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Reverse flotation separation of talc from molybdenite without addition of depressant: Effect of surface oxidation by thermal pre-treatment
Colloids and Surfaces A 594 (2020) 124671
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Reverse flotation separation of talc from molybdenite without addition of depressant: Effect of surface oxidation by thermal pre-treatment
T
Xuekun Tanga,b,1, Yanfei Chena,1, Kun Liua,b,*, Qian Penga,b, Guangsheng Zenga, Minlin Aoa,b, Zishun Lia,b a b
School of Minerals Processing and Bioengineering, Central South University, Changsha, 410083, China Hunan Key Laboratory of Mineral Materials and Application, Central South University, Changsha, 410083, China
G R A P H I C A L A B S T R A C T
A R T I C LE I N FO
A B S T R A C T
Keywords: Molybdenite Talc Thermal treatment Surface oxidation Flotation separation
The excellent inherent floatability of talc and molybdenite makes them very difficult to be separated in the flotation process. To conquer the problem, for the first time, an attempt was made to separate molybdenite and talc by calcining the ores under the air condition before flotation separation. Micro-flotation test results showed that the natural floatability of molybdenite vanished after thermal pretreatment at above 400 °C. In contrast, for that of talc, it barely changes. A satisfying flotation separation effect of molybdenite and talc in either mixed minerals or molybdenite-talc bulk concentrate was achieved through the thermal pretreatment method. The results of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis indicated that the surface of molybdenite underwent dramatical oxidation after thermal treatment at 400 °C. The formation of MoO3 and reduction in sulfur content on the surface of molybdenite were proposed to result in the poor floatability of molybdenite after thermal treatment.
1. Introduction Froth flotation, a physico-chemical separation method by utilization of difference surface hydrophilic/hydrophobic properties between
different minerals, is one of the most widely used industrial processes for beneficiation of valuable minerals from ore deposits [1–3]. Especially for the sulfide minerals, most of them were separated from unwanted gangue minerals through the flotation [4,5]. Talc, a kind of
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Corresponding author at: School of Minerals Processing and Bioengineering, Central South University, Changsha, 410083, China. E-mail address: [email protected] (K. Liu). 1 These authors contributed equally to this work. https://doi.org/10.1016/j.colsurfa.2020.124671 Received 19 November 2019; Received in revised form 21 February 2020; Accepted 4 March 2020 Available online 05 March 2020 0927-7757/ © 2020 Elsevier B.V. All rights reserved.
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Fig. 1. The XRD patterns of the as-prepared mineral samples: (a) Molybdenite sample; (b) Talc sample.
Cu(OH)2 and FeOOH, are coated on the surface of the chalcopyrite to make it difficult to be floated anymore [27–29]. On the contrary, the surface of molybdenite is slightly changed and remains good floatability under the same oxidation condition [27–29]. Based on this principle, molybdenite can be separated from chalcopyrite by utilization of the surface oxidation method. Talc is an oxide mineral, whose surface is bound to be much more stable for oxidation than that of molybdenite [30]. Thus, it would stand a good chance of realizing the separation of molybdenite and talc through the surface oxidation. However, the molybdenite has a relatively stable surface property in comparison to other sulfide minerals, as a result none of the above methods by using oxidant agents can effectively realize the surface oxidation of molybdenite [26,28]. Hence, in this research, we attempt to realize selective oxidation of molybdenite through a facile thermal pretreatment method for the first time. Micro-flotation tests were carried out to evaluate the effect of thermal pretreatment method on flotation separation of molybdenite and talc. Moreover, surface characterizations on talc and molybdenite were conducted to understand the mechanism of thermal pretreatment method.
magnesium-rich phyllosilicate mineral with theoretical chemical formula of Mg3Si4O10(OH)2, is a common unwanted gangue mineral encountered in sulphide ores around the world [6–8]. However, the surface of the grinded talc powder is mainly composed of basal plane (approximately 90 % of total surface), which is non-polar and hydrophobic [7,8]. Therefore, unlike the other silicate gangue (e.g. quartz, mica, chlorite, garnet) with hydrophilic surface, the talc has excellent natural floatability [7,9]. Molybdenite (MoS2) is the most essential commercial source for molybdenum (Mo) extraction in industry [10,11]. Similar to talc, molybdenite has a laminar crystalline structure and is also naturally hydrophobic with excellent floatability due to its non-polar face composed of weak unsaturated SeS bonds [12–14]. Thus, in the flotation process, talc is fairly easy to be brought into the molybdenite concentrates due to their similar floatability [15,16]. The existence of talc in molybdenite inevitably brings unfavorable consequences such as lowering the purity of concentrates, increasing smelting costs in metallurgy process [17]. It is therefore of significant importance to separate talc and molybdenite in flotation process. In sulfide ore flotation process, depressants, such as carboxymethyl cellulose [6,7] and polysaccharide reagents (e.g. chitosan [18] and Locust bean gum [19]), are used to depress talc in the flotation process. However, imperfect effects are obtained when these depressants used in molybdenite-talc separation due to the similar depression effect on molybdenite. To overcome the defect, reverse flotation process by selective depression of molybdenite has been also researched in laboratory to realize the separation of talc and molybdenite. Kelebek et al. [20] has found that the sodium lignosulphonate can selectively depress molybdenite. Dextrin [21,22], humic acid [15] and carboxymethylcellulose polymers [23] have been also researched as depressant in reverse flotation separation of molybdenite and talc with addition of frother only. However, in industry, the molybdenite is commonly required to be preferentially recovered since most molybdenite sources are presented as low-grade ores at present [24,25]. The molybdenite in the concentrate absorbed with collector (kerosene or collectors for sulfide minerals), which is very difficult to be separated from talc by application of depressant in the further re-flotation process. Thus, in industry, high dosage of these macromolecular organic depressants is required to obtain a satisfactory beneficiation effect, which would greatly increase chemical oxygen demand (COD) in wastewater. In addition to using depressant, surface oxidation is an alternative to depress the sulfide minerals [12,26–29]. Typically, the selective oxidation pretreatment on chalcopyrite has been achieved by application of various approaches, including ozone oxidation [26], H2O2 oxidation [26], plasma pretreatment [27] and Fenton-like oxidation [28,29]. After oxidation pretreatment, hydrophilic metallic oxide, such as CuO,
