Mining method suitable for coal mine overlying drainage type sandstone uranium mine

Abstract

The invention belongs to the technical field of mineral exploitation, and particularly relates to a mining method suitable for a coal mine overlying drainage type sandstone uranium ore, which comprises the following steps: acquiring the spatial position of a sandstone uranium ore body through a geological survey means; digging a shaft from the ground to the bottom layer of the sandstone uranium ore body, and digging a gate way below the sandstone uranium ore body; in the delineated area, dividing the sandstone uranium ore body into a plurality of in-situ leaching units through gate tunneling; continuous low-position grouting-liquid pumping dual-purpose drill holes are drilled in the side wall of the gate way in the in-situ leaching unit, and then a crack connected with the sandstone uranium ore body is transformed into a low-permeability crack through post-grouting; guniting is carried out in the gate way of the in-situ leaching unit to form an anti-seepage reinforcing wall; punching a high-level liquid injection hole in the sandstone uranium ore body corresponding to the in-situ leaching unit; and carrying out in-situ leaching treatment to obtain uranium-containing minerals. The mining-induced fracture in the coal mine overlying drainage type sandstone uranium mine can be treated, a local in-situ leaching uranium mining flow field unit is formed, and therefore in-situ leaching uranium mining in a coal mine overlying drainage type sandstone uranium mine reservoir is achieved.

Description

Technical Field

[0001] This invention belongs to the field of mineral development technology, and in particular to a method for mining uranium deposits in sandstone overlying coal mines. Background Technology

[0002] Natural uranium is an important strategic resource and energy source for my country. Over 70% of my country's uranium deposits are sandstone uranium deposits, and over 90% of natural uranium production comes from in-situ leaching mining of sandstone uranium deposits. Since both sandstone uranium reservoirs and coal seams are sedimentary rock strata, the occurrence of sandstone uranium ore bodies and coal ore bodies exhibits spatial superposition characteristics. The most typical example is the "uranium above coal" spatial relationship, where they are superimposed both horizontally and vertically, a phenomenon widely observed in Xinjiang and other regions of my country. The uranium-bearing aquifers where uranium deposits are located are the overlying strata of the coal seam. Uranium mining requires in-situ leaching to extract uranium using reservoir pore water. However, coal mining requires dewatering the aquifers in the overlying strata to eliminate water hazards. Since the uranium reservoir is the overlying strata of the coal seam, dewatering operations in coal mining will drain the pore water from the uranium reservoir. Simultaneously, coal mining causes vertical development of fractures in the overlying strata to the uranium-bearing aquifers, resulting in a drop in the water level or even complete dewatering of the aquifers. Early coal mining did not consider the impact on uranium aquifers, resulting in uranium deposits in the overlying strata of coal mine goafs and those affected by coal mining activities being unminable due to low reservoir water levels or water shortages. Therefore, there is an urgent need to develop a coordinated mining method suitable for dewatered sandstone uranium deposits overlying coal mines.

