A method for sequestration of phosphogypsum using underground mined-out areas

Abstract

The application discloses a method for sealing and storing phosphogypsum by using underground goaf, and comprises the following steps: S1, forming an outermost anti-seepage flexible support layer by a hollow grouting anchor rod, a grouting body and a roadway surrounding rock; S2, weaving a hanging net and hooking the net on the hollow grouting anchor rod, spraying grouting material to reinforce and forming a concrete spraying layer; S3, laying an anti-seepage geomembrane to form an inner anti-seepage membrane flexible layer; S4, after pumping and injecting the phosphogypsum slurry into the goaf, sealing the grouting inlet; and S5, pouring a concrete partition wall to block up. The application combines the two major hazard factors organically by reasonably utilizing the characteristics of the goaf and the phosphogypsum, forms intergrowth resources for use, can realize safe sealing and storage of the phosphogypsum with large capacity, avoids the risk of occupying a large amount of land and polluting the surface soil and water, realizes the resource utilization of the goaf, and creates good stoping conditions for future phosphogypsum resource utilization.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of phosphogypsum storage, and particularly relates to a method for storing phosphogypsum in underground goaf. BACKGROUND

[0002] Phosphogypsum is mainly derived from industrial solid waste generated in the wet-process phosphoric acid process, and its main component is calcium sulfate dihydrate (CaSO4·2H2O), and it also contains a small amount of phosphorus, fluorine, organic matter, oxides, and a small amount of heavy metals and radioactive substances and other impurities, which have a great impact on the environment. In China, 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 the present stage, it is still mainly stored. Large-scale storage not only occupies land resources, but also brings great safety hazards to the surrounding environment due to the harmful substances and corrosive elements in phosphogypsum. Therefore, the treatment and recycling of phosphogypsum has become an urgent problem.

[0003] In the traditional treatment measures of phosphogypsum, the most common method is to use phosphogypsum as a filling material to fill the goaf. For example, a Chinese patent with publication number CN115638019A discloses a full-solid waste filling system and method under the pretreatment of alkali washing phosphogypsum. The phosphogypsum alkali washing pretreatment system including a first belt conveyor, a NaOH solution storage tank, a sand washing and dewatering all-in-one machine, a clean water pump, and a buffer tank realizes the preliminary defluorination of high-fluorine phosphogypsum and the separation of defluorinated phosphogypsum and fluorine-containing alkaline wastewater. An alkaline wastewater defluorination system mainly using PAC as the main body adsorbs fluorine elements in alkaline wastewater through flocculation. High-fluorine blast furnace slag with potential pozzolanic activity is excited by alkaline wastewater to be used as a cementing material, thereby realizing the preparation of phosphogypsum cemented filling body. Although this method can reduce the leaching risk of fluorine elements in the filling body, it cannot completely remove phosphorus and fluorine impurities in phosphogypsum, and there is a problem of polluting groundwater, which increases the ecological restoration cost of mine production.

[0004] In the prior art, the more common treatment measure is solid waste resource utilization to prepare phosphogypsum by-products. For example, a Chinese patent with publication number CN112832424A discloses a gypsum-concrete mixed energy-saving building structure, which includes a concrete wall and a gypsum wall. The gypsum wall is located inside the concrete wall, and the gypsum wall uses chemical by-products phosphogypsum and fluorogypsum as raw materials, which not only reduces the manufacturing cost of the building structure, but also reasonably utilizes and absorbs part of the phosphogypsum, thereby realizing solid waste resource utilization. However, this method ignores the influence of radioactive substances in phosphogypsum on human comfort, and cannot realize large-scale treatment of phosphogypsum, and has problems such as low comprehensive utilization rate and low added value, and cannot solve the problem of large-scale storage of phosphogypsum.

