- Email: [email protected]
Study on the activation mechanism of lead ions in the flotation of ilmenite using benzyl hydroxamic acid as collector
G Model JIEC 3815 No. of Pages 8
Journal of Industrial and Engineering Chemistry xxx (2017) xxx–xxx
Contents lists available at ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
Study on the activation mechanism of lead ions in the flotation of ilmenite using benzyl hydroxamic acid as collector Qingyou Meng, Zhitao Yuan* , Li Yu, Yuankai Xu, Yusheng Du School of Resources and Civil Engineering, Northeastern University, Shenyang 110819, China
A R T I C L E I N F O
Article history: Received 14 October 2017 Received in revised form 19 December 2017 Accepted 25 December 2017 Available online xxx Keywords: Ilmenite Adsorption Lead ions Surface activation Flotation
A B S T R A C T
The activation mechanism of Pb2+ ions to ilmenite and the subsequent interaction with benzyl hydroxamic acid (BHA) were systematically investigated. The Pb2+ ions modification occurred via a chemical adsorption process, in which lead species interacted with iron hydroxyl compounds to form lead-containing complexes on the ilmenite surface. After lead ions activation, the surface of ilmenite became more active, and iron species and lead-containing complexes served as the main active sites to covalently bond with BHA in the form of metal-BHA chelate complexes. As a result, the BHA adsorption increased, giving rise to a concomitant increase in the floatability of ilmenite. © 2018 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Introduction Titanium has many extensive applications including medicine, aerospace, function materials and catalytic industries due to its high strength-to-weight ratio and corrosion resistance [1,2]. Two titanium phases, titanium dioxide and metal titanium, are produced presently from rutile and ilmenite. Ilmenite is becoming the major raw material in titanium industry resulting from the excessive consumption of limited rutile resources [3,4]. In the mineral processing of ilmenite ore, gravity separation, highintensity magnetic separation (HIMS), electrostatic separation or a conjunction of them are widely adopted to separate titanium minerals from gangues based on the difference of their physical properties. But for ilmenite freely disseminated in the gangues, the mentioned methods cannot effectively separate ilmenite from associated gangue minerals. In this case, froth flotation, a physicochemical separation process, has been considered suitable for processing ilmenite ore [5–7]. In the flotation process, one of the critical factors is to selectively modify the mineral surface property and improve the hydrophobicity of a desired mineral. Organic surfactants have been widely used as collectors because they can anchor on the mineral surface and render the attachment of particles to air bubbles. Among all surfactants, sodium oleate (aliphatic acids) and succinamate are commonly used in the flotation separation of
* Corresponding author. E-mail address: [email protected] (Z. Yuan).
ilmenite from siliceous gangues [3,8,9]. Successful separation of ilmenite could be achieved using benzyl arsenic acid (BAA) in the presence of acidified silicates, reported by Song and Tsai [10]. Phosphonic acid exhibits a strong affinity toward metal oxides, which is deemed to an impactful collector for the selective flotation of titanium minerals [7,11,12]. The mixed anionic/cationic collector shows more superior hydrophobicity and collecting property than an individual collector because of the remarkable synergistic effect, aiming to improve the flotation efficiency of ilmenite [13–15]. Hydroxamic acids and their salts have also been extensively studied and exploited as collectors due to the active chelation with some transition metal or rare-earth metal ions on mineral surfaces [16–18]. Relevant research using hydroxamate as the collector was reported in the flotation of titanium minerals [19]. Even if collectors are utilized to improve the hydrophobicity of mineral surface, ilmenite yet displays a poor flotation performance compared to rutile. It is because that only half of metallic ions (Ti4+ and Fe2+) on the ilmenite surface are serving as active sites and interact with anionic collectors at different pH ranges [5,20,21]. Therefore, considerable studies have been attempted to supply sufficient active sites for improving the flotation recovery of ilmenite. Surface oxidation, such as microwave irradiation, oxidation roasting, and surface dissolution, is discussed to enhance the ilmenite floatability, which converts ferrous ions to ferric ions in terms of increasing the adsorption of collectors on the ilmenite surface [22–24]. Surface activation by adding new active species on the mineral surfaces is another effective method in the flotation process. Lead ions have been investigated as activators for the
https://doi.org/10.1016/j.jiec.2017.12.059 1226-086X/© 2018 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Please cite this article in press as: Q. Meng, et al., Study on the activation mechanism of lead ions in the flotation of ilmenite using benzyl hydroxamic acid as collector, J. Ind. Eng. Chem. (2018), https://doi.org/10.1016/j.jiec.2017.12.059
G Model JIEC 3815 No. of Pages 8
2
Q. Meng et al. / Journal of Industrial and Engineering Chemistry xxx (2017) xxx–xxx
flotation of sulfide and oxide minerals. As early as 1960, Rey and Formanek firstly reported lead ions as the activator in the sphalerite flotation [25]. Correspondingly, lead ions as the activator of oxide minerals were studied far behind that of sulfide, but they are widely utilized at a plant scale until now. Fan and Rowson reported that Pb2+ and Pb(OH)+ species of lead ions could selectively adsorb onto ilmenite surfaces and enhance its floatability when sodium oleate was used as a collector [20]. Chen provided further insights to reveal the activation mechanism of lead ions. They found that lead species formed lead-containing complexes on ilmenite surfaces, which served as the main active sites to bond with oleate species [26,27]. Lead ions as the activator combined with hydroxamate collectors have attracted a lot of enthusiasm to apply in the flotation of oxide minerals. Feng discovered that the lead species adsorbed on the cassiterite surface led to the increase in the number of active sites and offered adequate chances for the adsorption of salicyl hydroxamic acid [28]. The effect of lead ions on the flotation of rare earth minerals using benzyl hydroxamic acid and naphthalenic hydroxamic acid as collectors was investigated in virtue of TOF-SIMS analyses by Xia. Lead species reversed the surface charge of ilmenite and promoted the adsorption of collectors [29]. Yue et al. found that the Pb-BHA complexes exercised the synergistic effect between chemical and physical adsorption and facilitated to improve the flotation recovery of tungsten minerals [30]. Zhao reported the activation mechanism of lead ions in the flotation of scheelite and wolframite with benzyl hydroxamic acid by means of DFT and XPS analysis. Their results indicated that benzyl hydroxamic acid preferentially coordinated with Pb2+ ions compared with Ca2+, Mn2 + and Fe2+ ions [31]. Nevertheless, the surface activation of ilmenite by lead ions with hydroxamate as the collector is hardly reported in the published literature. In the present study, the positive influence of lead ions in the ilmenite flotation with benzyl hydroxamic acid (BHA) as the collector was investigated. The activation mechanism of lead ions on ilmenite surfaces and subsequent response to BHA adsorption were further discussed via adsorption tests, zeta potential measurements, FT-IR and XPS analysis.
Fig. 1. X-ray diffraction spectra of ilmenite.
the experiments were prepared using deionized water (18.25 MV cm). Microflotation experiments Microflotation experiments were conducted in an XFG II flotation machine with a fixed stirring rate of 1800 rpm. 2 g ilmenite samples and 40 mL deionized water were used in each test. The suspension was firstly adjusted to the desired pH value by H2SO4 or NaOH solution for 2 min, and then the activator and collector were added one after another and conditioned for 3 min and 5 min, respectively. After that, terpenic oil was added as the frother. The flotation time was limited to 5 min, and the froth was scraped out every 10 s. The floated and sank fractions were filtered, dried, and weighed, respectively. The flotation recovery of ilmenite was calculated according to Eq. (1), R¼
Materials and methods Materials Ilmenite sample was obtained from the vanadium–titanium magnetite in Panzhihua Mine, Sichuan province, China. Mineral samples were repeatedly purified using low-intensity magnetic separation, high-intensity magnetic separation, and shaking table. The XRD result given in Fig. 1 demonstrated that the sample was composed of ilmenite with a trace of pyrite, and the XRF result presented that the titanium (TiO2) content was 50.45%, indicating that the purity of ilmenite was above 95%. The purified ilmenite was dry-ground in a porcelain ball mill and sieved to obtain the 74 mm fractions for the flotation experiments. Samples for measurements were further ground to less than 5 mm in an agate mortar. Benzyl hydroxamic acid (BHA), used as the anionic collector, was synthesized in laboratory through the reaction of benzoic acid with hydroxylamine. The element analysis showed that the BHA purity was above 95% after the purification process. Analytically pure lead nitrate (Pb(NO3)2), used as the activator, was supplied by Tianjin Kermil Reagent Co., Ltd., China. The pH value of aqueous suspensions was adjusted by sodium hydroxide (NaOH) and sulfuric acid (H2SO4) dilute solutions (1 mol L1). Analytical grade potassium chloride (KCl) was used as the background electrolyte for zeta potential measurements. All solution and suspension in
Mf 100% Mf þ Ms
ð1Þ
where R is the flotation recovery, Mf is the mass of the floated fractions (concentrates), and Ms is the mass of the sank fractions (tailings). Adsorption tests The adsorption amount of BHA on the ilmenite surface was determined by the UV1901PC UV–Vis spectrophotometer (China). BHA concentration was measured using UV absorbance at the wavelength of 520 nm according to the ferric hydroxamate method [32,33]. 1.0 g ilmenite sample was dispersed into 40 mL aqueous phase in the absence and presence of lead ions at a desired pH value and conditioned for 3 min. Sequentially, the BHA stock solution was added to interact with the mineral surface, and the mixing was stirred for 30 min. The conditioned mineral particles were separated out by centrifugation, and the BHA concentration of the separated supernatant was measured by the UV–Vis spectrophotometer. The adsorption amount was calculated by Eq. (2) based on the difference between the initial and final BHA concentrations. Q¼
VðC 0 C f Þ M
ð2Þ
where, Q is the adsorption amount of BHA on ilmenite surfaces (mg g1), C0 is the initial BHA concentration (mg L1), Cf is the final
Please cite this article in press as: Q. Meng, et al., Study on the activation mechanism of lead ions in the flotation of ilmenite using benzyl hydroxamic acid as collector, J. Ind. Eng. Chem. (2018), https://doi.org/10.1016/j.jiec.2017.12.059
G Model JIEC 3815 No. of Pages 8
Q. Meng et al. / Journal of Industrial and Engineering Chemistry xxx (2017) xxx–xxx
BHA concentration (mg L1), V is the volume of supernatant (L), and M is the mass of ilmenite (g).
