Method for assisting red mud dealkalization by using freeze-thaw method and red mud dealkalization system

Abstract

The invention provides a method for assisting red mud dealkalization by using a freeze-thaw method and a red mud dealkalization system. The red mud dealkalization method comprises the steps of water replenishing saturation, freezing, melting suction, component detection and repeated treatment, and the water replenishing saturation step comprises the steps of burying a bagged sand well into a tamped red mud soil body, replenishing water to the red mud soil body by replenishing an eluting agent solution into the bagged sand well, and forming a water-supplementing saturated soil body until the soil-water potential in the red soil body is balanced. Freeze-thaw circulation of the red mud is achieved through an artificial refrigeration method, a bagged sand well is used as a fluid infusion well method, effective dealkalization of the red mud is achieved in combination with an acid leaching method, alkali in the dealkalized red mud is remarkably reduced, the Na2O content can reach 1% or below, and the dealkalization effect is good. The material can be used for roadbed materials of roads, ground hardening materials for saline-alkali soil transformation, cement raw materials, building raw materials and the like. The invention also provides a red mud dealkalization system.

Description

Technical Field

[0001] The invention relates to the technical field of environmental protection, and in particular to a method for assisting red mud dealkalization by utilizing a freeze-thaw method and a red mud dealkalization system. Background Art

[0002] Red mud is a highly alkaline waste residue produced during the production of alumina. It is the largest solid waste discharged by the alumina industry. It is called red mud because it is rich in iron oxide and appears red. Due to different production processes, it can be divided into Bayer red mud, sintering red mud and combined red mud. The Bayer process is still the most economical method to extract alumina from bauxite. Currently, the aluminum production using this method accounts for 95% of the world's total.

[0003] According to the aluminum content of the processed raw materials and the extraction efficiency of alumina, about 1.5 to 2 tons of red mud are produced for every ton of alumina produced. According to statistics, as of 2023, the global red mud reserves have reached 4 billion tons. The red mud has a large output and strong alkalinity, which is difficult to comprehensively utilize. Stockpiling is still its main disposal method, but the stockpiling of red mud requires a large area of ​​land and a lot of money to build and maintain the red mud dam. Due to some special properties contained in the production process, the red mud will contain a large amount of heavy metal ions, fluoride and alkali. During the stockpiling process, these pollutants may enter the groundwater with rainfall or flow into the surrounding rivers, lakes and farmland, and then enter the food chain. If animals or humans consume contaminated water and food for a long time, it will inevitably have a serious impact on their health; high pH water infiltrates into the soil and farmland, causing the soil to compact and form dense soil blocks, and finally become a saline-alkali land with no grass; in addition, there is a risk of dam collapse during the stockpiling of red mud.

[0004] In the long run, comprehensive utilization of red mud is the fundamental solution to its environmental pollution and safety hazards, and is the only way for the sustainable development of China's aluminum industry.

[0005] Henan Polytechnic University disclosed a red mud dealkalization method achieved by phase control in its Chinese invention patent application CN 115318791 A, which includes the following steps: pretreatment: drying the raw red mud; mixed dissolution: dissolving the dried and crushed red mud; frozen crystallization: cooling crystallization; overall freezing: complete freezing of the mixture; thawing and rinsing: melting the frozen material; collecting the eluent; repeated elution; deionized elution; and finishing the processing. Although the invention patent application can achieve the purpose of dealkalization by utilizing the freeze-thaw cycle method, the method requires pre-drying and crushing of the red mud raw material, and the method mainly simulates natural freezing, which will be affected by the geographical location during actual application. The method may not be very applicable in southern my country; in addition, the technology disclosed in the above patent application is mainly in the laboratory research stage. Summary of the invention

[0006] In view of this, a main object of the present invention is to provide a method for red mud dealkalization assisted by freeze-thaw method, which mainly achieves red mud dealkalization by combining artificial refrigeration method, bagged sand well as rehydration well method and acid leaching method to solve the above technical problems.

[0007] Specifically, the technical solution provided by the present invention is as follows: A method for red mud dealkalization assisted by freeze-thaw method, comprising the steps of: Water replenishment and saturation: burying a bagged sand well in the compacted red mud body, replenishing water to the red mud body by adding a leaching agent solution to the bagged sand well, until the soil water potential in the red mud body reaches equilibrium, forming a water-saturated soil body; Freezing and freezing: continuously adding the eluent solution to the bagged sand well, and using artificial refrigeration to freeze the water-saturated soil until a freezing curtain is formed, so that the eluent and red mud soil are frozen as a whole to obtain a frozen soil; Melting and suction: firstly melt the frozen soil, then insert a drainage board into the melted soil, and then suck the leaching liquid in the soil under negative pressure to separate the leaching liquid from the soil, and obtain the red mud soil after acid leaching; Composition detection: Detection of Na in the red mud after acid leaching 2 O content; Repeat the freezing step to the component detection step until the Na 2 The O content is stable and less than 1%.

