Energy Sources, Part A: Recovery, Utilization, and Environmental Effects
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Effect of electrochemical oxidized kerosene on flotation rate of difficult-to-float fine coal Tao Zhang, Hongbo Zhang, Xiang Liu & Xiaofeng Ma To cite this article: Tao Zhang, Hongbo Zhang, Xiang Liu & Xiaofeng Ma (2019): Effect of electrochemical oxidized kerosene on flotation rate of difficult-to-float fine coal, Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, DOI: 10.1080/15567036.2019.1649758 To link to this article: https://doi.org/10.1080/15567036.2019.1649758
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ENERGY SOURCES, PART A: RECOVERY, UTILIZATION, AND ENVIRONMENTAL EFFECTS https://doi.org/10.1080/15567036.2019.1649758
Effect of electrochemical oxidized kerosene on flotation rate of difficult-to-float fine coal Tao Zhanga, Hongbo Zhang
a
, Xiang Liua, and Xiaofeng Mab
a
School of Mining Engineering, Inner Mongolia University of Technology, Hohhot, China; bSchool of Materials Science and Engineering, Inner Mongolia University of Technology, Hohhot, China ABSTRACT
In order to recover difficult-to-float fine coal, flotation rates of full-size coal are tested using electrochemical oxidized kerosene as a collector. The flotation rate of coal using oxidized kerosene is higher than that of adopting conventional kerosene. However, its flotation product contained more ash due to poor selectivity of oxidized kerosene. The maximum recovery and flotation rate constant of the model were calculated by Curve Fitting Tool in MATLAB software, and the correlation coefficient R2 of each model is obtained. It is found that the classic first-order kinetic model is the most suitable model for the flotation of kerosene and oxidized kerosene.
ARTICLE HISTORY
Received 26 May 2019 Revised 29 June 2019 Accepted 18 July 2019 KEYWORDS
Kerosene; flotation; difficult-to-float coal; flotation rate; kinetic model
Introduction In recent years, the content of ash and slime in coal is increasing in the application of mechanized mining. Currently, flotation is still one of the most effective methods to recover fine coal. Many factors affect the flotation process. This paper mainly discusses the interaction between particles and bubbles. Furthermore, the flotation rate is used to characterize the difference in flotation by common kerosene and the electrochemical oxidized kerosene as collectors. The flotation rate is the change in concentration or recovery of the mineral in the flotation per unit time. The influencing factors are the composition of coal slime, flotation reagents, the associated mineral and its properties, particle size, density composition, hydrophobicity, and so on.(Ren 1990) The actual flotation process and characteristics of minerals can be explained by the magnitude of parameter and variation laws in the flotation kinetic model. In addition, in order to realize the automation of flotation, scientific guidance on the reagent selection and the way of dosing should be strengthened (Lu and Liang 1983). In the 1960s, the flotation kinetic model was established based on kinetics of the chemical reaction process. The first-order flotation kinetic model was obtained by analogy to the rate equation of chemical reaction (Ren 1990). However, abundant flotation results showed that this model did not fit all flotation processes. Plaksin and Krasin (Ren 1990) put forward the n-class flotation kinetic model conforming to the actual flotation process. Lu and Liang (1983) considered that the flotation rate constant k is the flotation probability of particles in unit time, and it is influenced by many factors because of the complex diversity of the real flotation process. Therefore, it is necessary to investigate the flotation rate constant based on the analysis of flotation micro process. Chen (1978); Chen and Wu (1978) concluded that the variation of K is approximate to the distribution of β function by applying the method of integral restoration K distribution to the flotation data of different plants.
CONTACT Hongbo Zhang
[email protected] School of Mining Engineering, Inner Mongolia University of Technology, Hohhot 010051, China Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/ueso. © 2019 Taylor & Francis Group, LLC
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In this paper, flotation experiment and theory are studied by using the electrochemical oxidation of kerosene on the slime. Flotation kinetics equation of is obtained by experiment, which verifies the flotation rate of electrochemically oxidized kerosene is faster than that of conventional kerosene. At the same time, the best flotation time is determined by establishing a model to guide production and improve the efficiency of plant production.