2. Experimental 2.1. Ore samples The molybdenite and talc mineral samples were obtained from luanchuan, Henan province, china and Longsheng, Guangxi Province, china, respectively. The two mineral samples were hand-picked, crushed to −1 mm and then ground into powders by a mechanical powder machine. For molybdenite sample, the particles with size of -74 μm + 38 μm were collected by vibrating screen for flotation tests. While, for talc sample, particle sized of −74 μm was collected for flotation tests. X-ray diffraction spectra shown Fig. 1 points out the asprepared minerals are of high purity. Moreover, according to chemical analysis, the molybdenite sample has a Mo grade of 55.99 % and S grade of 34.93 %. The talc sample has a MgO grade of 31.31 % and SiO2 grade of 65.03 %. These results further confirming that the as-prepared ore samples are high purity. 2.2. Thermal pretreatment procedure Laboratory-scaled thermal pretreatment on the ore samples was conducted in a tube furnace. Typically, 3 g of the ore sample was heated under pre-determined temperature in air atmosphere by the tube furnace. The residence time for each sample in tube furnace was 30 min. After naturally cooling to room temperature, the treated samples were immediately applied for flotation tests. 2
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Table 1 Results of flotation separation of molybdenite and talc artificially mixed minerals. Conditions of flotation
Products
Yield (W/ %)
Mo grade (%)
Mo recovery (%)
Without Thermal pretreatment; Kerosene: 40 mg/L MIBC: 40 mg/L Thermally treated at 400 °C; MIBC: 40 mg/L
Concentrate
94.33
30.11
96.09
Tailing Feed Concentrate
5.67 100.00 48.61
20.40 29.56 6.91
3.91 100.00 11.36
Tailing Feed Concentrate
51.39 100.00 50.81
50.98 29.56 6.19
88.64 100.00 10.64
Tailing Feed
49.19 100.00
53.70 29.56
89.36 100.00
Thermally treated at 450 °C; Kerosene: 40 mg/L MIBC: 40 mg/L
purity) were applied as collector. Ultrapure water produced by reverse osmosis was used in all the experiments. In each test, 35 mL water and 2 g of the as-prepared ore samples were successively added in the cell (maximum volume: 40 mL) under agitation to form a uniform ore pulp. 0.1 mol/L sodium hydroxide (NaOH) solution or 0.1 mol/L dilute hydrochloric (HCl) acid solution was added to adjust pH value of the pulp to 6. After agitation for 5 min, designed amount of collector was added in the pulp. After 3 min of conditioning, certain amount of frother was added in the cell followed by 1 min of conditioning. The floated froth product in the cell was manually collected for 3 min. For single minerals flotation, the recovery was calculated according to the weight distributions between the froth products and un-floated tailings. For that of mixed mineral, it can be calculated according to the molybdenum grade of concentrates and feeds. 2.4. Analysis method X-ray photoelectron spectroscopy (XPS) measurements were performed on an ultrahigh vacuum electron spectrometer (K-Alpha 1063, Thermo Fisher, UK). Fourier transform infrared spectroscopy (FTIR) spectra were recorded on an infrared spectrometer (UV-2350, Shimadzu, Japan) from 4000 cm−1 to 400 cm−1 by potassium bromide (KBr) diffuse reflection method. 3. Results and discussion 3.1. Micro-flotation of single mineral Micro-flotation tests of single mineral were carried to evaluate the effect of thermal pretreatment on the flotation behavior of talc and molybdenite. In industry, kerosene and xanthate are usually employed as the collector for molybdenite, and kerosene is commonly used as collector for talc [31,32]. Thus, in this research, PBX (Dosage: 200 mg/ L) and kerosene (Dosage: 100 mg/L) were applied as the collector in flotation separation process of molybdenite and talc. MIBC (Dosage: 100 mg/L) was used as the frother in these tests. The flotation results are presented in Fig. 2. Fig. 2a shows flotation behavior of the talc and molybdenite under different thermal treatment temperature without collector (MIBC dosage: 40 mg/L). As shown in the figure, the flotation recoveries of untreated talc and molybdenite reach 83.43 % and 90.12 %, respectively, confirming excellent inherent floatability of the two minerals. This also indicates that the two untreated minerals can hardly be separated without application of depressant because both minerals are enriched in concentrates [19]. For molybdenite, the recovery is slightly changed when the thermal treatment temperature is below 200 °C. While, when the thermal treatment temperature is above 200 °C, dramatical
Fig. 2. Flotation of single talc and molybdenite as a function of thermal pretreatment temperature with different collectors: (a) Collectorless; (b) PBX; (c) Kerosene.
2.3. Micro-flotation tests All micro-flotation tests were performed on a mechanical agitation flotation machine (Type: XFG). Commercially obtained Methyl Isobutyl Carbinol (MIBC, 99 % purity) was applied as frother in all flotation tests. Kerosene (98 % purity) and Potassium Butyl Xanthate (PBX, 98 % 3
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Table 2 Results of flotation separation of molybdenite-talc bulk concentrate thermally treated under 450 °C. Conditions of flotation
Products
Yield (W/%)
Mo grade (%)
Mo recovery (%)
Thermally treated at 450 °C; Kerosene: 40 mg/L MIBC: 40 mg/L
Concentrate Tailing Feed
50.39 49.61 100.00
6.61 53.98 30.11
11.06 88.94 100.00
influence on the floatability of talc. Fig. 2b shows flotation behavior of the talc and molybdenite under different thermal treatment temperature by using PBX as collector (PBX dosage: 1 × 10−4 mol/L; MIBC dosage: 40 mg/L). It illustrates that the recovery of raw molybdenite reaches 96.03 % with the assistance of PBX. The recovery slowly decreases with the increase of thermal treatment temperature and sharply decreases when the thermal treatment temperature is above 300 °C. Moreover, it is noticeable that the recovery of molybdenite is 89.50 % when the thermal treatment temperature reaches 300 °C. While, for the collectorless condition (as presented in Fig. 2a), it is only 52.11 %. It is known that the xanthate collector can be adsorbed on the polar edge arranged with Mo-S through chemical adsorption [13,33]. This possibly implies that the polar edge of molybdenite is well maintained after thermal treatment under 300 °C. When the thermal treatment temperature reaches 400 °C, the recovery of molybdenite is only 2.62 % and remains constant as the increase of temperature. This implies that the polar edge of molybdenite is destructed under the temperature of 400 °C, which makes it impossible to absorb PBX. In comparison, for talc, the recovery maintains about 90 % as variation of the thermal pretreatment temperature, which is basically the same to that of the collectorless condition. Besides, this indicates the PBX has little collecting capacity on talc. Fig. 2c shows flotation behavior of the talc and molybdenite under different thermal treatment temperature by using kerosene as collector (kerosene dosage: 40 mg/L; MIBC dosage: 40 mg/L). As presented in the figure, the recoveries of raw molybdenite and talc are 96.56 % and 95.62 %, respectively, indicating the excellent collecting capacity of kerosene on the both minerals. For molybdenite, the recovery decreases along with the increase of the temperature. It is noteworthy that the recovery, in comparison to other condition (collectorless or PBX), still remains 13.01 % even at thermal treatment temperature of 400 °C. It indicates that the thermally treated molybdenite at the temperature of below 400 °C can also be partially absorbed with kerosene. Moreover, the recovery decreased to 2.59 % at the thermal treatment temperature of 450 °C。From the above results, it exhibits the excellent depress effect on molybdenite, which is better than the reported depressant. As reported by the previous reports, the recovery of molybdenite is at least reaches 5% when using humic as depressant [15]. When using lignosulphonate as depressant, the recovery of molybdenite reaches 15 % [20]. While, when using thermal pretreatment method, it is only 2.59 %. Overall, the single minerals flotation results show that the significant difference between the floatability of talc and molybdenite after thermal treatment. Thus, it implies that the possibly of flotation separation of molybdenite and talc can be achieved after thermal treatment and the optimum thermal pretreatment temperature should be equal or greater than 400 °C.