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

[0006] In summary, the prior art cannot solve the problem of significant phosphogypsum storage occupation, neither can it treat phosphogypsum on a large scale nor can it avoid the pollution risk of phosphogypsum to soil and water at the same time. Therefore, it is necessary to provide a method for sealing phosphogypsum in underground goaf to solve the above problems. SUMMARY

[0007] The present application aims to solve at least one technical problem in the prior art, and provides a method for sealing phosphogypsum in underground goaf. By setting three layers of anti-seepage flexible retaining walls, the anti-seepage capacity of the surrounding rock of the roadway is greatly improved, and the stability and bearing capacity of the surrounding rock of the roadway are also strengthened, so that the underground goaf can fully meet the demand of large-capacity sealing of phosphogypsum, effectively avoiding the pollution risk of sealing phosphogypsum to soil and water. In addition, the sealed phosphogypsum can be mined and utilized repeatedly, which is conducive to sustainable development.

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

[0009] S1, entering the goaf at the end of mining from the return air filling communication roadway, and driving hollow grouting anchor rods in a diamond arrangement in the surrounding rock of the roadway, and then grouting into the hollow grouting anchor rods, and sealing the rock joint fissure and the surrounding rock of the roadway with a high anti-seepage high-strength grouting liquid made of alum stone cement, modifier and water to form the outermost anti-seepage flexible support layer;

[0010] S2, weaving and hanging the net on the hollow grouting anchor rods of the top column and the interval column, and not hanging the net on the hollow grouting anchor rods of the bottom column, then erecting the formwork, and finally spraying the grout between the surrounding rock of the roadway and the formwork to reinforce and form the concrete shotcrete layer, which constitutes the intermediate anti-seepage flexible support layer; the grout is made by mixing the following raw materials by mass fraction under normal temperature conditions: 10 parts of anti-seepage cement, 18-22 parts of guami 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 the formwork is removed, the impermeable geomembrane is laid outside the concrete spraying layer, the impermeable geomembrane is compacted and adhered to the wall to form the inner layer impermeable membrane flexible layer;

[0012] S4, a concrete partition is poured at the outlet of the goaf to block, a slurry pipeline is laid in the return air filling connecting roadway, and a permeate liquid pressure reducing valve and a permeate pipeline are pre-buried in the ore mining transportation roadway, then phosphogypsum, impermeable cement and water with a mass ratio of (16-20):1:(0.4-0.6) are uniformly mixed at normal temperature to form phosphogypsum slurry, the phosphogypsum slurry is pumped and injected into the goaf through the slurry pipeline, and finally the injection port is sealed, so that the phosphogypsum is stored, and the initial percolate is transported to the underground impermeable storage through the permeate pipeline through the pressure reducing valve for storage of the percolate;

[0013] S5, after the phosphogypsum storage operation is completed, the impermeable geomembrane is laid on the top of the phosphogypsum storage area, the area where the phosphogypsum has been stored is separated from the to-be-mined body, a 0.15-0.2 m thick reinforced concrete bottom plate is laid outside the impermeable geomembrane, and a concrete partition is poured to block.

[0014] Optionally, in step S1, the hollow grouting anchor rod adopts an anchor rod with a diameter of 18 mm and a length of 2000-2500 mm, and the end thereof extends by 700 mm, and the hollow grouting anchor rod has a row distance of 500 mm.

[0015] Optionally, in steps S2 and S4, the impermeable cement adopts 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 meshing adopts a threaded steel mesh with a diameter of 6 mm, and the grid is 10 cm x 10 cm; the spraying process between the top column and the interval column and the formwork is divided into two times: first, the spraying material is sprayed between the top column and the interval column and the meshing to a thickness of 350 mm, when the slurry solidifies and does not fall, the spraying material is continuously sprayed between the meshing and the formwork to a thickness of 250 mm, and the two times of spraying material form the 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 and attached to the wall to form an anti-seepage membrane layer by using the threads at the ends of the hollow grouting anchor rod, cooperating with the gaskets and lock nuts.

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

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

[0023] 1. Compared with the traditional phosphogypsum treatment method, the present application provides a completely different new idea, i.e., storing phosphogypsum in the underground goaf, which effectively improves the utilization rate of the underground waste space. According to the difference in the occurrence of the underground waste space, the inventor fully considers the stability of the surrounding rock and the safety of utilization, flexibly uses the goaf of the abandoned mine and various underground waste spaces such as abandoned caverns, greatly improves the utilization rate of the underground waste space, and maximizes the available space volume in the waste roadway space.

