Modified material for backfilling desulfurization gypsum mine and preparation method and use method thereof

Abstract

The application discloses a modified material for backfilling of desulfurization gypsum mine pits and a preparation method and a use method thereof, and relates to the technical field of industrial solid waste resource utilization and mine ecological restoration. The modified material for backfilling of desulfurization gypsum mine pits comprises the following components in parts by weight: quicklime 0.15-0.25 parts, polyaluminum chloride 0.08-0.12 parts, functional additives 0.03-0.08 parts and composite stabilizers 0.02-0.05 parts. The application further provides a preparation method and a use method of the modified material for backfilling of desulfurization gypsum mine pits. Through the synergistic effect of multiple components, the fluorides and trace heavy metals are efficiently stabilized, and the physical and mechanical properties and long-term stability of the backfilling body are improved, so that the dual requirements of pit backfilling and ecological restoration are met. The technical problems that the fluorine-containing desulfurization gypsum is difficult to be safely used for pit backfilling due to the excessive leaching of fluorides and trace heavy metals, poor treatment effect of single reagent, insufficient mechanical properties and long-term stability of the backfilling body are solved.

Description

Technical Field

[0001] This invention relates to the field of industrial solid waste resource utilization and mine ecological restoration technology, specifically to modified materials for desulfurized gypsum mine pit backfilling, and their preparation and application methods. Background Technology

[0002] The coal-fired power generation industry is the primary source of desulfurization gypsum, whose main component is calcium sulfate dihydrate (CaSO4). While desulfurized gypsum contains pollutants such as fluorides and trace heavy metals (mercury, arsenic, etc.), direct storage can easily cause soil and groundwater pollution. Mine backfilling, as an important way to utilize desulfurized gypsum resources, has been clearly recognized by the "Standard for Pollution Control of Storage and Landfill of General Industrial Solid Waste" (GB 18599-2020). However, excessive fluoride leaching in some desulfurized gypsum (up to 25.6 mg / L, far exceeding the first-level standard limit of 10 mg / L in GB 8978-1996) has become the core bottleneck restricting its application.

[0003] Among existing technologies for the harmless treatment of desulfurized gypsum, single-use quicklime treatment suffers from the problems of adverse effects at low doses and escalating costs at high doses; polyaluminum chloride (PAC) alone has limited defluorination efficiency and is difficult to meet backfill requirements; water washing and calcination methods have drawbacks such as high energy consumption and the risk of secondary pollution. Furthermore, existing modified materials mostly focus on the removal of single pollutants, neglecting the synergistic stabilization of fluorides and trace heavy metals, and lack the ability to enhance the long-term mechanical stability of the backfill, leading to problems such as excessive leachate and backfill sedimentation after backfilling, seriously affecting the large-scale application of desulfurized gypsum in mine backfilling. Therefore, developing a composite harmless modified material with efficient defluorination, heavy metal stabilization, and mechanical property enhancement functions is of great significance for promoting the resource utilization of desulfurized gypsum and mine ecological restoration. Summary of the Invention

[0004] To address the aforementioned shortcomings in existing technologies, this invention provides a modified material for desulfurized gypsum mine pit backfill, along with its preparation and application methods. Through the synergistic effect of multiple components, it achieves efficient stabilization of fluorides and trace heavy metals, while simultaneously improving the physical and mechanical properties and long-term stability of the backfill material. This meets the dual needs of mine pit backfilling and ecological restoration, effectively solving the technical problems that prevent the safe use of fluorinated desulfurized gypsum for mine pit backfilling due to excessive leaching of fluorides and trace heavy metals, poor treatment effects of single agents, and insufficient mechanical and long-term stability of the backfill material.

[0005] To achieve the above objectives, the technical solution adopted by the present invention to solve its technical problem is as follows: a modified material for desulfurized gypsum mine pit backfilling is provided, comprising the following components by weight: 0.15-0.25 parts quicklime, 0.08-0.12 parts polyaluminum chloride, 0.03-0.08 parts functional additives, and 0.02-0.05 parts composite stabilizer. The functional additives include modified zeolite powder and hydroxyapatite, and the composite stabilizer includes magnesium sulfate and aminotrimethylenephosphonic acid.