Fig. 3. FTIR spectra of molybdenite thermally treated at different temperatures: (a) untreated; (b) 200 °C; (c) 300 °C; (d) 400 °C.
Fig. 4. FTIR spectra of Talc before and after thermal treatment at 400 °C.
decreases in the flotation recovery of molybdenite along with the increase of thermal treatment temperature can be observed. When the thermal treatment temperature reaches or exceeds 400 °C, the recovery of molybdenite is only about 2.39 %. Clearly, the excellent natural floatability of molybdenite vanishes after being treated at the temperature above 400 °C. It is known that the inherently hydrophobic surfaces of molybdenite are derived from its non-polar face arranged with weak unsaturated SeS bonds [13,14]. Thus, this flotation result can be explained as that the non-polar face is gradually destroyed as the increase of temperature in the thermal treatment process [14]. In comparison, for talc, the flotation recovery is barely changed and maintained at around 90 % even the thermal treatment temperature reaches 450 °C, indicating that the thermal treatment process has little
3.2. Micro-flotation of artificially mixed minerals According to the findings on the single minerals, micro-flotation tests on artificially mixed minerals were carried out on molybdenite and talc mixed at same-size ratio to verify the effect of thermal treatment method. Mixed minerals used in each mixed flotation test were prepared by homogeneous mixing 1 g talc minerals and 1 g molybdenite minerals. In thermal treatment process, the mixed minerals were treated as a mixture. In the tests, kerosene (40 mg/L) and MIBC (40 mg/ 4
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Fig. 5. The High-resolution XPS spectra of the molybdenite thermally treated at different temperatures: (a) Mo 3d; (b) S 2p; (c) O1 s.
L) were used as collector and frother, respectively, and the flotation results are shown in Table 1. It can be seen in the Table 1 that, for the untreated mixed ores, about 95 % of molybdenite and talc is enriched in the concentrates, indicating selective separation of the two minerals cannot be achieved under the condition. On contrast, for the mixed ore thermally treated at 400 °C (without addition of kerosene), 88.64 % of molybdenite is enriched in the tails with a Mo grade of 50.98 %. For the mixed ore thermally treated at 450 °C (with addition of kerosene), molybdenite is even better enriched in the tails with a Mo grade of 53.70 % and recovery of 89.36 %. Moreover, it noteworthy that recovery of thermally treated molybdenite in mixed mineral tests (around 10 %) were higher than that in single mineral test (less than 3%). This might be attributed to the entrainment effect in mixed ore flotation and interactions between talc and talc and molybdenite in pulp. All in all, it implies the mixed molybdenite and talc can be effectively separated after thermal treatment. In comparison conventional method, the application of thermal treatment method avoids using of macromolecular
organic depressant, which can greatly reduce chemical oxygen demand (COD) in wastewater. Besides, additional flotation tests were performed to evaluate the effect of thermal treatment method on separation of molybdenite and talc in bulk concentrates. The bulk concentrate was derived from the above concentrate of artificially mixed minerals floatation test (without thermal treatment). The concentrate was thermally heated at 450 °C in the air atmosphere. The result is present in Table 2. As seen in Table 2, the molybdenite is well enriched in the tailing with a Mo recovery of 88.94 % and a Mo grade of 53.98 %. Clearly, the molybdenite and talc in the bulk concentrate can be effectively separated after thermal treatment. This can be attribute to that the collector and frother absorbed on the surface of molybdenite were removed in the thermal treatment process. Because the boiling point of the flotation reagent applied in molybdenite beneficiation, e.g. MIBC (132 °C), PBX (168 °C) and Kerosene (150 °C–310 °C), is all far below than 450 °C.
5
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Fig. 6. The High-resolution XPS spectra of the talc before and after thermally treated at 400 °C: (a) Mg 1 s; (b) Si 2p; (c) O1 s.
3.3. FTIR analysis
3.4. XPS analysis
FTIR spectra of molybdenite thermally treated at different temperatures are shown in Fig. 3. The bands around 3437 cm−1 and 1631 cm−1 of all samples can be attributed to the stretching vibrations and bending vibrations of hydroxy from lattice water absorbed on the surface of molybdenite [34]. The bands at 1103 cm−1 is correspond to the asymmetric S]O stretching of the sulfate species [34]. Moreover, the FTIR spectra of molybdenite barely change when the thermal treatment temperature less than 300 °C. In comparison, for the molybdenite treated under 400 °C, new bond peaks at 995 cm−1, 824 cm−1, 549 cm−1 appear on the spectrum, which can be assigned to the terminal oxygen symmetry stretching mode (νs) of Mo]O, the bridge oxygen asymmetry of Mo-O-Mo (νas) and symmetry stretching modes (νs) of Mo-O-Mo, respectively [35–38]. Clearly, this indicates that the surface of molybdenite is dramatically oxidized when thermal treatment temperature reaches 400 °C and amount of MoO3 species are formed under the condition. In addition, the peaks at 590 cm−1 and 468 cm−1 are assigned to Mo-S vibration [34]. The two peaks of molybdenite thermally treated at 400 °C were greatly changed, confirming the dramatical oxidation of molybdenite’s surface. Fig. 4 displays the FTIR spectra of talc thermally treated under different temperatures. For the raw talc, the peak at 3681 cm−1 is correspond to the stretching vibration of hydroxyl group [30]. The peak at 452 cm−1 and 1012 cm−1 are related to the vibrations of Si-O bond [30]. The peak at 671 cm−1 is on account of the stretching vibration of Mg-O [30]. Obviously, these peaks of talc before and after thermal treatment (at 400 °C) are unchanged. This should be that the talc is oxidized ore with a stable surface property, which would not be affected in the current thermal treatment process.
