- Email: [email protected]
Evaluation of coal component liberation upon impact breakage by MLA
Fuel 258 (2019) 116136
Contents lists available at ScienceDirect
Fuel journal homepage: www.elsevier.com/locate/fuel
Full Length Article
Evaluation of coal component liberation upon impact breakage by MLA Yanhong Fu a b c
a,1
b,c,⁎,1
, Zhen Li
b,c
b
, Anning Zhou , Shanxin Xiong , Chao Yang
b
T
School of Chemical Engineering & Technology, China University of Mining and Technology, Xuzhou 221116, Jiangsu, PR China College of Chemistry and Chemical Engineering, Xi’an University of Science and Technology, Xi’an 710054, Shaanxi, PR China Key Laboratory of Coal Resources Exploration and Comprehensive Utilization, Ministry of Land and Resources, Xi’an 710054, Shaanxi, PR China
GRAPHICAL ABSTRACT
ARTICLE INFO
ABSTRACT
Keywords: Mineral liberation analysis Mechanical impact breakage Liberation mechanism Coal components
To elucidate the coal component liberation mechanisms upon typical impact breakage, the coal was selected from the Shangwan mine in China. Thereafter, mineral liberation analysis was adopted as the main method for investigating phase interface characteristics, classification characteristics of the various classes of comminuted products, and changes in the mineral area and length gradients upon mechanical impact breakage. The results indicate that the grain sizes of the comminuted products decreased in the following order: slag product > classifier product > bag product. Moreover, the disseminated grain size, dissemination mode, and original cleavages had a direct influence on the recovery rate of the completely liberated phase. The coal, which formed the main component of the samples, exhibited the highest cumulative mass recovery (CMR) in classified products and was most easily liberated. Furthermore, the kaolinitebearing coal and pyrite were moderately liberated, the quartz and kaolinite were difficult to liberate, and the illite was extremely difficult to liberate. Under mechanical impact breakage, intragranular and intergranular fractures mainly occurred in particles, with the changes in the mineral boundary and mineral area corresponding to varying fracture modes. To a certain extent, the particle comminution could be quantified by the changes in the slope of the equivalent circle diameter–-CMR curve. It was determined that the main cause of the increased liberation degree is the generation of the completely liberated phase of the component of interest. Furthermore, by adopting the liberation factor for quantification of the mineral liberation, the calculation model for coal component liberation was obtained.
Corresponding author at: College of Chemistry and Chemical Engineering, Xi’an University of Science and Technology, Xi’an 710054, Shaanxi, PR China. E-mail address: [email protected] (Z. Li). 1 These two authors contribute equally to this work. ⁎
https://doi.org/10.1016/j.fuel.2019.116136 Received 27 June 2019; Received in revised form 15 August 2019; Accepted 2 September 2019 Available online 17 September 2019 0016-2361/ © 2019 Elsevier Ltd. All rights reserved.
Fuel 258 (2019) 116136
Y. Fu, et al.
1. Introduction
2. Experimental materials and characterization methods
Mineral liberation is a key step in mineral processing, in which the energy consumption of the crushing process accounts for 75% of the energy consumption of the entire concentrator [1,2]. Comminution is mainly aimed at freeing valuable minerals from the gangue to enhance the efficiency of the subsequent selection [3,4]. The success of the separation is related to the liberation distribution of the feed particles, the performance of the separation technology applied, and the inherent characteristics of the feed material [5,6]. Among these, the fundamental characteristics of different ores, such as the grindability, volume ratio of components, texture and properties, will determine the ease of the mineral liberation and subsequent mineral separation [7–9]. Moreover, it is obvious that significant fracture will enhance the exposure liberation of minerals during comminution. which will consequently influence the mineral grinding ability and separation recovery rate [10–13]. Gasification and liquefaction for particle size and mineral composition of coal particles have higher requirements. Therefore, to a certain extent, studies on mineral cleavages, textures, and liberation characteristics are useful for the assessment of downstream processes [14,15]. At present, major research techniques and methods used in the investigation of the liberation and mineralogical characteristics of mineral particles include mineral liberation analysis (MLA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energydispersive X-ray spectroscopy (EDS) [16–19]. Furthermore, SEM coupled with EDS (SEM–EDS) has been applied to quantify the liberation, grade, and surface exposure conditions of minerals [20]. Little et al. published an approach to quantifying the fracture along grain boundaries based on the conservation of the grain shape of chromite using automated SEM–EDS [21]. Devasahayam S et al. adopted the method of quantitative evaluation of minerals by scanning electron microscopy to investigate the relationship between the grain size and mineral liberation in Australian zinc ore, and identified a direct correlation between the grain size distribution resulting from grinding and the liberated free minerals, as well as binary and ternary composites [22]. It was found that MLA can provides detailed information on the composition of single particles as well as particle populations exposed on the crosssectioned surface of a grain mount, which can be used to evaluate the process efficiency related to the liberation distribution of valuables, or to the distribution of a feature used for the separation of valuables from barren particles, and MLA data is applied in the magnetic separation process [23]. The mineralogy, grain size, dissemination, textural consistency, and mineral associations were determined for a commercially exploited porphyry copper ore using a mineral liberation analyzer [24]. And numerous studies have been conducted on the dissociation characteristics and modal mineralogy of useful minerals in ores of different types and structures (such as sulphide ores), and different Pb behaviors in the varying size fractions during magnetic separation, by means of MLA [25–28]. Besides, the MLA system was used to examine the Pphases in sewage sludge ashes [29]. Gräbner M et al. adopted MLA to estimate the water-bearing kaolinite content, and found that MLA also offered an advantage over XRD in the detection of amorphous material; that is, clay mineral types [30]. Based on the above review, MLA provides an effective means of quantifying the liberation characteristics of minerals, and it is the most extensively applied technique in the relevant research. However, its application has mainly been limited to the analysis of metallic and nonmetallic minerals; few studies have reported on the application of MLA in the investigation of coal liberation and the quantitative characterization of comminution mechanisms. Therefore, this study investigated the classification of the liberation mechanisms of coal and minerals upon mechanical impact breakage, as well as the influences of different fracture modes on the mineral liberation, with the aim of providing technical and theoretical support for future quantitative research on the multi-component liberation mechanisms of coal.
2.1. Experimental raw materials The samples used in this study were obtained from coals mined from the Shangwan coal mine of the Shendong mining area in China (henceforth referred to as SW). Table 1 lists the specifications regarding the proximate and ultimate analyses of the coal samples. The results of the analysis indicate relatively high carbon and fixed carbon contents and relatively low hydrogen, oxygen, and sulfur contents in the SW. Fig. 1 illustrates the polished coal rock sections of the SW. The coal petrography slices was prepared according to 《GB/T 8899-2013 Determination of maceral group composition and minerals in coal》and different mineals can be identified under commonreflected light with different colors. Pyrite shows pale yellow and white, the clay minerals are dark grey. It can be observed that the overall mineral content of the raw coal was relatively low (Fig. 1(a)), corresponding to the lower ash and sulfur contents in Table 1. The main minerals disseminated in the coal samples were pyrite, which exhibited a scattered stellate dissemination pattern (Fig. 1(b)), and clay minerals, which filled the cavities of the macerals (Fig. 1(c)). 2.2. Equipment and methods (1) Equipment The experimental equipment used in the study was a mechanical impact breakage system, developed and designed in-house at the Xi'an University of Science and Technology, which consisted of a grinder, classifier, and bag dust collector. The samples were comminuted upon impact with the rotor-driven parts and subsequently classified according to the grain size and density. The samples were comminuted upon impact with the rotor-driven parts and subsequently classified according to the grain size and density. The resultant classified products were the slag product (SP), classifier product (CP), and bag product (BP). Fig. 2 presents a schematic of the experimental equipment. Based on the results of a relevant experimental study conducted by our research group [31], the rotational speed of the classifier was set to 2000 r/min, while the feed grain size was set to > 6 mm. (2) Methods The Mineral Liberation Analyzer 250 (FEI, USA), obtained from the Oil Sands and Coal Interfacial Engineering Facility of the University of Alberta, Canada, was used to study the liberation characteristics of each coal component. The MLA is an automated mineralogy tool used for process mineralogy, which incorporates the technologies of Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Analysis (EDAX/BRUKER). MLA software controls the SEM and use images and x-rays to characteristic minerals, particles and rocks. The characterization parameters were as follows: a. Free surface (FS) The dissemination and liberation degrees of the minerals were quantitatively characterized based on the free surface calculated on the area% of the minerals of interest [32]. Fig. 3(a)–(c) illustrate the FS Table 1 The proximate analysis and ultimate analysis of raw coal. Item
SW
2
Proximate analysis
Ultimate analysis
Aad%
Mad%
Vad/%
FCad/%
Cad%
Had%
Oad%
Nad%
St,ad %
10.38
7.50
32.84
49.28
68.94
3.36
8.99
0.54
0.29
Fuel 258 (2019) 116136
Y. Fu, et al.
clay mineral
pyrite
clay mineral 50µm
50µm
(a)
50µm
(b )
(c )
Fig. 1. The coal petrography slices of raw coal.
b a g filt er
cla ssifier
ECD
classifier product
Fig. 4. The schematic of equivalent circle diameter.
d. Mean Phase Equivalent Circle Diameter (ECD)
pulver izer
main air blower slag
Implement point x-ray analysis to efficiently and effectively analyze mineral phases within a particle. The Mean Phase ECD was obtained by the DataView, which means the mean phase size of the mineral of interest.
bag product
Fig. 2. The equipment contact diagram of mechanical impact crushing system.
e. Boundary length gradient and area gradient of mineral of interest
calculations, with A and B indicating the mineral of interest (represented by coal) and other intergrown minerals (represented by pyrite), respectively.
