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The surface features of lead activation in amyl xanthate flotation of quartz
International Journal of Mineral Processing 151 (2016) 33–39
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International Journal of Mineral Processing journal homepage: www.elsevier.com/locate/ijminpro
The surface features of lead activation in amyl xanthate flotation of quartz Biao Liu a,b, Xuming Wang b, Hao Du a,⁎, Jing Liu b, Shili Zheng a, Yi Zhang a, Jan D. Miller b,⁎ a b
National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China Department of Metallurgical Engineering, University of Utah, 135 S 1460 E, Rm 412, Salt Lake City, UT 84112, USA
a r t i c l e
i n f o
Article history: Received 30 September 2015 Received in revised form 13 April 2016 Accepted 18 April 2016 Available online 22 April 2016 Keywords: FTIR AFM Activation Quartz flotation Amyl xanthate
a b s t r a c t It is confirmed in this study that silica can be activated with lead (II) ion and floated with potassium amyl xanthate in the alkaline region as evidenced from micro-flotation experiments. This conclusion is complimented with the results from electrophoresis experiments and by solution chemistry analysis. The PbOH+ and Pb(OH)2 (aq) species which are believed to be responsible for silica activation were found to precipitate at the silica surface. These island-like precipitate structures were clearly observed using AFM and SEM imaging. With amyl xanthate addition, lead amyl xanthate was formed as revealed by FTIR. Contact angle measurements further confirmed the nature of lead activation in silica flotation with amyl xanthate collector. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Due to the excellent characteristics quartz is widely used in the production of glass, ceramic, refractory material, and optical communication (Ding, 2010). As one of the most abundant minerals in the earth's crust, quartz frequently associates with other minerals, such as feldspar, talc, pyrite, hematite, smithsonite, and apatite (Zhou, 2013). The separation of quartz from other minerals has attracted increasing interest in recent years, especially for the separation of feldspar and quartz due to their similar tectosilicate structure (El-Salmawy et al., 1993; Vidyadhar and Hanumantha Rao, 2007). To obtain high purity quartz, froth flotation is generally used. Quartz can be satisfactorily floated by anionic collectors, such as sodium oleate (Sun et al., 1992), sodium alkylsulfonate (El-Salmawy et al., 1993; Fuerstenau et al., 1968), and sodium alkyl sulfate (Wang and Hu, 1988), with metal ions as activators. Metal ion activation has been a classic pretreatment method for quartz flotation (El-Salmawy et al., 1993). Quartz is also a typical gangue mineral in many flotation systems such as beryl (Fuerstenau et al., 1965b), sphalerite (Duarte and Grano, 2007), and other sulfide minerals. Although quartz possesses hydrophilic surface properties in nature and cannot be floated by anionic surfactants alone at any pH, hydrophobicity can be induced by adding polyvalent cations to the system. For example, quartz can be completely floated from pH 5.8 to 8.5 with Pb2+ as activator and amyl xanthate as collector. In the case of Zn2+, the activation pH range is from pH 7.5 to 8.1 (Fuerstenau et al., 1970; Fuerstenau et al., 1965a). Quartz can also be activated by Cu2+ or Ni2+ and floated with xanthate in the pH region ⁎ Corresponding authors. E-mail addresses: [email protected] (H. Du), [email protected] (J.D. Miller).
http://dx.doi.org/10.1016/j.minpro.2016.04.004 0301-7516/© 2016 Elsevier B.V. All rights reserved.
pH 7 to 10 (Fornasiero and Ralston, 2005). With oleate as collector, Ca2+, Mg2+, and Fe3+ are usually used for activation in quartz flotation. The results have shown that the effective flotation was attributed to the formation of a surface metal hydrous-oleate complex (Sun et al., 1992). Fe2+, Al3+, Pb2+, Mg2+, Mn2+ and Ca2+ are also shown to function as activators with long chain sulfonate as collector (Fuerstenau et al., 1963). Due to the slight dissolution of metal ions from metallic sulfides or oxides, the quartz can be activated inadvertently and floated by anionic collectors, which leads to unexpected presence of quartz in the concentrates (Fornasiero and Ralston, 2005). To obtain better separation of quartz from other minerals in quartz production, or to prevent the inadvertent activation of quartz when present as gangue, extensive fundamental studies have been carried out in the last fifty years to study polyvalent cation activation effect in the flotation of quartz. M. C. Fuerstenau and his co-workers (Fuerstenau et al., 1970; Fuerstenau et al., 1963; Fuerstenau et al., 1965a; Fuerstenau et al., 1965b) have done much research on anionic quartz flotation with metal ion activation. Electrophoretic, metal ion adsorption experiments and flotation tests were performed. In the case of lead activation, it was found that due to the adsorption of the lead species, quartz was positively charged from pH 7 to pH 11 in the presence of 1 × 10−4 M lead ions (Fuerstenau et al., 1970). Complete amyl xanthate flotation was achieved in this pH range. Correlation of the lead species distribution with the flotation response shows that Pb(OH)+ is probably responsible for the activation. A basic lead xanthate complex may be functioning as the collector (Fuerstenau et al., 1965a), which has been suggested by other researchers (Fornasiero and Ralston, 2005; James and Healy, 1972a, 1972b; Laskowski and Castro, 2012). However, there is no direct evidence to verify the adsorption of active species and subsequent collector adsorption.
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B. Liu et al. / International Journal of Mineral Processing 151 (2016) 33–39
MIBC was added as frother. The silica suspension was transferred to the Hallimond tube. The air was set to achieve the desired air flow rate of 40 mL/min. The hydrophobic silica particles attached to the bubbles and floated to the top of the tube. The flotation time was 5 min. The float and sink fractions were filtered, dried, and weighted. 2.4. Contact angle measurement
Fig. 1. Zeta potential of unactivated and activated silica as a function of pH.