[0006] The modified material for backfilling desulfurized gypsum mine pits includes the following components by weight: 0.2 parts quicklime, 0.1 parts polyaluminum chloride, 0.05 parts functional additives, and 0.03 parts composite stabilizer. The functional additives include modified zeolite powder and hydroxyapatite, and the composite stabilizer includes magnesium sulfate and aminotrimethylene phosphonic acid.

[0007] Furthermore, the calcium oxide content of quicklime is ≥90%.

[0008] Furthermore, the effective alumina content of polyaluminum chloride is ≥30%.

[0009] Furthermore, the functional additives include modified zeolite powder and hydroxyapatite.

[0010] Furthermore, the mass ratio of modified zeolite powder to hydroxyapatite is 2-3:1.

[0011] Furthermore, the modified zeolite powder was activated with a 5% hydrochloric acid solution.

[0012] Furthermore, the modified zeolite powder has a specific surface area ≥ 400 m². 2 / g, cation exchange capacity ≥180 mmol / 100 g.

[0013] Furthermore, the hydroxyapatite has a purity of ≥95% and a particle size of ≤5 μm.

[0014] Furthermore, the composite stabilizer includes magnesium sulfate and aminotrimethylenephosphonic acid.

[0015] Furthermore, the mass ratio of magnesium sulfate to aminotrimethylenephosphonic acid is 1:1.

[0016] Furthermore, the magnesium sulfate has a purity of ≥98% and a particle size of 100-200 mesh.

[0017] Furthermore, the effective content of aminotrimethylenephosphonic acid is ≥50%, and the applicable pH range is 4-10.

[0018] The preparation method of the above-mentioned composite harmless modified material for desulfurized gypsum mine pit backfill includes the following steps: first, quicklime, modified zeolite powder and hydroxyapatite are mixed, and then polyaluminum chloride, magnesium sulfate and aminotrimethylene phosphonic acid are added and mixed again to obtain the composite harmless modified material for desulfurized gypsum mine pit backfill.

[0019] Furthermore, mix at 800-1000 r / min for 5-8 min, and then continue mixing at 1200-1500 r / min for 10-15 min.

[0020] Further, the mixture is stirred in a high-speed mixer.

[0021] The method of using the above-mentioned composite harmless modified material for backfilling desulfurized gypsum mine pits includes the following steps: S1. After crushing and drying the desulfurized gypsum, add it to the composite harmless modification material for backfilling the desulfurized gypsum mine pit and stir it. Then pile it up for aging to obtain the aged modified desulfurized gypsum. S2. The slope of the mine pit is repaired, and the bottom of the mine pit is laid in sequence with a compacted clay layer, a long-fiber needle-punched non-woven geotextile, a pebble drainage layer and a long-fiber needle-punched non-woven geotextile to construct a composite seepage prevention and drainage foundation. S3. The aged modified desulfurized gypsum obtained in step S1 is backfilled in layers and then compacted. After each layer of backfilling, a drainage ditch is set up, filled with pebbles of the same size, and perforated drainage pipes are installed. A leachate collection system is constructed simultaneously. After the backfilling is completed, long-fiber needle-punched non-woven geotextile, HDPE geomembrane, long-fiber needle-punched non-woven geotextile, geogrid and planting soil are laid in sequence, and native shallow-rooted vegetation is planted.

[0022] Furthermore, in step S1, the desulfurized gypsum is the surface desulfurized gypsum of the stockpile.

[0023] Furthermore, in step S1, the total fluoride content of the desulfurized gypsum is ≤1600 mg / kg, the mercury content is ≤1.6 mg / kg, and the organic matter content is 0.3-1.0%.

[0024] Furthermore, in step S1, the desulfurized gypsum meets the relevant requirements of the "Soil Environmental Quality Standard for Agricultural Land Soil Pollution Risk Control (Trial)" (GB 15618-2018).

