Five main sources of dust in open-pit mines and their prevention measures

Open-pit mine is directly in the surface atmosphere of production operations, dust directly pollute the environment around the stope, the dispersion range is wide, the impact area is large. At the same time, due to the influence of natural conditions such as cold, summer and snow and geographical environment, it is difficult to remove dust from open pit mine. With the continuous increase of the mining depth of the open pit, due to the sharp reduction of wind speed in the pit, poor ventilation, resulting in the formation of a temperature inversion layer in the stope, which constantly makes the generated dust difficult to disperse, but also increases the accumulation of harmful gases. Therefore, reducing dust pollution of open pit mine is not only of great significance to continuous operation of open pit mine and improving labor production efficiency, but also a technical problem that can not be ignored to protect workers' health.

Hazard of dust

Dust hazards in open-pit mines are mainly as follows:

1) Affect the air quality around the mining area and pollute the workplace. Some dust falls on the leaves of plants, which will affect the photosynthesis of plants and cause the wilting of surface plants. Some dusts contain heavy metal ions, which fall to surface water sources and reduce the quality of water bodies.

2) Affect the health of mine workers. Long-term inhalation of mineral dust causes respiratory inflammation and skin diseases in mild cases, and pneumoconiosis in severe cases.

3) Some dust (such as coal dust) will explode under certain conditions.

4) Dust will accelerate mechanical wear, shorten the service life of precision instruments, and increase the maintenance cost of equipment. With the improvement of mine mechanization, electrification and automation, the impact of mine dust on equipment performance and service life will be more and more prominent.

5) Dust will reduce the visibility of the stope, affect the normal operation of the open pit, and reduce production efficiency. The dust on the open-pit road will affect the driver's vision, which is easy to cause crash, rollover and other safety accidents.

The main source of dust in open pit mines

The dust pollution source of open pit mine mainly comes from perforation, blasting, mining, crushing, transportation, soil discharge and other operations during the mining process. The amount of dust content in the mine is related to the meteorological conditions of the mine, the geological characteristics of the mine, the mining technology, the type of equipment, the mining intensity and so on.

1. The perforation operation produces dust

Drilling rig is one of the main equipment in open-pit mine production, and its dust intensity is second only to loading and transportation equipment, ranking third in the dust production volume of production equipment. When the drilling speed of a cone drill is 0.025m/s, the amount of dust with a diameter of 10-15mm can be produced up to 2-3.5kg/s. If no prevention and control measures are taken, under the action of wind currents, large areas of open pit mining operations can be polluted, and the amount of dust in the air far exceeds the national health standards, even in places far away from the drilling rig.

2. Blasting operation produces dust

The dust in blasting operation is mainly produced by explosive crushing rock, of which a large amount is respirable dust. At the same time, blasting also lifts up the dust on the surface, making the concentration of dust increase. The amount of dust generated instantaneously during blasting is large, but the high concentration of dust formed is maintained in the air for a short time.

3. Dust from loading operation

Dust produced by mining and loading is the main source of dust in open pit mines. The strength of the dust produced by the electric shovel used in the mine is between 400-2000mg/s. The causes of dust in mining and loading operations are as follows: when the rock is excavated by the electric shovel, the rock is broken by the electric shovel, and part of the dust is settled on the surface of the rock; The other part is the dust generated by friction and collision due to vibration and the formation of secondary dust. When the shovel discharges materials to the transportation or transfer equipment, a large amount of dust will be generated due to the reason of the drop. When bulldozers or other mining equipment are used to clean explosive piles and step floating coal, certain dust will also be generated.

4. Dust from transportation operations

When automobile transportation is used, the dust raised by the road surface due to automobile driving is not only one of the main dust sources of the air in the open pit, but also one of the main dust sources of the air pollution in the mining area. At the same time, the dust deposited on the road surface of automobile transportation is affected by the crushing, vibration and air flow generated by the car, and it moves irregularly, resulting in secondary dust. When the tape machine is used for transportation, due to the large cross-sectional area exposed to the air per unit time, certain dust will be generated under the action of wind flow, tape vibration and other factors. In particular, the use of tape to transport coal, in the absence of any protective measures, will continue to produce coal dust, and will also cause a waste of coal resources.