3
Results Microflotation and adsorption
Zeta potential measurements The zeta potential of ilmenite particles was determined using a Malvern Instrument Nano-ZS90 analyzer (Britain). In each test, 30 mg mineral sample (5 mm) was mixed in 40 mL electrolyte solution (103 mol L1 KCl). The suspension was magnetically stirred for 2 min after pH adjustment and followed by another 5 min for adding activators or collectors. And then the zeta potential of prepared samples was measured by the zeta-potential analyzer. The average value of three measurements was adopted as the final result of zeta potential, and the standard deviation was calculated for each point. FTIR spectra analysis Fourier transform infrared (FTIR) spectra were detected by the Nicolet 740 infrared spectrometer (USA) to characterize the interaction between collector and ilmenite with or without Pb2+ treatment. The mineral sample was ground to smaller than 5 mm, and the suspension was conditioned similar to the procedure of microflotation experiments, conditioning for 30 min. The prepared suspension was filtered, washed with deionized water for three times, then vacuum dried at 50 C. Approximately 1 mg mineral sample was mixed with 100 mg spectroscopic grade KBr, pressing disc pellets for measurements. XPS determinations The X-ray photoelectron spectroscopy (XPS) measurements were carried out using a Thermo Fisher ESCALAB 250Xi XPS system. An Al Ka X-ray source at 1486.6 eV was used in the XPS analysis. Binding energy values were calibrated using characteristic carbon (C1s = 284.8 eV) during data processing of XPS spectra. The mineral samples with the particle size of 5 mm were used, preparing similar to the microflotation experiment. After all reagents were added to adjust the suspension, the prepared samples were filtrated, washed three times with deionized water, and then dried in a vacuum oven for XPS measurements.
The effect of pH value on the flotation recovery of ilmenite in the absence and presence of Pb2+ ions, using 120 mg L1 BHA, is shown in Fig. 2a. The results showed that ilmenite treated with BHA alone displayed a relatively poor floatability, and the flotation recovery was obtained only 17.0% at pH 8.0. It seemed that BHA collector could not improve the floatability of ilmenite. After Pb2+ treatment, the flotation recovery of ilmenite increased with the rise in pH values ranging from 2.0 to 8.0 and then decreased until pH around 11.0. Over 69.0% of ilmenite particles were floated out when pH reached approximately 8.0. The flotation recovery of ilmenite with Pb2+ modification increased by around 52% in comparison with that without Pb2+ treatment. It could be seen that pH 8.0 was the best condition for ilmenite flotation, so that the effect of Pb2+ concentration on the flotation recovery of ilmenite was studied by fixing the pH at 8.0. Fig. 2b presents the effect of Pb2+ ions concentration on the flotation recovery of ilmenite with 120 mg L1 BHA at pH 8.0. The results in Fig. 2b showed that after ilmenite was activated by Pb2+ ions, its floatability was enhanced significantly. The flotation recovery of ilmenite increased with an increase in the initial concentration of lead ions and achieved 87.2% at Pb2+ ions of 2.0 104 mol L1. After that, the flotation recovery of ilmenite reached a high level platform when Pb2+ ions concentration was more than 2.0 104 mol L1. The adsorption amounts of BHA on ilmenite surfaces as functions of pH and Pb2+ ions concentration were measured, and the results are shown in Fig. 3. It could be found from Fig. 3a that the adsorption amounts of BHA on ilmenite surfaces firstly increased and then decreased with the increase of pH values, and the maximum value was obtained at pH 8.0. In the presence of Pb2+ ions, the adsorption of BHA on ilmenite surfaces performed a similar trend as that without Pb2+ treatment, but the adsorption amounts improved significantly in the entire pH range from 2.0 to 11.0. Furthermore, the BHA adsorption amounts increased with the Pb2+ ions concentration at pH 8.0 (in Fig. 3b). When Pb2+ ions concentration was greater than 2.0 104 mol L1, the BHA adsorption amounts increased slowly. Consistent variation trends
Fig. 2. Effect of pH and Pb2+ concentration on the recovery of ilmenite.
Please cite this article in press as: Q. Meng, et al., Study on the activation mechanism of lead ions in the flotation of ilmenite using benzyl hydroxamic acid as collector, J. Ind. Eng. Chem. (2018), https://doi.org/10.1016/j.jiec.2017.12.059
G Model JIEC 3815 No. of Pages 8
4
Q. Meng et al. / Journal of Industrial and Engineering Chemistry xxx (2017) xxx–xxx
Fig. 3. Effect of pH and Pb2+ concentration on the BHA adsorption.
were observed from Figs. 2 and 3 between ilmenite recovery and BHA adsorption. Hence, it was evident that Pb2+ ions enhanced the adsorption amounts of BHA on ilmenite surfaces, resulting in the improvement of ilmenite floatability. Zeta potentials Zeta potentials of mineral particles in the absence and presence of Pb2+ ions, using BHA as the collector, were conducted to study their interactions with ilmenite, and the results are presented in Fig. 4. It would be observed from Fig. 4 that the isoelectric points (IEP) of pure ilmenite was located at about pH 5.3, which was in agreement with the reported values [20,34]. After the addition of 104 mol L1 Pb2+ ions, zeta potentials of activated ilmenite exhibited an integral positive shift. The values of zeta potential increased by approximately 15 mV within the pH range from 7.0 to 9.0, and the IEP appeared at about 7.2. Fig. 5 shows the concentration distribution of lead species as a function of pH value under the total concentration of 1 104 mol L1 [35,36]. As presented in Fig. 5, the positively charged Pb2+ species existed over the acidic pH region, and at pH above 9.7, the dominant species of lead ions were soluble molecular Pb(OH)2(aq), PbðOHÞ 3 and
on the ilmenite/water interface, respectively. The correlation of lead species distributions with zeta potential results indicated that when pH value was below 9.7, the Pb2+ and Pb(OH)+ species would devoted to the positive shift of zeta potentials of ilmenite because of electrostatic interactions. Meanwhile, within the pH region from 7.0 to 9.0, Pb(OH)+ ions bearing positive charges were the dominant species, and the noticeable increase (15 mV) in the zeta potential of ilmenite was attributed to the specific adsorption of Pb (OH)+ species in the helmholtz layer of ilmenite. The electrokinetic behavior of ilmenite treated with Pb2+ ions could be attributed to the lead species being adsorbed onto the mineral surfaces. Fig. 4 also shows that with the addition of 120 mg L1 BHA, zeta potentials of ilmenite decreased in the whole pH range whether pretreated with Pb2+ ions or not. We should note that, in the presence of Pb2+ and BHA, the zeta potential of activated ilmenite changed more than that of BHA treatment alone and decreased by approximately 13 mV in the pH region from 7.0 to 9.0. BHA bore negative charge and further decreased the zeta potential of ilmenite, which was ascribed to the specific adsorption occurred between negatively charged hydroxamate species and ilmenite surfaces [28,37].
+ PbðOHÞ2 4 ions, whereas at pH 7.2–9.7, Pb(OH) species dominated
Fig. 4. Effect of pH on the zeta potentials of ilmenite treated with various conditions.
Fig. 5. Distribution diagram of lead species as a function of pH value (cPb = 1 104 mol L1).