The boundary length gradient of the mineral of interest was defined as the difference in the boundary lengths of the same mineral between different classified products, while the area gradient was defined as the difference in the areas of the same mineral between different classified products. Here, L1 denotes the difference in the boundary lengths of the same mineral between the SP and CP, L2 denotes the difference in the boundary lengths of the same mineral between the classifier product CP and BP, A1 denotes the difference in the areas of the same mineral between the SP and CP, and A2 denotes the difference in the areas of the same mineral between CP and BP, as expressed by Eqs. (3)–(6), respectively.
b. Phase specific surface area (PSSA) The PSSA of the coal components was calculated using Eq. (1):
PSSA =
Mineral Boundary Mineral Area
(1)
c. Equivalent circle diameter (ECD) The grain size measurements in the MLA were performed based on the equivalent circle diameter (ECD), which was calculated by converting the area (derived from the measured pixels) into an equivalent circle value. This approach is suitable for rounded particles or grains. Fig. 4 presents a schematic of the ECD, which was calculated using Eq. (2):
Equivalent Circle Diameter = 2
(2)
Area
(a)
(3)
L2 = BPM ineral boundary
CPMineral boundary
(4)
A1 = CPM ineral area
SPMineral area
(5)
A2 = BPM ineral area
CPMineral area
(6)
A
A 0%
SPMineral boundary
B
B
Liberation by free surface
L1 = CPM ineral boundary
A B
50% (b)
Fig. 3. The sketches of mineral liberation classes based on free surface. 3
100% (c)
Fuel 258 (2019) 116136
Y. Fu, et al.
3. Results and discussion
phase of 27.47% in the BP. Moreover, two-phase particles accounted for the highest content in the SP and an RV value of 49.44%, indicating a high degree of difficulty in achieving liberation. The recovery rates of the completely liberated phase of the quartz were higher in the CP and BP at 29.45% and 29.31%, respectively. Moreover, the two-phase particle contents were relatively high in all three products, at 43.96%, 49.94%, and 49.93%, respectively, indicating a high degree of difficulty in achieving liberation. Owing to the generally low liberation degree, the illite was mainly disseminated in binary or greater phase particles. The completely liberated phase was mainly distributed in the SP and BP, with recovery rates of 20.1% and 17.29%, respectively. This demonstrates that, upon strong impact, liberation first occurred in the easily liberated illite particles, while the other particles could only be liberated when a certain grain size was achieved, indicating an extremely high degree of difficulty in achieving liberation. The dissemination characteristics of the mica were similar to those of the illite, with the maximum recovery rate of the completely liberated phase reaching a maximum of 58.81% in the BP. Particles containing binary or greater phases were mainly distributed in the CP, indicating that a certain degree of liberation could be achieved in the mica and its associated minerals when the particle grain size was decreased to a certain extent through impact breakage; that is, the mica was moderately liberated. The above analysis demonstrates that the liberation of the coal and main disseminated minerals was influenced by the disseminated grain size, dissemination pattern and density, hardness, and original cleavages of the various associated minerals. The four levels of mineral liberation in the comminuted-classified products generated upon impact breakage were defined as follows: easily liberated (> 80% of Rv liberated of the mineral of interest), moderately liberated (80%–50% of Rv liberated of the mineral of interest), difficult to liberate (50%–20% of Rv liberated of the mineral of interest), and extremely difficult to liberate (< 20% of Rv liberated of the mineral of interest). Table 3 displays the changes in the FS and PSSA of the main components in the coal under different fracture modes. The analysis revealed that the FS and PSSA values of the kaolinite-bearing coal, quartz, kaolinite, illite, calcite, and siderite increased sequentially from the SP to BP, while the coal, mica, and pyrite exhibited inconsistent change patterns. This was attributed to the different fracture modes exhibited by the coal and major minerals upon impact breakage.
3.1. Analysis of dissemination characteristics and mineral components of raw coal Mix the coal sample in a glass vial to homogeneous and it can be mounted in a 30 mm diameter sample block, and then grinding and polishing to obtain a high quality polished sections. The prepared samples were used to analyse the dissemination characteristics and mineral components of raw coal. Table 2 displays the main mineral components of the SW, which included coal, quartz, kaolinite, calcite, mica, pyrite, and illite. Fig. 5 illustrates the dissemination patterns of the main components of the SW obtained by MLA. It can be observed that the different minerals exhibited varying dissemination modes and disseminated grain sizes. The disseminated grain sizes of the kaolinite and calcite were within the range of 10–80 μm; the pyrite and quartz were irregularly disseminated with grain sizes of 30–120 μm, while the paragenetic illite and mica exhibited laminated irregular flakes and scattered stellate dissemination patterns, with grain sizes of 1–50 μm. 3.2. Analysis of liberation characteristics of coal and minerals (1) Analysis of grain size distributions The liberation characteristics of each component in coal were further analyzed by sampling the classified products under mechanical impact comminution. In this particular example grain size was calculated by equivalent circle and it is based on the measured 2D surface. And the particle size is calculated by the Eq. (2). Fig. 6 presents the grain size distributions and MLA diagrams of the various products obtained under mechanical impact breakage conditions. It can be observed that comminution occurred in the coal and disseminated mineral particles upon mechanical impact breakage, with the comminuted particles settling into SP, CP, and BP in turn. The P values and particle size distribution curves indicate a decreasing trend of grain size from SP, CP and BP successively. And there are a few overlaps of particle size between CP and BP with different classification effects. According to the MLA diagrams, it can be observed that, in the SP, disseminated particles of mica and illite with grain sizes of approximately 10 μm were associated with coal, while calcite with grain sizes of 5–25 μm exhibited a dotted dissemination pattern within the coal (Fig. 6(A)). In the CP, the quartz was completely liberated, while the illite and mica were partially liberated (Fig. 6(B)); intergrowths were absent in the BP (Fig. 6(C)).
(3) Analysis of fracture modes
(2) Analysis of phase interface liberation characteristics
Further analysis was performed on the fracture modes of the coal and major minerals (kaolinite-bearing coal, quartz, siderite, calcite,
Fig. 7 illustrates the phase interface characteristics of the coal and minerals in the comminuted-classified products of the SW following mechanical impact breakage. In this case, RV denotes the recovery rate of each mineral from the various comminuted-classified products. Coal, which formed the main component of the samples, was easily liberated, and exhibited a high liberation degree in the various products, with the highest recovery rate for the completely liberated phase being 82.45% in the CP. The maximum recovery rate for the completely liberated phase of kaolinite-bearing coal was 52.36% in the BP. Particles containing binary or greater phases were mainly distributed in the SP, indicating that kaolinite-bearing coal particles with smaller grain sizes were more readily liberated; that is, the kaolinite-bearing coal was moderately liberated. The highest recovery rates of pyrite were achieved in the CP and BP, with RV values of 51.56% and 50.35%, respectively. In general, the completely liberated phase and two-phase particles dominated the comminuted products, indicating moderate liberation of the pyrite. For the kaolinite, the liberation degree increased sequentially from the SP to BP, with a maximum recovery rate of the completely liberated
Table 2 SW coal mineral phases identified by MLA analysis.
4
Mineral
Mineral weight (%)
Coal Coal (kaolinite) Kaolinite Illite Calcite Pyrite Quartz Muscovite Siderite Albite Orthoclase Silicate Ankerite Dolomite Barite Others Total
91.65 2.94 1.6 1.18 0.92 0.3 0.32 0.17 0.22 0.02 0.03 0.02 0.03 0.02 0.03 0.55 100
Fuel 258 (2019) 116136
Y. Fu, et al.
coal
30μm
kaolinite
quar tz
calcite
sider ite
illite
muscovite
pyr ite or thoclase
Fig. 5. Dissemination map of SW components.
kaolinite, and illite) under impact breakage. Fig. 8 illustrates the relationship between the liberation degree and cumulative mass recovery (CMR) for the coal and aforementioned major minerals, while Fig. 9 presents the changes in the mineral boundary length gradient and area gradient of the various comminuted-classified products. As indicated in Fig. 8, the CMR decreased with an increase in the liberation degree of the coal and major minerals. The results are summarized as follows: For the kaolinite-bearing coal, |L2| > |L1| and |A2| > |A1|, with the CMR of the BP being consistently higher than those of the SP and CP across all liberation levels. This indicates that the kaolinite-bearing coal exhibited a greater response to the impact breakage. As the particle grain size decreased, intragranular fracture became the dominant
fracture mode of the mineral of interest, corresponding to greater changes in |L2|. Moreover, the degree of liberation completeness increased as the grain size decreased, leading to a maximum CMR100% (which denotes that the liberation degree is 100%) of 38.14% in the BP. For the quartz, |L2| > |L1| and |A2| > |A1|, and the CMR decreased sequentially as follows: CMR(BP) > CMR(CP) > CMR(SP). This demonstrates that the quartz exhibited a greater response to the impact breakage. Both intragranular and intergranular fractures occurred in the larger particles of the mineral of interest, while intragranular fracture mainly occurred in the smaller disseminated particles. Correspondingly, more significant changes could be observed in |A2|. During the subsequent classification process, a portion of the quartz
110
bottom slag
90
bag product
Cumulative Passing(wt%)
100
A
classifier product
80 bottom classifier P-value
slag
product
product
(μm)
（μm）
（μm）
60
P10
41.28
12.66
6.78
50 40 30
50μm
bag
70
P20
63
18.23
6.89
P25
75.01
20.88
7.47
P50
124.15
34.55
11.9
P75
184.85
53.48
19.14
P80
199.75
58.92
21.92
P90
244.46
72.11
30.74
B
50μm
C
20 10 0 1
10
100
Particle Size(μm)
coal calcite
50μm kaolinite pyr ite illite quar tz sider ite muscovite
Fig. 6. MLA images and particles of SW crushing-classification products under mechanical impact and comminution. 5
Fuel 258 (2019) 116136
Y. Fu, et al.
Fig. 7. Analysis of the phase surface characteristics of SW coal and its primary minerals.
