Method for sealing phosphogypsum by using underground goaf

Abstract

The invention discloses a method for sealing phosphogypsum by using an underground goaf. The method comprises the following steps: S1, forming an outermost anti-seepage flexible support layer through a hollow grouting anchor rod, a grouting body and roadway surrounding rock; s2, a hanging net is woven and hooked on the hollow grouting anchor rod, slurry is sprayed for reinforcement, and a concrete guniting layer is formed; s3, an anti-seepage geomembrane is laid, and an inner anti-seepage membrane flexible layer is formed; s4, after phosphogypsum slurry is pumped and injected into the goaf, a grouting inlet is sealed; and S5, pouring concrete partition wall plugging. By reasonably utilizing the characteristics of the goaf and the ardealite, two major hazard factors are organically combined together to form alternate resources for use, large-capacity safe storage of the ardealite can be realized, the risks of occupying a large amount of land and polluting surface soil water are avoided, the resource utilization of the goaf is realized, and the resource utilization rate of the goaf is increased. And a good recovery condition is created for phosphogypsum resource utilization in the future.

Description

Technical Field

[0001] The present application relates to the technical field of phosphogypsum sealing, and in particular to a method for sealing phosphogypsum in underground goafs. Background Art

[0002] Phosphogypsum is mainly derived from industrial solid waste generated by the wet phosphoric acid process, and its main component is calcium sulfate dihydrate (CaSO 4 ·2H 2 O), and also contains a small amount of impurities such as phosphorus, fluorine, organic matter, oxides, and a small amount of heavy metals and radioactive substances, which have a great impact on the environment. my country's phosphogypsum shows a series of characteristics such as large production and discharge, large stockpile base and low resource utilization rate. Although the utilization rate of phosphogypsum is gradually increasing, the consumption is limited, and at this stage it is still mainly stored. Large-scale storage not only occupies land resources, but also the harmful substances and corrosive elements in phosphogypsum bring great safety hazards to the surrounding environment. Therefore, the treatment and recycling of phosphogypsum has become an urgent issue.

[0003] Among the traditional phosphogypsum treatment measures, the most common practice is to use phosphogypsum as a filling material to fill the goaf. For example, the Chinese patent with publication number CN115638019A discloses a full solid waste filling system and method under alkaline washing phosphogypsum pretreatment. The phosphogypsum alkaline washing pretreatment system of the first belt conveyor, NaOH solution storage barrel, sand washing and dehydration integrated machine, clean water pump and buffer tank realizes the preliminary defluorination of high-fluorine phosphogypsum and the separation of defluorinated phosphogypsum and fluorine-containing alkaline wastewater; the alkaline wastewater defluorination system with PAC as the main body absorbs the fluorine element in the alkaline wastewater through flocculation; the blast furnace slag with potential volcanic ash activity is stimulated by alkaline wastewater as a cementing material, thereby realizing the preparation of phosphogypsum cemented filling body. Although this method can reduce the risk of leaching of fluorine elements in the filling body, it cannot completely remove phosphorus and fluorine impurities in phosphogypsum, and there is a problem of groundwater pollution, which increases the ecological restoration cost of mine production.

[0004] In the prior art, the more common treatment measures are solid waste resource utilization and preparation of phosphogypsum byproducts. For example, a Chinese patent with publication number CN112832424A discloses a gypsum-concrete mixed energy-saving building structure, including a concrete wall and a gypsum wall, the gypsum wall is located inside the concrete wall, and the gypsum wall uses chemical byproducts phosphogypsum and fluorgypsum as raw materials, which can not only reduce the manufacturing cost of the building structure, but also reasonably utilize and consume part of the phosphogypsum to achieve solid waste resource utilization. However, this method ignores the impact of radioactive substances in phosphogypsum on human comfort, and cannot achieve large-scale processing of phosphogypsum. There are problems such as low comprehensive utilization rate and low added value, and it cannot solve the problem of large-scale storage of phosphogypsum.

[0005] At present, it is necessary to improve the treatment process of phosphogypsum, so a feasible solution for harmless treatment of phosphogypsum is proposed. For example, the Chinese patent with publication number CN111498940A discloses a separation and treatment method for phosphorus-containing and fluorine-containing water washing wastewater to solve the problem of harmless treatment of phosphogypsum. The patent obtains an adsorption material by calcining the precipitated impurities produced after pH adjustment of the phosphogypsum washing liquid, and uses it to separate phosphorus and fluorine in the new phosphogypsum washing liquid. The removal rate of fluorine is 89-94%, and the removal rate of phosphorus is 4-6%. However, the washing liquid treated by this method still contains a certain amount of phosphorus and fluorine impurities, and the recovery of phosphorus and fluorine is not thorough. In addition, the adsorption material needs to be calcined, which has the problems of energy waste and air pollution.