[0025] Furthermore, in step S1, the storage depth of the desulfurized gypsum is ≤50 cm.

[0026] Furthermore, in step S1, the particle size of the desulfurized gypsum is ≤5 mm.

[0027] Furthermore, in step S1, the moisture content of the desulfurized gypsum is 8-12%.

[0028] Furthermore, in step S1, a composite harmless modified material is used for backfilling the desulfurized gypsum mine pit.

[0029] Furthermore, in step S1, the amount of composite harmless modified material added for backfilling desulfurized gypsum mine pits is 0.28-0.50% of the dry weight of desulfurized gypsum.

[0030] Furthermore, in step S1, the mixture is stirred in a twin-shaft mixer.

[0031] Furthermore, in step S1, the stirring time is 15-20 min.

[0032] Furthermore, in step S1, the piling and aging time is 8-12 days, during which the mixture is turned over once every 2-3 days.

[0033] Furthermore, in step S1, the moisture content after stacking and aging is 10-15%.

[0034] Furthermore, in step S1, the reactor temperature is monitored periodically to ensure that there is no abnormal temperature rise.

[0035] Furthermore, in step S1, when the temperature of the pile exceeds 60°C during the aging and maturation process, it is promptly turned over to cool down and moisture is added.

[0036] The beneficial effect of taking the above-mentioned further measures is to ensure that the modification reaction proceeds fully.

[0037] Furthermore, in step S2, the mine pit slope is repaired by using C20 concrete spraying + φ6@150×150 mm galvanized steel wire mesh + φ20@200×200 cm steel anchor rods for mesh-hanging spraying and anchoring support of the mine pit slope.

[0038] Furthermore, in step S2, the thickness of the C20 concrete sprayed grout is 8-12 cm.

[0039] Furthermore, in step S2, the thickness of the C20 concrete sprayed grout is 10 cm.

[0040] Furthermore, in step S2, the thickness of the compacted clay layer is 75-85 cm.

[0041] Furthermore, in step S2, the thickness of the compacted clay layer is 80 cm.

[0042] Furthermore, in step S2, the compaction degree of the compacted clay layer is ≥94%.

[0043] Furthermore, in step S2, the first layer of filament needle-punched nonwoven geotextile has a specification of 600 g / m². 2 .

[0044] Furthermore, in step S2, the thickness of the pebble guide layer is 30-40 cm.

[0045] Furthermore, in step S2, the thickness of the pebble guide layer is 35 cm.

[0046] Furthermore, in step S2, the second layer of filament needle-punched nonwoven geotextile has a specification of 200 g / m². 2 .

[0047] Furthermore, in step S3, the thickness of each backfill layer is 30-40 cm.

[0048] Furthermore, in step S3, a stepped, layered backfilling method is adopted.

[0049] Furthermore, in step S3, the time interval between two adjacent backfill layers shall not exceed 72 hours.

[0050] The beneficial effect of adopting the above-mentioned further measures is to avoid the formation of weak interlayers.

[0051] Furthermore, in step S3, a vibratory roller is used for layered compaction.

[0052] Furthermore, in step S3, the compaction work is controlled to be 2000-2500 kN. m / m 2 After compaction, the dry density is ≥1.3 g / cm³. 3 .

[0053] Furthermore, in step S3, the blind drain pipe is trapezoidal.

[0054] Furthermore, in step S3, the pebble particle size is 10-60 mm.

[0055] Furthermore, in step S3, the perforated drainage pipe is a DN400 HDPE perforated drainage pipe.

[0056] Furthermore, in step S3, the slope of the main blind drain is 3%, and the slope of the branch blind drain is 2%.

[0057] Furthermore, in step S3, the leachate collection system includes a collection well and a collection tank.

[0058] Furthermore, in step S3, the water collection well has an inner diameter of 80 cm and a height of 21.5 m, with an inner wall lined with a ≥1.5 mm thick HDPE geomembrane and a built-in submersible pump.

