# Experimental Investigations and Field Applications of Chemical Suppressants for Dust Control in Coal Mines

Authors: Qi Liao; Guorui Feng; Yurong Fan; Shengyong Hu; He Shao; Yisheng Huang
Journal: Advances in Materials Science and Engineering
 (2018)

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## Abstract

It is known that high dust concentrations are severely hazardous to health of miners and the safe operations of coal mines. The results of the suppressions of coal dust via chemical dust suppressant methods have been of critical significance, and these methods have been widely applied in coal mines. In this research study, a type of complex dust suppressant composed of surfactants, synergists, and cellulose was prepared. The prepared suppressant was characterized by a high wetting ability and adhesive capacity. The results of the performance tests of this study’s proposed complex dust suppressant showed that its dust sedimentation time was only four seconds, which was observed to be much shorter than that of water alone. Also, the proposed suppressant displayed a viscosity which was 25 times that of water. In this study’s field tests, the proposed complex dust suppressant was used for dust control in a mining roadway of the Zhangcun Coal Mine. The field test results revealed that the average suppression efficiencies of the total dust and respirable dust had reached 89.2% and 87.7%, respectively. Furthermore, a 44.5% increase in the control of the total dust had been observed, and a 65.6% increase in the control of the respirable dust had been achieved with the proposed method, when compared with the results of the previously used water curtain technology.


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## Body

## 1. Introduction

During coal mining process in China, large amounts of dust are usually generated. These dust accumulations are not only considered to be serious threats to the health of miners but also have negative impacts on the overall safety of the production processes [1–6]. According to the China National Institute of Occupational Health and Poison Control, new cases of pneumoconiosis in coal workers (CWP) totaled 23,152 in 2013 [7]. It has been confirmed that CWP is mainly induced by high amounts of inhalable dust particles in mines and has become the most serious occupational disease for underground coal miners [8]. Furthermore, dust accumulations which reach certain concentrations may potentially cause explosion accidents. Such accidents have previously resulted in serious environmental damages and economic losses [9]. Therefore, it is of great significance to develop efficient dust suppressant methods which can be effectively used for reducing coal dust concentrations and protecting the health of coal miners [10].In recent years, many methods for dust suppression have been previously applied in underground coal mines. Among these methods, it had been found that water-spraying methods were the simplest [11]. Therefore, the water-spraying methods are presently the most widely used dust suppression strategy in coal mine production areas [12]. However, these methods have been observed to have low dust suppression efficiency as well as high water pressure demands. Also, the water-spraying nozzles are known to be easily blocked and damaged. Therefore, these negative factors have significantly restricted the practical application of water-spraying methods for dust suppression in underground coal mines [13, 14]. It has been determined that foam suppression methods have the ability to reduce dust concentrations by 89.73% and have been observed to present 30% increases in suppression efficiency when compared to water-spraying methods at belt transfer points [15]. However, the high costs related to the preparation of the foam, as well as the observed poor applicability and large pressure losses of the foaming devices, have all presented drawbacks to using foam for dust suppression in coal mines [16]. An alternative is the use of water infusion methods for dust suppression. However, it uses considerable amounts of water and demand high injection pressures, which may subsequently lead to poor permeation effects in coal seams, as well as causing water runoff from fractures and coal skeleton damages [17]. Therefore, it has become quite obvious that there are serious drawbacks among the abovementioned approaches. Meanwhile, the applications of chemical dust suppression methods have exhibited promising prospects in the research field concerning dust control in coal mines [2, 18].Since the advent of chemical dust suppression methods, the majority of the related Chinese and international research studies have focused on making these methods’ materials more environmentally friendly and efficient [19–22]. Fan et al. [23] integrated aliphatic organic compounds with wetting agents, which enabled dust particles to be controlled during coal mining processes. Zhou et al. [2] examined the applications of dust suppressants derived from the water-absorbing inorganic salt. Wang et al. [24] identified an additive with optimal wetting characteristics based on surfactant compositions for subsurface dust removal. Yan et al. [25] collectively integrated a sound wave-induced agglomeration with surfactants. Medeiros et al. [26] utilized a biodiesel glycerol by-product to produce a dust suppressant. Xiao et al. [27] prepared a novel dust suppressant with the characteristics of high stickiness and water-resistance. However, only a small number of the previous research studies which have focused on the control of coal dust particles have examined complex dust suppressants comprised of surfactants and binding agents.In order to further examine complex dust suppressants with high wetting abilities and adhesive capacities, this study investigated and applied such a suppressant in a fully mechanized excavation face. The performance results of the proposed complex dust suppressant were evaluated using sedimentation experiments and viscosity measurements. This study’s field applications were conducted in the Zhangcun Coal Mine located in China’s Shanxi Province.