L1| > |L2| and |A2| > |A1|, indicating that the changes in the mineral boundary length decreased, while the changes in the mineral surface increased across the SP, CP, and BP. This could be attributed to the occurrence of an intergranular fracture in a small portion of the largergrained pyrite disseminated around the coal, leading to the exposure of pyrite with a decrease in the coal grain size. In contrast, intragranular fracture mainly occurred in the smaller-grained disseminated pyrite, in parageneses with other minerals. During the classification process, large particles settled into the SP, moderately sized particles settled into the CP, and fine particles settled into the BP. Consequently, when the liberation degree was less than 35%, CMR (SP) > CMR (CP) > CMR (BP); when the liberation degree was within the range of 35%–90%, the CMR of the CP was highest, while the CMR of the SP and BP fluctuated between high and low values; and when the degree of liberation was 100%, CMR(BP) > CMR(CP) > CMR(SP). For the calcite, the phase interface change patterns were as follows: |L1| > |L2| and |A1| > |A2|, indicating that the changes in both the mineral boundary length and area decreased across the SP, CP, and BP. The dissemination pattern of the calcite in the coal resulted in a smaller
Table 3 Compilation of different parameters from MLA of crushing product. Mineral
Coal Coal (Kaolinite) Quartz Kaolinite Muscovite Illite Calcite Siderite Pyrite
PSSA/μm−1
FS/% SP
CP
BP
SP
CP
BP
81.97 25.22 36.6 12.52 5.55 6.67 29.93 19.83 57.27
93.04 45.88 56 35.92 25.85 24 42.57 51.38 67.15
92.02 71.68 65.53 54.89 44.97 36.49 50.57 58.61 66.94
0.12 0.61 0.45 0.32 0.64 0.33 0.24 0.52 0.43
0.27 0.71 0.46 0.51 0.71 0.64 0.45 0.65 0.69
0.69 1.09 0.62 0.65 0.68 0.79 0.9 1.08 1.13
was mainly distributed in the form of two-phase or multiple-phase particles in the SP and CP, while the other portion was completely liberated into fine particles, as illustrated in Fig. 7(a)–(c). The phase interface change patterns of the pyrite were as follows: 6
Fuel 258 (2019) 116136
Y. Fu, et al.
100
100
90
90
80 70 60
57.04
50
coal (slag product)
40
44.21
coal (classifier product)
38.14
30
coal (bag product)
34.52
20
coal (kaolinite) classifier product
coal (kaolinite) slag coal (kaolinite) bag product
10
14.17
quartz(classifier product) quartz(bag product) illite(slag product)
80
illite(classifier product)
70
illite(bag product)
60 50 40 30 20 10
calcite(slag product)
Cumulative Mass Recovery(%)
siderite(slag product) siderite(classifier product)
70
siderite(bag product)
60 50 40 30 20 10 0
100
90-95
95-100
80-85
85-90
75-80
65-70
70-75
60-65
50-55
55-60
45-50
35-40
pyrite (classifier product)
90
calcite(bag product)
80
pyrite (slag product)
100
calcite(classifier product)
90
40-45
(b ) qua r t z,ill it e
110
100
30-35
20-25
25-30
10-15
15-20
0-5
Liberation Classes(%)
(a ) coa l
110
5-10
100
95-100
85-90
90-95
80-85
75-80
70-75
60-65
65-70
55-60
50-55
45-50
40-45
35-40
25-30
30-35
20-25
15-20
10-15
0-5
Liberation Classes(%)
pyrite (bag product) kaolinite (slag product)
80
kaolinite (classifier product)
70
kaolinite (bag product)
60 50 40 30 20 10
100
90-95
95-100
85-90
75-80
Liberation Classes(%)
80-85
70-75
60-65
65-70
55-60
50-55
45-50
35-40
40-45
30-35
25-30
20-25
15-20
5-10
0-5
100
90-95
85-90
80-85
95-100
Liberation Classes(%)
75-80
70-75
65-70
60-65
55-60
50-55
45-50
35-40
40-45
30-35
25-30
20-25
15-20
10-15
0-5
5-10
0 10-15
Cumulative Mass Recovery(%)
quartz(slag product)
0 5-10
0
21.30
Cumulative Mass Recovery(%)
110
Cumulative Mass Recovery(%)
110
(d ) pyr it e,k a olin it e
(c) ca lcit e,s id er it e
Fig. 8. Relationship map of liberation degree and CMR on SW and its primary mineral components in mechanical impact crushing method.
response to the impact breakage. When the liberation degree was up to 35%, CMR(SP) > CMR(CP) > CMR(BP); when the liberation degree was within the range of 35%–85%, CMR(SP) > CMR(BP) > CMR(CP); and when the liberation degree was > 95%, CMR(SP) > CMR(CP) > CMR(BP), with the CMR of the completely liberated phase being extremely low in the SP (2.98%) and CP (9.25%). Based on these results, it could be deduced that the liberation of the calcite was contingent on the liberation of the other minerals, and was mainly dominated by intragranular fracture. The completely liberated fine particles settled into the BP, which had the highest CMR value of 21.11%. The phase interface change patterns of the illite were as follows: |L1| > |L2| and |A1| > |A2|. When the liberation degree of the illite was less than 30%, CMR(SP) > CMR(BP) > CMR(CP); when the liberation degree was > 55%, CMR(BP) > CMR(CP) > CMR(SP). This indicates that the illite had a relatively small disseminated grain size and was extremely difficult to liberate. Consequently, the illite exhibited a smaller response to the impact breakage, with the dominating fracture mode being intragranular fracture. Liberation only occurred in grains
that had been comminuted to small grain sizes, which led to low CMR values of 0.19%, 4.99%, and 12.84% for the completely liberated phases in the SP, CP, and BP, respectively. For the kaolinite, the disseminated particles in the coal had a smaller disseminated grain size, exhibited a multiphase distribution (Fig. 8), and were difficult to liberate. The phase interface change patterns were as follows: |L1| > |L2| and |A1| > |A2|, indicating that the changes in both the mineral boundary length and area of the kaolinite decreased across the SP, CP, and BP. Liberation only occurred when the particle grain size was smaller than the disseminated grain size (Fig. 6), leading to a maximum CMR100% of 24.06% in the BP. 3.3. Fracture classification characteristics of particles under mechanical impact breakage Fig. 10 illustrate the relationship between the mean phase ECD and CMR for the coal with different liberation degrees in the SP, CP, and BP. It can be observed that the different grain sizes corresponded to varying 7
Fuel 258 (2019) 116136
Y. Fu, et al.
L1
L2
4
×10
-80
-40 -20 0 20 40 4
60
80
80
2
Mineral Area(µm )
×10
Mineral Boundary(µm)
-60
60 40 20 0 -20 -40 -60 -80
coal (k) quartz
A1
A2 kaolinite
illite
calcite
siderite
pyrite
Fig. 9. The gradient variation of mineral boundary and mineral area on main components of SW.
liberation degrees. The CMR values of the completely liberated coal in the SP, CP, and BP were 34.52%, 57.04%, and 44.21%, respectively. When the liberation degree was within the range of 0%–60%, the changes in the CMR of the coal with the ECD were not significant, indicating that the recovery rate of the particles within 0%–60% liberation was influenced by the grain size to a smaller extent. When the liberation degree was within the range of 60%–80%, the gradient of the ECD–CMR curve began to increase significantly; when the liberation degree was within the range of 80%–100%, the particle recovery rate varied significantly with the grain size. The ascending order of the ECD–CMR curve gradients was as follows: K(SP) < K(CP) < K(BP), demonstrating that the grain size exerted a greater influence on the CMR at higher liberation degrees. This can be explained by the following: at lower liberation degrees, the component of interest was not liberated, leading to a smaller influence of the changes in the grain size on the CMR; at higher liberation degrees, a portion of the component of interest had been liberated, while the other portion remained disseminated in the form of two-phase or multiphase grains, leading to a greater influence of the fracture-induced grain size reduction on the CMR. The gradient of the ECD–CMR curve can reflect the amount of particle comminution to a certain extent. If K = 0, components of different grain sizes have the same CMR value, which indicates that the crushing method has resulted in maximum liberation of the component of interest. Therefore, the interface strength is equivalent to the grain strength, and a reduction in particle size will not influence the mineral liberation degree. Such a phenomenon typically occurs in the completely liberated phase or within purely intragranular fractures of components that are not of interest. Moreover, if K = 1, the components have identical grain sizes but different CMR values; consequently, the liberated grain size under the conditions of the highest liberation degree or the liberated grain size at the maximum CMR value can be determined, thereby providing a basis for evaluating the extent of the mineral liberation.
4. Model for changes in FS and phase interface length during coal liberation process Coal was selected as the mineral of interest for the MLA owing to its high contents in the samples, while the other minerals were regarded as disseminated minerals. Fig. 11(a)–(c) present the three typical dissemination modes selected for analysis: the dissemination of the mineral of interest and other minerals on the external surfaces, the encapsulation of other minerals by the mineral of interest, and the encapsulation of the mineral of interest by other minerals, respectively. Under impact breakage, intergranular and intragranular fractures will occur in the component of interest. For the dissemination mode in Fig. 11(a), if the intergranular fracture occurs between the mineral of interest and disseminated minerals (1), the changes in the boundary length and area of the mineral of interest will alter the liberation degree. If the mineral boundary length remains unchanged, the PSSA will increase with a reduction in the mineral area, leading to an increase in the completely liberated phase and liberation degree. If the mineral area remains unchanged, the PSSA will decrease with a reduction in the mineral boundary length, and the liberation degree of the mineral of interest will only increase when new FS are generated by changes in the boundary length. If intragranular fracture occurs in components that are not of interest, the new surface (NS) and ΔPSSA = 0. For the dissemination mode in Fig. 11(b), if the intergranular fracture occurs in the component of interest, bothΔL and PSSA will increase (1); if an intragranular fracture occurs in the component of interest and produces NSs, the NSs will be equivalent to the FS and the change in the PSSA (2); that is, ΔPSSA = NS = FS. A reduction in the grain size will not result in changes to the liberation degree of the component of interest; however, under this dissemination mode, the liberation degree of the component of interest will be maintained at 100%. Under the dissemination mode in Fig. 11(c), intragranular fracture occurs in the disseminated minerals in the particles, instead of in the component of interest (1). Therefore, no changes occur in the boundary length and area of the component of interest, and the liberation degree is 0% as the component of interest does not become exposed. If intragranular fracture occurs and produces FS in the mineral of interest 8
Fuel 258 (2019) 116136
Y. Fu, et al.
Fig. 10. The relationship of mean phase ECD and CMR on classifier product with different liberation classes by mechanical impact crushing method.
