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First, the status of tailings pond
The storage capacity is 84.76 million m 3 , and the design final library is 100 m high. It has occupied an effective storage capacity of 70.78 million m 3 and the remaining 13.98 million m 3 . It is calculated according to the design of 2.2 million tons per year, and can also be used for about 10 years. The design of the Chengmen Shanwei Mine Library is 23.5 million m3, and the design final library is 180m high. It has occupied an effective storage capacity of 9.53 million m 3 and the remaining 13.97 million m 3 . It is calculated according to the design of 2 million tons per year. 11 years. The current tailings flow direction is shown in Figure 1.
Figure 1 Schematic diagram of the tailings flow direction of Nanshan Mining Company
2. Reconstructing the tailings pond by using the open pit of the open mountain
(1) Feasibility
By the end of 2007, the total storage capacity of the Fushan total tailings pond and the Chengmen Shanwei mine is 27.95 million m 3 , while the mining of the Gaocun mining site will reach more than 90 million tons of tailings by the end of 2028, of which nearly 20 million tons are dry. tail into the dump, the rest of the nearly 70 million t tailings discharged; Heshangqiao upcoming mining iron ore, will produce nearly 60 million t of tailings into the tailings, tailings storage total more than 130 million t, capacity Nearly 90 million m 3 , the current reservoir capacity of the two banks is much smaller than the amount of tailings produced, and it is imperative to build a new tailings pond.
The open pit in the concave mountain is a suitable site. The concave mountain stope is scheduled to close at the end of 2009, and there will be no mining activities in the lower part. The use of the pit as a tailings reservoir can avoid hidden dangers such as displacement, cracking, leakage, water erosion and earthquake dam failure in the dam construction on the surface; at the same time, it does not occupy land, does not require dam construction, and has less investment. The advantage of high security.
The stope is bounded by a closed circle of 45m elevation, and a complete pit is below -45m from 45m elevation; there are three exits of west, east and north from 45m elevation to 90m elevation; Outside the Dawang Mountain in the west, it is an open-faced open-pit mine.
The 45m elevation closed circle has a circumference of 3615m and an area of ​​815,000 m 2 . The minimum excavation height is -201m according to mining design and 246m deep. After closing the pit, there is enough space to accommodate the tailings, and the bottom of the pit is -165 and -65m. There is a complete drainage tunnel system for tailings drainage. Therefore, it is feasible to convert an abandoned mine pit below 45m to a tailings pond.
(2) Storage capacity calculation
The upper margin of the mining step is used in the calculation of the storage capacity, ignoring the partial volume occupied by the width of the platform, and the calculation result can be directly used as an effective storage capacity, as shown in Table 1.
Table 1 Calculation of the storage capacity of the tailings reservoir of the concave mountain pit below 45m elevation
Elevation / m
Area / m 2
Storage capacity / m 3
Cumulative storage capacity / m 3
-201
-189
-177
-165
-150
-135
-120
-105
-90
-75
-60
-45
-30
-15
0
15
30
45
8510.57
12,816.48
24,801.95
43052.67
64,886.73
81506.63
128852.62
195953.39
231150.66
264941.93
314748.04
358474.64
421419.17
509260.43
592027.08
665755.93
737236.74
815133.67
127962.32
225710.57
407127.72
809545.50
1097950.17
1577694.37
2436045.09
32.3280.43
3720694.41
4347674.77
5049170.16
5849203.57
6980096.94
8259656.29
9433372.59
10522445.08
11642778.08
127962.32
353672.90
760800.62
1570346.12
2668296.29
4245990.65
6682035.74
9885316.17
13606010.58
17953685.35
23002855.52
28852059.09
35832156.03
44091812.32
53525184.92
64047630.00
75690408.08
It can be seen from Table 1 that the storage capacity of the concave mountain mining pit below 45m is as much as 70 million m 3 , and the capacity of the two reservoirs has exceeded 100 million m 3 to meet the future tailings of about 90 million m 3 produced by the ore processing in Nanshan Mine. capacity.
(3) Emission methods
The elevation of the ground around the pit is 45m. The use of abandoned mining pits below 45m elevation does not require the construction of the initial dam and the late dam. It only needs to solve the tailings discharge from the bottom to the top and normal consolidation. The lowest level is -201m elevation, which is then increased sequentially up to +45m according to the elevation in Table 1.
