Method for treating mine goaf by recycling magnesium-coal cinder solid waste

Abstract

The invention discloses a method for treating a mine goaf by recycling magnesium-coal cinder solid waste. The method comprises the following steps: 1, generating modified magnesium slag; 2, optimized magnesium slag is generated; 3, preparing a magnesium-coal cinder-based cementing material: firstly mixing the optimized magnesium slag, the coal gasification slag and the fly ash according to a pre-designed preferable proportion to prepare a waste slag mixture, then adding an activating agent, and grinding to prepare the magnesium-coal cinder-based cementing material; 4, preparing a magnesium-coal cinder-based filling material: taking any one, a mixture of two or three of coal gangue, aeolian sand and optimized magnesium slag as an aggregate, taking a magnesium-coal cinder-based cementing material as a cementing material, mixing the aggregate and the cementing material according to a pre-designed optimal proportion, and adding water to prepare the magnesium-coal cinder-based filling material; and 5, filling the mine goaf. The invention provides a solid waste treatment and goaf treatment scheme, which can effectively solve the severe problems of solid waste treatment and goaf treatment in the elm city of Shaanxi province.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of resource recycling, and particularly relates to a method for recycling magnesium-coal cinder solid waste for mine goaf treatment. BACKGROUND

[0002] Yulin City in Shaanxi Province is an important storage and development base for coal, magnesium, oil, gas and other energy sources. After energy development, production and processing, a large amount of solid waste materials (fly ash, magnesium slag, coal gangue, coal gasification slag, etc.) are produced, which has a great impact on local environmental protection. Solid waste treatment and goaf treatment have become a serious problem for the local government, as listed below:

[0003] First, for the treatment of magnesium slag, at present, most smelting plants dump magnesium slag in wasteland or deep ditch landfill treatment, which not only occupies a large amount of land resources, but also causes many environmental and health problems. In order to treat magnesium slag, many studies have proposed to use magnesium slag in the cement or concrete industry, produce wall materials and non-burning bricks and other building materials and many other applications, but most of them are still in the experimental stage, and there are still many problems such as insufficient performance, poor stability and high cost in practical application. Therefore, it is particularly important to find a reasonable and effective way to large-scale harmless treatment of magnesium slag and resource utilization. In the prior art, since the main component of magnesium slag is γ-Ca2SiO4, the hydration activity is low, and it also has swelling property, most of the applications of magnesium slag are through mixing with cement clinker or other cementitious materials, and magnesium slag is only used as a small amount, which leads to very low utilization rate of magnesium slag. Moreover, magnesium slag generally needs to be activated by rapid cooling, additives, alkali activators and crystal seed activation before application, but the above methods have very limited effect on the improvement of the hydration activity of magnesium slag, which leads to unsatisfactory performance of the magnesium slag cementitious material actually prepared, and on the contrary, it also increases a large amount of cost. At the same time, the existing magnesium slag cementitious materials all have the problems of low utilization rate, complex treatment, high cost and low strength, which affects the treatment of magnesium slag and the development and popularization of new magnesium slag cementitious materials.

[0004] Second, for the treatment of coal gasification slag, gasification slag is a waste by-product of the gasifier in the process of coal gasification to produce synthetic gas, including the bottom ash (coarse slag) and fly ash (fine slag). Coarse slag is produced at the slagging port of the gasifier, accounting for 60% to 80%; fine slag is mainly produced in the dust removal device of synthetic gas, accounting for 20% to 40%. The content of unburned carbon in coarse slag varies between 0 and 30%, while the content in fine slag is higher, usually between 10% and 30%. According to statistics, in 2016, there were about 12 million tons of fine slag and 20 million tons of coarse slag produced nationwide, with a cumulative total of more than 30 million tons (investigation data from the Yulin Municipal Science and Technology Bureau). With the rapid development of coal gasification technology, the cumulative amount of gasification slag will continue to grow rapidly. A large amount of coal gasification slag will occupy land, cause air pollution, and bring many ecological and environmental hazards. As people pay more and more attention to energy saving and environmental protection, the problem of gasification slag treatment has attracted the attention of many scholars. Gao Xuxia et al. determined the basic composition and characteristics of the gasification slag of the entrained-flow gasification process through thermogravimetric experiments and X-ray diffraction technology, and quantitatively analyzed and tested the activity of the combustible material in the slag; Matjie et al. discussed the mineral composition characteristics of the fixed-bed gasification slag; Wu et al. studied the physicochemical properties of unburned carbon in Texaco gasification slag. Research has found that gasification slag has a rich pore structure, with high specific surface area, low density, excellent heat insulation performance, and good air permeability, and has very wide application potential. Among them, Liu Dongxue et al. used the carbon in the flotation gasification slag as a raw material to prepare activated carbon; Acosta et al. controlled the loss on ignition of the gasifier slag within a certain range and mixed it with clay to prepare building bricks; Yin Hongfeng et al. successfully prepared a composite ceramic using Texaco gasification slag as a raw material in a nitrogen environment. However, all the above methods are plagued by high production costs and low operability.

[0005] Third, the empty area left after mining will cause geological disasters such as surface subsidence and mine earthquakes, and a large amount of solid waste (such as coal gangue) will be accumulated on the ground, causing serious environmental pollution in the mining area. According to statistics, the total amount of solid waste in Chinese mines has exceeded 25 billion tons, and is increasing by 600,000 tons per year. Filling mining method can effectively solve the above problems, and has the advantages of improving the recovery rate, maintaining the safety of the stope, and meeting the environmental needs. At present, cement is generally used in large quantities as a cementing material for mine filling, making the filling cost high. According to reports, the cost of cementing material accounts for about 70% to 80% of the total cost of filling. In addition, the supply of filling aggregate is insufficient and cannot meet the long-term and large-scale filling needs of the mine. High filling cost and shortage of aggregate seriously limit the application and promotion of filling technology. How to reduce the filling cost and seek abundant filling aggregate is a key problem that needs to be solved in mine filling.

[0006] Based on the above considerations, if the local characteristics of Yulin City, Shaanxi Province can be combined, a "where to go, where to go" mine filling, solid waste disposal, gob utilization organic combination of solid waste treatment and gob management scheme is provided, the bottleneck of magnesium-coal slag solid waste internal circulation and zero emission is broken through, the transformation of magnesium-coal slag solid waste to magnesium-coal slag-based new commodity is realized, and the serious problem of solid waste treatment and gob management in Yulin City, Shaanxi Province is effectively solved. SUMMARY

[0007] The technical problem to be solved by the present application is to provide a method for recycling magnesium-coal slag solid waste for mine gob management, which provides a "where to go, where to go" mine filling, solid waste disposal, gob utilization organic combination of solid waste treatment and gob management scheme, which effectively solves the serious problem of solid waste treatment and gob management in Yulin City, Shaanxi Province.

[0008] To solve the above technical problems, the technical scheme adopted by the present application is: a method for recycling magnesium-coal slag solid waste for mine gob management, characterized in that the method comprises the following steps:

[0009] Step one, producing modified magnesium slag: adding additives to the magnesium smelting pellets to produce modified magnesium smelting pellets that can stabilize β-C2S in magnesium slag, and then using the modified magnesium smelting pellets as raw materials for Pidgeon process magnesium smelting to maintain the activity and stability of magnesium slag produced by Pidgeon process magnesium smelting from the source, and to produce modified magnesium slag;

[0010] Step two, producing optimized magnesium slag: transporting the modified magnesium slag produced by magnesium smelting from the reduction workshop to the magnesium slag treatment site, placing magnesium slag of different ages into different magnesium slag piles, marking the age on the magnesium slag pile, and marking the modified magnesium slag with an age of two months or the magnesium slag after hot pouring treatment as optimized magnesium slag;

[0011] Step three, preparing magnesium-coal slag-based cementitious material: mixing the optimized magnesium slag, coal gasification slag and fly ash according to the pre-designed optimal ratio to produce a waste slag mixture, and then adding an activator to grind and produce a magnesium-coal slag-based cementitious material;

[0012] Step four, preparing magnesium-coal slag-based filling material: using any one, a mixture of two or a mixture of three of coal gangue, wind-blown sand and optimized magnesium slag as aggregate, using magnesium-coal slag-based cementitious material as cementitious material, mixing the aggregate and cementitious material according to the pre-designed optimal ratio, and adding water to produce magnesium-coal slag-based filling material;

[0013] Step five, mine gob filling: using magnesium-coal slag-based filling material for mine gob filling.

[0014] The method for recycling magnesium-coal cinder solid waste in the treatment of mined-out areas, characterized in that: the additive in the magnesium smelting pellets in step one is boron-iron alloy as the additive of the magnesium smelting pellets.

[0015] The method for recycling magnesium-coal cinder solid waste in the treatment of mined-out areas, characterized in that: in step three, when the optimized magnesium cinder, coal gasification cinder and fly ash are mixed according to the pre-designed optimal ratio to form the waste cinder mixture, the optimized magnesium cinder raw material is first pretreated by coarse crushing and fine crushing to obtain the optimized magnesium cinder material, and the coal gasification cinder is pretreated by screening, coarse crushing and fine crushing to obtain the coal gasification cinder material, and then the optimized magnesium cinder material and the coal gasification cinder material are mixed to form the waste cinder mixture; wherein the specific process of pretreating the optimized magnesium cinder raw material by coarse crushing and fine crushing to obtain the optimized magnesium cinder material is as follows:

[0016] Step 3A1, coarse crushing: the blocky optimized magnesium cinder in the optimized magnesium cinder raw material is coarsely crushed by using a jaw crusher;

[0017] Step 3A2, fine crushing: the coarsely crushed optimized magnesium cinder is finely crushed by using a roller crusher to obtain the optimized magnesium cinder material;

[0018] The specific process of pretreating the coal gasification cinder material by screening, coarse crushing and fine crushing to obtain the coal gasification cinder material is as follows:

[0019] Step 3B1, screening: the coal gasification coarse cinder is screened by a vibrating screen to obtain a pre-determined particle size meeting the requirements;

[0020] Step 3B2, coarse crushing: the screened coal gasification cinder is coarsely crushed by using a jaw crusher;

[0021] Step 3B3, fine crushing: the screened coal gasification cinder is finely crushed by using a roller crusher.