(2), both the mineral phase interface area and liberation degree will increase.
comminution process and single particles of the component of interest are not generated, the liberation degree L = 0%. If both intergranular and intragranular fractures occur, the mineral liberation model proposed by Stamboliadis [33] can be applied. Assuming that all particles (including single particles and intergrowths) have the same volume v, diameter d, and grade gi, the total number of V d 3 particles in the product N = vP gi ; similarly, N = P3 gi . The total volume d of component A can be calculated using VA = N ·v . If all particles with the same grade gi of component A in the product are combined into a single particle, VA = v . Therefore, the critical liberation volume and v critical liberation area can be determined as follows: VPL = g and
5. Calculation model for coal component liberation 1) When performing measurements in MLA, the particle diameter can be calculated by converting the area derived from the measured pixels into an equivalent circle value: dp = 2 × AP , where Ap is the mineral area. Furthermore, the particle volume can be calculated 1 3 using the formula VP = 4 - 2 Ap 2 . The volumes of components A and B in the particle are denoted by VA and VB, respectively, and the grades of components A and B in the raw particle can be calculated V using the formulae gA = V +AV and gB = 1 gA . A
dPL =
d 3 gi
i
, respectively. The liberation factor is defined as P =
di , dpL
where Vi is the volume of particles within the product. Moreover, P′ ≤ 1 indicates the occurrence of liberation in the component of interest, while P′ > 1 indicates the non-occurrence of liberation.
B
When intragranular fracture occurs in components A and B, resulting in the generation of multiple liberated single particles A1, A2⋯Ai and B1, B2⋯Bi, assuming that VA1 = VA2 =⋯= VAi and VB1 = VB2 =⋯= VBi, the grade of component A can be calculated by VA, gA,i 1 = V i - 1 . When VA,i−1 = VB,i−1, gA,i 1 = gB,i 1 and the liberation
2) During the comminution process, regardless of whether intergranular or intragranular fracture occurs, smaller particles with different volume fractions will be produced under the critical diameter dPL. The comminuted particles are divided into m grain size levels. As the particle originally contains k components, the particle
p, i 1
degrees of components A and B are identical; that is, LM = LN = 100%. If intragranular component liberation occurs during the
9
Fuel 258 (2019) 116136
Y. Fu, et al.
Fig. 11. The process model of particles liberation under mechanical impact crushing method.
volume is equal to the sum of the volumes of all components; that is, VP,k = v1, k + v2, k + ...+vk, k . The grade of component A at the ith grain v size level is defined as gA,i = VA,i , where di represents the average P, i geometric diameter of the ith grain size level and gi > gi+1 (denoting a sequential decrease in grain size). Furthermore, dj represents the average geometric diameter of the jth grain size level. When i = j, di = dj, and the liberation degree of component A at the jth grain size level can be determined using the formula j
LA(di) =
i=1 m i=1
g A,j
VP (di)
boundary length and mineral area of the component of interest, leading to an increase in the liberation degree. If intragranular fracture occurs in the component of interest and produces NSs, the NSs will be equivalent to the FS, but the liberation degree will not change. If intragranular fracture produces single particles of the component of interest, the liberation degree will increase. By adopting the interface liberation factor to characterize the liberation of microscopic components, where P′ ≤ 1 indicates the occurrence of liberation in the component of interest and P′ > 1 indicates the non-occurrence of liberation, the following calculation model for
. The liberation degree of the overall particle is then
calculated using the formula L¯0 = the jth grain size grade.
m j =1
the liberation of coal and other minerals was obtained: L¯0 =
L (di) j , where γj is the yield of
m
j =1
L (di) j .
Acknowledgements Financial support for this research, supported by Provincial Natural Science Foundation research project of Shaanxi (No. 2018JQ5017), China coal industry association 2017 annual science and technology research guidance project (Grant No. MTKJ 2017-306), and Key Laboratory of Coal Resources Exploration and Comprehensive Utilization, Ministry of Land and Resources (No. ZKF2018-2), are gratefully acknowledged. I also offer my sincere thanks to professor Zhenghe Xu from University of Alberta, who provided important advice and suggestions on amendments.
6. Conclusions The liberation degrees of minerals are influenced by the disseminated grain size, dissemination pattern and density, hardness, and original cleavages of the various associated minerals. Under mechanical impact breakage, intragranular and intergranular fractures mainly occur in the particles, with the changes in the mineral boundary length and area corresponding to different fracture modes. The gradient of the mean phase ECD–CMR curve can quantify the particle comminution to a certain extent, and provide a basis for determining the liberation grain sizes of the component of interest as well as the selection of comminution methods under certain liberation levels. The liberation degree cannot be characterized by the changes in the FS and PSSA under varying dissemination modes of the component of interest. The main cause of an increased liberation degree with the application of an external force is the generation of the completely liberated phase of the component of interest. When the intergranular fracture occurs between the component of interest and other disseminated components in a particle, changes take place in the mineral
References [1] Musa F, Morrison R. A more sustainable approach to assessing comminution efficiency. Miner Eng 2009;22(7):593–601. [2] Guanghui Y, Zhenxing Z, Bo Z, et al. Preferential sequence crushing of copper ore based upon high-voltage pulse technology. Miner Eng 2019;131:398–406. [3] Mariano RA, Evans CL, Manlapig E. Definition of random and non-random breakage in mineral liberation – A review. Miner Eng 2016;94:51–60. [4] Ueda T, Oki T, Koyanaka S. Stereological correction method based on sectional texture analysis for the liberation distribution of binary particle systems. Adv Powder Technol 2017;28(5):1–8. [5] Leißner T, Mütze T, Bachmann K, et al. Evaluation of mineral processing by assessment of liberation and upgrading. Miner Eng 2013;53(10):171–3.
10
Fuel 258 (2019) 116136
Y. Fu, et al. [6] Tromans D. Mineral comminution: energy efficiency considerations. Miner Eng 2008;21(8):613–20. [7] Shi F, Zuo W. Coal breakage characterisation – Part 1: breakage testing with the JKFBC. Fuel 2014;117:1148–55. [8] Shi F. Coal breakage characterisation – Part 2: multi-component breakage modelling. Fuel 2014;117:1156–62. [9] Xie W, He Y, Yang Y, et al. Experimental investigation of breakage and energy consumption characteristics of mixtures of different components in vertical spindle pulverizer. Fuel 2016;190:208–20. [10] Tungpalan K, Wightman E, Manlapig E, et al. The influence of veins on mineral liberation as described by random masking simulation. Miner Eng 2017;100:109–14. [11] Little L, Mainza AN, Becker M, et al. Fine grinding: how mill type affects particle shape characteristics and mineral liberation. Miner Eng 2017;111:148–57. [12] Samanli S. A comparison of the results obtained from grinding in a stirred media mill lignite coal samples treated with microwave and untreated samples. Fuel 2011;90(2):659–64. [13] Garcia D, Lin CL, Miller JD. Quantitative analysis of grain boundary fracture in the breakage of single multiphase particles using X-ray microtomography procedures. Miner Eng 2009;22(3):236–43. [14] Parian M, Mwanga A, Lamberg P, et al. Ore texture breakage characterization and fragmentation into multiphase particles. Powder Technol 2018;327:57–69. [15] Lee H, Klima MS, Saylor P. Evaluation of a laboratory rod mill when grinding bituminous coal. Fuel 2012;92(1):116–21. [16] Ueda T, Oki T, Koyanaka S. A general quantification method for addressing stereological bias in mineral liberation assessment in terms of volume fraction and size of mineral phase. Miner Eng 2018;119:156–65. [17] Fandrich R, Gu Y, Burrows D, et al. Modern SEM-based mineral liberation analysis. Int J Miner Process 2007;84(1):310–20. [18] Lastra R, Paktunc D. An estimation of the variability in automated quantitative mineralogy measurements through inter-laboratory testing. Miner Eng 2016;95:138–45. [19] Zhen L, Yanhong F, Anning Z, et al. Effect of multi-intensification on the liberation of maceral components in Coal. Fuel 2019;237:1003–12. [20] Reyes F, Lin Q, Cilliers JJ, et al. Quantifying mineral liberation by particle grade
and surface exposure using X-ray microCT. Miner Eng 2018;125:75–82. [21] Little L, Mainza AN, Becker M, et al. Using mineralogical and particle shape analysis to investigate enhanced mineral liberation through phase boundary fracture. Powder Technol 2016;301:794–804. [22] Devasahayam S. Predicting the liberation of sulfide minerals using the breakage distribution function. Miner Process Extr Metall Rev 2015;36(2):136–44. [23] Leißner T, Bachmann K, Gutzmer J, et al. MLA-based partition curves for magnetic separation. Miner Eng 2016;94:94–103. [24] Batchelor AR, Jones DA, Plint S, et al. Increasing the grind size for effective liberation and flotation of a porphyry copper ore by microwave treatment. Miner Eng 2016;94:61–75. [25] Albijanic B, Bradshaw DJ, Nguyen AV. The relationships between the bubble–particle attachment time, collector dosage and the mineralogy of a copper sulfide ore. Miner Eng 2012;36–38(10):309–13. [26] Wang E, Shi F, Manlapig E. Mineral liberation by high voltage pulses and conventional comminution with same specific energy levels. Miner Eng 2012;27–28:28–36. [27] Kukurugya F, Rahfeld A, Möckel R, et al. Recovery of iron and lead from a secondary lead smelter matte by magnetic separation. Miner Eng 2018;122:17–25. [28] Vizcarra TG, Wightman EM, Johnson NW, et al. The effect of breakage mechanism on the mineral liberation properties of sulphide ores. Miner Eng 2010;23(5):374–82. [29] Greb VG, Guhl AC, Weigand H, et al. Understanding phosphorus phases in sewage sludge ashes: a wet-process investigation coupled with automated mineralogy analysis. Miner Eng 2016;99:30–9. [30] Gräbner M, Lester E. Proximate and ultimate analysis correction for kaolinite-rich Chinese coals using mineral liberation analysis. Fuel 2016;186:190–8. [31] Jin Wang. Study on selective dissociation of low rank jurassic coal. Xi'an: Xi'an University of Science and Technology; 2016. [32] Quinteros J, Wightman E, Johnson NW, et al. Evaluation of the response of valuable and gangue minerals on a recovery, size and liberation basis for a low-grade silver ore. Miner Eng 2013;74:150–5. [33] Stamboliadis ET. The evolution of a mineral liberation model by the repetition of a simple random breakage pattern. Miner Eng 2008;21(3):213–23.
