Guangxi Liuzhou China Tin Group veinlets with copper fire pit area surface subsidence area in 1997 was listed as the Guangxi Zhuang Autonomous Region People's Government of accident potential zone. Geological disasters such as spontaneous combustion of ore rocks are extremely damaging to the local natural ecological environment. In particular, the toxic and harmful gases produced by the spontaneous combustion of the ore rock not only pollute the atmospheric environment, but also pollute the local soil and water sources to varying degrees. In order to ensure the safety and health of the mines and the local people, it is necessary to thoroughly control the exhaust pollution generated by the self-ignition of the fine veins in the fire zone.

So far, from the "seventh five-year" scientific and technological research, the mine has carried out a series of research and treatment work on the surface subsidence area of ​​the fire area and the treatment of waste gas, and the fire in the fire area has been controlled to a certain extent. Since 2003, in order to finally eliminate the hidden dangers in the fire zone, the mine intends to burn the fine veins in the fire zone through the means of underground sealing, surface blasting and blasting and surface absorption and alkali absorption engineering during the mine discharge control. The ore is completely extinguished, eliminating the emission of exhaust gas from the fire area and protecting the mining area and its surrounding environment. The implementation of the control measures has solved the problem of air pollution caused by the mine all the year round, and the local natural ecological environment has been gradually restored, and the hidden dangers of the local natural ecological environment pollution in the fire area have been fundamentally eliminated, creating a good life for the local people. The natural ecological environment is of great significance.

I. Project Overview

Pit copper mine is a large underground non-ferrous metal mines, China Tin Group is the main base for mine. Steep upper mine veinlets band, since most of the tin-containing pyrite and pyrrhotite, the sulfur content of up to 10.16%, and contacting the carbonaceous shale, in the case of exposure to good ventilation, easy to Cause spontaneous combustion. At the same time, due to the use of the sublevel caving method in the early stage of mining, the mining area has formed a caving zone to the surface and more than ten collapse pits of various sizes. Since the occurrence of spontaneous combustion of ore in the rock breakout zone in 1976, the mine has been conducting research on fire resistance and treatment.

Initially, the mine used the method of “under-sealed closed passages and surface collapse pits covering inert materials” to isolate the fire zone from oxygen and once controlled the fire zone. However, the fuel (sulphur-containing ore) in the fire zone still exists, and once oxygen supply conditions are formed, re-ignition occurs. For more than 20 years, due to underground mining and civil mining damage to the security pillars, there have been many occurrences of surface collapse, re-ignition of fire zones, high temperatures and SO ₂ and other toxic gases, resulting in downhole production and the ground environment. A serious impact.

Second, the surface subsidence of the exhaust gas is covered and treated

The method of surface subsidence covering is used to control the exhaust gas. According to the surface topography and surface soil conditions of the fire area, the mountain near the surface collapse pit is used to strengthen the loose blasting or throwing blasting through the construction of the roadway and the charging chamber. The mountain body of the collapsed pit wall collapses into the pit and fills the collapse pit. After the blasting, according to the sealing effect of the cover layer, further compacting measures such as spray cementing are adopted to form a good covering layer, that is, the chamber blasting scheme. Or in the area around the surface collapse pit, excavate the construction channel and enter the work area; then, in the vicinity of the subsidence area, use the excavator or scraper to excavate the soil loading and loading, and transport the soil through the east windmill and the Sichuan road car to the collapse pit to unload the cover. That is, the mechanical shovel loading plan. Due to the large amount of subsidence of the collapse pit, the mine chooses the blasting blasting scheme with high coverage efficiency, low cost and fast treatment speed, as shown in Figure 1.

Figure 1 Schematic diagram of the chamber blasting coverage plan

(1) Scheme engineering design and implementation

^# 2 at mine collapse pit, for example, disclosed in rock blasting site as limestone, shale, carbonaceous shale. The design collapses the hill of the side wall of the collapse pit into the pit to form a cover layer. The main blasting parameters obtained through calculation and analysis are: blasting index n is 0.6; unit explosive consumption k is 1kg/m ³ ; drug package minimum resistance line w=15m; drug package spacing is 12m; blasting charge is 4.8t, It is a Class D blast. The safety distance of blasting is 500-700m. The calculation results of the blasting funnel are shown in Table 1.