In this study, AFM, together with SEM, has been utilized to detect the changes in the silica surface state when lead and amyl xanthate were used to achieve effective silica flotation. By imaging the silica surface, the precipitation of lead and/or the formation of a lead-xanthate compound might be detected. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) was used to further identify the formation of the lead-xanthate compounds. In conjunction with the electrophoretic measurements, flotation tests and contact angle measurements, the mechanism of amyl xanthate flotation of quartz with lead as activator first studied by M. C. Fuerstenau and his co-workers will be better understood. 2. Experimental section 2.1. Chemicals and materials All solutions in this study were prepared using Millipore Milli-Q water (18 MΩ·cm). Potassium amyl xanthate (90%, TCI), lead nitrate (99%, Alfa Aesar) and 4-methyl-2-pentanol (MIBC, 98%, SigmaAldrich) were used as received, without further purification. Silica (−10 μm, U.S. Silica) was used for the electrophoresis measurements. Coarse silica (40 × 100 mesh, Acros) was used for the micro-flotation. An IR/UV grade fused silica disk (20 × 2 mm, Gold Dragon Optics Co., Ltd., China) was used in AFM, SEM and contact angle measurements. 2.2. Electrophoresis measurements Electrophoretic mobility of the silica was performed using a Zeta potential analyzer (Zeta PALS, Brookhaven Instruments Corporation, Holtsville, NY). Lead nitrate solutions of varying concentrations were prepared in a beaker. The pH was adjusted with sodium hydroxide and hydrochloric acid solutions, and then silica powders (− 10 μm) were dispersed in the lead nitrate solutions and a suspension with 0.025% silica was prepared. The suspensions were stirred for 20 min and then about 10 mL transferred to the Zeta PALS cell. The Zeta potentials of silica particles were measured. The instrument automatically calculated the mobilities of the particles and converted the results to zeta potential according to the Smoluchowski equation. To ensure precise zeta potential determination, five runs of 30 cycles per run were conducted for every sample and the average values were reported.
Similar to the silica treatment in micro-flotation, the fused silica disk was activated by lead and amyl xanthate was added for adsorption. The silica disk was taken out from the solutions and blown dry by high purity nitrogen. Then the contact angle of silica was measured by a contact angle goniometer (RAME-HART, Inc. NRL U.S.A.) using the sessile drop method. For each sample, at least five drops were measured and the average value from five measurements was calculated. 2.5. AFM measurement A Nanoscope AFM with Nanoscope IV controller (Veeco Instruments Inc., Santa Barbara, CA) was used with an E-type scanner. Triangular beam silicon nitride (Si3N4) cantilevers (Veeco Instrument Inc., Santa Barbara, CA) with pyramid-shaped tips were used. The sample holder was cleaned using acetone, ethanol, and water in order, and gently dried with ultra high purity N2 gas. The cantilevers were subsequently cleaned in a UV chamber for 30 min prior use. The silica disk treated with 150 mL lead and amyl xanthate solutions, was mounted on a piezo scanner. The contact mode was applied for imaging of the silica surface. The AFM instrument was kept in an acoustic and vibrational isolation chamber. The images of the silica surface were obtained at a scan rate of 1 Hz and a scan area of 5 × 5 μm. The images were processed offline using Nanoscope vs. 5.31R1 software. Flattening and low pass filtering were applied to remove noise. Image processing software, Gwyddion 2.15, was used to calculate the area covered by leadcontaining precipitates and lead-xanthate compounds at the silica surface. 2.6. SEM analysis The silica disk was firstly treated with 150 mL lead and amyl xanthate solutions and then analyzed using SEM. The SEM image of treated silica was collected using FEI Quanta 250 SEM. The energy spectra were analyzed using EDAX GENESIS energy dispersive spectroscopy. 2.7. DRIFT measurement Diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) equipped with a diffuse reflectance unit (PIKE Technologies) was used to identify adsorbed collector at the silica surface. The infrared spectra were recorded for all samples on the air dried 40 × 100 mesh silica
2.3. Micro-flotation tests The flotation response of silica was determined using a 125 mL Hallimond tube (20 × 220 mm) with a fine frit (10 μm) and a magnetic stirrer. Silica samples (40 × 100 mesh) of 2 g were used in each microflotation test. 150 mL lead nitrate solution of desired pH was first prepared and then the silica particles were added. The solution was conditioned for 20 min, and then additional 5 min was applied after amyl xanthate was added as collector. After collector adsorption, 0.02 mL of
Fig. 2. Relationship between flotation recovery and pH with various lead and amyl xanthate additions (the lead concentration equals the amyl xanthate concentration).
B. Liu et al. / International Journal of Mineral Processing 151 (2016) 33–39 Table 1 Sessile drop contact angles at the silica surface for various lead and potassium amyl xanthate concentrations at different pH values (the lead concentration equals the amyl xanthate concentration). Concentration, M
pH 7.0–7.5
pH 8.0–8.5
pH 9.0–9.6
pH 10.0–10.5
1 × 10−4 5 × 10−4 1 × 10−3
38 80 88
27 80 85
55 62 81
64 74 93
powders. The FTIR spectra were obtained by a BioRad FTS-6000 spectrometer. It is capable of data collection over a wave number range of 370–7800 cm−1. About 10% by weight of the solid samples were mixed with spectroscopic grade KBr powders with a refractive index
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of 1.559 and a particle size of 1–5 μm. These spectra were recorded with 500 scans measured at 4 cm−1 resolution. 3. Results and discussion 3.1. The electrophoresis behavior of activated silica The zeta potential of silica in the absence and presence of lead ions in solution is shown in Fig. 1. The zeta potential of fresh silica was negative and its value became more negative with increase in pH. The point of zero charge (PZC) of silica was reported to be pH 2 (Fuerstenau, 2005). The surface charge of the silica was all negative in the measured pH range. With the addition of lead, the zeta potential became less negative and even positive at higher lead concentration. When the lead
Fig. 3. The topography height images of fresh silica surface (A1 and A2), activated silica surface (B1 and B2) and collector adsorbed silica surface at pH 10 (C1 and C2).
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Fig. 4. The SEM image of lead treated silica surface and EDX of the given point at the image (the concentration of lead nitrate is 5 × 10−5 M, and the pH is 10).
concentrations are higher than 1 × 10−4 M, a positive zeta potential was observed in the pH region of 6 to 11, which agreed quite well with previous results (Fuerstenau et al., 1970; Rashchi et al., 1998). In the case of positively charged silica surface, the amyl xanthante anion will adsorb on the silica surface, which facilitates the flotation. So far, it is confirmed that the property of the silica surface can be changed by lead ions.