11
Contents lists available at ScienceDirect
Fuel journal homepage: www.elsevier.com/locate/fuel
Full Length Article
Evaluation of coal component liberation upon impact breakage by MLA Yanhong Fu a b c
a,1
b,c,⁎,1
, Zhen Li
b,c
b
, Anning Zhou , Shanxin Xiong , Chao Yang
b
T
School of Chemical Engineering & Technology, China University of Mining and Technology, Xuzhou 221116, Jiangsu, PR China College of Chemistry and Chemical Engineering, Xi’an University of Science and Technology, Xi’an 710054, Shaanxi, PR China Key Laboratory of Coal Resources Exploration and Comprehensive Utilization, Ministry of Land and Resources, Xi’an 710054, Shaanxi, PR China
GRAPHICAL ABSTRACT
ARTICLE INFO
ABSTRACT
Keywords: Mineral liberation analysis Mechanical impact breakage Liberation mechanism Coal components
To elucidate the coal component liberation mechanisms upon typical impact breakage, the coal was selected from the Shangwan mine in China. Thereafter, mineral liberation analysis was adopted as the main method for investigating phase interface characteristics, classification characteristics of the various classes of comminuted products, and changes in the mineral area and length gradients upon mechanical impact breakage. The results indicate that the grain sizes of the comminuted products decreased in the following order: slag product > classifier product > bag product. Moreover, the disseminated grain size, dissemination mode, and original cleavages had a direct influence on the recovery rate of the completely liberated phase. The coal, which formed the main component of the samples, exhibited the highest cumulative mass recovery (CMR) in classified products and was most easily liberated. Furthermore, the kaolinitebearing coal and pyrite were moderately liberated, the quartz and kaolinite were difficult to liberate, and the illite was extremely difficult to liberate. Under mechanical impact breakage, intragranular and intergranular fractures mainly occurred in particles, with the changes in the mineral boundary and mineral area corresponding to varying fracture modes. To a certain extent, the particle comminution could be quantified by the changes in the slope of the equivalent circle diameter–-CMR curve. It was determined that the main cause of the increased liberation degree is the generation of the completely liberated phase of the component of interest. Furthermore, by adopting the liberation factor for quantification of the mineral liberation, the calculation model for coal component liberation was obtained.
Corresponding author at: College of Chemistry and Chemical Engineering, Xi’an University of Science and Technology, Xi’an 710054, Shaanxi, PR China. E-mail address: [email protected] (Z. Li). 1 These two authors contribute equally to this work. ⁎
https://doi.org/10.1016/j.fuel.2019.116136 Received 27 June 2019; Received in revised form 15 August 2019; Accepted 2 September 2019 Available online 17 September 2019 0016-2361/ © 2019 Elsevier Ltd. All rights reserved.
Fuel 258 (2019) 116136
Y. Fu, et al.
1. Introduction
2. Experimental materials and characterization methods
Mineral liberation is a key step in mineral processing, in which the energy consumption of the crushing process accounts for 75% of the energy consumption of the entire concentrator [1,2]. Comminution is mainly aimed at freeing valuable minerals from the gangue to enhance the efficiency of the subsequent selection [3,4]. The success of the separation is related to the liberation distribution of the feed particles, the performance of the separation technology applied, and the inherent characteristics of the feed material [5,6]. Among these, the fundamental characteristics of different ores, such as the grindability, volume ratio of components, texture and properties, will determine the ease of the mineral liberation and subsequent mineral separation [7–9]. Moreover, it is obvious that significant fracture will enhance the exposure liberation of minerals during comminution. which will consequently influence the mineral grinding ability and separation recovery rate [10–13]. Gasification and liquefaction for particle size and mineral composition of coal particles have higher requirements. Therefore, to a certain extent, studies on mineral cleavages, textures, and liberation characteristics are useful for the assessment of downstream processes [14,15]. At present, major research techniques and methods used in the investigation of the liberation and mineralogical characteristics of mineral particles include mineral liberation analysis (MLA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energydispersive X-ray spectroscopy (EDS) [16–19]. Furthermore, SEM coupled with EDS (SEM–EDS) has been applied to quantify the liberation, grade, and surface exposure conditions of minerals [20]. Little et al. published an approach to quantifying the fracture along grain boundaries based on the conservation of the grain shape of chromite using automated SEM–EDS [21]. Devasahayam S et al. adopted the method of quantitative evaluation of minerals by scanning electron microscopy to investigate the relationship between the grain size and mineral liberation in Australian zinc ore, and identified a direct correlation between the grain size distribution resulting from grinding and the liberated free minerals, as well as binary and ternary composites [22]. It was found that MLA can provides detailed information on the composition of single particles as well as particle populations exposed on the crosssectioned surface of a grain mount, which can be used to evaluate the process efficiency related to the liberation distribution of valuables, or to the distribution of a feature used for the separation of valuables from barren particles, and MLA data is applied in the magnetic separation process [23]. The mineralogy, grain size, dissemination, textural consistency, and mineral associations were determined for a commercially exploited porphyry copper ore using a mineral liberation analyzer [24]. And numerous studies have been conducted on the dissociation characteristics and modal mineralogy of useful minerals in ores of different types and structures (such as sulphide ores), and different Pb behaviors in the varying size fractions during magnetic separation, by means of MLA [25–28]. Besides, the MLA system was used to examine the Pphases in sewage sludge ashes [29]. Gräbner M et al. adopted MLA to estimate the water-bearing kaolinite content, and found that MLA also offered an advantage over XRD in the detection of amorphous material; that is, clay mineral types [30]. Based on the above review, MLA provides an effective means of quantifying the liberation characteristics of minerals, and it is the most extensively applied technique in the relevant research. However, its application has mainly been limited to the analysis of metallic and nonmetallic minerals; few studies have reported on the application of MLA in the investigation of coal liberation and the quantitative characterization of comminution mechanisms. Therefore, this study investigated the classification of the liberation mechanisms of coal and minerals upon mechanical impact breakage, as well as the influences of different fracture modes on the mineral liberation, with the aim of providing technical and theoretical support for future quantitative research on the multi-component liberation mechanisms of coal.
2.1. Experimental raw materials The samples used in this study were obtained from coals mined from the Shangwan coal mine of the Shendong mining area in China (henceforth referred to as SW). Table 1 lists the specifications regarding the proximate and ultimate analyses of the coal samples. The results of the analysis indicate relatively high carbon and fixed carbon contents and relatively low hydrogen, oxygen, and sulfur contents in the SW. Fig. 1 illustrates the polished coal rock sections of the SW. The coal petrography slices was prepared according to 《GB/T 8899-2013 Determination of maceral group composition and minerals in coal》and different mineals can be identified under commonreflected light with different colors. Pyrite shows pale yellow and white, the clay minerals are dark grey. It can be observed that the overall mineral content of the raw coal was relatively low (Fig. 1(a)), corresponding to the lower ash and sulfur contents in Table 1. The main minerals disseminated in the coal samples were pyrite, which exhibited a scattered stellate dissemination pattern (Fig. 1(b)), and clay minerals, which filled the cavities of the macerals (Fig. 1(c)). 2.2. Equipment and methods (1) Equipment The experimental equipment used in the study was a mechanical impact breakage system, developed and designed in-house at the Xi'an University of Science and Technology, which consisted of a grinder, classifier, and bag dust collector. The samples were comminuted upon impact with the rotor-driven parts and subsequently classified according to the grain size and density. The samples were comminuted upon impact with the rotor-driven parts and subsequently classified according to the grain size and density. The resultant classified products were the slag product (SP), classifier product (CP), and bag product (BP). Fig. 2 presents a schematic of the experimental equipment. Based on the results of a relevant experimental study conducted by our research group [31], the rotational speed of the classifier was set to 2000 r/min, while the feed grain size was set to > 6 mm. (2) Methods The Mineral Liberation Analyzer 250 (FEI, USA), obtained from the Oil Sands and Coal Interfacial Engineering Facility of the University of Alberta, Canada, was used to study the liberation characteristics of each coal component. The MLA is an automated mineralogy tool used for process mineralogy, which incorporates the technologies of Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Analysis (EDAX/BRUKER). MLA software controls the SEM and use images and x-rays to characteristic minerals, particles and rocks. The characterization parameters were as follows: a. Free surface (FS) The dissemination and liberation degrees of the minerals were quantitatively characterized based on the free surface calculated on the area% of the minerals of interest [32]. Fig. 3(a)–(c) illustrate the FS Table 1 The proximate analysis and ultimate analysis of raw coal. Item
SW
2
Proximate analysis
Ultimate analysis
Aad%
Mad%
Vad/%
FCad/%
Cad%
Had%
Oad%
Nad%
St,ad %
10.38
7.50
32.84
49.28
68.94
3.36
8.99
0.54
0.29
Fuel 258 (2019) 116136
Y. Fu, et al.
clay mineral
pyrite
clay mineral 50µm
50µm
(a)
50µm
(b )
(c )
Fig. 1. The coal petrography slices of raw coal.
b a g filt er
cla ssifier
ECD
classifier product
Fig. 4. The schematic of equivalent circle diameter.
d. Mean Phase Equivalent Circle Diameter (ECD)
pulver izer
main air blower slag
Implement point x-ray analysis to efficiently and effectively analyze mineral phases within a particle. The Mean Phase ECD was obtained by the DataView, which means the mean phase size of the mineral of interest.
bag product
Fig. 2. The equipment contact diagram of mechanical impact crushing system.
e. Boundary length gradient and area gradient of mineral of interest
calculations, with A and B indicating the mineral of interest (represented by coal) and other intergrown minerals (represented by pyrite), respectively.