[0006] In summary, the existing technology cannot solve the significant land occupation problem of phosphogypsum storage, cannot process phosphogypsum on a large scale, and cannot avoid the pollution risk of phosphogypsum to soil and water bodies. In view of this, it is necessary to provide a method for sealing phosphogypsum in underground goaf to solve the above problems. Summary of the invention

[0007] In response to at least one technical problem existing in the prior art, the present application provides a method for sealing phosphogypsum in underground goafs. By setting up three layers of anti-seepage flexible protective walls, the anti-seepage capacity of the tunnel surrounding rock is greatly improved, while the stability and bearing capacity of the tunnel surrounding rock are enhanced, so that the underground goafs can fully meet the demand for large-capacity storage of phosphogypsum, and effectively avoid the risk of soil and water pollution caused by sealed phosphogypsum. In addition, the phosphogypsum sealed in this application can be subsequently repeatedly mined and utilized, which is conducive to achieving sustainable development.

[0008] The present application provides a method for sealing phosphogypsum in an underground goaf, comprising the following steps:

[0009] S1. Enter the goaf where mining is completed from the return air filling connecting tunnel, drive diamond-shaped hollow grouting anchor rods into the tunnel surrounding rock, and then inject grout into the hollow grouting anchor rods. Through the hollow grouting anchor rods, a high-impermeability and high-strength grouting liquid made of alum stone cement, modifier and water is used to seal the rock stratum joints and cracks and the tunnel surrounding rock to form the outermost anti-seepage flexible support layer;

[0010] S2, weaving a hanging net, hooking it on the hollow grouting anchor rods of the top column and the intermediate column, and not hooking the hanging net on the hollow grouting anchor rod of the bottom column, and then setting up a formwork, and finally spraying slurry between the tunnel surrounding rock and the formwork for reinforcement to form a concrete spraying layer, which constitutes an intermediate anti-seepage flexible supporting layer; the slurry is mixed by the following raw materials by mass at room temperature: 10 parts of anti-seepage cement, 18-22 parts of melon stone, 15-25 parts of mixed sand and 6-8 parts of water, and the mixed sand is composed of phosphogypsum and machine-made sand;

[0011] S3. After removing the formwork, an anti-seepage geomembrane is laid outside the concrete shotcrete layer, and the anti-seepage geomembrane is compacted and attached to the wall to form an inner anti-seepage membrane flexible layer;

[0012] S4. Concrete partition walls are poured at the exit of the goaf to seal it, slurry pipelines are laid in the return air filling connection tunnel, and seepage liquid pressure reducing valves and seepage liquid pipelines are pre-buried in the mine transport tunnel. Then, phosphogypsum, anti-seepage cement and water with a mass ratio of (16-20):1:(0.4-0.6) are mixed evenly at room temperature to form phosphogypsum slurry. The phosphogypsum slurry is pumped into the goaf through the slurry pipeline. Finally, the grouting inlet is sealed to achieve phosphogypsum sealing. The initial leachate is transported from the pressure reducing valve to the underground anti-seepage bin for storing the filtrate through the seepage liquid pipeline;

[0013] S5. After the sealing operation of phosphogypsum is completed, an impermeable geomembrane is laid on the top of the phosphogypsum sealing area to separate the area where the phosphogypsum has been sealed from the mining area. A reinforced concrete base plate with a thickness of 0.15 to 0.2 m is laid outside the impermeable geomembrane, and a concrete partition wall is poured to seal it.

[0014] Optionally, in step S1, the hollow grouting anchor rod is an anchor rod with a diameter of 18 mm and a length of 2000 to 2500 mm, and its end extends 700 mm, and the row spacing of the hollow grouting anchor rod is 500 mm.

[0015] Optionally, in steps S2 and S4, the anti-seepage cement uses sulphoaluminate cement with a strength grade of 42.5, and the water content of the phosphogypsum is 20%.

[0016] Optionally, in step S2, the mass ratio of the phosphogypsum to the machine-made sand is (0.4-0.6):1.

[0017] Optionally, in step S2, the average particle size of the phosphogypsum is controlled to be below 0.1 mm, the average particle size of the machine-made sand is controlled to be below 2 mm, and the average particle size of the guami stone is controlled to be below 15 mm.

[0018] Further optionally, in step S2, the spraying thickness of the slurry is 500-600 mm.

[0019] Further optionally, in step S2, the hanging mesh adopts a φ6mm threaded steel mesh with a grid size of 10cm×10cm; the spraying process between the top column and the intermediate column and the formwork is divided into two times: first, 350mm thick slurry is sprayed between the top column and the intermediate column and the hanging mesh, and when the slurry solidifies to no longer fall off, 250mm thick slurry is continued to be sprayed between the hanging mesh and the formwork, and the two sprayings form a concrete spraying layer.

