- Email: [email protected]
Effect of diesel on the froth stability and its antifoam mechanism in fine coal flotation used MIBC as the frother
Journal Pre-proof Effect of diesel on the froth stability and its antifoam mechanism in fine coal flotation used MIBC as the frother
Mengdi Xu, Yaowen Xing, Wei Jin, Ming Li, Yijun Cao, Xiahui Gui PII:
S0032-5910(19)31163-5
DOI:
https://doi.org/10.1016/j.powtec.2019.12.058
Reference:
PTEC 15066
To appear in:
Powder Technology
Received date:
9 April 2019
Revised date:
11 December 2019
Accepted date:
27 December 2019
Please cite this article as: M. Xu, Y. Xing, W. Jin, et al., Effect of diesel on the froth stability and its antifoam mechanism in fine coal flotation used MIBC as the frother, Powder Technology(2019), https://doi.org/10.1016/j.powtec.2019.12.058
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier.
Journal Pre-proof
Effect of diesel on the froth stability and its antifoam mechanism in fine coal flotation used MIBC as the frother Mengdi Xu1, 2,a, Yaowen Xing1,a, Wei Jin1, 2, Ming Li1, 2, Yijun Cao1, 3*, Xiahui Gui1, 3*
ro
of
1 Chinese National Engineering Research Center of Coal Preparation and Purification, China University of Mining and Technology, Xuzhou 221116, Jiangsu, China 2 School of Chemical Engineering and Technology, China University of Mining and Technology, Xuzhou 221116, Jiangsu, China 3 Henan Province Industrial Technology Research Institute of Resources and Materials, Zhengzhou University, Zhengzhou 450001, China a Co-first authors: These authors contributed equally to this work. * Address correspondence to: Xiahui Gui ([email protected]); Yijun Cao ([email protected])
-p
Abstract
re
Froth stability is one of the most important factors in fine coal flotation as it significantly affects the separation efficiency. Diesel is always used as the flotation collector while the effect of diesel on the
lP
froth stability is less investigated. In this study, effect of diesel on the froth stability and its antifoam
na
mechanism in fine coal flotation used MIBC as the frother was investigated. Three-phase and
Jo ur
two-phase froth stability tests were first carried out and the negative effect of diesel on froth stability was further explained by the single foam film drainage and spreading pressure experiments. The results of the three-phase dynamic froth stability showed that the maximum froth height and half-life of froth first increased and then decreased with the increase in diesel concentration. When diesel concentration increased to 8 kg/t, the maximum froth height and half-life of froth increased to 7.7 cm and 19 s. Deforming effect was observed when further increasing diesel dosage. Two-phase froth stability tests showed that the foaming ability and foam stability gradually decreased as the diesel concentration increased. When the diesel concentration increased from 0 to 20 and 40 ppm, the foam half-life decreased from 19 to 2.84 and 1.42 s, respectively. Single foam drainage tests showed that the diesel droplets dispersed into the middle of the foam film resulting in the formation of oil-bridge 1
Journal Pre-proof
and rupture of the foam film. Meanwhile, the oil-film spreading pressure was found increased as the diesel concentration increased, directly indicating the antifoam effect of diesel. MIBC molecules were competitively adsorbed at diesel droplets, which reduced the effective concentration of the frother at the gas-water interface. Throughout this study, a certain defoaming effect of diesel on the froth stability in coal flotation was identified.
of
Keywords: flotation; diesel; froth stability; foam film drainage; spreading pressure 1. Introduction
ro
Froth flotation is an effective separation process for fine coal upgrading, which occurs in the
-p
gas-liquid interface. According to the differences in the surface properties of coal and gangue
re
minerals, the hydrophobic coal particles can be separated from the pulp by their attachment to the
lP
rising air bubbles that form a particle-rich froth on the suspension surface [1-4]. There are three
na
sub-processes of the flotation kinetics: bubble-particle collision, attachment, and detachment [5].These sub-processes are strongly based on the bubble size and froth stability. The flotation
[6-7].
Jo ur
efficiency and product quality depend on the establishment of a carefully controlled and stable froth
Froth is very complex and influenced by multiple factors. In fine coal flotation, particles and flotation reagents (frothers and collectors) are the two important factors affecting the froth stability [8-9]. For particles, the solid concentration, particle size, shape, and hydrophobicity were found to have a critical impact on the forth stability [10]. The effects of particle size have been extensively studied and fine particles were found to have a greater influence on the froth stability compared with coarse particles [11-14]. Many researchers [15-18] used methylated quartz as model particles and found a critical particle contact angle around 65°, where the froth has the best stability and particles 2
Journal Pre-proof
with higher contact angle could collapse the froth. Liang et al. [19] also found that the fine coal particles with moderate hydrophobicity contribute to the maximum froth height in the froth formation process and are most beneficial to flotation. Frothers are used to promote air dispersion in fine bubbles and stabilise the froth [20-21]. They are generally considered as surfactants and can absorb at the gas-liquid interface, leading to changes in
of
interface properties such as surface tension, forces, charge, and rheology. These changes on the surface properties could eventually influence the froth stability. Some studies have stated that
ro
frothers with the same hydrophilic-lipophilic balance (HLB) but higher molecular weight could
-p
provide more persistent froth [22]. Schwarz [23] found that the polypropylene oxide, which has the
re
optimal molecular weight, could provide the maximum froth stability in water. Beyond this
lP
molecular weight, the foam stability starts declining. Dey et al. [24] also found that frothers with low
na
molecular weight are more selective but less effective compared with high molecular weight frothers that could cause the loss of combustible matter in tailings. Tan et al. [25] found that better foaming
Jo ur
properties can be obtained by using a mixture of selective and powerful polypropylene glycols in comparison with using a single frother.
Heretofore, non-polar oil (diesel) has been used as the flotation collector for fine coal while the effect of diesel on froth stability is less investigated. In this study, the effects of diesel on froth stability in coal flotation in the presence of methyl isobutyl carbinol (MIBC) were examined by conducting three-phase (with coal particles) and two-phase (without coal particles) froth stability tests. The negative effect of diesel on froth stability was further explained by the single foam film drainage and spreading pressure experiments. The outcome of this study can provide a comprehensive understanding of the antifoam mechanism of diesel. 3
Journal Pre-proof
2. Experiments 2.1 Materials MIBC (analytical reagent) was purchased from the Sinopharm Chemical Reagent Co., Ltd, (Shanghai, China). The diesel was obtained from the Qianjiaying Coal Preparation Plant (Tangshan City, Hebei Province, China) without further purification. Milli-Q water was used to configure
of
various solutions. In this paper, MIBC was used to generate bubbles and a MIBC solution of concentration 20 ppm prepared through ultrasonic emulsification for 10 min. Different
ro
concentrations of diesel solutions (20, 40, 80, and 120ppm) were compounded with the 20ppm
-p
MIBC solution, respectively. The mixed solution of MIBC and diesel was placed to a glass
re
container and put it into the ultrasonic clearing machine which operated at 53 KHZ. The ultrasonic
lP
emulsification continued for 10 min to uniformly disperse the diesel. When the ultrasonic wave
na
spread in the solution, the cavitation phenomenon will occur, and a high temperature and high pressure will be accompanied by cavitation [26]. In diesel/water system, when the cavitation
Jo ur
threshold is reached, the emulsification process will initiate. Ultrasound could provide additional energy for new interface formation, thus, it is possible to obtain the emulsions even in the absence of emulsifiers [27, 28]. After sonication, the solutions should be cooled to room temperature (25 °C). 2.2 Froth stability tests To systematically study the effects of diesel on froth stability in coal flotation, three-phase and two-phase froth stability tests were conducted. For the three-phase froth stability tests, highly metamorphosed anthracite samples were collected from the Xuehu Coal Preparation Plant, Yongcheng, Henan, China. Fractions with sizes < 0.25 mm were used in these tests. The proximate analysis of coal samples is showed in Table 1. The Mad and Aad represent the moisture content and 4
Journal Pre-proof
ash content based on air drying, respectively. The ash content is 21.95%, which is relative high and an upgrading process is needed before combustion. Vdaf and FCdaf are the contents of volatile matter and fixed carbon on the dry ash-free basis. The volatile content (Vdaf) is 27.57%, the sulfur content of coal samples (St.d) is 0.34% and the calorific value (Qb.ad) is 18.36 MJ/Kg. The particle size distribution of coal samples was conducted with the wetting screen test and the result is shown in
of
Table 2. The ash content increased as particle size decreased. The -0.045 mm is the main size fraction with 38.59% content and it also has a high ash content of 27.29%.