The boundary length gradient of the mineral of interest was defined as the difference in the boundary lengths of the same mineral between different classified products, while the area gradient was defined as the difference in the areas of the same mineral between different classified products. Here, L1 denotes the difference in the boundary lengths of the same mineral between the SP and CP, L2 denotes the difference in the boundary lengths of the same mineral between the classifier product CP and BP, A1 denotes the difference in the areas of the same mineral between the SP and CP, and A2 denotes the difference in the areas of the same mineral between CP and BP, as expressed by Eqs. (3)–(6), respectively.
b. Phase specific surface area (PSSA) The PSSA of the coal components was calculated using Eq. (1):
PSSA =
Mineral Boundary Mineral Area
(1)
c. Equivalent circle diameter (ECD) The grain size measurements in the MLA were performed based on the equivalent circle diameter (ECD), which was calculated by converting the area (derived from the measured pixels) into an equivalent circle value. This approach is suitable for rounded particles or grains. Fig. 4 presents a schematic of the ECD, which was calculated using Eq. (2):
Equivalent Circle Diameter = 2
(2)
Area
(a)
(3)
L2 = BPM ineral boundary
CPMineral boundary
(4)
A1 = CPM ineral area
SPMineral area
(5)
A2 = BPM ineral area
CPMineral area
(6)
A
A 0%
SPMineral boundary
B
B
Liberation by free surface
L1 = CPM ineral boundary
A B
50% (b)
Fig. 3. The sketches of mineral liberation classes based on free surface. 3
100% (c)
Fuel 258 (2019) 116136
Y. Fu, et al.
3. Results and discussion
phase of 27.47% in the BP. Moreover, two-phase particles accounted for the highest content in the SP and an RV value of 49.44%, indicating a high degree of difficulty in achieving liberation. The recovery rates of the completely liberated phase of the quartz were higher in the CP and BP at 29.45% and 29.31%, respectively. Moreover, the two-phase particle contents were relatively high in all three products, at 43.96%, 49.94%, and 49.93%, respectively, indicating a high degree of difficulty in achieving liberation. Owing to the generally low liberation degree, the illite was mainly disseminated in binary or greater phase particles. The completely liberated phase was mainly distributed in the SP and BP, with recovery rates of 20.1% and 17.29%, respectively. This demonstrates that, upon strong impact, liberation first occurred in the easily liberated illite particles, while the other particles could only be liberated when a certain grain size was achieved, indicating an extremely high degree of difficulty in achieving liberation. The dissemination characteristics of the mica were similar to those of the illite, with the maximum recovery rate of the completely liberated phase reaching a maximum of 58.81% in the BP. Particles containing binary or greater phases were mainly distributed in the CP, indicating that a certain degree of liberation could be achieved in the mica and its associated minerals when the particle grain size was decreased to a certain extent through impact breakage; that is, the mica was moderately liberated. The above analysis demonstrates that the liberation of the coal and main disseminated minerals was influenced by the disseminated grain size, dissemination pattern and density, hardness, and original cleavages of the various associated minerals. The four levels of mineral liberation in the comminuted-classified products generated upon impact breakage were defined as follows: easily liberated (> 80% of Rv liberated of the mineral of interest), moderately liberated (80%–50% of Rv liberated of the mineral of interest), difficult to liberate (50%–20% of Rv liberated of the mineral of interest), and extremely difficult to liberate (< 20% of Rv liberated of the mineral of interest). Table 3 displays the changes in the FS and PSSA of the main components in the coal under different fracture modes. The analysis revealed that the FS and PSSA values of the kaolinite-bearing coal, quartz, kaolinite, illite, calcite, and siderite increased sequentially from the SP to BP, while the coal, mica, and pyrite exhibited inconsistent change patterns. This was attributed to the different fracture modes exhibited by the coal and major minerals upon impact breakage.
3.1. Analysis of dissemination characteristics and mineral components of raw coal Mix the coal sample in a glass vial to homogeneous and it can be mounted in a 30 mm diameter sample block, and then grinding and polishing to obtain a high quality polished sections. The prepared samples were used to analyse the dissemination characteristics and mineral components of raw coal. Table 2 displays the main mineral components of the SW, which included coal, quartz, kaolinite, calcite, mica, pyrite, and illite. Fig. 5 illustrates the dissemination patterns of the main components of the SW obtained by MLA. It can be observed that the different minerals exhibited varying dissemination modes and disseminated grain sizes. The disseminated grain sizes of the kaolinite and calcite were within the range of 10–80 μm; the pyrite and quartz were irregularly disseminated with grain sizes of 30–120 μm, while the paragenetic illite and mica exhibited laminated irregular flakes and scattered stellate dissemination patterns, with grain sizes of 1–50 μm. 3.2. Analysis of liberation characteristics of coal and minerals (1) Analysis of grain size distributions The liberation characteristics of each component in coal were further analyzed by sampling the classified products under mechanical impact comminution. In this particular example grain size was calculated by equivalent circle and it is based on the measured 2D surface. And the particle size is calculated by the Eq. (2). Fig. 6 presents the grain size distributions and MLA diagrams of the various products obtained under mechanical impact breakage conditions. It can be observed that comminution occurred in the coal and disseminated mineral particles upon mechanical impact breakage, with the comminuted particles settling into SP, CP, and BP in turn. The P values and particle size distribution curves indicate a decreasing trend of grain size from SP, CP and BP successively. And there are a few overlaps of particle size between CP and BP with different classification effects. According to the MLA diagrams, it can be observed that, in the SP, disseminated particles of mica and illite with grain sizes of approximately 10 μm were associated with coal, while calcite with grain sizes of 5–25 μm exhibited a dotted dissemination pattern within the coal (Fig. 6(A)). In the CP, the quartz was completely liberated, while the illite and mica were partially liberated (Fig. 6(B)); intergrowths were absent in the BP (Fig. 6(C)).
(3) Analysis of fracture modes
(2) Analysis of phase interface liberation characteristics
Further analysis was performed on the fracture modes of the coal and major minerals (kaolinite-bearing coal, quartz, siderite, calcite,
Fig. 7 illustrates the phase interface characteristics of the coal and minerals in the comminuted-classified products of the SW following mechanical impact breakage. In this case, RV denotes the recovery rate of each mineral from the various comminuted-classified products. Coal, which formed the main component of the samples, was easily liberated, and exhibited a high liberation degree in the various products, with the highest recovery rate for the completely liberated phase being 82.45% in the CP. The maximum recovery rate for the completely liberated phase of kaolinite-bearing coal was 52.36% in the BP. Particles containing binary or greater phases were mainly distributed in the SP, indicating that kaolinite-bearing coal particles with smaller grain sizes were more readily liberated; that is, the kaolinite-bearing coal was moderately liberated. The highest recovery rates of pyrite were achieved in the CP and BP, with RV values of 51.56% and 50.35%, respectively. In general, the completely liberated phase and two-phase particles dominated the comminuted products, indicating moderate liberation of the pyrite. For the kaolinite, the liberation degree increased sequentially from the SP to BP, with a maximum recovery rate of the completely liberated
Table 2 SW coal mineral phases identified by MLA analysis.
4
Mineral
Mineral weight (%)
Coal Coal (kaolinite) Kaolinite Illite Calcite Pyrite Quartz Muscovite Siderite Albite Orthoclase Silicate Ankerite Dolomite Barite Others Total
91.65 2.94 1.6 1.18 0.92 0.3 0.32 0.17 0.22 0.02 0.03 0.02 0.03 0.02 0.03 0.55 100
Fuel 258 (2019) 116136
Y. Fu, et al.
coal
30μm
kaolinite
quar tz
calcite
sider ite
illite
muscovite
pyr ite or thoclase
Fig. 5. Dissemination map of SW components.
kaolinite, and illite) under impact breakage. Fig. 8 illustrates the relationship between the liberation degree and cumulative mass recovery (CMR) for the coal and aforementioned major minerals, while Fig. 9 presents the changes in the mineral boundary length gradient and area gradient of the various comminuted-classified products. As indicated in Fig. 8, the CMR decreased with an increase in the liberation degree of the coal and major minerals. The results are summarized as follows: For the kaolinite-bearing coal, |L2| > |L1| and |A2| > |A1|, with the CMR of the BP being consistently higher than those of the SP and CP across all liberation levels. This indicates that the kaolinite-bearing coal exhibited a greater response to the impact breakage. As the particle grain size decreased, intragranular fracture became the dominant
fracture mode of the mineral of interest, corresponding to greater changes in |L2|. Moreover, the degree of liberation completeness increased as the grain size decreased, leading to a maximum CMR100% (which denotes that the liberation degree is 100%) of 38.14% in the BP. For the quartz, |L2| > |L1| and |A2| > |A1|, and the CMR decreased sequentially as follows: CMR(BP) > CMR(CP) > CMR(SP). This demonstrates that the quartz exhibited a greater response to the impact breakage. Both intragranular and intergranular fractures occurred in the larger particles of the mineral of interest, while intragranular fracture mainly occurred in the smaller disseminated particles. Correspondingly, more significant changes could be observed in |A2|. During the subsequent classification process, a portion of the quartz
110
bottom slag
90
bag product
Cumulative Passing(wt%)
100
A
classifier product
80 bottom classifier P-value
slag
product
product
(μm)
（μm）
（μm）
60
P10
41.28
12.66
6.78
50 40 30
50μm
bag
70
P20
63
18.23
6.89
P25
75.01
20.88
7.47
P50
124.15
34.55
11.9
P75
184.85
53.48
19.14
P80
199.75
58.92
21.92
P90
244.46
72.11
30.74
B
50μm
C
20 10 0 1
10
100
Particle Size(μm)
coal calcite
50μm kaolinite pyr ite illite quar tz sider ite muscovite
Fig. 6. MLA images and particles of SW crushing-classification products under mechanical impact and comminution. 5
Fuel 258 (2019) 116136
Y. Fu, et al.
Fig. 7. Analysis of the phase surface characteristics of SW coal and its primary minerals.