Material and methods Materials Kerosene and sec-octyl alcohol are used as collector and frother, respectively, in this work. The kerosene is a colorless liquid with a molecular weight between 200 and 250, and density of 0.82g/cm3. The oxidized kerosene with an acid value of 7.42 mgKOH/g is obtained by electrochemical treatment of conventional kerosene under optimal conditions: electrode of graphite-stainless steel, electrolytic time of 40 min, the catalyst dosage of 4g/L, and electrolytic current density of 2000 A/m2. The coal sample used for flotation is taken from Gujiao plant, Shanxi province, China. Automatic Industrial Analyzer (Model: WS-G401) assayed 24.93% of ash in coal (Table 1). Various standard sieves (0.500, 0.250, 0.125, 0.075, 0.045 mm) are used to test the size distribution of coal samples. The screening test was conducted according to the Code MT/T 58–1993. The total weight of the coal sample used for screening is 200 g. Table 2 shows that the content of particles less than 0.045 mm is relatively high (21.76%) with high ash content of 35.28%. Therefore, it is concluded that the coal is the muddy grave. The fine coal readily adsorbs onto the surface of bubbles or coal particles, and it is difficult to separate these fine coals from coal particles by flotation, resulting in reduced quality of clean coal (Zhang 2016). The distributed release test is conducted according to MT/T259-91. Figure 1 shows that the ash content of cleaned coal is between 6% and 14% when the cleaned coal yield is between 10% and 83%. The ash content will also increase significantly when the cleaned coal yield continues to increase and eventually reaching 25%. Methods An XFD-III flotation machine is used for coal flotation. First, dry coal sample was mixed with water in the flotation cell at the concentration of 100g/L. After 2 min of stirring at the speed of 1800r/minute, the collector is added and conditioned for 1 min. Then, the frother is added and a gas volume of 0.15m3/h is used after 10 s. The frother was scraped out 5 times with interval time of 0.5, 0.5, 1, 1, and 2 min. X-ray diffraction (XRD, D/Max2500, Rigaku Company in Japan) pattern is used for crystalline phase identification. The setting conditions for the XRD are: 40 KV 100 mA, Cu Kα as X-ray source, graphite crystal monochromator, scanning speed is 8°/minute, sampling interval is 0.010 °. Table 1. Industrial analysis of coal sample. Mad (%) 0.96
Aad(%) 24.93
Vdaf(%) 19.58
FCdaf(%) 55.23
Table 2. The results of the screening test for coal slurry (mass fraction). Particle size,mm +0.5 0.50 ~ 0.25 0.25 ~ 0.125 0.125 ~ 0.075 0.075 ~ 0.045 −0.045 Total
γ, % 0.66 18.96 32.19 15.09 11.34 21.76 100.00
Ad, % 20.08 22.34 21.75 22.12 22.47 35.28 24.93
∑γ, % 0.66 19.62 51.81 66.90 78.24 100.00
∑Ad, % 20.08 22.26 21.94 21.98 22.05 24.93
ENERGY SOURCES, PART A: RECOVERY, UTILIZATION, AND ENVIRONMENTAL EFFECTS
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Figure 1. Curves of coal floatability.
Fourier Transform infrared spectroscopy (FTIR, FTIR8400S, Shimadzu Company in Japan) was used for functional groups identification. The spectra are recorded at a 4 cm−1 resolution in the 4000–500 cm−1 region, making use of KBr disks. The contact angles of coal are tested by a contact angle analyzer (HARKE-SPCA, Beijing, China) using the sessile drop method. In the measurements, lumps of kerosene covered coal sample were loaded on the goniometer stage and 1.5 μm of distilled water was dropped on them. The most suitable flotation kinetic model is obtained by fitting the flotation rate using MATLAB. Curve Fitting Tool in MATLAB was adopted to calculate the fitting parameters of each model. The flotation time and the recovery of the combustible product are used as the model vectors.
