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The relation between hydrophobic flocculation and combustion characteristics of coal
FUPROC-04495; No of Pages 6 Fuel Processing Technology xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Fuel Processing Technology journal homepage: www.elsevier.com/locate/fuproc
The relation between hydrophobic flocculation and combustion characteristics of coal S. Duzyol a,⁎, C. Sensogut b a b
Department of Mining Engineering, Selcuk University, 42075 Konya, Turkey Department of Mining Engineering, Dumlupinar University, 43100 Kutahya, Turkey
a r t i c l e
i n f o
Article history: Received 15 January 2015 Received in revised form 18 March 2015 Accepted 24 March 2015 Available online xxxx Keywords: Coal Hydrophobic flocculation Contact angle TGA DTGA
a b s t r a c t The hydrophobic flocculation of the lignite obtained from the Ermenek region was investigated under the different operating parameters such as pH, sodium silicate concentration and kerosene concentration in the present work. Determination of combustible recovery, ash content and zeta potential values were utilized in order to make sense of the hydrophobic flocculation behavior. To specify indirectly the hydrophobicity degree of the coal, contact angle measurements were performed on the flocks obtained from the experiments. The combustion characteristics of coal such as thermogravimetric analysis (TGA) and differential thermogravimetric analysis (DTGA), ignition temperature, and peak temperature were analyzed and correlated with the hydrophobic flocculation. In consequence, optimum pH value was determined as to be 4; optimum sodium silicate and kerosene concentration were also ascertained as to be 1 kg/t and 16 kg/t, respectively. When experimental conditions were set up optimally, the flocks were obtained with combustible recovery of 90% and ash content of 9.8%. The strong correlation was observed between the hydrophobic flocculation results and ignition temperatures and peak temperatures acquired from the DTGA curves. The surface tension of solution, however, showed no remarkable changing. It was confirmed that the contact angle values ranged from 114° to 130° and the surfaces were highly hydrophobic. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Hydrophobic flocculation is one of the aggregation methods based on the flocculation of hydrophobic fine particles in aqueous suspension. A particular mineral can be flocculated using specific collector/flocculant which is preferentially absorbed onto it, leaving the remainder of the particles in a suspension to achieve the selectivity. Sufficient kinetic energy is provided mechanically for the collision of hydrophobic particles to each other and surmount energy barrier between them owing to the electric double layer repulsion and water films. In addition, particle hydrophobicity can be enhanced by adding non-polar oil for hydrophobic surfaces. Owing to that, the hydrophobic flocs occurred and separated from the undesired dispersed materials [1]. The separation of fine coal from the impurities relies on the differences of surface properties between organic and mineral matter. Dispersants are usually used to increase the selectivity of the particles from being flocculated with the hydrophobic particles. Sodium silicate, sodium polystyrene sulfonate, tannic acid, sodium hexametaphosphate, sodium phosphate and sodiumpyrophosphate are some common dispersants.
⁎ Corresponding author. Tel.: +90 332 2232043; fax: +90 332 2410635. E-mail address: [email protected] (S. Duzyol).
Selective flocculation of coal from impurities has been studied by a number of authors [2–6]. Thermogravimetric analysis (TGA) is an analytical technique used to determine the characterization of coal for combustion. This analytical technique is based on the mass change of a sample as a function of temperature in the scanning mode or as a function of time in the isothermal mode [7]. This mechanism also provides the information about the purity of the sample, as well as its water, carbonate and organic content. When the material is subjected to heating or cooling, its chemical composition and crystal structure undergo such changes as reaction, oxidation, decomposition, fusion, expansion, contraction, crystallization or phase transition [8]. All these changes can be uncovered using differential thermal analysis. A derivative weight loss curve can be used to find out the points of the ignition temperature and peak temperature at which the weight loss is most apparent [9,10]. TGA has been extensively used by several researchers for investigation of basic combustion properties of solid fuels [11–14]. The purpose of the present work is to investigate the hydrophobic flocculation of coal in association with the other physical properties of coal such as zeta potential and hydrophobicity and to analyze the combustion characteristics of flocks. The correlation between hydrophobic flocculation and ignition temperatures, and DTG peak temperatures were also investigated and the results were interpreted comparatively.
http://dx.doi.org/10.1016/j.fuproc.2015.03.021 0378-3820/© 2015 Elsevier B.V. All rights reserved.
Please cite this article as: S. Duzyol, C. Sensogut, The relation between hydrophobic flocculation and combustion characteristics of coal, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.03.021
2
S. Duzyol, C. Sensogut / Fuel Processing Technology xxx (2015) xxx–xxx
Fig. 1. Schematic representation of experimental procedure.
2. Experimental 2.1. Materials Coal sample from Ermenek region was used to realize the hydrophobic flocculation experiments. The whole coal collected from the underground mine was ground by a steel ball mill. Cone and quarter and
gridding methods were utilized to obtain representative sample. The particle size of the coal was −200 μm with an ash content of 16.4%. Sodium silicate (Na2SiO3) was used as a dispersant and kerosene was employed as a collector. Sodium hydroxide (NaOH) and hydrochloric acid (HCl) were prepared as 1% and 5% (w/w) solutions for modification of pH values of the suspensions and measured by a Jenco 6230 model digital pH meter. The stirring of suspension was achieved by a
Fig. 2. The contact angle apparatus and the drop of water on the pellet surface.
Please cite this article as: S. Duzyol, C. Sensogut, The relation between hydrophobic flocculation and combustion characteristics of coal, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.03.021
S. Duzyol, C. Sensogut / Fuel Processing Technology xxx (2015) xxx–xxx
3
Fig. 3. The thermogravimetric analysis testing apparatus.