[0020] Optionally, in step S3, the anti-seepage geomembrane passes through the pre-buried hollow grouting anchor rod, and the anti-seepage geomembrane is compacted against the wall by using the thread at the end of the hollow grouting anchor rod, in combination with a gasket and a locking nut to form an anti-seepage membrane layer.

[0021] Optionally, the method further includes step S6: when phosphogypsum can be used as a resource, the lower opening of the goaf is opened, and the shovel loader directly digs the phosphogypsum, loads the phosphogypsum into a mine car and transports it to the surface to realize the recovery and reuse of the phosphogypsum, and finally the goaf is inspected and repaired.

[0022] In summary, the present application includes at least one of the following beneficial technical effects:

[0023] 1. Compared with the traditional method of treating phosphogypsum, this application provides a completely different new idea, that is, using underground goafs to seal phosphogypsum, effectively improving the utilization rate of underground abandoned space. Based on the differences in the distribution of underground abandoned space, the inventors fully considered the stability of the surrounding rock and the safety of utilization, and flexibly utilized the goafs of abandoned mines and various abandoned caverns and other underground abandoned spaces, greatly improving the utilization rate of underground abandoned space and maximizing the available space volume in abandoned tunnel space.

[0024] 2. The phosphogypsum sealed in this application can be subsequently mined and reused, and is convenient for later maintenance, which is conducive to achieving sustainable development. The traditional way of utilizing abandoned tunnels is mainly filling. Although this method is simple and effective, and can effectively prevent accidents such as ground subsidence and collapse, filling utilization is a one-time utilization method. After filling, the mine space is occupied by solid fillings and cannot be used later, which will directly cause the abandonment and waste of underground mine space.

[0025] 3. This application not only ensures the waterproofing and strength of the flexible protective wall, but also improves the safety of the construction workers. A number of hollow grouting anchor rods are anchored into the deep layer of the tunnel surrounding rock, and the hanging net is fixed on the surface of the tunnel surrounding rock to achieve flexible contact with the tunnel surrounding rock in the underground. The hollow grouting anchor rods anchored into the deep layer of the tunnel surrounding rock are used to resist the repeated deformation of the rock mass. The hollow grouting anchor rods and the hanging net are combined to form a relatively long whole. There is a certain bending deformation buffer range in the direction of deviation from the axis of the hollow grouting anchor rod, and it is not easy to break. At the same time, the anchor net can be connected and fixed on the surface of the tunnel surrounding rock, and a concrete spraying layer is set for reinforcement to form a bottom support effect for the flexible support system, which is used to prevent the top of the tunnel from collapsing and the gravel falling from the slab, ensuring the stability and safety of the surrounding rock during construction. Subsequently, not only can the abandoned tunnel space be used to seal phosphogypsum, but the tunnel space can also be supported, ensuring the stable support of the tunnel surrounding rock and effectively improving the safety of the abandoned mine tunnel.

[0026] 4. The construction process of this application is simple, the construction technology is not difficult, and it is convenient for personnel to construct. By optimizing the design of the construction method of the sealed phosphogypsum anti-seepage structure, it is convenient for operators to carry out construction operations on karst strata, that is, firstly, the outermost flexible support is formed by the combination of hollow grouting anchor rods, grouting bodies and surrounding rocks, and then the concrete reinforcement is formed by spraying concrete made of anti-seepage cement, melon stone, mixed sand and water in a specific ratio to form a concrete spraying layer, and finally the anti-seepage geomembrane is compacted and attached to the wall to form an anti-seepage membrane layer, thereby setting up a three-layer anti-seepage flexible protective wall for anti-seepage treatment, which is convenient for operators to carry out construction in the goaf.

[0027] 5. The overall cost of this application is low, the scope of application is wide, it has huge economic benefits and good promotion value, and it can be applied to various types of underground abandoned spaces, greatly improving the utilization of underground space. The underground goaf selected in this application itself has the characteristics of good deformation resistance and high strength, and does not require large-scale reinforcement of the original abandoned goaf and its tunnels, thereby greatly reducing the cost of engineering reconstruction. In addition, this application effectively avoids the risk of leaching of harmful elements in sealed phosphogypsum by setting up a three-layer anti-seepage flexible protective wall, thereby solving the problem of groundwater pollution and reducing the ecological restoration cost of mine production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The schematic diagram of the construction of the test ore body for this application;

[0029] Figure 2 for Figure 1 Middle AA section;

[0030] Figure 3 for Figure 2 Schematic diagram of the enlarged structure at D in the middle;

[0031] Figure 4 for Figure 2 Schematic diagram of the enlarged structure at E in the middle;

[0032] Figure 5 This is a schematic diagram of the structure of the hollow grouting anchor described in this application.