## 2. Experimental Details

### 2.1. Materials

The coal samples which were examined in this study were acquired from No. 480 (III) material roadway of a fully mechanized excavation face located in the Zhangcun Coal Mine (Shanxi, China). The main materials used for the dust suppression testing were as follows [28]:


#### 2.1.1. Surfactants

AES (fatty alcohol polyoxyethylene ether sodium sulfate); BS-12 (dodecyl dimethyl betaine); APG 06 (N-hexyl glucoside); AEC-9Na (fatty alcohol polyoxyethylene ether sodium 7 carboxylate); AEO 7 (fatty alcohol polyoxyethylene ether 7); SAS-60 (sodium paralkyl sulfonate); APG 08 (isooctyl glucoside); and CAO-30 (coconut oil amide acrylamide oxide amine).


#### 2.1.2. Synergist Ions

NaCl, CaCl2, NaSO4, and MgCl2·6H2O.


#### 2.1.3. Cellulose

PAM (polyacrylamide); HEC (hydroxyethyl cellulose); Xanthan gum; (C6H7NaO6)x (sodium alginate); PANA (sodium polyacrylate); CMC (sodium carboxymethylcellulose); HCPE (high-polychlorinated polyethylene); HPMC (Hydroxypropyl methyl cellulose); Snowtex (styrene-acrylic emulsion); and Arabic gum.


### 2.2. Experimental Method

In this research study, in order to develop a new complex dust suppressant with improved wetting ability and adhesive capacity, a total of eight surfactants, four synergist ions, and ten agglomerates were selected for the purpose of testing the performances of the proposed suppressant via sedimentation experiments and viscosity measurements. First, 50 mg amounts of ground coal dust were poured into eight beakers containing eight types of surfactant, respectively. All of the surfactant types which were used in this study’s sedimentation experiments were divided into 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% concentrations. The dust sedimentation times for each of the surfactants were recorded. Then, the surfactants with the shortest dust sedimentation times were selected, and their optimal material ratios were further determined using the aforementioned method. In addition, four synergists were added into the selected surfactants of the previous step, respectively. At this point, the improved performance results with the added synergists (from the viewpoint of the improved wetting abilities of the selected surfactants) were determined using the measured reductions in the dust sedimentation times. Finally, ten agglomerates with 0.1 wt.% concentrations were selected for the purpose of testing their viscosities using a NDJ-1 viscometer. It had previously been determined that the viscosity was an important parameter for characterizing the properties of the dust agglomerates. In previous related studies, it had been observed that the greater the viscosity was, the better the adhesive capacity would be.


## 2.1. Materials

The coal samples which were examined in this study were acquired from No. 480 (III) material roadway of a fully mechanized excavation face located in the Zhangcun Coal Mine (Shanxi, China). The main materials used for the dust suppression testing were as follows [28]:


### 2.1.1. Surfactants

AES (fatty alcohol polyoxyethylene ether sodium sulfate); BS-12 (dodecyl dimethyl betaine); APG 06 (N-hexyl glucoside); AEC-9Na (fatty alcohol polyoxyethylene ether sodium 7 carboxylate); AEO 7 (fatty alcohol polyoxyethylene ether 7); SAS-60 (sodium paralkyl sulfonate); APG 08 (isooctyl glucoside); and CAO-30 (coconut oil amide acrylamide oxide amine).


### 2.1.2. Synergist Ions

NaCl, CaCl2, NaSO4, and MgCl2·6H2O.


### 2.1.3. Cellulose

PAM (polyacrylamide); HEC (hydroxyethyl cellulose); Xanthan gum; (C6H7NaO6)x (sodium alginate); PANA (sodium polyacrylate); CMC (sodium carboxymethylcellulose); HCPE (high-polychlorinated polyethylene); HPMC (Hydroxypropyl methyl cellulose); Snowtex (styrene-acrylic emulsion); and Arabic gum.