0.000
100 90 80
o
-0.005
207 C
70
TG cu
60
rv e
50
rv e
ignition temperature
A cu
-0.010
A
D TG
2.2.1. Hydrophobic flocculation experiments A volume of 400 cm3 of glass beaker with four baffles on the interior surface was used to carry out the hydrophobic flocculation experiments. These baffles were attached in order to obtain a maximum collision efficiency of the suspended particles and to provide a homogeneous distribution of solution. Five grams of coal sample and 300 cm3 water were used in each experiment. The pH of the solution was adjusted to the desired value before the starting of hydrophobic experiments. After the 5 min of pH regulation, sodium silicate was added and the suspension was stirred for a period of 3 min. Then, kerosene and 100 cm3 of water were contemporaneously added. After the suspension was conditioned with kerosene for 3 min, the stirring speed was reduced to 180 rpm for 3 min to let the flocs growth. The stirring speed was arranged for 1000 rpm during the experiments except from flock growth period. The kerosene was added in case of water–oil emulsion to increase the surface area of oil. The schematic representation of experimental procedure was given in Fig. 1. After the experiments, the hydrophobic flocks were rolled up the upper part of the beaker. The unflocculated materials were decanted by using special unit and the remained flocks were collected. The obtained flocks were filtered and dried at 105 °C for 4 h in an oven and then weighed to quantify the percentage of flocculated material. The ash content of hydrophobic flocks was determined and the combustible recovery (CR%) of flocks is calculated using the following formula (1).
40
-0.015
30 20
o
M ð1−Ac Þ CR% ¼ c M f ð1−A f Þ
ð1Þ
where Ac is the ash content of clean coal, Af is the ash content of feed, Mc is mass of clean coal and Mf is mass of feed.
Weight Loss, %
2.2. Experimental procedures
2.2.2. Zeta potential measurements Zeta potential measurements were carried out using a Zeta Plus analyzer produced by Brookhaven Company having measurable range of zeta potential in between − 150 and + 150 mV with a standard deviation of 2 mV. Zeta Plus analyzer employs electrophoretic method to measure the zeta potential. After the hydrophobic flocculation experiments, a certain amount of solution was stored to qualify the zeta potential measurements. The solution was filled into an acrylic cell with 1.5 ml volume. The acrylic cell was then placed to the zeta potential analyzer and the zeta potential value was recorded directly from the instrument. The zeta potential measurements were repeated for four times to get concurrent reading and typical standard deviation was in the order of 0.21%.
d/dt
mechanical stirrer. Distilled water was used for preparing chemical solutions and the entire hydrophobic flocculation experiments.
497 C peak temperature
-0.020 0
100
200
300 400 500 600 Temperature, o C
700
800
10 900
Fig. 4. Typical TGA and DTGA curves of lignite sample.
Please cite this article as: S. Duzyol, C. Sensogut, The relation between hydrophobic flocculation and combustion characteristics of coal, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.03.021
4
S. Duzyol, C. Sensogut / Fuel Processing Technology xxx (2015) xxx–xxx
Temperature, C
500
400
o
400
peak temperature
80
250 200 100
80
60
15
40
10
20
5
combustible recovery ash
combustible recovery ash
60
20 40
15
20
Ash, %
Combustible Recovery, %
ignition temperature 200
10
0
5 4
6
-10
Ash, %
300
ignition temperature
Zeta Potential, mV
peak temperature
300
100
350
Combustible Recovery, %
o
8
10
pH
Zeta Potential, mV
Temperature, C
450
0
0 0
-5
2
4 6 8 Sodium Silicate Concentration, kg/t
10
-10 -15
Fig. 6. Variations of combustible recovery, ash content, zeta potential, ignition point and peak temperatures of flocks with the sodium silicate concentration (pH 4, kerosene conc. = 80 kg/t).
-20 -30 -40
Fig. 5. Variations of combustible recovery, ash content, zeta potential, ignition point and peak temperatures of flocks with the pH (kerosene conc. = 80 kg/t, sodium silicate conc. = 2 kg/t).
2.2.3. Contact angle measurements KSV CAM 101 contact angle goniometer was utilized for contact angle measurements. The pellets of the flocculated coal particles obtained from the experiments were prepared by using a hydraulic press under the 20 kN constant pressure in order to obtain highly smooth surfaces. The water was dropped on to the unpolished pellet surface with a special syringe and the static contact angle was measured. Each contact angle data presented in this paper was the average values approved from at least four measurements and maximum standard deviation among the measured values of contact angles was observed 2.4° with reproducibility. The contact angle apparatus and the drop of water on the pellet surface were given in Fig. 2.
Fig. 3. Ten milligrams of samples was spread uniformly on the bottom of the platinum crucible. The samples were heated up to 900 °C at a constant rate of 10 °C/min in a 5 mL/min flow of dry air. The ignition temperatures and peak temperatures of the samples were calculated using DTGA curves according to the formula (2) given below. T final −T inital dW ¼ dt t final −t inital
ð2Þ
where T is temperature (°C), t is time (min) and W is weight of sample. The peak temperature and the ignition temperatures of the lignite sample can be determined from the burning profile and the DTGA curve. Typical DTGA curve of lignite coal was given in Fig. 4. The ignition temperatures and peak temperatures were determined to be 207 °C and 497 °C, respectively from the DTGA curve. These values were very close to the values encountered in the literature [10]. It is stated from the literature that the lower the maximum peak temperature is an indicative of the more reactive a coal may be considered [15–17,10]. 3. Results and discussion
2.2.4. Thermogravimetric analyses The thermogravimetric analysis was performed using a Polymer Laboratories PL-TGA 1500 thermal analyzer as the setup presented in
The effect of pH on the hydrophobic flocculation of coal was investigated at a wide range of pH values and obtained results are given in Fig. 5. The sodium silicate concentration and kerosene concentration were kept constant as to be 80 kg/t and 2 kg/t of coal, respectively. It
Table 1 The measured contact angle values of coal and surface tension of solution at different pH levels.