[0033] In the figure: 1. Hollow grouting anchor rod, 2. Tunnel surrounding rock, 3. Concrete shotcrete layer, 4. Hanging net, 5. Anti-seepage geomembrane, 6. Gasket, 7. Lock nut, 8. Thread. DETAILED DESCRIPTION

[0034] The present application is further described in detail below with reference to the accompanying drawings and embodiments.

[0035] Unless otherwise specified, the raw materials used in the specific implementation of this application are conventional raw materials in this technical field, and can all be purchased on the market. Among them, the anti-seepage cement uses sulphoaluminate cement with a strength grade of 42.5, purchased from Foshan Xinqi Tuoda New Materials Group Co., Ltd.; M32.5 masonry cement, purchased from Hubei Daye Jianfeng Cement Co., Ltd.; water, taken from underground water in the well; melon stone, derived from limestone near the Jinshandian Iron Mine, crushed by a jaw crusher; machine-made sand, is the sand actually used by Wuhan Iron and Steel Resources Group Jinshandian Mining Co., Ltd.; phosphogypsum, taken from the phosphogypsum yard near the mining area, with a moisture content of 20%. In the following test methods and detection methods, unless otherwise specified, they are all conventional methods, and the instruments and instruments used in the test can be obtained through commercial channels. The parts not elaborated in detail in this specification belong to the prior art.

[0036] like Figure 1 to Figure 5 As shown, the present application designs a method for sealing phosphogypsum in underground goaf, comprising the following steps:

[0037] S1, entering the goaf where mining is completed from the return air filling connecting tunnel, driving the hollow grouting anchor rods 1 arranged in a diamond shape into the tunnel surrounding rock 2, and then injecting grout into the hollow grouting anchor rods 1, through the hollow grouting anchor rods 1, a high-impermeability and high-strength grouting liquid made of alum stone cement, modifier and water is mixed to seal the rock stratum joints and fissures and the tunnel surrounding rock 2 to form the outermost anti-seepage flexible support layer;

[0038] S2, weaving a hanging net 4, hooking on the hollow grouting anchor rods 1 of the top column and the intermediate column, and not hooking the hanging net 4 on the hollow grouting anchor rod 1 of the bottom column, and then setting up a template, and finally spraying slurry between the tunnel surrounding rock 2 and the template for reinforcement, forming a concrete spraying layer 3, and constituting an intermediate anti-seepage flexible supporting layer; the slurry is mixed by the following raw materials by mass at room temperature: 10 parts of anti-seepage cement, 18-22 parts of melon stone, 15-25 parts of mixed sand and 6-8 parts of water, and the mixed sand is composed of phosphogypsum and machine-made sand;

[0039] S3, after removing the formwork, laying the anti-seepage geomembrane 5 outside the concrete shotcrete layer 3, and compacting the anti-seepage geomembrane 5 to form an inner anti-seepage membrane flexible layer;

[0040] S4. Concrete partition walls are poured at the exit of the goaf to seal it, slurry pipelines are laid in the return air filling connection tunnel of the upper plate, and seepage liquid pressure reducing valves and seepage liquid pipelines are pre-buried in the mine transport tunnel. Then, phosphogypsum, anti-seepage cement and water with a mass ratio of (16-20):1:(0.4-0.6) are mixed evenly at room temperature to form phosphogypsum slurry. The phosphogypsum slurry is pumped into the goaf through the slurry pipeline. Finally, the grouting inlet is sealed to achieve phosphogypsum sealing. The initial leachate is transported from the pressure reducing valve to the underground anti-seepage bin for storing the filtrate through the seepage liquid pipeline;

[0041] S5. After the sealing operation of phosphogypsum is completed, an impermeable geomembrane 5 is laid on the top of the phosphogypsum sealing area to separate the area where the phosphogypsum has been sealed from the body to be mined. In order to prevent collapsed ore blocks from seeping into the phosphogypsum sealing area, a reinforced concrete base plate with a thickness of 0.15 to 0.2 m is laid outside the impermeable geomembrane 5, and a concrete partition wall is poured to seal it.

[0042] When phosphogypsum can be used as a resource, the lower mouth of the goaf is opened, and the shovel loader directly digs it, loads it into a mine car and transports it to the surface to realize the recovery and reuse of the phosphogypsum. Finally, the goaf is inspected and repaired.

[0043] The following is the preparation example of this application

[0044] Preparation Example 1

[0045] The preparation of the concrete shotcrete layer 3 test block of this preparation example includes the following steps:

[0046] Sa, the following raw materials by mass: 10 parts of anti-seepage cement, 20 parts of melon stone, 20 parts of mixed sand and 7 parts of water, are mixed evenly at room temperature to obtain slurry; wherein the mixed sand is composed of phosphogypsum and machine-made sand in a mass ratio of 4:1;

[0047] Sb. Set up a template and spray the slurry obtained in step Sa to obtain a cubic specimen with a side length of 150 mm.

