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Tailings pond
Under normal circumstances, more dams are built between the valleys or around the depressions, and the gold ore tailings are discharged into the deposits for sedimentation. This dam is called a tailings dam. The tailings pond is composed of drainage facilities, tailings dam and tailings. The drainage facilities refer to the hillside intercepting ditch or mountain stream drainage pipe that excludes the rainwater or mountain stream of the tailings pond, and excludes the drainage of the tailwater reservoir, the drainage of the tailings clarified water, and the exclusion of the infiltration in the tailings. Water, blind ditch at the bottom of the dam, and drainage pipes.
There are three types of tailings ponds: (1) valley type, damming on the valley side; (2) hillside type, using two sides and three sides of the hillside terrace to build dams; (3) opening type, damming around the flat land. From a practical and practical point of view, it is better to use a valley type tailings pond. When setting the capacity of the tailings pond, it should be based on the service boundary of the gold mining plant and the total amount of tailings stored.
The tailings dam is the most important component of the tailings pond facility and is related to the safety of the tailings pond. The choice of dam site should be as close as possible to the gold selection plant, so that the tailings transport distance is the shortest, and the lift height is reduced as much as possible. The soil layer and rock below the dam site should be structurally reliable, and engineering geological evaluation should be carried out before dam construction.
The initial dam of the tailings pond can be constructed with less soil and stone. It should be permeable to water, that is, the earth dam should be used. The bottom of the outer slope should have a permeable body of permeable stone and a sandstone with a certain level. Filter layer to protect the stability of the initial dam. The initial dam was built during the capital construction period of the gold-removing plant. The tailings capacity can only meet the tailings volume of the depositing and gold-removing plant for half a year to one year. The tailings storage capacity of the future tailings should rely on the tailings and nearby clay. The dam is to be solved.
Production practice indicates that fine sand of less than 37 μm in tailings is not suitable as a material for tailings dams. If the coarse-grained tailings are graded as a downhole filling, then the tailings dam should be re-classified with a cyclone at the tailings dam. The coarse-grained grade is kept close to the dam and the fine-grained grade is used. The overflow of the cyclone flows to the tail of the tailings pond. The fine tailings slurry is naturally graded during the flow process, and the thin and fine tailings flow the furthest. At the end of the tailings pond there is a section of clarified water.
The tailings in the reservoir near the slope of the dam are not only the foundation of the new dam, but also the material or part of the dam (or dam). There are many ways to increase the dam's capacity. Commonly used methods include upstream damming method, downstream damming method, and midline damming method.
First, the upstream dam construction method: the initial dam construction is at the most downstream point. The sub-dam is successively increased on the upstream side of the base dam by a certain gradient.
The valley type tailings pond adopts the upstream damming method. Many methods in China have adopted this method.
It should be specially noted that the collapse height of the sub-dam exceeds a certain limit. Caused a large number of tailings outflow. Therefore, it is necessary to determine the stacking height of the sub-dam through experiments.
In addition, it is strictly forbidden to plant deep-rooted plants on the outer layer of the tailings dam to prevent the dam from sucking a large amount of water, increasing the degree of wetting of the dam and reducing the stability of the dam.
Second, the downstream damming method: the method of using the coarse-grained tailings to move the downstream line on the basis of the initial dam to move the downstream dam. Large tailings dams use this method to increase the late dam and increase storage capacity. In the initial production beneficiation plant tailings pile dam use, can not meet the requirements on the amount, which need to find a point near the soil to soil or stope waste shipped out of line fill. This damming method is safe and reliable, but the cost of tailings treatment is increased, and some people have to build dams for a long time.
Third, the intermediate heightening method: using this method to increase the tailings dam, the dam center line is consistent with the initial dam. When using granulated tailings to build dams, the amount of tailings is lower than that of downstream dams and can form a certain storage capacity in a short period of time.
When the tailings dam is raised by the intermediate heightening dam method, the surface (inner slope) of the dam body upstream should maintain a certain slope, not steeply steep, and rush to find stability and affect the stability of the later dam.
If the mine has a waste rock output, it can be used to fill the tailings dam. It is also economically safe to mix waste rock and tailings dams under certain conditions. However, the mining pit entrance must be close to the tailings pond.
The return water utilization facility is also an important part of the entire tailings facility. From the perspective of environmental protection and economy, the clarification water of the tailings pond should be used as much as possible to minimize the proportion of new water supply to the concentrator. The use of flotation to treat polymetallic gold-bearing ores will limit the proportion and location of the return water. Even better treatment of tailings clarified water will also bring certain pollutants and interfere with the flotation process.
Some of the gold mine tailings are treated with lime before being sent to the tailings pond, neutralizing the acid, allowing the heavy metal ions to precipitate as insoluble hydroxides, and also destroying cyanide in the gold plant with cyanidation operations. . Some of the gold-removing plants, which are mainly cyanidation, remove the cyanide, sulfate and amine chemicals from the water by ozone and alkaline chlorination after leaving the factory. The tailings are stored in the warehouse for a period of time, and the dilution of the sun and the dilution of the surface turbulent water and rainwater flowing into the reservoir will also improve the water quality. In areas where water resources are scarce, efforts should be made to make full use of the re-use of tailings clarified water. In the tailings pond tailings clarified water installation floating pump station can pump a certain amount of tailings clarified water to the storage tank of the gold selection plant according to the amount of water and the degree of clarification. The new pool and the return pool can be divided into two compartments, and the ratio of new water to return water can be controlled before being sent to the gold selection plant. Some solids may be brought back in the return water, and the return water pool should be cleaned regularly and the quality of the return water should be monitored.
The tailings pond is similar to the reservoir. There is water in the reservoir. Therefore, the dam itself must be safe and reliable, and there must be flood control facilities. In order to prevent accidents, due to the large amount of surface runoff in the flood season, a intercepting ditch should be built to remove some of the surface runoff water from the upstream. Some drainage wells are built along the longitudinal slope of the tailings pond, and the excess clarified water is discharged to the outside of the reservoir through underground drains or drains.
In the production process of the tailings pond, the height of the dam should be higher than the actual tailings storage surface of the tailings in the reservoir by more than 1~2m to ensure a certain safety and high height of the tailings dam. If the height of the tailings storage surface is comparable to the height of the dam crest of the tailings dam, this will be a risk factor. A heavy rain may cause the tailings to overflow from the top of the dam, especially in the stage of using the tailings to build a sub-dam.
The tailings dams are all permeable dams. The water in the tailings pond continuously passes through the dam body (the dam wall, part of which is drained, and the dam below the drainage line is hydrated or wetted by water. This drainage line is usually called the wetting curve. The lower the wetting curve, The more stable the dam is, if the wetting curve has risen to the top of the sub-dam of the highest level, the tailings water has been submerged to the top of the sub-dam, and the tailing dam will be a sand beach that is blistered, ready to In order to ensure safety, the discharge of tailings slurry should be discharged uniformly from the top of the dam to the upstream of the reservoir, and the tailings water should be pushed into the reservoir as much as possible, so that the inner slope of the dam is at a considerable distance from the location where the tailings are accumulated. The length of the longitudinal slope of the tailings pond is usually 50-120 m. For small tailings ponds, this length is also shortened accordingly. The length of this dry slope (ie no water on the surface) is inversely proportional to the height of the wetting curve. .