ro
The three-phase froth tests were conducted by a foam column with the diameter and height of 50 and
-p
400mm. The solid content of the slurry was kept constant at 80 g/L. Diesel and MIBC were used as
re
the collector and frother, respectively, and gradually added into the pulp. The dosage of MIBC was
lP
250 g/t and the dosages of diesel were 1, 4, 8, 12, 16, and 20 kg/t. The conditioning periods for the
na
collector and frother were 2 and 1 min, respectively. Next, 200 ml of pulp was transferred into the foam column. The foaming ability and froth stability were investigated by changing the diesel
Jo ur
concentration.
The dynamic froth stability (DFS) is a function of the measured maximum steady-state froth height with continuous bubbling in the same flotation column [4], as shown in Eq. (1). In this study, both the gas flow rate and cross-section area of the foam column were kept consistent. Therefore, according to Eq. (1), the froth height at the equilibrium can be used to evaluate the froth stability. To ensure the accuracy of the experimental result, all experiments were conducted 3-5 times and the average maximum equilibrium froth height was calculated. 𝐷𝐹𝑆 =
𝑉𝑓 𝑄
=
𝐻𝑚𝑎𝑥 𝐴
Eq. (1)
𝑄
In Eq. (1), Vf is the volume of foam, Hmax is the maximum equilibrium height of the foam, A is the 5
Journal Pre-proof
cross-sectional area of the foam column, and Q is the gas volumetric flow rate. In addition to DFS, the half-life of froth also can be used to quantify the froth stability. The half-life refers to the time required by the discharge foam volume to be reduced to half of the maximum froth volume. Longer half-life indicates better froth stability. The commercially available instrument, FoamScan (TECLIS, France), which can combine image analysis and conductivity measurement, was used to study the two-phase froth stability. It should be
of
noted that the foaming time refers to the time when the foam volume reaches a fixed volume and the
ro
gas flow automatically stops. The foam volume is monitored by a CCD-camera according to the
-p
principle of reflection optics. The 50ml MIBC solution was extracted with the sampler and injected
re
into the glass tube five times and calibrated. The gas flow rate was set at 120 ml/min and the foam scanner software was used to monitor the experiment. In this case, the foaming ability and froth
lP
stability of the solution were investigated by changing the concentration of diesel.
na
2.3 Single foam film drainage experiment
Jo ur
Dynamic film apparatus (DFA) was used to analyse the drainage of single foam film in the presence of MIBC and diesel, as shown in Figure 1. Before the test, the glass cell (contact angle = 100°) and the capillary tube should be thoroughly cleaned according to the reported literature [29]. A single bubble with 3 mm diameter was generated at the bottom of the glass cell using a micro-syringe. Then, a bubble with the same size was produced at the end of the capillary tube. A piezo actuator was used to discharge the extra solution between the two bubbles, thereby creating a horizontal foam film. The time-dependent drainage of the foam film was monitored using monochromatic interference microscopy. The interference fringes were treated with the MATLAB software and the kinetics of the foam film and balanced film thickness were obtained. The two bubbles were in the same initial position for each test. Each group of tests was repeated at least 2 times. 6
Journal Pre-proof
2.3 Spreading pressure measurement An automatic surface tension meter (K100, KRUSS, Germany) was used to measure the surface tension of MIBC-diesel solutions by the Wilhelmy plate method. To evaluate the antifoam performance of diesel, the spreading pressure, which was equal to the reduction of surface tension caused by adding diesel, was calculated [30, 31]. A high spreading pressure value indicates a
of
remarkable defoaming effect of diesel.
ro
3. Results and discussion 3.1 Froth stability results
-p
The effect of diesel concentration on the three-phase froth stability is shown in Figure 2. The
re
maximum height and half-life of the froth first increased and then decreased with the increase in
lP
diesel concentration. The highest froth stability was obtained at diesel concentration of 8 kg/t. When
na
diesel concentration increased to 8 kg/t, the maximum height and half-life of the froth were 7.7 cm and 19 s. As diesel concentration continually increased, the froth stability decreased. When diesel
Jo ur
concentration increased to 20 kg/t, the maximum height and half-life of the froth decreased to 1.9 cm and 4 s. At low diesel concentrations, both the foaming ability and froth stability increased with the diesel concentration. This increase in froth stability may be caused by the capture of coal particles on the bubble surface. Hydrophobic coal particles stabilize the froth and prevent bubble coalescence. When diesel concentration was above 8 kg/t, the foaming ability and froth stability significantly decreased, thereby confirming the antifoam effect of diesel. To exclude the influence of coal particles, two-phase froth stability tests were conducted. The foaming ability and froth stability of the two-phase froth in the presence of 20 ppm MIBC is shown in Figure 3. 0-Tb and Tb-Te denote the foaming stage and defoaming stages, respectively. The 7
Journal Pre-proof
foaming ability and froth stability of the solution are evaluated by comparing the maximum foam height at the foaming stage Tb and the half-life at the defoaming stage (the time difference between Te and Tb). The gas flow rate was set at 120 ml/ min. The 20 ppm MIBC solution could easily reach the preset foam volume at 0-Tb. Meanwhile, the half-life of 20 ppm MIBC was 19 s at Tb-Te, which indicated that the 20 ppm MIBC solution has good foaming ability and froth stability.