[0048] In this preparation example, the average particle size of the phosphogypsum is controlled at 0.5 mm, the average particle size of the machine-made sand is controlled at 3 mm, and the average particle size of the guami stone is controlled at 20 mm.

[0049] Preparation Example 2

[0050] The preparation of the concrete shotcrete layer 3 test block of this preparation example includes the following steps:

[0051] Sa, the following raw materials by mass: 10 parts of anti-seepage cement, 20 parts of melon stone, 20 parts of mixed sand and 7 parts of water, are mixed evenly at room temperature to obtain slurry; wherein the mixed sand is composed of phosphogypsum and machine-made sand in a mass ratio of 0.1:1;

[0052] Sb. Set up a template and spray the slurry obtained in step Sa to obtain a cubic specimen with a side length of 150 mm.

[0053] In this preparation example, the average particle size of the phosphogypsum is controlled at 0.5 mm, the average particle size of the machine-made sand is controlled at 3 mm, and the average particle size of the guami stone is controlled at 20 mm.

[0054] Preparation Example 3

[0055] The preparation of the concrete shotcrete layer 3 test block of this preparation example includes the following steps:

[0056] Sa, the following raw materials by mass: 10 parts of anti-seepage cement, 20 parts of melon stone, 20 parts of mixed sand and 7 parts of water, are mixed evenly at room temperature to obtain slurry; wherein the mixed sand is composed of phosphogypsum and machine-made sand in a mass ratio of 4:1;

[0057] Sb. Set up a template and spray the slurry obtained in step Sa to obtain a cubic specimen with a side length of 150 mm.

[0058] In this preparation example, the average particle size of the phosphogypsum is controlled at 0.1 mm, the average particle size of the machine-made sand is controlled at 1 mm, and the average particle size of the guami stone is controlled at 10 mm.

[0059] Preparation Example 4

[0060] The preparation of the concrete shotcrete layer 3 test block of this preparation example includes the following steps:

[0061] Sa, the following raw materials by mass: 10 parts of anti-seepage cement, 20 parts of melon stone, 20 parts of mixed sand and 7 parts of water, are mixed evenly at room temperature to obtain slurry; wherein the mixed sand is composed of phosphogypsum and machine-made sand in a mass ratio of 0.8:1;

[0062] Sb. Set up a template and spray the slurry obtained in step Sa to obtain a cubic specimen with a side length of 150 mm.

[0063] In this preparation example, the average particle size of the phosphogypsum is controlled at 0.1 mm, the average particle size of the machine-made sand is controlled at 1 mm, and the average particle size of the guami stone is controlled at 10 mm.

[0064] Preparation Example 5

[0065] The preparation of the concrete shotcrete layer 3 test block of this preparation example includes the following steps:

[0066] Sa, the following raw materials by mass: 10 parts of anti-seepage cement, 20 parts of melon stone, 20 parts of mixed sand and 7 parts of water, are mixed evenly at room temperature to obtain slurry; wherein the mixed sand is composed of phosphogypsum and machine-made sand in a mass ratio of 0.5:1;

[0067] Sb. Set up a template and spray the slurry obtained in step Sa to obtain a cubic specimen with a side length of 150 mm.

[0068] In this preparation example, the average particle size of the phosphogypsum is controlled at 0.1 mm, the average particle size of the machine-made sand is controlled at 1 mm, and the average particle size of the guami stone is controlled at 10 mm.

[0069] Preparation Example 6

[0070] The preparation of the concrete shotcrete layer 3 test block of this preparation example includes the following steps:

[0071] Sa, the following raw materials by mass: 10 parts of anti-seepage cement, 20 parts of melon stone, 20 parts of mixed sand and 7 parts of water, are mixed evenly at room temperature to obtain slurry; wherein the mixed sand is composed of phosphogypsum and machine-made sand in a mass ratio of 0.5:1;

[0072] Sb. Set up the template and the hanging net 4. First, spray the slurry obtained in step Sa with a thickness of 85 mm between the hanging net 4 and the template on one side. When the slurry solidifies and does not fall off, continue to spray the slurry obtained in step Sa with a thickness of 65 mm between the hanging net 4 and the template on the other side. The two sprayings form a cubic specimen with a side length of 150 mm.

[0073] In this preparation example, the average particle size of the phosphogypsum is controlled at 0.1 mm, the average particle size of the machine-made sand is controlled at 1 mm, and the average particle size of the guami stone is controlled at 10 mm. The hanging mesh 4 adopts a φ6 mm threaded steel mesh with a mesh size of 10 cm×10 cm.