Please cite this article in press as: Q. Meng, et al., Study on the activation mechanism of lead ions in the flotation of ilmenite using benzyl hydroxamic acid as collector, J. Ind. Eng. Chem. (2018), https://doi.org/10.1016/j.jiec.2017.12.059
G Model JIEC 3815 No. of Pages 8
Q. Meng et al. / Journal of Industrial and Engineering Chemistry xxx (2017) xxx–xxx
5
FTIR analysis
XPS analysis
The infrared spectra were obtained to analyze the adsorption mechanism of benzyl hydroxamic acid (BHA) on the ilmenite surface. The infrared spectra of BHA, pure ilmenite, ilmenite treated with BHA alone, and ilmenite treated with both lead ions and BHA at pH 8.0 are shown in Fig. 6. On the FTIR spectrum of BHA (Fig. 6a), the band at 3294 cm1 was attributed to the overlap stretching vibrations of N H and O H groups. The band at around 3060 cm1 was assigned to N H stretching vibration. Due to the conjugate effect, the characteristic bands of benzene rings were observed at 1564 cm1, 1480 cm1, and 1453 cm1. The N O stretching vibrations were further divided into three bands at 1077 cm1, 1041 cm1, and 1019 cm1. The bands at 1648 cm1 and 1162 cm1 could be attributed to the C¼N stretching vibration and the C N stretching vibration of hydroxamate groups, respectively. The bands at 690 cm1 and 533 cm1 were attributed to the C H out-of-plane bending vibrations of benzene rings [38]. On the FTIR spectrum of ilmenite (Fig. 6a), the characteristic band for ilmenite was observed at 700 cm1, while the band at around 1650 cm1 was attributed to the bending mode of adsorbed water [9,39]. As shown in Fig. 6b, when ilmenite was only treated with BHA, no new bands appeared on the ilmenite spectrum, suggesting that BHA rarely adsorbed onto ilmenite surfaces. Nevertheless, the FTIR spectrum of Pb2+-activated ilmenite treated with BHA had new bands at around 1560 cm1, 1482 cm1, and 1153 cm1, of which the bands at 1560 cm1 and 1482 cm1 were attributed to the characteristic bands of benzene rings. The new bands at around 1153 cm1, shifting by 9 cm1, belonged to the CN stretching vibration in the BHA molecule, which could be attributed to the metal hydroxamate precipitates [38,40]. These components indicated that a chemisorption process was occurring during the interaction between benzyl hydroxamic acid and the activated ilmenite surface. The chelating group of BHA was able to bond with lead ions anchored on the ilmenite surface and formed stable Pb2+ chelate compounds. Through comparing the spectra of ilmenite in the presence and absence of lead ions, it could be deduced that lead species adsorbed onto ilmenite surfaces and then provided a binding affinity to interact with BHA. The presence of Pb2+ ions stimulated the BHA adsorption on ilmenite surfaces, which was in agreement with the adsorption results.
To further confirm the interaction mechanism between BHA and ilmenite activated with lead ions, XPS analysis of ilmenite treated with Pb2+ ions or/and BHA was conducted, and the results are shown in Fig. 7. It could be found from Fig. 7a that after Pb2+ and BHA treatment, the Pb4f and N1s XPS peaks were detected on the ilmenite surface. The atomic concentrations of elements C1s, O1s, N1s, Ti2p, Fe2p and Pb4f measured by XPS were summarized in Table 1. Table 1 shows that the Pb4f atomic concentration increased from 0.07% of pure ilmenite to 0.65% of Pb2+-activated ilmenite, indicating that Pb2+ ions successfully adsorbed on the ilmenite surface. Furthermore, the C1s and N1s atomic concentrations of Pb2+-activated ilmenite treated with BHA increased by 6.64% and 0.48%, respectively, evidencing that BHA adsorbed onto the surfaces of Pb2+-activated ilmenite. To obtain the detailed information about Pb2+ activation and BHA attachment, the chemical status of surface species was further characterized by high-resolution XPS spectra. Fig. 7b shows that the Fe2p3/2 peaks of pure ilmenite appeared at around 710.93 eV and 713.56 eV, respectively, in which the peak at 710.93 eV was attributed to ferrous species, and the peak close to 713.56 eV was assigned to ferric species [26,41]. After Pb2+ activation, the Fe2p3/2 binding energy of ferrous and ferric species decreased by 0.21 eV and 0.44 eV, respectively. The presence of Pb2+ ions changed the chemical circumstance of Fe species on the ilmenite surface. Besides, the addition of BHA further decreased the Fe2p3/2 binding energy of ferrous and ferric species to 710.51 eV and 712.76 eV, respectively, suggesting that BHA might bond with Fe species of ilmenite surfaces. As for Ti on ilmenite surfaces in Fig. 7c, the Ti2p3/2 peaks were determined at around 458.37 eV, corresponding to the Ti4+ oxidation state. Nevertheless, the binding energy of Ti2p3/2 peaks showed no obvious change after Pb2+ ions and BHA treatment. Fig. 7d shows the Pb4f7/2 spectra of Pb2+-activated ilmenite before and after BHA treatment. The peak at 138.70 eV on the spectrum of Pb2+-activated ilmenite belonged to PbO species [42]. The binding energy of Pb4f7/2 peak decreased by 0.22 eV, from 138.70 eV of Pb2+-activated ilmenite to 138.48 eV of BHA treatment, which was evidencing the BHA could interact with lead species adsorbed on the surface of ilmenite.
Fig. 6. FTIR spectra of benzyl hydroxamic acid and ilmenite treated with various conditions.
Please cite this article in press as: Q. Meng, et al., Study on the activation mechanism of lead ions in the flotation of ilmenite using benzyl hydroxamic acid as collector, J. Ind. Eng. Chem. (2018), https://doi.org/10.1016/j.jiec.2017.12.059
G Model JIEC 3815 No. of Pages 8
6
Q. Meng et al. / Journal of Industrial and Engineering Chemistry xxx (2017) xxx–xxx
Fig. 7. High-resolution XPS spectra of ilmenite before and after Pb2+ and BHA treatment.
Table 1 Atomic concentration of elements on ilmenite surfaces as determined by XPS. Samples
Atomic concentration of elements on ilmenite surfaces (%) C1s O1s N1s
Ti2p
Pb4f
Fe2p
Ilmenite Ilmenite + Pb2+ Ilmenite + Pb2+ + BHA
16.80 16.92 23.56
7.01 7.59 8.09
0.07 0.65 0.73
11.51 11.40 10.30
63.35 62.05 55.46
1.27 1.39 1.87
Please cite this article in press as: Q. Meng, et al., Study on the activation mechanism of lead ions in the flotation of ilmenite using benzyl hydroxamic acid as collector, J. Ind. Eng. Chem. (2018), https://doi.org/10.1016/j.jiec.2017.12.059
G Model JIEC 3815 No. of Pages 8
Q. Meng et al. / Journal of Industrial and Engineering Chemistry xxx (2017) xxx–xxx
The O1s XPS spectra recorded from pure ilmenite, ilmenite treated with Pb2+, and ilmenite treated with both Pb2+ and BHA are shown in Fig. 7e. The O1s peaks were composed of three components. The peaks at around 530.0 eV were attributed to TiO bonds [43,44], 531.3 eV attributed to FeO bonds [45], and 532.1 eV for hydroxyl bonded to metal ions (Me OH) [44], respectively. As suggested by the analysis of the corresponding O1s peaks for ilmenite modified by lead ions and subsequently treated with BHA (in Table 2), the relative intensity of O1s peaks belonged to FeO bonds increased from 21.40% of pure ilmenite to 30.53% of ilmenite modified by Pb2+ ions and 66.10% of Pb2+-activated ilmenite treated with BHA, while that of O H bonds decreased from 50.87% to 38.93% and further to 3.95%. These results illustrated that lead species would interact with active iron sites to form lead-containing complexes (Fe O Pb) on the ilmenite surface. Consequently, lead species adsorbed on ilmenite surfaces rendered new active sites for BHA adsorption. BHA replaced OH ions and bonded to the active metal sites in the form of metalhydroxamate chelate complexes, improving the hydrophobicity of ilmenite. Discussion Fig. 8 shows the surface species distribution of ilmenite as a function of pH [5]. The surface chemistry of ilmenite strongly depends on the solution pH value. The main metal ions of ilmenite, i.e., Fe2+ and Ti4+ ions, have different forms as the pH changes. Within the broad pH region from 3 to 11, ferrous ions exist in the forms of Fe2+ and Fe(OH)+, while titanium ions mainly dominate in the form of Ti(OH)4. Since Ti(OH)4 compounds (solubility product KTi(OH)4 = 1058.30) are so stable, ferrous ions on ilmenite surfaces are supposed to regard as the active sites to interact with collectors [5,34]. According to the foregoing results, the presence of Pb2+ ions stimulated the adsorption of BHA and enhanced the floatability of ilmenite. The zeta potential analysis showed that lead species made the zeta potential of ilmenite shift positively, in which Pb (OH)+ species played the critical role in the pH range from 7.0 to 9.0. The results of XPS analysis demonstrated that the addition of Pb2+ ions changed the chemical environment of iron species on the ilmenite surface, while that of titanium species remained the same. Moreover, the relative intensity of O species in FeO/Fe O Pb bonds of Pb2+-activated ilmenite increased significantly compared with pure ilmenite. These results indicated that it was the lead species that interacted with Fe species on ilmenite surfaces, which was inaugurated through dehydration reaction in the coating process of lead-hydroxyl compounds on ilmenite surfaces. As a result, the adsorption of lead species generated stable leadcontaining complexes and increased the amount of active sites on the ilmenite surface. Pb2+ ions motivated the surface property of ilmenite and provided active sites for BHA adsorption. The results of flotation Table 2 O1s parameters on ilmenite surfaces treated with various conditions. Sample
Binding energy (eV)
Assignment
Area ratio (%)
Ilmenite
530.07 531.39 532.11 530.02 531.28 532.07 530.00 531.36 532.10
Ti O FeO HO Ti O FeO/FeO Pb HO Ti O FeO/FeO Pb HO
27.74 21.40 50.87 30.55 30.53 38.93 29.95 66.10 3.95
2+
Ilmenite + Pb
Ilmenite + Pb2+ + BHA
7
Fig. 8. Distribution diagram of surface species on ilmenite as a function of pH values.