5. Dust is generated from soil disposal

When the transport equipment discharges materials in the dump, dust is generated due to the collision and friction of rocks. In addition, due to the large drop of the dump and the large amount of discharge, the amount of secondary dust is also large, which has a serious impact on the surrounding environment.

Five measures to prevent dust in open pit mines

Dust prevention measures for drilling operations

The dust prevention measures of drilling rig operation mainly include dry dust suppression, wet dust suppression and dry and wet combined dust suppression. For the cone drill commonly used in mines, the three-stage dust removal system is the most effective, which can make the air dust content in the working area of the drill meet the health standard, and the dust removal efficiency is more than 99%. The first stage usually uses a dust settling tank to remove drilling cuttings and coarse dust in the air stream, and the efficiency is generally 50%-70%. The second stage is a group of cyclone dust collector, which removes medium and fine particle dust in the air stream, and the efficiency is generally 70%-80%. The third pole is a belt filter for capturing fine dust with an efficiency of more than 99%. For dust with high dust humidity or that may be bonded on the surface of the bag, hydraulic dust removal or bubble dust collector is used as the third level dust removal.

Dust prevention measures for blasting operations

The methods of dust control in blasting operation are mainly divided into technical dust control and hydraulic dust control. Dust prevention in blasting process refers to the improvement of blasting process and the effective use of explosive blast wave to reduce the residual dust discharged from the gun hole and blasting funnel. For example, the direction of extrusion blasting in the formation of explosive pile to achieve the purpose of reducing dust; Directional initiation of deep hole charge can reduce the discharge of residual dust from the hole. Water can not only wet the surface of ore rock and dust, but also penetrate into the ore body through cracks, and play a good dust-proof effect. Hydraulic dust removal methods include water-filled chamber blasting, water plug blasting, using glue paste to plug, spraying water in the explosion area, foam covering the explosion area, etc.

Dust prevention measures for mining operations

The mining operation sprinkles or sprays a chemical additive solution on the explosive pile before excavating the nearest work surface, while spraying water while excavating. When the moisture content of the ore is increased from 4% to 8%, the dust content in the air of the shovel face can be reduced from 200mg/m³ to 20mg/m³, that is, the dust concentration in the air of the working face can be reduced by 9 times. In addition, spray dust sprinklers can be installed on the shovel, and the distance the sprayer moves at one time is related to the water pressure, the speed of the stope wind, the wind direction, and the speed of the shovel. Generally, the distance that the sprayer moves once should be less than the maximum range of the nozzle.

Dust prevention measures for transportation operations

For open-pit mines that are transported by automobile, dust prevention measures during transportation should mainly be taken for the dust produced on the road surface. At present, the dust prevention measures on the surface of the open-pit mine transport road are mainly: laying fixed water pipelines along the route, installing sprayers every other section, spraying water on the road through the sprayer, spraying calcium or magnesium salt solution with strong moisture absorption, mixing powdered or granular calcium chloride in the road surface, treating the special paving road surface with emulsion. For open-pit mines that use tape transportation, the dust prevention measures are mainly to set up dust walls to prevent dust from floating into the stope with wind flow, or to use closed transportation to reduce the time and area of the transportation material exposed to the atmosphere.

Dust prevention measures for dumping operations

Water or sodium chloride solution can be sprayed to the secondary dust points, and trees with high value can be planted around the dump site to strengthen the reclamation and greening work of the dump site.

There are many sources of dust in open-pit mines, the prevention and control of which can not be based on single-machine protection, according to the actual situation of open-pit mines, on the basis of single-machine protection, further improve other protective measures to achieve comprehensive dust prevention in open-pit mines, reduce the dust content in open-pit mines to a minimum, and provide a good working environment for mine employees.