[0074] Comparative Example 1

[0075] The preparation of the concrete shotcrete layer 3 test block of this comparative example includes the following steps:

[0076] Sa, the following raw materials by mass: 10 parts of anti-seepage cement, 16 parts of melon stone, 26 parts of mixed sand and 7 parts of water are mixed evenly at room temperature to obtain slurry; wherein the mixed sand is composed of phosphogypsum and machine-made sand in a mass ratio of 4:1;

[0077] Sb. Set up a template and spray the slurry obtained in step Sa to obtain a cubic specimen with a side length of 150 mm.

[0078] In this comparative example, the average particle size of the phosphogypsum is controlled at 0.5 mm, the average particle size of the machine-made sand is controlled at 3 mm, and the average particle size of the guami stone is controlled at 20 mm.

[0079] Comparative Example 2

[0080] The preparation of the concrete shotcrete layer 3 test block of this comparative example includes the following steps:

[0081] Sa, the following raw materials by mass: 10 parts of anti-seepage cement, 24 parts of melon stone, 12 parts of mixed sand and 7 parts of water, are mixed evenly at room temperature to obtain slurry; wherein the mixed sand is composed of phosphogypsum and machine-made sand in a mass ratio of 4:1;

[0082] Sb. Set up a template and spray the slurry obtained in step Sa to obtain a cubic specimen with a side length of 150 mm.

[0083] In this comparative example, the average particle size of the phosphogypsum is controlled at 0.5 mm, the average particle size of the machine-made sand is controlled at 3 mm, and the average particle size of the guami stone is controlled at 20 mm.

[0084] The compressive strength of the concrete sprayed layer 3 test blocks (cube test pieces) prepared in Preparation Examples 1 to 6 and Comparative Examples 1 to 2 was tested, and the results are shown in Table 1. Note: The strength grade of sprayed concrete is determined according to the standard value of cube compressive strength, and the evaluation of the compressive strength of sprayed concrete is carried out according to the current national standard "Concrete Strength Test and Evaluation Standard" GB / T50107.

[0085] Table 1 Test results of preparation examples 1 to 6 and comparative examples 1 to 2

[0086] 28d compressive strength of cubic specimen / MPa specification Preparation Example 1 15.64 C15 Preparation Example 2 16.78 C15 Preparation Example 3 19.12 C15 Preparation Example 4 20.10 C20 Preparation Example 5 23.56 C20 Preparation Example 6 27.30 C25 Comparative Example 1 10.21 C10 Comparative Example 2 11.36 C10

[0087] It can be seen from the data in Table 1 that the compressive strength of the concrete spraying layer 3 test block prepared by the present application with a specific ratio of anti-seepage cement, melon stone, phosphogypsum and machine-made sand as raw materials can fully meet the needs, and it has the advantages of low cost and can consume a large amount of phosphogypsum. In addition, it can be seen from the comparison of Preparation Example 3 and Preparation Example 1 that when the particle size of the phosphogypsum is controlled below 0.1mm, the particle size of the machine-made sand is controlled below 2mm, and the particle size of the melon stone is controlled below 15mm, the compressive strength of the test block can be further improved. It can be seen from the comparison of Preparation Example 5 and Preparation Examples 3 to 4 that when the mass ratio of the phosphogypsum and the machine-made sand is (0.4 to 0.6): 1, the compressive strength of the test block can be greatly improved. It can be seen from the comparison of Preparation Example 6 and Preparation Example 5 that after adding a mesh of 10cm×10cm, φ6mm threaded steel bar mesh to the test block, its strength is greatly improved, thereby ensuring that the support system of this application can meet safety requirements.

[0088] The following are application examples of this application

[0089] The ore body used in the application example of this application is the Zhangfushan ore body of Jinshandian Iron Mine of Wuhan Iron and Steel Resources Group Jinshandian Mining Co., Ltd. Figure 1 and Figure 2 As shown, the ore body is first mined using a gently inclined thin ore body mining method, and then the underground goaf is used to seal the phosphogypsum.

[0090] The specific steps of mining are as follows: (1) Mining preparation: Use the full-length wall-type mining face along the inclined length of the ore block to construct a mining preparation tunnel every 42 meters along the strike direction. The lower plate is the ore discharge transportation tunnel, and the upper plate is the return air filling connecting tunnel; (2) Cutting work: In the mining preparation tunnel within the vein, cut uphill every 23 meters along the inclined direction of the ore body, connect the return air filling connecting tunnel with the ore discharge transportation tunnel, and form a 32m long and 20m wide mine room; (3) Mining work: Carry out shallow hole rock drilling and blasting mining in the mine room and reserve 3m wide intermediate pillars and 3m wide top and bottom pillars.