experiments and adsorption measurements indicated that the Pb2+ modification improved the floatability of ilmenite by increasing the adsorption of BHA on the ilmenite surface. After BHA treatment, the zeta potential of ilmenite appeared a negative shift, furthermore, the zeta potential of the activated ilmenite showed a more noticeable shift than that of the non-activated one, which was in good agreement with the adsorption results. It was a remarkable fact that the negatively-charged BHA collector could adsorb onto the negatively-charged ilmenite surface, suggesting that the special attractive force between BHA and ilmenite was larger than their electrostatic physical repulsion force, which was ascribed to the chemisorption between BHA and ilmenite. The FTIR results further confirmed that BHA could chemisorb onto the surface of lead activated ilmenite. The XPS analysis showed that the binding energy of Fe2p3/2 and Pb4f7/2 presented significant shifts (0.2–0.4 eV) after Pb2+-activated ilmenite was treated by BHA, inferring the change of their chemical environments. Otherwise, the relative intensity of Fe O/Fe OPb bonds (at 531.36 eV) increased significantly, and that of O H bonds (at 532.10 eV) decreased. These findings indicated that the adsorbed BHA would substitute hydroxyls bonded to the Pb or Fe species of Pb2+-activated ilmenite, and then the active O active atoms (in the form of C¼O and N OH, respectively) in the chelating group of BHA reacted with lead(iron) ions to form metal-BHA complexes on the ilmenite surface, which was in consistent with the results of zeta potentials and FTIR. Based on the results and discussion above mentioned, Pb2+ ions played a critical role in the flotation of ilmenite by using BHA as a collector. It was believed that lead species firstly adsorbed onto the ilmenite surface and then reacted with BHA to form hydrophobic species of metal-BHA chelate complexes, which were responsible for improving the floatability of ilmenite. A potential mechanism about the Pb2+ activation and subsequent BHA adsorption on the ilmenite surface was proposed in Fig. 9. Conclusions This study systematically studied a series of experiments associated with the activation of Pb2+ ions in the flotation of ilmenite using benzyl hydroxamic acid (BHA) as the collector. The flotation and adsorption tests showed that the addition of lead ions could stimulate BHA to adsorb onto mineral surfaces and contribute to the improved floatability of ilmenite, especially at pH 7.0–9.0. The results of zeta potential and XPS measurements
Please cite this article in press as: Q. Meng, et al., Study on the activation mechanism of lead ions in the flotation of ilmenite using benzyl hydroxamic acid as collector, J. Ind. Eng. Chem. (2018), https://doi.org/10.1016/j.jiec.2017.12.059
G Model JIEC 3815 No. of Pages 8
8
Q. Meng et al. / Journal of Industrial and Engineering Chemistry xxx (2017) xxx–xxx
Fig. 9. A potential mechanism for Pb2+ activation and BHA adsorption on the ilmenite surface.
suggested that the adsorption of lead ions onto ilmenite surfaces was mainly a chemically dominating process, along with the electrostatic attractions between the positively charged lead species and ilmenite surface. Pb(OH)+ species reacted with the iron hydroxyl compounds on the ilmenite surface to form leadcontaining complexes, which were the main active sites for BHA adsorption. Consequently, FTIR and XPS analysis confirmed that BHA species chemically adsorbed on the surface of Pb2+-activated ilmenite and generated the hydrophobic species of lead-BHA complexes, improving the floatability of ilmenite. Acknowledgments This work was supported by the Fundamental Research Funds for the Central Universities (N160103004); and China Postdoctoral Science Foundation (2017M611249). References [1] D. Chen, L. Zhao, T. Qi, G. Hu, H. Zhao, J. Li, L. Wang, Trans. Nonferrous Met. Soc. 23 (2013) 3076. [2] S. Samal, B.K. Mohapatra, P.S. Mukherjee, S.K. Chatterjee, J. Alloy. Compd. 474 (2009) 484. [3] S. Bulatovic, D.M. Wyslouzil, Miner. Eng. 12 (1999) 1407. [4] F. Chachula, Q. Liu, Fuel 82 (2003) 929. [5] X. Fan, K.E. Waters, N.A. Rowson, D.J. Parker, J. Colloid Interf. Sci. 329 (2009) 167. [6] G. Belardi, L. Piga, S. Quaresima, N. Shehu, Int. J. Miner. Process. 53 (1998) 145. [7] F. Li, H. Zhong, G. Zhao, S. Wang, G. Liu, Colloids Surf. A 490 (2016) 67. [8] K.H. Rao, K.S.E. Forssberg, Miner. Eng. 4 (1991) 879. [9] W. Liu, J. Zhang, W. Wang, J. Deng, B. Chen, W. Yan, S. Xiong, Y. Huang, J. Liu, Miner. Eng. 72 (2015) 1. [10] Q. Song, S.C. Tsai, Int. J. Miner. Process. 26 (1989) 111. [11] G. Guerrero, H. Mutin, A. Vioux, Chem. Mater. 13 (2001) 4367. [12] Q. Liu, Y. Peng, Miner. Eng. 12 (1999) 1419. [13] J. Tian, L. Xu, Y. Yang, J. Liu, X. Zeng, W. Deng, Int. J. Miner. Process. 166 (2017) 102. [14] L. Xu, Y. Hu, J. Tian, H. Wu, Y. Yang, X. Zeng, Z. Wang, J. Wang, Miner. Eng. 89 (2016) 84.
[15] L. Xu, Y. Hu, J. Tian, H. Wu, L. Wang, Y. Yang, Z. Wang, Colloids Surf. A 492 (2016) 181. [16] A.N. Buckley, G.K. Parker, Int. J. Miner. Process. 121 (2013) 70. [17] O. Pavez, P.R.G. Brandao, A.E.C. Peres, Miner. Eng. 9 (1996) 357. [18] Q. Meng, Q. Feng, Q. Shi, L. Ou, Miner. Eng. 79 (2015) 133. [19] R. Nagaraj, in: M.J. Jones, R. Oblatt (Eds.), Reagents in the Minerals Industry, Institute of Mining and Metallurgy, London, 1984. [20] X. Fan, N.A. Rowson, Miner. Eng. 13 (2000) 205. [21] X. Fan, N.A. Rowson, Dev. Chem. Eng. Mineral. Process. 8 (2000) 167. [22] O.S. Nuri, A. Mehdilo, M. Irannajad, Appl. Surf. Sci. 311 (2014) 27. [23] A. Mehdilo, M. Irannajad, J. Ind. Eng. Chem. 33 (2016) 59. [24] P.S. Parapari, M. Irannajad, A. Mehdilo, Miner. Eng. 92 (2016) 160. [25] M. Rey, V. Formanek, Some factors affecting selectivity in the differential flotation of lead-zinc ores, particularly in the presence of oxidized lead minerals, Proceedings, 5th Int. Miner. Process. Congr (1960). [26] P. Chen, J. Zhai, W. Sun, Y. Hu, Z. Yin, X. Lai, J. Ind. Eng. Chem. 53 (2017) 285. [27] P. Chen, J. Zhai, W. Sun, Y. Hu, Z. Yin, Miner. Eng. 111 (2017) 100. [28] Q. Feng, W. Zhao, S. Wen, Q. Cao, Sep. Purif. Technol. 178 (2017) 193. [29] L. Xia, B. Hart, B. Loshusan, Miner. Eng. 70 (2015) 119. [30] T. Yue, H. Han, Y. Hu, W. Sun, X. Li, R. Liu, Z. Gao, L. Wang, P. Chen, C. Zhang, M. Tian, JOM 69 (2017) 2345. [31] G. Zhao, S. Wang, H. Zhong, Minerals 5 (2015) 247. [32] B. Zhang, H. Zhong, Res. Chem. Intermed. 36 (2010) 495. [33] R. Roncucci, M.J. Simon, V. Briesen, Anal. Lett. 4 (1971) 197. [34] A. Mehdilo, M. Irannajad, B. Rezai, Int. J. Miner. Process. 137 (2015) 71. [35] M.C. Fuerstenau, J.D. Miller, M.C. Kuhn, Chemistry of Flotation, Society of Mining Engineers of AIME, 1985. [36] P. Somasundaran, D.Z. Wang, Solution Chemistry: Minerals and Reagents, Elsevier, 2006. [37] Y. Hu, D. Wang, Z. Xu, Miner. Eng. 10 (1997) 623. [38] X. Qiu, Y. Gao, Nonferrous Met. (Mineral Processing Section) (2005) p. 38 (in Chinese). [39] P.J. Thistlethwaite, M.S. Hook, Langmuir 16 (2000) 4993. [40] Y. Gao, X. Qiu, Q. Xia, Q. Feng, J. Guangdong Non-Ferrous Met. 11 (2001) 92 (in Chinese). [41] T. Yamashita, P. Hayes, Appl. Surf. Sci. 254 (2008) 2441. [42] L. Largitte, S. Gervelas, T. Tant, P.C. Dumesnil, A. Hightower, R. Yasami, Y. Bercion, P. Lodewyckx, Adsorption 20 (2014) 689. [43] D. Soccol, J. Martens, S. Claessens, J. Fransaer, J. Electrochem. Soc. 158 (2011) D515. [44] A. Ouerd, C. Alemany-Dumont, G. Berthomé, B. Normand, S. Szunerits, J. Electrochem. Soc. 154 (2007) C593. [45] T.J. Daou, S. Begin-Colin, J.M. Grenèche, F. Thomas, A. Derory, P. Bernhardt, P. Legaré, G. Pourroy, Chem. Mater. 19 (2007) 4494.
