Taniguchi damming tailings is constituted of or surrounded, for the storage of ore for metal and nonmetal mine tailings discharged after sorting, or other industrial waste sites. The types of tailings ponds usually include valley-type tailings ponds, Lushan-type tailings ponds, flat-type tailings ponds, and intercepting tailings reservoirs.
In recent years, with the rapid development of China's mining industry, the number of tailings reservoirs in China has increased rapidly. The outstanding characteristics of China's tailings ponds are the large number, small scale, low safety, and most residents of the tailings reservoir have residents or other disasters. facility. At present, the tailings of most mining enterprises are treated by wet in-line treatment. The tailings are naturally precipitated and the dewatering efficiency is very low. A large amount of clarified water and floods are often stored in the tailings reservoir area, which leads to the formation of a tailings reservoir over the tailings. When the immersion line emerges from the dam slope, it is easy to form a dam failure risk. In order to solve the problems of safety and environmental aspects of tailings ponds, in the 1960s, the gold system began to study the dry tailing technology of tailings from the perspective of environmental protection. At present, the dry storage of tailings is vigorously promoted, and the tailings are dry. The safety of the reactor and the environmental protection are of great significance. At present, the safety department and the environmental protection department are promoting the dry storage of tailings to improve the safety of the tailings pond and reduce its impact on the environment.
I. The pursuit and research of tailings dry storage technology
The stocking methods of wet tailings in direct discharge mainly include upstream tailings damming method, midline tailings damming method, and downstream tailings damming method. The upstream tailings dam method is that the center line of the sub-dam is continuously moved to the upstream direction of the initial dam, and the dam body is filled by the flowing slurry. The mid-line tailing dam is grading by the swirl at the initial dam axis. Dam damming method for coarse tailings alluvial tailings; downstream tailings damming method is a damming method for cascading tailings with swirling grading of coarse tailings in the downstream direction of the initial dam. In view of the advantages of simple dam construction, convenient management and low operating costs, the upstream tailings dam method is widely used at home and abroad.
Upstream tailings damming is affected by the method of mine discharge, which often contains more fine-grained interlayers, poor permeability, higher immersion line position, and poor dam stability. And the storage of water in the reservoir during the operation of the tailings pond may cause dam breach and groundwater infiltration pollution, which may endanger the safety of downstream residents and facilities and may contaminate surface water. A suspended lake is formed above the tailings of the conventional tailings reservoir (see Figure 1). When the immersion line emerges from the dam slope, the risk of dam failure is formed. The tailings after classification are prone to liquefaction, which in turn affects the safety of the dam; The dam will form a debris flow, which is destructive.
Figure 1 Tailings reservoir hanging lake formed by conventional tailings pond
In summary, it can be seen that upstream tailings dam construction is the most economical tailings storage method. At the same time, if the safety management is not in place, the upstream tailings dam is also the most dangerous method of storage. The safety of the tailings pond is mainly Mastered in the hands of the tailings storage unit, large enterprises are equipped with tailings storage safety management institutions and equipped with professional safety management personnel. The safety of tailings storage is relatively high, and the safety management institutions of small enterprises' tailings storage are not perfect. The professional level of safety management personnel is uneven, laying a hidden danger to the safety of the tailings pond.
The number of tailings ponds in China, the large storage capacity, and the height of the dam are rare in the world, especially in the earthquake zone, using the upstream method to construct high tailings dam, tailings dam drainage and precipitation technology, and karst area tailings reservoir construction. All aspects are at the leading level. On the other hand, we must also see that the safety situation of China's tailings ponds is not optimistic. Safety accidents and even vicious accidents in tailings ponds often occur, causing irreparable damage to people's lives and property.
In order to better solve the safety and environmental protection problems of the tailings pond, and provide relevant technical countermeasures for the design and safety management of tailings dry storage, we should vigorously promote the tailings dry storage process.
Second, the type of tailings dry storage
The tailings dry storage refers to the use of a large plate and frame filter press to discharge the tailings slurry from the ore dressing into the agitation tank and pump it to the filter press workshop with the slurry. The filter press is fully extruded into a dry sheet-like tail. The slag cake has a concentration of more than 80% and a water content of only about 20%. It is transported by a belt conveyor or dump truck to the tailings stacking method in the tailings dry yard.
