fig. 3. Flotation recovery of hemimorphite as a function of pH with 4 10 (II) and 2 10 4 M NaOl.
4
M Pb
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The effects of pH value on the zeta potential and of hemimorphite are shown in Fig. 5. The point of zero charge (PZC) hemimorphite occurred at pH 5.1 without reagent. When pH > PZC, the charge of the mineral surface switched from positive to negative. In the presence of lead ions, the zeta potential of hemimorphite showed a significant change, the positive surface charge of the mineral hinders adsorption of the lead ions. The minerals acquire increasing positive charge until approximately pH 5, lead ions positively shift the zeta potential of hemimorphite at a similar pH. The zeta potential of hemimorphite decreases with a charge reversal occurring at approximately pH 9.5. This behavior of zeta potential could be attributed to the lead ions being adsorbed/precipitated onto the negatively charged mineral surfaces through electrostatic interactions. The NaOl collector decreases the negative charge of the hemimorphite at acidic pH. In the presence of lead ions and NaOl collector, the zeta potential of the minerals is less negative compared to NaOl alone. The species distribution diagrams for lead ions (4 10 4 M) and NaOl (2 10 4 M) as a function of pH are shown in Fig. 6. All the species of NaOl collector have a negative charge when pH > 8.41, thereby benefiting the electrostatic interactions between the minerals and collector. The negatively charged NaOl ions and dimers exist in the basic pH region and below pH 8.41, where NaOl is in the form of RCOOH(l), oleate ions existed mainly as RCOO and R(COO)22 when pH > 8.41 (Ozkan et al., 2009). The positively charged Pb(II) species dominates at pH < 7.8 and PbOH (I) species dominates at pH 7.8–8.6, whereas lead ions were
80 75
Recovery (%)
70 65 60 55 50 45
0
30 20 10 0 -10 -20 -30 -40
Hemimorphite
-50 -60 2
3.2. Zeta-potential
40
40
Zeta potentials (mV)
anions and ionic–molecular complexes. In the presence of lead ions, the flotation recovery of hemimorphite oscillated with increasing pH and reached maximum values at a pH of 8.5, and approximately 70% was obtained. The recovery of the minerals is increased about 20% compared to solution in the absence of lead ions. Fig. 4 shows the effect of lead ions concentration on the flotation of hemimorphite in the presence of 2 10 4 mol/L NaOl at pH 8.5. The results in Fig. 4 demonstrated that hemimorphite flotation recovery of hemimorphite increased sharply with increases of lead ions initial concentration when it was less than 3 10 4 mol/L, above 3 10 4 mol/L lead ions, the flotation recovery of hemimorphite reached a maximum and remained constant.
1
Concentration
2
3
4
5
Fig. 4. Flotation recovery as a function of Pb(II) concentration at pH 9 with 2 10 4 M NaOl.
Hemimorphite+NaOl: 2
0-4 M
Hemimorphite+Pb(II):4
0 M
Hemimorphite+Pb(II):4
0 M+NaOl:2
4
6
-4
pH
-4
8
-4
0 M
10
12
Fig. 5. Zeta potentials of hemimorphite mineral as a function of pH.