[0003] Regarding the coordinated mining of coal and uranium, existing methods include an in-situ mining system and application method for composite superimposed resources (CN202110490682.9) and a coal, uranium, and oil gasification combined mining system and application method (CN202410276815.6). These methods utilize underground coal gasification for coal mining, with the CO2 generated used for in-situ leaching of uranium. However, they do not consider reservoir dewatering-type uranium mining. Another existing method for the in-situ co-development of coal-rock and sandstone-type uranium deposits (CN202410582257.6) combines underground coal gasification with in-situ neutral leaching to mine uranium resources in both coal-rock and sandstone-type uranium deposits. However, this method is difficult to apply to dewatering-type uranium mining. One existing method for preventing groundwater level decline during uranium leaching (CN201510929534.7) involves constructing a global hydraulic barrier around the uranium ore area by designing the distribution of water injection boreholes to prevent the groundwater level from dropping when the coal mine drains groundwater. However, this method maintains the uranium ore layer water level through water replenishment, consumes a large amount of water, does not seal fissures, and the replenished water enters the coal mine, affecting coal mining. Furthermore, it does not consider how to mine uranium ore under conditions of no or little water in the reservoir. Existing wellless fluidized bed mining methods for coal-type uranium deposits (CN201910208825.5) achieve coal fluidized bed mining and in-situ leaching of uranium-bearing ash slag through boreholes, but are difficult to apply to the mining of overlying, drained sandstone uranium deposits. Existing methods for co-mining coal and associated uranium deposits (CN202410028335.8) address the spatial distribution of uranium deposits in coal mines where coal is above and uranium is below. This involves constructing a shaft to the coal seam, drilling into the uranium ore layer below, and using grouting reinforcement technology to seal cracks in the coal seam floor to prevent water inrush from the underlying uranium ore layer. However, this method does not consider mining schemes under conditions requiring uranium ore layer dewatering. A new rapid mining method for sandstone-type uranium resources in uranium-coal superimposed areas (CN202211592393.0) shortens the in-situ leaching uranium mining cycle through high-density adjustable in-situ leaching well networks, digital well construction technology, and enhanced leaching, resolving the mining contradictions in coal-uranium superimposed areas. However, this method does not consider specific mining schemes for dewatered uranium deposits. There is a coal-uranium co-mining method based on delamination grouting (CN202410057674.9), which drills from the ground to the bottom of the uranium-bearing ore layer to form an anti-seepage curtain to prevent leaching liquid from entering the coal seam, thereby resolving the contradiction between coal and uranium mining. However, this method is difficult to guarantee the effect because it involves global grouting, and uranium mining requires sufficient water in the uranium-bearing aquifer, making it difficult to apply to uranium mining schemes under uranium dewatering conditions.

[0004] The above-mentioned technologies all aim to mine uranium using traditional in-situ leaching techniques when there is sufficient water in the uranium-bearing aquifer. They reduce the impact of coal mining on uranium mining by constructing hydraulic curtains or grouting, making it easier to maintain the original in-situ leaching water level conditions. However, they cannot solve the problem of mining dewatered uranium deposits in the overlying strata of coal mines that are affected by coal mining. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a coordinated mining method suitable for overlying, dewatered sandstone uranium deposits in coal mines.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The present invention provides a method for mining uranium deposits in overlying, dehydrated sandstone in coal mines, characterized by comprising the following steps:

[0008] Step 1: Obtain hydrogeological parameters such as the specific spatial location of the sandstone uranium ore body, the stress field parameters of the maximum principal stress direction in the sandstone uranium ore occurrence area, and the permeability of the sandstone matrix through geological surveys and other means.

[0009] Step 2: Excavate a shaft from the surface to the sandstone uranium ore body's host stratum, excavate a horizontal tunnel below the sandstone uranium ore body, delineate the entire sandstone uranium ore body's host area through the horizontal tunnel, and determine the uranium mining area;

[0010] Step 3: In the delineated mining area, continue to excavate through horizontal tunnels to form a continuous planar frame structure covering the uranium mining area. The continuous frame structure divides the sandstone uranium ore body into multiple in-situ leaching units, with each in-situ leaching unit corresponding to the sandstone uranium ore body above it.

[0011] Step 4: In a pair of long-side horizontal tunnels in the leaching unit, drill continuous low-level grouting-extraction dual-purpose boreholes on the sidewalls of the horizontal tunnels. Grouting is then carried out through the low-level grouting-extraction dual-purpose boreholes, and the grout enters the mining-induced fractures, reducing the permeability of the mining-induced fractures in the leaching unit to below the permeability of the sandstone matrix, and transforming the high-permeability mining-induced fractures into low-permeability fractures.

[0012] Step 5: Shotcrete is sprayed onto the sidewalls, roof, and floor of the horizontal tunnel in the ground immersion unit to form an anti-seepage reinforcement wall, establishing a low-permeability boundary for the ground immersion unit;

[0013] Step 6: Drill a high-level injection hole above the sandstone uranium ore body corresponding to the leaching unit, and enlarge the low-level grouting-extraction dual-purpose borehole to expose the rock matrix on the inner wall of the hole as an extraction hole.