of
The effect of different diesel concentration on the foaming ability and froth stability of the two-phase froth in the presence of 20 ppm MIBC is shown in Figure 4. When diesel with 20 ppm concentration
ro
was added into the solution, the maximum foam volume could not reach the preset volume of 30 ml
-p
but it easily reached the preset volume of 11 ml, which suggested that the foaming ability of the
re
solution was weakened after adding the diesel. When the concentration of the diesel increased to 40
lP
or 80 ppm, the maximum foam volume reached 10 or 9 ml, respectively. When diesel with
na
concentration 120 ppm was used, the maximum foam volume was between 8-9 ml. The results showed that the foaming ability gradually decreased with the increase in diesel concentration in the
Jo ur
absence of coal particles. In contrast, the foam delay rate increased with the addition of diesel. When the diesel concentration increased from 0 to 20 and 40 ppm, the foam half-life decreased from 19 to 2.84 and 1.42 s. As diesel concentration continually increased to 80 and 120 ppm, the foam delayed instantly which did not plot in Figure 4 as the preset froth volume could not reach (could not enter defoaming stage). The foam became unstable with the increased concentration of diesel, this phenomenon confirmed the antifoam effect of diesel 3.2 Single foam film drainage results To explain the antifoam mechanism of diesel, single foam film drainage tests were conducted. The foam film is a basic unit in froth and plays a critical role in the froth stability. The effect of diesel 8
Journal Pre-proof
concentration on the foam film drainage in the presence of 20 ppm MIBC is shown in Figure 5. In the absence of diesel, the liquid film thinned in the initial stage and reached at an equilibrium film thickness with 139 nm as shown in Figure 5 (a). It can be seen in Figure 5 (b) that when the diesel concentration increased to 40 ppm, the liquid film was still at equilibrium, while the thickness of the equilibrium film decreased to 112 mm. In Figure 5 (a) and (b), the foam films had clear and stable
of
interference fringes when the foam film reached equilibrium. This indicates that MIBC molecules can be absorbed by the diesel droplets, leading to a decrease in the concentration of MIBC and an
ro
increase in the surface tension in the middle of the film. The increase in Laplace pressure could
-p
reduce the thickness of the liquid film. As the diesel concentration increased to 80 and 120 ppm, the
re
liquid film became unstable and ruptured and the thicknesses of the ruptured film were 149.07 and
lP
128.27 nm as shown in Figure 5 (c) and (d), respectively. It can be seen that diesel droplets spread
na
between the foam films through the images of interference fringe before foam film ruptured. Interference fringes disappeared as film ruptured. However, it should be noted that the critical
Jo ur
rupture thickness of the liquid film was related to the size of diesel droplet in the foam film. Single foam film drainage results are consistent with the results of former froth stability tests. The antifoam mechanism of diesel can be described by the oil “bridging-stretching” theory [32], as shown in Figure 6. In the initial stages of foaming, the liquid film between bubbles was stable and diesel droplets dispersed in the middle of the liquid film, as shown in Figure 6 (a) and 6 (b). Because of the non-polarity of diesel droplets, the diesel oil droplets and MIBC molecules present a repulsive interaction, which causes MIBC molecules to move away from the center to the two ends of the liquid film, as shown in Figure 6 (c). Simultaneously, the hydrophobic effects between diesel and air bubbles facilitate liquid drainage between the two bubbles, resulting in the thinning of liquid film 9
Journal Pre-proof
and appearance of oil-bridge. As the liquid drains, the oil-bridge is radially stretched and thinned and transforms into the oil film between the two bubbles. The oil film is unstable and its rupture results in the coalescence of bubbles, as shown in Figure 6 (d). The optical interference patterns at the time of rupture of the liquid film in 80 and 120 ppm diesel solution (Figure 5) also verify the existence of the oil-bridge. Therefore, the increases in diesel concentration accelerate the rupture of foam film
of
and deteriorates the froth stability. 3.3 Spreading pressure results
ro
The surface tension and oil-film spreading pressure of MIBC-diesel solutions in the presence of 20
-p
ppm MIBC is shown in Table 3. The surface tension was decreased while the spreading pressure was
re
increased with the increase in diesel concentration. When diesel was not added to the solution, the
lP
surface tension was around 71.66 mN/m, which is lower than that of Milli-Q water (73.8 mN/m).
na
Because the addition of MIBC decreased the surface tension of the solution. When the diesel concentration increased to 20 and 40 ppm, the surface tension decreased slightly. As diesel
Jo ur
concentration continued to increase to 80 and 120 ppm, the surface tension of solution decreased to around 65 and 62 mN/m, respectively. The oil-film spreading pressure increased from 0 to 8.90 mN/m when the diesel concentration increased from 0 to 120 ppm. These results also indicated antifoam effect of diesel. Figure 7 illustrated the interactions between diesel droplet and MIBC molecules in the flotation column. When MIBC molecules adsorbed at the oil-water interface, the hydrophilic groups oriented to water and the hydrophobic tail oriented to oil. In addition to the oil-bridge effect, MIBC molecules could be adsorbed at the oil-water interface, decreasing the oil-water interfacial tension. This reduces the effective concentration of frother at the gas-water interface, resulting in decreased froth stability, which is consistent with the research results of Wang 10
Journal Pre-proof
[33]. 4. Conclusion Throughout this study, a certain defoaming effect of diesel on the froth stability in coal flotation was identified. The froth stability decreased with the increase of diesel concentration in three-phase froth dynamic tests. Deforming effect of diesel was indeed observed in following two-phase froth stability,
of
single foam drainage, and spreading pressure tests. On one hand, the dispersion of diesel droplets in foam film and the appearance of oil-bridge between foam films is one of important reason for
ro
antifoam effect of diesel. On the other hand, MIBC molecules competitively adsorbed at diesel
-p
droplets, which reduced the effective concentration of frother at gas-water interface. Further
re
investigation should be carried out to develop new approach to eliminate the negative effect of diesel
Acknowledgement
na
lP
on the froth stability.
Jo ur
This work was supported by Outstanding Innovation Scholarship for Doctoral Candidate of “Double First Rate” Construction Disciplines of CUMT. Declaration of interests
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.
References [1] Xing Y, Gui X, Pan L, et al. Recent experimental advances for understanding bubble-particle attachment in flotation. Advances in Colloid and Interface Science, 2017, 246: 105-132. [2] Reis A S, Barrozo M A S. A study on bubble formation and its relation with the performance of 11
Journal Pre-proof
apatite flotation. Separation and Purification Technology, 2016, 161: 112-120. [3] Nguyen A, Schulze H. Colloid Science of Flotation, Marcel Dekker, New York, 2004. [4] Xing Y, Gui X, Cao Y, et al. Effect of compound collector and blending frother on froth stability and flotation performance of oxidized coal. Powder Technology, 2017, 305: 166-173. [5] Cho Y S, Laskowski J S. Effect of flotation frothers on bubble size and foam stability[J].
of
International Journal of Mineral Processing, 2002, 64(2-3): 69-80. [6] Johansson G, Pugh R J. The influence of particle size and hydrophobicity on the stability of
ro
mineralized froths. International Journal of Mineral Processing, 1992, 34(1-2): 1-21.
-p
[7] Schwarz S, Grano S. Effect of particle hydrophobicity on particle and water transport across a
re
flotation froth. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2005, 256(2-3):
lP
157-164.
na
[8] Johansson G, Pugh R J. The influence of particle size and hydrophobicity on the stability of mineralized froths. International Journal of Mineral Processing, 1992, 34(1-2): 1-21.
Jo ur
[9] Schwarz S, Grano S. Effect of particle hydrophobicity on particle and water transport across a flotation froth. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2005, 256(2-3): 157-164.
[10] Hunter T N, Pugh R J, Franks G V, et al. The role of particles in stabilising foams and emulsions. Advances in Colloid and Interface Science, 2008, 137(2): 57-81. [11] Ozmak M, Aktas Z. Coal froth flotation: Effects of reagent adsorption on the froth structure. Energy & Fuels, 2006, 20(3): 1123-1130. [12] Aktas Z, Cilliers J J, Banford A W. Dynamic froth stability: Particle size, airflow rate and conditioning time effects. International Journal of Mineral Processing, 2008, 87(1-2): 65-71. 12
Journal Pre-proof
[13] Rahman R M, Ata S, Jameson G J. The effect of flotation variables on the recovery of different particle size fractions in the froth and the pulp. International Journal of Mineral Processing, 2012, 106: 70-77. [14] Wang B, Peng Y, Vink S. Effect of saline water on the flotation of fine and coarse coal particles in the presence of clay minerals. Minerals Engineering, 2014, 66: 145-151.
of
[15] Ata S, Ahmed N, Jameson G J. Collection of hydrophobic particles in the froth phase. International Journal of Mineral Processing, 2002, 64(2-3): 101-122.