[0008] Based on the above, in the step of replenishing water and saturation, the bagged sand wells are arranged in a square or regular triangle in the red mud soil. In this way, the bagged sand wells are used as liquid replenishment wells in the present invention to replenish water for the soil, which can reduce the soil replenishment path and increase the water replenishment efficiency.

[0009] Based on the above, the step of replenishing water and saturation includes: before freezing begins, burying the bagged sand well in the red mud soil body, replenishing the eluent solution into the bagged sand well through an automatic water replenishing device, and maintaining the water level in the bagged sand well flush with the upper end of the red mud soil body; until the water level in the bagged sand well remains unchanged, the soil water potential reaches equilibrium, and the water-replenished saturated soil body is formed.

[0010] Based on the above, the freezing step includes: circulating brine to the freezing plate in the saturated soil, continuously replenishing the eluent into the bagged sand well during the cooling process, freezing the hydrated saturated soil in a step-by-step stepped cooling mode until a freezing curtain is formed therein, wherein the eluent is frozen into a solid state and is frozen as a whole with the red mud soil, completing the freezing and obtaining the frozen soil; in this way, the hydrated saturated soil forms a temperature difference according to the distance from the freezing plate, controls the temperature, and implements a stepped cooling mode to ensure the movement speed of the freezing front.

[0011] Preferably, the eluent in the freezing step is supplemented by pressureless supplementation through the freezing suction force generated by the frost heave effect.

[0012] Among them, the step-by-step cooling mode includes using a brine tank to circulate brine to treat the hydrated saturated soil, wherein the initial temperature of the brine tank is set to -4°C, and then dropped to -15°C to -30°C at a freezing rate of -2°C / d, and then maintained at a constant temperature until the freezing curtain is formed.

[0013] The eluent is a citric acid solution, an oxalic acid solution, etc. Preferably, the concentration of the eluent is 0.3-0.5 mol / L.

[0014] In order to further improve the dealkalization rate of red mud, the eluent is a magnetized eluent obtained by magnetizing the eluent. The magnetization method of the eluent includes providing a magnetization device, which includes a container for holding the eluent, two magnetic energy activators, a self-priming booster pump and a pipeline installed between the two magnetic energy activators, wherein the container, the magnetic energy activator, and the self-priming booster pump are connected by a pipeline, one of the two magnetic energy activators is connected to the container through a liquid inlet pipe, and the other is connected to the container through a liquid outlet pipe; firstly, the eluent is placed in the container, and then the liquid inlet pipe and the liquid outlet pipe are respectively inserted into the eluent in the container, and then the eluent is magnetized for 5-12 hours using a magnetic field strength of 5000 GS-10000GS to obtain the magnetized eluent.

[0015] Based on the above, the melting and suction step includes: melting the frozen soil by natural melting, inserting the drainage board into the melted soil, connecting the drainage board to a vacuum pump to form a negative pressure state, completely extracting the leachate in the soil, and collecting the leachate. The suction rate of the leachate is changed by adjusting the pressure of the vacuum pump.

[0016] Based on the above, the step of component detection includes: drilling core sampling at the cross-section position of the central axis of the red mud body after acid leaching, digesting and chemical component detection of the obtained soil sample, and calculating the red mud de-alkali rate. Among them, the soil sample digestion method is the electric hot plate method (wet digestion). The chemical component detection method is the flame photometer method, that is, the content of sodium element in the digestion test solution is detected by a flame photometer, and the red mud de-alkali rate is calculated according to the sodium content.

[0017] Based on the above, the step of repeated treatment includes: repeating the freezing step to the component detection step 3-6 times, detecting the Na 2 When the O content is stable and less than 1%, the dealkalization of red mud is completed.

[0018] Based on the above, the method for preparing the compacted red mud body comprises: compacting the red mud raw materials in layers to prepare the compacted red mud body.

[0019] Another object of the present invention is to provide a red mud dealkalization system, comprising an earth trough box for filling a compacted red mud body, wherein bagged sand wells are evenly distributed in the red mud body, and the bagged sand wells are connected to an automatic water replenishment device; freezing plates are inserted between adjacent bagged sand wells, and the freezing plates are respectively connected to a circulation pump and a brine tank, and the three constitute a temperature-controlled brine circulation system; a drainage board is inserted between the freezing plate and the bagged sand well.