[0059] Furthermore, in step S3, the collection pool has dimensions of 10 m × 5 m × 2 m, is constructed with C30 reinforced concrete, and has anti-corrosion and anti-seepage treatment on its inner wall.

[0060] Furthermore, in step S3, the first layer of filament needle-punched nonwoven geotextile has a specification of 600 g / m². 2 .

[0061] Furthermore, in step S3, the thickness of the HDPE geomembrane is 1.5-2 mm.

[0062] Furthermore, in step S3, the second layer of filament needle-punched nonwoven geotextile has a specification of 600 g / m². 2 .

[0063] Furthermore, in step S3, the thickness of the geogrid is 5 cm.

[0064] Furthermore, in step S3, the thickness of the planting soil is 40 cm.

[0065] Furthermore, in step S3, biochar with a mass fraction of 0.5-1% is added to the planting soil.

[0066] Furthermore, in step S3, the biochar has a specific surface area ≥ 500 m². 2 / g, pH 7.5-8.5.

[0067] The beneficial effects of taking the above-mentioned further measures are: improving the soil's water and fertilizer retention capacity and vegetation survival rate.

[0068] Furthermore, in step S3, the native shallow-rooted vegetation includes rhododendron, raspberry, and wild rose.

[0069] In summary, the present invention has the following beneficial effects: 1. The composite modified material of this invention is based on the principle of "multiple-action synergistic enhancement." Through the scientific ratio of the main agent, synergist, functional additive, and composite stabilizer, it achieves efficient fixation of pollutants and improvement of backfill performance. The main agent, quicklime, provides Ca... 2+ The fluoride precipitate forms a poorly soluble CaF2 precipitate with fluoride ions, while simultaneously adjusting the pH of the system to a suitable range to create conditions for subsequent reactions. The synergist, polyaluminum chloride, hydrolyzes to produce polynuclear hydroxyl complexes, which enhance the coagulation of the CaF2 precipitate through adsorption and flocculation, while also adsorbing some trace heavy metal ions. Among the functional additives, modified zeolite powder, with its high specific surface area and cation exchange capacity, adsorbs residual fluoride ions and heavy metals such as mercury and arsenic. Hydroxyapatite embeds heavy metal ions into the crystal lattice through ion exchange to form stable complexes, achieving long-term fixation and enhancing the adsorption and complexation of residual pollutants. Simultaneously, the composite stabilizer inhibits the re-dissolution of pollutants, significantly improving long-term stability. The addition of the composite stabilizer inhibits the re-dissolution of fluoride and heavy metals; after a 180-day immersion test, the fluoride leaching concentration remained stable below 5 mg / L, with no rebound phenomenon. Magnesium sulfate provides SO4. 2- , with Ca 2+ Forms slightly soluble CaSO4 2H₂O crystals fill the pores of the backfill material, increasing its density; aminotrimethylenephosphonic acid, as a highly efficient chelating agent, forms stable chelates with heavy metal ions, while simultaneously inhibiting the redissolution of fluorides and enhancing long-term stability. This application achieves synergistic stabilization of fluorides and trace heavy metals through multiple mechanisms, solving the technical bottlenecks of low fluoride removal efficiency and difficulty in simultaneous removal of heavy metals by single agents.

[0070] 2. The synergistic treatment effect of this invention is significant: the composite modified material reduces the fluoride leaching concentration of desulfurized gypsum from 25.6 mg / L to below 5 mg / L through multiple mechanisms of "precipitation-adsorption-complexation-solidification", and the leaching concentration of heavy metals such as mercury and arsenic is below the detection limit, which is far superior to the treatment effect of single agent and meets the requirements of Class I general industrial solid waste.

[0071] 3. Excellent backfill performance: The dry density of the modified desulfurized gypsum backfill is ≥1.3 g / cm³. 3 28-day compressive strength ≥ 1.2 MPa, permeability coefficient ≤ 5.0 × 10⁻⁶ -6 With a speed of cm / s, its resistance to settlement and seepage is significantly improved, which can effectively ensure the geological stability of the mine.