[0022] The method for recycling magnesium-coal cinder solid waste in the treatment of mined-out areas, characterized in that: the specific method for pre-determining the particle size meeting the requirements in step 3B1 is as follows:

[0023] Step 3B11, the coal gasification coarse cinder is screened by a multi-stage vibrating screen according to the mesh number, and the screening is multi-stage; the coal gasification coarse cinder is the coal gasification cinder raw material generated after the production of synthetic gas in a coal chemical enterprise;

[0024] Step 3B12, the mass and carbon content of the coal gasification coarse cinder in different particle size ranges are determined;

[0025] Step 3B13, the mass is weighted, and the formula Calculate the weighted carbon content ω of the coal gasification coarse slag, and determine the particle size range of the coal gasification coarse slag that meets the carbon content requirement according to the national standard GB / T 1596-2017 “Loss on ignition of fly ash for use in cement or concrete shall be ≤8%”, and determine the particle size that meets the requirement as the particle size that meets the requirement; wherein j is the maximum particle size corresponding to the grade that meets the carbon content requirement, i is a natural number from 1 to j, m i w is the mass of the i-th grade coal gasification coarse slag i ω is the carbon content of the i-th grade coal gasification coarse slag.

[0026] 5. The method of claim 1, wherein the step of mixing the magnesium slag, the coal gasification slag, the fly ash, and the activator is preceded by a process of pre-designing an optimal ratio of the magnesium slag, the coal gasification slag, the fly ash, and the activator, and the process comprises:

[0027] Step 3C1, selecting different weight percentages of the optimized magnesium slag, the coal gasification slag, the fly ash, and the activator within an experience formula range of the optimized magnesium slag, the coal gasification slag, the fly ash, and the activator;

[0028] Step 3C2, inputting the different weight percentages of the optimized magnesium slag, the coal gasification slag, the fly ash, and the activator in combination with different days into a pre-trained Tensorflow network for selecting an optimal ratio of cementitious materials to obtain a predicted strength of the magnesium-coal slag-based cementitious material;

[0029] Step 3C3, selecting a ratio corresponding to the highest strength at 28 days as the optimal ratio.

[0030] The method of claim 1, wherein the step of mixing the magnesium slag, the coal gasification slag, the fly ash, and the activator is preceded by a process of pre-designing an optimal ratio of the magnesium slag, the coal gasification slag, the fly ash, and the activator, and the process comprises:

[0031] Step 3D1, obtaining a predicted strength parameter of the magnesium-coal slag-based cementitious material, and the process comprises:

[0032] Step 3D11, selecting different weight percentages of the optimized magnesium slag, the coal gasification slag, the fly ash, and the activator within an experience formula range of the optimized magnesium slag, the coal gasification slag, the fly ash, and the activator;

[0033] Step 3D12, inputting the different weight percentages of the optimized magnesium slag, the coal gasification slag, the fly ash, and the activator in combination with different days into a pre-trained Tensorflow network for selecting an optimal ratio of cementitious materials to obtain a predicted strength of the magnesium-coal slag-based cementitious material;

[0034] Step 3D13, according to the formula The predicted strength of the magnesium-coal cinder-based cementing material obtained in step B12 is normalized to obtain a normalized strength value y" 1nor ; wherein y"1 is the predicted strength of different days under the proportioning of the material, miny"1 is the minimum predicted strength, and maxy"1 is the maximum predicted strength.

[0035] Step 3D2, obtaining the economic index parameter of the magnesium-coal cinder-based cementing material, the specific process is:

[0036] Step 3D21, setting the unit prices of the optimized magnesium slag, coal gasification slag, fly ash and activator as a"1, a"2, a"3 and a"4 respectively, and constructing an economic index function y"2 = a"1x"1 + a"2x"2 + a"3x"3 + a"4x"4; wherein y"2 is the economic index, x"1 is a coefficient related to the content of the optimized magnesium slag and x"1 e (0.05, 0.3), x"2 is a coefficient related to the content of the coal gasification slag and x"2 e (0.6, 0.9), x"3 is a coefficient related to the content of the fly ash and x"3 e (0.05, 0.3), and x"4 is a coefficient related to the content of the activator and x"4 e (0, 0.15);

[0037] Step 3D22, according to the economic index function y"2 = a"1x"1 + a"2x"2 + a"3x"3 + a"4x"4, and the values of x"1, x"2, x"3 and x"4, the maximum value maxy"2 of the economic index and the minimum value miny"2 of the economic index are solved;

[0038] Step 3D23, according to the formula The economic index obtained in step B22 is normalized to obtain a normalized economic index y" 2nor ;

[0039] Step 3D3, according to the normalized strength value y" 1nor and the normalized economic index y" 2nor , the target function for determining the preferred proportioning according to strength and economy is The proportioning corresponding to the maximum value of the target function y" is determined as the preferred proportioning; wherein a"1 is the weight coefficient of strength, a"2 is the weight coefficient of economy, TH"1 is the minimum standard strength value of strength, and TH"2 is the highest acceptable price threshold in the economic index.

[0040] The above-mentioned method for recycling magnesium-coal cinder solid waste in the treatment of mine goaf, characterized in that: the training process of the Tensorflow network for selecting the preferred proportioning of the cementing material is:

[0041] Step 3E1, a four-layer Tensorflow network is established, the input layer has 5 nodes, the middle two layers each have 5 nodes, and the output layer has 1 node; wherein the 5 nodes of the input layer are the content of the optimized magnesium slag, the content of the coal gasification slag, the content of the fly ash, the content of the activator and the number of days; the 1 node of the output layer is the predicted strength;

[0042] Step 3E2, obtain the strength of the different weight percentages of the optimized magnesium slag, the coal gasification slag, the fly ash and the activator at different days obtained by multiple experiments as sample data;

[0043] Step 3E3, normalize the number of days in the sample data;

[0044] Step 3E4, using the normalized sample data, the Tensorflow network established in step 3E1 is trained, and multiple iterations are performed to obtain the trained Tensorflow network for selecting the optimal ratio of cementitious materials.

[0045] The above-mentioned method for recycling magnesium-coal slag solid waste in the treatment of mine goaf, characterized in that: the design method of the optimal ratio of the aggregate and the cementitious material in step four is:

[0046] Step 4A1, select different weight percentages of aggregate and cementitious material within the range of the empirical formula of the aggregate and the cementitious material;

[0047] Step 4A2, input the different weight percentages of the aggregate and the cementitious material combined with different days into the pre-trained Tensorflow network for selecting the optimal ratio of the filling material to obtain the predicted strength of the magnesium-coal slag-based filling material;

[0048] Step 4A3, select the ratio corresponding to the highest strength of 28 days as the optimal ratio.

[0049] The method for recycling magnesium-coal cinder solid waste in the treatment of mined-out areas according to the above, characterized in that: in step four, the preparation of the magnesium-coal cinder-based filling material is carried out by using a magnesium-coal cinder-based filling material preparation system, which comprises an aggregate bin for placing aggregate, a cementitious material bin for placing cementitious material, and a water pool for storing water, as well as a stirrer and a material controller for controlling the preparation; the discharge port of the aggregate bin is connected with the aggregate inlet of the stirrer through an aggregate conveying pipeline and an aggregate conveying pump arranged on the aggregate conveying pipeline; the discharge port of the cementitious material bin is connected with the cementitious material inlet of the stirrer through a cementitious material conveying pipeline and a cementitious material conveying pump arranged on the cementitious material conveying pipeline; the water outlet of the water pool is connected with the water inlet of the stirrer through a water conveying pipeline, a flow meter and a water pump arranged on the water conveying pipeline; the discharge port of the aggregate bin is connected with an aggregate discharge electromagnetic valve and an aggregate weighing sensor; the discharge port of the cementitious material bin is connected with a cementitious material discharge electromagnetic valve and a cementitious material weighing sensor; the stirrer, the aggregate conveying pump, the cementitious material conveying pump, the water pump, the aggregate discharge electromagnetic valve and the cementitious material discharge electromagnetic valve are connected with the output end of the material controller; the aggregate weighing sensor, the cementitious material weighing sensor and the flow meter are connected with the input end of the material controller; the input end of the material controller is also connected with a start-stop switch.

[0050] The specific process for preparing the magnesium-coal cinder-based filling material in step four is as follows:

[0051] Step 401: Place any one, a mixture of two, or a mixture of all three of coal gangue, wind-blown sand and optimized magnesium cinder as aggregate into the aggregate bin.

[0052] Step 402: Place magnesium-coal cinder-based cementitious material as cementitious material into the cementitious material bin.

[0053] Step 403: Start the start-stop switch, and the material controller controls the aggregate discharge electromagnetic valve and the cementitious material discharge electromagnetic valve to open, and controls the stirrer, the aggregate conveying pump, the cementitious material conveying pump and the water pump to start; under the power action of the aggregate conveying pump, the aggregate in the aggregate bin enters the stirrer through the aggregate conveying pipeline; under the power action of the cementitious material conveying pump, the cementitious material in the cementitious material bin enters the stirrer through the cementitious material conveying pipeline; under the power action of the water pump, the water in the water pool enters the stirrer through the water conveying pipeline; the stirrer stirs the aggregate, the cementitious material and the water uniformly to prepare the magnesium-coal cinder-based filling material.

[0054] In the process of preparing the magnesium-coal cinder-based filling material above, the aggregate weighing sensor weighs the weight of the aggregate entering the stirrer and outputs to the material preparation controller; the cementing material weighing sensor weighs the weight of the cementing material entering the stirrer and outputs to the material preparation controller; the flow meter detects the flow of water entering the stirrer and outputs to the material preparation controller; the material preparation controller controls the aggregate discharge electromagnetic valve, the cementing material discharge electromagnetic valve, the aggregate conveying pump, the cementing material conveying pump and the water pump according to the data received thereby, so that the aggregate and the cementing material are mixed according to the preferred ratio designed in advance to prepare the magnesium-coal cinder-based filling material.

[0055] The method for recycling magnesium-coal cinder solid waste in the treatment of mined-out areas of mines has the characteristics that an additive adding port for adding other additives is arranged on the stirrer.

[0056] Compared with the prior art, the present application has the following advantages:

[0057] 1. The method for producing modified magnesium slag of the present application uses a new Pidgeon process magnesium smelting pellet with boron iron as an additive, and does not need to make any major adjustments and changes to the original production process and equipment, and is very convenient to implement.