[0020] Wherein, the bagged sand wells are arranged in a square or regular triangle in the red mud body.

[0021] Furthermore, the red mud dealkalization system also includes a plurality of temperature sensors evenly distributed in the red mud body.

[0022] Furthermore, the red mud dealkalization system also includes a leachate vacuum collection device connected to the drainage board.

[0023] Therefore, compared with the prior art, the method for red mud dealkalization assisted by freeze-thaw method and the red mud dealkalization system provided by the present invention mainly have the following advantages: 1) Due to the extremely fine particle size of red mud, the conventional acid leaching method requires a large amount of eluent and is difficult to collect samples after acid leaching; the freeze-thaw cycle method can effectively store the samples after the reaction in the container. At the same time, during the freezing process, the soil body frosts and expands, and the large-size soil particles are destroyed. The structural alkali in them is also destroyed and becomes free alkali, achieving the purpose of dealkalization; in addition, the use of artificial refrigeration can overcome the influence of geographical location on the dealkalization effect of red mud; 2) As the number of small-sized soil particles increases, the contact area with the eluent becomes larger, and the acid-base neutralization reaction is more complete, thereby effectively reducing the use of eluent; and by adding bagged sand wells as replenishment wells, the water replenishment path can be shortened and the water replenishment efficiency can be improved; 3) Through the above method provided by the present invention, the pH of the red mud after the test is reduced to neutral and slightly acidic, and no three wastes are generated during the process; 4) The bagged sand wells used in the method provided by the present invention are easily available, convenient to construct, and low in cost, so that the red mud dealkalization method provided by the present invention is easy to promote and apply on a large scale.

[0024] Therefore, the above-mentioned method of utilizing freeze-thaw method to assist red mud dealkalization provided by the present invention realizes freeze-thaw cycle of red mud body by artificial refrigeration method, utilizes bagged sand well as replenishment well method, and realizes effective dealkalization of red mud by combining acid leaching method. After dealkalization, the alkali in red mud is significantly reduced, and Na 2 The O content can be less than 1%, and it can be used for roadbed materials, ground hardening materials for saline-alkali land reconstruction, cement raw materials, building materials raw materials, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of a square arrangement of bagged sand wells provided by the present invention; Figure 2 It is a magnetizing device for oxalic acid solution; Figure 3 It is the surface tension bar graph of magnetized oxalic acid solution.

[0026] Figure 4 A red mud dealkalization system provided in Example 1 of the present invention; Among them, the component symbols in the above figures are: soil trough box 1, red mud soil body 2, multiple bagged sand wells 3, multiple automatic water replenishment devices 30, multiple freezing plates 4, brine tank 41, circulation pump 42, multiple drainage plates 5, vacuum pump 51, leachate collection container 52, water bucket 6, liquid inlet pipe 61, liquid outlet pipe 62, magnetic energy activator 7, self-priming booster pump 8. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the present invention more clear, the technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0028] Unless otherwise specified, the terms used in the present invention are commonly used terms in the relevant field. The preparation processes, testing methods, etc. used in each embodiment are conventional means well known to those skilled in the art unless otherwise specified. The raw materials and equipment used can be obtained from public commercial channels.

[0029] One object of the present invention is to achieve red mud dealkalization by combining artificial refrigeration, bagged sand well and acid leaching. The specific technical scheme is as follows: A method for red mud dealkalization assisted by freeze-thaw method, comprising the steps of: Water replenishment and saturation: burying a bagged sand well in the compacted red mud body, replenishing water to the red mud body by adding a leaching agent solution to the bagged sand well, until the soil water potential in the red mud body reaches equilibrium, forming a water-saturated soil body; Freezing and freezing: continuously adding the eluent solution to the bagged sand well, and freezing the water-saturated soil by artificial refrigeration until a freezing curtain is formed, so that the eluent and the red mud soil are frozen as a whole to obtain a frozen soil; Melting and suction: firstly melt the frozen soil, then insert a drainage board into the melted soil, and then suck the leaching liquid in the soil under negative pressure to separate the leaching liquid from the soil, and obtain the red mud soil after acid leaching; Composition detection: Detection of Na in the red mud after acid leaching 2 O content; Repeat the freezing step to the component detection step until the Na 2 The O content is stable and less than 1%.