[0014] Step 7: In the in-situ leaching unit, by injecting liquid from the high-level injection hole and pumping liquid from the low-level grouting-pumping dual-purpose borehole, a local seepage field is formed between the high-level injection hole and the low-level grouting-pumping dual-purpose borehole. Based on the local flow field, the sandstone uranium ore body in the in-situ leaching unit is subjected to in-situ leaching treatment to obtain uranium-bearing minerals.

[0015] As a further preferred option, in step three, when dividing the leaching units, the primary consideration is to arrange the length of the leaching units along the dip of the rock stratum floor so that gravity becomes one of the driving forces for pore water seepage. The secondary consideration is to extend the tunnel along the direction of the maximum principal stress to facilitate the maintenance of the tunnel structure stability.

[0016] As a further preferred option, in step four, the first and last two low-level grouting-extraction dual-purpose boreholes are located near the sidewalls of a pair of short sides in the ground immersion unit.

[0017] As a further preferred option, in step four, the particle size of the grouting material should be close to 1 / 10 to 1 / 15 of the average particle size of the uranium-bearing sandstone; and the permeability of the grout after solidification should be less than or equal to the permeability of the uranium-bearing sandstone.

[0018] As a further preferred option, in step four, multiple low-pressure grouting can be used, that is, the next grouting is carried out after the previous grout has initially set, until no more grout can be injected into the borehole.

[0019] As a further preferred option, a covered culvert is excavated at the bottom of the anti-seepage reinforcement wall on the side of the horizontal tunnel to collect the leaching liquid leaking from the anti-seepage reinforcement wall.

[0020] As a further preferred option, in step six, if the sandstone uranium ore body is a coal seam overlying drainage-type uranium ore affected by vertically developed fractures, then there are multiple high-level injection holes parallel to the low-level grouting-drainage dual-purpose boreholes. If the sandstone uranium ore body is a coal seam overlying drainage-type uranium ore affected by coal mining drainage operations, then the high-level injection holes can be either multiple boreholes parallel to the low-level grouting-drainage dual-purpose boreholes or a single borehole perpendicular to the low-level grouting-drainage dual-purpose borehole.

[0021] As a further preferred option, step six, the ground immersion treatment stage, is divided into four stages;

[0022] Phase 1: Close the low-level grouting-extraction dual-purpose borehole and pump the leaching solution into the high-level grouting hole at pressure p1;

[0023] Second stage: When the pressure of the low-level grouting-extraction dual-purpose borehole gradually increases to p1, close the low-level grouting-extraction dual-purpose borehole, maintain the pressure of the high-level injection hole p1, and perform hole sealing.

[0024] In the third stage, the valve of the low-level grouting-extraction dual-purpose borehole is opened to release the pore pressure in the rock mass. The pore water is then collected into the low-level grouting-extraction dual-purpose borehole through the pore pressure difference, thereby allowing the uranium-containing leachate in the rock mass of the in-situ leaching unit to seep out.

[0025] In the fourth stage, liquid is injected from the high-level injection hole and extracted from the low-level grouting-extraction dual-purpose borehole to carry out in-situ leaching. During the fourth stage of in-situ leaching, the hole-clogging operation of the third stage can be repeated multiple times to maximize the release of uranium-containing minerals.

[0026] Beneficial effects: Traditional in-situ leaching uranium mining schemes form a globally interconnected pore water flow field throughout the entire uranium reservoir; however, this globally interconnected pore water flow field consumes a large amount of water during operation, making it difficult to apply to dewatered uranium mines; moreover, it is difficult to isolate the seepage field from the fractures, especially when sandstone uranium ore bodies are affected by mining-induced fractures, making it difficult to achieve precise fracture sealing; ultimately, this leads to difficulty in replenishing pore water in the uranium reservoir and easy leakage, making it difficult to meet the pore water environment required for in-situ leaching of dewatered sandstone uranium ore overlying coal mines. Unlike traditional in-situ leaching methods that utilize a global pore water seepage field, this invention divides the sandstone uranium ore body into several in-situ leaching units. Within each unit, fractures connected to the sandstone uranium ore body are transformed into low-permeability fractures, creating a localized small-scale seepage field. This more precisely isolates the sandstone uranium ore body from the fractures, allowing for circulation of smaller volumes of water within the local seepage field. This makes it easier to maintain the pore water environment required for in-situ leaching, enabling in-situ leaching of uranium from overlying, desiccant-type sandstone uranium ore reservoirs in coal mines. This method of dividing sandstone uranium ore bodies into in-situ leaching units is more adaptable to mining scattered sandstone uranium ore bodies. Attached Figure Description