[0058] 2. The present application uses boron iron alloy (i.e., boron iron) as an additive for magnesium smelting pellets. Boron iron is very brittle and can be easily ground with other raw materials of the pellet through a 100-mesh screen. The boron iron will not oxidize during fine grinding. In addition, boron iron has strong thermal conductivity, which can improve the thermal conductivity of the pellet, accelerate the heating speed of the magnesium smelting pellet and the speed of the reduction reaction inside the pellet. In addition, the C, Si and Al elements in boron iron can participate in the reduction reaction of magnesium oxide, which helps to improve the yield of metallic magnesium. Boron iron does not contain any oxide impurities and crystal water that are harmful to Pidgeon magnesium smelting, and will not have any adverse effects on magnesium smelting. It can also improve the reduction rate of MgO and the utilization rate of Si, which helps to reduce the cost and improve the efficiency of Pidgeon magnesium production, and save energy and reduce emissions.

[0059] 3. In this invention, magnesium slag is smelted using magnesium pellets that stabilize β-C2S in magnesium slag. After the magnesium smelting process, air can enter the reduction tank immediately upon opening the lid. The pellets, after magnesium oxide reduction, contain numerous micropores, allowing air to easily enter. At approximately 1000°C, the oxygen in the air rapidly oxidizes the boron in the ferroboron within the pellets. Boron is highly reactive at high temperatures, and the resulting B2O3 is also highly active. It quickly enters the nearby dicalcium orthosilicate lattice and stabilizes the high-temperature β-C2S through a chemical reaction, preventing its transformation into γ-C2S during cooling. This makes β-C2S the room-temperature main crystalline phase within the pellets, optimizing the magnesium slag into a volume-stable (non-pulverizing) and highly reactive building material. Modified magnesium slag with these excellent physicochemical properties is easy to transport and homogenize, enabling its widespread application in cement or concrete. This is highly beneficial for energy conservation, emission reduction, and sustainable development for magnesium metal and building material production enterprises.

[0060] 4. The ferroborone alloy additive used in this invention can initiate a series of chemical reactions to optimize magnesium slag as soon as air enters the reduction tank after magnesium smelting, including the oxidation of boron to generate B2O3 and the stabilization of β-C2S by B2O3. Under a high temperature of around 1000℃ and an air atmosphere, all these chemical reactions proceed spontaneously and rapidly within the magnesium slag pellets after production. Before, during, and after these chemical reactions, normal production operations after opening the reduction tank, including removing the potassium and sodium traps, magnesium crystallizer, and heat insulation plates, shoveling magnesium slag into the slag hopper for cooling, and adding the next batch of magnesium pellets, can be carried out without any disruption.

[0061] 5. This invention proposes a method for preparing modified magnesium slag and optimized magnesium slag. The optimized magnesium slag is used to prepare magnesium-coal slag-based cementitious materials. By utilizing the mutual excitation effect between fly ash, coal gasification slag and optimized magnesium slag, the hidden dangers of cracking, spalling and significant reduction in strength of the solidified body caused by the separate mixing of magnesium slag are solved. It can completely replace high-cost cement, greatly reduce the cost of cementitious materials, and thus reduce the cost of filling materials.

[0062] 6. This invention fully considers the local characteristics of Yulin City, Shaanxi Province, and can effectively utilize the magnesium slag, fly ash, coal gasification slag and coal gangue produced in the area. It can also achieve the treatment of mining subsidence areas in the area, realize the use of local materials, which is very convenient and avoids the pollution of the environment by a large amount of solid waste.

[0063] 7、The present application takes industrial solid waste as the main material, adopts a non-toxic and harmless common cheap chemical reagent as the activator, and the addition amount is very small, the magnesium-coal cinder-based cementing material is low in cost, can greatly reduce the cost by replacing cement, simultaneously provides a new utilization way for the solid waste disposal of the two pillar industries of coal chemical industry and magnesium smelting, can be used for mine goaf filling, has a good effect on the treatment of mine goaf, provides a solid waste treatment and mine goaf treatment scheme of organic combination of "from where to where" mine filling, solid waste disposal and goaf utilization, breaks the bottleneck of magnesium-coal cinder solid waste internal circulation and zero emission, realizes the transformation of magnesium-coal cinder solid waste into magnesium-coal cinder-based new commodities, and effectively solves the serious problem of solid waste treatment and goaf treatment in Yulin City, Shaanxi Province.

[0064] The technical scheme of the present application will be further described in detail below with reference to the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0065] Figure 1 The method flow chart of the method for recycling magnesium-coal cinder solid waste for mine goaf treatment in example 1 and example 2 of the present application;

[0066] Figure 2 The principle diagram of preparing the magnesium-coal cinder-based filling material in example 1 and example 2 of the present application;

[0067] Figure 3 The macroscopic photo of the magnesium cinder sample generated in comparative experiment 1;

[0068] Figure 4 The macroscopic photo of the magnesium cinder sample generated in experiment 1 of the present application;

[0069] Figure 5 The XRD diffraction spectrum of the magnesium cinder sample generated in experiment 1 and comparative experiment 1 of the present application;

[0070] Figure 6 The column chart of the compressive strength values of the magnesium cinder cement prepared from the magnesium cinder obtained in experiment 1 of the present application and the magnesium cinder cement prepared from the magnesium cinder obtained in comparative experiment 1;

[0071] Figure 7 The principle diagram of the magnesium-coal cinder-based filling material preparation system of the present application.

[0072] EXPLANATION OF REFERENCE NUMERALS:

[0073] 1 - aggregate bin; 2 - cementing material bin; 3 - water pool;

[0074] 4 - stirrer; 5 - material preparation controller; 6 - aggregate conveying pipeline;

[0075] 7 - aggregate conveying pump; 8 - cementing material conveying pipeline; 9 - cementing material conveying pump;

[0076] 10 - water delivery pipe; 11 - flow meter; 12 - water pump;

[0077] 13 - aggregate feeding electromagnetic valve; 14 - cementitious material feeding electromagnetic valve; 15 - start-stop switch;

[0078] 16 - aggregate weighing sensor; 17 - cementitious material weighing sensor; 18 - additive adding port. DETAILED DESCRIPTION

[0079] Example 1

[0080] As shown in Figure 1 and Figure 2 , the method for recycling magnesium-coal cinder solid waste for goaf treatment of the embodiment is characterized in that the method comprises the following steps:

[0081] Step one, generating modified magnesium slag: adding an additive to the magnesium smelting pellet to make a modified magnesium smelting pellet capable of stabilizing β-C2S in the magnesium slag, and then using the modified magnesium smelting pellet as a raw material for the Pidgeon process for smelting magnesium, thereby keeping the activity and stability of the magnesium slag generated by the Pidgeon process for smelting magnesium from the source, and generating modified magnesium slag;

[0082] Step two, generating optimized magnesium slag: transporting the modified magnesium slag generated by smelting magnesium from the reduction workshop to the magnesium slag treatment site, placing magnesium slags of different ages into different magnesium slag piles, marking the age on the magnesium slag pile, and marking the modified magnesium slag with an age of two months or the magnesium slag after hot pouring treatment as optimized magnesium slag;

[0083] Generally, 5% or more free MgO remains in the modified magnesium slag. Since the hydration of free MgO in the modified magnesium slag is slow, if the modified magnesium slag is directly used for preparing magnesium-coal cinder-based cementitious material without treatment, after the construction of the cemented filling body, with the slow hydration of MgO, Mg(OH)2 is generated, the volume expands, causing cracking, falling, etc. of the cemented filling body, the strength of the cemented filling body is significantly reduced, and potential production safety hazards exist. By naturally aging or hot pouring treatment of the modified magnesium slag to form optimized magnesium slag, and then preparing magnesium-coal cinder-based cementitious material from the optimized magnesium slag, the above problems can be effectively avoided.

[0084] Step three, preparing magnesium-coal cinder-based cementitious material: according to the pre-designed optimal ratio, first mix the optimized magnesium slag, coal gasification slag and fly ash to make a waste slag mixture, and then add an activator to grind to make a magnesium-coal cinder-based cementitious material;

[0085] Step four, preparation of magnesium-coal cinder-based filling material: taking any one, two kinds of mixture or three kinds of mixture of the optimized magnesium cinder, coal gangue and wind-blown sand as aggregate, taking magnesium-coal cinder-based cementing material as cementing material, mixing the aggregate and cementing material according to the pre-designed preferred ratio, and adding water to prepare the magnesium-coal cinder-based filling material;

[0086] In addition, in specific implementation, other components of aggregate or other additives can also be added according to actual needs, which are not limited herein.

[0087] Step five, mine goaf filling: using the magnesium-coal cinder-based filling material to fill the mine goaf.

[0088] In the embodiment, the activator is a combination of one or more of gypsum, anhydrous sodium sulfate, calcium hydroxide, lime, soda, baking soda, heavy calcium, sodium silicate, polyhalite, sodium chloride and caustic soda; the gypsum is natural gypsum, phosphogypsum, fluorogypsum or industrial desulfurization gypsum.

[0089] In the embodiment, the additive added in the magnesium smelting pellets in step one is boron-iron alloy as the additive of the magnesium smelting pellets.

[0090] In specific implementation, the weight percentage of each raw material in the modified magnesium smelting pellets is as follows: calcined white 81% to 82.8%, silicon iron 15% to 16.6%, fluorite 1.25% to 2.71%, and boron-iron alloy 0.23% to 0.29%; the weight percentage of each element in the boron-iron alloy is as follows: B 16% to 20.5%, C 0.5% to 1.0%, Si 1.5% to 2.5%, Al 0.05% to 0.5%, and the balance is Fe. The mass percentage of S in the boron-iron alloy is less than 0.01%, the mass percentage of P is less than 0.1%, and the particle size of the boron-iron alloy is not greater than 5 mm.

[0091] The method for producing modified magnesium cinder by using the modified magnesium smelting pellets to smelt crude magnesium ingots is as follows:

[0092] Step 1A1, according to the weight percentage of each raw material in the modified magnesium smelting pellets, the raw materials are sent into a mill for mixing and fine grinding, and then the undersize material is pressed through a 100-mesh screen to obtain the modified magnesium smelting pellets;

[0093] Step 1A2, the modified magnesium smelting pellets in step 1A1 are loaded into a reduction pot, and reduced at a vacuum degree of 5 Pa to 10 Pa and a temperature of 1200℃ to 1220℃ for 7 h to 8 h. After reduction, the crude magnesium ingots are taken out of the pot, and the magnesium cinder in the reduction pot is scraped out to obtain block-shaped modified magnesium cinder.