predominantly in the form of Pb(OH)2(s) when pH > 8.5, respectively (Somasundaran and Dianzuo, 2006). At pH 5.1–9.5, the zeta-potential tests have shown the Pb(II) species to be positively changed. The positively charged Pb(II), PbOH(I) and Pb(OH)(s) species are expected to adsorb on the hemimorphite surfaces though electrostatic attraction, lead ions positively shift the zeta potential of hemimorphite was conducted to anion adsorption. The precipitates Pb(OH)2(s) increased when pH > 8.4, and Pb(OH)3 when pH > 9. The flotation recovery of hemimorphite reached a maximum about pH 9 for Pb(II) ions, the concentrations of Pb(II) and PbOH(I) decreased along with and Pb(OH)3 increased opposite tendency with the flotation of hemimorphite. These results were consistent with the results of the micro-flotation experiments (see Fig. 3). 3.3. FT-IR analysis Fig. 7 shows the FT-IR spectra of sodium oleate, and hemimorphite. In the FT-IR spectrum of sodium oleate, the bands at 2921.3 cm 1 and 2851.2 cm 1 can be attributed to the CAH stretching vibration of the ACH2A and ACH3 groups. respectively (Fukami et al., 1998). The bands at 1712.8 cm 1, 1559.2 cm 1, 1446.5 cm 1, and 1424.9 cm 1 can be attributed to the ACOOA vibration. Among these bands, the band at 1712.9 cm 1 can be attributed to the C@O stretching vibration, whereas the band at 1559.2 cm 1 can be attributed to the ACOOCA asymmetric stretching vibration. The bands at 1446.5 cm 1 and 1424.9 cm 1 can be attributed to the ACOOCA symmetric stretching vibration. The band at 721.8 cm 1 can be attributed to the A(CH2)nA deformation (Nájera, 2007; Tandon et al., 2001). Several characteristic bands for hemimorphite were observed (Poulet and Mathieu, 1975). The FT-IR spectra of hemimorphite with 3 10 4 mol/L Pb(II) ions at pH 9 in the presence and absence of NaOl are shown in Fig. 8. In the present of Pb(II) ions, there is no new peak in the spectra of hemimorphite. However, New peaks at 2922.5 cm 1, 2852.4 cm 1 1507.4 cm 1 and 1398.8 cm 1 were observed in the FT-IR spectra of activated hemimorphite after adding NaOl. The peaks at 2922.5 cm 1, 2852.4 cm 1 can be attributed to the CAH stretching vibration of the ACH2A and ACH3A group, respectively. The peak at 1507.4 cm 1 and 1398.8 cm 1 belonged to PbAOl complex appeared on hemimorphite surfaces (Wang, 2008). It’s different from the FTIR spectra of hemimorphite with NaOl (Liu et al., 2015). The crystal structure of hemimorphite on the (1 1 0) projection plane. Because the water molecules are arranged on the (1 1 0) surface. The bond of ZnAO is weaker than SiAO, fracture orientation
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Fig. 6. Species distribution diagrams of 4 10
4
M Pb(II) (a) and 2.0 10
4
M NaOl (b) as a function of pH.
occurs in the ZnAO bond direction. Therefore, one would expect an increased amount of surface Zn compared to Si. The Zn served as the main active site of the mineral surface. According to the results of zeta potentials and FT-IR analyses, a chemical interaction occurred between the hydroxy complexes (PbOH(I)) and precipitates (Pb (OH)2) and the Zn atoms on the mineral surface. After hemimorphite was treated in the presence of NaOl, the oleate was hydrolyzed to product dissolved species of the form RCOO and R (COO)22 , the dissolved species of RCOO and R(COO)22 NaOl interacted with Pb(II) ions in aqueous solution and the hydroxy complexes on the hemimorphite surface maybe to form lead oleate. 4. Conclusion The micro-flotation tests achieved flotation recoveries of the hemimorphite in the presence of NaOl, The floatability of the three minerals was enhanced by adding Pb(II) ions. A maximum flotation recovery of the mineral with iron activation was increased from about 50% to 70% at pH 9. Zeta-potential measurements result showed the hemimorphite were negatively charged below pH 5.1 in the water, However, the minerals became positively charged at pH 5.1–8.5 in the presence of Pb(II) ions. Under these solutions, the Pb(II) ions formed hydroxy complexes (PbOH(I) and precipitates (Pb(OH)2. Chemical interactions occurred between the hydroxy complexes and the precipitates of Pb(II) ions and Zn atoms on the mineral surface. The hydroxy complexes on the hemimorphite surface interacted with the RCOO and R(COO)22 portions of NaOl to form lead oleate and resulted in the activated flotation of hemimorphite.
