Application of Water Space Charge Dust-blasting Technology in Gaocun Iron Mine

Blasting dust is one of the harmful effects of blasting. It contains a large number of fine particles, which seriously pollutes the environment and leads to high incidence of occupational diseases such as silicosis. [1] Many blasting engineering technicians have done a lot of research work in solving the problem of blasting dust, and have achieved certain dust removal effects. However, blasting dust has the characteristics of high production speed, large dust volume, high dispersion and small particle size, which makes blasting. Dust research is very difficult and does not completely eliminate blasting dust. With the continuous improvement of blasting requirements, reducing the pollution of blasting dust on the working surface and surrounding environment has become one of the technical problems that need to be solved [2]. In order to reduce the high iron ore stope village and nearby dust concentration, dust By analyzing the mechanism of water mist, research and the use of bag space blasting field test, and the test results were analyzed to provide guidance for mine blasting dust control.
1 Mine Overview
The Gaocun Iron Mine is located in the hilly area of ​​the south of the Yangtze River. The terrain is not fluctuating, and the natural elevation is generally 30 to 60m. The main wind direction of the mining area is east wind and summer is southwest wind. The ore body is shallowly buried and suitable for open pit mining. The ore and surrounding rock are stable and the hydrogeological conditions are medium. There are several villages in the surrounding area, such as lock library and sand gang. There is also a residential resettlement community in the southwest. The surrounding environment is complex, and the control of blasting pollution, especially blasting dust control is high.
The Gaocun Iron Mine is designed to produce 7 million tons of iron ore per year, and the total amount of mining and stripping is 16 million tons. It is perforated with KY250-type cone rig and 10m3 electric shovel. The ore is mainly magnetite, mainly in the shape of his shape, a small amount of semi-self-shaped - self-shaped, with a particle size of 0.05 ~ 2mm. The main harmful elements of ore are sulfur and phosphorus , followed by calcium, magnesium , potassium, sodium, silicon and aluminum . The surrounding rocks of the top and bottom of the ore body are all diorite porphyrites. The basic properties of ore bodies and surrounding rocks are shown in Table 1.

Gaocun Iron Mine uses Orica high-precision detonator to achieve the order-by-hole sequential detonation. The original continuous charging structure is used, and emulsion explosives and granular ammonium explosives (produced by the charging vehicle) are used. The emulsion with large water content is emulsion explosive. The specific blasting parameters and indicators are shown in Table 2.

2 Analysis of dust removal mechanism
The main components of blasting dust are silica, clay and silicates, which are highly hydrophilic. It is an effective and simple dustproof measure to wet the nascent or deposited dust before blasting, but it is difficult to exert obvious effects on the dust generated during the blasting process. The explosion water mist dust reduction method is a newly proposed method. The explosive energy is used to drive the atomized water to form a water mist with a certain pressure, particle size, velocity and concentration, and the collision, interception, capture and collision of the dust particles by the droplets. Settling, to achieve the purpose of accelerating sedimentation after liquid droplets and solid dust particles condense into larger particles [3].
There are two main ways to reduce dust: one is to increase the density of dust, and the other is to increase the particle size of dust. Water mist removal is the use of these two basic principles. The density of dust particles increases significantly after water absorption, which is conducive to sedimentation. At the same time, it absorbs dust and coagulates after water absorption, and the particle size increases, which promotes dust deposition. According to the Stokes settlement formula (Equation 1), the agglomeration of any two small dust particles will increase the sedimentation rate by a factor of three [4].

Where vt is the sedimentation velocity of the particles, m/s; ρp, ρg are settleable particles and air density, kg/m3; dp is the diameter of the settled particles, m; μ is the air viscosity, kg/(m·s) .
The factors affecting the dust removal of the explosion water mist are the particle size of the water mist, the relative velocity of the water droplets and the dust particles, the water volume, the dust concentration and the wettability, and the particle concentration. The structure of the water interval blasting charge is shown in Figure 1.

3 field test
3.1 test plan
The test is divided into a rock powder interval charge structure and a water space charge structure. For different charging structures, the FCS-30 dust sampler was used for the corresponding dust test.
Working principle of FCS-30 dust sampler: Install the fiber filter of known quality in the sampling head of the sampler, collect the dust-containing air, and calculate the dust concentration per unit volume of air from the increment of the filter after sampling. . The calculation formula is

Where R is the total dust concentration, mg/m3; m2 is the mass of the filter after sampling, mg; m1 is the mass of the filter before sampling, mg; Q is the flow rate during sampling, L/min; t is the sampling time, Min.
The design was carried out in the -42, -54m step for 9 blasting tests, in which -42, -54m steps were each subjected to rock powder interval charge blasting as a control test; -42m step was carried out 3 times, -54m step was carried out 4 times in water interval Drug blasting. In the field test, the diameter of the blasthole is 250mm, the depth of the blasthole is 15.5m, and the plastic bag is used for water. The blasting water bag is 1.5~2m long and the diameter is 220mm. The measuring point is arranged in the middle of the explosion zone, and the closest distance to the blasthole of the explosion zone is 40m. The FCS-30 dust sampler is used. In the case of breeze, the sampling point is fixed from the working surface and the height is fixed. The sampling time is 5 min and the sampling flow rate is 10 L/min. The measuring point instrument adopts steel mesh protection to prevent the blasting flying stone from damaging the instrument.
3.2 Test results
The dust test results of different charge structures are shown in Table 3. It can be seen that after the dust is removed by the water interval, the concentration of the blasting dust is significantly reduced. The average dust concentration of the three tests in the north of the -42m step is reduced by 51.20%, and the average dust concentration of the four tests in the north of the -54m step is reduced by 46. 72 percentage points indicates that the dust-removing effect of the charge structure is very obvious (Figure 2 and Figure 3). At the same time, after on-site industrial test comparison, water-spaced charge blasting is superior to rock powder interval charge structure blasting in improving fracture blockiness and reducing bulk rate.

4 Conclusion
Through field tests, it is feasible and effective for mines to use water-spaced charge structure blasting technology. Based on the mechanism of water mist dust removal, the explosion of the explosive is used to instantaneously atomize the water interval. The high-pressure atomized water molecules adsorb the dust and agglomerate the dust, which greatly reduces the blasting dust. At the same time, the water column absorbs the peak energy of the shock wave and reduces its peak value. Pressure, the absorbed energy in the water column is transmitted to the surrounding rock, effectively breaking the surrounding rock, improving the energy utilization rate of the explosive, thereby improving the blasting effect. After the mine is blasted with water-spaced charge structure, the dust concentration is reduced by 46.72~51.20%, and the dust-reducing effect is remarkable. This technology is not only suitable for open pit mines, but also for other non-mine mines.
The engineering blasting in the field has broad application prospects.
references
[1] Yang Guoyan, Li Huaiyu, Cheng Xuejun. Mechanical analysis of the process of blasting dust particles [J]. Journal of Hebei Institute of Technology, 1996 (4): 1-5.
[2] Hu Tao, Yan Wei, Cui Zhenghui, et al. Application of water bag in blasting water mist dust removal technology [J]. Hydraulic Science and Engineering Technology, 2012(4): 52-54.
[3] Li Zhanjun, Wang Xuguang, Zheng Bingxu. Study on the mechanism of water pre-wet by explosives to reduce blasting dust [J]. Blasting, 2004, 21(3): 20-23.
[4] Xue Li, Yan Shilong. Discussion on the application of explosion water mist dust reduction in demolition blasting [J]. Mining Technology, 2004, 4(3): 65-67.