Please cite this article in press as: Q. Meng, et al., Study on the activation mechanism of lead ions in the flotation of ilmenite using benzyl hydroxamic acid as collector, J. Ind. Eng. Chem. (2018), https://doi.org/10.1016/j.jiec.2017.12.059
Journal of Industrial and Engineering Chemistry xxx (2017) xxx–xxx
Contents lists available at ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
Study on the activation mechanism of lead ions in the flotation of ilmenite using benzyl hydroxamic acid as collector Qingyou Meng, Zhitao Yuan* , Li Yu, Yuankai Xu, Yusheng Du School of Resources and Civil Engineering, Northeastern University, Shenyang 110819, China
A R T I C L E I N F O
Article history: Received 14 October 2017 Received in revised form 19 December 2017 Accepted 25 December 2017 Available online xxx Keywords: Ilmenite Adsorption Lead ions Surface activation Flotation
A B S T R A C T
The activation mechanism of Pb2+ ions to ilmenite and the subsequent interaction with benzyl hydroxamic acid (BHA) were systematically investigated. The Pb2+ ions modification occurred via a chemical adsorption process, in which lead species interacted with iron hydroxyl compounds to form lead-containing complexes on the ilmenite surface. After lead ions activation, the surface of ilmenite became more active, and iron species and lead-containing complexes served as the main active sites to covalently bond with BHA in the form of metal-BHA chelate complexes. As a result, the BHA adsorption increased, giving rise to a concomitant increase in the floatability of ilmenite. © 2018 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Introduction Titanium has many extensive applications including medicine, aerospace, function materials and catalytic industries due to its high strength-to-weight ratio and corrosion resistance [1,2]. Two titanium phases, titanium dioxide and metal titanium, are produced presently from rutile and ilmenite. Ilmenite is becoming the major raw material in titanium industry resulting from the excessive consumption of limited rutile resources [3,4]. In the mineral processing of ilmenite ore, gravity separation, highintensity magnetic separation (HIMS), electrostatic separation or a conjunction of them are widely adopted to separate titanium minerals from gangues based on the difference of their physical properties. But for ilmenite freely disseminated in the gangues, the mentioned methods cannot effectively separate ilmenite from associated gangue minerals. In this case, froth flotation, a physicochemical separation process, has been considered suitable for processing ilmenite ore [5–7]. In the flotation process, one of the critical factors is to selectively modify the mineral surface property and improve the hydrophobicity of a desired mineral. Organic surfactants have been widely used as collectors because they can anchor on the mineral surface and render the attachment of particles to air bubbles. Among all surfactants, sodium oleate (aliphatic acids) and succinamate are commonly used in the flotation separation of
* Corresponding author. E-mail address: [email protected] (Z. Yuan).
ilmenite from siliceous gangues [3,8,9]. Successful separation of ilmenite could be achieved using benzyl arsenic acid (BAA) in the presence of acidified silicates, reported by Song and Tsai [10]. Phosphonic acid exhibits a strong affinity toward metal oxides, which is deemed to an impactful collector for the selective flotation of titanium minerals [7,11,12]. The mixed anionic/cationic collector shows more superior hydrophobicity and collecting property than an individual collector because of the remarkable synergistic effect, aiming to improve the flotation efficiency of ilmenite [13–15]. Hydroxamic acids and their salts have also been extensively studied and exploited as collectors due to the active chelation with some transition metal or rare-earth metal ions on mineral surfaces [16–18]. Relevant research using hydroxamate as the collector was reported in the flotation of titanium minerals [19]. Even if collectors are utilized to improve the hydrophobicity of mineral surface, ilmenite yet displays a poor flotation performance compared to rutile. It is because that only half of metallic ions (Ti4+ and Fe2+) on the ilmenite surface are serving as active sites and interact with anionic collectors at different pH ranges [5,20,21]. Therefore, considerable studies have been attempted to supply sufficient active sites for improving the flotation recovery of ilmenite. Surface oxidation, such as microwave irradiation, oxidation roasting, and surface dissolution, is discussed to enhance the ilmenite floatability, which converts ferrous ions to ferric ions in terms of increasing the adsorption of collectors on the ilmenite surface [22–24]. Surface activation by adding new active species on the mineral surfaces is another effective method in the flotation process. Lead ions have been investigated as activators for the
https://doi.org/10.1016/j.jiec.2017.12.059 1226-086X/© 2018 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Please cite this article in press as: Q. Meng, et al., Study on the activation mechanism of lead ions in the flotation of ilmenite using benzyl hydroxamic acid as collector, J. Ind. Eng. Chem. (2018), https://doi.org/10.1016/j.jiec.2017.12.059
G Model JIEC 3815 No. of Pages 8
2
Q. Meng et al. / Journal of Industrial and Engineering Chemistry xxx (2017) xxx–xxx
flotation of sulfide and oxide minerals. As early as 1960, Rey and Formanek firstly reported lead ions as the activator in the sphalerite flotation [25]. Correspondingly, lead ions as the activator of oxide minerals were studied far behind that of sulfide, but they are widely utilized at a plant scale until now. Fan and Rowson reported that Pb2+ and Pb(OH)+ species of lead ions could selectively adsorb onto ilmenite surfaces and enhance its floatability when sodium oleate was used as a collector [20]. Chen provided further insights to reveal the activation mechanism of lead ions. They found that lead species formed lead-containing complexes on ilmenite surfaces, which served as the main active sites to bond with oleate species [26,27]. Lead ions as the activator combined with hydroxamate collectors have attracted a lot of enthusiasm to apply in the flotation of oxide minerals. Feng discovered that the lead species adsorbed on the cassiterite surface led to the increase in the number of active sites and offered adequate chances for the adsorption of salicyl hydroxamic acid [28]. The effect of lead ions on the flotation of rare earth minerals using benzyl hydroxamic acid and naphthalenic hydroxamic acid as collectors was investigated in virtue of TOF-SIMS analyses by Xia. Lead species reversed the surface charge of ilmenite and promoted the adsorption of collectors [29]. Yue et al. found that the Pb-BHA complexes exercised the synergistic effect between chemical and physical adsorption and facilitated to improve the flotation recovery of tungsten minerals [30]. Zhao reported the activation mechanism of lead ions in the flotation of scheelite and wolframite with benzyl hydroxamic acid by means of DFT and XPS analysis. Their results indicated that benzyl hydroxamic acid preferentially coordinated with Pb2+ ions compared with Ca2+, Mn2 + and Fe2+ ions [31]. Nevertheless, the surface activation of ilmenite by lead ions with hydroxamate as the collector is hardly reported in the published literature. In the present study, the positive influence of lead ions in the ilmenite flotation with benzyl hydroxamic acid (BHA) as the collector was investigated. The activation mechanism of lead ions on ilmenite surfaces and subsequent response to BHA adsorption were further discussed via adsorption tests, zeta potential measurements, FT-IR and XPS analysis.
Fig. 1. X-ray diffraction spectra of ilmenite.
the experiments were prepared using deionized water (18.25 MV cm). Microflotation experiments Microflotation experiments were conducted in an XFG II flotation machine with a fixed stirring rate of 1800 rpm. 2 g ilmenite samples and 40 mL deionized water were used in each test. The suspension was firstly adjusted to the desired pH value by H2SO4 or NaOH solution for 2 min, and then the activator and collector were added one after another and conditioned for 3 min and 5 min, respectively. After that, terpenic oil was added as the frother. The flotation time was limited to 5 min, and the froth was scraped out every 10 s. The floated and sank fractions were filtered, dried, and weighed, respectively. The flotation recovery of ilmenite was calculated according to Eq. (1), R¼
Materials and methods Materials Ilmenite sample was obtained from the vanadium–titanium magnetite in Panzhihua Mine, Sichuan province, China. Mineral samples were repeatedly purified using low-intensity magnetic separation, high-intensity magnetic separation, and shaking table. The XRD result given in Fig. 1 demonstrated that the sample was composed of ilmenite with a trace of pyrite, and the XRF result presented that the titanium (TiO2) content was 50.45%, indicating that the purity of ilmenite was above 95%. The purified ilmenite was dry-ground in a porcelain ball mill and sieved to obtain the 74 mm fractions for the flotation experiments. Samples for measurements were further ground to less than 5 mm in an agate mortar. Benzyl hydroxamic acid (BHA), used as the anionic collector, was synthesized in laboratory through the reaction of benzoic acid with hydroxylamine. The element analysis showed that the BHA purity was above 95% after the purification process. Analytically pure lead nitrate (Pb(NO3)2), used as the activator, was supplied by Tianjin Kermil Reagent Co., Ltd., China. The pH value of aqueous suspensions was adjusted by sodium hydroxide (NaOH) and sulfuric acid (H2SO4) dilute solutions (1 mol L1). Analytical grade potassium chloride (KCl) was used as the background electrolyte for zeta potential measurements. All solution and suspension in
Mf 100% Mf þ Ms
ð1Þ
where R is the flotation recovery, Mf is the mass of the floated fractions (concentrates), and Ms is the mass of the sank fractions (tailings). Adsorption tests The adsorption amount of BHA on the ilmenite surface was determined by the UV1901PC UV–Vis spectrophotometer (China). BHA concentration was measured using UV absorbance at the wavelength of 520 nm according to the ferric hydroxamate method [32,33]. 1.0 g ilmenite sample was dispersed into 40 mL aqueous phase in the absence and presence of lead ions at a desired pH value and conditioned for 3 min. Sequentially, the BHA stock solution was added to interact with the mineral surface, and the mixing was stirred for 30 min. The conditioned mineral particles were separated out by centrifugation, and the BHA concentration of the separated supernatant was measured by the UV–Vis spectrophotometer. The adsorption amount was calculated by Eq. (2) based on the difference between the initial and final BHA concentrations. Q¼
VðC 0 C f Þ M
ð2Þ
where, Q is the adsorption amount of BHA on ilmenite surfaces (mg g1), C0 is the initial BHA concentration (mg L1), Cf is the final
Please cite this article in press as: Q. Meng, et al., Study on the activation mechanism of lead ions in the flotation of ilmenite using benzyl hydroxamic acid as collector, J. Ind. Eng. Chem. (2018), https://doi.org/10.1016/j.jiec.2017.12.059
G Model JIEC 3815 No. of Pages 8
Q. Meng et al. / Journal of Industrial and Engineering Chemistry xxx (2017) xxx–xxx
BHA concentration (mg L1), V is the volume of supernatant (L), and M is the mass of ilmenite (g).