[0030] The method for preparing the compacted red mud body comprises: compacting the red mud raw material in layers to obtain the compacted red mud body. Specifically, the red mud raw material is first compacted in layers, and then allowed to stand to obtain a red mud body with uniform moisture content. The maximum diameter of the red mud raw material particles is less than 5 mm. Preferably, the amount of red mud used is 1000-2000 kg.

[0031] In the water replenishment measures, setting bagged sand wells as vertical water replenishment bodies can effectively increase the water replenishment path of the soil, shorten the water replenishment distance, accelerate the water absorption of the soil, and has the advantages of wide application range, convenient process, high cost performance, etc. In the water replenishment saturation step, the bagged sand wells are arranged in a square or regular triangle in the red mud soil body, and the specific arrangement of the bagged sand wells in the red mud soil body can be simulated and designed with reference to the existing method.

[0032] Among them, the bagged sand wells are arranged in a square shape in the red mud body. Figure 1 As shown, the effective water replenishment diameter of the bagged sand well is d e With spacing l The relationship is: .

[0033] When the bagged sand wells are arranged in an equilateral triangle in the red mud body, the effective water replenishment diameter of the bagged sand wells is de With spacing l The relationship is: .

[0034] Among them, in formula (1-1) and (1-2): d e is the effective cylindrical diameter of the sand well; d w is the diameter of the sand well. Spacing between bagged sand wells l The selection is generally determined by the well diameter ratio n, where the well diameter ratio n= d e / d w The spacing of bagged sand wells can be selected as n=15~22.

[0035] Specifically, the step of replenishing water and saturation includes: before the freezing begins, burying the bagged sand well in the red mud soil body in a square or equilateral triangle manner, replenishing the eluent solution into the bagged sand well through an automatic water replenishing device, and maintaining the water level in the bagged sand well flush with the upper end of the red mud soil body; until the water level in the bagged sand well remains unchanged, the soil water potential reaches equilibrium, and the water-replenished saturated soil body is formed.

[0036] The freezing step includes: subjecting the freezing plate in the saturated soil to brine circulation treatment, while continuously replenishing the eluent into the bagged sand well during the cooling process, freezing the water-supplemented saturated soil in a step-by-step stepped cooling mode until the freezing curtain is formed, so that the eluent therein is frozen into a solid state and is frozen as a whole with the red mud soil, completing the freezing and forming the frozen soil; in this way, the water-supplemented saturated soil forms a temperature difference according to the distance from the freezing plate, controls the temperature, implements a stepped cooling mode, and ensures the movement speed of the freezing front.

[0037] Among them, the step-by-step cooling mode includes using a brine tank to circulate brine to treat the hydrated saturated soil, wherein the initial temperature of the brine tank is set to -4°C, and then dropped to -15°C to -30°C at a freezing rate of -2°C / d, and then maintained at a constant temperature until the freezing curtain is formed.

[0038] The eluent is supplemented by pressureless supplementation through the freezing suction force generated by the frost heave effect. The eluent is a citric acid solution, an oxalic acid solution, etc. Preferably, the concentration of the eluent is 0.3-0.5 mol / L.

[0039] In order to further improve the dealkalization rate of red mud, the eluent is a magnetized solution formed after magnetization treatment. The preparation method of the magnetized solution includes: providing a magnetization device, the magnetization device includes a container for holding the eluent, two magnetic energy activators and a self-priming booster pump installed between the two magnetic energy activators, wherein the container, the magnetic energy activator and the self-priming booster pump are connected by a pipeline, one of the two magnetic energy activators is connected to the container through a liquid inlet pipe, and the other is connected to the container through a liquid outlet pipe; firstly put the eluent into the container, then insert the liquid inlet pipe and the liquid outlet pipe into the eluent in the container respectively, and then use a magnetic field strength of 5000 GS-10000 GS to magnetize the eluent for 5-12 hours to obtain the magnetized eluent.

[0040] Compared with the unmagnetized eluent, the physical and chemical properties of the magnetized eluent are changed, the surface tension and viscosity are reduced, thereby reducing the seepage or migration resistance of the eluent into the soil, increasing the migration rate of the eluent and allowing more eluent to enter the soil.

[0041] The melting and suction step includes: melting the frozen soil by natural melting, inserting the drainage board into the melted soil, connecting the drainage board to a vacuum pump to form a negative pressure state, completely extracting the leachate in the soil, and collecting the leachate. The suction rate of the leachate can be changed by adjusting the pressure of the vacuum pump.