[0027] Figure 1 Diagram showing the development of the shaft and horizontal tunnel;

[0028] Figure 2 Schematic diagram of the division of inundation units;

[0029] Figure 3 A schematic diagram of fracture grouting to reduce seepage in sandstone uranium ore bodies affected by mining-induced fractures and the construction of anti-seepage reinforcement walls for roadways;

[0030] Figure 4 Schematic diagram of the planar layout of injection and extraction holes in a sandstone uranium ore body affected by coal mining drainage operations.

[0031] Figure 5 Schematic diagram of the construction of the anti-seepage isolation wall for the roof slab;

[0032] Figure 6 A schematic diagram of the planar layout of injection and extraction holes in a sandstone uranium ore body affected by coal mining drainage operations;

[0033] In the diagram: 1-Sandstone uranium ore body; 2-Coal seam; 3-Uranium ore overlying aquitard; 4-Uranium ore underlying aquitard; 5-Mining-induced fracture; 6-Boundary line of water-conducting fracture zone; 7-Coal mine goaf; 8-Shaft; 9-Horizontal tunnel; 10-Low-level grouting-drainage dual-purpose borehole; 11-Uranium ore host rock stratum floor delamination fracture; 12-Liquid collection culvert; 13-High-level liquid injection hole; 14-Roof anti-seepage isolation wall; 15-Directional fracturing borehole. Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0035] Example 1: Mining of dewatered uranium deposits over coal seams affected by vertically developed fractures;

[0036] In a certain area of ​​Ordos, the Jurassic Yan'an Formation and Zhiluo Formation contain coal and uranium deposits, respectively. Coal seam 2 is 7m thick, and the sandstone uranium ore layer is 4m thick. The uranium ore is hosted in the overlying strata of the coal mine, located within the coal mining area in plan view, and vertically located directly above coal seam 2, with a vertical interval of approximately 100m. The coal mine shaft is relatively far from the sandstone uranium ore body 1. Due to the prior mining of the lower coal mine, drilling upwards to the uranium ore layer for water drainage operations caused the pore water in the uranium reservoir to dry out. Simultaneously, fractures formed by coal mining disturbance developed upwards, with the boundary line 6 of the water-conducting fracture zone extending to the uranium ore layer, causing a decrease in the water level and even depletion of pore water in the uranium ore layer. For this type of drained uranium reservoir affected by coal mining fractures, traditional in-situ leaching uranium mining methods are unusable due to water shortage or loss of water-retaining capacity in the uranium ore layer. For this type of dewatering uranium mining affected by coal mine fractures, the present invention provides the following solution:

[0037] (1) First, through geological surveys and other means, information such as the specific spatial location of sandstone uranium ore body 1, stress field parameters and hydrogeological parameters of the sandstone uranium ore occurrence area were obtained.

[0038] Excavate a shaft or inclined shaft from the surface to the sandstone uranium ore body 1. Then, in the sandstone uranium ore body 1 stratum, excavate a horizontal tunnel 9 along the floor of the sandstone uranium ore body 1 stratum to the area of ​​sandstone uranium ore body 1, so that sandstone uranium ore body 1 is higher than the tunnel floor. Use the tunnel to delineate the mining area of ​​sandstone uranium ore body 1.