Table 2 The measured contact angle values of coal and surface tension of solution at a variety of sodium silicate concentrations.
pH
3
4
6.2
8
10
Na2SiO3 conc., kg/t
0
1
2
4
10
Contact angle, degree Surface tension, mN/m
123 71.9
126 71.6
124 71.3
129 71.8
122 71.6
Contact angle, degree Surface tension, mN/m
114 71.8
114 71.6
126 71.4
130 71.6
121 71.7
Please cite this article as: S. Duzyol, C. Sensogut, The relation between hydrophobic flocculation and combustion characteristics of coal, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.03.021
S. Duzyol, C. Sensogut / Fuel Processing Technology xxx (2015) xxx–xxx
450
Temperature, C
400 o
350 peak temperature
300
ignition temperature 250 200
80
60
15
40
10
20
5
combustible recovery ash
Zeta Potential, mV
Ash, %
Combustible Recovery, %
100
0
0 0
40
80 120 Kerosene Concentration, kg/t
160
-5
-10
Fig. 7. Variations of combustible recovery, ash content, zeta potential, ignition point and peak temperatures of flocks with the kerosene concentration (pH 4, sodium silicate conc. = 2 kg/t).
can be seen in Fig. 5, the ash content of hydrophobic flocks was low at lower pH values. However, the combustible recoveries of flocks were determined to be high at low pH values. A maximum combustible recovery value of 90% was achieved at pH 4 while the ash content was 10.16% at this level of pH. In addition, the zeta potentials of particles were negative at all pH values. At pH 4, the zeta potential of particle surfaces was determined as to be − 7.5 mV in comparison with the value of −21.4 mV measured at pH 6.2 which is the natural pH value of the suspension. In alkali solutions, the high ash content of flocks indicates that the hydrophobic interaction between the coal particles almost loses its selectivity due to the strong electrostatic interactions and the greater zeta potential of particles increased the electrostatic repulsion between the particles [18,19]. Consequently, a low combustible recovery was obtained similar to other works in the literature [20, 21]. At a low pH, H+ is adsorbed onto the particle surface and the zeta potential of particles is positive or the magnitude of zeta potential value is less negative. In contrast, if the pH is high, H+ is released from the particle surface, and the zeta potential becomes more negative. The low zeta potential indicates that these particles have very little surface charge thus lacking sufficient electrostatic repulsion to prevent Table 3 The measured contact angle values of coal and surface tension of solution at a variety of kerosene concentrations. Kerosene conc., kg/t
0
16
80
160
Contact angle, degree Surface tension, mN/m
115 71.7
118 71.6
114 71.8
123 71.7
5
particles from hydrophobic flocculation [22] from the knowledge of DLVO (Derjaguin–Landau–Verwey–Overbeek) theory [23]. It is also known that the pH is the most important parameter controlling the surface potential of coal surfaces [24]. However, the hydrophobic interaction between the hydrophobic particles shows strong attraction in aqueous solution and arises due to the re-arrangements of hydrogen bond configurations in the overlapping solvation zones as two hydrophobic species coming together [25]. It is also reported in the literature that the hydrophobic force is one or two orders of magnitude larger than the DLVO forces in some range of particle separation [26,27]. As a result, hydrophobic attraction is a dominant factor for interaction between hydrophobic particles in aqueous solution. The determined ignition temperatures and the peak temperatures of flocks were also given in Fig. 5. The peak temperatures of flocks were decreased with decreasing the pH of suspension. At high temperatures (600–800 °C) which are defined as secondary de-volatilization period, further bond breaking occurs and evolution of organic matter, gases [13] with remaining ash at the end. A high peak temperature is an indicator for less reactive coal. These peak temperatures and ignition temperatures of flocks showed strong correlation with ash content. The contact angles of particles and surface tension of solutions were also measured and given in Table 1 at the same pH values. The hydrophobic flocks have high contact angle values at all pH values. The higher contact angle indicates the higher hydrophobicity of coal particles. Choung and his co-workers [28] reported that the main parameter of fine coal beneficiation is surface hydrophobicity. Also in some previous experiments, it was reported the higher contact angle recorded for the high particle hydrophobicity enhancing the recovery of minerals [29–31]. The surface tension of solution showed no remarkable changing. Hence, the optimum pH value of the suspension was selected as to be 4 due to having the lowest ash content and the highest combustible recovery. The effect of sodium silicate concentration on the hydrophobic flocculation of coal was also investigated in the presence of 80 kg/t kerosene at pH 4 and the acquired results were presented in Fig. 6. The slight increase was observed in the combustible recovery with a raise in the sodium silicate, however, the conspicuous decrease was seen in the ash content at a concentration of 1 kg/t. The ash content of hydrophobic flocks was determined to be 10.74%. Therefore 1 kg/t of the concentration of the sodium silicate was selected to be optimum. In addition, the surface potential was raised with the increasing sodium silicate concentration. Similar behavior for albite mineral was reported [32] in the literature. However, the increase of the zeta potential showed no negative effect on the hydrophobicity of flocks. The ignition temperatures and the peak temperatures of flocks were determined and presented in Fig. 6. However, these values showed no significant variation. The measured contact angles of hydrophobic coal flocks and surface tension of solutions were also given in Table 2. The contact angle values were recorded high as 130° at 4 kg/t and the surface tensions of solutions were nearly the same at all concentrations of sodium silicate. Fig. 7 illustrates the effect of kerosene concentration on the hydrophobic flocculation in the presence of 1 kg/t sodium silicate concentration at pH 4. Small amount of kerosene addition enhanced the hydrophobic flocculation and reached the minimum ash content at 16 kg/t of kerosene concentration. Slight increase was seen in the combustible recovery and no remarkable change was seen in the surface potential of coal. Fig. 7 also shows the ignition temperatures and the peak temperatures of flocks. The peak temperature value was fairly high at the absence of kerosene and determined to be 442 °C. With an exception of this value, no notable difference was seen in the measurements. The contact angles of hydrophobic flocks were high enough causing flocculation without any remarkable variation in the surface tension of the suspension, which may be observed in Table 3.