## 2.1.1. Surfactants

AES (fatty alcohol polyoxyethylene ether sodium sulfate); BS-12 (dodecyl dimethyl betaine); APG 06 (N-hexyl glucoside); AEC-9Na (fatty alcohol polyoxyethylene ether sodium 7 carboxylate); AEO 7 (fatty alcohol polyoxyethylene ether 7); SAS-60 (sodium paralkyl sulfonate); APG 08 (isooctyl glucoside); and CAO-30 (coconut oil amide acrylamide oxide amine).


## 2.1.2. Synergist Ions

NaCl, CaCl2, NaSO4, and MgCl2·6H2O.


## 2.1.3. Cellulose

PAM (polyacrylamide); HEC (hydroxyethyl cellulose); Xanthan gum; (C6H7NaO6)x (sodium alginate); PANA (sodium polyacrylate); CMC (sodium carboxymethylcellulose); HCPE (high-polychlorinated polyethylene); HPMC (Hydroxypropyl methyl cellulose); Snowtex (styrene-acrylic emulsion); and Arabic gum.


## 2.2. Experimental Method

In this research study, in order to develop a new complex dust suppressant with improved wetting ability and adhesive capacity, a total of eight surfactants, four synergist ions, and ten agglomerates were selected for the purpose of testing the performances of the proposed suppressant via sedimentation experiments and viscosity measurements. First, 50 mg amounts of ground coal dust were poured into eight beakers containing eight types of surfactant, respectively. All of the surfactant types which were used in this study’s sedimentation experiments were divided into 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% concentrations. The dust sedimentation times for each of the surfactants were recorded. Then, the surfactants with the shortest dust sedimentation times were selected, and their optimal material ratios were further determined using the aforementioned method. In addition, four synergists were added into the selected surfactants of the previous step, respectively. At this point, the improved performance results with the added synergists (from the viewpoint of the improved wetting abilities of the selected surfactants) were determined using the measured reductions in the dust sedimentation times. Finally, ten agglomerates with 0.1 wt.% concentrations were selected for the purpose of testing their viscosities using a NDJ-1 viscometer. It had previously been determined that the viscosity was an important parameter for characterizing the properties of the dust agglomerates. In previous related studies, it had been observed that the greater the viscosity was, the better the adhesive capacity would be.


## 3. Results and Discussion

### 3.1. Proportional Designs of the Surfactants

It was observed that the surfactants with inherent hydrophilic and oleophilic radicals were able to align in fixed directions on the solution surfaces and caused surface tensions to decrease. It had been previously determined that the wetting behaviors of coal dust could be greatly improved by the addition of surfactants [29]. Figure 1 illustrates that the dust sedimentation times when using surfactants AEO 7, SAS-60, APG 08, and CAO-30 were much shorter than those when the surfactants AES, BS-12, APG 06 and AEC-9Na were used. Furthermore, it was observed that, for the AEO 7, SAS-60, APG 08 and CAO-30 surfactants, small time gaps (1 to 2 seconds) had occurred among the surfactants under the high dust concentration conditions. Meanwhile, it was determined that the sedimentation times of the AEO 7 and SAS-60 surfactants were significantly less than those of the AEO 7 and CAO-30 surfactants under the low dust concentration conditions. However, the APG 08 surfactant was determined to have easily formed colloids when it had come in contact with the air, which could potentially block pipelines in practical coal mine applications. As a result, the surfactants AEO 7 and SAS-60 were selected in this study as the most effective material of the SSC. As detailed in Figure 2, when the SAS-60 : AEO 7 ratio was 1 : 1, the dust sedimentation time was observed to be the lowest.Figure 1
Dust sedimentation times of the different surfactants.Figure 2
Impacts of the SAS-60 : AEO 7 ratio on the wetting performance results.


### 3.2. Effects of the Synergists on the Wetting Performance Results of the Surfactants

As detailed in Figure3, when NaSO4 and MgCl2·6H2O were added into the SAS-60 and AEO 7 surfactants, the dust sedimentation times were observed to be shorter than those of the other synergists. It was determined in this study that the addition of NaSO4 and MgCl2·6H2O had improved the wetting abilities of the surfactants. Furthermore, the uses of a combination of the SAS-60 and AEO 7 surfactants and the NaSO4 and MgCl2·6H2O synergists was determined to enable hydrophobic lattices on the surfaces of the coal dust particles, which had resulted in the absorption of the surfactants and generation of the hydrophilic effects.Figure 3
Impacts of the synergists on the wetting performances of SAS-60 and AEO 7.