Fig. 7. FT-IR spectra of sodium oleate and hemimorphite.
hemimorphite+Pb(II)
hemimorphite+Pb(II)+NaOl
3500
3000
2500
pH
2000
1500
1000
864.1 678.6 601.4 558.0
1087.1
4000
1087.1 931.8
2922.5 2852.4
1635.4 1507.4 1398.8
Acknowledgement
500
Fig. 8. FT-IR spectra of hemimorphite with Pb(II) ions at pH 9 in the absence and in the presence of NaOl.
The authors acknowledge the support of the Major State Basic Research Development Program of China (973 program) (2014CB643402). References Anthony, J.W., Bideaux, R.A., Bladh, K.W., Nichols, M.C., 1995. Handbook of Mineralogy. Silica, Silicates (Part 1), vol. 2. Mineral Data Publishing, Tuscon, Arizona, USA. Ejtemaei, M., Irannajai, M., Gharabaghi, M., Irannajad, M., 2012. Role of dissolved mineral species in selective flotation of smithsonite from quartz using oleate as collector. Int. J. Miner. Process. 114–117, 40–47. Fan, X., Rowson, N.A., 2000. The effect of Pb(NO3)2 on ilmenite flotation. Miner. Eng. 13 (2), 105–115.
C. Liu et al. / Minerals Engineering 89 (2016) 163–167 Frost, Ray L., Bouzaid, Jocelyn M., Jagannadha Reddy, B., 2007. Vibrational spectroscopy of the sorosilicate mineral hemimorphite Zn4(OH)2Si2O7H2O. Polyhedron 26, 2405–2412. Fukami, Y., Maeda, Y., Awazu, K., 1998. Raman and FT-IR studies of photodynamic processes of cholesteryl oleate using IRFELs. Nucl. Instrum. Methods Phys. Res. B 144, 229–235. Ghosh, M.K., Das, R.P., Biswas, A.K., 2002. Oxidative ammonia leaching of sphalerit. Part I. Noncatalytic kinetics. Int. J. Miner. Proc. 66, 241–254. Liu, C., Feng, Q.-M., Zhang, G.-F., 2015. Electrokinetic and flotation behaviors of hemimorphite in the presence of sodium oleate. Miner Eng 84, 74–76. Nájera, J.J., 2007. Phase transition behaviour of sodium oleate aerosol particles. Atmos. Nakamura, R., Arikata, K., Suginohara, Y., Yanagase, T., 1977. Structure of silicates as studies by trimethylsilylation. Kogaku Shuho-Kyushu Daigaku 50 (5), 635–641. Ozkan, A., Ucbeyiay, H., Duzyol, S., 2009. Comparison of stages in oil agglomeration process of quartz with sodium oleate in the presence of Ca(II) and Mg(II) ions. J. Colloid Interf. Sci. 329, 81–88. Poulet, H., Mathieu, J.P., 1975. Vibration spectra and structure of hemimorphite. Bulletin de la Societe Francaise de Mineral. et de Crystallographica 98, 3–5.
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Salum, M.J.G., de Araujo, A.C., Peres, A.E.C., 1992. The role of sodium sulphide in amine flotation of silicate zinc minerals. Miner. Eng. 5, 411–419. Shirin, E., Fereshteh, R., Sadrnezhaad, S.K., 2006. Hydrometallurgical treatment of tailings with high zinc content. Hydrometallurgy 82, 54–62. Somasundaran, P., Dianzuo, W., 2006. Solution Chemistry: Minerals and Reagents. Elsevier. Tandon, P., Raudenkolb, S., Neubert, R.H.H., Rettig, W., Wartewig, S., 2001. X-ray diffraction and spectroscopic studies of oleic acid–sodium oleate. Chem. Phys. Lipids 109, 37–45. Wang Fuliang, 2008. Fundamental Research of Flotation on Typical Sulphides/ Carbonates/Oxides of Cu, Pb, Zn and Fe. Ph.D Thesis. Northeast University, pp. 182–183 (in chinese). Zhang, J., Wang, W.-Q., Liu, J., Huang, Y., Feng, Q.-M., Zhao, H., 2014. Fe(III) as an activator for the flotation of spodumene, albite, and quartz minerals. Miner. Eng. 61, 16–22. Zhu, Y.-G., Zhang, G.-F., Feng, Q.-M., Yan, D.-C., Wang, W.-Q., 2012. Effect of surface dissolution on flotation separation of fine ilmenite from titanaugite. Trans. Nonferr. Met. Soc. China 21, 1149–1154.