[0042] The drain board is preferably a plastic drain board. The size of the plastic drain board used in the project is generally 100 mm wide and 4 mm thick. It can be cut into the required size during the experiment. In order to achieve the pumping effect, the equivalent diameter of the drain board needs to be considered. d eq . Equivalent diameter d eq The calculation of can be done using Long and Covo's equation, as shown in formula (1-3): d eq = 0.5 d +0.7 t (1-3); In formula (1-3): d eq To calculate the equivalent diameter; d To adopt width; t To adopt thickness.

[0043] The step of component detection includes: drilling core sampling at the cross-section position of the central axis of the red mud body after acid leaching, digesting and chemical component detection of the obtained soil sample, and calculating the red mud de-alkali rate. The soil sample digestion method is the electric hot plate method (wet digestion). The chemical component detection method is the flame photometer method, that is, the sodium content in the digestion test solution is detected by a flame photometer, and the red mud de-alkali rate is calculated according to the sodium content.

[0044] The step of repeated treatment includes: repeating the freezing step to the component detection step 3-6 times, detecting the Na 2 When the O content is stable and less than 1%, the dealkalization of red mud is completed.

[0045] Another object of the present invention is to provide a red mud dealkalization system, comprising a soil trough box for filling a compacted red mud body, wherein bagged sand wells are evenly distributed in the red mud body, and the bagged sand wells are connected to an automatic water replenishment device; freezing plates are inserted between adjacent bagged sand wells, and the freezing plates are respectively connected to a circulation pump and a brine tank, and the three constitute a temperature-controlled brine circulation system; a drainage board is inserted between the freezing plate and the bagged sand well. The bagged sand wells are arranged in a square or regular triangle in the red mud body.

[0046] Furthermore, the red mud dealkalization system also includes a plurality of temperature sensors evenly distributed in the red mud body, so as to realize artificial refrigeration of the red mud body.

[0047] Furthermore, the red mud dealkalization system further comprises a leachate vacuum collection device connected to the drain board, wherein the leachate vacuum collection device comprises a vacuum pump and a leachate collection container mounted on the vacuum pump, and the leachate collection container is connected to the drain board via a pipeline.

[0048] Due to the extremely fine particle size of red mud, the conventional acid leaching method requires a large amount of eluent and is not easy to collect samples after acid leaching; the freeze-thaw cycle method can effectively store the samples after the reaction in the container. At the same time, during the freezing process, the soil body frosts and swells, and the large-sized soil particles are destroyed. The structural alkali in them is also destroyed and becomes free alkali, achieving the purpose of de-alkali; as the number of small-sized soil particles increases, the contact area with the eluent becomes larger, and the acid-base neutralization reaction is more complete, which effectively reduces the use of eluent; and by adding bagged sand wells as replenishment wells, the water replenishment path can be shortened and the water replenishment efficiency can be improved. In addition, the use of a brine circulation system to achieve artificial refrigeration can overcome the influence of geographical location on the de-alkali effect of red mud.

[0049] The technical solution protected by the present invention is further explained below through specific embodiments.

[0050] (1) The soil sample digestion method in the following examples includes: weighing 0.2 g of soil sample (with an error of 0.02%) into a polytetraethylene beaker (crucible); adding 5 ml of hydrofluoric acid, and then adding 10 ml of mixed acid (HCl:HNO 3 : HClO 4 =3:2:1); place the crucible on a hot plate, set the temperature to 170 ℃, and heat for 1 h; raise the temperature of the hot plate to 230 ℃, heat and dissolve for 1 h (or dissolve at 170 ℃ for 2 h, then directly raise to 320 ℃); raise the temperature to 320 ℃, and heat until there is only solid in the crucible and no white smoke; wait until the white smoke dissipates, lower the temperature to 170 ℃, first add 3 ml of reverse aqua regia (HCl: HNO 3 =1:3) to dissolve, remove it after slight heat, and then add 20 ml of distilled water and let it stand overnight (you can also do this: remove the crucible without white smoke from the heating plate, add 3 ml of aqua regia after 1 min, add 20 ml of distilled water after an interval of 2 min, and let it stand overnight for use), and you can get the digestion solution.

[0051] (2) Calculation formula of dealkalization rate: , where in formula (1-4): W is the dealkalization rate, %; is the sodium content in the original red mud, %; is the sodium content in red mud after dealkalization, %.