[0094] In order to verify the performance of the modified magnesium cinder, the following experiments 1 to 4 are performed:

[0095] Experiment 1

[0096] The weight percentage of each raw material in the modified magnesium smelting pellets of this experiment is as follows: calcined white (molar ratio of CaO / MgO close to 1) 81%, ferrosilicon (containing Si about 75%) 16.5%, fluorite (CaF2 content in fluorite not less than 95%) 2.25%, boron iron alloy 0.25%; the weight percentage of each element in the boron iron alloy is as follows: B 20%, C 0.5%, Si 1.5%, Al 0.5%, S <0.01%, P <0.1%, and the balance is Fe; the particle size of the boron iron alloy is not greater than 5 mm. (The boron iron of FeB20C0.5B grade can be selected according to GB / T 5682-2015.)

[0097] The method for producing modified magnesium slag by smelting crude magnesium ingot with the modified magnesium smelting pellets of this experiment includes the following steps:

[0098] Step D1, according to the weight percentage of each raw material in the modified magnesium smelting pellets, the raw materials are sent into the mill for uniform mixing and fine grinding, then the undersize is added to the pellet press through a 100 mesh screen, and the modified magnesium smelting pellets which can stabilize β-C2S in magnesium slag are obtained by pressing;

[0099] Step D2, the modified magnesium smelting pellets in step D1 are loaded into a reduction pot, and reduced under the conditions of a vacuum degree of 8 Pa and a temperature of 1210℃ for 7h. After reduction, the potassium and sodium traps and magnesium crystallizers are taken out of the pot, the crude magnesium ingot is taken out of the magnesium crystallizer, and the magnesium slag in the reduction pot is scraped out. The magnesium slag scraped out is cooled to room temperature in the magnesium slag hopper to obtain the blocky modified magnesium slag after activity and stability maintenance treatment. After opening the lid of the reduction pot, air enters the pot, and there are many micropores in the pellets after reduction. Oxygen in the air can immediately enter the pellets through the micropores and oxidize boron in the boron iron to B2O3 at a high temperature of about 1000℃. The B2O3 generated by oxidation is very active at high temperature and can quickly contact the nearby dicalcium silicate and enter its crystal lattice, then stabilize β-C2S through chemical reaction, so that β-C2S becomes the main crystal phase at room temperature and exists in the waste pellets after magnesium smelting. Since the chemical reaction of oxidation of boron to B2O3 and stabilization of β-C2S by B2O3 only occurs inside the waste magnesium smelting pellets, all production operations after opening the reduction pot, including taking out the potassium and sodium traps, magnesium crystallizers, heat insulation plates, and scraping out the magnesium slag, can be carried out normally without being affected.

[0100] Comparative Experiment 1

[0101] The traditional Pidgeon process was used in the comparative experiment. The weight percentage of each raw material in the pellets is as follows: white calcium (molar ratio of CaO / MgO close to 1) 81%, ferrosilicon (containing Si about 75%) 16.5%, and fluorite (CaF2 content in fluorite not less than 95%) 2.5%. The crude magnesium ingot was prepared according to the magnesium smelting method of experiment 1, and the magnesium slag was scraped out from the reduction pot and cooled to room temperature in the magnesium slag bucket.

[0102] After the magnesium slag was scraped out and cooled to room temperature, it was observed that the magnesium slag of comparative experiment 1 was mostly pulverized, as shown in Figure 3 . The magnesium slag of experiment 1 was in block shape, and the size of most of the magnesium slag was close to the size of the pellets before magnesium smelting, as shown in Figure 4 . The magnesium slag samples produced by the two groups of pellets in experiment 1 and comparative experiment 1 were taken for XRD analysis, and the results are shown in Figure 5 . From Figure 5 (b) PMS spectrum, it can be seen that the main mineral phase in the magnesium slag produced by comparative experiment 1 is γ-C2S. This analysis result confirms that the volume expansion caused by the β-γ phase transformation of C2S (dicalcium silicate) is the main reason for the pulverization of the magnesium slag shown in Figure 1 . From Figure 5 (a) MMS spectrum, it can be seen that the main mineral phase in the magnesium slag produced by experiment 1 is β-C2S. Such magnesium slag is not pulverized and basically maintains the original block shape (see Figure 4 ), so it will not produce dust pollution in the process of transportation and homogenization. The use of β-C2S as the main mineral phase at room temperature also greatly improves the activity of the magnesium slag. Such modified and optimized magnesium slag can be widely used in cement or concrete, thereby effectively promoting the energy saving and emission reduction and sustainable development of metal magnesium and building material production enterprises.

[0103] According to the standard method in GB75-2007, the stability and compressive strength values at different ages of the magnesium slag cement prepared from the magnesium slag obtained by experiment 1 of the present application and the magnesium slag cement prepared from the magnesium slag obtained by comparative experiment 1 were measured. The weight percentage of cement and magnesium slag in the magnesium slag cement is 65% of cement and 35% of magnesium slag. The stability experiments of the two kinds of magnesium slag cement were both qualified using the test cake method. The results of the compressive strength experiment are shown in Figure 6 . The figure shows that the 3-day compressive strength values of the two groups of magnesium slag cement are basically the same, and the 28-90-day compressive strength of the magnesium slag cement of experiment 1 is higher than that of the magnesium slag cement of comparative experiment 1, especially at the ages of 60 and 90 days. The compressive strength value of the magnesium slag cement of experiment 1 is greatly improved compared with that of the magnesium slag cement of comparative experiment 1, which confirms that the magnesium smelting pellets with added boron iron can produce modified magnesium slag with high activity as a high-quality admixture for preparing magnesium-coal cinder-based cementitious materials.

[0104] Experiment 2

[0105] The weight percentage of each raw material in the modified magnesium smelting pellets of the experiment is as follows: calcined white (the molar ratio of CaO / MgO is close to 1) 81.2%, ferrosilicon (containing Si about 75%) 16.6%, fluorite (the content of CaF2 in fluorite is not less than 95%) 1.94%, boron iron alloy 0.26%; the weight percentage of each element in the boron iron alloy is as follows: B 18%, C 0.5%, Si 1.5%, Al 0.5%, S <0.01%, P <0.1%, and the balance is Fe; the particle size of the boron iron alloy is not greater than 5 mm. (The boron iron with the FeB20C0.5B brand can be selected according to GB / T 5682-2015.)

[0106] The method for producing modified magnesium slag by smelting crude magnesium ingot with the modified magnesium smelting pellets of the experiment comprises the following steps:

[0107] Step D1, according to the weight percentage of each raw material in the modified magnesium smelting pellets, the raw materials are sent into the mill for mixing and fine grinding, then the undersize material is added into the pellet press through a 100 mesh screen, and the modified magnesium smelting pellets which can stabilize β-C2S in magnesium slag are obtained by pressing;

[0108] Step D2, the modified magnesium smelting pellets in step D1 are loaded into a reduction pot, and reduced under the conditions of a vacuum degree of 10 Pa and a temperature of 1200℃ for 8h. After the reduction is completed, the potassium-sodium trap and the magnesium crystallizer are taken out of the pot, the crude magnesium ingot is taken out of the magnesium crystallizer, and the magnesium slag in the reduction pot is scraped out. The magnesium slag scraped out is cooled to room temperature in the magnesium slag hopper to obtain the blocky modified magnesium slag after the activity and stability maintaining treatment. After the cover of the reduction pot is opened, air enters the pot. There are many micropores in the smelting pellets after reduction, and the oxygen in the air can immediately enter the pellets through the micropores to oxidize the boron element in the boron iron into B2O3 at a high temperature of about 1000℃. The generated B2O3 is very active at high temperature and can quickly contact the nearby dicalcium silicate and enter its crystal lattice, then stabilize β-C2S through chemical reaction, so that β-C2S becomes the main crystal phase at room temperature and exists in the waste smelting pellets after magnesium smelting. Since the chemical reaction of the oxidation of boron element into B2O3 and the stabilization of β-C2S by B2O3 only occurs inside the waste magnesium smelting pellets, all production operations after the reduction pot is opened, including the removal of the potassium-sodium trap, the magnesium crystallizer, the heat insulation plate and the magnesium slag, can be normally carried out without any influence.

[0109] Comparative Experiment 2

[0110] The weight percentages of each raw material in the magnesium pellets used in this comparative experiment are as follows: calcined white (caO / MgO molar ratio close to 1) 81.2%, ferrosilicon (containing about 75% Si) 16.6%, fluorite (containing no less than 95% CaF2) 0.5%, and anhydrous sodium tetraborate (Na2B4O7) 1.7%. Crude magnesium ingots were prepared according to the magnesium smelting method in Experiment 2, and magnesium slag was removed and cooled to room temperature in a magnesium slag hopper.

[0111] Experiment 3

[0112] The weight percentages of each raw material in the modified magnesium pellets of this experiment are as follows: calcined white metal (CaO / MgO molar ratio close to 1) 82%, ferrosilicon (Si content approximately 75%) 15%, fluorite (CaF2 content in fluorite not less than 95%) 2.71%, and ferroboron alloy 0.29%. The weight percentages of each element in the ferroboron alloy are as follows: B 16%, C 1.0%, Si 2.5%, Al 0.5%, S < 0.01%, P < 0.1%, with the balance being Fe. The particle size of the ferroboron alloy is not greater than 5 mm. (FeB16C1.0 grade ferroboron can be selected according to GB / T 5682-2015.)

[0113] The method for producing modified magnesium slag by refining crude magnesium ingots using modified magnesium pellets in this experiment includes the following steps:

[0114] Step D1: According to the weight percentage of each raw material in the modified magnesium smelting pellets, feed the raw materials into the mill for mixing and fine grinding, then pass them through a 100-mesh sieve, add the sieve material to the briquetting machine, and press them to obtain modified magnesium smelting pellets that can stabilize β-C2S in magnesium slag.