To further investigate the mechanism of thermal treatment process, XPS analysis was employed to detect variation of the surface chemical states of the talc and molybdenite. The High-resolution XPS spectra of the molybdenite thermally treated at different temperatures are presented in Fig. 5. Fig. 5a presents the high-resolution spectra of Mo 3d. For the raw molybdenite, the spectra show Mo 3d5/2 and Mo 3d3/2 peaks centered at binding energy of 228.5 eV and 231.7 eV, respectively, which are the expected values of the tetravalent molybdenum species (Mo4+) [27,28]. The peak centered at binding energy of 228.5 eV is S 2 s in MoS2 [28,39]. For the thermally treated molybdenite (as marked in the Fig. 5a), the Mo 3d5/2, Mo 3d3/2, S 2 s peaks are shifted to relatively higher binding energy after thermal treatment. Possibly, this implies the combination of oxygen and Mo in the thermal treatment is attributed to the higher electronegativity of oxygen in comparison to that of sulfur. Moreover, the intensity of Mo3d5/2 peaks centered at around 235 eV is increased as thermal treatment temperature goes up, indicating the gradual formation of molybdenum trioxide (MoO3) [39,40]. Besides, this MoO3 peaks of the molybdenite treated at 400 °C is notably higher than that of the other samples, which gives a good indication for the dramatical oxidation reaction taken place on the surface of MoS2 at this temperature [40]. In the same way, XPS analysis were also conducted on talc before and after thermal treatment at the temperature of 400 °C and the results are presented in Fig. 6. The Fig. 6a–c illustrate the high-resolution spectra of Mg 1 s, Si 2p and O1 s, respectively. Clearly, these spectra of the talc before and after thermally treated at 400 °C change barely. This confirms that the thermal treatment process has little effect on the 6
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surface of talc. Combining the FTIR and XPS analysis results, in summary, it is indicated that molybdenite’s surface is partially oxidized in the thermal treatment process and the oxidation product is the MoO3. The oxidation degree of molybdenite’s surface increases along with the increase of thermal treatment temperature. Notably, the oxidation degree increases by leaps when the thermal treatment temperature reaches 400 °C. Moreover, conspicuous reduction of sulfur content on molybdenite’s surface was taken place at the thermal treatment temperature. Thus, overall, the surface property of molybdenite changes significantly after treated at 400 °C. The mass-formed MoO3 content on the surface is hydrophilic and do not interact with collector, which should be the reason for the poor floatability of thermally treated molybdenite. While, in comparison, the talc’s surface changes barely during the thermal treatment and maintains the excellent floatability as same as the untreated talc.
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[28] G.P.W. Suyantaraa, T. Hirajimaa, H. Mikia, K. Sasakia, A. Yamaneb, E. Takidab, S. Kuroiwab, Y. Imaizumib, Selective flotation of chalcopyrite and molybdenite using H2O2 oxidation method with the addition of ferrous sulfate, Miner. Eng. 122 (2018) 312–326. [29] G.P.W. Suyantara, T. Hirajima, H. Mikia, K. Sasaki, M. Yamane, E. Takida, S. Kuroiwa, Y. Imaizumi, Effect of Fenton-like oxidation reagent on hydrophobicity and floatability of chalcopyrite and molybdenite, Colloids Surf. A 554 (2018) 34–48. [30] H. Yia, Y. Zhao, Y. Liu, W. Wang, S. Song, C. Liu, H. Li, W. Zhan, X. Liu, A novel method for surface wettability modification of talc through thermal treatment, Appl. Clay Sci. 176 (2019) 21–28. [31] Mahmoud M. Ahmed, Galal A. Ibrahim, Mohamed M.A. Hassan, Improvement of Egyptian talc quality for industrial uses by flotation process and leaching, Int. J. Miner. Process. 83 (2007) 132–145. [32] A. Ozkan, V. Dudnik, K. Esmeli, Hydrophobic flocculation of talc with kerosene and effects of anionic surfactants, Particul. Sci. Technol. 34 (2016) 235–240. [33] Z. Wei, Y. Li, Anisotropy of molybdenite surface and its effects on flotation mechanism, Conserv. Util. Miner. Resour. 3 (2018) 32–36. [34] J. Zhao, Z. Zhang, S. Yang, H. Zheng, Y. Li, Facile synthesis of MoS2 nanosheetsilver nanoparticles composite for surface enhanced Raman scattering and
4. Conclusions This research presents the effect of thermal pretreatment on the flotation behavior of molybdenite and talc with excellent natural floatability. The floatability of molybdenite was dramatically decreased after thermal treatment. In the single mineral flotation process, the recovery of molybdenite was less than 3% after thermally pretreated under 400 °C. While, on contrast, the floatability of talc changed barely after thermal treatment. As a result, satisfying flotation separation effects of molybdenite and talc in artificially mixed ores or in the bulk concentrates were obtained by application of thermal pretreatment at 400 °C. The results of FTIR and XPS analysis on molybdenite before and after thermal treatment illustrated that the surface of molybdenite was dramatically oxidized at 400 °C. The formation of MoO3 and reduction of sulfur content on the molybdenite’s surface should be the reason for vanishing floatability of molybdenite after thermal treatment. While, for talc, its surface changed barely in the thermal treatment process and thus maintained excellent floatability. In comparison to application of depressant, the application of thermal treatment method avoids using of organic depressant, possess better separation effect. Moreover, the thermal treatment method can be even used to separate molybdenite and talc in bulk concentrate. CRediT authorship contribution statement Xuekun Tang: Conceptualization, Formal analysis, Resources, Writing - review & editing, Visualization, Supervision. Yanfei Chen: Investigation, Data curation, Validation, Writing - original draft. Kun Liu: Funding acquisition, Project administration, Supervision, Methodology, Writing - review & editing. Qian Peng: Investigation, Data curation. Guangsheng Zeng: Resources, Data curation. Minlin Ao: Investigation, Formal analysis. Zishun Li: Investigation. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgement This work was financially supported by the National Natural Science Foundation of China (No.51774330). References [1] M.P. Schwarz, P.T.L. Koh, D.I. Verrelli, Y. Feng, Sequential multi-scale modelling of mineral processing operations, with application to flotation cells, Miner. Eng. 90 (2016) 2–16.