-p
Journal of Mineral Processing, 2003, 72(1-4): 255-266.
ro
[16] Ata S, Ahmed N, Jameson G J. A study of bubble coalescence in flotation froths. International
re
[17] Ata S, Ahmed N, Jameson G J. The effect of hydrophobicity on the drainage of gangue minerals
lP
in flotation froths. Minerals Engineering, 2004, 17(7-8): 897-901.
na
[18] Kaptay G. Interfacial criteria for stabilization of liquid foams by solid particles. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2003, 230(1-3): 67-80.
Jo ur
[19] Liang L, Li Z, Peng Y, et al. Influence of coal particles on froth stability and flotation performance. Minerals Engineering, 2015, 81: 96-102. [20] Castro S, Miranda C, Toledo P, et al. Effect of frothers on bubble coalescence and foaming in electrolyte solutions and seawater. International Journal of Mineral Processing, 2013, 124: 8-14. [21] Liao Y, Cao Y, Huang S, et al. Water-carrying properties of flotation frothers and its effect on fine coal flotation. International Journal of Coal Preparation and Utilization, 2015, 35(2): 88-98. [22] Aston J, Drummond C, Scales F, Healy T. In: Whitmore RI, editor. Proc. 2nd Australian Coal Preparation Congress, Brisbane: Westminster Press; 1983 [23] Schwarz S. The relationship between froth recovery and froth structure, Adelaide: University of 13
Journal Pre-proof
South Australia; 2004 [24] Dey S, Pani S, Singh R. Study of interactions of frother blends and its effect on coal flotation. Powder Technology, 2014, 260: 78-83. [25] Tan S N, Pugh R J, Fornasiero D, et al. Foaming of polypropylene glycols and glycol/MIBC mixtures. Minerals Engineering, 2005, 18(2): 179-188.
of
[26] Suslick K S. Sonochemistry. Science, 1990, 247(49): 1439–1445. [27] Wood R W, Loomis A L. The physicial and biological effects of intense audible sound on living
ro
organisms and cells. Phil. Mag, 1927, 4: 417.
-p
[28] Gaikwad S G, Pandit A B. Ultrasound emulsification: effect of ultrasonic and physicochemical
re
properties on dispersed phase volume and droplet size. Ultrasonics sonochemistry, 2008, 15(4):
lP
554-563.
na
[29] Pan L, Jung S, Yoon R H. A fundamental study on the role of collector in the kinetics of bubble–particle interaction. International Journal of Mineral Processing, 2012, 106: 37-41.
Jo ur
[30] Jha B K, Christiano S P, Shah D O. Silicone antifoam performance: correlation with spreading and surfactant monolayer packing. Langmuir, 2000, 16(26): 9947-9954. [31] Wang J, Nguyen A V, Farrokhpay S. Foamability of sodium dodecyl sulfate solutions: Anomalous effect of dodecanol unexplained by conventional theories. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2016, 495: 110-117. [32] Denkov N D. Mechanisms of foam destruction by oil-based antifoams. Langmuir, 2004, 20(22): 9463-9505. [33] Wang J. Effects of reagents and solid particles on drainage and stability of liquid film, foam and froth. 2015. 14
Jo ur
na
lP
re
-p
ro
of
Journal Pre-proof
15
Jo ur
na
lP
re
-p
ro
of
Journal Pre-proof
16
Journal Pre-proof
Jo ur
na
lP
re
-p
ro
of
Figure 1 The DFA system
17
of
Journal Pre-proof
Jo ur
na
lP
re
-p
ro
Figure 2 Effect of diesel concentration on three-phase froth stability
18
of
Journal Pre-proof
Jo ur
na
lP
re
-p
ro
Figure 3 Foaming ability and froth stability of two-phase froth in presence of 20 ppm MIBC
19
of
Journal Pre-proof
Figure 4 Effect of different diesel concentration on foaming ability and froth stability of two-phase
Jo ur
na
lP
re
-p
ro
froth in presence of 20 ppm MIBC
20
Journal Pre-proof 700
700 600
Thickness (nm)
600
Thickness (nm)
20 ppm MIBC 1+40 ppm diesel 20 ppm MIBC 2+40 ppm diesel
20 ppm MIBC 1 20 ppm MIBC 2
500 400 300 200 100
5
10
15
20
25
400 300 200
Equilibrium film 0
500
Equilibrium film 100
30
0
5
Time (s)
.
10
25
30
(b)
700
700
20 ppm MIBC 1+80 ppm diesel 20 ppm MIBC 2+80 ppm diesel
20 ppm MIBC 1+120 ppm diesel 20 ppm MIBC 2+120 ppm diesel
600
500
-p
Thickness (nm)
500
ro
600
400
200
5
10
15
Time (s)
20
25
30
100
Film rupture 0
na
(c)
300 200
Film rupture 0
400
re
300
lP
Thickness (nm)
20
of
(a)
100
15
Time (s)
5
10
15
20
25
30
Time (s)
(d)
Jo ur
Figure 5 The thickness at the center point of foam film as a function of time with different diesel concentrations. Insets pictures were the images of foam film which at equilibrium and rupture. Two parallel trials were shown.
21
Journal Pre-proof
Figure 6 Schematic diagrams of bridging-stretching mechanism of foam film rupture by diesel
Jo ur
na
lP
re
-p
ro
of
droplets
22
Journal Pre-proof
of
Figure 7 Schematic of the interactions between diesel droplets and MIBC molecules in the flotation
Jo ur
na
lP
re
-p
ro
column
23
Journal Pre-proof
Deforming effect of diesel Formation of oil-bridge
diesel Competitive adsorption
Jo ur
na
lP
re
-p
ro
of
Deforming mechanism
24
Jo ur
na
lP
re
-p
ro
of
Journal Pre-proof
25
Journal Pre-proof Table 1 Proximate analysis of the high-metamorphosed anthracite Vdaf (%) 27.57
na
lP
re
-p
ro
of
Aad (%) 21.95
Jo ur
Mad (%) 4.86
26
FCdaf (%) 45.62
Journal Pre-proof
Table 2 Particle size distributions of the coal samples Yield, %
Ash,%
0.25-0.125 0.125-0.074 0.074-0.045 -0.045 Total
20.09 23.90 17.41 38.59 100
16.99 18.61 20.24 27.49 22.00
Positive cumulative Yield, % Ash,% 20.09 16.99 44.00 17.87 61.41 18.54 100.00 22.00
Jo ur
na
lP
re
-p
ro
of
Size, mm
27
Negative cumulative Yield, % Ash,% 100.00 22.00 79.91 23.26 56.00 25.24 38.59 27.49
Journal Pre-proof
Table 3 The surface tension and oil-film spreading pressure of MIBC-diesel solutions in the presence of 20 ppm MIBC Diesel concentration (ppm) 0 20 40 80 120
Surface tension, σ (mN/m) 71.66 ± 0.04 71.50 ± 0.08 70.07 ± 0.40 65.52 ± 0.51 62.76 ± 0.56
Spreading pressure, σ (mN/m) 0.00 -0.16 1.59 6.14 8.90
na
lP
re
-p
ro
Effect of diesel on froth stability in coal flotation was studied. Froth stability first increased then decreased as diesel increased. Oil-bridge was formed in foam film leading to film rupture. Oil-film spreading pressure increased as diesel increased.