The new tailings dry-type stockpiling tailings are self-flowing to deep cone thickener for concentrated dewatering, increasing the slurry concentration from 26%-29% to 62%-65%, and then pumping the concentrated bottom slurry to the ceramic The filter is filtered and dehydrated, and the water content of the tailings dry slag is less than 13%. The tailings dry slag is transported to the tailings yard by belt conveyor or dump truck, paved by loader, layer-by-layer rolling, tamping and covering soil, ie Vegetation or reclamation can be restored.
Dry storage includes two types, one is pure dry storage: tailings dehydration → dewatering tailings moisture content does not exceed 20% → can be transported to the tailings pond by car or belt. The other is paste discharge (high concentration discharge): tailings concentration → incomplete dehydration → tailings concentration of 70% or more (similar to tailings filled with wells), paste tailings discharge is forced settlement, coarse, medium The fine particles sink. It should be noted here that the tailings with a concentration below 65% are discharged into the tailings pond and are hydro-deposited. There is a process of natural sedimentation. Under the action of gravity, the coarse particles sink first, the fine particles sink, and the dam is thick. The finer the inside.
At present, there are 332 tailings ponds in China that use dry tailing.
The tailings of Wangshi Company's andalusite selection plant adopts dry storage technology, and the physical properties of tailings are shown in Table 1.
Table 1 Physical properties of tailings
Particle size / mm | Distribution rate /% | Heap specific gravity / (t / m 3 ) | Stacking angle / (°) | Friction angle / (°) |
-10-3 | 55.51 | 1.54 | 33.44 | 23.6 |
-3-0.3 | 35.08 | 1.66 | 32.93 | 24.84 |
-0.3 | 9.41 | 1.73 | 32.56 | 28.08 |
Total (average) | 100.0 | 1.60 | 33.18 | 24.46 |
The tailings are dry-stacked and the tailings have a coarser grain size. The 20t dump truck transports the dry tailings from the plant to the tailings pond. When the tailings are piled up to a certain thickness, the tailings are loaded by the loader. Flatten, layered and compacted.
Third, the main way of tailings dehydration
The ways of draining the water in the tailings mainly include pressure filtration, vacuum filtration, multi-stage thickening and sedimentation tanks.
Pressure filtration: The tailings extrude part of the tailings sand under the design pressure. Commonly used equipments include plate and frame filter presses and box filter presses. The effect of pressure filtration on the treatment of coarser particle size tailings is relatively good, and the water content in tailings after pressure filtration is about 20%.
Vacuum filtration: The water in the tailings is sucked out by vacuum negative pressure. Commonly used equipments include ceramic filters and belt vacuum filters. Vacuum adsorption is better for finer-grained tailings, and the water content in tailings is about 20% after vacuum adsorption.
Multi-stage thickening: multi-stage thickening of high-efficiency thickener can be used to control the concentration of tailings in the range of 50%-60% to form a highly concentrated tailings paste. The commonly used equipments include high-efficiency thickener, high-pressure thickener, deep cone thickener, etc. . According to the degree of concentration of tailings, it can be divided into high concentration tailings slurry, which can form a natural slope angle of 2%-3% after discharge; the low yield stress paste can form a natural slope angle of 3%-5% after discharge; The high yield stress paste can form a natural slope angle of 4%-7% after discharge. By using the characteristics of thick tailings, it can obtain a much larger storage capacity than the traditional hydraulic filling method. Two key factors for the storage of the tailings after the tailings are thickened: no classification of coarse and fine particles occurs after the tailings are discharged; the tailings paste must have sufficient time for drying and consolidation. The safety of paste storage: no tailings reservoir can be formed; the tailings are not saturated and are not easy to liquefy; once they are unstable, they will not flow long distances.
Sedimentation tank: The advection type multiple sedimentation tanks are used in series. The tailings are concentrated according to the natural sedimentation rules of the tailings, and the tailings water is clarified and discharged. At the same time, the flocculation agent can accelerate the sedimentation of the tailings particles. The concentrated concentration of tailings increases with the drying time, which generally takes a long time, resulting in a small amount of concentrated tailings treatment in the sedimentation tank.