[0039] In the mining area, the sandstone uranium ore body 1 is divided into several rectangular leaching units by means of roadways. Each leaching unit corresponds to the sandstone uranium ore body 1 above it. When dividing the leaching units, the layout of the horizontal roadway 9 should first consider the length of the leaching unit along the dip of the bottom of the rock stratum, so that gravity becomes one of the driving forces for pore water seepage. Secondly, the roadway should be extended along the direction of the maximum principal stress to facilitate the maintenance of the roadway structure stability.

[0040] Specifically, well shaft and tunnel excavation employs relatively mature methods such as mechanized excavation or blasting.

[0041] (2) Grouting to reduce seepage in fissures.

[0042] Within a rectangular leaching unit, low-level grouting-extraction dual-purpose boreholes are drilled from the roadway along the bottom of the uranium-bearing rock strata. The boreholes in each leaching unit are drilled from the roadway side toward the rock mass on both sides. The low-level grouting-extraction dual-purpose boreholes 10 are parallel to the short side horizontal roadway 9 of the leaching unit.

[0043] In particular, the first and last sets of boreholes should be close to the roadway walls to prevent seepage blind spots from appearing in the roadway walls during ground saturation. The spacing and location of the remaining boreholes are determined according to the production schedule. The denser the boreholes, the faster the mining rate, and vice versa.

[0044] By using a dual-purpose "low-level grouting-extraction" borehole, grout is injected into the borehole to form an impermeable layer in mining-induced fracture 5 and delamination fracture 11 of the bottom plate of the uranium-bearing rock stratum.

[0045] Specifically, the particle size of the grouting material should be close to 1 / 10 to 1 / 15 of the average particle size of the rock; the permeability of the grout within the fissures after solidification should be less than the permeability of the rock; multiple low-pressure grouting sessions can be used, with the next grouting session performed only after the previous one has initially solidified, until no more grout can be injected into the borehole; the grouting pressure range should refer to the pressure range given in patent CN2025103144455 that does not form macroscopic cracks. Within the leaching unit, the grouting material fills the fissures, reducing their permeability. Ultimately, grouting transforms the originally high-permeability fissures into low-permeability fissures, reducing the impact of the dominant seepage channels formed by high-permeability fissures on leaching; thus achieving the goal of improving the permeability of the sandstone uranium ore body within the leaching unit to the state before being affected by mining-induced fissures, thereby meeting the rock permeability requirements for leaching. Specifically, low-permeability cement grout can be used as the grouting material, and related technologies and equipment are relatively mature.

[0046] During production, the flow rate of the low-level grouting-extraction dual-purpose borehole is monitored comprehensively; for boreholes with low flow rates, additional boreholes are drilled on both sides to increase the borehole density; the aforementioned operations are repeated to grout and reduce fracture permeability; and manual local plugging is performed.

[0047] (3) The side walls and bottom slab of the alley are sprayed with grout to form a seepage-resistant and reinforced wall.

[0048] Within the rectangular leaching unit, grout is sprayed onto the sidewalls of the tunnel. Its main function is to form a low-permeability anti-seepage wall, and its secondary function is to reinforce the tunnel. The anti-seepage wall, together with the overlying aquitard 3 and the underlying aquitard 4 of the uranium ore, forms the seepage boundary of the leaching unit, thereby intercepting most of the leaching liquid in the rock mass of the leaching unit. This facilitates its convergence and outflow from the dual-purpose "low-level grouting-extraction" borehole, creating the external boundary conditions for the formation of a local flow field.

[0049] Along the base of the anti-seepage wall in the tunnel, a covered culvert 12 is excavated to collect the leaching liquid leaking from the anti-seepage wall, thereby controlling environmental pollution and recovering minerals.

[0050] (4) Construction of local uranium ore leaching extraction system.

[0051] For sandstone uranium orebody 1 affected by mining-induced fractures, a high-level short borehole is drilled in the vertical tunnel 9 as an injection port. This increases the flexibility of constructing the local seepage field during in-situ leaching and allows for the addition of additional boreholes based on the leaching effect to locally modify fractures or avoid the influence of faults. In the top region of sandstone uranium orebody 1, a high-level injection port 13 is drilled; the high-level injection port 13 is located between the low-level grouting-extraction dual-purpose borehole 10, and is parallel to the low-level grouting-extraction dual-purpose borehole 10. The low-level grouting-extraction dual-purpose borehole 10 is enlarged to expose the rock matrix on its inner wall, serving as an extraction port.

