From drilling, blasting to soil removal, read the 6 processes of open-pit mining in one article!
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The mining process of open-pit mines is relatively simple, mainly including drilling, blasting, mining and transportation, and rock removal. Next, let's talk about the mining process of open-pit mines in detail.
1. Drilling work
Drilling work is the primary process of open-pit mining. In the entire open-pit mining process,
The cost of drilling accounts for about 10%-15% of its total production cost.
1. Down-the-hole drill
The drilling angle of the down-the-hole drill is large, the degree of mechanization is high, the auxiliary operation time is reduced, the operation rate of the drill is improved, and the down-the-hole drill is flexible, the equipment is light, and the investment cost is low. In particular, it controls the ore grade by drilling various inclined holes, which can eliminate the foundation, reduce large pieces, and improve the blasting quality. Therefore, down-the-hole drills are currently widely used in small and medium-sized mines at home and abroad, and are suitable for drilling medium-hard ore rocks.
2. Rotary Drilling Machine
The rotary drill is a modern new type of drilling equipment developed on the basis of the rotary drill. It has the characteristics of high drilling efficiency, low operating cost, mechanization, and high degree of automation. It is suitable for drilling operations of various hardness of ore rocks. At present, it has become a drilling equipment commonly used in open-pit mines around the world.
3. Rock Drilling Machine
The rock drilling machine is a new type of rock drilling equipment that has emerged with the development of the mining industry. It is to install one or several rock drills together with automatic propellers on a special drill arm or stand, and has a walking mechanism to mechanize the operation of the rock drill.
2. Blasting Work
The purpose of blasting work is to break hard solid ore rocks and provide excavated materials of suitable size for mining and loading work. In the total cost of open-pit mining, blasting costs account for about 15%-20%. The quality of blasting not only directly affects the efficiency of mining, transportation, coarse crushing and other equipment, but also affects the total cost of the mine.
1. Shallow hole blasting
The diameter of the blast-hole used in shallow hole blasting is relatively small, generally about 30-75 mm, and the depth of the blast-hole is generally less than 5 meters, sometimes up to about 8 meters. If a drilling trolley is used to drill the hole, the hole depth can be increased.
Shallow hole blasting is mainly used for small-scale open-pit mines or quarries, cave stones, tunnel excavation, secondary blasting, new open-pit mine bag processing, the formation of open-pit single-wall ditch transportation channels on hillsides, and some other special blasting.
2. Deep hole blasting
Deep hole blasting is a method of blasting the charging space of mining explosives by drilling deeper holes with drilling equipment. The deep hole blasting of open-pit mines is mainly based on the production blasting of steps.
The drilling equipment for deep hole blasting mainly uses down-the-hole drills and cone drills. The drilling can drill vertical deep holes or inclined blast-holes. The charging of inclined blast-holes is more uniform, and the blasting quality of ore and rock is better, creating good conditions for mining and loading work.
In order to reduce the seismic effect and improve the quality of blasting, under certain conditions, measures such as large-area micro-difference blasting, interval charging in the blast-hole or air interval charging at the bottom can be adopted to reduce the blasting cost and achieve better economic benefits.
3. Chamber blasting
Chamber blasting is a method of blasting with relatively large or large amounts of explosives in the blasting chamber tunnel. Open-pit mines are only used during the capital construction period and under specific conditions, and quarries are used when conditions permit and the demand for mining is large.
4. Multi-row hole micro-difference blasting method
In recent years, with the rapid increase in excavator bucket capacity and open-pit mine production capacity, the normal mining and blasting of open-pit mines requires more and more blasting each time. For this reason, large-scale blasting methods such as multi-row hole micro-difference blasting and multi-row hole micro-difference extrusion blasting are widely used in open-pit mining at home and abroad.