3.2. The flotation response of activated silica Fig. 2 illustrates the flotation response after silica was activated at different lead nitrate concentrations. Excellent flotation recovery was obtained when lead ions were introduced into the flotation pulp. With a lead concentration increasing to 5 × 10−4 M, complete recovery occurred from pH 6 to pH 12, which is similar to results reported from previous flotation research (Fuerstenau et al., 1965a). In correlation with the surface charge of activated silica, it is believed that the adsorbed lead ions make the silica surface positive, which allows the adsorption of amyl xanthate and makes the silica surface hydrophobic. To reveal the change of silica surface hydrophobicity, the contact angles of the silica surface under different lead ions and potassium amyl xanthate concentrations, 1 × 10−4 M,5 × 10− 4 M and 1 × 10− 3 M, were measured and the results are shown in Table 1. It is clear that the contact angle measurement is correlated with the flotation response. When the contact angles were high, a good flotation recovery was obtained for the hydrophobic silica. Interestingly, there was a slight decrease of recovery in the vicinity of pH 9 when the concentration of lead and amyl xanthante was 5 × 10−4 M or higher. At lower concentration, the decrease occurred at about pH 7. Similar results were also reported by M. C. Fuerstenou et al. (Fuerstenau et al., 1965a). No flotation occurred at the intermediate region when the lead concentration was 1 × 10−4 M and the amyl xanthate concentration was 1 × 10−5 M or 2.5 × 10−5 M.
3.3. The topography of silica before and after collector treatment AFM is a powerful tool for surface chemistry research. It can describe the surface topography without damaging the delicate surface. In this study, AFM was used to examine the silica surface topography to see if the formation of lead hydroxide and/or lead-collector compounds could be detected. The AFM images of a silica surface after conditioning with 1 × 10−4 M lead and amyl xanthate are shown in Fig. 3. As revealed in Fig. 3, the fresh silica surface is flat and smooth. After conditioning in 1 × 10−4 M lead nitrate solutions for 10 min (at pH 10), the island-like patches with average size of 0.3 μm were found at the silica surface and the surface became rough (B1 and B2). The patches were also found in the SEM image as shown in Fig. 4. To detect the composition of the precipitates, the EDX was performed and the results are presented in Fig. 4. It is shown that the main elements of the patches were O, Si and Pb. The Si is expected to be originated from the silica substrate and the Pb element should be resulted from the lead-containing precipitates at the silica surface. It was confirmed that lead-containing compounds precipitated at the silica surface and formed lead oxide or lead hydroxide as suggested in the literature (Finkelstein, 1997). When amyl xanthate was added during the conditioning, it was expected that the amyl xanthate would adsorb at the silica surface. As shown in Fig. 3C1 and C2, the surface became rougher than the pure lead activated surface without the addition of collector, due to the fact that collector was mainly adsorbed on the lead precipitate. The root-mean-square roughness of fresh silica, lead activated silica and collector adsorbed silica were 0.703 nm, 1.76 nm and 9.44 nm respectively. It is concluded that the formation of the lead-containing precipitate facilitated the adsorption of collector and made the silica surface hydrophobic. If the silica was conditioned in an acidic solution (pH 4), there was no lead adsorbed at the surface as revealed in Fig. 5A. There is no adsorption of amyl xanthate at the silica surface as shown in Fig. 5B and no effective flotation of silica is observed (Fig. 2). Even at basic pH,
Fig. 5. The topography height images of fresh silica surface: A, lead activated silica at pH 4; B, collector treated silica at pH 4; C, collector treated silica at pH 10 without lead activation.
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without lead activation the collector adsorption at the silica surface was not occurred, as revealed by Fig. 5C. Therefore, it is believed that metal ion activation is necessary for the effective flotation of silica by xanthate. Fig. 6 shows the images of lead activated silica and collector treated silica with lead and amyl xanthate concentrations of 5 × 10−4 M. With higher concentration, large island-like lead-containing patches were formed and unevenly scattered at the silica surface. After collector treatment, plenty of amyl xanthate was adsorbed onto the island-like patches. These island-like patches are believed to account for the hydrophobicity during flotation. According to the island area from the AFM image, the collector coverage at the silica surface can be calculated. The coverage under three concentrations, 1 × 10−4 M, 5 × 10−4 M and 1 × 10−3 M, were 5.9%, 6.7% and 6.6% respectively (the condition pH was within the effective flotation range of pH 10–10.5). The coverage did not raise when the xanthate concentration increases from 1 × 10−4 M to 1 × 10−3 M. But the hydrophobicity increased with their concentrations, which can be seen in the contact angle measurements presented in Table 1. It may due to the fact that the adsorption layer of lead amyl xanthate is formed at the activated silica surface, which contains not only chemisorbed lead amyl xanthate, but also physically adsorbed lead amyl xanthate. The physically adsorbed lead amyl xanthate forms the second layer of the collector at high concentration of xanthate, which intensifies the hydrophobicity. The multilayer physically adsorbed lead ethyl xanthate (Pb(EX)2) was also detected during the activation and flotation process of Pb(II) on galena and sphalerite (Vučinić et al., 2006).Therefore, the coverage of xanthate does not raise when the xanthate concentration increases from 1 × 10−4 M to 1 × 10−3 M, while the contact angle raises significantly, which will be well discussed in the following part.
flotation response showed that the formation of hydroxo complex PbOH+ and Pb(OH)2 (aq) was closely related to the effective flotation of silica. Complete flotation was obtained at alkaline pH where PbOH+ and Pb(OH)2 (aq) are the major species, which indicates that the lead hydroxo complexes are responsible for silica activation. To form stable lead-containing precipitates at the silica surface, the lead hydroxo complexes may react with silica in two ways. One is the reaction of PbOH+ with the silica surface:
3.4. The lead activation discussion
These two ways have been confirmed by previous work (Wang and Hu, 1988).The xanthate is ready to chemically adsorb at the activated silica site and form stable lead amyl xanthate (PbAX) which makes the surface hydrophobic. The nucleation and growth of Pb(OH)2 at the silica surface were observed as revealed in the AFM images. It is believed that the lead and amyl xanthate react with silica surface in sequence, which makes the silica hydrophobic. It is noted that there is another possibility for adsorption. The lead and amyl xanthate may first react in basic solution to form lead amyl xanthate which is then adsorbed at the silica surface, making the silica hydrophobic. To test this reaction path, the contact angle measurements under this situation were carried out. The potassium amyl xanthate was immediately added into lead nitrate solution after the pH was set to pH 10–10.5 which was the optimal flotation condition pH, conditioned
As previous literature suggested (Fuerstenau et al., 1970; Fuerstenau et al., 1963; Fuerstenau et al., 1965a), hydroxo complexes of metal ions account for activation and flotation of silica. The distribution of various lead species as a function of pH can be calculated according to the stability constants and solubility products (Wang and Hu, 1988). In this work, the species distribution of lead under three concentrations, 1 × 10−4 M, 5 × 10−4 M and 1 × 10−3 M, were calculated and shown in Fig. 7. The system is unsaturated with respect to lead hydroxide at all pH values when the total lead concentration is 1 × 10−4 M (Fig. 7A). But when the total lead concentration increased to 5 × 10−4 M and 1 × 10−3 M, the solid lead hydroxide started to form at pH 8.51 and pH 8.23 respectively (Figs. 7B and 7C). Correlation of lead ion species distribution with
The other one is the reaction of Pb(OH)2 (aq) with the silica surface:
Fig. 6. The topography height images of fresh lead activated silica surface (left) and collector treated silica surface (right) at pH 10 with lead and amyl xanthate concentration of 5 × 10−4 M.