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[38] Tzu Hsuan Chiang, Hung Che Yeh, A novel synthesis of α-MoO3 nanobelts and the characterization, J. Alloys Compd. 585 (2014) 535–541. [39] M. Farahat, A.M. Elmahdy, T. Hirajima, Influence of microwave radiation on the magnetic properties of molybdenite and arsenopyrite, Powder Technol. 315 (2017) 276–281 585 (2014) 535–541. [40] F. Jia, C. Liu, B. Yang, S. Song, Microscale control of edge defect and oxidation on molybdenum disulfide through thermal treatment in air and nitrogen atmospheres, Appl. Surf. Sci. 462 (2018) 471–479.
electrochemical activity, J. Alloys Compd. 559 (2013) 87–91. [35] Q. Xia, H. Zhao, Z. Du, Z. Zeng, C. Gao, Z. Zhang, X. Du, A. Kulkad, K. Swierczek, Facile synthesis of MoO3/carbon nanobelts as high-performance anode material for lithium ion batteries, Electrochim. Acta 180 (2015) 947–956. [36] Ch.V.S. Reddy, E.H. Walker Jr, C. Wen, S. Mho, Hydrothermal synthesis of MoO3 nanobelts utilizing poly(ethylene glycol), J. Power Sources 183 (2008) 330–333. [37] Q. Xia, H. Zhao, Z. Du, J. Wang, T. Zhang, J. Wang, P. Lv, Synthesis and electrochemical properties of MoO3/C composite as anode material for lithium-ion batteries, J. Power Sources 226 (2013) 107–111.
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Colloids and Surfaces A journal homepage: www.elsevier.com/locate/colsurfa
Reverse flotation separation of talc from molybdenite without addition of depressant: Effect of surface oxidation by thermal pre-treatment
T
Xuekun Tanga,b,1, Yanfei Chena,1, Kun Liua,b,*, Qian Penga,b, Guangsheng Zenga, Minlin Aoa,b, Zishun Lia,b a b
School of Minerals Processing and Bioengineering, Central South University, Changsha, 410083, China Hunan Key Laboratory of Mineral Materials and Application, Central South University, Changsha, 410083, China
G R A P H I C A L A B S T R A C T
A R T I C LE I N FO
A B S T R A C T
Keywords: Molybdenite Talc Thermal treatment Surface oxidation Flotation separation
The excellent inherent floatability of talc and molybdenite makes them very difficult to be separated in the flotation process. To conquer the problem, for the first time, an attempt was made to separate molybdenite and talc by calcining the ores under the air condition before flotation separation. Micro-flotation test results showed that the natural floatability of molybdenite vanished after thermal pretreatment at above 400 °C. In contrast, for that of talc, it barely changes. A satisfying flotation separation effect of molybdenite and talc in either mixed minerals or molybdenite-talc bulk concentrate was achieved through the thermal pretreatment method. The results of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis indicated that the surface of molybdenite underwent dramatical oxidation after thermal treatment at 400 °C. The formation of MoO3 and reduction in sulfur content on the surface of molybdenite were proposed to result in the poor floatability of molybdenite after thermal treatment.
1. Introduction Froth flotation, a physico-chemical separation method by utilization of difference surface hydrophilic/hydrophobic properties between
different minerals, is one of the most widely used industrial processes for beneficiation of valuable minerals from ore deposits [1–3]. Especially for the sulfide minerals, most of them were separated from unwanted gangue minerals through the flotation [4,5]. Talc, a kind of
⁎
Corresponding author at: School of Minerals Processing and Bioengineering, Central South University, Changsha, 410083, China. E-mail address: [email protected] (K. Liu). 1 These authors contributed equally to this work. https://doi.org/10.1016/j.colsurfa.2020.124671 Received 19 November 2019; Received in revised form 21 February 2020; Accepted 4 March 2020 Available online 05 March 2020 0927-7757/ © 2020 Elsevier B.V. All rights reserved.
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Fig. 1. The XRD patterns of the as-prepared mineral samples: (a) Molybdenite sample; (b) Talc sample.
Cu(OH)2 and FeOOH, are coated on the surface of the chalcopyrite to make it difficult to be floated anymore [27–29]. On the contrary, the surface of molybdenite is slightly changed and remains good floatability under the same oxidation condition [27–29]. Based on this principle, molybdenite can be separated from chalcopyrite by utilization of the surface oxidation method. Talc is an oxide mineral, whose surface is bound to be much more stable for oxidation than that of molybdenite [30]. Thus, it would stand a good chance of realizing the separation of molybdenite and talc through the surface oxidation. However, the molybdenite has a relatively stable surface property in comparison to other sulfide minerals, as a result none of the above methods by using oxidant agents can effectively realize the surface oxidation of molybdenite [26,28]. Hence, in this research, we attempt to realize selective oxidation of molybdenite through a facile thermal pretreatment method for the first time. Micro-flotation tests were carried out to evaluate the effect of thermal pretreatment method on flotation separation of molybdenite and talc. Moreover, surface characterizations on talc and molybdenite were conducted to understand the mechanism of thermal pretreatment method.