[0024] 2. The stored phosphogypsum can be subsequently recovered and used repeatedly, and is convenient for later maintenance, which is conducive to the realization of sustainable development. The traditional waste roadway utilization method is mainly filling, which is a simple and effective method and can effectively prevent ground subsidence and collapse accidents, but the filling utilization is a one-time utilization method, and after filling, the mine space is occupied by solid filling materials, which cannot be used subsequently, and will directly cause the waste and waste of underground mine space.

[0025] 3. The present application guarantees the flexibility of the anti-seepage and the strength of the wall protection, and improves the safety of the construction personnel. A plurality of hollow grouting anchor rods are anchored into the deep position of the roadway surrounding rock, and the mesh is fixed on the surface position of the roadway surrounding rock, realizing flexible contact with the roadway surrounding rock. The hollow grouting anchor rod anchored in the deep layer of the roadway surrounding rock resists the repeated deformation of the rock mass, and the combination of the hollow grouting anchor rod and the mesh forms a long whole, which has a certain bending deformation buffer range in the direction deviating from the axis of the hollow grouting anchor rod, and is not easy to break. At the same time, the anchor net can be connected and fixed on the surface of the roadway surrounding rock, and a concrete shotcrete layer is set to form a bottom support effect for the flexible support system, which can block the falling sand and gravel from the top of the roadway, ensuring the stability and safety of the surrounding rock during construction. In turn, not only can the phosphogypsum be stored in the waste roadway space, but also the roadway space can be supported, ensuring the stable support of the roadway surrounding rock and effectively improving the safety of the waste mine roadway.

[0026] 4. The construction process of the application is simple, the construction technology is difficult, and the personnel construction is convenient. Through the optimization design of the construction method of the sealing phosphogypsum anti-seepage structure, the operation personnel can conveniently carry out construction operation on the karst stratum, that is, first, the hollow grouting anchor rod, the grouting body and the surrounding rock are combined to form the outermost flexible support, then the concrete formed by the specific proportion of the anti-seepage cement, the melon stone, the mixed sand and the water is sprayed and reinforced to form the concrete shotcrete layer, and finally the anti-seepage geomembrane is compacted and adhered to form the anti-seepage membrane layer, so that the three-layer anti-seepage flexible retaining wall is set to carry out anti-seepage treatment, and the operation personnel can conveniently carry out construction in the goaf.

[0027] 5. The overall cost of the application is low, the application range is wide, and the application has great economic benefits and good popularization value. That is, the application can be applied to various types of underground abandoned space, greatly improving the utilization of underground space. The underground goaf selected by the application has the characteristics of good anti-deformation ability and high strength, and does not need to be large-scale reinforced and treated to the original abandoned goaf and its roadway, thereby greatly reducing the construction cost of the engineering reconstruction. In addition, by setting the three-layer anti-seepage flexible retaining wall, the leaching risk of harmful elements in the sealing phosphogypsum is effectively avoided, thereby solving the problem of groundwater pollution, and reducing the ecological restoration cost of mine production. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a construction schematic view of the test ore body of the application;

[0029] Figure 2 is Figure 1 is a middle A-A sectional view;

[0030] Figure 3 is Figure 2 is an enlarged structural schematic view of D;

[0031] Figure 4 is Figure 2 is an enlarged structural schematic view of E;

[0032] Figure 5 is a structural schematic view of the hollow grouting anchor rod of the application.

[0033] In the figure: 1, hollow grouting anchor rod, 2, roadway surrounding rock, 3, concrete shotcrete layer, 4, mesh, 5, anti-seepage geomembrane, 6, gasket, 7, locking nut, 8, thread. DETAILED DESCRIPTION

[0034] The application will be further described in detail below in combination with the drawings and examples.

[0035] Unless otherwise specified, the raw materials used in the present application are conventional raw materials in the technical field, which can be purchased in the market. Among them, the impermeable cement is sulphoaluminate cement with a strength grade of 42.5, purchased from Foshan Xinqida New Material Group Co., Ltd.; M32.5 masonry cement, purchased from Hubei Daye Jianfeng Cement Co., Ltd.; water, taken from underground water; melon stone, derived from limestone near the Jinshandian Iron Mine, crushed by a jaw crusher; machine-made sand, actually used sand by Wugang 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, if not specifically stated, they are all conventional methods, and the instruments used in the test can be obtained through commercial channels. The parts not elaborated in the specification are all prior art.