[0052] Within the in-situ leaching unit, the anti-seepage reinforcement wall seals the seepage boundary, and the fissure grouting and seepage reduction operation eliminates the influence of the dominant seepage channels formed by the original high-permeability fissures on the migration of the in-situ leaching solution. Through the injection of solution through the high-level injection hole 13 and the extraction of solution through the low-level grouting-extraction dual-purpose borehole 10, a local seepage field is formed from the injection hole to the low-level grouting-extraction dual-purpose borehole; based on the seepage field, in-situ leaching is carried out on the sandstone uranium ore body 1 covered by it.

[0053] If a leak occurs in the extraction hole during leaching, causing leakage of the leaching solution, it is only necessary to perform fissure grouting to reduce permeability, and then enlarge the hole to expose the rock matrix before continuing leaching. Valves, pressure sensors, and flow sensors are installed in the injection and extraction holes to facilitate pore pressure monitoring, flow rate monitoring, extraction control, and injection control.

[0054] (5) The infiltration treatment is divided into 4 stages.

[0055] First stage: Close the extraction hole and pump the leaching solution into the injection hole at pressure p1;

[0056] Second stage: When the pressure in the extraction hole gradually increases to p1, the injection hole is closed, and the pressure in the extraction hole is maintained at p1 to block the hole; the purpose of blocking the hole is to allow the leaching liquid with pressure p1 to fully enter all areas of the rock mass within the leaching unit.

[0057] In the third stage, the valve of the extraction hole is opened to release the pore pressure in the rock mass. The pore pressure difference drives the pore water to converge into the low-level grouting-extraction dual-purpose borehole 10, thereby allowing the uranium-containing leachate in the rock mass of the in-situ leaching unit to seep out. This operation is to eliminate the leaching dead zones in the rock mass, and this operation can be performed multiple times.

[0058] In the fourth stage, leaching is carried out by injecting leaching solution through the injection holes and extracting it through the extraction holes. During the fourth stage of leaching, the hole-sealing operation of the third stage can be repeated multiple times to maximize the release of uranium-bearing minerals. Generally, the injection pressure in leaching is greater than the extraction pressure to facilitate the seepage of the leaching solution from the injection holes to the extraction holes.

[0059] (6) Leachate treatment.

[0060] Natural uranium can be obtained by directly installing a leachate adsorption tower in the tunnel. Alternatively, the leachate can be transported to the surface via the tunnel for hydrometallurgical treatment and then returned underground. The wastewater from hydrometallurgical treatment can be mixed with a leaching agent to form a leaching solution for recycling, thus requiring less water to maintain the leaching process of one leaching unit. The water used in this leaching unit can also be recycled to other leaching units.

[0061] (7) Ventilation.

[0062] One tunnel uses forced ventilation. Two tunnels use either exhaust or forced ventilation.

[0063] (8) Roadway treatment.

[0064] After in-situ leaching is completed, carbon dioxide is injected into the reservoir for geological sequestration. In cases where the goaf below contains uranium and the working face has been sealed, this tunnel can also be used to drill down to the lower coal seam 2 for leaching uranium ore from coal seam 2, directly treating the entire large goaf as a unit to complete the in-situ leaching cycle.

[0065] Example 2: Mining of overlying uranium deposits affected by coal seam drainage operations;

[0066] In a certain area of ​​Ordos, the Jurassic Yan'an Formation and Zhiluo Formation contain coal and uranium deposits, respectively. Coal seam 2 is 7m thick, and sandstone uranium ore body 1 is 7m thick. In this example, sandstone uranium ore body 1 is relatively close to the coal mine shaft, while the coal mine goaf is far from the uranium deposit. The fractures formed by coal mining disturbance have not developed to the uranium ore layer. However, the drainage operations at the distant coal mining face have drained the pore water from the strata hosting sandstone uranium ore body 1, making it impossible to mine the uranium using traditional methods. This situation belongs to a drained uranium deposit overlying coal seam 2, affected by coal mining drainage operations.