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Fig. 7. Logarithmic concentration diagram for the addition of 1 × 10−4 M (A), 5 × 10−4 M (B) and 1 × 10−3 M (C) lead nitrate to water respectively.
20 min, and then the silica disk was immersed in the solution and conditioned for additional 5 min before contact angle measurement. The contact angles for the three concentrations of lead/collector, 1 × 10−4 M, 5 × 10−4 M and 1 × 10−3 M, were 24°, 43° and 65° respectively. The corresponding contact angles with lead and potassium amyl xanthate added separately were 64°, 74° and 93° respectively (Table 1). Comparing with the normal treatment, the contact angle becomes small markedly in the former case, which means that the hydrophobicity decreases accordingly. It is because that in the former case the lead ion reacts with amyl xanthate to form Pb(AX)2 in the condition solutions. The physically adsorbed of Pb(AX)2 makes the silica surface possess slight hydrophobicity. However, in the latter case, the lead ion reacts with silanol groups to form activated sites at the silica surface, and the amyl xanthate chemically adsorbs the activated sites to form hydrophobic surface. So we can conclude that the previous flotation mechanism is more reasonable. With the adsorption of amyl xanthate, lead amyl xanthate was expected to form at the silica surface. To confirm the formation, the infrared spectra of collector treated silica at pH 10 were obtained. The infrared spectra of fresh silica, treated silica and synthesized lead amyl xanthate at the same pH are shown in Fig. 8. There are no specific adsorption bands for fresh silica within the wavenumber range of 900– 1300 cm−1. This is due to the fact that the major specific adsorption bands appear at 1500–3500 cm−1 (Al-Oweini and El-Rassy, 2009; Shokri et al., 2009). However, with treating by lead ion and collector, some specific adsorption bands appear at 900–1300 cm− 1, which is agreed well with those of synthesized lead amyl xanthate (Pb(AX)2). The characteristic adsorption bands of lead amyl xanthate are assigned as follows (Leppinen et al., 1989). The broad band at 1218 cm−1 is due to the asymmetric stretching vibrations of C–O–C and S–C–S groups, while those at 1023 and 1006 cm−1 are due to the stretching vibrations of S–C–S groups. The adsorption bands at 1125 and 1064 cm−1 are also due to the stretching vibrations of the C–O–C and S–C–S groups. Therefore, the infrared analysis demonstrates convincingly that the lead amyl
xanthate was formed at the surface of silica, which was believed to be responsible for hydrophobic character of the silica surface. 4. Conclusion This study has systematically investigated the electrophoresis, micro-flotation and solution chemistry associated with lead activation in the flotation of silica with amyl xanthate. The results confirm that silica can be activated with lead and floated with potassium amyl xanthate in the alkaline region. The PbOH+ and Pb(OH)2 (aq) species are believed to be the active species to account for activation by precipitation of Pb(OH)2 (s) at the silica surface. The island-like precipitate patches of Pb(OH)2 (s) were clearly observed using AFM and SEM imaging. Amyl xanthate was readily adsorbed onto the island-like precipitate and lead amyl xanthate was formed at the surface as revealed by FTIR. The previously proposed flotation mechanism has been confirmed and supported by contact angle measurements.
Fig. 8. The FTIR of synthesized lead amyl xanthate, silica and collector treated silica at pH 10 (the concentrations of lead nitrate and potassium amyl xanthate are 1 × 10−3 M).
B. Liu et al. / International Journal of Mineral Processing 151 (2016) 33–39
Acknowledgment We appreciate the financial support from the Major State Basic Research Development Program of China (973 program) under grant No. 2013CB632605 and 2013CB632601, and the National Natural Science Foundation of China under Grant No. 51274179. References Al-Oweini, R., El-Rassy, H., 2009. Synthesis and characterization by FTIR spectroscopy of silica aerogels prepared using several Si(OR)4 and R″Si(OR′)3 precursors. J. Mol. Struct. 919, 140–145. Ding, Y., 2010. Investigation on the Preparation of High Purity Quartz from Low Grade Silica. Northeastern University, Shen Yang. Duarte, A.C., Grano, S.R., 2007. Mechanism for the recovery of silicate gangue minerals in the flotation of ultrafine sphalerite. Miner. Eng. 20, 766–775. El-Salmawy, M., Nakahiro, Y., Wakamatsu, T., 1993. The role of alkaline earth cations in flotation separation of quartz from feldspar. Miner. Eng. 6, 1231–1243. Finkelstein, N., 1997. The activation of sulphide minerals for flotation: a review. Int. J. Miner. Process. 52, 81–120. Fornasiero, D., Ralston, J., 2005. Cu (II) and Ni (II) activation in the flotation of quartz, lizardite and chlorite. Int. J. Miner. Process. 76, 75–81. Fuerstenau, D., 2005. Zeta potentials in the flotation of oxide and silicate minerals. Adv. Colloid Interf. Sci. 114, 9–26. Fuerstenau, M., Martin, C., Bhappu, R., 1963. The role of hydrolysis in sulfonate flotation of quartz. Soc. Min. Eng. 449–454. Fuerstenau, M., Miller, J., Pray, R., Perinne, B., 1965a. Metal ion activation in xanthate flotation of quartz. Trans. AIME 232, 359–365. Fuerstenau, M., Rice, D., Somasundaran, P., Fuerstenau, D., 1965b. Metal Ion Hydrolysis and Surface Charge in Beryl Flotation, General Meeting, Denver. pp. 381–391.