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

[0037] S1, enter the goaf at the end of the recovery from the air backfill connecting lane, and punch hollow grouting anchor rods 1 in a diamond arrangement in the surrounding rock 2 of the roadway, and then grout into the hollow grouting anchor rods 1, and 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 joint fissure and the surrounding rock 2 of the roadway to form the outermost impermeable flexible support layer;

[0038] S2, weave and hang the net 4 on the hollow grouting anchor rods 1 of the top column and the intermediate column, and do not hang the net 4 on the hollow grouting anchor rods 1 of the bottom column, then set up the formwork, and finally spray the slurry between the surrounding rock 2 of the roadway and the formwork to reinforce and form the concrete shotcrete layer 3, which constitutes the intermediate impermeable flexible support layer; the slurry is mixed by the following raw materials in parts by mass at room temperature: impermeable cement 10 parts, melon stone 18-22 parts, mixed sand 15-25 parts and water 6-8 parts, and the mixed sand is composed of phosphogypsum and machine-made sand;

[0039] S3, after removing the formwork, lay impermeable geomembrane 5 outside the concrete shotcrete layer 3, and compact and adhere the impermeable geomembrane 5 to form the inner impermeable membrane flexible layer;

[0040] S4, pour the concrete partition wall to seal at the outlet of the goaf, lay the slurry pipeline in the air backfill connecting lane of the upper disc, and pre-bury the osmotic liquid pressure reducing valve and the osmotic pipeline in the ore transportation lane, then mix the phosphogypsum, the impermeable cement and the water in a mass ratio of (16-20):1:(0.4-0.6) uniformly at room temperature to form the phosphogypsum slurry, pump the phosphogypsum slurry into the goaf through the slurry pipeline, and finally seal the grouting inlet, so as to realize the sealing of the phosphogypsum, and the initial percolate is transported to the underground impermeable warehouse for storing the filtrate through the osmotic pipeline by the pressure reducing valve;

[0041] S5, after the sealing operation of phosphogypsum is completed, laying a waterproof geomembrane 5 on the top of the phosphogypsum sealing area, separating the area where the phosphogypsum has been sealed from the ore body to be mined, laying a 0.15-0.2 m thick reinforced concrete bottom plate outside the waterproof geomembrane 5, and pouring a concrete partition to block.

[0042] When the phosphogypsum can be used as a resource, the lower opening of the mined-out area is opened, the shovel loader directly digs, and the mined-out area is transported to the ground in a mine car to realize the recovery and reuse of the phosphogypsum, and finally the mined-out area is inspected and repaired.

[0043] The following is a preparation example of the present application

[0044] Preparation Example 1

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

[0046] Sa, uniformly mix the following raw materials by mass parts: 10 parts of impermeable cement, 20 parts of guami stone, 20 parts of mixed sand, and 7 parts of water under normal temperature conditions to obtain a slurry; wherein the mixed sand is composed of phosphogypsum and machine-made sand in a mass ratio of 4:1;

[0047] Sb, erect a formwork and spray the slurry obtained in step Sa to obtain a cube test piece with a side length of 150 mm.

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

[0049] Preparation Example 2

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

[0051] Sa, uniformly mix the following raw materials by mass parts: 10 parts of impermeable cement, 20 parts of guami stone, 20 parts of mixed sand, and 7 parts of water under normal temperature conditions to obtain a slurry; wherein the mixed sand is composed of phosphogypsum and machine-made sand in a mass ratio of 0.1:1;

[0052] Sb, erect a formwork and spray the slurry obtained in step Sa to obtain a cube test piece with a side length of 150 mm.