Contents lists available at ScienceDirect
Minerals Engineering journal homepage: www.elsevier.com/locate/mineng
Effects of lead ions on the flotation of hemimorphite using sodium oleate Cheng Liu, Qiming Feng, Guofan Zhang ⇑, Wankun Ma, Qingyou Meng, Yanfei Chen School of Mineral Processing and Bioengineering, Central South University, Changsha 410083, China
a r t i c l e
i n f o
Article history: Received 31 October 2015 Revised 5 February 2016 Accepted 6 February 2016 Available online 9 February 2016 Keywords: Lead ions Hemimorphite Flotation Sodium oleate
a b s t r a c t The effects of Pb(II) ions on the flotation of hemimorphite was investigated by micro-flotation tests, zeta-potential measurements, solution chemistry and Fourier transform infrared spectroscopy. The micro-flotation results indicated that the Pb(II) effectively improved the flotation of hemimorphite minerals. Good floatability of minerals was obtained in the pH region 7 to 9. Adsorption/precipitation of the hydrolyzed species of lead cations occurred in this pH region, these species promote sodium oleate adsorption and from lead oleate on the surface of hemimorphite. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction Zinc is an important base metal that used in the galvanizing, alloys, as well as other industries (Ghosh et al., 2002; Shirin et al., 2006). Hemimorphite is a sorosilicate of formula Zn4Si2O7(OH)2H2O. The termination of the crystal is rather blunt being dominated by a pedion face while the opposite end, is terminated by the point of a pyramid (Anthony et al., 1995). The crystal structure contains tetrahedrons of ZnO3OH, interlocked with Si2O7 groups and water molecules. The zinc is at the center of the tetrahedron while the three oxygens, along with an OH group, are at the four points of the tetrahedron. The mineral is orthorhombic with point group mm2 (Frost et al., 2007; Nakamura et al., 1977). A molecular model of hemimorphite is shown in Fig. 1. In industrial flotation, the existence of unavoidable metal ions such as ions of iron, copper and lead, significantly influence the flotation performance of target mineral (Fan and Rowson, 2000; Zhu et al., 2012). They determined that metal ions formed precipitate, the precipitate and the hydroxy complexes could adsorb onto the surfaces of minerals, and increasing their flotation by promoting collector adsorption. (Zhang et al., 2014; Ejtemaei et al., 2012) examined the flotation responses of quartz and feldspar with collectors in the presence of metal ions. They found that quartz floated in the presence of Pb(II), Zn(II) and Fe(II) ions. On the flotation of hemimorphite with collectors in the absence of metal ions was studies by Liu et al. (2015), Salum et al. (1992), however, no one reported use of lead ions as an activator for hemimorphite
⇑ Corresponding author. E-mail address: [email protected] (G. Zhang). http://dx.doi.org/10.1016/j.mineng.2016.02.002 0892-6875/Ó 2016 Elsevier Ltd. All rights reserved.
flotation, lead ions as an activator for the flotation mechanism of hemimorphite is unclear. Before the study, the hemimorphite activated by lead ions cannot be depressed, whereas Pb(II) ion activation of quartz and calcite as the major gangue mineral found in the zinc oxide ores can be depressed using calcium lignosulfonate as a depressant in the presence of NaOl though single minerals tests. Therefore, achieving a selective separation from the hemimorphite ores is possible in the presence of lead ions. In consequence, the main objective of the present research was to examine the interaction of the hemimorphite surface with lead ions and NaOl. This was accomplished through the use of various techniques, including micro-flotation, zeta-potential analysis, adsorption measurements, lead ions and NaOl species in solution and FT-IR.