Jo ur
of
Highlights
28
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Mengdi Xu, Yaowen Xing, Wei Jin, Ming Li, Yijun Cao, Xiahui Gui PII:
S0032-5910(19)31163-5
DOI:
https://doi.org/10.1016/j.powtec.2019.12.058
Reference:
PTEC 15066
To appear in:
Powder Technology
Received date:
9 April 2019
Revised date:
11 December 2019
Accepted date:
27 December 2019
Please cite this article as: M. Xu, Y. Xing, W. Jin, et al., Effect of diesel on the froth stability and its antifoam mechanism in fine coal flotation used MIBC as the frother, Powder Technology(2019), https://doi.org/10.1016/j.powtec.2019.12.058
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier.
Journal Pre-proof
Effect of diesel on the froth stability and its antifoam mechanism in fine coal flotation used MIBC as the frother Mengdi Xu1, 2,a, Yaowen Xing1,a, Wei Jin1, 2, Ming Li1, 2, Yijun Cao1, 3*, Xiahui Gui1, 3*
ro
of
1 Chinese National Engineering Research Center of Coal Preparation and Purification, China University of Mining and Technology, Xuzhou 221116, Jiangsu, China 2 School of Chemical Engineering and Technology, China University of Mining and Technology, Xuzhou 221116, Jiangsu, China 3 Henan Province Industrial Technology Research Institute of Resources and Materials, Zhengzhou University, Zhengzhou 450001, China a Co-first authors: These authors contributed equally to this work. * Address correspondence to: Xiahui Gui ([email protected]); Yijun Cao ([email protected])
-p
Abstract
re
Froth stability is one of the most important factors in fine coal flotation as it significantly affects the separation efficiency. Diesel is always used as the flotation collector while the effect of diesel on the
lP
froth stability is less investigated. In this study, effect of diesel on the froth stability and its antifoam
na
mechanism in fine coal flotation used MIBC as the frother was investigated. Three-phase and
Jo ur
two-phase froth stability tests were first carried out and the negative effect of diesel on froth stability was further explained by the single foam film drainage and spreading pressure experiments. The results of the three-phase dynamic froth stability showed that the maximum froth height and half-life of froth first increased and then decreased with the increase in diesel concentration. When diesel concentration increased to 8 kg/t, the maximum froth height and half-life of froth increased to 7.7 cm and 19 s. Deforming effect was observed when further increasing diesel dosage. Two-phase froth stability tests showed that the foaming ability and foam stability gradually decreased as the diesel concentration increased. When the diesel concentration increased from 0 to 20 and 40 ppm, the foam half-life decreased from 19 to 2.84 and 1.42 s, respectively. Single foam drainage tests showed that the diesel droplets dispersed into the middle of the foam film resulting in the formation of oil-bridge 1
Journal Pre-proof
and rupture of the foam film. Meanwhile, the oil-film spreading pressure was found increased as the diesel concentration increased, directly indicating the antifoam effect of diesel. MIBC molecules were competitively adsorbed at diesel droplets, which reduced the effective concentration of the frother at the gas-water interface. Throughout this study, a certain defoaming effect of diesel on the froth stability in coal flotation was identified.
of
Keywords: flotation; diesel; froth stability; foam film drainage; spreading pressure 1. Introduction
ro
Froth flotation is an effective separation process for fine coal upgrading, which occurs in the
-p
gas-liquid interface. According to the differences in the surface properties of coal and gangue
re
minerals, the hydrophobic coal particles can be separated from the pulp by their attachment to the
lP
rising air bubbles that form a particle-rich froth on the suspension surface [1-4]. There are three
na
sub-processes of the flotation kinetics: bubble-particle collision, attachment, and detachment [5].These sub-processes are strongly based on the bubble size and froth stability. The flotation
[6-7].
Jo ur
efficiency and product quality depend on the establishment of a carefully controlled and stable froth
Froth is very complex and influenced by multiple factors. In fine coal flotation, particles and flotation reagents (frothers and collectors) are the two important factors affecting the froth stability [8-9]. For particles, the solid concentration, particle size, shape, and hydrophobicity were found to have a critical impact on the forth stability [10]. The effects of particle size have been extensively studied and fine particles were found to have a greater influence on the froth stability compared with coarse particles [11-14]. Many researchers [15-18] used methylated quartz as model particles and found a critical particle contact angle around 65°, where the froth has the best stability and particles 2
Journal Pre-proof
with higher contact angle could collapse the froth. Liang et al. [19] also found that the fine coal particles with moderate hydrophobicity contribute to the maximum froth height in the froth formation process and are most beneficial to flotation. Frothers are used to promote air dispersion in fine bubbles and stabilise the froth [20-21]. They are generally considered as surfactants and can absorb at the gas-liquid interface, leading to changes in
of
interface properties such as surface tension, forces, charge, and rheology. These changes on the surface properties could eventually influence the froth stability. Some studies have stated that
ro
frothers with the same hydrophilic-lipophilic balance (HLB) but higher molecular weight could
-p
provide more persistent froth [22]. Schwarz [23] found that the polypropylene oxide, which has the
re
optimal molecular weight, could provide the maximum froth stability in water. Beyond this
lP
molecular weight, the foam stability starts declining. Dey et al. [24] also found that frothers with low
na
molecular weight are more selective but less effective compared with high molecular weight frothers that could cause the loss of combustible matter in tailings. Tan et al. [25] found that better foaming
Jo ur
properties can be obtained by using a mixture of selective and powerful polypropylene glycols in comparison with using a single frother.
Heretofore, non-polar oil (diesel) has been used as the flotation collector for fine coal while the effect of diesel on froth stability is less investigated. In this study, the effects of diesel on froth stability in coal flotation in the presence of methyl isobutyl carbinol (MIBC) were examined by conducting three-phase (with coal particles) and two-phase (without coal particles) froth stability tests. The negative effect of diesel on froth stability was further explained by the single foam film drainage and spreading pressure experiments. The outcome of this study can provide a comprehensive understanding of the antifoam mechanism of diesel. 3
Journal Pre-proof
2. Experiments 2.1 Materials MIBC (analytical reagent) was purchased from the Sinopharm Chemical Reagent Co., Ltd, (Shanghai, China). The diesel was obtained from the Qianjiaying Coal Preparation Plant (Tangshan City, Hebei Province, China) without further purification. Milli-Q water was used to configure
of
various solutions. In this paper, MIBC was used to generate bubbles and a MIBC solution of concentration 20 ppm prepared through ultrasonic emulsification for 10 min. Different
ro
concentrations of diesel solutions (20, 40, 80, and 120ppm) were compounded with the 20ppm
-p
MIBC solution, respectively. The mixed solution of MIBC and diesel was placed to a glass
re
container and put it into the ultrasonic clearing machine which operated at 53 KHZ. The ultrasonic
lP
emulsification continued for 10 min to uniformly disperse the diesel. When the ultrasonic wave
na
spread in the solution, the cavitation phenomenon will occur, and a high temperature and high pressure will be accompanied by cavitation [26]. In diesel/water system, when the cavitation
Jo ur
threshold is reached, the emulsification process will initiate. Ultrasound could provide additional energy for new interface formation, thus, it is possible to obtain the emulsions even in the absence of emulsifiers [27, 28]. After sonication, the solutions should be cooled to room temperature (25 °C). 2.2 Froth stability tests To systematically study the effects of diesel on froth stability in coal flotation, three-phase and two-phase froth stability tests were conducted. For the three-phase froth stability tests, highly metamorphosed anthracite samples were collected from the Xuehu Coal Preparation Plant, Yongcheng, Henan, China. Fractions with sizes < 0.25 mm were used in these tests. The proximate analysis of coal samples is showed in Table 1. The Mad and Aad represent the moisture content and 4
Journal Pre-proof
ash content based on air drying, respectively. The ash content is 21.95%, which is relative high and an upgrading process is needed before combustion. Vdaf and FCdaf are the contents of volatile matter and fixed carbon on the dry ash-free basis. The volatile content (Vdaf) is 27.57%, the sulfur content of coal samples (St.d) is 0.34% and the calorific value (Qb.ad) is 18.36 MJ/Kg. The particle size distribution of coal samples was conducted with the wetting screen test and the result is shown in
of
Table 2. The ash content increased as particle size decreased. The -0.045 mm is the main size fraction with 38.59% content and it also has a high ash content of 27.29%.