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Fuerstenau, M., Kuhn, M., Elgillani, D., 1968. The role of dixanthogen in xanthate flotation of pyrite. Trans. AIME 241, 148–156. Fuerstenau, M., Elgillani, D., Miller, J., 1970. Adsorption mechanisms in nonmetallic activation systems. Trans. AIME 247, 11–14. James, R.O., Healy, T.W., 1972a. Adsorption of hydrolyzable metal ions at the oxide–water interface. I. Co (II) adsorption on SiO2 and TiO2 as model systems. J. Colloid Interface Sci. 40, 42–52. James, R.O., Healy, T.W., 1972b. Adsorption of hydrolyzable metal ions at the oxide–water interface. III. A thermodynamic model of adsorption. J. Colloid Interface Sci. 40, 65–81. Laskowski, J.S., Castro, S., 2012. Hydrolyzing ions in flotation circuits: sea water flotation. Proc. 13th International Mineral Processing Symposium. IMPS, pp. 219–227. Leppinen, J., Basilio, C., Yoon, R., 1989. In-situ FTIR study of ethyl xanthate adsorption on sulfide minerals under conditions of controlled potential. Int. J. Miner. Process. 26, 259–274. Rashchi, F., Xu, Z., Finch, J.A., 1998. Adsorption on silica in Pb- and Ca–SO4–CO3 systems. Colloids Surf. A Physicochem. Eng. Asp. 132, 159–171. Shokri, B., Firouzjah, M.A., Hosseini, S., 2009. FTIR analysis of silicon dioxide thin film deposited by metal organic-based PECVD. Proceedings of 19th International Symposium on Plasma Chemistry Society, Bochum, Germany. Sun, Z., Willis, F., Chen, J., 1992. The SiO2 H2O Interface and effects on quartz activation in flotation system. Trans. Nonferrous Met. Soc. China 2, 16–22. Vidyadhar, A., Hanumantha Rao, K., 2007. Adsorption mechanism of mixed cationic/ anionic collectors in feldspar-quartz flotation system. J. Colloid Interface Sci. 306, 195–204. Vučinić, D.R., Lazić, P.M., Rosić, A.A., 2006. Ethyl xanthate adsorption and adsorption kinetics on lead-modified galena and sphalerite under flotation conditions. Colloids Surf. A Physicochem. Eng. Asp. 279, 96–104. Wang, D., Hu, Y.-h., 1988. Solution Chemistry of Flotation. Science & Technology Press, Beijing. Zhou, K., 2013. The Study on Improving the Flotation Performance for Quartz Purification. South China University of Technology.
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The surface features of lead activation in amyl xanthate flotation of quartz Biao Liu a,b, Xuming Wang b, Hao Du a,⁎, Jing Liu b, Shili Zheng a, Yi Zhang a, Jan D. Miller b,⁎ a b
National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China Department of Metallurgical Engineering, University of Utah, 135 S 1460 E, Rm 412, Salt Lake City, UT 84112, USA
a r t i c l e
i n f o
Article history: Received 30 September 2015 Received in revised form 13 April 2016 Accepted 18 April 2016 Available online 22 April 2016 Keywords: FTIR AFM Activation Quartz flotation Amyl xanthate
a b s t r a c t It is confirmed in this study that silica can be activated with lead (II) ion and floated with potassium amyl xanthate in the alkaline region as evidenced from micro-flotation experiments. This conclusion is complimented with the results from electrophoresis experiments and by solution chemistry analysis. The PbOH+ and Pb(OH)2 (aq) species which are believed to be responsible for silica activation were found to precipitate at the silica surface. These island-like precipitate structures were clearly observed using AFM and SEM imaging. With amyl xanthate addition, lead amyl xanthate was formed as revealed by FTIR. Contact angle measurements further confirmed the nature of lead activation in silica flotation with amyl xanthate collector. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Due to the excellent characteristics quartz is widely used in the production of glass, ceramic, refractory material, and optical communication (Ding, 2010). As one of the most abundant minerals in the earth's crust, quartz frequently associates with other minerals, such as feldspar, talc, pyrite, hematite, smithsonite, and apatite (Zhou, 2013). The separation of quartz from other minerals has attracted increasing interest in recent years, especially for the separation of feldspar and quartz due to their similar tectosilicate structure (El-Salmawy et al., 1993; Vidyadhar and Hanumantha Rao, 2007). To obtain high purity quartz, froth flotation is generally used. Quartz can be satisfactorily floated by anionic collectors, such as sodium oleate (Sun et al., 1992), sodium alkylsulfonate (El-Salmawy et al., 1993; Fuerstenau et al., 1968), and sodium alkyl sulfate (Wang and Hu, 1988), with metal ions as activators. Metal ion activation has been a classic pretreatment method for quartz flotation (El-Salmawy et al., 1993). Quartz is also a typical gangue mineral in many flotation systems such as beryl (Fuerstenau et al., 1965b), sphalerite (Duarte and Grano, 2007), and other sulfide minerals. Although quartz possesses hydrophilic surface properties in nature and cannot be floated by anionic surfactants alone at any pH, hydrophobicity can be induced by adding polyvalent cations to the system. For example, quartz can be completely floated from pH 5.8 to 8.5 with Pb2+ as activator and amyl xanthate as collector. In the case of Zn2+, the activation pH range is from pH 7.5 to 8.1 (Fuerstenau et al., 1970; Fuerstenau et al., 1965a). Quartz can also be activated by Cu2+ or Ni2+ and floated with xanthate in the pH region ⁎ Corresponding authors. E-mail addresses: [email protected] (H. Du), [email protected] (J.D. Miller).
http://dx.doi.org/10.1016/j.minpro.2016.04.004 0301-7516/© 2016 Elsevier B.V. All rights reserved.