magnesium-rich phyllosilicate mineral with theoretical chemical formula of Mg3Si4O10(OH)2, is a common unwanted gangue mineral encountered in sulphide ores around the world [6–8]. However, the surface of the grinded talc powder is mainly composed of basal plane (approximately 90 % of total surface), which is non-polar and hydrophobic [7,8]. Therefore, unlike the other silicate gangue (e.g. quartz, mica, chlorite, garnet) with hydrophilic surface, the talc has excellent natural floatability [7,9]. Molybdenite (MoS2) is the most essential commercial source for molybdenum (Mo) extraction in industry [10,11]. Similar to talc, molybdenite has a laminar crystalline structure and is also naturally hydrophobic with excellent floatability due to its non-polar face composed of weak unsaturated SeS bonds [12–14]. Thus, in the flotation process, talc is fairly easy to be brought into the molybdenite concentrates due to their similar floatability [15,16]. The existence of talc in molybdenite inevitably brings unfavorable consequences such as lowering the purity of concentrates, increasing smelting costs in metallurgy process [17]. It is therefore of significant importance to separate talc and molybdenite in flotation process. In sulfide ore flotation process, depressants, such as carboxymethyl cellulose [6,7] and polysaccharide reagents (e.g. chitosan [18] and Locust bean gum [19]), are used to depress talc in the flotation process. However, imperfect effects are obtained when these depressants used in molybdenite-talc separation due to the similar depression effect on molybdenite. To overcome the defect, reverse flotation process by selective depression of molybdenite has been also researched in laboratory to realize the separation of talc and molybdenite. Kelebek et al. [20] has found that the sodium lignosulphonate can selectively depress molybdenite. Dextrin [21,22], humic acid [15] and carboxymethylcellulose polymers [23] have been also researched as depressant in reverse flotation separation of molybdenite and talc with addition of frother only. However, in industry, the molybdenite is commonly required to be preferentially recovered since most molybdenite sources are presented as low-grade ores at present [24,25]. The molybdenite in the concentrate absorbed with collector (kerosene or collectors for sulfide minerals), which is very difficult to be separated from talc by application of depressant in the further re-flotation process. Thus, in industry, high dosage of these macromolecular organic depressants is required to obtain a satisfactory beneficiation effect, which would greatly increase chemical oxygen demand (COD) in wastewater. In addition to using depressant, surface oxidation is an alternative to depress the sulfide minerals [12,26–29]. Typically, the selective oxidation pretreatment on chalcopyrite has been achieved by application of various approaches, including ozone oxidation [26], H2O2 oxidation [26], plasma pretreatment [27] and Fenton-like oxidation [28,29]. After oxidation pretreatment, hydrophilic metallic oxide, such as CuO,
2. Experimental 2.1. Ore samples The molybdenite and talc mineral samples were obtained from luanchuan, Henan province, china and Longsheng, Guangxi Province, china, respectively. The two mineral samples were hand-picked, crushed to −1 mm and then ground into powders by a mechanical powder machine. For molybdenite sample, the particles with size of -74 μm + 38 μm were collected by vibrating screen for flotation tests. While, for talc sample, particle sized of −74 μm was collected for flotation tests. X-ray diffraction spectra shown Fig. 1 points out the asprepared minerals are of high purity. Moreover, according to chemical analysis, the molybdenite sample has a Mo grade of 55.99 % and S grade of 34.93 %. The talc sample has a MgO grade of 31.31 % and SiO2 grade of 65.03 %. These results further confirming that the as-prepared ore samples are high purity. 2.2. Thermal pretreatment procedure Laboratory-scaled thermal pretreatment on the ore samples was conducted in a tube furnace. Typically, 3 g of the ore sample was heated under pre-determined temperature in air atmosphere by the tube furnace. The residence time for each sample in tube furnace was 30 min. After naturally cooling to room temperature, the treated samples were immediately applied for flotation tests. 2
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Table 1 Results of flotation separation of molybdenite and talc artificially mixed minerals. Conditions of flotation
Products
Yield (W/ %)
Mo grade (%)
Mo recovery (%)
Without Thermal pretreatment; Kerosene: 40 mg/L MIBC: 40 mg/L Thermally treated at 400 °C; MIBC: 40 mg/L
Concentrate
94.33
30.11
96.09
Tailing Feed Concentrate
5.67 100.00 48.61
20.40 29.56 6.91
3.91 100.00 11.36
Tailing Feed Concentrate
51.39 100.00 50.81
50.98 29.56 6.19
88.64 100.00 10.64
Tailing Feed
49.19 100.00
53.70 29.56
89.36 100.00
Thermally treated at 450 °C; Kerosene: 40 mg/L MIBC: 40 mg/L
purity) were applied as collector. Ultrapure water produced by reverse osmosis was used in all the experiments. In each test, 35 mL water and 2 g of the as-prepared ore samples were successively added in the cell (maximum volume: 40 mL) under agitation to form a uniform ore pulp. 0.1 mol/L sodium hydroxide (NaOH) solution or 0.1 mol/L dilute hydrochloric (HCl) acid solution was added to adjust pH value of the pulp to 6. After agitation for 5 min, designed amount of collector was added in the pulp. After 3 min of conditioning, certain amount of frother was added in the cell followed by 1 min of conditioning. The floated froth product in the cell was manually collected for 3 min. For single minerals flotation, the recovery was calculated according to the weight distributions between the froth products and un-floated tailings. For that of mixed mineral, it can be calculated according to the molybdenum grade of concentrates and feeds. 2.4. Analysis method X-ray photoelectron spectroscopy (XPS) measurements were performed on an ultrahigh vacuum electron spectrometer (K-Alpha 1063, Thermo Fisher, UK). Fourier transform infrared spectroscopy (FTIR) spectra were recorded on an infrared spectrometer (UV-2350, Shimadzu, Japan) from 4000 cm−1 to 400 cm−1 by potassium bromide (KBr) diffuse reflection method. 3. Results and discussion 3.1. Micro-flotation of single mineral Micro-flotation tests of single mineral were carried to evaluate the effect of thermal pretreatment on the flotation behavior of talc and molybdenite. In industry, kerosene and xanthate are usually employed as the collector for molybdenite, and kerosene is commonly used as collector for talc [31,32]. Thus, in this research, PBX (Dosage: 200 mg/ L) and kerosene (Dosage: 100 mg/L) were applied as the collector in flotation separation process of molybdenite and talc. MIBC (Dosage: 100 mg/L) was used as the frother in these tests. The flotation results are presented in Fig. 2. Fig. 2a shows flotation behavior of the talc and molybdenite under different thermal treatment temperature without collector (MIBC dosage: 40 mg/L). As shown in the figure, the flotation recoveries of untreated talc and molybdenite reach 83.43 % and 90.12 %, respectively, confirming excellent inherent floatability of the two minerals. This also indicates that the two untreated minerals can hardly be separated without application of depressant because both minerals are enriched in concentrates [19]. For molybdenite, the recovery is slightly changed when the thermal treatment temperature is below 200 °C. While, when the thermal treatment temperature is above 200 °C, dramatical
Fig. 2. Flotation of single talc and molybdenite as a function of thermal pretreatment temperature with different collectors: (a) Collectorless; (b) PBX; (c) Kerosene.