Please cite this article as: S. Duzyol, C. Sensogut, The relation between hydrophobic flocculation and combustion characteristics of coal, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.03.021
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S. Duzyol, C. Sensogut / Fuel Processing Technology xxx (2015) xxx–xxx
4. Conclusions The hydrophobic flocculation experiments were conducted on the Ermenek lignite. The effects of pH, sodium silicate concentration and kerosene concentration on the hydrophobic flocculation behavior were investigated in detail. The combustion characteristics of coal were also analyzed by using TGA and DTGA. The optimum operating parameters such as pH, sodium silicate concentration and kerosene concentration were determined as 4 kg/t, 1 kg/t, and 16 kg/t, respectively for hydrophobic flocculation. The hydrophobic flocks were achieved with combustible recovery of 90% and ash content of 9.8%. The ignition temperature and the peak temperature of flocks were also determined to be 205 °C and 394 °C, respectively. The contact angle measurements showed the flock surfaces with high hydrophobicity. The surface tensions of solutions were almost the same at all experimental conditions. Strong correlation was observed between the hydrophobic flocculation and thermogravimetric results. The ignition temperatures and peak temperature of flock were strongly dependent on its ash content. Acknowledgment The authors greatly acknowledge the financial support provided by the Scientific Research Project Fund of Selcuk University. References [1] S. Song, A. Lopez-Valdivieso, Hydrophobic flocculation flotation for beneficiating fine coal and minerals, Sep. Sci. Technol. 33 (1998) 1195–1212. [2] Z. Xu, R. Yoon, The role of hydrophobic interactions in coagulation, J. Colloid Interface Sci. 132 (1989) 532–541. [3] L.J. Warren, Colloid Chemistry in Mineral Processing, in: J.S. Laskowski, J. Ralston (Eds.), Elsevier, Amsterdam 1992, pp. 309–329. [4] J. Skvarla, On the decay of polar surface forces between hydrophobic surfaces and colloids: 1. Coagulation, J. Colloid Interface Sci. 155 (1993) 506–508. [5] S. Song, O. Trass, Floc flotation of Prince coal with simultaneous grinding and hydrophobic flocculation in a Szego mill, Fuel 76 (1997) 839–844. [6] Z. Yu, Flocculation, hydrophobic agglomeration and filtration of ultrafine coal(PhD thesis) The University of British Columbia, 1998. 246. [7] B. Feng, S.K. Bhatia, On the validity of thermogravimetric determination of carbon gasification kinetics, Chem. Eng. Sci. 57 (2002) 2907–2920. [8] P.J. Haines, Thermal Methods of Analysis: Principles, Applications and Problems, Blackie Academic and Professional, England, 1995. [9] J.W. Cumming, J. McLaughlin, The thermogravimetric behaviour of coal, Thermochim. Acta 57 (1982) 253–272. [10] C. Sensogut, H. Ozsen, A. Demirbas, Combustion characteristics of 24 lignite samples, Energy Sources A Recover. Util. Environ. Eff. 30 (5) (2008) 420–428.
[11] J. Podder, T. Hossain, Kh.M. Mannan, An investigation into the thermal behaviour of Bangladeshi coals, Thermochim. Acta 255 (1995) 221–226. [12] N. Choudhury, P. Boral, T. Mitra, A.K. Adak, A. Choudhury, P. Sarkar, Assessment of nature and distribution of inertinite in Indian coals for burning characteristics, Int. J. Coal Geol. 72 (2007) 141–152. [13] T. Das, B.K. Saikia, D.K. Dutta, D. Bordoloi, B.P. Baruah, Agglomeration of low rank Indian coal fines with an organic binder and the thermal behaviour of the agglomerate produced: part I, Fuel 147 (2014) 269–278. [14] B. Li, G. Chen, H. Zhang, C. Sheng, Development of non-isothermal TGA–DSC for kinetics analysis of low temperature coal oxidation prior to ignition, Fuel 118 (2014) 385–391. [15] J.W. Cumming, Reactivity assessment of coals via a weighted mean activation energy, Fuel 63 (1984) 1436–1440. [16] W.A. Kneller, Physicochemical characterization of coal and coal reactivity: a review, Thermochim. Acta 108 (1986) 357–388. [17] N.B. Sarkar, P. Sarkar, A. Choudhury, Effect of hydrothermal treatment of coal on the oxidation susceptibility and electrical resistivity, Fuel Process. Technol. 86 (5) (2005) 487–497. [18] O. Ozdemir, E. Taran, M.A. Hampton, S.I. Karakashev, A.V. Nguyen, Surface chemistry aspects of coal flotation in bore water, Int. J. Miner. Process. 92 (2009) 177–183. [19] S. Duzyol, C. Sensogut, A.O. Aksu, H.S. Erisir, K. Aspir, Benefication of Tuncbilek lignites by oil agglomeration, in: M.E. Bilir, K. Kel, E. Kaymakci (Eds.),Proceedings of the 19th Coal Congress of Turkey, Zonguldak/Turkey 2014, pp. 237–244 (in Turkish). [20] J. Pinerres, J. Barazza, Energy barrier of aggregates coal particle–bubble through the extended DLVO theory, Int. J. Miner. Process. 100 (2011) 14–20. [21] J. Pinerres, J. Barazza, Effect of pH, air velocity and frother concentration on combustible recovery, ash and sulphur rejection using column flotation, Fuel Process. Technol. 97 (2012) 30–37. [22] R. Xu, C. Wu, H. Xu, Particle size and zeta potential of carbon black in liquid media, Carbon 45 (2007) 2806–2809. [23] E.J.W. Verwey, J.T.G. Overbeek, Theory of the Stability of Lyophobic Colloids 1948, Elsevier; Amsterdam. [24] Y.K. Leong, D.V. Boger, Surface chemistry effects on concentrated suspension rheology, J. Colloid Interface Sci. 136 (1990) 249–258. [25] J.N. Israelachvili, Intermolecular & Surface Forces, 2nd edition Academic Press, London, 1992. [26] R.M. Pashley, P.M. McGuiggan, B.W. Ninham, D.F. Evans, Attractive forces between uncharged hydrophobic surfaces—direct measurements in aqueous-solution, Science 229 (1985) 1088–1089. [27] J.L. Parker, V.V. Yaminsky, P.M. Claesson, Surface forces between glass surfaces in cetyltrimethylammonium bromide solutions, J. Phys. Chem. 97 (1993) 7706–7710. [28] J. Choung, Z. Xu, J. Szymanski, An integrated approach for coal tailings management, Can. J. Chem. Eng. 78 (2000) 780–784. [29] S. Duzyol, A. Ozkan, Role of hydrophobicity and surface tension on shear flocculation and oil agglomeration of magnesite, Sep. Purif. Technol. 72 (2010) 7–12. [30] S. Duzyol, A. Ozkan, Correlation of flocculation and agglomeration of dolomite with its wettability, Sep. Sci. Technol. 46 (2011) 1–6. [31] S. Duzyol, A. Ozkan, Effect of contact angle, surface tension and zeta potential on oil agglomeration of celestite, Miner. Eng. 65 (2014) 74–78. [32] I. Kursun, Determination of flocculation and adsorption-desorption characteristic of Na–feldispar concentrate in the presence of different polymers, Physicochem. Probl. Miner. Process. 44 (2010) 127–142.