Results and discussion Exploration of the optimum dosage of flotation reagents The XRD pattern of the coal in Figure 2 indicates that the gangue minerals in the raw coal sample mainly constituted montmorillonite, kaolin, quartz, pyrite, and so on. Among them, pyrite possesses relatively high float ability. Montmorillonite is unfavorable for coal flotation because it is swollen with water and has a strong ion-exchange ability (Zhang 2016, 2015). Kaolin causes trouble to flotation because it is easy to generate a large number of dispersed fine muds, which is extremely hydrophilic. All these clay minerals decline the quality of coal product because of the lowered contact probability between bubble and the coal particle as well as flotation selectivity. The FTIR spectra of conventional and oxidized kerosene is shown in Figure 3. From the spectra of the conventional kerosene, the wideband appearing between 725 and 720 cm−1 was due to the vibration of aromatic hydrocarbon. The peaks appearing at around 1470 cm−1 and 1380 cm−1 are attributed to -CH3 while cycloalkane or aliphatic hydrocarbon is responsible for the characteristic bands between 2850 and 2960 cm−1. After electrochemical oxidation treatment, the band at 2850–2960 cm−1, 1470 cm−1, 1380 cm−1 and 725–720 cm−1 still exist while the intensity weakened gradually. It suggests that only portion of conventional kerosene is oxidized. The appearance of the band at 1700–1720 cm−1 resulted from the bending vibration of C = O, indicating the formation of carbonyl compounds in the oxidized kerosene. At the same time, the bands located between 1000 and 1300 cm−1 suggest the existence of alcohol, ether, or ester in oxidized kerosene. The components of oxidized kerosene can be classified into three groups. Carboxyl acid substances, which act as a collector, are the main component in carbonyl compounds. Non-oxidized kerosene (or higher alkane) plays a role in diluting carboxyl acid in oxidized kerosene and making carboxyl acid easier
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Figure 2. XRD pattern of raw coal.
Figure 3. FTIR spectra of conventional and oxidized kerosene.
to disperse in a flotation slurry. Polar substances, including alcohols, ketones, aldehydes, and other compounds function as a frother in the flotation process (Gui, Liu, and Tao Xiu et al. 2011; Jian 1985). The indexes to judge the optimum dosage of collector and frother are the yield of clean coal (γj) and the recovery of combustible product (E, E = γj(100-Aj)/(100- Ay)×100%, in which Aj is the ash of clean coal, Ay is the ash of raw coal. Obviously, the value of E increases as value of Aj decreases). Sec-octyl alcohol is used as a frother in the experiment. Conventional kerosene (Figures 4 and 5) and oxidized kerosene (acid value of 7.42 mg KOH/g, Figures 6 and 7) are used as collectors, respectively. Figure 4 shows the coal floatation results as a function of conventional kerosene dosage. The yield of clean coal and recovery of the combustible product increases from 79.2% to 82.8% and 92.7% to 95.2% respectively with the increase of collector dosage from 200 to 800 g/t. It then remains virtually constant at around 82.4% and 95.1%, respectively, with the further increase of collector dosage to 1200 g/t. So 800 g/t conventional kerosene is used to determine the optimum frother dosage. Figure 5 shows the floatation index as a function of frother dosage. The yield of clean coal and the recovery of combustible product increases markedly from 45.1% to 82.8% and from 57% to 94.7% respectively with the increase of frother dosage from 0 to 160 g/t, and then it remains virtually constant
ENERGY SOURCES, PART A: RECOVERY, UTILIZATION, AND ENVIRONMENTAL EFFECTS
Figure 4. Flotation index as a function of collector dosage using conventional kerosene.
Figure 5. Flotation index as a function of frother dosage using conventional kerosene.
Figure 6. Flotation index as a function of collector dosage using oxidized kerosene.
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Figure 7. Flotation index as a function of frother dosage using oxidized kerosene.
at 81.5–82.8% and 94.7–95.5%, respectively, with the further increase of frother dosage to 250 g/t. It indicates that the optimal frother dosage is 160 g/t. Figures 6 and 7 show the flotation index as a function of oxidized kerosene and frother dosage. The maximum yield of clean coal (82.8%) and the recovery of the combustible product (94.6%) are achieved with the addition of 400 g/t oxidized kerosene and 80 g/t frother. In order to make a comparison between conventional kerosene and oxidized kerosene, 400 g/t collector and 80g/t frother are used in the following experiments. The contact angle and density of conventional kerosene and oxidized kerosene are shown in Table 3. Oxidized kerosene shows stronger hydrophobicity compared to conventional kerosene due to the existence of carbonyl compounds in oxidized kerosene. The wetting heat of carbonyl compounds is greater than that of saturated hydrocarbons, which makes kerosene containing carbonyl compounds easier to adsorb onto the coal surface, and therefore, the hydrophobicity was enhanced. In addition, the density of different kerosene keeps virtually constant.