### 3.3. Viscosity Measurements of the Cellulose

The testing data shown in Figure4 demonstrate that the viscosity of the 0.1 wt.% PAM was observed to be 13.73 times that of the water. Also, the viscosity of the 0.1 wt.% HPMC was determined to be 23.64 times that of the water. These findings indicated that the viscosities of the PAM and HPMC were much higher under the conditions of the same concentration levels when compared with the other cellulose. Also, these cellulose types were determined to have been maintained for long periods of time without condensing. There were found to be many active groups within the molecules of the cellulose. These active groups were available to combine with the dust particles and form larger flocculants. It was observed that, under the effects of the flocculation, the different compositions, properties, and sizes of the dust particles were combined, which had resulted in improvements in the sediment rates. As can be seen in Figure 5, the most effective PAM : HPMC ratio was determined to be 1 : 4. Therefore, it was verified that the SSC materials had effectively reinforced the adhesive capacities.Figure 4
Viscosities of the different cellulose.Figure 5
Impacts of the PAM : HPMC ratios on the adhesive capacities.


### 3.4. Material Formulation of the SSC

Sedimentation experiments and viscosity measurements were used in this research study to determine that the optimal proportions of the SSC were as follows: 0.025 wt.% MgCl2·6H2O; 0.01 wt.% NaSO4; 0.015 wt.% PAM; 0.005 wt.% AEO 7; 0.005 wt.% SAS-60; and 0.005 wt.% HPMC.


### 3.5. Performance Testing Process

In this study’s sedimentation experiment, drops of 0.1 wt.% SSC, along with drops of water were added to the examined coal sample surfaces using a glue head dropper, and the sedimentation times were tested. As shown in Figure6(a), the SSC was observed to have rapidly permeated the coal dust, resulting in the wet coal dust coagulating. Meanwhile, it was observed that the water droplets had floated on the sample’s surfaces without infiltration occurring. Figure 6(b) illustrates that, when compared with SAS-60 and AEO 7, this study’s proposed complex dust suppressant (SSC) had displayed a greater wettability for capturing the dust particles. Its sedimentation time was only four seconds, which was found to be shorter than the sedimentation time of SAS-60 and AEO 7. As shown in Figure 7(a), the diluted SSC was sprayed onto a glass slide covered with coal dust. The dust was observed to become quickly moistened and condensed. As detailed in Figure 7(b), when compared with PAM and HPMC, SSC had displayed more effective adhesive capacities for capturing the dust particles. In this study, the viscosity of the SCC was found to be 1.85 times that of the PAM, and 1.08 times that of the HPMC.Figure 6
Wetting performance results of the SSC. (a) Comparison diagram of the wetting performances of the SSC and water. (b) Comparison of the dust sedimentation times of the SAS-60, AEO-7, and SSC.
(a)
(b)Figure 7
(a) Adhesive capacity of the SSC for the coal dust particles. (b) Comparison of the viscosities of the PAM, HPMC, and SSC.
(a)
(b)


## 3.1. Proportional Designs of the Surfactants

It was observed that the surfactants with inherent hydrophilic and oleophilic radicals were able to align in fixed directions on the solution surfaces and caused surface tensions to decrease. It had been previously determined that the wetting behaviors of coal dust could be greatly improved by the addition of surfactants [29]. Figure 1 illustrates that the dust sedimentation times when using surfactants AEO 7, SAS-60, APG 08, and CAO-30 were much shorter than those when the surfactants AES, BS-12, APG 06 and AEC-9Na were used. Furthermore, it was observed that, for the AEO 7, SAS-60, APG 08 and CAO-30 surfactants, small time gaps (1 to 2 seconds) had occurred among the surfactants under the high dust concentration conditions. Meanwhile, it was determined that the sedimentation times of the AEO 7 and SAS-60 surfactants were significantly less than those of the AEO 7 and CAO-30 surfactants under the low dust concentration conditions. However, the APG 08 surfactant was determined to have easily formed colloids when it had come in contact with the air, which could potentially block pipelines in practical coal mine applications. As a result, the surfactants AEO 7 and SAS-60 were selected in this study as the most effective material of the SSC. As detailed in Figure 2, when the SAS-60 : AEO 7 ratio was 1 : 1, the dust sedimentation time was observed to be the lowest.Figure 1
Dust sedimentation times of the different surfactants.Figure 2
Impacts of the SAS-60 : AEO 7 ratio on the wetting performance results.