[0072] 4. This application optimizes the preparation process of composite modified materials and the backfill construction process, taking into account both pollutant control and the mechanical properties of the backfill body, forming an integrated technical solution of "pretreatment-modification-backfilling-seepage prevention-revegetation", which is highly replicable.

[0073] 5. Significant cost advantage: The amount of composite modified material used is only 0.28-0.50% of the dry weight of desulfurized gypsum. The raw materials are widely available and inexpensive, which can reduce the disposal cost by more than 35% compared with traditional treatment technologies.

[0074] 6. Outstanding environmental benefits: It enables large-scale disposal of desulfurized gypsum, reduces land occupation and pollution risks, and promotes the ecological restoration of abandoned mine pits, forming a virtuous cycle of "treating waste with waste and ecological recycling". Detailed Implementation

[0075] The principles and features of this invention are described below. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0076] Example 1 The modified material for desulfurized gypsum mine pit backfill includes the following components by weight: 0.2 parts quicklime, 0.1 parts polyaluminum chloride, 0.05 parts functional additive (modified zeolite powder and hydroxyapatite in a mass ratio of 2.5:1), and 0.03 parts composite stabilizer (magnesium sulfate and aminotrimethylenephosphonic acid in a mass ratio of 1:1).

[0077] The preparation method of the above-mentioned modified material for desulfurized gypsum mine pit backfill includes the following steps: first, quicklime, modified zeolite powder and hydroxyapatite are mixed at 900 r / min for 6 min, then polyaluminum chloride, magnesium sulfate and aminotrimethylene phosphonic acid are added and mixed at 1300 r / min for 12 min to obtain the composite harmless modified material for desulfurized gypsum mine pit backfill.

[0078] Example 2 The modified material for desulfurized gypsum mine pit backfill includes the following components by weight: 0.15 parts quicklime, 0.08 parts polyaluminum chloride, 0.03 parts functional additive (modified zeolite powder and hydroxyapatite in a mass ratio of 2:1), and 0.02 parts composite stabilizer (magnesium sulfate and aminotrimethylenephosphonic acid in a mass ratio of 1:1).

[0079] The preparation method of the above-mentioned modified material for desulfurized gypsum mine pit backfill includes the following steps: first, quicklime, modified zeolite powder and hydroxyapatite are mixed at 800 r / min for 5 min, then polyaluminum chloride, magnesium sulfate and aminotrimethylene phosphonic acid are added and mixed at 1200 r / min for 10 min to obtain the composite harmless modified material for desulfurized gypsum mine pit backfill.

[0080] Example 3 The modified material for desulfurized gypsum mine pit backfill includes the following components by weight: 0.25 parts quicklime, 0.12 parts polyaluminum chloride, 0.08 parts functional additive (modified zeolite powder and hydroxyapatite in a mass ratio of 3:1), and 0.05 parts composite stabilizer (magnesium sulfate and aminotrimethylenephosphonic acid in a mass ratio of 1:1).

[0081] The preparation method of the above-mentioned modified material for desulfurized gypsum mine pit backfill includes the following steps: first, quicklime, modified zeolite powder and hydroxyapatite are mixed at 1000 r / min for 8 min, then polyaluminum chloride, magnesium sulfate and aminotrimethylene phosphonic acid are added and mixed at 1500 r / min for 15 min to obtain the composite harmless modified material for desulfurized gypsum mine pit backfill.

[0082] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 contains only quicklime.

[0083] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 does not contain functional additives or composite stabilizers.

[0084] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that Comparative Example 3 does not contain a composite stabilizer.