2.3. Micro-flotation tests All micro-flotation tests were performed on a mechanical agitation flotation machine (Type: XFG). Commercially obtained Methyl Isobutyl Carbinol (MIBC, 99 % purity) was applied as frother in all flotation tests. Kerosene (98 % purity) and Potassium Butyl Xanthate (PBX, 98 % 3
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Table 2 Results of flotation separation of molybdenite-talc bulk concentrate thermally treated under 450 °C. Conditions of flotation
Products
Yield (W/%)
Mo grade (%)
Mo recovery (%)
Thermally treated at 450 °C; Kerosene: 40 mg/L MIBC: 40 mg/L
Concentrate Tailing Feed
50.39 49.61 100.00
6.61 53.98 30.11
11.06 88.94 100.00
influence on the floatability of talc. Fig. 2b shows flotation behavior of the talc and molybdenite under different thermal treatment temperature by using PBX as collector (PBX dosage: 1 × 10−4 mol/L; MIBC dosage: 40 mg/L). It illustrates that the recovery of raw molybdenite reaches 96.03 % with the assistance of PBX. The recovery slowly decreases with the increase of thermal treatment temperature and sharply decreases when the thermal treatment temperature is above 300 °C. Moreover, it is noticeable that the recovery of molybdenite is 89.50 % when the thermal treatment temperature reaches 300 °C. While, for the collectorless condition (as presented in Fig. 2a), it is only 52.11 %. It is known that the xanthate collector can be adsorbed on the polar edge arranged with Mo-S through chemical adsorption [13,33]. This possibly implies that the polar edge of molybdenite is well maintained after thermal treatment under 300 °C. When the thermal treatment temperature reaches 400 °C, the recovery of molybdenite is only 2.62 % and remains constant as the increase of temperature. This implies that the polar edge of molybdenite is destructed under the temperature of 400 °C, which makes it impossible to absorb PBX. In comparison, for talc, the recovery maintains about 90 % as variation of the thermal pretreatment temperature, which is basically the same to that of the collectorless condition. Besides, this indicates the PBX has little collecting capacity on talc. Fig. 2c shows flotation behavior of the talc and molybdenite under different thermal treatment temperature by using kerosene as collector (kerosene dosage: 40 mg/L; MIBC dosage: 40 mg/L). As presented in the figure, the recoveries of raw molybdenite and talc are 96.56 % and 95.62 %, respectively, indicating the excellent collecting capacity of kerosene on the both minerals. For molybdenite, the recovery decreases along with the increase of the temperature. It is noteworthy that the recovery, in comparison to other condition (collectorless or PBX), still remains 13.01 % even at thermal treatment temperature of 400 °C. It indicates that the thermally treated molybdenite at the temperature of below 400 °C can also be partially absorbed with kerosene. Moreover, the recovery decreased to 2.59 % at the thermal treatment temperature of 450 °C。From the above results, it exhibits the excellent depress effect on molybdenite, which is better than the reported depressant. As reported by the previous reports, the recovery of molybdenite is at least reaches 5% when using humic as depressant [15]. When using lignosulphonate as depressant, the recovery of molybdenite reaches 15 % [20]. While, when using thermal pretreatment method, it is only 2.59 %. Overall, the single minerals flotation results show that the significant difference between the floatability of talc and molybdenite after thermal treatment. Thus, it implies that the possibly of flotation separation of molybdenite and talc can be achieved after thermal treatment and the optimum thermal pretreatment temperature should be equal or greater than 400 °C.
Fig. 3. FTIR spectra of molybdenite thermally treated at different temperatures: (a) untreated; (b) 200 °C; (c) 300 °C; (d) 400 °C.
Fig. 4. FTIR spectra of Talc before and after thermal treatment at 400 °C.
decreases in the flotation recovery of molybdenite along with the increase of thermal treatment temperature can be observed. When the thermal treatment temperature reaches or exceeds 400 °C, the recovery of molybdenite is only about 2.39 %. Clearly, the excellent natural floatability of molybdenite vanishes after being treated at the temperature above 400 °C. It is known that the inherently hydrophobic surfaces of molybdenite are derived from its non-polar face arranged with weak unsaturated SeS bonds [13,14]. Thus, this flotation result can be explained as that the non-polar face is gradually destroyed as the increase of temperature in the thermal treatment process [14]. In comparison, for talc, the flotation recovery is barely changed and maintained at around 90 % even the thermal treatment temperature reaches 450 °C, indicating that the thermal treatment process has little
3.2. Micro-flotation of artificially mixed minerals According to the findings on the single minerals, micro-flotation tests on artificially mixed minerals were carried out on molybdenite and talc mixed at same-size ratio to verify the effect of thermal treatment method. Mixed minerals used in each mixed flotation test were prepared by homogeneous mixing 1 g talc minerals and 1 g molybdenite minerals. In thermal treatment process, the mixed minerals were treated as a mixture. In the tests, kerosene (40 mg/L) and MIBC (40 mg/ 4
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Fig. 5. The High-resolution XPS spectra of the molybdenite thermally treated at different temperatures: (a) Mo 3d; (b) S 2p; (c) O1 s.
L) were used as collector and frother, respectively, and the flotation results are shown in Table 1. It can be seen in the Table 1 that, for the untreated mixed ores, about 95 % of molybdenite and talc is enriched in the concentrates, indicating selective separation of the two minerals cannot be achieved under the condition. On contrast, for the mixed ore thermally treated at 400 °C (without addition of kerosene), 88.64 % of molybdenite is enriched in the tails with a Mo grade of 50.98 %. For the mixed ore thermally treated at 450 °C (with addition of kerosene), molybdenite is even better enriched in the tails with a Mo grade of 53.70 % and recovery of 89.36 %. Moreover, it noteworthy that recovery of thermally treated molybdenite in mixed mineral tests (around 10 %) were higher than that in single mineral test (less than 3%). This might be attributed to the entrainment effect in mixed ore flotation and interactions between talc and talc and molybdenite in pulp. All in all, it implies the mixed molybdenite and talc can be effectively separated after thermal treatment. In comparison conventional method, the application of thermal treatment method avoids using of macromolecular
organic depressant, which can greatly reduce chemical oxygen demand (COD) in wastewater. Besides, additional flotation tests were performed to evaluate the effect of thermal treatment method on separation of molybdenite and talc in bulk concentrates. The bulk concentrate was derived from the above concentrate of artificially mixed minerals floatation test (without thermal treatment). The concentrate was thermally heated at 450 °C in the air atmosphere. The result is present in Table 2. As seen in Table 2, the molybdenite is well enriched in the tailing with a Mo recovery of 88.94 % and a Mo grade of 53.98 %. Clearly, the molybdenite and talc in the bulk concentrate can be effectively separated after thermal treatment. This can be attribute to that the collector and frother absorbed on the surface of molybdenite were removed in the thermal treatment process. Because the boiling point of the flotation reagent applied in molybdenite beneficiation, e.g. MIBC (132 °C), PBX (168 °C) and Kerosene (150 °C–310 °C), is all far below than 450 °C.