[0052] (3) Magnetized oxalic acid solution The preparation method of the magnetized oxalic acid solution provided in the embodiment of the present invention is as follows: See also Figure 2 , providing a magnetizing device, the magnetizing device comprising a water bucket 6 for containing eluent, two magnetic energy activators 7 and a self-priming booster pump 8 installed between the two magnetic energy activators 7, the water bucket 6, the two magnetic energy activators 7 and the self-priming booster pump 8 are connected by a PVC pipe; the magnetic field strengths of the two magnetic energy activators 7 are about 10000 GS and about 6000 GS respectively; wherein the magnetic energy activator 7 with a magnetic field strength of about 10000 GS is connected to the water bucket 6 through a liquid inlet pipe 61, and the other magnetic energy activator 7 with a magnetic field strength of about 6000 GS is connected to the water bucket 6 through a liquid outlet pipe 62; firstly, 40 L of 0.5 mol / L oxalic acid solution is put into the water bucket 6, and then the liquid inlet pipe 61 and the liquid outlet pipe 62 are respectively inserted into the oxalic acid solution contained in the water bucket 6, and then the oxalic acid solution is magnetized at a flow rate of 0.44 m / s for 1, 2, 3, 4, ..., 11 h, 12 h, and at the same time test the surface tension of the solution at different magnetization times (surface tension meter test) to determine the optimal magnetization time. The results are as follows Figure 3 shown.

[0053] from Figure 3It can be seen that the surface tension of the oxalic acid solution after magnetization will decrease, and the surface tension of the oxalic acid solution after magnetization for 11 h is reduced to the minimum, with the maximum reduction of 22.3%, and the magnetic field intensity remains unchanged. As the magnetization time increases, the surface tension of the oxalic acid solution first decreases and then increases. This is because as the magnetization time increases, the oxalic acid solution undergoes three changes, namely: ① The magnetic field destroys the macromolecular water clusters into many small molecular water clusters, thereby weakening the surface tension. ② The magnetic field can break the hydrogen bonds between water molecules, making the oxalic acid solution have a stronger polarity and easier to enter the interior of the red mud particles. ③ The appropriate magnetization time will make the hydrophilic groups on the surface of the solution more compact, thereby enhancing the wettability of the solution. The increase in magnetization time gradually expands the influence of these three aspects, which is manifested as the surface tension of the solution gradually decreasing. However, excessive magnetization can cause the hydrophilic groups on the surface of the solution to fall off, making the wettability of the solution worse, which is manifested as the surface tension of the solution gradually increasing after excessive magnetization. Therefore, the following embodiment five adopts the magnetized oxalic acid solution obtained after magnetization for 11 h.

[0054] Embodiment 1 See also Figure 4 The present embodiment provides a red mud dealkalization system, including a soil trough box 1, a red mud body 2, a plurality of bagged sand wells 3, a plurality of automatic water replenishment devices 30, a plurality of freezing plates 4, a brine tank 41, a circulation pump 42, a plurality of drainage plates 5, a vacuum pump 51 and a leachate collection container 52.

[0055] The outer surface of the soil trough box 1 is installed with an insulation board to ensure the insulation effect of the soil trough box 1. The red mud body 2 is compacted and filled in the soil trough 1 in layers. In this embodiment, the volume of the soil trough box 1 is 140 cm×100 cm×50 cm. Multiple temperature sensors are evenly distributed in the red mud body to facilitate artificial precise temperature control.

[0056] The bagged sand wells 3 are arranged in a square array in the red mud body 2 with a spacing of 0.3 m. The effective cylindrical diameter of the sand well d e is 33.9 cm, and the affected area covers the entire soil trough box. According to the above formula (1-1), the size of the bagged sand well is calculated to be 2.26 cm in diameter. Considering that the test size is too small and the water replenishment effect is not good, the size of the bagged sand well is expanded. In this embodiment, the diameter of the bagged sand well 3 is 4 cm and the length is the same as the depth of the red mud body 2; the bagged sand well 3 is made of polypropylene woven material, and the sand is medium and coarse sand with high water permeability. The main function of the automatic water replenishment device 30 is to replenish the eluent solution into the bagged sand well 3, and the amount is the same as the number of bagged sand wells 3. The automatic water replenishment device 30 includes a water container and a pipe connecting the water in the water container and the bagged sand well 3.

[0057] The plurality of freezing plates 4, the brine tank 41 and the circulation pump 42 are connected by pipelines to form a temperature-controlled brine circulation system. The brine tank 41 is a low-temperature brine tank. By controlling the temperature of the brine tank 41, the freezing temperature of the red mud body 2 can be controlled, and artificial refrigeration of the red mud body 2 can be achieved. In this embodiment, the number of the freezing plates 4 is two.

[0058] The drain board 5 is a plastic drain board, which is connected to the leachate collection container 52 through a pipeline. The leachate collection container 52 is installed on the vacuum pump 51. The suction rate of the leachate can be changed by adjusting the pressure of the vacuum pump 51. In this embodiment, the width of the drain board 5 is 100 mm and the thickness is 4 mm.