3
Results Microflotation and adsorption
Zeta potential measurements The zeta potential of ilmenite particles was determined using a Malvern Instrument Nano-ZS90 analyzer (Britain). In each test, 30 mg mineral sample (5 mm) was mixed in 40 mL electrolyte solution (103 mol L1 KCl). The suspension was magnetically stirred for 2 min after pH adjustment and followed by another 5 min for adding activators or collectors. And then the zeta potential of prepared samples was measured by the zeta-potential analyzer. The average value of three measurements was adopted as the final result of zeta potential, and the standard deviation was calculated for each point. FTIR spectra analysis Fourier transform infrared (FTIR) spectra were detected by the Nicolet 740 infrared spectrometer (USA) to characterize the interaction between collector and ilmenite with or without Pb2+ treatment. The mineral sample was ground to smaller than 5 mm, and the suspension was conditioned similar to the procedure of microflotation experiments, conditioning for 30 min. The prepared suspension was filtered, washed with deionized water for three times, then vacuum dried at 50 C. Approximately 1 mg mineral sample was mixed with 100 mg spectroscopic grade KBr, pressing disc pellets for measurements. XPS determinations The X-ray photoelectron spectroscopy (XPS) measurements were carried out using a Thermo Fisher ESCALAB 250Xi XPS system. An Al Ka X-ray source at 1486.6 eV was used in the XPS analysis. Binding energy values were calibrated using characteristic carbon (C1s = 284.8 eV) during data processing of XPS spectra. The mineral samples with the particle size of 5 mm were used, preparing similar to the microflotation experiment. After all reagents were added to adjust the suspension, the prepared samples were filtrated, washed three times with deionized water, and then dried in a vacuum oven for XPS measurements.
The effect of pH value on the flotation recovery of ilmenite in the absence and presence of Pb2+ ions, using 120 mg L1 BHA, is shown in Fig. 2a. The results showed that ilmenite treated with BHA alone displayed a relatively poor floatability, and the flotation recovery was obtained only 17.0% at pH 8.0. It seemed that BHA collector could not improve the floatability of ilmenite. After Pb2+ treatment, the flotation recovery of ilmenite increased with the rise in pH values ranging from 2.0 to 8.0 and then decreased until pH around 11.0. Over 69.0% of ilmenite particles were floated out when pH reached approximately 8.0. The flotation recovery of ilmenite with Pb2+ modification increased by around 52% in comparison with that without Pb2+ treatment. It could be seen that pH 8.0 was the best condition for ilmenite flotation, so that the effect of Pb2+ concentration on the flotation recovery of ilmenite was studied by fixing the pH at 8.0. Fig. 2b presents the effect of Pb2+ ions concentration on the flotation recovery of ilmenite with 120 mg L1 BHA at pH 8.0. The results in Fig. 2b showed that after ilmenite was activated by Pb2+ ions, its floatability was enhanced significantly. The flotation recovery of ilmenite increased with an increase in the initial concentration of lead ions and achieved 87.2% at Pb2+ ions of 2.0 104 mol L1. After that, the flotation recovery of ilmenite reached a high level platform when Pb2+ ions concentration was more than 2.0 104 mol L1. The adsorption amounts of BHA on ilmenite surfaces as functions of pH and Pb2+ ions concentration were measured, and the results are shown in Fig. 3. It could be found from Fig. 3a that the adsorption amounts of BHA on ilmenite surfaces firstly increased and then decreased with the increase of pH values, and the maximum value was obtained at pH 8.0. In the presence of Pb2+ ions, the adsorption of BHA on ilmenite surfaces performed a similar trend as that without Pb2+ treatment, but the adsorption amounts improved significantly in the entire pH range from 2.0 to 11.0. Furthermore, the BHA adsorption amounts increased with the Pb2+ ions concentration at pH 8.0 (in Fig. 3b). When Pb2+ ions concentration was greater than 2.0 104 mol L1, the BHA adsorption amounts increased slowly. Consistent variation trends
Fig. 2. Effect of pH and Pb2+ concentration on the recovery of ilmenite.
Please cite this article in press as: Q. Meng, et al., Study on the activation mechanism of lead ions in the flotation of ilmenite using benzyl hydroxamic acid as collector, J. Ind. Eng. Chem. (2018), https://doi.org/10.1016/j.jiec.2017.12.059
G Model JIEC 3815 No. of Pages 8
4
Q. Meng et al. / Journal of Industrial and Engineering Chemistry xxx (2017) xxx–xxx
Fig. 3. Effect of pH and Pb2+ concentration on the BHA adsorption.
were observed from Figs. 2 and 3 between ilmenite recovery and BHA adsorption. Hence, it was evident that Pb2+ ions enhanced the adsorption amounts of BHA on ilmenite surfaces, resulting in the improvement of ilmenite floatability. Zeta potentials Zeta potentials of mineral particles in the absence and presence of Pb2+ ions, using BHA as the collector, were conducted to study their interactions with ilmenite, and the results are presented in Fig. 4. It would be observed from Fig. 4 that the isoelectric points (IEP) of pure ilmenite was located at about pH 5.3, which was in agreement with the reported values [20,34]. After the addition of 104 mol L1 Pb2+ ions, zeta potentials of activated ilmenite exhibited an integral positive shift. The values of zeta potential increased by approximately 15 mV within the pH range from 7.0 to 9.0, and the IEP appeared at about 7.2. Fig. 5 shows the concentration distribution of lead species as a function of pH value under the total concentration of 1 104 mol L1 [35,36]. As presented in Fig. 5, the positively charged Pb2+ species existed over the acidic pH region, and at pH above 9.7, the dominant species of lead ions were soluble molecular Pb(OH)2(aq), PbðOHÞ 3 and
on the ilmenite/water interface, respectively. The correlation of lead species distributions with zeta potential results indicated that when pH value was below 9.7, the Pb2+ and Pb(OH)+ species would devoted to the positive shift of zeta potentials of ilmenite because of electrostatic interactions. Meanwhile, within the pH region from 7.0 to 9.0, Pb(OH)+ ions bearing positive charges were the dominant species, and the noticeable increase (15 mV) in the zeta potential of ilmenite was attributed to the specific adsorption of Pb (OH)+ species in the helmholtz layer of ilmenite. The electrokinetic behavior of ilmenite treated with Pb2+ ions could be attributed to the lead species being adsorbed onto the mineral surfaces. Fig. 4 also shows that with the addition of 120 mg L1 BHA, zeta potentials of ilmenite decreased in the whole pH range whether pretreated with Pb2+ ions or not. We should note that, in the presence of Pb2+ and BHA, the zeta potential of activated ilmenite changed more than that of BHA treatment alone and decreased by approximately 13 mV in the pH region from 7.0 to 9.0. BHA bore negative charge and further decreased the zeta potential of ilmenite, which was ascribed to the specific adsorption occurred between negatively charged hydroxamate species and ilmenite surfaces [28,37].
+ PbðOHÞ2 4 ions, whereas at pH 7.2–9.7, Pb(OH) species dominated
Fig. 4. Effect of pH on the zeta potentials of ilmenite treated with various conditions.
Fig. 5. Distribution diagram of lead species as a function of pH value (cPb = 1 104 mol L1).