Please cite this article as: S. Duzyol, C. Sensogut, The relation between hydrophobic flocculation and combustion characteristics of coal, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.03.021
Contents lists available at ScienceDirect
Fuel Processing Technology journal homepage: www.elsevier.com/locate/fuproc
The relation between hydrophobic flocculation and combustion characteristics of coal S. Duzyol a,⁎, C. Sensogut b a b
Department of Mining Engineering, Selcuk University, 42075 Konya, Turkey Department of Mining Engineering, Dumlupinar University, 43100 Kutahya, Turkey
a r t i c l e
i n f o
Article history: Received 15 January 2015 Received in revised form 18 March 2015 Accepted 24 March 2015 Available online xxxx Keywords: Coal Hydrophobic flocculation Contact angle TGA DTGA
a b s t r a c t The hydrophobic flocculation of the lignite obtained from the Ermenek region was investigated under the different operating parameters such as pH, sodium silicate concentration and kerosene concentration in the present work. Determination of combustible recovery, ash content and zeta potential values were utilized in order to make sense of the hydrophobic flocculation behavior. To specify indirectly the hydrophobicity degree of the coal, contact angle measurements were performed on the flocks obtained from the experiments. The combustion characteristics of coal such as thermogravimetric analysis (TGA) and differential thermogravimetric analysis (DTGA), ignition temperature, and peak temperature were analyzed and correlated with the hydrophobic flocculation. In consequence, optimum pH value was determined as to be 4; optimum sodium silicate and kerosene concentration were also ascertained as to be 1 kg/t and 16 kg/t, respectively. When experimental conditions were set up optimally, the flocks were obtained with combustible recovery of 90% and ash content of 9.8%. The strong correlation was observed between the hydrophobic flocculation results and ignition temperatures and peak temperatures acquired from the DTGA curves. The surface tension of solution, however, showed no remarkable changing. It was confirmed that the contact angle values ranged from 114° to 130° and the surfaces were highly hydrophobic. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Hydrophobic flocculation is one of the aggregation methods based on the flocculation of hydrophobic fine particles in aqueous suspension. A particular mineral can be flocculated using specific collector/flocculant which is preferentially absorbed onto it, leaving the remainder of the particles in a suspension to achieve the selectivity. Sufficient kinetic energy is provided mechanically for the collision of hydrophobic particles to each other and surmount energy barrier between them owing to the electric double layer repulsion and water films. In addition, particle hydrophobicity can be enhanced by adding non-polar oil for hydrophobic surfaces. Owing to that, the hydrophobic flocs occurred and separated from the undesired dispersed materials [1]. The separation of fine coal from the impurities relies on the differences of surface properties between organic and mineral matter. Dispersants are usually used to increase the selectivity of the particles from being flocculated with the hydrophobic particles. Sodium silicate, sodium polystyrene sulfonate, tannic acid, sodium hexametaphosphate, sodium phosphate and sodiumpyrophosphate are some common dispersants.
⁎ Corresponding author. Tel.: +90 332 2232043; fax: +90 332 2410635. E-mail address: [email protected] (S. Duzyol).
Selective flocculation of coal from impurities has been studied by a number of authors [2–6]. Thermogravimetric analysis (TGA) is an analytical technique used to determine the characterization of coal for combustion. This analytical technique is based on the mass change of a sample as a function of temperature in the scanning mode or as a function of time in the isothermal mode [7]. This mechanism also provides the information about the purity of the sample, as well as its water, carbonate and organic content. When the material is subjected to heating or cooling, its chemical composition and crystal structure undergo such changes as reaction, oxidation, decomposition, fusion, expansion, contraction, crystallization or phase transition [8]. All these changes can be uncovered using differential thermal analysis. A derivative weight loss curve can be used to find out the points of the ignition temperature and peak temperature at which the weight loss is most apparent [9,10]. TGA has been extensively used by several researchers for investigation of basic combustion properties of solid fuels [11–14]. The purpose of the present work is to investigate the hydrophobic flocculation of coal in association with the other physical properties of coal such as zeta potential and hydrophobicity and to analyze the combustion characteristics of flocks. The correlation between hydrophobic flocculation and ignition temperatures, and DTG peak temperatures were also investigated and the results were interpreted comparatively.
http://dx.doi.org/10.1016/j.fuproc.2015.03.021 0378-3820/© 2015 Elsevier B.V. All rights reserved.
Please cite this article as: S. Duzyol, C. Sensogut, The relation between hydrophobic flocculation and combustion characteristics of coal, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.03.021
2
S. Duzyol, C. Sensogut / Fuel Processing Technology xxx (2015) xxx–xxx
Fig. 1. Schematic representation of experimental procedure.
2. Experimental 2.1. Materials Coal sample from Ermenek region was used to realize the hydrophobic flocculation experiments. The whole coal collected from the underground mine was ground by a steel ball mill. Cone and quarter and
gridding methods were utilized to obtain representative sample. The particle size of the coal was −200 μm with an ash content of 16.4%. Sodium silicate (Na2SiO3) was used as a dispersant and kerosene was employed as a collector. Sodium hydroxide (NaOH) and hydrochloric acid (HCl) were prepared as 1% and 5% (w/w) solutions for modification of pH values of the suspensions and measured by a Jenco 6230 model digital pH meter. The stirring of suspension was achieved by a
Fig. 2. The contact angle apparatus and the drop of water on the pellet surface.
Please cite this article as: S. Duzyol, C. Sensogut, The relation between hydrophobic flocculation and combustion characteristics of coal, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.03.021
S. Duzyol, C. Sensogut / Fuel Processing Technology xxx (2015) xxx–xxx
3
Fig. 3. The thermogravimetric analysis testing apparatus.