2. Materials and methods 2.1. Samples and reagents The ore samples of hemimorphite minerals were obtained from Changsha of Hunan Province, China. The samples were crushed and ground using an agate mortar. The products were then dry sieved to obtain a particle size of 74 lm. The ore was analyzed via a chemical method and phase-examined using powder X-ray diffraction (XRD) showed in Fig. 2. The chemical compositions of the samples are listed in Table 1. According to the result of the XRD analysis, the purities of hemimorphite was very high. Sodium oleate (CH3(CH2)7CH@CH(CH2)7COONa) (NaOl) was used as the anionic collector for the micro-flotation tests. Lead nitrate (PbNO3) was used as the source of lead ions activator. HCl
164
C. Liu et al. / Minerals Engineering 89 (2016) 163–167
2.3. Zeta potential tests Zeta measurements were performed in 1 10 3 mol/L KNO3 background electrolyte solution using Coulter Delsa440sx Zeta analyzer instrument. The suspensions (0.01% mass fraction) with small amount of the minerals were dispersed in a beaker magnetically stirred for 15 min in the presence of different concentration of reagents at various pH values. After 20 min of settling, the pH value of the suspension was measured and the supernatant was obtained for zeta-potential measurements. The zeta-potential of each sample was measured three times in this paper, and the average was reported as the final value. 2.4. FT-IR spectroscopy measurements The FT-IR spectra were obtained using a Spectrum One FT-IR (Japan) spectrometer to characterize the nature of the interaction between the collector and minerals. Approximately 1% (mass fraction) of the solid sample was mixed with spectroscopic grade KBr. The wave number range of the spectra was 400–4000 cm 1. Each spectra was recorded with 30 scans measured at 2 cm 1 resolution. To prepare the samples for FT-IR analysis, pure mineral particles were ground to 5 lm using an agate mortar. A suspension was prepared by adding 2.0 g of the pure mineral particles to 35 mL of deionized water in a Plexiglas cell (40 mL). The suspension was conditioned for 5 min using HCl and NaOH as the pH regulators. Then, the suspension was conditioned for 5 min with lead ions. Afterward, the suspension was conditioned for 3 min with NaOl. Finally, the solid samples were washed three times using distilled water with the same pH and allowed to dry prior to FT-IR analyses.
Fig. 1. Model of hemimorphite structure.
3. Results and discussion 3.1. Micro-flotation The objective of this study was to investigate the effects of lead ions on the flotation of hemimorphite in the presence of NaOl. Fig. 3 shows the flotation recovery of hemimorphite as a function of pH with and without lead ions, and with 2 10 4 mol/L NaOl. The flotation recovery of hemimorphite showed a better floatability throughout the pH range of 4.0–9.0 in the absence of lead ions which is attributed to increases in the concentrations of oleate
Fig. 2. XRD of the hemimorphite sample.
Table 1 Chemical composition of hemimorphite ore.
80
ZnO
SiO2
Al2O3
Fe
Pb
Cu
Other
66.75
24.34
0.086
0.141
0.032
0.018
8.633
70
and NaOH were used for the pH adjustment in the experiments. All the reagents were of analytical grade, and the water used in all the experiments was distilled water. 2.2. Micro-flotation tests
Recovery (%)
60 50 40 30 20
The micro-flotation were carried out in a mechanical agitation flotation machine. The mineral suspension was prepared by adding 2.0 g of mineral to 35 ml of solution. The pulp was continuously stirred for 1 min using a pH regulator, 3 min with the activator, and 3 min with the collector. The pH of the solution was measured before the flotation, and the flotation was conducted for 4 min. The floated and tailing fractions were collected separately and dried and weighed for calculations.
Hemimorphite Hemimorphite+Pb(II)
10
0
4
6
8
10
12
pH Fig. 3. Flotation recovery of hemimorphite as a function of pH with 4 10 (II) and 2 10 4 M NaOl.