[0067] Unlike Embodiment 1, in this embodiment, a coal mine shaft can be directly used as the shaft to be excavated in the invention. The shaft can be used to directly reach the sandstone uranium ore body 1, and a horizontal tunnel can be excavated along the bottom of the sandstone uranium ore body 1 to the area of ​​sandstone uranium ore body 1. The tunnel can be used to delineate the mining area of ​​sandstone uranium ore body 1.

[0068] Unlike Example 1, in this example, since the sandstone uranium ore body 1 is less affected by mining-induced fractures 5 and the rock mass is relatively intact, the high-level injection hole 13 can be either the scheme in Example 1 or a longer hole perpendicular to the low-level grouting-extraction dual-purpose drill hole 10, thereby saving drilling costs; by using the hole-blocking operation, the purpose of fully leaching the uranium-bearing minerals in the in-situ leaching unit can be achieved.

[0069] Unlike Example 1, in this example, the sandstone uranium ore body 1 is thicker; the tunnel height cannot reach the overlying aquitard 3 of the uranium ore; based on the anti-seepage reinforcement wall in Example 1, a fracture surface along the axial direction of the tunnel 9 is formed in the sandstone layer of the tunnel roof through directional fracturing, and grout is injected into the fracture surface to form a roof anti-seepage isolation wall 14, thereby achieving the purpose of isolating the leaching liquid in the leaching unit. Specifically, firstly, directional fracturing boreholes 15 are drilled in the sandstone layer of the roof of the horizontal tunnel 9 around the leaching unit to the interface between the overlying aquitard 3 of the uranium ore and the sandstone uranium ore body 1. The directional fracturing boreholes 15 are arranged along the long axis of the horizontal tunnel 9 to delineate the uranium ore body in the leaching unit; then, the fracture surface is formed by directional fracturing to connect the directional fracturing boreholes 15 around the leaching unit. Specifically, the permeability of the solidified grouting material is lower than that of sandstone, such as existing low-permeability cement grout. Specifically, mature directional hydraulic fracturing technology, directional blasting, directional splitting, and other technologies can be used for directional fracturing. The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for mining uranium deposits in overlying, dehydrated sandstone in coal mines, characterized in that, Includes the following steps: Step 1: Obtain the specific spatial location of the sandstone uranium ore body (1), the stress field parameters of the maximum principal stress direction in the sandstone uranium ore occurrence area, and hydrogeological parameters such as the permeability of the sandstone matrix through geological surveys and other means; Step 2: Excavate the shaft (8) from the ground to the sandstone uranium ore body (1) stratum, excavate the horizontal tunnel (9) below the sandstone uranium ore body (1), delineate the entire sandstone uranium ore body (1) occurrence area through the horizontal tunnel (9), and determine the uranium mining area; Step 3: In the delineated mining area, continue to excavate through the horizontal tunnel (9) to divide the sandstone uranium ore body into multiple leaching units, each leaching unit corresponding to the sandstone uranium ore body (1) above the leaching unit; Step 4: In a pair of long-side horizontal tunnels (9) in the immersion unit, drill continuous low-level grouting-extraction dual-purpose boreholes (10) on the sidewall of the horizontal tunnel (9). Grouting is then carried out through the low-level grouting-extraction dual-purpose boreholes (10), and the grout enters the mining-induced fracture (5), reducing the permeability of the mining-induced fracture in the immersion unit to below the permeability of the sandstone matrix, and transforming the high-permeability mining-induced fracture into a low-permeability fracture. Step 5: Shotcrete is sprayed onto the sidewalls, roof, and floor of the horizontal tunnel (9) of the ground immersion unit to form an anti-seepage reinforcement wall and establish a low-permeability boundary for the ground immersion unit; Step 6: Drill a high-level injection hole (13) above the sandstone uranium ore body (1) corresponding to the leaching unit, and enlarge the low-level grouting-extraction dual-purpose borehole (10) so that the inner wall of the hole exposes the rock matrix as an extraction hole; Step 7: In the leaching unit, by injecting liquid from the high-level injection hole (13) and extracting liquid from the low-level grouting-extraction dual-purpose borehole (10), a local seepage field is formed between the high-level injection hole (13) and the low-level grouting-extraction dual-purpose borehole (10). Based on the local flow field, the sandstone uranium ore body (1) in the leaching unit is subjected to leaching treatment to obtain uranium-bearing minerals.