0.000
100 90 80
o
-0.005
207 C
70
TG cu
60
rv e
50
rv e
ignition temperature
A cu
-0.010
A
D TG
2.2.1. Hydrophobic flocculation experiments A volume of 400 cm3 of glass beaker with four baffles on the interior surface was used to carry out the hydrophobic flocculation experiments. These baffles were attached in order to obtain a maximum collision efficiency of the suspended particles and to provide a homogeneous distribution of solution. Five grams of coal sample and 300 cm3 water were used in each experiment. The pH of the solution was adjusted to the desired value before the starting of hydrophobic experiments. After the 5 min of pH regulation, sodium silicate was added and the suspension was stirred for a period of 3 min. Then, kerosene and 100 cm3 of water were contemporaneously added. After the suspension was conditioned with kerosene for 3 min, the stirring speed was reduced to 180 rpm for 3 min to let the flocs growth. The stirring speed was arranged for 1000 rpm during the experiments except from flock growth period. The kerosene was added in case of water–oil emulsion to increase the surface area of oil. The schematic representation of experimental procedure was given in Fig. 1. After the experiments, the hydrophobic flocks were rolled up the upper part of the beaker. The unflocculated materials were decanted by using special unit and the remained flocks were collected. The obtained flocks were filtered and dried at 105 °C for 4 h in an oven and then weighed to quantify the percentage of flocculated material. The ash content of hydrophobic flocks was determined and the combustible recovery (CR%) of flocks is calculated using the following formula (1).
40
-0.015
30 20
o
M ð1−Ac Þ CR% ¼ c M f ð1−A f Þ
ð1Þ
where Ac is the ash content of clean coal, Af is the ash content of feed, Mc is mass of clean coal and Mf is mass of feed.
Weight Loss, %
2.2. Experimental procedures
2.2.2. Zeta potential measurements Zeta potential measurements were carried out using a Zeta Plus analyzer produced by Brookhaven Company having measurable range of zeta potential in between − 150 and + 150 mV with a standard deviation of 2 mV. Zeta Plus analyzer employs electrophoretic method to measure the zeta potential. After the hydrophobic flocculation experiments, a certain amount of solution was stored to qualify the zeta potential measurements. The solution was filled into an acrylic cell with 1.5 ml volume. The acrylic cell was then placed to the zeta potential analyzer and the zeta potential value was recorded directly from the instrument. The zeta potential measurements were repeated for four times to get concurrent reading and typical standard deviation was in the order of 0.21%.
d/dt
mechanical stirrer. Distilled water was used for preparing chemical solutions and the entire hydrophobic flocculation experiments.
497 C peak temperature
-0.020 0
100
200
300 400 500 600 Temperature, o C
700
800
10 900
Fig. 4. Typical TGA and DTGA curves of lignite sample.
Please cite this article as: S. Duzyol, C. Sensogut, The relation between hydrophobic flocculation and combustion characteristics of coal, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.03.021
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S. Duzyol, C. Sensogut / Fuel Processing Technology xxx (2015) xxx–xxx
Temperature, C
500
400
o
400
peak temperature
80
250 200 100
80
60
15
40
10
20
5
combustible recovery ash
combustible recovery ash
60
20 40
15
20
Ash, %
Combustible Recovery, %
ignition temperature 200
10
0
5 4
6
-10
Ash, %
300
ignition temperature
Zeta Potential, mV
peak temperature
300
100
350
Combustible Recovery, %
o
8
10
pH
Zeta Potential, mV
Temperature, C
450
0
0 0
-5
2
4 6 8 Sodium Silicate Concentration, kg/t
10
-10 -15
Fig. 6. Variations of combustible recovery, ash content, zeta potential, ignition point and peak temperatures of flocks with the sodium silicate concentration (pH 4, kerosene conc. = 80 kg/t).
-20 -30 -40
Fig. 5. Variations of combustible recovery, ash content, zeta potential, ignition point and peak temperatures of flocks with the pH (kerosene conc. = 80 kg/t, sodium silicate conc. = 2 kg/t).
2.2.3. Contact angle measurements KSV CAM 101 contact angle goniometer was utilized for contact angle measurements. The pellets of the flocculated coal particles obtained from the experiments were prepared by using a hydraulic press under the 20 kN constant pressure in order to obtain highly smooth surfaces. The water was dropped on to the unpolished pellet surface with a special syringe and the static contact angle was measured. Each contact angle data presented in this paper was the average values approved from at least four measurements and maximum standard deviation among the measured values of contact angles was observed 2.4° with reproducibility. The contact angle apparatus and the drop of water on the pellet surface were given in Fig. 2.
Fig. 3. Ten milligrams of samples was spread uniformly on the bottom of the platinum crucible. The samples were heated up to 900 °C at a constant rate of 10 °C/min in a 5 mL/min flow of dry air. The ignition temperatures and peak temperatures of the samples were calculated using DTGA curves according to the formula (2) given below. T final −T inital dW ¼ dt t final −t inital
ð2Þ
where T is temperature (°C), t is time (min) and W is weight of sample. The peak temperature and the ignition temperatures of the lignite sample can be determined from the burning profile and the DTGA curve. Typical DTGA curve of lignite coal was given in Fig. 4. The ignition temperatures and peak temperatures were determined to be 207 °C and 497 °C, respectively from the DTGA curve. These values were very close to the values encountered in the literature [10]. It is stated from the literature that the lower the maximum peak temperature is an indicative of the more reactive a coal may be considered [15–17,10]. 3. Results and discussion
2.2.4. Thermogravimetric analyses The thermogravimetric analysis was performed using a Polymer Laboratories PL-TGA 1500 thermal analyzer as the setup presented in
The effect of pH on the hydrophobic flocculation of coal was investigated at a wide range of pH values and obtained results are given in Fig. 5. The sodium silicate concentration and kerosene concentration were kept constant as to be 80 kg/t and 2 kg/t of coal, respectively. It
Table 1 The measured contact angle values of coal and surface tension of solution at different pH levels.
Table 2 The measured contact angle values of coal and surface tension of solution at a variety of sodium silicate concentrations.
pH
3
4
6.2
8
10
Na2SiO3 conc., kg/t
0
1
2
4
10
Contact angle, degree Surface tension, mN/m
123 71.9
126 71.6
124 71.3
129 71.8
122 71.6
Contact angle, degree Surface tension, mN/m
114 71.8
114 71.6
126 71.4
130 71.6
121 71.7
Please cite this article as: S. Duzyol, C. Sensogut, The relation between hydrophobic flocculation and combustion characteristics of coal, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.03.021
S. Duzyol, C. Sensogut / Fuel Processing Technology xxx (2015) xxx–xxx
450
Temperature, C
400 o
350 peak temperature
300
ignition temperature 250 200
80
60
15
40
10
20
5
combustible recovery ash
Zeta Potential, mV
Ash, %
Combustible Recovery, %
100
0
0 0
40
80 120 Kerosene Concentration, kg/t
160
-5
-10
Fig. 7. Variations of combustible recovery, ash content, zeta potential, ignition point and peak temperatures of flocks with the kerosene concentration (pH 4, sodium silicate conc. = 2 kg/t).