pH 7 to 10 (Fornasiero and Ralston, 2005). With oleate as collector, Ca2+, Mg2+, and Fe3+ are usually used for activation in quartz flotation. The results have shown that the effective flotation was attributed to the formation of a surface metal hydrous-oleate complex (Sun et al., 1992). Fe2+, Al3+, Pb2+, Mg2+, Mn2+ and Ca2+ are also shown to function as activators with long chain sulfonate as collector (Fuerstenau et al., 1963). Due to the slight dissolution of metal ions from metallic sulfides or oxides, the quartz can be activated inadvertently and floated by anionic collectors, which leads to unexpected presence of quartz in the concentrates (Fornasiero and Ralston, 2005). To obtain better separation of quartz from other minerals in quartz production, or to prevent the inadvertent activation of quartz when present as gangue, extensive fundamental studies have been carried out in the last fifty years to study polyvalent cation activation effect in the flotation of quartz. M. C. Fuerstenau and his co-workers (Fuerstenau et al., 1970; Fuerstenau et al., 1963; Fuerstenau et al., 1965a; Fuerstenau et al., 1965b) have done much research on anionic quartz flotation with metal ion activation. Electrophoretic, metal ion adsorption experiments and flotation tests were performed. In the case of lead activation, it was found that due to the adsorption of the lead species, quartz was positively charged from pH 7 to pH 11 in the presence of 1 × 10−4 M lead ions (Fuerstenau et al., 1970). Complete amyl xanthate flotation was achieved in this pH range. Correlation of the lead species distribution with the flotation response shows that Pb(OH)+ is probably responsible for the activation. A basic lead xanthate complex may be functioning as the collector (Fuerstenau et al., 1965a), which has been suggested by other researchers (Fornasiero and Ralston, 2005; James and Healy, 1972a, 1972b; Laskowski and Castro, 2012). However, there is no direct evidence to verify the adsorption of active species and subsequent collector adsorption.
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MIBC was added as frother. The silica suspension was transferred to the Hallimond tube. The air was set to achieve the desired air flow rate of 40 mL/min. The hydrophobic silica particles attached to the bubbles and floated to the top of the tube. The flotation time was 5 min. The float and sink fractions were filtered, dried, and weighted. 2.4. Contact angle measurement
Fig. 1. Zeta potential of unactivated and activated silica as a function of pH.
In this study, AFM, together with SEM, has been utilized to detect the changes in the silica surface state when lead and amyl xanthate were used to achieve effective silica flotation. By imaging the silica surface, the precipitation of lead and/or the formation of a lead-xanthate compound might be detected. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) was used to further identify the formation of the lead-xanthate compounds. In conjunction with the electrophoretic measurements, flotation tests and contact angle measurements, the mechanism of amyl xanthate flotation of quartz with lead as activator first studied by M. C. Fuerstenau and his co-workers will be better understood. 2. Experimental section 2.1. Chemicals and materials All solutions in this study were prepared using Millipore Milli-Q water (18 MΩ·cm). Potassium amyl xanthate (90%, TCI), lead nitrate (99%, Alfa Aesar) and 4-methyl-2-pentanol (MIBC, 98%, SigmaAldrich) were used as received, without further purification. Silica (−10 μm, U.S. Silica) was used for the electrophoresis measurements. Coarse silica (40 × 100 mesh, Acros) was used for the micro-flotation. An IR/UV grade fused silica disk (20 × 2 mm, Gold Dragon Optics Co., Ltd., China) was used in AFM, SEM and contact angle measurements. 2.2. Electrophoresis measurements Electrophoretic mobility of the silica was performed using a Zeta potential analyzer (Zeta PALS, Brookhaven Instruments Corporation, Holtsville, NY). Lead nitrate solutions of varying concentrations were prepared in a beaker. The pH was adjusted with sodium hydroxide and hydrochloric acid solutions, and then silica powders (− 10 μm) were dispersed in the lead nitrate solutions and a suspension with 0.025% silica was prepared. The suspensions were stirred for 20 min and then about 10 mL transferred to the Zeta PALS cell. The Zeta potentials of silica particles were measured. The instrument automatically calculated the mobilities of the particles and converted the results to zeta potential according to the Smoluchowski equation. To ensure precise zeta potential determination, five runs of 30 cycles per run were conducted for every sample and the average values were reported.
Similar to the silica treatment in micro-flotation, the fused silica disk was activated by lead and amyl xanthate was added for adsorption. The silica disk was taken out from the solutions and blown dry by high purity nitrogen. Then the contact angle of silica was measured by a contact angle goniometer (RAME-HART, Inc. NRL U.S.A.) using the sessile drop method. For each sample, at least five drops were measured and the average value from five measurements was calculated. 2.5. AFM measurement A Nanoscope AFM with Nanoscope IV controller (Veeco Instruments Inc., Santa Barbara, CA) was used with an E-type scanner. Triangular beam silicon nitride (Si3N4) cantilevers (Veeco Instrument Inc., Santa Barbara, CA) with pyramid-shaped tips were used. The sample holder was cleaned using acetone, ethanol, and water in order, and gently dried with ultra high purity N2 gas. The cantilevers were subsequently cleaned in a UV chamber for 30 min prior use. The silica disk treated with 150 mL lead and amyl xanthate solutions, was mounted on a piezo scanner. The contact mode was applied for imaging of the silica surface. The AFM instrument was kept in an acoustic and vibrational isolation chamber. The images of the silica surface were obtained at a scan rate of 1 Hz and a scan area of 5 × 5 μm. The images were processed offline using Nanoscope vs. 5.31R1 software. Flattening and low pass filtering were applied to remove noise. Image processing software, Gwyddion 2.15, was used to calculate the area covered by leadcontaining precipitates and lead-xanthate compounds at the silica surface. 2.6. SEM analysis The silica disk was firstly treated with 150 mL lead and amyl xanthate solutions and then analyzed using SEM. The SEM image of treated silica was collected using FEI Quanta 250 SEM. The energy spectra were analyzed using EDAX GENESIS energy dispersive spectroscopy. 2.7. DRIFT measurement Diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) equipped with a diffuse reflectance unit (PIKE Technologies) was used to identify adsorbed collector at the silica surface. The infrared spectra were recorded for all samples on the air dried 40 × 100 mesh silica
2.3. Micro-flotation tests The flotation response of silica was determined using a 125 mL Hallimond tube (20 × 220 mm) with a fine frit (10 μm) and a magnetic stirrer. Silica samples (40 × 100 mesh) of 2 g were used in each microflotation test. 150 mL lead nitrate solution of desired pH was first prepared and then the silica particles were added. The solution was conditioned for 20 min, and then additional 5 min was applied after amyl xanthate was added as collector. After collector adsorption, 0.02 mL of
Fig. 2. Relationship between flotation recovery and pH with various lead and amyl xanthate additions (the lead concentration equals the amyl xanthate concentration).