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

[0054] Preparation Example 3

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

[0056] Sa. The following raw materials, in parts 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 uniformly at room temperature to obtain a 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 spraying layer 3 test block of this preparation example includes the following steps:

[0061] Sa. The following raw materials, in parts 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 uniformly at room temperature to obtain a 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 spraying layer 3 test block of this preparation example includes the following steps:

[0066] Sa. The following raw materials, in parts 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 uniformly at room temperature to obtain a 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 spraying layer 3 test block of this preparation example includes the following steps:

[0071] Sa, the following raw materials by mass parts: water-repellent cement 10 parts, guami stone 20 parts, mixed sand 20 parts and water 7 parts, under normal temperature conditions, uniform mixing, get slurry; wherein, the mixed sand is composed of phosphogypsum and machine-made sand with a mass ratio of 0.5:1;

[0072] Sb, erecting formwork and hanging net 4, first spraying the slurry obtained in step Sa with a thickness of 85mm between the hanging net 4 and one side of the formwork, and then spraying the slurry obtained in step Sa with a thickness of 65mm between the hanging net 4 and the other side of the formwork when the slurry is solidified to not fall off, and the two times of spraying slurry form a cube test piece with a side length of 150mm.

[0073] In the preparation example, the average particle size of the phosphogypsum is controlled at 0.1mm, the average particle size of the machine-made sand is controlled at 1mm, and the average particle size of the guami stone is controlled at 10mm, and the hanging net 4 adopts a threaded steel mesh with a diameter of 6mm, and the grid is 10cm×10cm.

[0074] Comparative Example 1

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

[0076] Sa, the following raw materials by mass parts: water-repellent cement 10 parts, guami stone 20 parts, mixed sand 20 parts and water 7 parts, under normal temperature conditions, uniform mixing, get slurry; wherein, the mixed sand is composed of phosphogypsum and machine-made sand with a mass ratio of 0.5:1;

[0077] Sb, erecting formwork and hanging net 4, first spraying the slurry obtained in step Sa with a thickness of 85mm between the hanging net 4 and one side of the formwork, and then spraying the slurry obtained in step Sa with a thickness of 65mm between the hanging net 4 and the other side of the formwork when the slurry is solidified to not fall off, and the two times of spraying slurry form a cube test piece with a side length of 150mm.

[0078] In the preparation example, the average particle size of the phosphogypsum is controlled at 0.1mm, the average particle size of the machine-made sand is controlled at 1mm, and the average particle size of the guami stone is controlled at 10mm, and the hanging net 4 adopts a threaded steel mesh with a diameter of 6mm, and the grid is 10cm×10cm.

[0079] Comparative Example 2

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

[0081] Sa, the following raw materials by mass parts: water-repellent cement 10 parts, guami stone 20 parts, mixed sand 20 parts and water 7 parts, under normal temperature conditions, uniform mixing, get slurry; wherein, the mixed sand is composed of phosphogypsum and machine-made sand with a mass ratio of 0.5:1;

[0082] Sb, erecting formwork and hanging net 4, first spraying the slurry obtained in step Sa with a thickness of 85mm between the hanging net 4 and one side of the formwork, and then spraying the slurry obtained in step Sa with a thickness of 65mm between the hanging net 4 and the other side of the formwork when the slurry is solidified to not fall off, and the two times of spraying slurry form a cube test piece with a side length of 150mm.

[0083] In the present 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 shotcrete layer 3 test blocks (cubic test specimens) prepared according to Preparation Examples 1-6 and Comparative Examples 1-2 is detected, and the results are shown in Table 1 below. Note that the strength grade of the shotcrete is determined according to the standard value of the cubic compressive strength, and the evaluation of the compressive strength of the shotcrete is performed according to the current national standard "Standard for Testing and Evaluation of Concrete Strength" GB / T50107.

[0085] Table 1: Test results of Preparation Examples 1-6 and Comparative Examples 1-2

[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] As can be seen from the data in Table 1, the compressive strength of the concrete shotcrete layer 3 test blocks prepared according to the present application using the specific proportion of the water-proof cement, guami stone, phosphogypsum and machine-made sand as raw materials can fully meet the needs, while having the advantages of low cost and being able to consume a large amount of phosphogypsum. In addition, as can be seen from the comparison between Preparation Example 3 and Preparation Example 1, when the particle size of the phosphogypsum is controlled to be below 0.1 mm, the particle size of the machine-made sand is controlled to be below 2 mm, and the particle size of the guami stone is controlled to be below 15 mm, the compressive strength of the test blocks can be further improved. As can be seen from the comparison between Preparation Example 5 and Preparation Examples 3-4, when the mass ratio of the phosphogypsum and machine-made sand is (0.4-0.6):1, the compressive strength of the test blocks can be greatly improved. As can be seen from the comparison between Preparation Example 6 and Preparation Example 5, after adding the 10 cm x 10 cm, φ6 mm threaded steel mesh to the test blocks, the strength of the test blocks is greatly improved, thereby ensuring that the support system of the present application can meet the safety requirements.