Fourth, dry tailings discharge type
According to the order of dry tailings storage, dry tailings discharge types can be divided into upstream, neutral, downstream and inverted. Among them, the upstream, mid-line and downstream type are more expensive than the inverted type of infrastructure, and it is necessary to increase the drainage facilities in the upper part of the reservoir area. Due to the accumulation of water in the reservoir, the effect of dry discharge of tailings is not achieved. Therefore, dry-type, mid-line, and downstream tailings dry emissions are rarely used, but are used in individual old warehouse renovations.
At present, the dry storage of tailings mostly adopts the inverted discharge mode, which is piled up from the end of the reservoir and gradually advanced downstream, forming a high tail and a low downstream. Advantages of inverted row: no water is stored in the reservoir, and the surrounding and upstream floods are discharged to the downstream through the intercepting ditch; the waterless tailings in the reservoir are not saturated and do not liquefy; once they are unstable, they will not flow over long distances and will not form. Large mudslide hazards. The biggest source of accidents in tailings storage is water. After the water is removed, the safety of the tailings pond is greatly improved, and the inverted dry heap is promoted.
The tailings warehouse of the Hongshi Stone Concentrator of Wangshi Company adopts the inverted row tailing method to intercept the flood in the upper part of the reservoir area. The dam is built at the end of the ditch near the upper part of the reservoir area. The dam bottom elevation is 621m and the dam crest elevation is 63lm. The height is 10m, the width of the dam crest is 3 m, the axis of the dam is 24.5 m long, the ratio of the slope of the upstream dam is 1:0.1, and the ratio of the slope of the downstream dam is 1:0.5. The Mingkou tunnel is built on the right side of the upper reaches of the retaining dam, and the flood intercepted by the retaining dam is discharged into the ditch on the other side of the mountain. The drainage tunnel adopts a straight arched straight wall type with a section size B×H=2.5m×2.5m.
The intercepting ditch is arranged on the left and right sides of the mountain, and is connected with the drainage ditch of the left and right abutment of the initial dam. The intercepting flood ditch adopts a rectangular cross section, the cross section of the left intercepting ditch is B×H=1.9m×2.0m, the starting point of the intercepting ditch is 652 m, the ending elevation is 620m, the length of the intercepting ditch is about 1.6km, and the intercepting ditch slope ratio It is 2%; the section size of the right intercepting ditch is B×H=1.0m×1.0m, the starting point of the intercepting ditch is 640m, the ending elevation is 620m, the length of the intercepting ditch is about 1.3km, and the slope ratio of the intercepting ditch is 1.54%.
The drainage facilities in the reservoir area are drained by the drainage well-drainage tunnel-exit drainage open channel, and the drainage well is placed 15m away from the upstream slope of the initial dam. Set a frame-type reinforced concrete structure drainage well, the drainage well is a 6-column frame type drainage well, the inner diameter of the drainage well is 3.5m, the inner diameter of the well is 3.0m, and the bottom of the drainage well is set to a depth of 2m. The momentum of the water flow. The average slope ratio of the bottom of the drainage tunnel is 3%, and the straight arch type is adopted. The section size is B×H=2.5 m×2.5m.
The flood in the upstream of the tailings pond of the Hongshi Petrochemical Plant of Wangshi Company is discharged by the dam-Mingkou tunnel drainage system, and the flood in the upstream of the tailings pond is not in the reservoir; the catchment on the hillsides on the left and right sides of the tailings pond is from the left and right sides of the mountain. The intercepting ditch is discharged to the lower reaches of the reservoir area, and the floods on the left and right sides of the tailings pond are not in the reservoir; the pooling floods in the effective space of the tailings pond are limited, and the collected floods quickly pass through the initial drainage wells in the upper reaches of the reservoir. - Drainage tunnel - drains the open channel to drain the reservoir area. There is no water in the tailings reservoir area, which greatly improves the safety of the tailings pond and greatly reduces the pollution to the surrounding environment of the tailings pond.
5. Advantages and disadvantages of tailings dry heap process
According to the characteristics of the tailings dry storage technology combined with the characteristics of the traditional tailings straight discharge process, it is known that the advantages and disadvantages of the tailings pond dry storage process and the traditional tailings straight discharge process are shown in Table 2.