can be seen in Fig. 5, the ash content of hydrophobic flocks was low at lower pH values. However, the combustible recoveries of flocks were determined to be high at low pH values. A maximum combustible recovery value of 90% was achieved at pH 4 while the ash content was 10.16% at this level of pH. In addition, the zeta potentials of particles were negative at all pH values. At pH 4, the zeta potential of particle surfaces was determined as to be − 7.5 mV in comparison with the value of −21.4 mV measured at pH 6.2 which is the natural pH value of the suspension. In alkali solutions, the high ash content of flocks indicates that the hydrophobic interaction between the coal particles almost loses its selectivity due to the strong electrostatic interactions and the greater zeta potential of particles increased the electrostatic repulsion between the particles [18,19]. Consequently, a low combustible recovery was obtained similar to other works in the literature [20, 21]. At a low pH, H+ is adsorbed onto the particle surface and the zeta potential of particles is positive or the magnitude of zeta potential value is less negative. In contrast, if the pH is high, H+ is released from the particle surface, and the zeta potential becomes more negative. The low zeta potential indicates that these particles have very little surface charge thus lacking sufficient electrostatic repulsion to prevent Table 3 The measured contact angle values of coal and surface tension of solution at a variety of kerosene concentrations. Kerosene conc., kg/t
0
16
80
160
Contact angle, degree Surface tension, mN/m
115 71.7
118 71.6
114 71.8
123 71.7
5
particles from hydrophobic flocculation [22] from the knowledge of DLVO (Derjaguin–Landau–Verwey–Overbeek) theory [23]. It is also known that the pH is the most important parameter controlling the surface potential of coal surfaces [24]. However, the hydrophobic interaction between the hydrophobic particles shows strong attraction in aqueous solution and arises due to the re-arrangements of hydrogen bond configurations in the overlapping solvation zones as two hydrophobic species coming together [25]. It is also reported in the literature that the hydrophobic force is one or two orders of magnitude larger than the DLVO forces in some range of particle separation [26,27]. As a result, hydrophobic attraction is a dominant factor for interaction between hydrophobic particles in aqueous solution. The determined ignition temperatures and the peak temperatures of flocks were also given in Fig. 5. The peak temperatures of flocks were decreased with decreasing the pH of suspension. At high temperatures (600–800 °C) which are defined as secondary de-volatilization period, further bond breaking occurs and evolution of organic matter, gases [13] with remaining ash at the end. A high peak temperature is an indicator for less reactive coal. These peak temperatures and ignition temperatures of flocks showed strong correlation with ash content. The contact angles of particles and surface tension of solutions were also measured and given in Table 1 at the same pH values. The hydrophobic flocks have high contact angle values at all pH values. The higher contact angle indicates the higher hydrophobicity of coal particles. Choung and his co-workers [28] reported that the main parameter of fine coal beneficiation is surface hydrophobicity. Also in some previous experiments, it was reported the higher contact angle recorded for the high particle hydrophobicity enhancing the recovery of minerals [29–31]. The surface tension of solution showed no remarkable changing. Hence, the optimum pH value of the suspension was selected as to be 4 due to having the lowest ash content and the highest combustible recovery. The effect of sodium silicate concentration on the hydrophobic flocculation of coal was also investigated in the presence of 80 kg/t kerosene at pH 4 and the acquired results were presented in Fig. 6. The slight increase was observed in the combustible recovery with a raise in the sodium silicate, however, the conspicuous decrease was seen in the ash content at a concentration of 1 kg/t. The ash content of hydrophobic flocks was determined to be 10.74%. Therefore 1 kg/t of the concentration of the sodium silicate was selected to be optimum. In addition, the surface potential was raised with the increasing sodium silicate concentration. Similar behavior for albite mineral was reported [32] in the literature. However, the increase of the zeta potential showed no negative effect on the hydrophobicity of flocks. The ignition temperatures and the peak temperatures of flocks were determined and presented in Fig. 6. However, these values showed no significant variation. The measured contact angles of hydrophobic coal flocks and surface tension of solutions were also given in Table 2. The contact angle values were recorded high as 130° at 4 kg/t and the surface tensions of solutions were nearly the same at all concentrations of sodium silicate. Fig. 7 illustrates the effect of kerosene concentration on the hydrophobic flocculation in the presence of 1 kg/t sodium silicate concentration at pH 4. Small amount of kerosene addition enhanced the hydrophobic flocculation and reached the minimum ash content at 16 kg/t of kerosene concentration. Slight increase was seen in the combustible recovery and no remarkable change was seen in the surface potential of coal. Fig. 7 also shows the ignition temperatures and the peak temperatures of flocks. The peak temperature value was fairly high at the absence of kerosene and determined to be 442 °C. With an exception of this value, no notable difference was seen in the measurements. The contact angles of hydrophobic flocks were high enough causing flocculation without any remarkable variation in the surface tension of the suspension, which may be observed in Table 3.