Please cite this article in press as: Q. Meng, et al., Study on the activation mechanism of lead ions in the flotation of ilmenite using benzyl hydroxamic acid as collector, J. Ind. Eng. Chem. (2018), https://doi.org/10.1016/j.jiec.2017.12.059
G Model JIEC 3815 No. of Pages 8
Q. Meng et al. / Journal of Industrial and Engineering Chemistry xxx (2017) xxx–xxx
5
FTIR analysis
XPS analysis
The infrared spectra were obtained to analyze the adsorption mechanism of benzyl hydroxamic acid (BHA) on the ilmenite surface. The infrared spectra of BHA, pure ilmenite, ilmenite treated with BHA alone, and ilmenite treated with both lead ions and BHA at pH 8.0 are shown in Fig. 6. On the FTIR spectrum of BHA (Fig. 6a), the band at 3294 cm1 was attributed to the overlap stretching vibrations of N H and O H groups. The band at around 3060 cm1 was assigned to N H stretching vibration. Due to the conjugate effect, the characteristic bands of benzene rings were observed at 1564 cm1, 1480 cm1, and 1453 cm1. The N O stretching vibrations were further divided into three bands at 1077 cm1, 1041 cm1, and 1019 cm1. The bands at 1648 cm1 and 1162 cm1 could be attributed to the C¼N stretching vibration and the C N stretching vibration of hydroxamate groups, respectively. The bands at 690 cm1 and 533 cm1 were attributed to the C H out-of-plane bending vibrations of benzene rings [38]. On the FTIR spectrum of ilmenite (Fig. 6a), the characteristic band for ilmenite was observed at 700 cm1, while the band at around 1650 cm1 was attributed to the bending mode of adsorbed water [9,39]. As shown in Fig. 6b, when ilmenite was only treated with BHA, no new bands appeared on the ilmenite spectrum, suggesting that BHA rarely adsorbed onto ilmenite surfaces. Nevertheless, the FTIR spectrum of Pb2+-activated ilmenite treated with BHA had new bands at around 1560 cm1, 1482 cm1, and 1153 cm1, of which the bands at 1560 cm1 and 1482 cm1 were attributed to the characteristic bands of benzene rings. The new bands at around 1153 cm1, shifting by 9 cm1, belonged to the CN stretching vibration in the BHA molecule, which could be attributed to the metal hydroxamate precipitates [38,40]. These components indicated that a chemisorption process was occurring during the interaction between benzyl hydroxamic acid and the activated ilmenite surface. The chelating group of BHA was able to bond with lead ions anchored on the ilmenite surface and formed stable Pb2+ chelate compounds. Through comparing the spectra of ilmenite in the presence and absence of lead ions, it could be deduced that lead species adsorbed onto ilmenite surfaces and then provided a binding affinity to interact with BHA. The presence of Pb2+ ions stimulated the BHA adsorption on ilmenite surfaces, which was in agreement with the adsorption results.
To further confirm the interaction mechanism between BHA and ilmenite activated with lead ions, XPS analysis of ilmenite treated with Pb2+ ions or/and BHA was conducted, and the results are shown in Fig. 7. It could be found from Fig. 7a that after Pb2+ and BHA treatment, the Pb4f and N1s XPS peaks were detected on the ilmenite surface. The atomic concentrations of elements C1s, O1s, N1s, Ti2p, Fe2p and Pb4f measured by XPS were summarized in Table 1. Table 1 shows that the Pb4f atomic concentration increased from 0.07% of pure ilmenite to 0.65% of Pb2+-activated ilmenite, indicating that Pb2+ ions successfully adsorbed on the ilmenite surface. Furthermore, the C1s and N1s atomic concentrations of Pb2+-activated ilmenite treated with BHA increased by 6.64% and 0.48%, respectively, evidencing that BHA adsorbed onto the surfaces of Pb2+-activated ilmenite. To obtain the detailed information about Pb2+ activation and BHA attachment, the chemical status of surface species was further characterized by high-resolution XPS spectra. Fig. 7b shows that the Fe2p3/2 peaks of pure ilmenite appeared at around 710.93 eV and 713.56 eV, respectively, in which the peak at 710.93 eV was attributed to ferrous species, and the peak close to 713.56 eV was assigned to ferric species [26,41]. After Pb2+ activation, the Fe2p3/2 binding energy of ferrous and ferric species decreased by 0.21 eV and 0.44 eV, respectively. The presence of Pb2+ ions changed the chemical circumstance of Fe species on the ilmenite surface. Besides, the addition of BHA further decreased the Fe2p3/2 binding energy of ferrous and ferric species to 710.51 eV and 712.76 eV, respectively, suggesting that BHA might bond with Fe species of ilmenite surfaces. As for Ti on ilmenite surfaces in Fig. 7c, the Ti2p3/2 peaks were determined at around 458.37 eV, corresponding to the Ti4+ oxidation state. Nevertheless, the binding energy of Ti2p3/2 peaks showed no obvious change after Pb2+ ions and BHA treatment. Fig. 7d shows the Pb4f7/2 spectra of Pb2+-activated ilmenite before and after BHA treatment. The peak at 138.70 eV on the spectrum of Pb2+-activated ilmenite belonged to PbO species [42]. The binding energy of Pb4f7/2 peak decreased by 0.22 eV, from 138.70 eV of Pb2+-activated ilmenite to 138.48 eV of BHA treatment, which was evidencing the BHA could interact with lead species adsorbed on the surface of ilmenite.
Fig. 6. FTIR spectra of benzyl hydroxamic acid and ilmenite treated with various conditions.
Please cite this article in press as: Q. Meng, et al., Study on the activation mechanism of lead ions in the flotation of ilmenite using benzyl hydroxamic acid as collector, J. Ind. Eng. Chem. (2018), https://doi.org/10.1016/j.jiec.2017.12.059
G Model JIEC 3815 No. of Pages 8
6
Q. Meng et al. / Journal of Industrial and Engineering Chemistry xxx (2017) xxx–xxx
Fig. 7. High-resolution XPS spectra of ilmenite before and after Pb2+ and BHA treatment.
Table 1 Atomic concentration of elements on ilmenite surfaces as determined by XPS. Samples
Atomic concentration of elements on ilmenite surfaces (%) C1s O1s N1s
Ti2p
Pb4f
Fe2p
Ilmenite Ilmenite + Pb2+ Ilmenite + Pb2+ + BHA
16.80 16.92 23.56
7.01 7.59 8.09
0.07 0.65 0.73
11.51 11.40 10.30
63.35 62.05 55.46
1.27 1.39 1.87
Please cite this article in press as: Q. Meng, et al., Study on the activation mechanism of lead ions in the flotation of ilmenite using benzyl hydroxamic acid as collector, J. Ind. Eng. Chem. (2018), https://doi.org/10.1016/j.jiec.2017.12.059
G Model JIEC 3815 No. of Pages 8
Q. Meng et al. / Journal of Industrial and Engineering Chemistry xxx (2017) xxx–xxx
The O1s XPS spectra recorded from pure ilmenite, ilmenite treated with Pb2+, and ilmenite treated with both Pb2+ and BHA are shown in Fig. 7e. The O1s peaks were composed of three components. The peaks at around 530.0 eV were attributed to TiO bonds [43,44], 531.3 eV attributed to FeO bonds [45], and 532.1 eV for hydroxyl bonded to metal ions (Me OH) [44], respectively. As suggested by the analysis of the corresponding O1s peaks for ilmenite modified by lead ions and subsequently treated with BHA (in Table 2), the relative intensity of O1s peaks belonged to FeO bonds increased from 21.40% of pure ilmenite to 30.53% of ilmenite modified by Pb2+ ions and 66.10% of Pb2+-activated ilmenite treated with BHA, while that of O H bonds decreased from 50.87% to 38.93% and further to 3.95%. These results illustrated that lead species would interact with active iron sites to form lead-containing complexes (Fe O Pb) on the ilmenite surface. Consequently, lead species adsorbed on ilmenite surfaces rendered new active sites for BHA adsorption. BHA replaced OH ions and bonded to the active metal sites in the form of metalhydroxamate chelate complexes, improving the hydrophobicity of ilmenite. Discussion Fig. 8 shows the surface species distribution of ilmenite as a function of pH [5]. The surface chemistry of ilmenite strongly depends on the solution pH value. The main metal ions of ilmenite, i.e., Fe2+ and Ti4+ ions, have different forms as the pH changes. Within the broad pH region from 3 to 11, ferrous ions exist in the forms of Fe2+ and Fe(OH)+, while titanium ions mainly dominate in the form of Ti(OH)4. Since Ti(OH)4 compounds (solubility product KTi(OH)4 = 1058.30) are so stable, ferrous ions on ilmenite surfaces are supposed to regard as the active sites to interact with collectors [5,34]. According to the foregoing results, the presence of Pb2+ ions stimulated the adsorption of BHA and enhanced the floatability of ilmenite. The zeta potential analysis showed that lead species made the zeta potential of ilmenite shift positively, in which Pb (OH)+ species played the critical role in the pH range from 7.0 to 9.0. The results of XPS analysis demonstrated that the addition of Pb2+ ions changed the chemical environment of iron species on the ilmenite surface, while that of titanium species remained the same. Moreover, the relative intensity of O species in FeO/Fe O Pb bonds of Pb2+-activated ilmenite increased significantly compared with pure ilmenite. These results indicated that it was the lead species that interacted with Fe species on ilmenite surfaces, which was inaugurated through dehydration reaction in the coating process of lead-hydroxyl compounds on ilmenite surfaces. As a result, the adsorption of lead species generated stable leadcontaining complexes and increased the amount of active sites on the ilmenite surface. Pb2+ ions motivated the surface property of ilmenite and provided active sites for BHA adsorption. The results of flotation Table 2 O1s parameters on ilmenite surfaces treated with various conditions. Sample
Binding energy (eV)
Assignment
Area ratio (%)
Ilmenite
530.07 531.39 532.11 530.02 531.28 532.07 530.00 531.36 532.10
Ti O FeO HO Ti O FeO/FeO Pb HO Ti O FeO/FeO Pb HO
27.74 21.40 50.87 30.55 30.53 38.93 29.95 66.10 3.95
2+
Ilmenite + Pb
Ilmenite + Pb2+ + BHA
7
Fig. 8. Distribution diagram of surface species on ilmenite as a function of pH values.