[0088] The following is an application example of the present application

[0089] The ore body used in the application example of the present application is the Zhangfushan ore body of the Jinshandian Iron Mine of the Wugang Resources Group Jinshandian Mining Co., Ltd. As shown in Figure 1 and Figure 2 First, the ore body is mined using the gently inclined thin ore body mining method, and then the underground goaf is used for the sequestration of phosphogypsum.

[0090] The specific steps of mining are as follows: (1) preparation work: a preparation roadway is constructed every 42m along the strike with a wall-type stope face of the whole length of the ore block, the lower panel is a ore transportation roadway, and the upper panel is a return air filling connecting roadway; (2) cutting work: a cutting rise is constructed every 23m along the ore body inclined direction in the preparation roadway in the vein, the return air filling connecting roadway and the ore transportation roadway are connected, a 32m long and 20m wide ore room is formed; (3) mining work: the ore room is mined by shallow hole drilling and blasting, and 3m wide inter-column and 3m wide top and bottom columns are reserved.

[0091] The method for sealing phosphogypsum in underground goaf of the application comprises the following steps:

[0092] S1, entering the goaf where mining is completed from the return air filling connecting roadway, pre-drilling a hole in the roadway surrounding rock 2, inserting a φ18mm, 2500mm long hollow grouting anchor rod 1 into the hole, using an anchor rod drill hammer to firmly connect the hollow grouting anchor rod 1 with the roadway surrounding rock 2, 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 distance of 500mm, and then grouting is performed into the pre-embedded hollow grouting anchor rod 1, a high anti-seepage and high-strength grouting liquid made of alum stone cement, a modifier and water is mixed to form a high anti-seepage and high-strength grouting liquid, the grouting liquid is injected from the middle of the tail of the hollow grouting anchor rod 1, the rock layer cracks in the roadway surrounding rock 2 are filled, and the external seepage of underground water is isolated, the hollow grouting anchor rod 1, the grouting body and the roadway surrounding rock 2 form the outermost flexible support;

[0093] S2, a woven mesh 4 is hooked on the hollow grouting anchor rods 1 of the top column and the inter-column, and the hollow grouting anchor rods 1 of the bottom column are not hooked on the mesh 4, the mesh 4 is a φ6mm threaded steel mesh with a grid of 10cm*10cm, a formwork is then erected, and finally the mesh 4 is sprayed with a grouting material 350mm thick between the top column and the inter-column and the mesh 4, when the grouting material is solidified and does not fall off, the mesh 4 is continuously sprayed with a grouting material 250mm thick between the mesh 4 and the formwork, the two times of grouting material form a concrete shotcreting layer 3, the bottom column and the formwork are directly sprayed with a grouting material 600mm thick once to form the concrete shotcreting layer 3, so as to strengthen the stability and bearing capacity of the roadway surrounding rock 2; the grouting material is mixed by the following raw materials in the quality parts under the normal temperature condition: 10 parts of anti-seepage cement, 20 parts of guami stone, 20 parts of mixed sand and 7 parts of water, the mixed sand is composed of phosphogypsum and machine-made sand with a mass ratio of 0.5:1, the average particle size of the phosphogypsum is controlled to be 0.1mm, the average particle size of the machine-made sand is controlled to be 1mm, and the average particle size of the guami stone is controlled to be 10mm;

[0094] S3, after the formwork is removed, an anti-seepage geomembrane 5 is laid outside the concrete shotcreting layer 3, the anti-seepage geomembrane 5 passes through the pre-embedded hollow grouting anchor rod 1, and the anti-seepage geomembrane 5 is compacted and adhered to form an anti-seepage membrane layer by using the threads 8 at the end of the hollow grouting anchor rod 1, cooperating with the gaskets 6 and the locking nuts 7.