Table 2 Comparison of advantages and disadvantages of tailings dry storage technology and traditional tailings straight discharge process
index | Tailings dry storage process | Traditional inline process |
advantage | 1. Significant environmental benefits | 1. The traditional process is mature without risk |
2. Save a lot of production water to ensure the normal production of the plant in arid areas | 2. Low production and operation costs | |
3. Conducive to the recovery of metals contained in tailings wastewater | 3. The construction period is short, which can enable enterprises to start production early and see benefits | |
4. Reduce a large amount of pharmaceutical consumption | 4. Infrastructure investment is relatively small | |
5. There will be no tailings reservoir hanging lake, no tailings water accumulation in the reservoir, and evaporating water is the non-recyclable pore water in the tailings. | ||
6. Tailings are not saturated and are not easy to liquefy | ||
7. Once the instability is achieved, it will not flow long distances. Move, the impact on the downstream of the tailings pond is small | ||
8. No classification of coarse and fine particles occurs after tailings discharge, no mud sandwich is formed | ||
9. Under the same conditions, the storage capacity is larger than the traditional straight-line process | ||
10. Closed warehouse re-cultivation period is short, can be covered in stages, and the tailings surface leveling work is small | ||
Disadvantage | 1. Higher equipment investment | 1. It is extremely unfavorable to environmental protection. Once the management is not in place, the tailings will directly harm the production and life of the downstream residents. |
2. High production and operation costs | 2. The tailings water is stored in the tailings pond for a long time, which will inevitably cause harmful substances to penetrate into the underground and pollute the groundwater resources. | |
3. The processing capacity of filter presses, filters, etc. is effective, resulting in large-scale mining enterprises unable to implement tailings dry storage | 3. Due to various reasons, the vicious accidents of tailings pond dam breaks frequently, causing great losses to the lives and property of the people. | |
4. Less likely to be realized in areas with large rainfall | 4. It covers a large area and requires a large amount of funds to invest in forests and land acquisition. | |
5. Forming a tailings pond hanging lake | ||
6. The immersion line forms a risk of dam failure when it emerges from the dam slope | ||
7. Tailings are prone to liquefaction after classification | ||
8. Debris flow after dam break, destructive |
6. Key points for safety precautions of dry storage tailings ponds
The focus of dry tailings storage operation management and safety precautions should be placed on the tailings reservoir flood control and drainage system. Its main tasks are to discharge and crush dry tailings, maintain and reinforce the dam body, flood control during flood season, and earthquake resistance. Monitoring and environmental protection work to ensure the safe operation of dry dump tailings, prevent landslides and destructive disasters, and reduce environmental pollution.
(1) When dry tailings are stored in inverted stratified discharge and crushed to the final design elevation, it must be ensured that the top surface of the tailings is from the tail of the reservoir to the downstream of the reservoir (the slope is generally 0.5%-l%) To prevent the accumulation of water in the reservoir; the final accumulation of the outer slope and the rolling is an important measure to ensure the safety of the dam, and the construction should be carried out in strict accordance with the design after review and filing.
(2) When designing the flood control and drainage system of the tailings reservoir, the flood around the reservoir area shall be intercepted and discharged to the lower reaches of the reservoir area. The floods within the effective utilization space of the tailings pond shall be provided with special flood control and drainage structures.
(3) It is necessary to regularly check the structural integrity, safety and reliability of the flood control and drainage structures of the tailings reservoir to ensure smooth drainage of flood control and drainage structures.
(4) Before the annual flood season, the initial dam should have a certain storage capacity and safety super high, to ensure that the storage floods wash away the muddy sand under the entrainment, and prevent the tailings from flowing out of the dam, and at the same time, according to the situation of silt tailings in front of the dam Sealing the drainage arches to ensure safe and effective flood control and drainage systems in the reservoir.
(5) The drainage layer should be set in the appropriate range at the bottom of the reservoir area to ensure timely dewatering of the tailings sand during the rainy season.
(6) In order to prevent the polluted environment caused by the accumulation of surface tailings dust during the use of the dry-end storage tailings pond, measures such as sprinkling spray or spraying chemical consolidation agent may be adopted to keep the surface wet and consolidated, and the tailings are piled up to the final design. When the elevation is high, the vegetation should be covered in stages in time.
(7) The slope of the downstream slope of the final tailings accumulation dam should be covered in time to ensure that the downstream slope of the pile dam is not washed by rain, and the downstream slope of the pile dam is safe and stable. The repair of the downstream slope should be reviewed and filed. The design files are carried out.