experiments and adsorption measurements indicated that the Pb2+ modification improved the floatability of ilmenite by increasing the adsorption of BHA on the ilmenite surface. After BHA treatment, the zeta potential of ilmenite appeared a negative shift, furthermore, the zeta potential of the activated ilmenite showed a more noticeable shift than that of the non-activated one, which was in good agreement with the adsorption results. It was a remarkable fact that the negatively-charged BHA collector could adsorb onto the negatively-charged ilmenite surface, suggesting that the special attractive force between BHA and ilmenite was larger than their electrostatic physical repulsion force, which was ascribed to the chemisorption between BHA and ilmenite. The FTIR results further confirmed that BHA could chemisorb onto the surface of lead activated ilmenite. The XPS analysis showed that the binding energy of Fe2p3/2 and Pb4f7/2 presented significant shifts (0.2–0.4 eV) after Pb2+-activated ilmenite was treated by BHA, inferring the change of their chemical environments. Otherwise, the relative intensity of Fe O/Fe OPb bonds (at 531.36 eV) increased significantly, and that of O H bonds (at 532.10 eV) decreased. These findings indicated that the adsorbed BHA would substitute hydroxyls bonded to the Pb or Fe species of Pb2+-activated ilmenite, and then the active O active atoms (in the form of C¼O and N OH, respectively) in the chelating group of BHA reacted with lead(iron) ions to form metal-BHA complexes on the ilmenite surface, which was in consistent with the results of zeta potentials and FTIR. Based on the results and discussion above mentioned, Pb2+ ions played a critical role in the flotation of ilmenite by using BHA as a collector. It was believed that lead species firstly adsorbed onto the ilmenite surface and then reacted with BHA to form hydrophobic species of metal-BHA chelate complexes, which were responsible for improving the floatability of ilmenite. A potential mechanism about the Pb2+ activation and subsequent BHA adsorption on the ilmenite surface was proposed in Fig. 9. Conclusions This study systematically studied a series of experiments associated with the activation of Pb2+ ions in the flotation of ilmenite using benzyl hydroxamic acid (BHA) as the collector. The flotation and adsorption tests showed that the addition of lead ions could stimulate BHA to adsorb onto mineral surfaces and contribute to the improved floatability of ilmenite, especially at pH 7.0–9.0. The results of zeta potential and XPS measurements
Please cite this article in press as: Q. Meng, et al., Study on the activation mechanism of lead ions in the flotation of ilmenite using benzyl hydroxamic acid as collector, J. Ind. Eng. Chem. (2018), https://doi.org/10.1016/j.jiec.2017.12.059
G Model JIEC 3815 No. of Pages 8
8
Q. Meng et al. / Journal of Industrial and Engineering Chemistry xxx (2017) xxx–xxx
Fig. 9. A potential mechanism for Pb2+ activation and BHA adsorption on the ilmenite surface.
suggested that the adsorption of lead ions onto ilmenite surfaces was mainly a chemically dominating process, along with the electrostatic attractions between the positively charged lead species and ilmenite surface. Pb(OH)+ species reacted with the iron hydroxyl compounds on the ilmenite surface to form leadcontaining complexes, which were the main active sites for BHA adsorption. Consequently, FTIR and XPS analysis confirmed that BHA species chemically adsorbed on the surface of Pb2+-activated ilmenite and generated the hydrophobic species of lead-BHA complexes, improving the floatability of ilmenite. Acknowledgments This work was supported by the Fundamental Research Funds for the Central Universities (N160103004); and China Postdoctoral Science Foundation (2017M611249). References [1] D. Chen, L. Zhao, T. Qi, G. Hu, H. Zhao, J. Li, L. Wang, Trans. Nonferrous Met. Soc. 23 (2013) 3076. [2] S. Samal, B.K. Mohapatra, P.S. Mukherjee, S.K. Chatterjee, J. Alloy. Compd. 474 (2009) 484. [3] S. Bulatovic, D.M. Wyslouzil, Miner. Eng. 12 (1999) 1407. [4] F. Chachula, Q. Liu, Fuel 82 (2003) 929. [5] X. Fan, K.E. Waters, N.A. Rowson, D.J. Parker, J. Colloid Interf. Sci. 329 (2009) 167. [6] G. Belardi, L. Piga, S. Quaresima, N. Shehu, Int. J. Miner. Process. 53 (1998) 145. [7] F. Li, H. Zhong, G. Zhao, S. Wang, G. Liu, Colloids Surf. A 490 (2016) 67. [8] K.H. Rao, K.S.E. Forssberg, Miner. Eng. 4 (1991) 879. [9] W. Liu, J. Zhang, W. Wang, J. Deng, B. Chen, W. Yan, S. Xiong, Y. Huang, J. Liu, Miner. Eng. 72 (2015) 1. [10] Q. Song, S.C. Tsai, Int. J. Miner. Process. 26 (1989) 111. [11] G. Guerrero, H. Mutin, A. Vioux, Chem. Mater. 13 (2001) 4367. [12] Q. Liu, Y. Peng, Miner. Eng. 12 (1999) 1419. [13] J. Tian, L. Xu, Y. Yang, J. Liu, X. Zeng, W. Deng, Int. J. Miner. Process. 166 (2017) 102. [14] L. Xu, Y. Hu, J. Tian, H. Wu, Y. Yang, X. Zeng, Z. Wang, J. Wang, Miner. Eng. 89 (2016) 84.
[15] L. Xu, Y. Hu, J. Tian, H. Wu, L. Wang, Y. Yang, Z. Wang, Colloids Surf. A 492 (2016) 181. [16] A.N. Buckley, G.K. Parker, Int. J. Miner. Process. 121 (2013) 70. [17] O. Pavez, P.R.G. Brandao, A.E.C. Peres, Miner. Eng. 9 (1996) 357. [18] Q. Meng, Q. Feng, Q. Shi, L. Ou, Miner. Eng. 79 (2015) 133. [19] R. Nagaraj, in: M.J. Jones, R. Oblatt (Eds.), Reagents in the Minerals Industry, Institute of Mining and Metallurgy, London, 1984. [20] X. Fan, N.A. Rowson, Miner. Eng. 13 (2000) 205. [21] X. Fan, N.A. Rowson, Dev. Chem. Eng. Mineral. Process. 8 (2000) 167. [22] O.S. Nuri, A. Mehdilo, M. Irannajad, Appl. Surf. Sci. 311 (2014) 27. [23] A. Mehdilo, M. Irannajad, J. Ind. Eng. Chem. 33 (2016) 59. [24] P.S. Parapari, M. Irannajad, A. Mehdilo, Miner. Eng. 92 (2016) 160. [25] M. Rey, V. Formanek, Some factors affecting selectivity in the differential flotation of lead-zinc ores, particularly in the presence of oxidized lead minerals, Proceedings, 5th Int. Miner. Process. Congr (1960). [26] P. Chen, J. Zhai, W. Sun, Y. Hu, Z. Yin, X. Lai, J. Ind. Eng. Chem. 53 (2017) 285. [27] P. Chen, J. Zhai, W. Sun, Y. Hu, Z. Yin, Miner. Eng. 111 (2017) 100. [28] Q. Feng, W. Zhao, S. Wen, Q. Cao, Sep. Purif. Technol. 178 (2017) 193. [29] L. Xia, B. Hart, B. Loshusan, Miner. Eng. 70 (2015) 119. [30] T. Yue, H. Han, Y. Hu, W. Sun, X. Li, R. Liu, Z. Gao, L. Wang, P. Chen, C. Zhang, M. Tian, JOM 69 (2017) 2345. [31] G. Zhao, S. Wang, H. Zhong, Minerals 5 (2015) 247. [32] B. Zhang, H. Zhong, Res. Chem. Intermed. 36 (2010) 495. [33] R. Roncucci, M.J. Simon, V. Briesen, Anal. Lett. 4 (1971) 197. [34] A. Mehdilo, M. Irannajad, B. Rezai, Int. J. Miner. Process. 137 (2015) 71. [35] M.C. Fuerstenau, J.D. Miller, M.C. Kuhn, Chemistry of Flotation, Society of Mining Engineers of AIME, 1985. [36] P. Somasundaran, D.Z. Wang, Solution Chemistry: Minerals and Reagents, Elsevier, 2006. [37] Y. Hu, D. Wang, Z. Xu, Miner. Eng. 10 (1997) 623. [38] X. Qiu, Y. Gao, Nonferrous Met. (Mineral Processing Section) (2005) p. 38 (in Chinese). [39] P.J. Thistlethwaite, M.S. Hook, Langmuir 16 (2000) 4993. [40] Y. Gao, X. Qiu, Q. Xia, Q. Feng, J. Guangdong Non-Ferrous Met. 11 (2001) 92 (in Chinese). [41] T. Yamashita, P. Hayes, Appl. Surf. Sci. 254 (2008) 2441. [42] L. Largitte, S. Gervelas, T. Tant, P.C. Dumesnil, A. Hightower, R. Yasami, Y. Bercion, P. Lodewyckx, Adsorption 20 (2014) 689. [43] D. Soccol, J. Martens, S. Claessens, J. Fransaer, J. Electrochem. Soc. 158 (2011) D515. [44] A. Ouerd, C. Alemany-Dumont, G. Berthomé, B. Normand, S. Szunerits, J. Electrochem. Soc. 154 (2007) C593. [45] T.J. Daou, S. Begin-Colin, J.M. Grenèche, F. Thomas, A. Derory, P. Bernhardt, P. Legaré, G. Pourroy, Chem. Mater. 19 (2007) 4494.
Please cite this article in press as: Q. Meng, et al., Study on the activation mechanism of lead ions in the flotation of ilmenite using benzyl hydroxamic acid as collector, J. Ind. Eng. Chem. (2018), https://doi.org/10.1016/j.jiec.2017.12.059