B. Liu et al. / International Journal of Mineral Processing 151 (2016) 33–39 Table 1 Sessile drop contact angles at the silica surface for various lead and potassium amyl xanthate concentrations at different pH values (the lead concentration equals the amyl xanthate concentration). Concentration, M
pH 7.0–7.5
pH 8.0–8.5
pH 9.0–9.6
pH 10.0–10.5
1 × 10−4 5 × 10−4 1 × 10−3
38 80 88
27 80 85
55 62 81
64 74 93
powders. The FTIR spectra were obtained by a BioRad FTS-6000 spectrometer. It is capable of data collection over a wave number range of 370–7800 cm−1. About 10% by weight of the solid samples were mixed with spectroscopic grade KBr powders with a refractive index
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of 1.559 and a particle size of 1–5 μm. These spectra were recorded with 500 scans measured at 4 cm−1 resolution. 3. Results and discussion 3.1. The electrophoresis behavior of activated silica The zeta potential of silica in the absence and presence of lead ions in solution is shown in Fig. 1. The zeta potential of fresh silica was negative and its value became more negative with increase in pH. The point of zero charge (PZC) of silica was reported to be pH 2 (Fuerstenau, 2005). The surface charge of the silica was all negative in the measured pH range. With the addition of lead, the zeta potential became less negative and even positive at higher lead concentration. When the lead
Fig. 3. The topography height images of fresh silica surface (A1 and A2), activated silica surface (B1 and B2) and collector adsorbed silica surface at pH 10 (C1 and C2).
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Fig. 4. The SEM image of lead treated silica surface and EDX of the given point at the image (the concentration of lead nitrate is 5 × 10−5 M, and the pH is 10).
concentrations are higher than 1 × 10−4 M, a positive zeta potential was observed in the pH region of 6 to 11, which agreed quite well with previous results (Fuerstenau et al., 1970; Rashchi et al., 1998). In the case of positively charged silica surface, the amyl xanthante anion will adsorb on the silica surface, which facilitates the flotation. So far, it is confirmed that the property of the silica surface can be changed by lead ions.
3.2. The flotation response of activated silica Fig. 2 illustrates the flotation response after silica was activated at different lead nitrate concentrations. Excellent flotation recovery was obtained when lead ions were introduced into the flotation pulp. With a lead concentration increasing to 5 × 10−4 M, complete recovery occurred from pH 6 to pH 12, which is similar to results reported from previous flotation research (Fuerstenau et al., 1965a). In correlation with the surface charge of activated silica, it is believed that the adsorbed lead ions make the silica surface positive, which allows the adsorption of amyl xanthate and makes the silica surface hydrophobic. To reveal the change of silica surface hydrophobicity, the contact angles of the silica surface under different lead ions and potassium amyl xanthate concentrations, 1 × 10−4 M,5 × 10− 4 M and 1 × 10− 3 M, were measured and the results are shown in Table 1. It is clear that the contact angle measurement is correlated with the flotation response. When the contact angles were high, a good flotation recovery was obtained for the hydrophobic silica. Interestingly, there was a slight decrease of recovery in the vicinity of pH 9 when the concentration of lead and amyl xanthante was 5 × 10−4 M or higher. At lower concentration, the decrease occurred at about pH 7. Similar results were also reported by M. C. Fuerstenou et al. (Fuerstenau et al., 1965a). No flotation occurred at the intermediate region when the lead concentration was 1 × 10−4 M and the amyl xanthate concentration was 1 × 10−5 M or 2.5 × 10−5 M.
3.3. The topography of silica before and after collector treatment AFM is a powerful tool for surface chemistry research. It can describe the surface topography without damaging the delicate surface. In this study, AFM was used to examine the silica surface topography to see if the formation of lead hydroxide and/or lead-collector compounds could be detected. The AFM images of a silica surface after conditioning with 1 × 10−4 M lead and amyl xanthate are shown in Fig. 3. As revealed in Fig. 3, the fresh silica surface is flat and smooth. After conditioning in 1 × 10−4 M lead nitrate solutions for 10 min (at pH 10), the island-like patches with average size of 0.3 μm were found at the silica surface and the surface became rough (B1 and B2). The patches were also found in the SEM image as shown in Fig. 4. To detect the composition of the precipitates, the EDX was performed and the results are presented in Fig. 4. It is shown that the main elements of the patches were O, Si and Pb. The Si is expected to be originated from the silica substrate and the Pb element should be resulted from the lead-containing precipitates at the silica surface. It was confirmed that lead-containing compounds precipitated at the silica surface and formed lead oxide or lead hydroxide as suggested in the literature (Finkelstein, 1997). When amyl xanthate was added during the conditioning, it was expected that the amyl xanthate would adsorb at the silica surface. As shown in Fig. 3C1 and C2, the surface became rougher than the pure lead activated surface without the addition of collector, due to the fact that collector was mainly adsorbed on the lead precipitate. The root-mean-square roughness of fresh silica, lead activated silica and collector adsorbed silica were 0.703 nm, 1.76 nm and 9.44 nm respectively. It is concluded that the formation of the lead-containing precipitate facilitated the adsorption of collector and made the silica surface hydrophobic. If the silica was conditioned in an acidic solution (pH 4), there was no lead adsorbed at the surface as revealed in Fig. 5A. There is no adsorption of amyl xanthate at the silica surface as shown in Fig. 5B and no effective flotation of silica is observed (Fig. 2). Even at basic pH,
Fig. 5. The topography height images of fresh silica surface: A, lead activated silica at pH 4; B, collector treated silica at pH 4; C, collector treated silica at pH 10 without lead activation.
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without lead activation the collector adsorption at the silica surface was not occurred, as revealed by Fig. 5C. Therefore, it is believed that metal ion activation is necessary for the effective flotation of silica by xanthate. Fig. 6 shows the images of lead activated silica and collector treated silica with lead and amyl xanthate concentrations of 5 × 10−4 M. With higher concentration, large island-like lead-containing patches were formed and unevenly scattered at the silica surface. After collector treatment, plenty of amyl xanthate was adsorbed onto the island-like patches. These island-like patches are believed to account for the hydrophobicity during flotation. According to the island area from the AFM image, the collector coverage at the silica surface can be calculated. The coverage under three concentrations, 1 × 10−4 M, 5 × 10−4 M and 1 × 10−3 M, were 5.9%, 6.7% and 6.6% respectively (the condition pH was within the effective flotation range of pH 10–10.5). The coverage did not raise when the xanthate concentration increases from 1 × 10−4 M to 1 × 10−3 M. But the hydrophobicity increased with their concentrations, which can be seen in the contact angle measurements presented in Table 1. It may due to the fact that the adsorption layer of lead amyl xanthate is formed at the activated silica surface, which contains not only chemisorbed lead amyl xanthate, but also physically adsorbed lead amyl xanthate. The physically adsorbed lead amyl xanthate forms the second layer of the collector at high concentration of xanthate, which intensifies the hydrophobicity. The multilayer physically adsorbed lead ethyl xanthate (Pb(EX)2) was also detected during the activation and flotation process of Pb(II) on galena and sphalerite (Vučinić et al., 2006).Therefore, the coverage of xanthate does not raise when the xanthate concentration increases from 1 × 10−4 M to 1 × 10−3 M, while the contact angle raises significantly, which will be well discussed in the following part.