Flotation rate tests Table 4–5 and the slopes of the two curves in Figure 8 suggest that the flotation rate using oxidized kerosene is obviously faster than that of using conventional kerosene as the collector. The recovery of the product increases sharply within 2 min, and it increases gradually with the further increase of time. In the early stages, flotation rate of coal using the two collectors is close within 2 min, and the cumulative recovery of combustible product using oxide kerosene is apparently higher in the same time range 2 to 3 min. It indicates that the flotation rate using oxidized kerosene is higher than another one. Flotation rate slows down gradually, and the flotation rate of both tends to the same because the clean coal in the raw coal had been floated, and the remaining particles took off easily from bubble due to their jumbo size and big weight or lower hydrophobicity resulted from associated minerals. Table 4-5 and Figure 9 shows the accumulative ash in clean coal as a function of flotation time. The ash in clean coal using conventional and oxidized coal as a collector differs slightly within 2 min because Table 3. Properties of different kerosene. Reagents Conventional kerosene Oxidized kerosene
Contact angle (°) 82.291 85.143
Density (g/cm3) 0.8232 0.8326
ENERGY SOURCES, PART A: RECOVERY, UTILIZATION, AND ENVIRONMENTAL EFFECTS
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Figure 8. Recovery of combustible product as a function of flotation time.
Table 4. Flotation results using conventional kerosene as a collector. Cumulative clean coal,% Product J1 J2 J3 J4 J5 Tailing Total
Yield,% 29.69 21.86 14.86 5.45 7.10 21.04 100.00
Ash,% 7.96 9.05 10.98 14.18 16.95 69.86 24.23
Yield 29.69 51.55 66.41 71.86 78.96 100.00
Ash 7.96 8.54 9.56 11.26 12.07 24.23
Cumulative Tailing,% Yield 100 70.31 48.45 33.59 28.14 21.04
Ash 24.23 31.10 40.92 53.23 57.35 69.86
Cumulative recovery of combustible product,% 36.07 62.22 79.27 84.16 91.63 100.00
Table 5. Flotation results using oxidized kerosene as a collector. Cumulative clean coal,% Product J1 J2 J3 J4 J5 Tailing Total
Yield,% 31.15 22.69 15.95 6.25 6.25 17.71 100.00
Ash,% 8.05 9.26 11.35 15.02 17.12 75.71 24.23
Yield 31.15 53.84 69.79 76.04 82.29 100.00
Ash 8.05 8.76 9.84 11.82 13.56 24.23
Cumulative Tailing,% Yield 100 68.85 46.16 30.21 23.96 17.71
Ash 24.23 31.55 42.27 57.47 63.61 75.71
Cumulative recovery of combustible product,% 37.80 64.83 83.04 88.49 94.32 100.00
the clean coal was enough at the beginning of flotation. However, the difference in cumulative ash content increases gradually in the time range of 3–5 min. The cumulative ash content in clean coal using oxidized kerosene is 1.5% higher than that using conventional kerosene at 5 min. It indicates that oxidized kerosene as collector lead to the decline of selectivity with the improvement of collecting power compared to that of conventional kerosene. The ash in clean coal increases because coal associated with a high content of fine ash is floated when the easy to be floated products gradually reduced in the flotation cell. According to Figure 8–9, the flotation time should be kept at 3 min.
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Figure 9. Accumulative ash in clean coal as a function of flotation time.
Flotation kinetic models The maximum recovery of the combustible product can be calculated from kinetic models, and the ε∞ can be solved by using the following common flotation kinetic models (Gui, Liu, and Tao Xiu et al. 2011). Classical first-order dynamics model: ε ¼ ε1 1 ekt First-order rectangular distribution model: 1 1 ekt ε ¼ ε1 1 kt Classic second-order kinetic model: ε¼
ε21 kt 1 þ ε1 kt
Secondary rectangular distribution model: 1 ε ¼ ε1 1 ½lnð1 þ ktÞ kt Liu Yichao Model:
h i k Gt ε ¼ ε0 1 eGð1e Þ
Xu Changlian Model: h i km ε ¼ ε0 1 ð1 þ ct Þ c The fitting results are plotted in Figure 10–11. The ε∞, K, error sum of squares, mean square error, standard deviation, and correlation coefficient of the flotation kinetic models of two collectors are calculated by MATLAB. The correlation coefficient determines the fitting accuracy of different collectors in various models.