## 3.2. Effects of the Synergists on the Wetting Performance Results of the Surfactants

As detailed in Figure3, when NaSO4 and MgCl2·6H2O were added into the SAS-60 and AEO 7 surfactants, the dust sedimentation times were observed to be shorter than those of the other synergists. It was determined in this study that the addition of NaSO4 and MgCl2·6H2O had improved the wetting abilities of the surfactants. Furthermore, the uses of a combination of the SAS-60 and AEO 7 surfactants and the NaSO4 and MgCl2·6H2O synergists was determined to enable hydrophobic lattices on the surfaces of the coal dust particles, which had resulted in the absorption of the surfactants and generation of the hydrophilic effects.Figure 3
Impacts of the synergists on the wetting performances of SAS-60 and AEO 7.


## 3.3. Viscosity Measurements of the Cellulose

The testing data shown in Figure4 demonstrate that the viscosity of the 0.1 wt.% PAM was observed to be 13.73 times that of the water. Also, the viscosity of the 0.1 wt.% HPMC was determined to be 23.64 times that of the water. These findings indicated that the viscosities of the PAM and HPMC were much higher under the conditions of the same concentration levels when compared with the other cellulose. Also, these cellulose types were determined to have been maintained for long periods of time without condensing. There were found to be many active groups within the molecules of the cellulose. These active groups were available to combine with the dust particles and form larger flocculants. It was observed that, under the effects of the flocculation, the different compositions, properties, and sizes of the dust particles were combined, which had resulted in improvements in the sediment rates. As can be seen in Figure 5, the most effective PAM : HPMC ratio was determined to be 1 : 4. Therefore, it was verified that the SSC materials had effectively reinforced the adhesive capacities.Figure 4
Viscosities of the different cellulose.Figure 5
Impacts of the PAM : HPMC ratios on the adhesive capacities.


## 3.4. Material Formulation of the SSC

Sedimentation experiments and viscosity measurements were used in this research study to determine that the optimal proportions of the SSC were as follows: 0.025 wt.% MgCl2·6H2O; 0.01 wt.% NaSO4; 0.015 wt.% PAM; 0.005 wt.% AEO 7; 0.005 wt.% SAS-60; and 0.005 wt.% HPMC.


## 3.5. Performance Testing Process

In this study’s sedimentation experiment, drops of 0.1 wt.% SSC, along with drops of water were added to the examined coal sample surfaces using a glue head dropper, and the sedimentation times were tested. As shown in Figure6(a), the SSC was observed to have rapidly permeated the coal dust, resulting in the wet coal dust coagulating. Meanwhile, it was observed that the water droplets had floated on the sample’s surfaces without infiltration occurring. Figure 6(b) illustrates that, when compared with SAS-60 and AEO 7, this study’s proposed complex dust suppressant (SSC) had displayed a greater wettability for capturing the dust particles. Its sedimentation time was only four seconds, which was found to be shorter than the sedimentation time of SAS-60 and AEO 7. As shown in Figure 7(a), the diluted SSC was sprayed onto a glass slide covered with coal dust. The dust was observed to become quickly moistened and condensed. As detailed in Figure 7(b), when compared with PAM and HPMC, SSC had displayed more effective adhesive capacities for capturing the dust particles. In this study, the viscosity of the SCC was found to be 1.85 times that of the PAM, and 1.08 times that of the HPMC.Figure 6
Wetting performance results of the SSC. (a) Comparison diagram of the wetting performances of the SSC and water. (b) Comparison of the dust sedimentation times of the SAS-60, AEO-7, and SSC.
(a)
(b)Figure 7
(a) Adhesive capacity of the SSC for the coal dust particles. (b) Comparison of the viscosities of the PAM, HPMC, and SSC.
(a)
(b)