[0095] S4, pouring concrete partition wall to seal the cut-up mountain bottom of the stope area, the concrete for pouring the partition wall is mixed by M32.5 masonry cement and water with a mass ratio of 1:0.5, a slurry pipeline is laid in the air return filling connecting lane of the upper panel, a pressure reducing valve and a liquid seepage pipeline are buried in the ore extraction and transportation lane of the lower panel, then phosphogypsum, water-proof cement and water with a mass ratio of 18:1:0.5 are mixed uniformly at room temperature to form phosphogypsum slurry, the slurry pipeline is closely attached to the roof beam, and the phosphogypsum slurry is pumped and injected into the stope area by the slurry pipeline, which is erected in the central part of the cut-up mountain and inclined upward by 5°, finally the injection port is sealed, and the phosphogypsum is sealed, and the initial leachate is transported to the underground water-proof storage by the pressure reducing valve and the liquid seepage pipeline, pumped out of the ground and treated in the chemical plant to realize the recovery of phosphogypsum leachate;

[0096] S5, after the sealing operation of the phosphogypsum is completed, a water-proof geomembrane 5 is laid on the top of the phosphogypsum sealing area, and the area where the phosphogypsum has been sealed is separated from the to-be-mined ore body, a 0.15-0.2 m thick reinforced concrete bottom plate is laid outside the water-proof geomembrane 5, and concrete partition wall is poured and sealed, the concrete for pouring the partition wall is mixed by M32.5 masonry cement and water with a mass ratio of 1:0.5.

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

[0098] The above are preferred embodiments of the present application, and are not intended to limit the protection scope of the present application, therefore: any equivalent changes made on the structure, shape, principle of the present application should be covered within 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 diamond-shaped hollow grouting anchor rods (1) into the tunnel surrounding rock (2), and then injecting grout into the hollow grouting anchor rods (1), through which a high-impermeability and high-strength grouting liquid made of alum stone cement, modifier, and water is mixed to seal the joints and fissures of the rock stratum and the tunnel surrounding rock (2) to form the outermost anti-seepage 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 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), constituting an intermediate anti-seepage flexible supporting layer; the slurry is made 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, the mixed sand is composed of phosphogypsum and machine-made sand, the mass ratio of the phosphogypsum to machine-made sand is (0.4-0.6): 1, 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 melon stone is controlled to be less than 15 mm; S3, after removing the formwork, laying an anti-seepage geomembrane (5) outside the concrete spraying layer (3), and compacting the anti-seepage geomembrane (5) to adhere to the wall to form an inner anti-seepage membrane flexible layer; S4. Concrete partition walls are cast to seal the goaf exit, slurry pipelines are laid in the return air filling connecting tunnel, and seepage liquid pressure reducing valves and seepage liquid pipelines are pre-buried in the mine transport tunnel. Phosphogypsum, anti-seepage cement, and water are then mixed evenly at room temperature in a mass ratio of (16-20):1:(0.4-0.6) 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 then transported from the pressure reducing valve through the seepage liquid pipeline to an underground anti-seepage tank for storing the filtrate. S5. After the sealing operation of the phosphogypsum is completed, an anti-seepage 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 anti-seepage geomembrane (5), and a concrete partition wall is poured to seal the area; In step S2, the hanging mesh (4) uses a φ6mm threaded steel mesh with a grid 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 (4), and when the slurry solidifies to no longer fall off, 250mm thick slurry is continued to be sprayed between the hanging mesh (4) and the formwork, and the two sprayings form a concrete spraying layer (3).

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

4. The method for sealing phosphogypsum in underground goaf according to claim 2, wherein: In step S2, the spraying thickness of the slurry between the bottom column and the template is 500-600 mm.

5. The method for storing 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 thread (8) at the end of the hollow grouting anchor rod (1) is used in conjunction with the gasket (6) and the locking nut (7) to compact the anti-seepage geomembrane (5) against the wall to form an anti-seepage membrane layer.

6. The method for storing phosphogypsum in underground goaf according to claim 1, characterized in that: The method further includes step S6: when phosphogypsum can be used as a resource, the lower opening of the goaf is opened, 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.

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