ro
The three-phase froth tests were conducted by a foam column with the diameter and height of 50 and
-p
400mm. The solid content of the slurry was kept constant at 80 g/L. Diesel and MIBC were used as
re
the collector and frother, respectively, and gradually added into the pulp. The dosage of MIBC was
lP
250 g/t and the dosages of diesel were 1, 4, 8, 12, 16, and 20 kg/t. The conditioning periods for the
na
collector and frother were 2 and 1 min, respectively. Next, 200 ml of pulp was transferred into the foam column. The foaming ability and froth stability were investigated by changing the diesel
Jo ur
concentration.
The dynamic froth stability (DFS) is a function of the measured maximum steady-state froth height with continuous bubbling in the same flotation column [4], as shown in Eq. (1). In this study, both the gas flow rate and cross-section area of the foam column were kept consistent. Therefore, according to Eq. (1), the froth height at the equilibrium can be used to evaluate the froth stability. To ensure the accuracy of the experimental result, all experiments were conducted 3-5 times and the average maximum equilibrium froth height was calculated. 𝐷𝐹𝑆 =
𝑉𝑓 𝑄
=
𝐻𝑚𝑎𝑥 𝐴
Eq. (1)
𝑄
In Eq. (1), Vf is the volume of foam, Hmax is the maximum equilibrium height of the foam, A is the 5
Journal Pre-proof
cross-sectional area of the foam column, and Q is the gas volumetric flow rate. In addition to DFS, the half-life of froth also can be used to quantify the froth stability. The half-life refers to the time required by the discharge foam volume to be reduced to half of the maximum froth volume. Longer half-life indicates better froth stability. The commercially available instrument, FoamScan (TECLIS, France), which can combine image analysis and conductivity measurement, was used to study the two-phase froth stability. It should be
of
noted that the foaming time refers to the time when the foam volume reaches a fixed volume and the
ro
gas flow automatically stops. The foam volume is monitored by a CCD-camera according to the
-p
principle of reflection optics. The 50ml MIBC solution was extracted with the sampler and injected
re
into the glass tube five times and calibrated. The gas flow rate was set at 120 ml/min and the foam scanner software was used to monitor the experiment. In this case, the foaming ability and froth
lP
stability of the solution were investigated by changing the concentration of diesel.
na
2.3 Single foam film drainage experiment
Jo ur
Dynamic film apparatus (DFA) was used to analyse the drainage of single foam film in the presence of MIBC and diesel, as shown in Figure 1. Before the test, the glass cell (contact angle = 100°) and the capillary tube should be thoroughly cleaned according to the reported literature [29]. A single bubble with 3 mm diameter was generated at the bottom of the glass cell using a micro-syringe. Then, a bubble with the same size was produced at the end of the capillary tube. A piezo actuator was used to discharge the extra solution between the two bubbles, thereby creating a horizontal foam film. The time-dependent drainage of the foam film was monitored using monochromatic interference microscopy. The interference fringes were treated with the MATLAB software and the kinetics of the foam film and balanced film thickness were obtained. The two bubbles were in the same initial position for each test. Each group of tests was repeated at least 2 times. 6
Journal Pre-proof
2.3 Spreading pressure measurement An automatic surface tension meter (K100, KRUSS, Germany) was used to measure the surface tension of MIBC-diesel solutions by the Wilhelmy plate method. To evaluate the antifoam performance of diesel, the spreading pressure, which was equal to the reduction of surface tension caused by adding diesel, was calculated [30, 31]. A high spreading pressure value indicates a
of
remarkable defoaming effect of diesel.
ro
3. Results and discussion 3.1 Froth stability results
-p
The effect of diesel concentration on the three-phase froth stability is shown in Figure 2. The
re
maximum height and half-life of the froth first increased and then decreased with the increase in
lP
diesel concentration. The highest froth stability was obtained at diesel concentration of 8 kg/t. When
na
diesel concentration increased to 8 kg/t, the maximum height and half-life of the froth were 7.7 cm and 19 s. As diesel concentration continually increased, the froth stability decreased. When diesel
Jo ur
concentration increased to 20 kg/t, the maximum height and half-life of the froth decreased to 1.9 cm and 4 s. At low diesel concentrations, both the foaming ability and froth stability increased with the diesel concentration. This increase in froth stability may be caused by the capture of coal particles on the bubble surface. Hydrophobic coal particles stabilize the froth and prevent bubble coalescence. When diesel concentration was above 8 kg/t, the foaming ability and froth stability significantly decreased, thereby confirming the antifoam effect of diesel. To exclude the influence of coal particles, two-phase froth stability tests were conducted. The foaming ability and froth stability of the two-phase froth in the presence of 20 ppm MIBC is shown in Figure 3. 0-Tb and Tb-Te denote the foaming stage and defoaming stages, respectively. The 7
Journal Pre-proof
foaming ability and froth stability of the solution are evaluated by comparing the maximum foam height at the foaming stage Tb and the half-life at the defoaming stage (the time difference between Te and Tb). The gas flow rate was set at 120 ml/ min. The 20 ppm MIBC solution could easily reach the preset foam volume at 0-Tb. Meanwhile, the half-life of 20 ppm MIBC was 19 s at Tb-Te, which indicated that the 20 ppm MIBC solution has good foaming ability and froth stability.