[0115] Step D2, the modified magnesium smelting pellets in step D1 are loaded into a reduction pot, and reduced for 7.5 h under the condition of a vacuum degree of 9 Pa and a temperature of 1215 ℃. After the reduction is completed, the potassium-sodium trap and the magnesium crystallizer are taken out of the reduction pot, and the crude magnesium ingot is taken out of the magnesium crystallizer. The magnesium slag in the reduction pot is scraped out and cooled to room temperature in the magnesium slag hopper to obtain the modified magnesium slag after the activity and stability maintaining treatment; after the cover of the reduction pot is opened, air enters the pot. There are many micropores in the pellets after reduction, and oxygen in the air can immediately enter the pellets through the micropores to oxidize the boron element in the boron iron into B2O3 at a high temperature of about 1000 ℃. The generated B2O3 is very active at high temperature and can quickly contact the nearby dicalcium silicate and enter its crystal lattice, and then stabilize the β-C2S through a chemical reaction, so that the β-C2S cannot be converted into γ-C2S in the process of cooling down, so that the β-C2S becomes the main crystal phase at room temperature and exists in the waste magnesium smelting pellets. Since the chemical reaction of the oxidation of the boron element into B2O3 and the stabilization of the β-C2S by B2O3 only occurs inside the waste magnesium smelting pellets, all production operations after the reduction pot is opened, including the taking out of the potassium-sodium trap, the magnesium crystallizer, the heat insulation plate and the scraping out of the magnesium slag, can be normally carried out without any influence.

[0116] Comparative Experiment 3

[0117] The weight percentage of each raw material in the magnesium smelting pellets used in this comparative experiment is as follows: calcined white (the molar ratio of CaO / MgO is close to 1) 82%, silicon iron (containing Si about 75%) 15%, fluorite (the content of CaF2 in fluorite is not less than 95%) 1.1%, and sodium borate (Na2B4O7) 1.9%. The crude magnesium ingot is prepared according to the magnesium smelting method of experiment 3, and the magnesium slag is scraped out and cooled to room temperature in the magnesium slag hopper.

[0118] Experiment 4

[0119] The weight percentage of each raw material in the modified magnesium smelting pellets of this experiment is as follows: calcined white (the molar ratio of CaO / MgO is close to 1) 82.8%, silicon iron (containing Si about 75%) 15.72%, fluorite (the content of CaF2 in fluorite is not less than 95%) 1.25%, and boron iron alloy 0.23%. The weight percentage of each element in the boron iron alloy is as follows: B 20.5%, C 0.5%, Si 1.5%, Al 0.05%, S <0.01%, P <0.1%, and the balance is Fe. The particle size of the boron iron alloy is not greater than 5 mm. (The boron iron with the brand FeB20C0.5A can be selected according to GB / T 5682-2015.)

[0120] The method for smelting the crude magnesium ingot by using the modified magnesium smelting pellets of this experiment to produce the modified magnesium slag, comprising the following steps:

[0121] Step Dl, the raw materials are mixed and finely ground in a mill according to the weight percentage of each raw material in the modified magnesium refining pellet, and then the undersize is added to a pellet press through a 100 mesh screen to obtain the modified magnesium refining pellet which can stabilize β-C2S in magnesium slag by pressing;

[0122] Step D2, the modified magnesium refining pellet in Step Dl is loaded into a reduction pot, and reduced at a vacuum degree of 5 Pa and a temperature of 1220°C for 7.9 h. After reduction, the potassium and sodium trap and the magnesium crystallizer are taken out of the pot, the crude magnesium ingot is taken out of the magnesium crystallizer, and the magnesium slag in the reduction pot is scraped out. The magnesium slag scraped out is cooled to room temperature in the magnesium slag hopper to obtain the blocky modified magnesium slag after the activity and stability maintaining treatment. After the pot cover is opened, air enters the pot, and the oxidized boron element in the boro-iron in the pellet at a high temperature of about 1000°C is immediately oxidized to B2O3 through the micropores in the pellet. The oxidized B2O3 is very active at high temperature, can quickly contact the nearby dicalcium silicate, and enter the crystal lattice of the dicalcium silicate, and then stabilize the β-C2S through a chemical reaction so that it cannot be converted into γ-C2S in the process of cooling down. Thus, the β-C2S becomes the main crystal phase at room temperature and exists in the waste pellet after magnesium refining. Since the chemical reaction of the oxidation of the boron element into B2O3 and the stabilization of the β-C2S by B2O3 only occurs inside the waste magnesium refining pellet, all the production operations after the pot is opened, including the removal of the potassium and sodium trap, the magnesium crystallizer, the heat insulation plate, and the scraping of the magnesium slag, can be normally performed without any influence.

[0123] The magnesium slag in the modified magnesium refining pellet of the present application and the magnesium slag obtained after the pellet in Comparative Experiment 1-3 is refined into magnesium are measured for the ratio of the material to magnesium (material / magnesium ratio = weight of the magnesium refining pellet / weight of the obtained crude magnesium), and the magnesium slag obtained in Experiment 1-3 and Comparative Experiment 1-3 is chemically analyzed to obtain the analysis value of the magnesium oxide content in the magnesium slag sample. The results are shown in Table 1. (The values of the parameters used for comparison in the following discussion are the average values of more than three measured or analyzed values under the same conditions.)

[0124] Table 1: Material / magnesium ratio and analysis value of MgO in magnesium slag sample (%)

[0125] Magnesium smelting pellets Magnesium to charge ratio MgO % in magnesium slag Additives to magnesium smelting pellets Experiment 1 5.92 5.21 Boron iron gold content Comparative Experiment 1 6.23 7.06 None Experiment 2 6.05 5.93 Boron iron gold content Comparative Experiment 2 6.31 6.51 Anhydrous sodium tetraborate Experiment 3 6.12 5.65 Boron iron gold content Comparative Experiment 3 6.28 6.83 Boric acid

[0126] From the table, it can be seen that the material-magnesium ratios of the three experimental modified magnesium smelting pellets (5.92-6.12) are lower than the material-magnesium ratios (6.23-6.31) obtained after smelting the comparative experiment pellets. The magnesia content in the magnesium slag samples discharged from the pellets smelting of experiments 1-3 (5.21%-5.92%) is also relatively low. The comparison of these parameters shows that, compared with other additives containing impurities Na2O and crystal water harmful to the Pidgeon process for smelting magnesium, the boron-iron used as an additive for smelting magnesium pellets can obtain a higher MgO reduction rate and Si utilization rate, thus helping to reduce costs, improve efficiency, and save energy and reduce emissions in the Pidgeon process for smelting magnesium; moreover, the block-shaped modified magnesium slag obtained after the activity and stability of the magnesium slag produced in the Pidgeon process for smelting magnesium are maintained can be better used to prepare magnesium-coal slag-based cementitious materials.

[0127] In this embodiment, when the optimized magnesium slag, coal gasification slag and fly ash are mixed according to the pre-designed preferred ratio to prepare the waste slag mixture in step three, the optimized magnesium slag raw material is first pretreated by coarse crushing and fine crushing to obtain the optimized magnesium slag material, and the coal gasification slag is pretreated by screening, coarse crushing and fine crushing to obtain the coal gasification slag material, and then the optimized magnesium slag material and the coal gasification slag material are mixed to prepare the waste slag mixture; wherein the specific process of pretreating the optimized magnesium slag raw material by coarse crushing and fine crushing to obtain the optimized magnesium slag material is as follows:

[0128] Step 3A1, coarse crushing: using a jaw crusher to coarsely crush the block-shaped optimized magnesium slag in the optimized magnesium slag raw material;

[0129] Step 3A2, fine crushing: using a roller crusher to finely crush the coarsely crushed optimized magnesium slag to obtain the optimized magnesium slag material;

[0130] In specific implementation, the selection of the crusher is not limited to the above two types, and factors such as particle size, strength, grindability index, humidity and viscosity of the raw material should be considered to select a suitable crusher.

[0131] The specific process of pretreating the coal gasification slag material by screening, coarse crushing and fine crushing to obtain the coal gasification slag material is as follows:

[0132] Step 3B1, screening: screening the coal gasification coarse slag with a vibrating screen to obtain a pre-determined particle size meeting the requirements;

[0133] In this embodiment, the specific method for pre-determining the particle size meeting the requirements in step 3B1 is as follows:

[0134] Step 3B11, screening the coal gasification coarse slag by mesh number using a multi-stage vibrating screen; the screening is multi-stage; the coal gasification coarse slag is the coal gasification slag raw slag produced after the production of synthesis gas in a coal chemical enterprise;

[0135] In the embodiment, the coal gasification coarse slag is screened according to mesh size by using multi-stage vibrating screen, and the screening is divided into 10 stages, i.e., less than 8 mesh, 8 mesh-10 mesh, 10 mesh-14 mesh, 14 mesh-18 mesh, 18 mesh-24 mesh, 24 mesh-35 mesh, 35 mesh-50 mesh, 50 mesh-120 mesh, 120 mesh-200 mesh, and more than 200 mesh;

[0136] Step 3B12, measuring the mass and carbon content of the coal gasification coarse slag in different particle size ranges;

[0137] In the embodiment, the mass of the coal gasification coarse slag less than 8 mesh is m1 (m1 = 253.1 g) and the carbon content is w1 (w1 = 0.37%) based on the total sample amount of 1000 g; the mass of the coal gasification coarse slag of 8 mesh-10 mesh is m2 (m2 = 39.6 g) and the carbon content is w2 (w2 = 0.81%); the mass of the coal gasification coarse slag of 10 mesh-14 mesh is m3 (m3 = 82.5 g) and the carbon content is w3 (w3 = 2.18%); the mass of the coal gasification coarse slag of 14 mesh-18 mesh is m4 (m4 = 46.8 g) and the carbon content is w4 (w4 = 6.25%); the mass of the coal gasification coarse slag of 18 mesh-24 mesh is m5 (m5 = 96.4 g) and the carbon content is w5 (w5 = 12.88%); the mass of the coal gasification coarse slag of 24 mesh-35 mesh is m6 (m6 = 147.4 g) and the carbon content is w6 (w6 = 26.49%); the mass of the coal gasification coarse slag of 35 mesh-50 mesh is m7 (m7 = 164.2 g) and the carbon content is w7 (w7 = 24.48%); the mass of the coal gasification coarse slag of 50 mesh-120 mesh is m8 (m8 = 113.9 g) and the carbon content is w8 (w8 = 34.46%); the mass of the coal gasification coarse slag of 120 mesh-200 mesh is m9 (m9 = 34.3 g) and the carbon content is w9 (w9 = 17.55%); the mass of the coal gasification coarse slag more than 200 mesh is m10 (m10 = 21.8 g) and the carbon content is w10 (w10 = 20.68%); the mass and carbon content of the coal gasification coarse slag in different particle size ranges are shown in Table 2;

[0138] Table 2 Mass and carbon content of the coal gasification coarse slag in different particle size ranges

[0139]

[0140] Step 3B13, taking the mass as weight, and calculating the carbon content of the coal gasification coarse slag in different particle size ranges according to the formula The weighted carbon content ω of the coal gasification coarse slag is calculated, and the particle size range of the coal gasification coarse slag meeting the carbon content requirement is determined according to the requirement in the national standard GB / T 1596-2017 (Fly ash for use in cement and concrete) that the loss on ignition of fly ash for use in cement or concrete should be ≤8%, and the particle size range is determined as the particle size meeting the requirement; wherein j is the grade number corresponding to the maximum particle size meeting the carbon content requirement, i is a natural number from 1 to j, and m i m is the mass of the i-th grade coal gasification coarse slag, w i ω is the carbon content of the i-th grade coal gasification coarse slag.