[0091] A method for sealing phosphogypsum in an underground goaf in this application example includes the following steps:

[0092] S1, enter the goaf where the mining is finished from the return air filling connecting tunnel, use a drilling rig to pre-drill a hole in the tunnel surrounding rock 2, insert a φ18mm, 2500mm long hollow grouting anchor rod 1 into the drill hole, use an anchor drill hammer to firmly connect the hollow grouting anchor rod 1 to the tunnel surrounding rock 2, and the end of the hollow grouting anchor rod 1 extends 700mm. In order to improve the strength, the hollow grouting anchor rod 1 is arranged in a diamond shape with a row spacing of 500mm, and then grouting is injected into the pre-buried hollow grouting anchor rod 1. The high-impermeability and high-strength grouting liquid made of alum stone cement, modifier, and water is injected from the middle of the tail of the hollow grouting anchor rod 1 to fill the rock stratum cracks in the tunnel surrounding rock 2 and isolate the external leakage of groundwater. The hollow grouting anchor rod 1, the grouting body and the tunnel surrounding rock 2 form the outermost flexible support;

[0093] S2, weave the hanging net 4, hook on the hollow grouting anchor rod 1 of the top column and the intermediate column, and do not hook the hanging net 4 on the hollow grouting anchor rod 1 of the bottom column. The hanging net 4 adopts a φ6mm threaded steel mesh with a mesh of 10cm×10cm. Then set up the formwork, and finally spray 350mm thick grout between the top column and the intermediate column and the hanging net 4. When the grout solidifies and does not fall off, continue to spray 250mm thick grout between the hanging net 4 and the formwork. The two sprayings form a concrete spraying layer 3, and the bottom column and the formwork are directly sprayed once. Spraying a 600 mm thick slurry for reinforcement to form a concrete spraying layer 3 to enhance the stability and bearing capacity of the tunnel surrounding rock 2; the slurry is formed by mixing the following raw materials by mass at room temperature: 10 parts of anti-seepage cement, 20 parts of melon stone, 20 parts of mixed sand and 7 parts of water, the mixed sand is composed of phosphogypsum and machine-made sand in a mass ratio of 0.5:1, the average particle size of the phosphogypsum is controlled at 0.1 mm, the average particle size of the machine-made sand is controlled at 1 mm, and the average particle size of the melon stone is controlled at 10 mm;

[0094] S3, after removing the formwork, laying an anti-seepage geomembrane 5 outside the concrete shotcrete layer 3, the anti-seepage geomembrane 5 passes through the pre-buried hollow grouting anchor rod 1, and using the thread 8 at the end of the hollow grouting anchor rod 1, the anti-seepage geomembrane 5 is compacted against the wall in cooperation with the gasket 6 and the locking nut 7 to form an anti-seepage membrane layer;

[0095] S4. Concrete partition walls are poured at the bottom of the cut-up hill in the goaf of the mine room to seal it. The concrete for pouring the sealing wall is made of M32.5 masonry cement and water mixed in a mass ratio of 1:0.5. A slurry pipeline is laid in the return air filling connection tunnel of the upper plate, and a pressure reducing valve and a seepage pipeline are buried in the mine transportation tunnel of the lower plate. Then, phosphogypsum, anti-seepage cement and water in a mass ratio of 18:1:0.5 are mixed evenly at room temperature to form phosphogypsum slurry. The slurry pipeline is erected close to the top beam in the center of the cut-up hill and tilted upward by 5°. The phosphogypsum slurry is pumped into the goaf by the slurry pipeline, and finally the grouting inlet is sealed to achieve phosphogypsum sealing. The initial leachate is transported by the pressure reducing valve through the seepage pipeline to the underground anti-seepage bin for storing the filtrate, and is pumped out of the surface by a pump to a chemical plant for special treatment to achieve phosphogypsum filtrate recovery;

[0096] S5. After the sealing operation of phosphogypsum is completed, an impermeable geomembrane 5 is laid on the top of the phosphogypsum sealing area to separate the area where the phosphogypsum has been sealed from the body to be mined. In order to prevent the collapsed ore blocks from seeping into the phosphogypsum sealing area, a 0.15-0.2m thick reinforced concrete base plate is laid outside the impermeable geomembrane 5, and a concrete partition wall is cast to seal it. The concrete for casting the sealing wall is made of a mixture of M32.5 masonry cement and water with a mass ratio of 1:0.5.

[0097] After the large-volume sealing of phosphogypsum was carried out using the sealing method described in this application example, no accidents such as leaching of harmful elements in the phosphogypsum, ground subsidence and collapse have occurred so far.