[0085] Experimental Example 1 The desulfurized gypsum modified material for mine backfilling prepared in Example 1 was used for backfilling the mine pit of Shangluotianjia Stone Powder Factory in Gong County. The mine pit area is 10865 m². 2 The backfill volume is 360,000 m³. 3 This includes the following steps: S1. Select surface desulfurized gypsum with a stockpiling depth of 40-50 cm, crush it to a particle size ≤5 mm, dry it until the moisture content is 10%, add the desulfurized gypsum mine pit backfill composite harmless modification material prepared in Example 1, and stir in a twin-shaft mixer for 18 min. The amount of desulfurized gypsum mine pit backfill composite harmless modification material added is 0.38%. Then, pile it up and age it for 10 days, turning it over every 2 days during the period, and controlling the moisture content to 12% to obtain the aged modified desulfurized gypsum. S2. The mine pit slope is repaired using a 10 cm thick C20 concrete sprayed grout + φ6@150×150 mm galvanized steel wire mesh + φ20@200×200 cm steel anchor bolts for mesh-sprayed anchor support. At the bottom of the mine pit, an 80 cm thick layer of compacted clay (94% compaction) and 600 g / m³ of concrete are laid sequentially. 2 Long-filament needle-punched nonwoven geotextile, a 35 cm thick pebble drainage layer, and 200 g / m 2 Long-filament needle-punched nonwoven geotextile is used to construct a composite seepage-proof and drainage foundation. S3. The aged modified desulfurized gypsum obtained in step S1 is backfilled in a stepped manner, with each layer being 35 cm thick. The time interval between two adjacent backfill layers should not exceed 72 hours. Then, a vibratory roller is used to compact each layer, with the compaction energy controlled at 2000-2500 kN. m / m 2 The dry density after compaction is 1.3 g / cm³. 3 After each backfill layer, trapezoidal drainage blind ditches are installed, filled with pebbles with a particle size of 10-60 mm, and equipped with DN400 HDPE perforated drainage pipes. The main blind ditch has a slope of 3%, and the branch blind ditches have a slope of 2%. A leachate collection system is constructed simultaneously, including a collection well and a collection tank. The collection well has an inner diameter of 80 cm and a height of 21.5 m, with a 1.5 mm thick HDPE geomembrane lining the inner wall and an internal submersible pump. The collection tank measures 10 m × 5 m × 2 m and is constructed with C30 reinforced concrete, with anti-corrosion and anti-seepage treatment on the inner wall. After backfilling, 600 g / m³ of leachate is laid sequentially. 2 Long-filament needle-punched nonwoven geotextile, 1.5 mm thick HDPE geomembrane, 600 g / m³ 2The planting soil consists of long-filament needle-punched nonwoven geotextile, a 5 cm thick geogrid, and a 40 cm thick planting soil. 0.5-1% biochar is added to the planting soil. The biochar has a specific surface area ≥500 m² / g and a pH of 7.5-8.5. Rhododendron, Rubus, and Rosa rugosa are planted on the soil.

[0086] Monitoring after one year of operation showed that the backfill had no settlement or deformation, the fluoride concentration in the groundwater was 0.6 mg / L, and mercury and arsenic were not detected, meeting the Class III requirements of the Groundwater Quality Standard (GB / T 14848-2017). The vegetation coverage rate reached 90%.

[0087] Experimental Example 2 The surface layer of desulfurized gypsum (total fluoride 1160 mg / kg, water leaching fluoride concentration 18.9 mg / L, mercury content 1.3 mg / kg, arsenic content 0.968 mg / kg) from the power plant stockpile in Gongxian County, Sichuan Province, was selected for backfilling in the mine pit using the modified desulfurized gypsum material for mine pit backfilling prepared in Example 1 and Comparative Examples 1-3. The backfilling method was the same as in Experiment 1.

[0088] Experimental results showed that in Example 1, the fluoride leaching concentration decreased to 4.59 mg / L, and mercury and arsenic were undetectable; the 28-day compressive strength of the backfill was 1.42 MPa. In Comparative Example 1, the fluoride leaching concentration was 15.05 mg / L, and the mercury and arsenic leaching concentrations showed no significant decrease. In Comparative Example 2, the fluoride leaching concentration was 8.33 mg / L, and the mercury and arsenic leaching concentrations were 0.00057 mg / L and 0.00037 mg / L, respectively. In Comparative Example 3, the fluoride leaching concentration was 7.18 mg / L, and the mercury and arsenic leaching concentrations were 0.00023 mg / L and 0.00030 mg / L, respectively. These results indicate that the composite modified material of this invention has a significant synergistic effect on fluoride removal and heavy metal stabilization, and can effectively improve the mechanical properties of the backfill.