[0141] In this embodiment, the determined particle size range of the coal gasification coarse slag meeting the carbon content requirement is less than 24 mesh (-24 mesh coal gasification slag carbon content is 3.54%, -35 mesh coal gasification slag carbon content is 8.63%).

[0142] The specific calculation process is as follows:

[0143] Carbon content of -24 mesh coal gasification slag:

[0144]

[0145] Carbon content of -35 mesh coal gasification slag:

[0146]

[0147] Step 3B2, coarse crushing: a jaw crusher is used to coarsely crush the sieved coal gasification slag;

[0148] Step 3B3, fine crushing: a roller crusher is used to finely crush the sieved coal gasification slag.

[0149] In this embodiment, the process before step three includes the process of pre-designing and optimizing the preferred ratio of magnesium slag, coal gasification slag, fly ash and activator, which is specifically:

[0150] Step 3C1, within the experience formula range of the optimized magnesium slag, coal gasification slag, fly ash and activator, different weight percentages of the optimized magnesium slag, coal gasification slag, fly ash and activator are selected;

[0151] In this embodiment, the experience formula range of the optimized magnesium slag, coal gasification slag, fly ash and activator is the following weight percentage of raw materials: waste slag mixture 85%-100%, activator 0%-15%; the waste slag mixture includes the following weight percentage of raw materials: optimized magnesium slag 5%-30%, coal gasification slag 60%-90%, fly ash 5%-30%;

[0152] In specific implementation, the proportion of each component constituting the magnesium-coal slag-based cementitious material can be adjusted according to cost, fluidity, strength, environment, etc.

[0153] In order to verify the feasibility of the experience formula range of the optimized magnesium slag, coal gasification slag, fly ash and activator, the following experiments 5 to 15 were carried out, and the ingredients in each experiment are shown in Tables 3-1 and 3-2;

[0154] Table 3-1 Ingredients of magnesium-coal slag-based cementitious materials in experiments 5 to 15 Table 1

[0155]

[0156] Table 3-1 Ingredients of magnesium-coal slag-based cementitious materials in experiments 5 to 15 Table 2

[0157]

[0158] According to the ingredients in each experiment, standard samples were prepared, and the magnesium-coal slag-based cementitious materials were cured in a standard curing box for 120 days (curing temperature was 20℃ and humidity was 95%), and the compressive strength test was carried out according to the relevant methods specified in "Cement Mortar Strength Test Method" GB / T17671-1999, and Table 4 was obtained;

[0159] Table 4 Performance test results of magnesium-coal slag-based cementitious materials in experiments 5 to 15

[0160]

[0161]

[0162] Step 3C2, input different weight percentage contents of the optimized magnesium slag, coal gasification slag, fly ash and activator combined with different days into the pre-trained cementitious material optimal formula selection Tensorflow network to obtain the predicted strength of the magnesium-coal slag-based cementitious material;

[0163] In specific implementation, the different days include 3 days, 7 days, 14 days, 28 days, 56 days, 90 days and 120 days, and the different weight percentage contents of the optimized magnesium slag, coal gasification slag, fly ash and activator are within the optimal formula range of the optimized magnesium slag, coal gasification slag, fly ash and activator, and each time the step size is 0.01, and all possible cases are changed cyclically.

[0164] Step 3C3, the optimal formula corresponding to the highest strength of 28 days is selected as the optimal formula.

[0165] In this embodiment, the training process of the cementitious material optimal formula selection Tensorflow network is as follows:

[0166] Step 3E1, a four-layer Tensorflow network is established, the input layer has 5 nodes, the middle two layers each have 5 nodes, and the output layer has 1 node; wherein the 5 nodes of the input layer are the content of the optimized magnesium slag, the content of the coal gasification slag, the content of the fly ash, the content of the activator, and the number of days (3 days, 7 days, 14 days, 28 days, 56 days, 90 days, 120 days) respectively; the 1 node of the output layer is the predicted strength;

[0167] In specific implementation, the content of the optimized magnesium slag, the coal gasification slag, the fly ash, and the activator is as follows: 85% to 100% of the waste slag mixture, and 0% to 15% of the activator; the waste slag mixture includes the following raw materials in the following weight percentages: 5% to 30% of the optimized magnesium slag, 60% to 90% of the coal gasification slag, and 5% to 30% of the fly ash;

[0168] Step 3E2, obtain the strength of the optimized magnesium slag, the coal gasification slag, the fly ash, and the activator in different weight percentages obtained from multiple groups of experiments at different days as sample data;

[0169] In specific implementation, the number of sample data is 200 to 1000 groups;

[0170] Step 3E3, normalize the number of days in the sample data;

[0171] That is, the number of days is mapped between 0 and 1; in specific implementation, the number of days is 3 days, 7 days, 14 days, 28 days, 56 days, 90 days, and 120 days, 3 days is mapped as 0, and 120 days is mapped as 1;

[0172] Step 3E4, use the normalized sample data to train the Tensorflow network established in step 3E1, and iterate multiple times to obtain a trained Tensorflow network for selecting the optimal ratio of cementitious materials.

[0173] In specific implementation, the process of first mixing the optimized magnesium slag, the coal gasification slag, and the fly ash to form a waste slag mixture, and then adding the activator and grinding to form the magnesium-coal slag-based cementitious material in step three is as follows:

[0174] Step 301, weigh the coal gasification slag, the optimized magnesium slag, and the fly ash according to the proportion and mix them to form a waste slag mixture;

[0175] In specific implementation, the proportion can be adjusted according to cost, liquidity, strength, and environment;

[0176] Step 302, weigh the waste slag mixture and the activator according to the proportion and mix them;

[0177] The weight percentage of the waste slag mixture and the activator is as follows: 85% to 100% of the waste slag mixture, and 0% to 15% of the activator.

[0178] Step 303, pour the mixture into the ball mill for grinding to obtain the optimized magnesium slag-based cementitious material.

[0179] When the mixture is poured into the ball mill for grinding, the particle size is less than 40 μm, and the specific surface area ranges from 300 m 2 / kg to 350 m 2 / kg.

[0180] In this embodiment, the design method of the preferred ratio of the aggregate and the cementitious material in step four is as follows:

[0181] Step 4A1, select different weight percentages of the aggregate and the cementitious material within the empirical formula range of the aggregate and the cementitious material.

[0182] In this embodiment, the empirical formula range of the aggregate and the cementitious material is as follows: the aggregate is 75% to 95%, and the cementitious material is 5% to 25%.

[0183] In order to verify the feasibility of the empirical formula range of the aggregate and the cementitious material, experiments 16 to 22 are carried out, and the ingredients in each experiment are shown in Table 5.

[0184] Table 5 Ingredients of magnesium-coal slag-based filling materials in experiments 16 to 22

[0185]

[0186]

[0187] According to the ingredients in each experiment, standard samples are prepared, and the magnesium-coal slag-based filling materials are cured in a standard curing box for 120 days (the curing temperature is 20°C, and the humidity is 95%). The compressive strength of the magnesium-coal slag-based filling materials is tested according to the relevant methods specified in the “Cement Mortar Strength Test Method” GB / T17671-1999, and the test results are shown in Table 6.

[0188] Table 6 Performance test results of magnesium-coal slag-based filling materials in experiments 5 to 15

[0189]

[0190] Step 4A2, input the aggregate and the cementitious material with different weight percentages and different days into the pre-trained filling material preferred ratio selection Tensorflow network to obtain the predicted strength of the magnesium-coal slag-based filling material.

[0191] Step 4A3, select the ratio corresponding to the highest strength at 28 days as the preferred ratio.

[0192] In this embodiment, the filling material preferably selects the training process of the Tensorflow network as:

[0193] Step 3E1, a four-layer Tensorflow network is established, the input layer has 3 nodes, the middle two layers each have 5 nodes, and the output layer has 1 node; wherein the 3 nodes of the input layer are the content of the aggregate, the content of the cementitious material and the days; the 1 node of the output layer is the predicted strength;

[0194] Step 3E2, obtain the strength of the aggregate and the cementitious material with different weight percentages at different days obtained by multiple experiments as sample data;

[0195] Step 3E3, normalize the days in the sample data;

[0196] Step 3E4, using the normalized sample data, the Tensorflow network established in step 3E1 is trained, and the trained filling material preferred ratio selection Tensorflow network is obtained through multiple iterations.