(8) It is forbidden to appear dry and wet mixing in the tailings storage of dry storage.
(9) Tailings warehouse enterprises shall formulate emergency rescue plans for major accidents such as landslides, dams and other production safety accidents, mudslides, landslides, earthquakes, etc., equip with necessary emergency rescue equipment and equipment, and conduct pre-planning exercises.
VII. Focus on disease prevention and control of dry storage tailings pond
Since the tailings facility is a long-term operation of the mine, the maintenance and management of the tailings pond is particularly important. It is required to strengthen the tailings storage technology and management archives data storage in operation, set up a separate tailings section and be equipped with full-time tailings management personnel, and formulate various regulations and procedures for the management of tailings ponds.
According to engineering geology, hydrogeological conditions, topographic conditions, physical and mechanical properties of tailings and construction effects, risk factors such as landslides, collapses, subsidences, cracks, and drainage system failures should be comprehensively analyzed and studied. And develop practical and feasible safety technical measures, and implement the principle of safety first and prevention first.
In the dry tailings stacking process, reliable safety techniques and management measures should be taken to prevent landslides caused by human and natural factors. When there are signs of landslides, it should be prevented and rectified as soon as possible. To prevent the occurrence and development of landslides, the following treatment measures can be taken.
1. According to the "Working Survey Report" and design requirements, the foundation of the dam should be treated. The stability of the slope should be checked according to the engineering, hydrogeological survey data and stacking height analysis. For the soft soil slope with poor stability, the original slope should be Push it into a step to increase stability.
2, the surrounding interception ditch should be set to prevent the surrounding collection of water into the store, necessary fashion to take anti-seepage measures. When the groundwater level has a high impact on the stability of the tailings pond, underground drainage facilities should be set up according to the geological conditions to reduce the groundwater level and prevent groundwater from immersing in the tailings pond.
3. According to the predicted size, direction and action point of the landslide thrust, gravity anti-sliding retaining wall, anti-sliding pile and other anti-sliding structures may be selected. The base of the anti-sliding retaining wall and the pile end of the anti-slide pile shall be buried. In a stable rock formation below the sliding surface.
In the karst rock areas such as carbonates, when there are karst caves, dissolution fissures, soil caves, etc., the effects on tailings dry storage and tailings dam stability should be considered, and necessary preventive measures should be taken in time. .
In the aspect of safe operation management, special personnel should be inspected and maintained according to the post responsibility system, and abnormal phenomena such as subsidence, cracks and landslides should be reported in a timely manner.
When the tailings dam is piled up to the later stage, a comprehensive survey of the dam should be carried out, and a special evaluation of stability should be carried out to verify the status quo and design the stability of the final dam, and determine the corresponding technical measures.
If the design needs to be partially modified during construction, it shall be approved by the original design unit or a higher qualification design unit; when major design proposals involving tailings reservoir site, etc., tailings dam type, flood discharge mode, etc. are changed, It should be redesigned by the original design unit or a higher qualification design unit, and submitted to the original approval department for the design of the safety facilities of the tailings pond construction project for approval.
Eight, the conclusion
The tailings pond is the necessary facility to maintain the normal production of the mine. The dry tailings storage process has great practical significance for safety and environmental protection, and has become the development direction of tailings storage in the future. At present, the tailings dry storage has higher construction cost and higher operating cost. The processing capacity of filter presses, filters and other equipment is limited. Generally, each processing capacity is about 100 t/d, and each processing capacity is larger. 300t / d, so smaller mines can achieve dry dumping of tailings, large-scale mines to achieve dry dumping of tailings is more difficult. Call on the tailings dewatering equipment research and development enterprises and manufacturers to accelerate the development and production of large-scale tailings dewatering equipment, and provide necessary basic conditions for large-scale mining enterprises to realize the dry tailing of tailings as soon as possible.
references
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[2] Wang Anli, Li Jianzheng. The harmless treatment process and practice of new tailings[J].Metal Mine,2010(S):116-118.
[3] Chi Chunxia, ​​Shen Qiang. Discussion on tailings dry heap technology [J]. Gold. 2008 (10): 47-49.
[4] Fu Yongxiang. Design concept and example of large-scale valley tailings yard [J]. Metal Mine, 2009 (10): 1-4.
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