of
The effect of different diesel concentration on the foaming ability and froth stability of the two-phase froth in the presence of 20 ppm MIBC is shown in Figure 4. When diesel with 20 ppm concentration
ro
was added into the solution, the maximum foam volume could not reach the preset volume of 30 ml
-p
but it easily reached the preset volume of 11 ml, which suggested that the foaming ability of the
re
solution was weakened after adding the diesel. When the concentration of the diesel increased to 40
lP
or 80 ppm, the maximum foam volume reached 10 or 9 ml, respectively. When diesel with
na
concentration 120 ppm was used, the maximum foam volume was between 8-9 ml. The results showed that the foaming ability gradually decreased with the increase in diesel concentration in the
Jo ur
absence of coal particles. In contrast, the foam delay rate increased with the addition of diesel. When the diesel concentration increased from 0 to 20 and 40 ppm, the foam half-life decreased from 19 to 2.84 and 1.42 s. As diesel concentration continually increased to 80 and 120 ppm, the foam delayed instantly which did not plot in Figure 4 as the preset froth volume could not reach (could not enter defoaming stage). The foam became unstable with the increased concentration of diesel, this phenomenon confirmed the antifoam effect of diesel 3.2 Single foam film drainage results To explain the antifoam mechanism of diesel, single foam film drainage tests were conducted. The foam film is a basic unit in froth and plays a critical role in the froth stability. The effect of diesel 8
Journal Pre-proof
concentration on the foam film drainage in the presence of 20 ppm MIBC is shown in Figure 5. In the absence of diesel, the liquid film thinned in the initial stage and reached at an equilibrium film thickness with 139 nm as shown in Figure 5 (a). It can be seen in Figure 5 (b) that when the diesel concentration increased to 40 ppm, the liquid film was still at equilibrium, while the thickness of the equilibrium film decreased to 112 mm. In Figure 5 (a) and (b), the foam films had clear and stable
of
interference fringes when the foam film reached equilibrium. This indicates that MIBC molecules can be absorbed by the diesel droplets, leading to a decrease in the concentration of MIBC and an
ro
increase in the surface tension in the middle of the film. The increase in Laplace pressure could
-p
reduce the thickness of the liquid film. As the diesel concentration increased to 80 and 120 ppm, the
re
liquid film became unstable and ruptured and the thicknesses of the ruptured film were 149.07 and
lP
128.27 nm as shown in Figure 5 (c) and (d), respectively. It can be seen that diesel droplets spread
na
between the foam films through the images of interference fringe before foam film ruptured. Interference fringes disappeared as film ruptured. However, it should be noted that the critical
Jo ur
rupture thickness of the liquid film was related to the size of diesel droplet in the foam film. Single foam film drainage results are consistent with the results of former froth stability tests. The antifoam mechanism of diesel can be described by the oil “bridging-stretching” theory [32], as shown in Figure 6. In the initial stages of foaming, the liquid film between bubbles was stable and diesel droplets dispersed in the middle of the liquid film, as shown in Figure 6 (a) and 6 (b). Because of the non-polarity of diesel droplets, the diesel oil droplets and MIBC molecules present a repulsive interaction, which causes MIBC molecules to move away from the center to the two ends of the liquid film, as shown in Figure 6 (c). Simultaneously, the hydrophobic effects between diesel and air bubbles facilitate liquid drainage between the two bubbles, resulting in the thinning of liquid film 9
Journal Pre-proof
and appearance of oil-bridge. As the liquid drains, the oil-bridge is radially stretched and thinned and transforms into the oil film between the two bubbles. The oil film is unstable and its rupture results in the coalescence of bubbles, as shown in Figure 6 (d). The optical interference patterns at the time of rupture of the liquid film in 80 and 120 ppm diesel solution (Figure 5) also verify the existence of the oil-bridge. Therefore, the increases in diesel concentration accelerate the rupture of foam film
of
and deteriorates the froth stability. 3.3 Spreading pressure results
ro
The surface tension and oil-film spreading pressure of MIBC-diesel solutions in the presence of 20
-p
ppm MIBC is shown in Table 3. The surface tension was decreased while the spreading pressure was
re
increased with the increase in diesel concentration. When diesel was not added to the solution, the
lP
surface tension was around 71.66 mN/m, which is lower than that of Milli-Q water (73.8 mN/m).
na
Because the addition of MIBC decreased the surface tension of the solution. When the diesel concentration increased to 20 and 40 ppm, the surface tension decreased slightly. As diesel
Jo ur
concentration continued to increase to 80 and 120 ppm, the surface tension of solution decreased to around 65 and 62 mN/m, respectively. The oil-film spreading pressure increased from 0 to 8.90 mN/m when the diesel concentration increased from 0 to 120 ppm. These results also indicated antifoam effect of diesel. Figure 7 illustrated the interactions between diesel droplet and MIBC molecules in the flotation column. When MIBC molecules adsorbed at the oil-water interface, the hydrophilic groups oriented to water and the hydrophobic tail oriented to oil. In addition to the oil-bridge effect, MIBC molecules could be adsorbed at the oil-water interface, decreasing the oil-water interfacial tension. This reduces the effective concentration of frother at the gas-water interface, resulting in decreased froth stability, which is consistent with the research results of Wang 10
Journal Pre-proof
[33]. 4. Conclusion Throughout this study, a certain defoaming effect of diesel on the froth stability in coal flotation was identified. The froth stability decreased with the increase of diesel concentration in three-phase froth dynamic tests. Deforming effect of diesel was indeed observed in following two-phase froth stability,
of
single foam drainage, and spreading pressure tests. On one hand, the dispersion of diesel droplets in foam film and the appearance of oil-bridge between foam films is one of important reason for
ro
antifoam effect of diesel. On the other hand, MIBC molecules competitively adsorbed at diesel
-p
droplets, which reduced the effective concentration of frother at gas-water interface. Further
re
investigation should be carried out to develop new approach to eliminate the negative effect of diesel
Acknowledgement
na
lP
on the froth stability.
Jo ur
This work was supported by Outstanding Innovation Scholarship for Doctoral Candidate of “Double First Rate” Construction Disciplines of CUMT. Declaration of interests
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.
References [1] Xing Y, Gui X, Pan L, et al. Recent experimental advances for understanding bubble-particle attachment in flotation. Advances in Colloid and Interface Science, 2017, 246: 105-132. [2] Reis A S, Barrozo M A S. A study on bubble formation and its relation with the performance of 11
Journal Pre-proof
apatite flotation. Separation and Purification Technology, 2016, 161: 112-120. [3] Nguyen A, Schulze H. Colloid Science of Flotation, Marcel Dekker, New York, 2004. [4] Xing Y, Gui X, Cao Y, et al. Effect of compound collector and blending frother on froth stability and flotation performance of oxidized coal. Powder Technology, 2017, 305: 166-173. [5] Cho Y S, Laskowski J S. Effect of flotation frothers on bubble size and foam stability[J].
of
International Journal of Mineral Processing, 2002, 64(2-3): 69-80. [6] Johansson G, Pugh R J. The influence of particle size and hydrophobicity on the stability of
ro
mineralized froths. International Journal of Mineral Processing, 1992, 34(1-2): 1-21.
-p
[7] Schwarz S, Grano S. Effect of particle hydrophobicity on particle and water transport across a
re
flotation froth. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2005, 256(2-3):
lP
157-164.
na
[8] Johansson G, Pugh R J. The influence of particle size and hydrophobicity on the stability of mineralized froths. International Journal of Mineral Processing, 1992, 34(1-2): 1-21.
Jo ur
[9] Schwarz S, Grano S. Effect of particle hydrophobicity on particle and water transport across a flotation froth. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2005, 256(2-3): 157-164.
[10] Hunter T N, Pugh R J, Franks G V, et al. The role of particles in stabilising foams and emulsions. Advances in Colloid and Interface Science, 2008, 137(2): 57-81. [11] Ozmak M, Aktas Z. Coal froth flotation: Effects of reagent adsorption on the froth structure. Energy & Fuels, 2006, 20(3): 1123-1130. [12] Aktas Z, Cilliers J J, Banford A W. Dynamic froth stability: Particle size, airflow rate and conditioning time effects. International Journal of Mineral Processing, 2008, 87(1-2): 65-71. 12
Journal Pre-proof
[13] Rahman R M, Ata S, Jameson G J. The effect of flotation variables on the recovery of different particle size fractions in the froth and the pulp. International Journal of Mineral Processing, 2012, 106: 70-77. [14] Wang B, Peng Y, Vink S. Effect of saline water on the flotation of fine and coarse coal particles in the presence of clay minerals. Minerals Engineering, 2014, 66: 145-151.
of
[15] Ata S, Ahmed N, Jameson G J. Collection of hydrophobic particles in the froth phase. International Journal of Mineral Processing, 2002, 64(2-3): 101-122.