[0197] In this embodiment, as shown in Figure 7 , in step four, when preparing the magnesium-coal cinder-based filling material, a magnesium-coal cinder-based filling material preparation system is used, which includes an aggregate bin 1 for placing aggregate, a cementitious material bin 2 for placing cementitious material, and a water pool 3 for storing water, as well as a stirrer 4 and a material controller 5 for controlling the preparation of materials. The discharge outlet of the aggregate bin 1 is connected to the aggregate inlet of the stirrer 4 through an aggregate conveying pipeline 6 and an aggregate conveying pump 7 arranged on the aggregate conveying pipeline 6. The discharge outlet of the cementitious material bin 2 is connected to the cementitious material inlet of the stirrer 4 through a cementitious material conveying pipeline 8 and a cementitious material conveying pump 9 arranged on the cementitious material conveying pipeline 8. The water outlet of the water pool 3 is connected to the water inlet of the stirrer 4 through a water conveying pipe 10, a flow meter 11 and a water pump 12 arranged on the water conveying pipe 10. The discharge outlet of the aggregate bin 1 is connected to an aggregate discharge electromagnetic valve 13 and an aggregate weighing sensor 16. The discharge outlet of the cementitious material bin 2 is connected to a cementitious material discharge electromagnetic valve 14 and a cementitious material weighing sensor 17. The stirrer 4, the aggregate conveying pump 7, the cementitious material conveying pump 9, the water pump 12, the aggregate discharge electromagnetic valve 13 and the cementitious material discharge electromagnetic valve 14 are all connected to the output end of the material controller 5. The aggregate weighing sensor 16, the cementitious material weighing sensor 17 and the flow meter 11 are all connected to the input end of the material controller 5. The input end of the material controller 5 is also connected to a start-stop switch 15.

[0198] In specific implementation, the aggregate weighing sensor 16 and the cementitious material weighing sensor 17 can both be nuclear scales;

[0199] The specific process for preparing the magnesium-coal cinder-based filling material in step four is as follows:

[0200] Step 401: Put any one, a mixture of two, or a mixture of three of the coal gangue, wind-blown sand, and optimized magnesium slag into the aggregate bin 1 as the aggregate.

[0201] Step 402: Put the magnesium-coal cinder-based cementitious material into the cementitious material bin 2 as the cementitious material.

[0202] Step 403: Start the start-stop switch 15, and the material preparation controller 5 controls the aggregate feeding electromagnetic valve 13 and the cementitious material feeding electromagnetic valve 14 to open, and controls the stirrer 4, the aggregate conveying pump 7, the cementitious material conveying pump 9, and the water pump 12 to start. Under the power of the aggregate conveying pump 7, the aggregate in the aggregate bin 1 enters the stirrer 4 through the aggregate conveying pipeline 6. Under the power of the cementitious material conveying pump 9, the cementitious material in the cementitious material bin 2 enters the stirrer 4 through the cementitious material conveying pipeline 8. Under the power of the water pump 12, the water in the water pool 3 enters the stirrer 4 through the water conveying pipeline 10. The stirrer 4 stirs the aggregate, the cementitious material, and the water uniformly to prepare the magnesium-coal cinder-based filling material.

[0203] In the above process for preparing the magnesium-coal cinder-based filling material, the aggregate weighing sensor 16 weighs the weight of the aggregate entering the stirrer 4 and outputs the weight to the material preparation controller 5. The cementitious material weighing sensor 17 weighs the weight of the cementitious material entering the stirrer 4 and outputs the weight to the material preparation controller 5. The flow meter 11 detects the flow of the water entering the stirrer 4 and outputs the flow to the material preparation controller 5. The material preparation controller 5 controls the aggregate feeding electromagnetic valve 13, the cementitious material feeding electromagnetic valve 14, the aggregate conveying pump 7, the cementitious material conveying pump 9, and the water pump 12 according to the data received thereby, so that the aggregate and the cementitious material are mixed according to the pre-designed optimal ratio to prepare the magnesium-coal cinder-based filling material.

[0204] In this embodiment, the stirrer 4 is provided with an additive adding port 18 for adding other additives (such as retarders, water-reducing agents, early strength agents, and drag reducers).

[0205] Embodiment 2

[0206] The difference between this embodiment and embodiment 1 is that the process before step three in this embodiment includes the process of pre-designing the optimal ratio of the optimized magnesium slag, the coal gasification slag, the fly ash, and the activator, which is as follows:

[0207] Step 3D1: Obtain the predicted strength parameters of the magnesium-coal cinder-based cementitious material, and the specific process is as follows:

[0208] Step 3D11: Within the range of optimized empirical formulas for magnesium slag, coal gasification slag, fly ash, and activator, select optimized magnesium slag, coal gasification slag, fly ash, and activator with different weight percentages.

[0209] In this embodiment, the empirical formulation range of the optimized magnesium slag, coal gasification slag, fly ash and activator is the following weight percentage of raw materials: waste residue mixture 85% to 100%, activator 0% to 15%; the waste residue mixture includes the following weight percentage of raw materials: optimized magnesium slag 5% to 30%, coal gasification slag 60% to 90%, fly ash 5% to 30%;

[0210] Step 3D12: Optimized magnesium slag, coal gasification slag, fly ash and activator with different weight percentages, combined with different number of days, are input into the pre-trained Tensorflow network for selecting the optimal ratio of cementitious materials to obtain the predicted strength of magnesium-coal slag-based cementitious materials.

[0211] Step 3D13, according to the formula The predicted strength of the magnesium-slag-based cementitious material obtained in step B12 is normalized to obtain the normalized strength value y″. 1nor Where y″1 is the predicted intensity for different days under the material ratio, miny″1 is the minimum predicted intensity, and maxy″1 is the maximum predicted intensity.

[0212] Step 3D2: Obtain the economic index parameters of magnesium-coal slag-based cementitious materials. The specific process is as follows:

[0213] Step 3D21: Let the unit prices of optimized magnesium slag, coal gasification slag, fly ash, and activator be a″1, a″2, a″3, and a″4, respectively. Construct the economic index function as y″2 = a″1x″1 + a″2x″2 + a″3x″3 + a″4x″4; where y″2 is the economic index, x″1 is the coefficient related to the content of optimized magnesium slag and x″1∈(0.05,0.3), x″2 is the coefficient related to the content of coal gasification slag and x′2∈(0.6,0.9), x″3 is the coefficient related to the content of fly ash and x′3∈(0.05,0.3), and x″4 is the coefficient related to the content of activator and x′4∈(0,0.15).

[0214] Step 3D22: Based on the economic indicator function y″2=a″1x″1+a″2x″2+a″3x″3+a″4x″4, and the values ​​of x″1, x″2, x″3 and x″4, solve for the maximum value maxy″2 and the minimum value miny″2 of the economic indicator.

[0215] Step 3D23, according to the formula The economic index obtained in step B22 is normalized to obtain a normalized economic index y" 2nor ;

[0216] Step 3D3, according to the normalized intensity value y" 1nor and the normalized economic index y" 2nor , the objective function for determining the preferred ratio according to intensity and economy is The ratio corresponding to the maximum value of the objective function y" is determined as the preferred ratio; wherein α"1 is the weight coefficient of intensity, α"2 is the weight coefficient of economy, TH"1 is the minimum standard intensity value of intensity, and TH"2 is the highest acceptable price threshold in the economic index.

[0217] The remaining method steps are the same as those in Example 1.

[0218] In this embodiment, the Tensorflow selection ratio is first selected by using the cementitious material preferred ratio, and then the preferred ratio is determined in combination with the economic index, so that the magnesium-coal cinder-based cementitious material with good economy and meeting the demand for compressive strength can be obtained.

[0219] The above is only a preferred embodiment of the present application, and does not limit the present application in any way. Any simple modification, change and equivalent structural change made according to the technical essence of the present application to the above embodiments are still within the protection scope of the technical solution of the present application.

Claims

1. A method for recycling magnesium-coal slag solid waste for the treatment of mining subsidence areas, characterized in that, The method includes the following steps: Step 1: Production of modified magnesium slag: Additives are added to magnesium slag pellets to produce modified magnesium slag pellets that can stabilize β-C2S in magnesium slag. These modified magnesium slag pellets are then used as raw materials for the Pidgeon process magnesium slag production. This process maintains the activity and stability of magnesium slag produced by the Pidgeon process magnesium slag from the source, thus producing modified magnesium slag. Step 2: Generating optimized magnesium slag: The modified magnesium slag produced by magnesium smelting is transported from the reduction workshop to the magnesium slag processing site. Magnesium slag of different ages is placed into different magnesium slag piles. Age marking signs are made on the magnesium slag piles. Modified magnesium slag that has reached two months of age or magnesium slag that has undergone hot casting treatment is marked as optimized magnesium slag. Step 3: Preparation of magnesium-coal slag-based cementitious material: According to the pre-designed optimal ratio, first mix the optimized magnesium slag, coal gasification slag and fly ash to make waste residue mixture, then add activator and grind to make magnesium-coal slag-based cementitious material; Step 4: Preparation of magnesium-coal slag-based backfill material: Using any one, two, or three of the following as aggregates: coal gangue, aeolian sand, and optimized magnesium slag, and magnesium-coal slag-based cementitious material as cementing material, the aggregates and cementing material are mixed according to the pre-designed preferred ratio, and water is added to prepare magnesium-coal slag-based backfill material. Step 5: Filling the goaf in the mine: Use magnesium-slag based filling material to fill the goaf in the mine.

2. The method for recycling magnesium-coal slag solid waste for the treatment of mining subsidence areas according to claim 1, characterized in that: The additives added to the magnesium pellets mentioned in step one are made by using ferroborone alloy as the additives for magnesium pellets.

3. The method for recycling magnesium-coal slag solid waste for the treatment of mining subsidence areas according to claim 1, characterized in that: In step three, when mixing optimized magnesium slag, coal gasification slag, and fly ash according to a pre-designed preferred ratio to prepare waste residue mixture, the optimized magnesium slag raw material is first pre-treated by coarse and fine crushing to obtain optimized magnesium slag material, and the coal gasification slag is pre-treated by screening, coarse and fine crushing to obtain coal gasification slag material. Then, the optimized magnesium slag material and the coal gasification slag material are mixed to prepare waste residue mixture. The specific process of pre-treating the optimized magnesium slag raw material by coarse and fine crushing to obtain optimized magnesium slag material is as follows: Step 3A1, coarse crushing: a jaw crusher is used to coarsely crush the lumpy optimized magnesium slag in the optimized magnesium slag raw material; Step 3A2, Fine crushing: The optimized magnesia slag after coarse crushing is finely crushed using a double roller crusher to obtain optimized magnesia slag material; The specific process for obtaining coal gasification slag through pretreatment including screening, coarse crushing, and fine crushing is as follows: Step 3B1, Screening: Use a vibrating screen to screen the coarse coal gasification slag to obtain a predetermined particle size that meets the requirements; Step 3B2, coarse crushing: a jaw crusher is used to coarsely crush the screened coal gasification slag; Step 3B3, Fine crushing: The screened coal gasification slag is finely crushed using a double roller crusher.