Third, tailings reservoir flood control and drainage, backwater
(1) Draining drainage system
The two-stage tunnel drainage and drainage system has been built in the open pit of the concave mountain. The first stage drainage channel is set at -65m elevation and the second stage is set at -165m elevation. The -165m drainage roadway has three inlets respectively communicating with the Φ600mm drain holes of the -105, -90 and -75m pit steps; the -65m drainage roadway also has a water discharge port communicating with the pit steps.
Since the tailings pond is lower than the ground, the -165 and -65m two-stage roadway drainage system used in the original pit can be used to build a drainage well on the corresponding step in the pit. The Φ1.0m window-type drainage well is used, and the bottom of the well is drained. (Φ0.6m) is connected to the drainage roadway. Both the flood and the tailings return water enter the roadway through the passage, and then flow from the roadway to the water tank, and the pump is discharged to the ground through the inclined shaft.
At the beginning of the use of the concave mountain pit tailings pond, the backwater of the pit bottom is discharged to the surface by the -165m drainage roadway; in the later stage, it is discharged to the surface by the -65m drainage roadway. Bottom drainage tunnel due to the lowest level for the -165m, -165m to and below -177 ~ 201m 3 Ge steps, can be pre-built pontoon pump shaft plus pumping, beat well with a hose to the drain, came to -165m roadway.
Since the tailings pond is lower than the ground, and the drainage capacity is determined by the water pump in the roadway, the flood is mainly stored and supplemented. The deeper the water storage area, the smaller the flood storage capacity (Table 2). Take the lowest drainage well as an example. The inlet level of the inlet is -150m, which is equivalent to a major flood with a daily rainfall of 303.6mm. The total amount of flood is 389,000 m 3 , so that the -150m step is submerged by about 5 to 6 m, and -165 m. The drainage capacity of the pump in the roadway is 4000t/h, and all the floods need only 97.25 hours.
Table 2 - Step storage capacity above -150m
Elevation / m
Area / m 2
Volume / m 3
Cumulative volume / m 3
-150
-149
-148
-147
-146
-145
-144
64,886.73
65994.72
67102.71
68210.71
69318.70
70,426.69
71534.69
65,440.72
66548.72
67,656.71
68764.70
69872.70
70080.69
65,440.72
131989.44
199646.15
268410.85
338.283.55
409264.24
The water surface area of ​​the upper steps is getting larger and larger, the pressure of the drainage is getting lighter and lighter, and there is no flood overflow. In the case of a major flood with a daily rainfall of 303.6mm, the 30m step is only about 0.5m, and the drainage capacity of the pump in the -65m roadway is 4000t/h, and all flood discharges take 105 hours.
Inclined wellhead water in two ways: 1, the establishment of backwater pumping station near the wellhead at the surface, back to the mineral processing plant; 2, to maintain the old way, by the surface water system bus to concave Hill processing plant pumping station # 2, was selected by the large circulation mine Factory use.
(2) Floating boat pump flood discharge
As mentioned above, it is possible to use both the flood discharge and the possibility of flooding for several days, so it is conceivable to use the floating boat pump to return water and discharge. The floating capacity of the pontoon pump is 2,000-4000t/h, which should not be too small, so as to avoid the long-term immersion time and acidity of the mining site after heavy rain, which brings new problems in environmental protection. The key to returning water from a pontoon pump is a large-flow (2000-4000 t/h), high-lift (250 m maximum) pontoon pump.
In addition, a floating pump can be used for a combined flood discharge. The lower tunnel discharges the flood, and the upper part (-65m or more) uses the floating boat pump to return water and discharge. The floating pump lift head only needs about 100m, and the -65m tunnel has been abandoned for a long time and does not need to be restored.