Table 1 Calculation results of the blasting funnel

The flat and pharmacy specifications (width × height) are 1.4m × 1.7m, and the road is sloping. The bag is packed with fine mud and stone sand, and the guiding and drug chambers are blocked from the inside to the outside. The total length of the blockage is 30m, and the blockage is 71.4m ³ . Block the dense connection and use a non-conducting explosive cord to detonate the network.

(II) Analysis of governance effects

The throwing blasting causes a large amount of earthwork that has collapsed to be directly smashed into the collapse pit to achieve the purpose of covering. At the same time, through comprehensive research on the topography, geological conditions and corresponding underground mining conditions, the mine has compared the coverage methods in terms of technical feasibility, economic rationality, safety and reliability, and developed multiple chamber blasting coverage techniques. The program successfully implemented eleven surface blasting projects. The total amount of rock and soil covered is 318,500 m ³ , which forms a large area coverage of the hidden danger zone of the fine veins, effectively igniting the burning of the fire zone and achieving the treatment effect. The blasting effect is shown in Figure 2 (after processing).

Figure 2 Surface subsidence coverage effect

Third, the surface waste gas alkali absorption treatment

Surface collapse pits that do not have blasting coverage, use sprayed lime water to absorb poisonous gas. According to the exhaust gas monitoring result, the main hazardous gas is SO ₂ toxic gas, and the treatment method is alkali absorption method-calcium hydroxide wet washing method. The misty lime water first absorbs and reacts with the SO ₂ emerging from the ground, and then infiltrates into the collapse pit to absorb the exhaust gas and suppress the combustion in the fire zone. Practice has proved that evenly spraying lime water has a significant effect on the treatment of surface collapse pits. Lime water reacts with SO ₂ , O ₂ and other gases. It is mainly divided into two steps of absorption and oxidation, but the reaction mechanism is very complicated. The main reaction equation is as follows:

The calcium hydroxide wet scrubbing method has a wide source of raw materials, simple process operation, mature and reliable, low operating cost, and the secondary products do not cause secondary pollution to the environment.

(1) Process

A lime water injection station is established near the surface collapse pit, and a nozzle is arranged around the collapse pit, and the high-pressure pump lime water is used to evenly spray the ground smoke outlet. When the span of the collapse pit is large, the high-pressure pump and the conveying pipe are laid from the cable bridge to the middle of the collapse pit by spraying the iron bridge of the collapsed pit. The process flow is shown in Figure 3.

Fig. 3 Flow chart of alkali absorption process of surface collapse pit

Choose two 98kW 125D high-pressure pumps, each with a flow rate of 120m ³ /h, the conveying pipe is φ159mm steel pipe, and install two high-pressure nozzles that can rotate 180° freely with a range of 60m. Spraying misty lime water (concentration 5%) on the surface collapse pit around the clock.

(II) Program implementation and effect

The effect of sprayed lime water on the SO ₂ concentration of the surface collapse pit is shown in Figure 4 since the completion of the process system. The monitoring results show that the SO ₂ emission concentration of the surface collapse pit has a downward trend after spraying lime water. After 2007, the SO ₂ emission concentration is basically controlled below 2 ppm, meeting the national emission standards. Figure 4 shows the SO ₂ monitoring value of the surface 6 ^#流井.

Figure 4 Surface 6 ^#流井SO ₂ monitoring value

Fourth, the conclusion

In view of the air pollution caused by the exhaust gas emission from the surface collapse pit in the fire pit area of ​​the Dachang Tongkeng Mine in Guangxi, and the damage to the local natural ecological environment, on the basis of the on-site investigation, the surface chamber blasting is used for analysis and comparison. Covering the collapse pit and the surface exhaust alkali absorption method for comprehensive treatment. After the implementation of the scheme, a large area coverage of the hidden danger zone of the fine veins and effective absorption of SO ₂ toxic gas were formed. The governance project achieved the expected results, greatly improved the mining environment and achieved good social benefits.

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