[0059] Embodiment 2 This embodiment provides a method for red mud dealkalization assisted by freeze-thaw method. The method uses the red mud dealkalization system provided in Example 1 to dealkalize red mud. The specific method includes the following steps: Step 1, filling and sampling: taking several bags of red mud raw materials to measure their moisture content, and then taking 1500 kg of red mud raw materials into the soil trough box 1, and compacting them layer by layer to form a 140 cm×100 cm×50 cm (length×width×height) soil body. After the soil is filled, let it stand for 72 hours to ensure that the moisture content in the soil is uniform, and obtain the red mud soil body 2, wherein the maximum diameter of the red mud raw materials is less than 5 mm; Step 2: water saturation: before freezing begins, add 0.35 mol / L oxalic acid solution to the bagged sand well 3 through the automatic water replenishment device 30 to ensure that the water level is flush with the upper end of the red mud soil body 2; when the water level in the bagged sand well 3 remains unchanged and the soil water potential reaches equilibrium, a water-saturated soil body is formed; Step 3, freezing crystallization: the oxalic acid solution is continuously added to the bagged sand well 3 through the automatic water replenishment device 30, and the water-saturated soil is circulated with salt water to start freezing the soil, and the red mud mixture formed by the water-saturated soil and the oxalic acid solution is cooled. The red mud mixture is at different distances from the freezing plate 4 to form a temperature difference, and the temperature is controlled. A step-by-step cooling mode is implemented to ensure the moving speed of the freezing front, wherein the replenishment method of the eluent is a pressure-free replenishment through the freezing suction force generated by the frost heave effect; Step 4, overall freezing: After the freezing and crystallization in step 3, the solid eluent and red mud raw material mixture is completely frozen, and the soil between the two freezing plates is completely frozen to form a freezing curtain; wherein, the freezing and crystallization in step 3 and the overall freezing in step 4 refer to freezing the soil in a step-by-step step cooling mode, and the freezing is stopped when the soil no longer absorbs water, and the initial temperature of the brine tank 41 is set to -4°C, and then dropped to a set value of -22°C at a freezing rate of -2°C / d, and remains unchanged after dropping to the set value; Step 5, melting and suction: remove the insulation board on the surface of the soil trough box 1, and naturally melt the frozen soil in step 4. After the frozen soil melts, use the vacuum pump 51 to connect the plastic drainage board 5 to negatively pressure suck the leachate in the soil trough box 1 to complete the separation of the leachate and the soil; Step 6, collecting the leaching liquid: collecting the eluent obtained in the step 5 into the leaching liquid collection container 52, and after the collection is completed, turning off the vacuum pump 51; Step 7: Drilling and sampling: After the test, drill core samples are taken from the soil centerline section in the soil tank box 1; Step 8: soil sample testing: digest the soil sample obtained in step 7 to obtain a digestion test solution; use a flame photometer to detect the sodium content in the digestion test solution, and calculate the dealkalization rate.

[0060] Examples 3 to 6 each provide a method for red mud dealkalization assisted by freeze-thaw method, which is basically the same as the method provided in Example 2, with the main difference being that Examples 3 to 5 respectively use the red mud dealkalized in the previous example as raw material for further dealkalization, that is, the composition of the red mud raw material is different; the concentration of the eluent is different, and the results are shown in Table 1.

[0061] Table 1 Red mud dealkalization effect table of Examples 2 to 5

[0062] The "total dealkalization rate" in Table 1 is calculated based on the raw materials of Example 2.

[0063] It can be seen from Table 1 that the red mud dealkalization method and dealkalization system provided in the embodiment of the present invention adopt artificial refrigeration technology and perform a step-by-step freeze-thaw method, and after four treatments, the alkali in the red mud can be effectively removed.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or some technical features can be replaced by equivalents without departing from the spirit of the technical solution of the present invention, which should be included in the scope of the technical solution for protection of the present invention.

Claims

1. A method for red mud dealkalization assisted by freeze-thaw method, comprising the steps of: Water replenishment and saturation: burying a bagged sand well in the compacted red mud body, replenishing water to the red mud body by adding a leaching agent solution to the bagged sand well, until the soil water potential in the red mud body reaches equilibrium, forming a water-saturated soil body; Freezing and freezing: continuously adding the eluent solution to the bagged sand well, and using artificial refrigeration to freeze the water-saturated soil until a freezing curtain is formed, so that the eluent and red mud soil are frozen as a whole to obtain a frozen soil; Melting and suction: firstly melt the frozen soil, then insert a drainage board into the melted soil, and then suck the leaching liquid in the soil under negative pressure to separate the leaching liquid from the soil, and obtain the red mud soil after acid leaching; Component detection: detecting the Na2O content in the red mud body after acid leaching; Repeat the treatment: Repeat the freezing step to the component detection step until the Na2O content in the red mud body after acid leaching is stable and less than 1%.