2. The method for mining uranium deposits in overlying sandstone as described in claim 1, characterized in that: In step three, when dividing the leaching unit, the primary consideration is to arrange the length of the leaching unit along the dip of the bottom of the rock stratum so that gravity becomes one of the driving forces for pore water seepage. The secondary consideration is to extend the tunnel (9) along the direction of the maximum principal stress so as to facilitate the maintenance of the stability of the tunnel (9) structure.

3. The method for mining uranium deposits in overlying sandstone as described in claim 1, characterized in that: In step four, in the continuous low-level grouting-extraction dual-purpose boreholes (10), the first and last two low-level grouting-extraction dual-purpose boreholes (10) are close to the sidewalls of a pair of short-side horizontal tunnels (9) in the ground immersion unit.

4. The mining method for uranium deposits in overlying sandstone as described in claim 1, characterized in that: In step four, the particle size of the grouting material should be close to 1 / 10 to 1 / 15 of the average particle size of the uranium-bearing sandstone; the permeability of the grout after solidification should be less than or equal to the permeability of the uranium-bearing sandstone.

5. The method for mining uranium deposits in overlying sandstone as described in claim 1, characterized in that: In step four, multiple low-pressure grouting can be used, that is, the next grouting is carried out after the previous grout has initially set, until no more grout can be injected into the borehole.

6. The method for mining uranium deposits in overlying sandstone as described in claim 1, characterized in that: At the bottom of the anti-seepage reinforcement wall on the side of the horizontal lane (9), a covered culvert (12) is dug to collect the leaching liquid leaking from the anti-seepage reinforcement wall.

7. The method for mining uranium deposits in overlying sandstone as described in claim 1, characterized in that: In step six, if the sandstone uranium ore body (1) is a coal seam overlying drainage type uranium ore affected by vertically developed fractures, then the high-level injection holes (13) are multiple and parallel to the low-level grouting-drainage dual-purpose boreholes (10). If the sandstone uranium ore body (1) is a coal seam overlying drainage type uranium ore affected by coal mining drainage operations, then the high-level injection holes (13) can be either multiple boreholes parallel to the low-level grouting-drainage dual-purpose boreholes (10) or a single borehole perpendicular to the low-level grouting-drainage dual-purpose boreholes (10).

8. The method for mining uranium deposits in overlying sandstone as described in claim 1, characterized in that: In step six, the inundation treatment stage is divided into four phases; First stage: Close the low-level grouting-extraction dual-purpose borehole (10) and pump the leaching solution into the high-level injection hole (13) with pressure p1; Second stage: When the pressure of the low-level grouting-extraction dual-purpose borehole (10) gradually increases to p1, close the low-level grouting-extraction dual-purpose borehole (10), maintain the pressure of the high-level injection hole (13) at p1, and block the hole. In the third stage, the valve of the low-level grouting-extraction dual-purpose borehole (10) is opened to release the pore pressure in the rock mass. The pore water is collected in the low-level grouting-extraction dual-purpose borehole (10) through the pore pressure difference, thereby allowing the uranium-containing leachate in the rock mass of the in-situ leaching unit to seep out. In the fourth stage, liquid is injected from the high-level injection hole (13) and liquid is extracted from the low-level grouting-extraction dual-purpose borehole (10) to carry out in-situ leaching; during the in-situ leaching process in the fourth stage, the hole-clogging operation of the third stage can be repeated multiple times to release the uranium-containing minerals to the maximum extent.

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