Please cite this article as: S. Duzyol, C. Sensogut, The relation between hydrophobic flocculation and combustion characteristics of coal, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.03.021
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S. Duzyol, C. Sensogut / Fuel Processing Technology xxx (2015) xxx–xxx
4. Conclusions The hydrophobic flocculation experiments were conducted on the Ermenek lignite. The effects of pH, sodium silicate concentration and kerosene concentration on the hydrophobic flocculation behavior were investigated in detail. The combustion characteristics of coal were also analyzed by using TGA and DTGA. The optimum operating parameters such as pH, sodium silicate concentration and kerosene concentration were determined as 4 kg/t, 1 kg/t, and 16 kg/t, respectively for hydrophobic flocculation. The hydrophobic flocks were achieved with combustible recovery of 90% and ash content of 9.8%. The ignition temperature and the peak temperature of flocks were also determined to be 205 °C and 394 °C, respectively. The contact angle measurements showed the flock surfaces with high hydrophobicity. The surface tensions of solutions were almost the same at all experimental conditions. Strong correlation was observed between the hydrophobic flocculation and thermogravimetric results. The ignition temperatures and peak temperature of flock were strongly dependent on its ash content. Acknowledgment The authors greatly acknowledge the financial support provided by the Scientific Research Project Fund of Selcuk University. References [1] S. Song, A. Lopez-Valdivieso, Hydrophobic flocculation flotation for beneficiating fine coal and minerals, Sep. Sci. Technol. 33 (1998) 1195–1212. [2] Z. Xu, R. Yoon, The role of hydrophobic interactions in coagulation, J. Colloid Interface Sci. 132 (1989) 532–541. [3] L.J. Warren, Colloid Chemistry in Mineral Processing, in: J.S. Laskowski, J. Ralston (Eds.), Elsevier, Amsterdam 1992, pp. 309–329. [4] J. Skvarla, On the decay of polar surface forces between hydrophobic surfaces and colloids: 1. Coagulation, J. Colloid Interface Sci. 155 (1993) 506–508. [5] S. Song, O. Trass, Floc flotation of Prince coal with simultaneous grinding and hydrophobic flocculation in a Szego mill, Fuel 76 (1997) 839–844. [6] Z. Yu, Flocculation, hydrophobic agglomeration and filtration of ultrafine coal(PhD thesis) The University of British Columbia, 1998. 246. [7] B. Feng, S.K. Bhatia, On the validity of thermogravimetric determination of carbon gasification kinetics, Chem. Eng. Sci. 57 (2002) 2907–2920. [8] P.J. Haines, Thermal Methods of Analysis: Principles, Applications and Problems, Blackie Academic and Professional, England, 1995. [9] J.W. Cumming, J. McLaughlin, The thermogravimetric behaviour of coal, Thermochim. Acta 57 (1982) 253–272. [10] C. Sensogut, H. Ozsen, A. Demirbas, Combustion characteristics of 24 lignite samples, Energy Sources A Recover. Util. Environ. Eff. 30 (5) (2008) 420–428.
[11] J. Podder, T. Hossain, Kh.M. Mannan, An investigation into the thermal behaviour of Bangladeshi coals, Thermochim. Acta 255 (1995) 221–226. [12] N. Choudhury, P. Boral, T. Mitra, A.K. Adak, A. Choudhury, P. Sarkar, Assessment of nature and distribution of inertinite in Indian coals for burning characteristics, Int. J. Coal Geol. 72 (2007) 141–152. [13] T. Das, B.K. Saikia, D.K. Dutta, D. Bordoloi, B.P. Baruah, Agglomeration of low rank Indian coal fines with an organic binder and the thermal behaviour of the agglomerate produced: part I, Fuel 147 (2014) 269–278. [14] B. Li, G. Chen, H. Zhang, C. Sheng, Development of non-isothermal TGA–DSC for kinetics analysis of low temperature coal oxidation prior to ignition, Fuel 118 (2014) 385–391. [15] J.W. Cumming, Reactivity assessment of coals via a weighted mean activation energy, Fuel 63 (1984) 1436–1440. [16] W.A. Kneller, Physicochemical characterization of coal and coal reactivity: a review, Thermochim. Acta 108 (1986) 357–388. [17] N.B. Sarkar, P. Sarkar, A. Choudhury, Effect of hydrothermal treatment of coal on the oxidation susceptibility and electrical resistivity, Fuel Process. Technol. 86 (5) (2005) 487–497. [18] O. Ozdemir, E. Taran, M.A. Hampton, S.I. Karakashev, A.V. Nguyen, Surface chemistry aspects of coal flotation in bore water, Int. J. Miner. Process. 92 (2009) 177–183. [19] S. Duzyol, C. Sensogut, A.O. Aksu, H.S. Erisir, K. Aspir, Benefication of Tuncbilek lignites by oil agglomeration, in: M.E. Bilir, K. Kel, E. Kaymakci (Eds.),Proceedings of the 19th Coal Congress of Turkey, Zonguldak/Turkey 2014, pp. 237–244 (in Turkish). [20] J. Pinerres, J. Barazza, Energy barrier of aggregates coal particle–bubble through the extended DLVO theory, Int. J. Miner. Process. 100 (2011) 14–20. [21] J. Pinerres, J. Barazza, Effect of pH, air velocity and frother concentration on combustible recovery, ash and sulphur rejection using column flotation, Fuel Process. Technol. 97 (2012) 30–37. [22] R. Xu, C. Wu, H. Xu, Particle size and zeta potential of carbon black in liquid media, Carbon 45 (2007) 2806–2809. [23] E.J.W. Verwey, J.T.G. Overbeek, Theory of the Stability of Lyophobic Colloids 1948, Elsevier; Amsterdam. [24] Y.K. Leong, D.V. Boger, Surface chemistry effects on concentrated suspension rheology, J. Colloid Interface Sci. 136 (1990) 249–258. [25] J.N. Israelachvili, Intermolecular & Surface Forces, 2nd edition Academic Press, London, 1992. [26] R.M. Pashley, P.M. McGuiggan, B.W. Ninham, D.F. Evans, Attractive forces between uncharged hydrophobic surfaces—direct measurements in aqueous-solution, Science 229 (1985) 1088–1089. [27] J.L. Parker, V.V. Yaminsky, P.M. Claesson, Surface forces between glass surfaces in cetyltrimethylammonium bromide solutions, J. Phys. Chem. 97 (1993) 7706–7710. [28] J. Choung, Z. Xu, J. Szymanski, An integrated approach for coal tailings management, Can. J. Chem. Eng. 78 (2000) 780–784. [29] S. Duzyol, A. Ozkan, Role of hydrophobicity and surface tension on shear flocculation and oil agglomeration of magnesite, Sep. Purif. Technol. 72 (2010) 7–12. [30] S. Duzyol, A. Ozkan, Correlation of flocculation and agglomeration of dolomite with its wettability, Sep. Sci. Technol. 46 (2011) 1–6. [31] S. Duzyol, A. Ozkan, Effect of contact angle, surface tension and zeta potential on oil agglomeration of celestite, Miner. Eng. 65 (2014) 74–78. [32] I. Kursun, Determination of flocculation and adsorption-desorption characteristic of Na–feldispar concentrate in the presence of different polymers, Physicochem. Probl. Miner. Process. 44 (2010) 127–142.
Please cite this article as: S. Duzyol, C. Sensogut, The relation between hydrophobic flocculation and combustion characteristics of coal, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.03.021