   Fourth, security and stability
The width of the steps of the concave mountain stop is ≥7m, the angle of the step slope is 60°, and the overall slope angle is 35~43. The shale of the stope is hard and complete, and the stability is good. The stope is only 30~30m in the upper part of the surface. The slopes of the northern, northern and eastern gangs of the Xibang are scattered structures. The lithology is tuff , andesite , diorite and pyrite . The slope rocks are soft to semi-hard, with collapses and landslides, but After the slope cutting and reinforcement measures such as anchors and anchors, the possible safety hazards are eliminated. For decades, there has not been a large slope safety accident in the concave mountain mining pit. It is generally a rock slope and is in a stable state. After storing tailings in the pit, it has the effect of reducing the sliding force and has no adverse effect on the original rock slope.
The tailings are stored in the pit, and the drainage wells are drained and drained. With the passage of time, the layers can be gradually consolidated from the bottom to the top, and the safety and stability are reliable. At the beginning of the tail storage, the treatment of the sulfur-free side should be considered. The sprayed concrete can be used to form a sealing layer to block the direct contact between water, air and sulfur to avoid water pollution.
   5. Mining area production and tailings balance
The change in the delivery volume of the tailings storage in the concave mountain pit can be divided into four stages:
The first stage: In 2010, the concave mountain pit tailings pond was put into production at the beginning, and the tailings volume increased year by year until 2014.
The second stage: in 2014, the two stopes of the Shangshangqiao and Gaocun and the three tailings ponds maintained their best state until the end of 2018, the total tailings reservoir of the concave mountain and the closure of the Chengmen tailings reservoir. The amount of tailings in the pit tailings reservoir can be stabilized at 3.42 million tons (2.28 million m 3 ) per year.
The third stage: after the original concave mountain total tailings reservoir and the Chengmen tailings reservoir are closed, from 2019 onwards, the amount of tailings in the tailings of the concave mountain pit is stable at the maximum amount of 7.617 million tons (50.78 million m 3 ). ), can be maintained until around 2022.
The fourth stage: After 2022, with the reduction of the production of the two villages of Gaocun and Heshangqiao, the amount of tailings in the reservoir will decrease year by year. If there is no new resource development, the tailings pond will be closed after the closure of the two stopes around 2030. The remaining effective storage capacity is nearly 10 million m 3 .
In the first and second stages, all tailings are divided into new and old systems:
Old system: Laoshan old plant -1 #æ€»å°¾ç ‚-2 #æ€»å°¾ç ‚-3 #æ€»å°¾ç ‚-è€å°¾çŸ¿åº“(including Chengmen), the maximum transportation volume is 4.2 million tons per year.
The new system: the new plant of Heshangqiao - the new pump station of Heshangqiao - the concave mountain pit tailings pond, the maximum transport volume at this stage is 3.42 million tons per year.
The third stage of the concave mountain pit tailings reservoir became the only tailings pond, and both the new and old systems were to be transformed into a single conveying system. The old system is routed from the 2 # total tailings, and the pipeline is led to the Shanshangqiao pumping station. The maximum conveying capacity is 3.9 million tons per year; 30 total tailings and subsequent sections are abolished.
The new system and the new pump station's export volume will be increased to 7.62 million tons per year. Beginning in 2023, as ore production declined, tailings decreased year by year until 2030.
Sixth, the key technology to be studied in the reconstruction of tailings pond
(1) Research on engineering geological and hydrogeological conditions of open pits;
(2) Experimental study on physical and mechanical properties of the rock mass of the bank slope;
(3) Experimental study on physical and mechanical properties of tailings slurry and tailings;
(4) Technical and economic analysis of the feasibility of concentration and solidification of tailings slurry;
(5) Research on the technology of transportation and discharge of tailings deep pit discharge;
(6) Analysis and calculation of the dynamic variation law of the seepage field of the bank slope during tailings discharge;
(7) Analysis and calculation of the stability of the bank slope;
(8) Analysis of energy transfer analysis and impact damage analysis of sliding blocks;
(9) Research on control technology for stability and safety of bank slopes.
   Conclusion
Through the research on the key technology of rebuilding the tailings pond in the closed pit open pit of the concave mountain, not only can the land acquisition of the tailings pond and the large amount of capital investment (more than 200 million) be saved, so that the closed pit can be fully and effectively utilized. It can improve and improve the environmental quality of mines and surrounding areas, and effectively control environmental geological disasters in mining areas, which plays an important role in ensuring the normal safety of mines and people's lives.
April 29, 2023