2. The method for red mud dealkalization assisted by freeze-thaw method according to claim 1, characterized in that: The eluent is citric acid solution, oxalic acid solution, magnetized citric acid solution or magnetized oxalic acid solution.

3. The method for red mud dealkalization assisted by freeze-thaw method according to claim 2, characterized in that: The concentration of the eluent is 0.3-0.5 mol / L.

4. The method for red mud dealkalization assisted by freeze-thaw method according to any one of claims 1 to 3, characterized in that: In the step of replenishing water and saturating, the bagged sand wells are arranged in the red mud body in a square or regular triangle arrangement.

5. The method for red mud dealkalization assisted by freeze-thaw method according to claim 4, characterized in that: The step of replenishing water and saturation includes: before freezing begins, burying the bagged sand well in the red mud soil body, replenishing the eluent solution into the bagged sand well through an automatic water replenishing device, and maintaining the water level in the bagged sand well flush with the upper end of the red mud soil body; until the water level in the bagged sand well remains unchanged, the soil water potential reaches equilibrium, and the water-replenished saturated soil body is formed.

6. The method for red mud dealkalization assisted by freeze-thaw method according to claim 5, characterized in that: The freezing step includes: subjecting the freezing plates in the saturated soil to brine circulation treatment, while continuously replenishing the eluent into the bagged sand well during the cooling process, freezing the water-supplemented saturated soil in a step-by-step cooling mode until a freezing curtain is formed, so that the eluent therein is frozen into a solid state and is frozen as a whole with the red mud soil to obtain the frozen soil.

7. The method for red mud dealkalization assisted by freeze-thaw method according to claim 6, characterized in that: The step-by-step cooling mode includes using a brine tank to circulate brine on the water-saturated soil, wherein the initial temperature of the brine tank is set to -4°C, and is reduced to -15°C to -30°C at a freezing rate of -2°C / d, and then maintained at a constant temperature until a freezing curtain is formed.

8. The method for red mud dealkalization assisted by freeze-thaw method according to claim 7, characterized in that: The melting and suction steps include: naturally melting the frozen soil in the soil trough box, inserting the drainage board into the melted soil, connecting the drainage board to a vacuum pump to form a negative pressure state, completely extracting the leachate in the soil, and collecting the leachate.

9. The method for red mud dealkalization assisted by freeze-thaw method according to claim 8, characterized in that: The step of component detection includes: taking core samples at the cross-section position of the central axis of the red mud body after acid leaching, digesting and detecting the chemical composition of the obtained soil samples, and calculating the red mud de-alkali rate.

10. The method for red mud dealkalization assisted by freeze-thaw method according to any one of claims 1-3 and 5-9, characterized in that: The repeated treatment step includes: repeating the freezing step to the component detection step 3-6 times, and when the Na2O content in the red mud body after acid leaching is detected to be stable and less than 1%, the dealkalization of the red mud is completed.

11. The method for red mud dealkalization assisted by freeze-thaw method according to claim 1, characterized in that: The method for preparing the compacted red mud body comprises: compacting the red mud raw material in layers to prepare the compacted red mud body.

12. A red mud dealkalization system, characterized in that: include: An earth trough box is used to fill the compacted red mud body, wherein bagged sand wells are evenly distributed in the red mud body, and the bagged sand wells are connected to an automatic water replenishing device; freezing plates are inserted between adjacent bagged sand wells, and the freezing plates are respectively connected to a circulation pump and a brine tank, and the three constitute a temperature-controlled brine circulation system; a drainage board is inserted between the freezing plate and the bagged sand well.

13. The red mud dealkalization system according to claim 12, characterized in that: The bagged sand wells are arranged in a square or regular triangle shape in the red mud body.

14. The red mud dealkalization system according to claim 12 or 13, characterized in that: Also included are a plurality of temperature sensors uniformly distributed in the terracotta body.

15. The red mud dealkalization system according to claim 14, characterized in that: Also included is a leachate vacuum collection device connected to the drainage board.

16. The red mud dealkalization system according to claim 15, characterized in that: The leachate vacuum collection device comprises a vacuum pump and a leachate collection container mounted on the vacuum pump, and the leachate collection container is connected to the drainage board through a pipeline.

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