ENERGY SOURCES, PART A: RECOVERY, UTILIZATION, AND ENVIRONMENTAL EFFECTS
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Figure 10. Various flotation kinetic models for fine coal using conventional kerosene.
Figure 11. Various flotation kinetic models for fine coal using oxidized kerosene.
Table 6 shows the correlation coefficient R2 of the classical first-order kinetic equation is the closest to 1, thus it can be concluded that the flotation rate of conventional and oxidized kerosene conforms to the classical first-order kinetic model.
Conclusion The flotation of fine coal using different kerosene is studied in this paper. The optimal conditions for flotation are listed as follows: 800g/t conventional kerosene mixed with 160g/t spec-octyl alcohol, or 400g/t-oxidized kerosene mixed with 80g/t spec-octyl alcohol. Flotation using electrochemical oxidized kerosene as a collector shows higher flotation rate from 2 to 3 min than that of using conventional kerosene as a collector. However, the ash in the clean coal rises faster 3 min later because of the strong collecting power and poor selectivity of oxidized kerosene. According to the fitting of the kinetic
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Table 6. Calculated values of the fitting parameters in each model. Conventional kerosene Parameters of model Classical first-order dynamics model First-order rectangular distribution model Classic second-order kinetic model Second-order rectangular distribution model Liu Yichao Model Xu Changlian Model
ε∞ 91.63 95.62 98.95 99.82 92.27 91.73
k 1.042 2.218 0.0153 4.305 1.113 1.116
R2 0.9884 0.9880 0.9564 0.8973 0.9811 0.9801
Oxidized kerosene ε∞ 94.32 99.62 99.75 99.23 95.21 94.63
k 1.189 2.497 0.0175 5.035 1.174 1.163
R2 0.9934 0.9782 0.9291 0.8578 0.9877 0.9918
equation, the classical first-order kinetic model suits most for fine coal flotation with a correlation coefficient of 0.9934.
Acknowledgments The financial supports from Inner Mongolia University of Technology (Project approval number: X201719) for this work are gratefully acknowledged.
Funding This work was supported by the Inner Mongolia University of Technology [X201719].
Notes on contributors Tao Zhang, born in 1987, teacher of Mining Institute of Inner Mongolia University of Technology, engaged in mineral processing research. Hongbo Zhang, born in 1970, professor of Mining College of Inner Mongolia University of Technology, engaged in teaching and scientific research of mineral processing engineering. Xiang Liu, born in 1992, teacher of Mining Institute of Inner Mongolia University of Technology, engaged in mineral processing research. Xiaofeng Ma, born in 1987, teacher of Materials science and engineering Institute of Inner Mongolia University of Technology, engaged in Material research.
ORCID Hongbo Zhang
http://orcid.org/0000-0002-8546-4597
References Chen, Z. M. 1978. Study on flotation kinetics the restoration of the distribution density function of the two flotation velocity constants. Nonferrous Metals (smelting Part) (11):27–33. Chen, Z. M., and D. C. Wu. 1978. One of flotation kinetics studies mineral flotation velocity model. Nonferrous Metals (smelting Part) (10):28–33. Gui, X. H., J. T. Liu, . 2011. Experimental study on flotation rate of refractory coal slime. Coal Journal 36 (11):1895–900. Jian, B. X. 1985. Flotation reagent, 96–98. Beijing: Metallurgical Industry Press. Lu, S. C., and Y. M. Liang. 1983. Development of kinetic model of flotation process. Mineral Processing of Foreign Metals (9):1–6. Ren, T. Z. 1990. Mathematical model and simulation of mineral processing, 24–30. Changsha: Zhongnan University of Technology Press. Zhang, T. 2015. Preparation of oxidized kerosene and its flotation effect. Coal Technology 34 (06):258–60. Zhang, T. 2016. Electrochemical oxidation of kerosene and its flotation effect. Coal Technology 35 (03):303–05.