4
M Pb
165
C. Liu et al. / Minerals Engineering 89 (2016) 163–167
The effects of pH value on the zeta potential and of hemimorphite are shown in Fig. 5. The point of zero charge (PZC) hemimorphite occurred at pH 5.1 without reagent. When pH > PZC, the charge of the mineral surface switched from positive to negative. In the presence of lead ions, the zeta potential of hemimorphite showed a significant change, the positive surface charge of the mineral hinders adsorption of the lead ions. The minerals acquire increasing positive charge until approximately pH 5, lead ions positively shift the zeta potential of hemimorphite at a similar pH. The zeta potential of hemimorphite decreases with a charge reversal occurring at approximately pH 9.5. This behavior of zeta potential could be attributed to the lead ions being adsorbed/precipitated onto the negatively charged mineral surfaces through electrostatic interactions. The NaOl collector decreases the negative charge of the hemimorphite at acidic pH. In the presence of lead ions and NaOl collector, the zeta potential of the minerals is less negative compared to NaOl alone. The species distribution diagrams for lead ions (4 10 4 M) and NaOl (2 10 4 M) as a function of pH are shown in Fig. 6. All the species of NaOl collector have a negative charge when pH > 8.41, thereby benefiting the electrostatic interactions between the minerals and collector. The negatively charged NaOl ions and dimers exist in the basic pH region and below pH 8.41, where NaOl is in the form of RCOOH(l), oleate ions existed mainly as RCOO and R(COO)22 when pH > 8.41 (Ozkan et al., 2009). The positively charged Pb(II) species dominates at pH < 7.8 and PbOH (I) species dominates at pH 7.8–8.6, whereas lead ions were
80 75
Recovery (%)
70 65 60 55 50 45
0
30 20 10 0 -10 -20 -30 -40
Hemimorphite
-50 -60 2
3.2. Zeta-potential
40
40
Zeta potentials (mV)
anions and ionic–molecular complexes. In the presence of lead ions, the flotation recovery of hemimorphite oscillated with increasing pH and reached maximum values at a pH of 8.5, and approximately 70% was obtained. The recovery of the minerals is increased about 20% compared to solution in the absence of lead ions. Fig. 4 shows the effect of lead ions concentration on the flotation of hemimorphite in the presence of 2 10 4 mol/L NaOl at pH 8.5. The results in Fig. 4 demonstrated that hemimorphite flotation recovery of hemimorphite increased sharply with increases of lead ions initial concentration when it was less than 3 10 4 mol/L, above 3 10 4 mol/L lead ions, the flotation recovery of hemimorphite reached a maximum and remained constant.
1
Concentration
2
3
4
5
Fig. 4. Flotation recovery as a function of Pb(II) concentration at pH 9 with 2 10 4 M NaOl.
Hemimorphite+NaOl: 2
0-4 M
Hemimorphite+Pb(II):4
0 M
Hemimorphite+Pb(II):4
0 M+NaOl:2
4
6
-4
pH
-4
8
-4
0 M
10
12
Fig. 5. Zeta potentials of hemimorphite mineral as a function of pH.