Advantages of multi-row hole micro-difference blasting:
The blasting volume is large at one time, which reduces the number of blasting and the time to avoid blasting, and improves the utilization rate of mining equipment;
Improve the quality of ore and rock crushing, and its large block rate is 40%-50% less than that of single-row hole blasting;
Improve the efficiency of perforating equipment by about 10%-15%, which is due to the increase in the utilization coefficient of working time and the reduction in the number of operations of perforating equipment and post-blasting filling area;
Improve the efficiency of mining and transportation equipment by about 10%-15%.
5. Multi-row hole micro-difference extrusion blasting method
It refers to multi-row hole micro-difference blasting when there is a blast pile remaining on the working face. The existence of slag pile creates conditions for extrusion. On the one hand, it can extend the effective action time of blasting, improve the utilization of explosive energy and the crushing effect; on the other hand, it can control the width of the blast pile and avoid the scattering of ore and rock. The micro-difference interval time of multi-row hole micro-difference extrusion blasting is preferably 30% to 50% larger than that of ordinary micro-difference blasting. 50 to 100ms is often used in open-pit mines in my country.
The advantages of multi-row hole micro-difference extrusion blasting are:
(1) Better ore and rock crushing effect. This is mainly due to the slag pile blocking in front. Each row of drill holes, including the first row, can increase the charge and fully crush under the pressure of the slag pile;
(2) The blast pile is more concentrated. For mines that use railway transportation, the track can be left untouched before blasting, thereby improving the efficiency of mining and transportation equipment.
The disadvantages of multi-row hole micro-difference extrusion blasting are:
(1) Large consumption of explosives;
(2) The working platform requires a wider width to accommodate the slag pile;
(3) The height of the blast pile is relatively large, which may affect the safety of excavator operations.
III. Blasting measures near the slope
As the open-pit mine extends downward, the stability of the slope becomes increasingly prominent. In order to protect the slope, the blasting near the slope must be strictly controlled. According to domestic and foreign experience, the main measures are to use micro-difference blasting, pre-splitting blasting and smooth blasting.
1. Use micro-difference blasting to reduce vibration
One of the main functions of micro-difference blasting is to reduce the seismic effect of blasting. In order to give full play to the shock-absorbing effect of micro-difference blasting, the key is to try to increase the number of blasting sections and control the micro-difference interval time.
2. Use pre-splitting blasting to isolate the slope
Pre-splitting blasting near the slope is to drill a row of dense parallel boreholes along the boundary of the slope, load a small amount of explosives into each hole, and detonate before the mining zone is blasted, so as to obtain a crack with a certain width and running through each borehole. Because this pre-crack separates the mining zone and the slope, the seismic waves of the subsequent mining blasting will produce a strong reflection on the crack surface, which greatly weakens the seismic waves passing through it, thereby protecting the slope.
3. Use smooth blasting to protect the slope
Smooth blasting near the slope is to drill a row of dense parallel boreholes along the boundary line, load a small amount of explosives into the holes, and blast after the mining boreholes are blasted, so as to form parallel rock walls along the dense boreholes. The main difference between smooth blasting and pre-splitting blasting is the detonation time. The detonation of the smooth blasthole is later than that of the previous rows of mining holes, usually with a lag of 50 to 75ms.
In addition, there is another measure to control the blasting of the last few rows of holes. The amount of charge and resistance line of the last few rows of holes near the slope should be reduced, which is called "buffer blasting", which can reduce the damage of the drilling blasting to the slope.
4. Mining and transportation
Mining and loading
Mining and loading is to use loading machinery to dig the ore and rock directly from the underground or blast pile, and load it into the carriage of the transportation machinery or unload it directly to the designated location. It is the central link of the open-pit mining process, and other production processes such as blasting and transportation are all for mining and loading.
Main mining and loading equipment: excavator, dragline, hydraulic shovel and tire front loader.
Transportation
In the process of open-pit mining, the capital construction investment of mine transportation accounts for about 60% of the total investment in mine capital construction, and the transportation cost and labor account for more than half of the total cost of ore and total labor respectively. This shows the important position of transportation in open-pit mining.
Open-pit mine transportation methods: automobile transportation, railway transportation, belt transportation, slope bucket lifting transportation and combined transportation methods, among which dump truck transportation is the most common.