-p
Journal of Mineral Processing, 2003, 72(1-4): 255-266.
ro
[16] Ata S, Ahmed N, Jameson G J. A study of bubble coalescence in flotation froths. International
re
[17] Ata S, Ahmed N, Jameson G J. The effect of hydrophobicity on the drainage of gangue minerals
lP
in flotation froths. Minerals Engineering, 2004, 17(7-8): 897-901.
na
[18] Kaptay G. Interfacial criteria for stabilization of liquid foams by solid particles. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2003, 230(1-3): 67-80.
Jo ur
[19] Liang L, Li Z, Peng Y, et al. Influence of coal particles on froth stability and flotation performance. Minerals Engineering, 2015, 81: 96-102. [20] Castro S, Miranda C, Toledo P, et al. Effect of frothers on bubble coalescence and foaming in electrolyte solutions and seawater. International Journal of Mineral Processing, 2013, 124: 8-14. [21] Liao Y, Cao Y, Huang S, et al. Water-carrying properties of flotation frothers and its effect on fine coal flotation. International Journal of Coal Preparation and Utilization, 2015, 35(2): 88-98. [22] Aston J, Drummond C, Scales F, Healy T. In: Whitmore RI, editor. Proc. 2nd Australian Coal Preparation Congress, Brisbane: Westminster Press; 1983 [23] Schwarz S. The relationship between froth recovery and froth structure, Adelaide: University of 13
Journal Pre-proof
South Australia; 2004 [24] Dey S, Pani S, Singh R. Study of interactions of frother blends and its effect on coal flotation. Powder Technology, 2014, 260: 78-83. [25] Tan S N, Pugh R J, Fornasiero D, et al. Foaming of polypropylene glycols and glycol/MIBC mixtures. Minerals Engineering, 2005, 18(2): 179-188.
of
[26] Suslick K S. Sonochemistry. Science, 1990, 247(49): 1439–1445. [27] Wood R W, Loomis A L. The physicial and biological effects of intense audible sound on living
ro
organisms and cells. Phil. Mag, 1927, 4: 417.
-p
[28] Gaikwad S G, Pandit A B. Ultrasound emulsification: effect of ultrasonic and physicochemical
re
properties on dispersed phase volume and droplet size. Ultrasonics sonochemistry, 2008, 15(4):
lP
554-563.
na
[29] Pan L, Jung S, Yoon R H. A fundamental study on the role of collector in the kinetics of bubble–particle interaction. International Journal of Mineral Processing, 2012, 106: 37-41.
Jo ur
[30] Jha B K, Christiano S P, Shah D O. Silicone antifoam performance: correlation with spreading and surfactant monolayer packing. Langmuir, 2000, 16(26): 9947-9954. [31] Wang J, Nguyen A V, Farrokhpay S. Foamability of sodium dodecyl sulfate solutions: Anomalous effect of dodecanol unexplained by conventional theories. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2016, 495: 110-117. [32] Denkov N D. Mechanisms of foam destruction by oil-based antifoams. Langmuir, 2004, 20(22): 9463-9505. [33] Wang J. Effects of reagents and solid particles on drainage and stability of liquid film, foam and froth. 2015. 14
Jo ur
na
lP
re
-p
ro
of
Journal Pre-proof
15
Jo ur
na
lP
re
-p
ro
of
Journal Pre-proof
16
Journal Pre-proof
Jo ur
na
lP
re
-p
ro
of
Figure 1 The DFA system
17
of
Journal Pre-proof
Jo ur
na
lP
re
-p
ro
Figure 2 Effect of diesel concentration on three-phase froth stability
18
of
Journal Pre-proof
Jo ur
na
lP
re
-p
ro
Figure 3 Foaming ability and froth stability of two-phase froth in presence of 20 ppm MIBC
19
of
Journal Pre-proof
Figure 4 Effect of different diesel concentration on foaming ability and froth stability of two-phase
Jo ur
na
lP
re
-p
ro
froth in presence of 20 ppm MIBC
20
Journal Pre-proof 700
700 600
Thickness (nm)
600
Thickness (nm)
20 ppm MIBC 1+40 ppm diesel 20 ppm MIBC 2+40 ppm diesel
20 ppm MIBC 1 20 ppm MIBC 2
500 400 300 200 100
5
10
15
20
25
400 300 200
Equilibrium film 0
500
Equilibrium film 100
30
0
5
Time (s)
.
10
25
30
(b)
700
700
20 ppm MIBC 1+80 ppm diesel 20 ppm MIBC 2+80 ppm diesel
20 ppm MIBC 1+120 ppm diesel 20 ppm MIBC 2+120 ppm diesel
600
500
-p
Thickness (nm)
500
ro
600
400
200
5
10
15
Time (s)
20
25
30
100
Film rupture 0
na
(c)
300 200
Film rupture 0
400
re
300
lP
Thickness (nm)
20
of
(a)
100
15
Time (s)
5
10
15
20
25
30
Time (s)
(d)
Jo ur
Figure 5 The thickness at the center point of foam film as a function of time with different diesel concentrations. Insets pictures were the images of foam film which at equilibrium and rupture. Two parallel trials were shown.
21
Journal Pre-proof
Figure 6 Schematic diagrams of bridging-stretching mechanism of foam film rupture by diesel
Jo ur
na
lP
re
-p
ro
of
droplets
22
Journal Pre-proof
of
Figure 7 Schematic of the interactions between diesel droplets and MIBC molecules in the flotation
Jo ur
na
lP
re
-p
ro
column
23
Journal Pre-proof
Deforming effect of diesel Formation of oil-bridge
diesel Competitive adsorption
Jo ur
na
lP
re
-p
ro
of
Deforming mechanism
24
Jo ur
na
lP
re
-p
ro
of
Journal Pre-proof
25
Journal Pre-proof Table 1 Proximate analysis of the high-metamorphosed anthracite Vdaf (%) 27.57
na
lP
re
-p
ro
of
Aad (%) 21.95
Jo ur
Mad (%) 4.86
26
FCdaf (%) 45.62
Journal Pre-proof
Table 2 Particle size distributions of the coal samples Yield, %
Ash,%
0.25-0.125 0.125-0.074 0.074-0.045 -0.045 Total
20.09 23.90 17.41 38.59 100
16.99 18.61 20.24 27.49 22.00
Positive cumulative Yield, % Ash,% 20.09 16.99 44.00 17.87 61.41 18.54 100.00 22.00
Jo ur
na
lP
re
-p
ro
of
Size, mm
27
Negative cumulative Yield, % Ash,% 100.00 22.00 79.91 23.26 56.00 25.24 38.59 27.49
Journal Pre-proof
Table 3 The surface tension and oil-film spreading pressure of MIBC-diesel solutions in the presence of 20 ppm MIBC Diesel concentration (ppm) 0 20 40 80 120
Surface tension, σ (mN/m) 71.66 ± 0.04 71.50 ± 0.08 70.07 ± 0.40 65.52 ± 0.51 62.76 ± 0.56
Spreading pressure, σ (mN/m) 0.00 -0.16 1.59 6.14 8.90
na
lP
re
-p
ro
Effect of diesel on froth stability in coal flotation was studied. Froth stability first increased then decreased as diesel increased. Oil-bridge was formed in foam film leading to film rupture. Oil-film spreading pressure increased as diesel increased.
Jo ur
of
Highlights
28
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7