4. A method for recycling magnesium-coal slag solid waste for the treatment of mining subsidence areas according to claim 3, characterized in that: The specific method for pre-determining the particle size that meets the requirements in step 3B1 is as follows: Step 3B11: The coarse coal gasification slag is screened according to mesh size using a multi-stage vibrating screen, and the screening is divided into multiple stages; the coarse coal gasification slag is the raw coal gasification slag produced by coal chemical enterprises after producing syngas; Step 3B12: Determine the mass and carbon content of coal gasification coarse slag with different particle size ranges; Step 3B13: Using quality as the weight, according to the formula... Calculate the weighted carbon content ω of the coarse coal gasification slag, and determine the particle size range of the coarse coal gasification slag that meets the carbon content requirement based on the national standard GB / T 1596-2017, which states that "the loss on ignition of fly ash used in cement or concrete should be ≤8%". This range is then defined as the particle size that meets the requirement. Here, j represents the order corresponding to the maximum particle size that meets the carbon content requirement, i is a natural number from 1 to j, and m... i For the quality of the coarse slag from the i-th stage coal gasification, w i The carbon content of the coarse slag from the i-th stage coal gasification is given.

5. A method for recycling magnesium-coal slag solid waste for the treatment of mining subsidence areas according to claim 1, characterized in that: Step three, which previously included the process of pre-designing and optimizing the optimal ratio of magnesium slag, coal gasification slag, fly ash, and activator, specifically involves: Step 3C1: Within the range of empirical formulas for optimizing magnesium slag, coal gasification slag, fly ash, and activator, select optimized magnesium slag, coal gasification slag, fly ash, and activator with different weight percentages. Step 3C2: Optimized magnesium slag, coal gasification slag, fly ash and activator with different weight percentages, combined with different number of days, are input into the pre-trained Tensorflow network for selecting the optimal ratio of cementitious materials to obtain the predicted strength of magnesium-coal slag-based cementitious materials. Step 3C3: Select the ratio corresponding to the highest intensity over 28 days as the preferred ratio.

6. A method for recycling magnesium-coal slag solid waste for the treatment of mining subsidence areas according to claim 1, characterized in that: Step three, which previously included the process of pre-designing and optimizing the optimal ratio of magnesium slag, coal gasification slag, fly ash, and activator, specifically involves: Step 3D1: Obtain the predicted strength parameters of magnesium-coal slag-based cementitious materials. The specific process is as follows: Step 3D11: Within the range of optimized empirical formulas for magnesium slag, coal gasification slag, fly ash, and activator, select optimized magnesium slag, coal gasification slag, fly ash, and activator with different weight percentages. Step 3D12: Optimized magnesium slag, coal gasification slag, fly ash and activator with different weight percentages, combined with different number of days, are input into the pre-trained Tensorflow network for selecting the optimal ratio of cementitious materials to obtain the predicted strength of magnesium-coal slag-based cementitious materials. Step 3D13, according to the formula The predicted strength of the magnesium-slag-based cementitious material obtained in step B12 is normalized to obtain the normalized strength value y″. 1nor Where y″1 is the predicted intensity for different days under the material ratio, min y″1 is the minimum predicted intensity, and max y″1 is the maximum predicted intensity. Step 3D2: Obtain the economic index parameters of magnesium-coal slag-based cementitious materials. The specific process is as follows: Step 3D21: Let the unit prices of optimized magnesium slag, coal gasification slag, fly ash, and activator be a″1, a″2, a″3, and a″4, respectively. Construct the economic index function as y″2 = a″1x″1 + a″2x″2 + a″3x″3 + a″4x″4; where y″2 is the economic index, x″1 is the coefficient related to the content of optimized magnesium slag and x″1∈(0.05,0.3), x″2 is the coefficient related to the content of coal gasification slag and x′2∈(0.6,0.9), x″3 is the coefficient related to the content of fly ash and x3′∈(0.05,0.3), and x″4 is the coefficient related to the content of activator and x′4∈(0,0.15). Step 3D22: Based on the economic indicator function y″2=a″1x″1+a″2x″2+a″3x″3+a″4x″4, and the values ​​of x″1, x″2, x″3 and x″4, solve for the maximum value max y″2 and the minimum value min y″2 of the economic indicator. Step 3D23, according to the formula The economic indicators obtained in step B22 are normalized to obtain the normalized economic indicator y″. 2nor ; Step 3D3: Based on the normalized intensity value y″ 1nor and the normalized economic indicators y″ 2nor The objective function for determining the optimal ratio based on strength and economy is constructed as follows: The optimal allocation ratio is determined when the objective function y″ reaches its maximum value; where α″1 is the weighting coefficient of intensity, α″2 is the weighting coefficient of economy, TH″1 is the minimum standard intensity value, and TH″2 is the highest acceptable price threshold among economic indicators.

7. A method for recycling magnesium-coal slag solid waste for the treatment of mining subsidence areas according to claim 5 or 6, characterized in that: The preferred ratio of the cementitious material is selected based on the training process of the Tensorflow network: Step 3E1: Establish a four-layer Tensorflow network with 5 nodes in the input layer, 5 nodes in each of the two middle layers, and 1 node in the output layer. The 5 nodes in the input layer are for optimizing the content of magnesium slag, the content of coal gasification slag, the content of fly ash, the content of activator, and the number of days, respectively. The 1 node in the output layer is for predicting the intensity. Step 3E2: Obtain the strength of optimized magnesium slag, coal gasification slag, fly ash and activator at different weight percentages under different days from multiple sets of experiments, as sample data; Step 3E3: Normalize the number of days in the sample data; Step 3E4: Using the normalized sample data, train the Tensorflow network established in Step 3E1, iterate multiple times, and obtain the trained Tensorflow network for selecting the optimal proportion of cementitious materials.

8. A method for recycling magnesium-coal slag solid waste for the treatment of mining subsidence areas according to claim 1, characterized in that: The design method for the optimal proportion of aggregates and cementitious materials mentioned in step four is as follows: Step 4A1: Within the range of empirical formulas for aggregates and cementitious materials, select aggregates and cementitious materials with different weight percentages; Step 4A2: Input the aggregates and cementitious materials with different weight percentages and different numbers of days into the pre-trained Tensorflow network for selecting the optimal ratio of backfill materials to obtain the predicted strength of the magnesium-coal slag-based backfill material. Step 4A3: Select the ratio corresponding to the highest intensity over 28 days as the preferred ratio.

9. A method for recycling magnesium-coal slag solid waste for the treatment of mining subsidence areas according to claim 1, characterized in that: In step four, the preparation of magnesium-coal slag-based backfill material is carried out using a magnesium-coal slag-based backfill material preparation system. This system includes an aggregate bin (1) for holding aggregates, a cementitious material bin (2) for holding cementitious materials, and a water tank (3) for storing water, as well as a mixer (4) and a material control unit (5) for controlling the material preparation. The outlet of the aggregate bin (1) is connected to the aggregate inlet of the mixer (4) via an aggregate conveying pipe (6) and an aggregate conveying pump (7) installed on the aggregate conveying pipe (6). The outlet of the cementitious material bin (2) is connected to the cementitious material inlet of the mixer (4) via a cementitious material conveying pipe (8) and a cementitious material conveying pump (9) installed on the cementitious material conveying pipe (8). The outlet of the water tank (3) is connected to the water outlet via a water supply pipe (10) and... A flow meter (11) and a water pump (12) installed on the water supply pipe (10) are connected to the water inlet of the agitator (4). The outlet of the aggregate bin (1) is connected to an aggregate discharge solenoid valve (13) and an aggregate weighing sensor (16). The outlet of the cementitious material bin (2) is connected to a cementitious material discharge solenoid valve (14) and a cementitious material weighing sensor (17). The agitator (4), aggregate conveying pump (7), cementitious material conveying pump (9), water pump (12), aggregate discharge solenoid valve (13) and cementitious material discharge solenoid valve (14) are all connected to the output end of the material preparation controller (5). The aggregate weighing sensor (16), cementitious material weighing sensor (17) and flow meter (11) are all connected to the input end of the material preparation controller (5). The input end of the material preparation controller (5) is also connected to a start / stop switch (15). The specific process for preparing the magnesium-slag-based backfill material described in step four is as follows: Step 401: Use any one, two or three of the following as aggregates: coal gangue, aeolian sand and optimized magnesium slag, and place them into the aggregate bin (1); Step 402: Using magnesium-slag-based cementitious material as cementing material, place it into the cementing material silo (2); Step 403: Start the start / stop switch (15). The material control controller (5) controls the aggregate discharge solenoid valve (13) and the cementitious material discharge solenoid valve (14) to open, and controls the start of the agitator (4), aggregate conveying pump (7), cementitious material conveying pump (9) and water pump (12). Under the power of the aggregate conveying pump (7), the aggregate in the aggregate bin (1) enters the agitator (4) through the aggregate conveying pipe (6); under the power of the cementitious material conveying pump (9), the cementitious material in the cementitious material bin (2) enters the agitator (4) through the cementitious material conveying pipe (8); under the power of the water pump (12), the water in the pool (3) enters the agitator (4) through the water supply pipe (10); the agitator (4) mixes the aggregate, cementitious material and water evenly to make magnesium-coal slag-based filling material. In the process of preparing magnesium-coal slag-based filling material, the aggregate weighing sensor (16) weighs the aggregate entering the mixer (4) and outputs the weight to the material control controller (5); the cementitious material weighing sensor (17) weighs the cementitious material entering the mixer (4) and outputs the weight to the material control controller (5); the flow meter (11) detects the flow rate of water entering the mixer (4) and outputs the flow rate to the material control controller (5); the material control controller (5) controls the aggregate discharge solenoid valve (13), the cementitious material discharge solenoid valve (14), the aggregate conveying pump (7), the cementitious material conveying pump (9), and the water pump (12) according to the data it receives, so that the aggregate and cementitious material are mixed according to the pre-designed preferred ratio to produce magnesium-coal slag-based filling material.

10. A method for recycling magnesium-coal slag solid waste for the treatment of mining subsidence areas according to claim 9, characterized in that: The stirrer (4) is provided with an additive inlet (18) for adding other additives.

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