predominantly in the form of Pb(OH)2(s) when pH > 8.5, respectively (Somasundaran and Dianzuo, 2006). At pH 5.1–9.5, the zeta-potential tests have shown the Pb(II) species to be positively changed. The positively charged Pb(II), PbOH(I) and Pb(OH)(s) species are expected to adsorb on the hemimorphite surfaces though electrostatic attraction, lead ions positively shift the zeta potential of hemimorphite was conducted to anion adsorption. The precipitates Pb(OH)2(s) increased when pH > 8.4, and Pb(OH)3 when pH > 9. The flotation recovery of hemimorphite reached a maximum about pH 9 for Pb(II) ions, the concentrations of Pb(II) and PbOH(I) decreased along with and Pb(OH)3 increased opposite tendency with the flotation of hemimorphite. These results were consistent with the results of the micro-flotation experiments (see Fig. 3). 3.3. FT-IR analysis Fig. 7 shows the FT-IR spectra of sodium oleate, and hemimorphite. In the FT-IR spectrum of sodium oleate, the bands at 2921.3 cm 1 and 2851.2 cm 1 can be attributed to the CAH stretching vibration of the ACH2A and ACH3 groups. respectively (Fukami et al., 1998). The bands at 1712.8 cm 1, 1559.2 cm 1, 1446.5 cm 1, and 1424.9 cm 1 can be attributed to the ACOOA vibration. Among these bands, the band at 1712.9 cm 1 can be attributed to the C@O stretching vibration, whereas the band at 1559.2 cm 1 can be attributed to the ACOOCA asymmetric stretching vibration. The bands at 1446.5 cm 1 and 1424.9 cm 1 can be attributed to the ACOOCA symmetric stretching vibration. The band at 721.8 cm 1 can be attributed to the A(CH2)nA deformation (Nájera, 2007; Tandon et al., 2001). Several characteristic bands for hemimorphite were observed (Poulet and Mathieu, 1975). The FT-IR spectra of hemimorphite with 3 10 4 mol/L Pb(II) ions at pH 9 in the presence and absence of NaOl are shown in Fig. 8. In the present of Pb(II) ions, there is no new peak in the spectra of hemimorphite. However, New peaks at 2922.5 cm 1, 2852.4 cm 1 1507.4 cm 1 and 1398.8 cm 1 were observed in the FT-IR spectra of activated hemimorphite after adding NaOl. The peaks at 2922.5 cm 1, 2852.4 cm 1 can be attributed to the CAH stretching vibration of the ACH2A and ACH3A group, respectively. The peak at 1507.4 cm 1 and 1398.8 cm 1 belonged to PbAOl complex appeared on hemimorphite surfaces (Wang, 2008). It’s different from the FTIR spectra of hemimorphite with NaOl (Liu et al., 2015). The crystal structure of hemimorphite on the (1 1 0) projection plane. Because the water molecules are arranged on the (1 1 0) surface. The bond of ZnAO is weaker than SiAO, fracture orientation
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Fig. 6. Species distribution diagrams of 4 10
4
M Pb(II) (a) and 2.0 10
4
M NaOl (b) as a function of pH.
occurs in the ZnAO bond direction. Therefore, one would expect an increased amount of surface Zn compared to Si. The Zn served as the main active site of the mineral surface. According to the results of zeta potentials and FT-IR analyses, a chemical interaction occurred between the hydroxy complexes (PbOH(I)) and precipitates (Pb (OH)2) and the Zn atoms on the mineral surface. After hemimorphite was treated in the presence of NaOl, the oleate was hydrolyzed to product dissolved species of the form RCOO and R (COO)22 , the dissolved species of RCOO and R(COO)22 NaOl interacted with Pb(II) ions in aqueous solution and the hydroxy complexes on the hemimorphite surface maybe to form lead oleate. 4. Conclusion The micro-flotation tests achieved flotation recoveries of the hemimorphite in the presence of NaOl, The floatability of the three minerals was enhanced by adding Pb(II) ions. A maximum flotation recovery of the mineral with iron activation was increased from about 50% to 70% at pH 9. Zeta-potential measurements result showed the hemimorphite were negatively charged below pH 5.1 in the water, However, the minerals became positively charged at pH 5.1–8.5 in the presence of Pb(II) ions. Under these solutions, the Pb(II) ions formed hydroxy complexes (PbOH(I) and precipitates (Pb(OH)2. Chemical interactions occurred between the hydroxy complexes and the precipitates of Pb(II) ions and Zn atoms on the mineral surface. The hydroxy complexes on the hemimorphite surface interacted with the RCOO and R(COO)22 portions of NaOl to form lead oleate and resulted in the activated flotation of hemimorphite.
Fig. 7. FT-IR spectra of sodium oleate and hemimorphite.
hemimorphite+Pb(II)
hemimorphite+Pb(II)+NaOl
3500
3000
2500
pH
2000
1500
1000
864.1 678.6 601.4 558.0
1087.1
4000
1087.1 931.8
2922.5 2852.4
1635.4 1507.4 1398.8
Acknowledgement
500
Fig. 8. FT-IR spectra of hemimorphite with Pb(II) ions at pH 9 in the absence and in the presence of NaOl.
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