flotation response showed that the formation of hydroxo complex PbOH+ and Pb(OH)2 (aq) was closely related to the effective flotation of silica. Complete flotation was obtained at alkaline pH where PbOH+ and Pb(OH)2 (aq) are the major species, which indicates that the lead hydroxo complexes are responsible for silica activation. To form stable lead-containing precipitates at the silica surface, the lead hydroxo complexes may react with silica in two ways. One is the reaction of PbOH+ with the silica surface:
3.4. The lead activation discussion
These two ways have been confirmed by previous work (Wang and Hu, 1988).The xanthate is ready to chemically adsorb at the activated silica site and form stable lead amyl xanthate (PbAX) which makes the surface hydrophobic. The nucleation and growth of Pb(OH)2 at the silica surface were observed as revealed in the AFM images. It is believed that the lead and amyl xanthate react with silica surface in sequence, which makes the silica hydrophobic. It is noted that there is another possibility for adsorption. The lead and amyl xanthate may first react in basic solution to form lead amyl xanthate which is then adsorbed at the silica surface, making the silica hydrophobic. To test this reaction path, the contact angle measurements under this situation were carried out. The potassium amyl xanthate was immediately added into lead nitrate solution after the pH was set to pH 10–10.5 which was the optimal flotation condition pH, conditioned
As previous literature suggested (Fuerstenau et al., 1970; Fuerstenau et al., 1963; Fuerstenau et al., 1965a), hydroxo complexes of metal ions account for activation and flotation of silica. The distribution of various lead species as a function of pH can be calculated according to the stability constants and solubility products (Wang and Hu, 1988). In this work, the species distribution of lead under three concentrations, 1 × 10−4 M, 5 × 10−4 M and 1 × 10−3 M, were calculated and shown in Fig. 7. The system is unsaturated with respect to lead hydroxide at all pH values when the total lead concentration is 1 × 10−4 M (Fig. 7A). But when the total lead concentration increased to 5 × 10−4 M and 1 × 10−3 M, the solid lead hydroxide started to form at pH 8.51 and pH 8.23 respectively (Figs. 7B and 7C). Correlation of lead ion species distribution with
The other one is the reaction of Pb(OH)2 (aq) with the silica surface:
Fig. 6. The topography height images of fresh lead activated silica surface (left) and collector treated silica surface (right) at pH 10 with lead and amyl xanthate concentration of 5 × 10−4 M.
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Fig. 7. Logarithmic concentration diagram for the addition of 1 × 10−4 M (A), 5 × 10−4 M (B) and 1 × 10−3 M (C) lead nitrate to water respectively.
20 min, and then the silica disk was immersed in the solution and conditioned for additional 5 min before contact angle measurement. The contact angles for the three concentrations of lead/collector, 1 × 10−4 M, 5 × 10−4 M and 1 × 10−3 M, were 24°, 43° and 65° respectively. The corresponding contact angles with lead and potassium amyl xanthate added separately were 64°, 74° and 93° respectively (Table 1). Comparing with the normal treatment, the contact angle becomes small markedly in the former case, which means that the hydrophobicity decreases accordingly. It is because that in the former case the lead ion reacts with amyl xanthate to form Pb(AX)2 in the condition solutions. The physically adsorbed of Pb(AX)2 makes the silica surface possess slight hydrophobicity. However, in the latter case, the lead ion reacts with silanol groups to form activated sites at the silica surface, and the amyl xanthate chemically adsorbs the activated sites to form hydrophobic surface. So we can conclude that the previous flotation mechanism is more reasonable. With the adsorption of amyl xanthate, lead amyl xanthate was expected to form at the silica surface. To confirm the formation, the infrared spectra of collector treated silica at pH 10 were obtained. The infrared spectra of fresh silica, treated silica and synthesized lead amyl xanthate at the same pH are shown in Fig. 8. There are no specific adsorption bands for fresh silica within the wavenumber range of 900– 1300 cm−1. This is due to the fact that the major specific adsorption bands appear at 1500–3500 cm−1 (Al-Oweini and El-Rassy, 2009; Shokri et al., 2009). However, with treating by lead ion and collector, some specific adsorption bands appear at 900–1300 cm− 1, which is agreed well with those of synthesized lead amyl xanthate (Pb(AX)2). The characteristic adsorption bands of lead amyl xanthate are assigned as follows (Leppinen et al., 1989). The broad band at 1218 cm−1 is due to the asymmetric stretching vibrations of C–O–C and S–C–S groups, while those at 1023 and 1006 cm−1 are due to the stretching vibrations of S–C–S groups. The adsorption bands at 1125 and 1064 cm−1 are also due to the stretching vibrations of the C–O–C and S–C–S groups. Therefore, the infrared analysis demonstrates convincingly that the lead amyl
xanthate was formed at the surface of silica, which was believed to be responsible for hydrophobic character of the silica surface. 4. Conclusion This study has systematically investigated the electrophoresis, micro-flotation and solution chemistry associated with lead activation in the flotation of silica with amyl xanthate. The results confirm that silica can be activated with lead and floated with potassium amyl xanthate in the alkaline region. The PbOH+ and Pb(OH)2 (aq) species are believed to be the active species to account for activation by precipitation of Pb(OH)2 (s) at the silica surface. The island-like precipitate patches of Pb(OH)2 (s) were clearly observed using AFM and SEM imaging. Amyl xanthate was readily adsorbed onto the island-like precipitate and lead amyl xanthate was formed at the surface as revealed by FTIR. The previously proposed flotation mechanism has been confirmed and supported by contact angle measurements.
Fig. 8. The FTIR of synthesized lead amyl xanthate, silica and collector treated silica at pH 10 (the concentrations of lead nitrate and potassium amyl xanthate are 1 × 10−3 M).
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