L1| > |L2| and |A2| > |A1|, indicating that the changes in the mineral boundary length decreased, while the changes in the mineral surface increased across the SP, CP, and BP. This could be attributed to the occurrence of an intergranular fracture in a small portion of the largergrained pyrite disseminated around the coal, leading to the exposure of pyrite with a decrease in the coal grain size. In contrast, intragranular fracture mainly occurred in the smaller-grained disseminated pyrite, in parageneses with other minerals. During the classification process, large particles settled into the SP, moderately sized particles settled into the CP, and fine particles settled into the BP. Consequently, when the liberation degree was less than 35%, CMR (SP) > CMR (CP) > CMR (BP); when the liberation degree was within the range of 35%–90%, the CMR of the CP was highest, while the CMR of the SP and BP fluctuated between high and low values; and when the degree of liberation was 100%, CMR(BP) > CMR(CP) > CMR(SP). For the calcite, the phase interface change patterns were as follows: |L1| > |L2| and |A1| > |A2|, indicating that the changes in both the mineral boundary length and area decreased across the SP, CP, and BP. The dissemination pattern of the calcite in the coal resulted in a smaller
Table 3 Compilation of different parameters from MLA of crushing product. Mineral
Coal Coal (Kaolinite) Quartz Kaolinite Muscovite Illite Calcite Siderite Pyrite
PSSA/μm−1
FS/% SP
CP
BP
SP
CP
BP
81.97 25.22 36.6 12.52 5.55 6.67 29.93 19.83 57.27
93.04 45.88 56 35.92 25.85 24 42.57 51.38 67.15
92.02 71.68 65.53 54.89 44.97 36.49 50.57 58.61 66.94
0.12 0.61 0.45 0.32 0.64 0.33 0.24 0.52 0.43
0.27 0.71 0.46 0.51 0.71 0.64 0.45 0.65 0.69
0.69 1.09 0.62 0.65 0.68 0.79 0.9 1.08 1.13
was mainly distributed in the form of two-phase or multiple-phase particles in the SP and CP, while the other portion was completely liberated into fine particles, as illustrated in Fig. 7(a)–(c). The phase interface change patterns of the pyrite were as follows: 6
Fuel 258 (2019) 116136
Y. Fu, et al.
100
100
90
90
80 70 60
57.04
50
coal (slag product)
40
44.21
coal (classifier product)
38.14
30
coal (bag product)
34.52
20
coal (kaolinite) classifier product
coal (kaolinite) slag coal (kaolinite) bag product
10
14.17
quartz(classifier product) quartz(bag product) illite(slag product)
80
illite(classifier product)
70
illite(bag product)
60 50 40 30 20 10
calcite(slag product)
Cumulative Mass Recovery(%)
siderite(slag product) siderite(classifier product)
70
siderite(bag product)
60 50 40 30 20 10 0
100
90-95
95-100
80-85
85-90
75-80
65-70
70-75
60-65
50-55
55-60
45-50
35-40
pyrite (classifier product)
90
calcite(bag product)
80
pyrite (slag product)
100
calcite(classifier product)
90
40-45
(b ) qua r t z,ill it e
110
100
30-35
20-25
25-30
10-15
15-20
0-5
Liberation Classes(%)
(a ) coa l
110
5-10
100
95-100
85-90
90-95
80-85
75-80
70-75
60-65
65-70
55-60
50-55
45-50
40-45
35-40
25-30
30-35
20-25
15-20
10-15
0-5
Liberation Classes(%)
pyrite (bag product) kaolinite (slag product)
80
kaolinite (classifier product)
70
kaolinite (bag product)
60 50 40 30 20 10
100
90-95
95-100
85-90
75-80
Liberation Classes(%)
80-85
70-75
60-65
65-70
55-60
50-55
45-50
35-40
40-45
30-35
25-30
20-25
15-20
5-10
0-5
100
90-95
85-90
80-85
95-100
Liberation Classes(%)
75-80
70-75
65-70
60-65
55-60
50-55
45-50
35-40
40-45
30-35
25-30
20-25
15-20
10-15
0-5
5-10
0 10-15
Cumulative Mass Recovery(%)
quartz(slag product)
0 5-10
0
21.30
Cumulative Mass Recovery(%)
110
Cumulative Mass Recovery(%)
110
(d ) pyr it e,k a olin it e
(c) ca lcit e,s id er it e
Fig. 8. Relationship map of liberation degree and CMR on SW and its primary mineral components in mechanical impact crushing method.
response to the impact breakage. When the liberation degree was up to 35%, CMR(SP) > CMR(CP) > CMR(BP); when the liberation degree was within the range of 35%–85%, CMR(SP) > CMR(BP) > CMR(CP); and when the liberation degree was > 95%, CMR(SP) > CMR(CP) > CMR(BP), with the CMR of the completely liberated phase being extremely low in the SP (2.98%) and CP (9.25%). Based on these results, it could be deduced that the liberation of the calcite was contingent on the liberation of the other minerals, and was mainly dominated by intragranular fracture. The completely liberated fine particles settled into the BP, which had the highest CMR value of 21.11%. The phase interface change patterns of the illite were as follows: |L1| > |L2| and |A1| > |A2|. When the liberation degree of the illite was less than 30%, CMR(SP) > CMR(BP) > CMR(CP); when the liberation degree was > 55%, CMR(BP) > CMR(CP) > CMR(SP). This indicates that the illite had a relatively small disseminated grain size and was extremely difficult to liberate. Consequently, the illite exhibited a smaller response to the impact breakage, with the dominating fracture mode being intragranular fracture. Liberation only occurred in grains
that had been comminuted to small grain sizes, which led to low CMR values of 0.19%, 4.99%, and 12.84% for the completely liberated phases in the SP, CP, and BP, respectively. For the kaolinite, the disseminated particles in the coal had a smaller disseminated grain size, exhibited a multiphase distribution (Fig. 8), and were difficult to liberate. The phase interface change patterns were as follows: |L1| > |L2| and |A1| > |A2|, indicating that the changes in both the mineral boundary length and area of the kaolinite decreased across the SP, CP, and BP. Liberation only occurred when the particle grain size was smaller than the disseminated grain size (Fig. 6), leading to a maximum CMR100% of 24.06% in the BP. 3.3. Fracture classification characteristics of particles under mechanical impact breakage Fig. 10 illustrate the relationship between the mean phase ECD and CMR for the coal with different liberation degrees in the SP, CP, and BP. It can be observed that the different grain sizes corresponded to varying 7
Fuel 258 (2019) 116136
Y. Fu, et al.
L1
L2
4
×10
-80
-40 -20 0 20 40 4
60
80
80
2
Mineral Area(µm )
×10
Mineral Boundary(µm)
-60
60 40 20 0 -20 -40 -60 -80
coal (k) quartz
A1
A2 kaolinite
illite
calcite
siderite
pyrite
Fig. 9. The gradient variation of mineral boundary and mineral area on main components of SW.
liberation degrees. The CMR values of the completely liberated coal in the SP, CP, and BP were 34.52%, 57.04%, and 44.21%, respectively. When the liberation degree was within the range of 0%–60%, the changes in the CMR of the coal with the ECD were not significant, indicating that the recovery rate of the particles within 0%–60% liberation was influenced by the grain size to a smaller extent. When the liberation degree was within the range of 60%–80%, the gradient of the ECD–CMR curve began to increase significantly; when the liberation degree was within the range of 80%–100%, the particle recovery rate varied significantly with the grain size. The ascending order of the ECD–CMR curve gradients was as follows: K(SP) < K(CP) < K(BP), demonstrating that the grain size exerted a greater influence on the CMR at higher liberation degrees. This can be explained by the following: at lower liberation degrees, the component of interest was not liberated, leading to a smaller influence of the changes in the grain size on the CMR; at higher liberation degrees, a portion of the component of interest had been liberated, while the other portion remained disseminated in the form of two-phase or multiphase grains, leading to a greater influence of the fracture-induced grain size reduction on the CMR. The gradient of the ECD–CMR curve can reflect the amount of particle comminution to a certain extent. If K = 0, components of different grain sizes have the same CMR value, which indicates that the crushing method has resulted in maximum liberation of the component of interest. Therefore, the interface strength is equivalent to the grain strength, and a reduction in particle size will not influence the mineral liberation degree. Such a phenomenon typically occurs in the completely liberated phase or within purely intragranular fractures of components that are not of interest. Moreover, if K = 1, the components have identical grain sizes but different CMR values; consequently, the liberated grain size under the conditions of the highest liberation degree or the liberated grain size at the maximum CMR value can be determined, thereby providing a basis for evaluating the extent of the mineral liberation.
4. Model for changes in FS and phase interface length during coal liberation process Coal was selected as the mineral of interest for the MLA owing to its high contents in the samples, while the other minerals were regarded as disseminated minerals. Fig. 11(a)–(c) present the three typical dissemination modes selected for analysis: the dissemination of the mineral of interest and other minerals on the external surfaces, the encapsulation of other minerals by the mineral of interest, and the encapsulation of the mineral of interest by other minerals, respectively. Under impact breakage, intergranular and intragranular fractures will occur in the component of interest. For the dissemination mode in Fig. 11(a), if the intergranular fracture occurs between the mineral of interest and disseminated minerals (1), the changes in the boundary length and area of the mineral of interest will alter the liberation degree. If the mineral boundary length remains unchanged, the PSSA will increase with a reduction in the mineral area, leading to an increase in the completely liberated phase and liberation degree. If the mineral area remains unchanged, the PSSA will decrease with a reduction in the mineral boundary length, and the liberation degree of the mineral of interest will only increase when new FS are generated by changes in the boundary length. If intragranular fracture occurs in components that are not of interest, the new surface (NS) and ΔPSSA = 0. For the dissemination mode in Fig. 11(b), if the intergranular fracture occurs in the component of interest, bothΔL and PSSA will increase (1); if an intragranular fracture occurs in the component of interest and produces NSs, the NSs will be equivalent to the FS and the change in the PSSA (2); that is, ΔPSSA = NS = FS. A reduction in the grain size will not result in changes to the liberation degree of the component of interest; however, under this dissemination mode, the liberation degree of the component of interest will be maintained at 100%. Under the dissemination mode in Fig. 11(c), intragranular fracture occurs in the disseminated minerals in the particles, instead of in the component of interest (1). Therefore, no changes occur in the boundary length and area of the component of interest, and the liberation degree is 0% as the component of interest does not become exposed. If intragranular fracture occurs and produces FS in the mineral of interest 8
Fuel 258 (2019) 116136
Y. Fu, et al.
Fig. 10. The relationship of mean phase ECD and CMR on classifier product with different liberation classes by mechanical impact crushing method.
