Tailings mining under special conditions

An Iron Ore is a large accumulation of residual slope type iron deposits, founded in the early 1970s, after decades of mining, resources are depleting, while tailings have been piled up millions of tons TFe27% High quality tailings resources around. Through the mineral processing technology research and the “re-election + high gradient magnetic separation” mineral processing technology, it has obtained better technical and economic indicators, which has become a way for the mine to increase revenue and increase efficiency and extend service years. However, due to the complicated technical conditions of the tailings mining and the special nature of the rhythm of the tailings during the discharge process, it is impossible to adopt the conventional “water mining” process, and only another way to explore the “dry mining” method of the tailings.
1 mining technical conditions
1.1 Type and status of tailings pond
The mine tailings pond is surrounded by mountains on three sides. It is a typical canyon-type tailings pond. The lowest elevation of the reservoir is 2260m. The final stacking elevation is 2300m, the storage thickness is 0~40m, and the final (length × width) is 1110m×330m.
1.2 Hydrogeological conditions
The tailings reservoir deposit is a loosely packed, water-rich artificial accumulation layer; the tailings pond is located in the low-concave zone of the mining area, and the production water, domestic wastewater, and atmospheric precipitation of the mine basically flow into the tailings pond; the tailings pond In the karst area, underground karst is very developed.
Accordingly, if water mining is used, it is necessary to prevent leakage of the tailings pond; if dry mining is used, it is necessary to solve the problem of drainage and drainage of the tailings.
1.3 Engineering geological conditions
The tailings pond was originally a large-scale natural depression developed in the karst area. The lithology of the stratum is relatively simple. The bottom surface of the reservoir is a Quaternary accumulation layer with a thickness of 0-20 m. Below the topsoil is the Kunyang Group. Longkou Formation carbonate rock.
1.4 Environmental geological conditions
Because the tailings pond is located in the Dalongkou Formation limestone area where karst development is extremely strong, its karst characteristics are karst fissures, funnels, dissolution tanks, karst caves, and karst depressions on the ground, and wedges, wells, and ducts in the ground. Vertical development, connected with the underground river channel distributed in the deep part of the mining area, formed a complete set of above-ground and underground karst channels. There have been many accidents of tailings reservoir leakage and pollution of underground river channels and nearby villagers drinking Longtan water source.
1.5 sedimentary rhythm
There are many factors that constitute the rhythm of tailings sedimentation, including the type of ore selected, the process of beneficiation, the nature of tailings, the tailings discharge method and the type of tailings pond. The sediment rhythm of the mine tailings has the following characteristics: 1 Because the ore is selected as the residual slope, the tailings contain more mud; 2 Because there is no grinding process in the beneficiation process, the size of the tailings discharged is not uniform ( 0～35mm); 3 In order to prevent leakage accidents in the tailings pond, the discharge process of peripheral ore mining is adopted; 4 The ore dressing process has undergone continuous improvement, the grade of tailings discharged at the beginning is higher, and the grade of tailings discharged later is gradually reduced. .
In the early stage of mine production, because the tailings pond is in the bottom shape (upper width and lower width), the tailings that were previously collected into the reservoir are accumulated in the narrow intermediate area of ​​the bottom of the reservoir. According to the size and grade of the mineral particles carried by the tailings slurry. And the difference in mineral body weight, the minerals with large particles, high grade and large body settled at the bottom of the tailings pond, which formed the phenomenon that the grain size gradually became coarser from top to bottom and the grade of iron contained gradually higher; As the process progresses, the thickness of the tailings accumulation gradually increases, the water level of the tailings reservoir expands continuously, and the handling distance of the tailings on the horizontal surface increases. The minerals in the tailings slurry are transported according to the particle size, grade, weight, and water flow. Settling in order from near to far.
In summary, the sedimentary rhythm of the mine tailings is: from the outside to the inside (from the periphery of the tailings pond to the center), the iron content of the minerals is from high to low, the mineral particles are coarse to fine, and the mud content is gradually increased; From top to bottom, the iron content of the mineral is gradually increased from low to high, and the mineral particles are gradually thicker and thicker. see picture 1.

1.6 tailings structure
The mine tailings are mainly composed of clay, powdery, fragmented limonite and hematite and rock debris, which precipitate in a natural state, with short curing time and weak compaction. The tailings with less mud have loose structure and poor cohesiveness; the tailings with more mud have stronger cohesiveness, and it is easy to form a block after losing water.
2Speciality and mining method of tailings mining
2.1 The particularity of tailings mining
According to the analysis of the technical conditions of the tailings mining, the tailings have the following special characteristics: 1 the mineral particles of the tailings are uneven and have a special sedimentary rhythm; 2 the tailings reservoir is located in the karst area, and the karst is very strong; The mine is in a "pot bottom type", and the topography of the floor is undulating and the terrain conditions are complex; 4 the mine is located above 2300m.
In the alpine mountainous area, the freezing phenomenon is often prone to occur in winter; 5 the mine has insufficient water resources, and the production water pipeline is as long as 13.5km, and the fourth-stage pumping station is delivered by the relay, and the cost of taking water is high.
2.2 Water mining
The tailings water mining is divided into two types of water gun-sand pump and dredger. For conventional tailings, the water mining capacity is strong and the production cost is low. It is widely used by mines at home and abroad.
The premise of water gun-sand pump mining is pulping. Due to the special sedimentary rhythm of the tailings, the grain size is uneven, and the tailings with less mud and coarse particles are too fast to form a slurry in the process of water gun flushing. The tailings with more mud have stronger cementation, and it is easy to form a block after dewatering. It is very difficult to shoot with water guns.
Dredger mining requires that the tailings pond maintain a certain water level, and the bottom of the tailings pond should be relatively flat and open. According to the above analysis, the tailings are not suitable for mining by this method.
2.3 dry mining
Starting from the reality of the mine, the methods of single tailing method, direct bottoming method and combined layering method for three types of tailings dry mining are summarized.
2.3.1 Single layering method
The main transportation trunk line and the transportation branch line are laid in the water level of the tailings pond, and the backhoe type excavator is used to retreat along the transportation branch line, and the top-down and layer-by-layer mining is carried out. See Figure 2.