[0089] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A modified material for backfilling desulfurized gypsum mine pits, characterized in that, It comprises the following components by weight: 0.15-0.25 parts quicklime, 0.08-0.12 parts polyaluminum chloride, 0.03-0.08 parts functional additives, and 0.02-0.05 parts composite stabilizer. The functional additives include modified zeolite powder and hydroxyapatite, and the composite stabilizer includes magnesium sulfate and aminotrimethylenephosphonic acid.

2. The modified material for backfilling desulfurized gypsum mine pits as described in claim 1, characterized in that, It includes the following components by weight: 0.2 parts quicklime, 0.1 parts polyaluminum chloride, 0.05 parts functional additives, and 0.03 parts composite stabilizer.

3. The modified material for backfilling desulfurized gypsum mine pits as described in claim 1, characterized in that, The mass ratio of the modified zeolite powder to hydroxyapatite is 2-3:

1.

4. The modified material for backfilling desulfurized gypsum mine pits as described in claim 1, characterized in that, The mass ratio of magnesium sulfate to aminotrimethylenephosphonic acid is 1:

1.

5. The method for preparing the modified material for backfilling desulfurized gypsum mine pits according to any one of claims 1-4, characterized in that, Includes the following steps: First, quicklime, modified zeolite powder and hydroxyapatite are mixed, and then polyaluminum chloride, magnesium sulfate and aminotrimethylene phosphonic acid are added and mixed again to obtain a composite harmless modified material for desulfurized gypsum mine pit backfill.

6. The method of using the modified material for backfilling desulfurized gypsum mine pits as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. After crushing and drying the desulfurized gypsum, add it to the composite harmless modification material for backfilling the desulfurized gypsum mine pit and stir it. Then pile it up for aging to obtain the aged modified desulfurized gypsum. S2. The slope of the mine pit is repaired, and the bottom of the mine pit is laid in sequence with a compacted clay layer, a long-fiber needle-punched non-woven geotextile, a pebble drainage layer and a long-fiber needle-punched non-woven geotextile to construct a composite seepage prevention and drainage foundation. S3. The aged modified desulfurized gypsum obtained in step S1 is backfilled in layers in the pit built in step S2 and then compacted. After each layer of backfilling, a drainage ditch is set up, filled with pebbles of the same size, and perforated drainage pipes are built in. At the same time, a leachate collection system is constructed. After the backfilling is completed, long-fiber needle-punched non-woven geotextile, HDPE geomembrane, long-fiber needle-punched non-woven geotextile, geogrid and planting soil are laid in sequence, and native shallow-rooted vegetation is planted.

7. The method of using the modified material for backfilling desulfurized gypsum mine pits as described in claim 6, characterized in that, In step S1, the total fluoride content of the desulfurized gypsum is ≤1600 mg / kg, the mercury content is ≤1.6 mg / kg, and the organic matter content is 0.3-1.0%.

8. The method of using the modified material for backfilling desulfurized gypsum mine pits as described in claim 6, characterized in that, In step S1, the piling and aging time is 8-12 days, during which the mixture is turned over once every 2-3 days.

9. The method of using the modified material for backfilling desulfurized gypsum mine pits as described in claim 6, characterized in that, In step S2, the slope repair of the mine pit is carried out by using C20 concrete spraying + φ6@150×150 mm galvanized steel wire mesh + φ20@200×200 cm steel anchor rods for mesh-hanging spraying and anchoring support.

10. The method of using the modified material for backfilling desulfurized gypsum mine pits as described in claim 6, characterized in that, In step S3, biochar with a mass fraction of 0.5-1% is added to the planting soil.