(2), both the mineral phase interface area and liberation degree will increase.
comminution process and single particles of the component of interest are not generated, the liberation degree L = 0%. If both intergranular and intragranular fractures occur, the mineral liberation model proposed by Stamboliadis [33] can be applied. Assuming that all particles (including single particles and intergrowths) have the same volume v, diameter d, and grade gi, the total number of V d 3 particles in the product N = vP gi ; similarly, N = P3 gi . The total volume d of component A can be calculated using VA = N ·v . If all particles with the same grade gi of component A in the product are combined into a single particle, VA = v . Therefore, the critical liberation volume and v critical liberation area can be determined as follows: VPL = g and
5. Calculation model for coal component liberation 1) When performing measurements in MLA, the particle diameter can be calculated by converting the area derived from the measured pixels into an equivalent circle value: dp = 2 × AP , where Ap is the mineral area. Furthermore, the particle volume can be calculated 1 3 using the formula VP = 4 - 2 Ap 2 . The volumes of components A and B in the particle are denoted by VA and VB, respectively, and the grades of components A and B in the raw particle can be calculated V using the formulae gA = V +AV and gB = 1 gA . A
dPL =
d 3 gi
i
, respectively. The liberation factor is defined as P =
di , dpL
where Vi is the volume of particles within the product. Moreover, P′ ≤ 1 indicates the occurrence of liberation in the component of interest, while P′ > 1 indicates the non-occurrence of liberation.
B
When intragranular fracture occurs in components A and B, resulting in the generation of multiple liberated single particles A1, A2⋯Ai and B1, B2⋯Bi, assuming that VA1 = VA2 =⋯= VAi and VB1 = VB2 =⋯= VBi, the grade of component A can be calculated by VA, gA,i 1 = V i - 1 . When VA,i−1 = VB,i−1, gA,i 1 = gB,i 1 and the liberation
2) During the comminution process, regardless of whether intergranular or intragranular fracture occurs, smaller particles with different volume fractions will be produced under the critical diameter dPL. The comminuted particles are divided into m grain size levels. As the particle originally contains k components, the particle
p, i 1
degrees of components A and B are identical; that is, LM = LN = 100%. If intragranular component liberation occurs during the
9
Fuel 258 (2019) 116136
Y. Fu, et al.
Fig. 11. The process model of particles liberation under mechanical impact crushing method.
volume is equal to the sum of the volumes of all components; that is, VP,k = v1, k + v2, k + ...+vk, k . The grade of component A at the ith grain v size level is defined as gA,i = VA,i , where di represents the average P, i geometric diameter of the ith grain size level and gi > gi+1 (denoting a sequential decrease in grain size). Furthermore, dj represents the average geometric diameter of the jth grain size level. When i = j, di = dj, and the liberation degree of component A at the jth grain size level can be determined using the formula j
LA(di) =
i=1 m i=1
g A,j
VP (di)
boundary length and mineral area of the component of interest, leading to an increase in the liberation degree. If intragranular fracture occurs in the component of interest and produces NSs, the NSs will be equivalent to the FS, but the liberation degree will not change. If intragranular fracture produces single particles of the component of interest, the liberation degree will increase. By adopting the interface liberation factor to characterize the liberation of microscopic components, where P′ ≤ 1 indicates the occurrence of liberation in the component of interest and P′ > 1 indicates the non-occurrence of liberation, the following calculation model for
. The liberation degree of the overall particle is then
calculated using the formula L¯0 = the jth grain size grade.
m j =1
the liberation of coal and other minerals was obtained: L¯0 =
L (di) j , where γj is the yield of
m
j =1
L (di) j .
Acknowledgements Financial support for this research, supported by Provincial Natural Science Foundation research project of Shaanxi (No. 2018JQ5017), China coal industry association 2017 annual science and technology research guidance project (Grant No. MTKJ 2017-306), and Key Laboratory of Coal Resources Exploration and Comprehensive Utilization, Ministry of Land and Resources (No. ZKF2018-2), are gratefully acknowledged. I also offer my sincere thanks to professor Zhenghe Xu from University of Alberta, who provided important advice and suggestions on amendments.
6. Conclusions The liberation degrees of minerals are influenced by the disseminated grain size, dissemination pattern and density, hardness, and original cleavages of the various associated minerals. Under mechanical impact breakage, intragranular and intergranular fractures mainly occur in the particles, with the changes in the mineral boundary length and area corresponding to different fracture modes. The gradient of the mean phase ECD–CMR curve can quantify the particle comminution to a certain extent, and provide a basis for determining the liberation grain sizes of the component of interest as well as the selection of comminution methods under certain liberation levels. The liberation degree cannot be characterized by the changes in the FS and PSSA under varying dissemination modes of the component of interest. The main cause of an increased liberation degree with the application of an external force is the generation of the completely liberated phase of the component of interest. When the intergranular fracture occurs between the component of interest and other disseminated components in a particle, changes take place in the mineral
References [1] Musa F, Morrison R. A more sustainable approach to assessing comminution efficiency. Miner Eng 2009;22(7):593–601. [2] Guanghui Y, Zhenxing Z, Bo Z, et al. Preferential sequence crushing of copper ore based upon high-voltage pulse technology. Miner Eng 2019;131:398–406. [3] Mariano RA, Evans CL, Manlapig E. Definition of random and non-random breakage in mineral liberation – A review. Miner Eng 2016;94:51–60. [4] Ueda T, Oki T, Koyanaka S. Stereological correction method based on sectional texture analysis for the liberation distribution of binary particle systems. Adv Powder Technol 2017;28(5):1–8. [5] Leißner T, Mütze T, Bachmann K, et al. Evaluation of mineral processing by assessment of liberation and upgrading. Miner Eng 2013;53(10):171–3.
10
Fuel 258 (2019) 116136
Y. Fu, et al. [6] Tromans D. Mineral comminution: energy efficiency considerations. Miner Eng 2008;21(8):613–20. [7] Shi F, Zuo W. Coal breakage characterisation – Part 1: breakage testing with the JKFBC. Fuel 2014;117:1148–55. [8] Shi F. Coal breakage characterisation – Part 2: multi-component breakage modelling. Fuel 2014;117:1156–62. [9] Xie W, He Y, Yang Y, et al. Experimental investigation of breakage and energy consumption characteristics of mixtures of different components in vertical spindle pulverizer. Fuel 2016;190:208–20. [10] Tungpalan K, Wightman E, Manlapig E, et al. The influence of veins on mineral liberation as described by random masking simulation. Miner Eng 2017;100:109–14. [11] Little L, Mainza AN, Becker M, et al. Fine grinding: how mill type affects particle shape characteristics and mineral liberation. Miner Eng 2017;111:148–57. [12] Samanli S. A comparison of the results obtained from grinding in a stirred media mill lignite coal samples treated with microwave and untreated samples. Fuel 2011;90(2):659–64. [13] Garcia D, Lin CL, Miller JD. Quantitative analysis of grain boundary fracture in the breakage of single multiphase particles using X-ray microtomography procedures. Miner Eng 2009;22(3):236–43. [14] Parian M, Mwanga A, Lamberg P, et al. Ore texture breakage characterization and fragmentation into multiphase particles. Powder Technol 2018;327:57–69. [15] Lee H, Klima MS, Saylor P. Evaluation of a laboratory rod mill when grinding bituminous coal. Fuel 2012;92(1):116–21. [16] Ueda T, Oki T, Koyanaka S. A general quantification method for addressing stereological bias in mineral liberation assessment in terms of volume fraction and size of mineral phase. Miner Eng 2018;119:156–65. [17] Fandrich R, Gu Y, Burrows D, et al. Modern SEM-based mineral liberation analysis. Int J Miner Process 2007;84(1):310–20. [18] Lastra R, Paktunc D. An estimation of the variability in automated quantitative mineralogy measurements through inter-laboratory testing. Miner Eng 2016;95:138–45. [19] Zhen L, Yanhong F, Anning Z, et al. Effect of multi-intensification on the liberation of maceral components in Coal. Fuel 2019;237:1003–12. [20] Reyes F, Lin Q, Cilliers JJ, et al. Quantifying mineral liberation by particle grade
and surface exposure using X-ray microCT. Miner Eng 2018;125:75–82. [21] Little L, Mainza AN, Becker M, et al. Using mineralogical and particle shape analysis to investigate enhanced mineral liberation through phase boundary fracture. Powder Technol 2016;301:794–804. [22] Devasahayam S. Predicting the liberation of sulfide minerals using the breakage distribution function. Miner Process Extr Metall Rev 2015;36(2):136–44. [23] Leißner T, Bachmann K, Gutzmer J, et al. MLA-based partition curves for magnetic separation. Miner Eng 2016;94:94–103. [24] Batchelor AR, Jones DA, Plint S, et al. Increasing the grind size for effective liberation and flotation of a porphyry copper ore by microwave treatment. Miner Eng 2016;94:61–75. [25] Albijanic B, Bradshaw DJ, Nguyen AV. The relationships between the bubble–particle attachment time, collector dosage and the mineralogy of a copper sulfide ore. Miner Eng 2012;36–38(10):309–13. [26] Wang E, Shi F, Manlapig E. Mineral liberation by high voltage pulses and conventional comminution with same specific energy levels. Miner Eng 2012;27–28:28–36. [27] Kukurugya F, Rahfeld A, Möckel R, et al. Recovery of iron and lead from a secondary lead smelter matte by magnetic separation. Miner Eng 2018;122:17–25. [28] Vizcarra TG, Wightman EM, Johnson NW, et al. The effect of breakage mechanism on the mineral liberation properties of sulphide ores. Miner Eng 2010;23(5):374–82. [29] Greb VG, Guhl AC, Weigand H, et al. Understanding phosphorus phases in sewage sludge ashes: a wet-process investigation coupled with automated mineralogy analysis. Miner Eng 2016;99:30–9. [30] Gräbner M, Lester E. Proximate and ultimate analysis correction for kaolinite-rich Chinese coals using mineral liberation analysis. Fuel 2016;186:190–8. [31] Jin Wang. Study on selective dissociation of low rank jurassic coal. Xi'an: Xi'an University of Science and Technology; 2016. [32] Quinteros J, Wightman E, Johnson NW, et al. Evaluation of the response of valuable and gangue minerals on a recovery, size and liberation basis for a low-grade silver ore. Miner Eng 2013;74:150–5. [33] Stamboliadis ET. The evolution of a mineral liberation model by the repetition of a simple random breakage pattern. Miner Eng 2008;21(3):213–23.
11