## 4. Field Applications

In order to investigate the application effects of fog gun dust removal technology, this study’s field applications were carried out in the No. 480 (III) material roadway of a fully mechanized excavation face, which was under construction in the Zhangcun Coal Mine located in China’s Shanxi Province.In accordance with this study’s analysis of the borehole data, the thickness of the No. 3 coal seam was between 5.45 and 6.03 m. It was determined that the average thickness of the coal seam was 5.69 m, and the average absolute gas emission during the excavation processes was found to be between 1.5 and 2 m3/min. Then, in accordance with the explosive report data for coal dust, the #3 coal dust was considered to be explosive, with a 15 mm flame length. The examined coal seam in the study area was determined to be a noncombustible coal seam, with ground temperatures ranging between 15 and 17°C. The excavation roadway was driven with a rectangular sectional area of 18 m2 (5.0 m wide; 3.6 m high). Also, the diameter of the FBD No. 7.0 local ventilator duct was 1 m, and the outlet air volume was 690 m3/min. Figure 8 details the connection of the duct interconnection which was required to use the SSC in the coal mine roadway. Figure 9 illustrates the layout of the water curtain, along with the four concentration measurement points (#1, #2, #3, and #4) in the coal mine roadway. Among these points, #1 and #2 measurement points were located in front of water curtain, and #3 and #4 measurement points were located behind the water curtain.Figure 8
Connection of the duct interconnection required for the SSC application in the coal mine roadway.Figure 9
Layout of the water curtain and measurement points in the coal mine roadway.Figure10 illustrates the field application of the SSC in the study area. The dust concentrations and dust suppression efficiencies of the measuring points were tested after applying the SSC in the examined mining roadway of the Zhangcun Coal Mine. Table 1 details the suppression efficiency results obtained under the different conditions. The average efficiency rates for suppressing the total dust concentrations and respirable dust concentration were determined to be 44.7% and 22.1%, respectively, when only the water curtain method was used. However, the average efficiency for suppressing the total dust concentrations and respirable dust concentrations were determined to be 89.2% and 87.7%, respectively, when the proposed SSC method was applied. The results indicated that the dust concentrations had been efficiently controlled within a confined area in the coal mine roadway.Figure 10
Effects of the SSC on the dust suppression in the Zhangcun Coal Mine. (a) Water curtain front. (b) Water curtain back without the SSC. (c) Water curtain back with the SSC.
(a)
(b)
(c)Table 1
Suppression efficiency rates under the different conditions.
Measure points
Water
SSC
Dust concentration (mg/m3)
Suppression efficiency (%)
Dust concentration (mg/m3)
Suppression efficiency (%)
Total dust
Respirable dust
Total dust
Respirable dust
Total dust
Respirable dust
Total dust
Respirable dust
#1
528.1
216
44.7
22.1
531.2
253.1
89.2
87.7
#3
293.5
165.1
58.3
30.9
#2
510.3
199.7
526.3
230.4
#4
281.2
158.3
55.6
28.6


## 5. Conclusions

A new complex dust suppressant (SSC) was proposed in this study, which was comprised of surfactants, synergists, and cellulose. The obtained experimental results indicated that the proposed SCC method had improved wettability and viscosity characteristics for capturing dust particles in coal mines. The optimal material formation of the SSC was determined using sedimentation experiments and viscosity measurements. This study’s experimental investigations revealed that the optimum SSC proportions were composed as follows: 0.025 wt.% MgCl2·6H2O; 0.01 wt.% NaSO4; 0.015 wt.% PAM; 0.005 wt.% AEO 7; 0.005 wt.% SAS-60; and 0.005 wt.% HPMC. The dust sedimentation time of the SCC was determined to be only 4 seconds, which was shorter than those of the single material SAS-60 and AEO 7. Futhermore, the viscosity of the SCC was observed to be 1.85 times that of the PAM, and 1.08 times that of the HPMC.In this research study, the proposed SSC was mixed with water in a water curtain technique for the suppression of the coal mine dust particles. The field test results revealed that the concentrations of the total dust and respirable dust particles behind the water curtain were 57.0 mg/m3 and 29.8 mg/m3, respectively. It was confirmed in this study that the average increased efficiency for the suppression of the total dust concentrations using the proposed SSC was 44.5% higher than using water only. Also, the proposed SSC method demonstrated an increased suppression efficiency of the respirable dust concentrations in the coal mine roadway of 65.6%.



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*Source: 6487459-2018-12-23.xml*