(1) Applicable conditions. All tailings ponds can be harvested by this method, especially for tailings mining with a thickness of more than 10m or a large undulation of the tailings pond floor and complex terrain.
(2) Mining process and steps: 1 laying the main transport trunk line in the tailings pond; 2 arranging the return transport branch line on both sides of the main transport trunk line; 3 using the backhoe type excavator-dumping car, retreating along the branch line Style mining.
(3) The constituent elements of the stope. 1 The width of the main transport trunk line and the return transport branch line depends on the selected mining and transportation equipment, generally 4~5m, which is laid by reinforced concrete precast block; 2 the width of the mining belt is equal to the mining branch line, which is twice the excavation radius of the excavator; 3 The depth of one mining is determined by the selected excavation equipment, and the bucket capacity is 1m3.
The depth of the mining machine is about 5m.
(4) Main advantages and disadvantages. Advantages: strong applicability, no ore depletion, safe and reliable; Disadvantages: heavy traffic of the main line and mining branch line, high mining cost, low recovery efficiency, tailings dredging and drainage of working face is difficult.
2.3.2 Direct bottoming

A permanent transportation road will be built along the tailings pond to reach the bottom of the tailings pond, and then the tailings will be upgraded horizontally, which is similar to open pit mining. See Figure 3.

(1) Applicable conditions. The thickness of tailings in the tailings pond is less than 10m, and the bottom of the tailings reservoir is relatively flat.

(2) Mining process and steps. 1 Using a backhoe excavator from a group of tailings stocks, directly to the main transport trunk of the tailings reservoir floor; 2 using a positive shovel excavator along the tailings pond floor horizontally to form a horizontal section ditch; 3 in the horizontal section The sides of the ditch are shovel-type excavators, and the mining is carried out horizontally along the contour line of the original topography of the tailings pond. During the mining process, waste rock can be used to pave and level the bottom of the tailings reservoir to improve mining and transportation conditions.
(3) The constituent elements of the stope. 1 step height is not more than 10m; 2 step slope angle is 45°; 3 mining belt width is twice the digging radius of the shovel excavator; 4 when the trunk width is 6~8m, the maximum longitudinal slope ratio is not more than 8%.
(4) Working surface drainage. 1 Excavate the intercepting ditch along the periphery of the tailings pond to prevent the mining industry, domestic wastewater, and surface runoff from entering the tailings pond during the rainy season; 2 Set up a precipitation well in the low depression of the mining area to introduce the working surface overflow and tailings permeate water In the middle, the horizontal pump is used for pumping outward.

(5) Main advantages and disadvantages. Advantages: high mining efficiency, low cost and easy implementation. Disadvantages: The scope of application has certain limitations, because the bottom of the tailings reservoir is uneven, and when the bottom of the reservoir is soft, it needs to be leveled with waste concrete, so the tailings are depleted.
2.3.3 combined layering method
When mining, first digging into and out of the ditch, forming a mining step, and then laying back to the mining road, using the forward shovel excavator for forward mining. After the upper layer of ore is taken out, the backhoe type excavator is used to retreat along the recovery road, and the layered ore is recovered. See Figure 4.

(1) Applicable conditions. The tailings in the tailings reservoir are more than 15m thick; the bottom of the tailings reservoir has a large undulation, which is not suitable for mining by the second method.
(2) Mining process and steps. The backhoe excavator is used to excavate a group of tailings and shovel to the next level of the access trunk as the main transport trunk; 2 use the horizontal shovel excavator to horizontally advance to form a horizontal section ditch; 3 in the horizontal section ditch The mining belt is arranged on the side, and the reinforced concrete precast block is used to lay the mining and transportation branch line, and the mining work surface is extended synchronously; 4 the front shovel type excavator is used, and the upper layer ore is advanced along the mining and transportation branch line; After that, the backhoe excavator is used to retreat the layered ore along the mining and transportation branch line; 6 the level of ore is harvested and extends into and out of the trench to the next level for the next level of mining.
(3) The components of the stope are the same as the second method.
(4) The drainage of the working face is the same as the second method.
(5) Main advantages and disadvantages. Advantages: Applicability is stronger than the second method, and the mining cost is lower than the first method; Disadvantages: the process is cumbersome, and the mining and transportation branch lines are difficult to lay.
2.3.4 tailings dry mining system
The three dry mining methods have their own advantages and disadvantages. The actual mining process is interconnected. The three complement each other and complement each other to form a complete “dry mining” system for tailings. See Figure 5.

3 conclusions
With the acceleration of the development of the national circular economy, the scale of tailings development and utilization has been continuously expanded, and higher requirements have been placed on the tailings mining technology and production capacity. As a kind of unconventional mining method, tailings dry mining has formed a complete tailings through the “single layering method”, “direct bottoming method” and “combination layering method” adopted for many years. Dry mining technology, and successfully applied to mine production practices, provide reference and reference for tailings mining that is not suitable for water mining.