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Fig. 6. The High-resolution XPS spectra of the talc before and after thermally treated at 400 °C: (a) Mg 1 s; (b) Si 2p; (c) O1 s.
3.3. FTIR analysis
3.4. XPS analysis
FTIR spectra of molybdenite thermally treated at different temperatures are shown in Fig. 3. The bands around 3437 cm−1 and 1631 cm−1 of all samples can be attributed to the stretching vibrations and bending vibrations of hydroxy from lattice water absorbed on the surface of molybdenite [34]. The bands at 1103 cm−1 is correspond to the asymmetric S]O stretching of the sulfate species [34]. Moreover, the FTIR spectra of molybdenite barely change when the thermal treatment temperature less than 300 °C. In comparison, for the molybdenite treated under 400 °C, new bond peaks at 995 cm−1, 824 cm−1, 549 cm−1 appear on the spectrum, which can be assigned to the terminal oxygen symmetry stretching mode (νs) of Mo]O, the bridge oxygen asymmetry of Mo-O-Mo (νas) and symmetry stretching modes (νs) of Mo-O-Mo, respectively [35–38]. Clearly, this indicates that the surface of molybdenite is dramatically oxidized when thermal treatment temperature reaches 400 °C and amount of MoO3 species are formed under the condition. In addition, the peaks at 590 cm−1 and 468 cm−1 are assigned to Mo-S vibration [34]. The two peaks of molybdenite thermally treated at 400 °C were greatly changed, confirming the dramatical oxidation of molybdenite’s surface. Fig. 4 displays the FTIR spectra of talc thermally treated under different temperatures. For the raw talc, the peak at 3681 cm−1 is correspond to the stretching vibration of hydroxyl group [30]. The peak at 452 cm−1 and 1012 cm−1 are related to the vibrations of Si-O bond [30]. The peak at 671 cm−1 is on account of the stretching vibration of Mg-O [30]. Obviously, these peaks of talc before and after thermal treatment (at 400 °C) are unchanged. This should be that the talc is oxidized ore with a stable surface property, which would not be affected in the current thermal treatment process.
To further investigate the mechanism of thermal treatment process, XPS analysis was employed to detect variation of the surface chemical states of the talc and molybdenite. The High-resolution XPS spectra of the molybdenite thermally treated at different temperatures are presented in Fig. 5. Fig. 5a presents the high-resolution spectra of Mo 3d. For the raw molybdenite, the spectra show Mo 3d5/2 and Mo 3d3/2 peaks centered at binding energy of 228.5 eV and 231.7 eV, respectively, which are the expected values of the tetravalent molybdenum species (Mo4+) [27,28]. The peak centered at binding energy of 228.5 eV is S 2 s in MoS2 [28,39]. For the thermally treated molybdenite (as marked in the Fig. 5a), the Mo 3d5/2, Mo 3d3/2, S 2 s peaks are shifted to relatively higher binding energy after thermal treatment. Possibly, this implies the combination of oxygen and Mo in the thermal treatment is attributed to the higher electronegativity of oxygen in comparison to that of sulfur. Moreover, the intensity of Mo3d5/2 peaks centered at around 235 eV is increased as thermal treatment temperature goes up, indicating the gradual formation of molybdenum trioxide (MoO3) [39,40]. Besides, this MoO3 peaks of the molybdenite treated at 400 °C is notably higher than that of the other samples, which gives a good indication for the dramatical oxidation reaction taken place on the surface of MoS2 at this temperature [40]. In the same way, XPS analysis were also conducted on talc before and after thermal treatment at the temperature of 400 °C and the results are presented in Fig. 6. The Fig. 6a–c illustrate the high-resolution spectra of Mg 1 s, Si 2p and O1 s, respectively. Clearly, these spectra of the talc before and after thermally treated at 400 °C change barely. This confirms that the thermal treatment process has little effect on the 6
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surface of talc. Combining the FTIR and XPS analysis results, in summary, it is indicated that molybdenite’s surface is partially oxidized in the thermal treatment process and the oxidation product is the MoO3. The oxidation degree of molybdenite’s surface increases along with the increase of thermal treatment temperature. Notably, the oxidation degree increases by leaps when the thermal treatment temperature reaches 400 °C. Moreover, conspicuous reduction of sulfur content on molybdenite’s surface was taken place at the thermal treatment temperature. Thus, overall, the surface property of molybdenite changes significantly after treated at 400 °C. The mass-formed MoO3 content on the surface is hydrophilic and do not interact with collector, which should be the reason for the poor floatability of thermally treated molybdenite. While, in comparison, the talc’s surface changes barely during the thermal treatment and maintains the excellent floatability as same as the untreated talc.
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4. Conclusions This research presents the effect of thermal pretreatment on the flotation behavior of molybdenite and talc with excellent natural floatability. The floatability of molybdenite was dramatically decreased after thermal treatment. In the single mineral flotation process, the recovery of molybdenite was less than 3% after thermally pretreated under 400 °C. While, on contrast, the floatability of talc changed barely after thermal treatment. As a result, satisfying flotation separation effects of molybdenite and talc in artificially mixed ores or in the bulk concentrates were obtained by application of thermal pretreatment at 400 °C. The results of FTIR and XPS analysis on molybdenite before and after thermal treatment illustrated that the surface of molybdenite was dramatically oxidized at 400 °C. The formation of MoO3 and reduction of sulfur content on the molybdenite’s surface should be the reason for vanishing floatability of molybdenite after thermal treatment. While, for talc, its surface changed barely in the thermal treatment process and thus maintained excellent floatability. In comparison to application of depressant, the application of thermal treatment method avoids using of organic depressant, possess better separation effect. Moreover, the thermal treatment method can be even used to separate molybdenite and talc in bulk concentrate. CRediT authorship contribution statement Xuekun Tang: Conceptualization, Formal analysis, Resources, Writing - review & editing, Visualization, Supervision. Yanfei Chen: Investigation, Data curation, Validation, Writing - original draft. Kun Liu: Funding acquisition, Project administration, Supervision, Methodology, Writing - review & editing. Qian Peng: Investigation, Data curation. Guangsheng Zeng: Resources, Data curation. Minlin Ao: Investigation, Formal analysis. Zishun Li: Investigation. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgement This work was financially supported by the National Natural Science Foundation of China (No.51774330). References [1] M.P. Schwarz, P.T.L. Koh, D.I. Verrelli, Y. Feng, Sequential multi-scale modelling of mineral processing operations, with application to flotation cells, Miner. Eng. 90 (2016) 2–16.
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