[0098] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for sealing phosphogypsum in underground goaf, characterized in that: The following steps are involved: S1, entering the goaf where mining has ended from the return air filling connecting tunnel, driving hollow grouting anchor rods (1) arranged in a diamond shape into the tunnel surrounding rock (2), and then injecting grout into the hollow grouting anchor rods (1), and sealing the rock stratum joints and fissures and the tunnel surrounding rock (2) with a high-impermeability and high-strength grouting liquid made of alum stone cement, a modifier and water through the hollow grouting anchor rods (1) to form the outermost outermost impermeability flexible support layer; S2, weaving a hanging net (4), hooking it on the hollow grouting anchor rods (1) of the top column and the intermediate column, and not hooking the hanging net (4) on the hollow grouting anchor rods (1) of the bottom column, and then setting up a formwork, and finally spraying slurry between the tunnel surrounding rock (2) and the formwork for reinforcement, forming a concrete spraying layer (3), and constituting an intermediate anti-seepage flexible supporting layer; the slurry is formed by mixing the following raw materials by mass at room temperature: 10 parts of anti-seepage cement, 18-22 parts of melon stone, 15-25 parts of mixed sand and 6-8 parts of water, and the mixed sand is composed of phosphogypsum and machine-made sand; S3, after removing the formwork, laying an impermeable geomembrane (5) outside the concrete shotcrete layer (3), and compacting the impermeable geomembrane (5) to adhere to the wall to form an inner impermeable membrane flexible layer; S4. Concrete partition walls are poured at the exit of the goaf to seal it, slurry pipelines are laid in the return air filling connection tunnel, and seepage liquid pressure reducing valves and seepage liquid pipelines are pre-buried in the mine transport tunnel. Then, phosphogypsum, anti-seepage cement and water with a mass ratio of (16-20):1:(0.4-0.6) are mixed evenly at room temperature to form phosphogypsum slurry. The phosphogypsum slurry is pumped into the goaf through the slurry pipeline. Finally, the grouting inlet is sealed to achieve phosphogypsum sealing. The initial leachate is transported from the pressure reducing valve to the underground anti-seepage bin for storing the filtrate through the seepage liquid pipeline; S5. After the sealing operation of the phosphogypsum is completed, an impermeable geomembrane (5) is laid on the top of the phosphogypsum sealing area to separate the area where the phosphogypsum has been sealed from the body to be mined. A reinforced concrete base plate with a thickness of 0.15 to 0.2 m is laid outside the impermeable geomembrane (5), and a concrete partition wall is poured to seal it.

2. A method for sealing phosphogypsum using underground goaf according to claim 1, characterized in that: In step S1, the hollow grouting anchor rod (1) is an anchor rod with a diameter of 18 mm and a length of 2000-2500 mm, and its end extends 700 mm. The row spacing of the hollow grouting anchor rod (1) is 500 mm.

3. A method for sealing phosphogypsum using underground goaf according to claim 1, characterized in that: In steps S2 and S4, the anti-seepage cement adopts sulphoaluminate cement with a strength grade of 42.5, and the water content of the phosphogypsum is 20%.

4. The method for storing phosphogypsum in underground goaf according to claim 1, characterized in that: In step S2, the mass ratio of the phosphogypsum to the machine-made sand is (0.4-0.6):

1.

5. The method for storing phosphogypsum in underground goaf according to claim 1, characterized in that: In step S2, the average particle size of the phosphogypsum is controlled to be less than 0.1 mm, the average particle size of the machine-made sand is controlled to be less than 2 mm, and the average particle size of the guami stone is controlled to be less than 15 mm.

6. A method for sealing phosphogypsum using underground goaf according to claim 2, characterized in that: In step S2, the spraying thickness of the slurry is 500-600 mm.

7. A method for sealing phosphogypsum using underground goaf according to claim 6, characterized in that: In step S2, the mesh (4) is made of a φ6mm threaded steel mesh with a mesh size of 10cm×10cm; the spraying process between the top column and the intermediate column and the formwork is divided into two times: first, 350mm thick slurry is sprayed between the top column and the intermediate column and the mesh (4), and when the slurry solidifies and does not fall off, 250mm thick slurry is sprayed between the mesh (4) and the formwork, and the two sprayings form a concrete spraying layer (3).

8. The method for sealing phosphogypsum in underground goaf according to claim 1, characterized in that: In step S3, the anti-seepage geomembrane (5) passes through the pre-buried hollow grouting anchor rod (1), and the anti-seepage geomembrane (5) is compacted and attached to the wall by using the thread (8) at the end of the hollow grouting anchor rod (1), in combination with the gasket (6) and the locking nut (7) to form an anti-seepage membrane layer.

9. The method for sealing phosphogypsum in underground goaf according to claim 1, characterized in that: The method also includes step S6: when phosphogypsum can be used as a resource, the lower opening of the goaf is opened, and the shovel loader directly digs and loads the phosphogypsum into a mine car and transports it to the surface to realize the recovery and reuse of the phosphogypsum, and finally the goaf is inspected and repaired.

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